Amp building

Paolo_M

Lads,

A few of you mentioned a while back that you are interested in building amps. Well I've eventually got started myself. So far I've the features tied down, block diagram (see below), prelim design and parts sourced and ordered.
I was thinking of posting progress as I go if anyones interested, maybe on a weekly basis. The group in Dublin sounds like a great idea but being that I live in the real capital it's a no go for me.

Well here goes update one:

Two preamp channels; A = clean to crunch, B = hi gain to facemelt
Channel and channel A/B modes will be footswitchable
Each channel has independant gain, level and bass, mid treb controls
Post Phase Inverter Master Volume
Switchable feedback with Resosnace/Presence control. Turned off => Voxy loose kinda' power amp, turned on => tighter more focused like 50 Watter
Power amp will be switchable from Class AB to Class A to Pseudo Single ended, found a power transformer with 190 / 285 Vac secondaries to allow this.
Pentode/Triode switch give total power options from 2W, 4W, 5W, 8W, 10W and 18W
Rectifier valve emulator switchable for saggy or stiff feel

Next job is to do the componant layout drawings as well as front and rear panel designs along with the circuit board layouts. I'll be finalising tone shaping componant selection as I go by experimenting with different values. I've the power supply designed but haven't drawn it out yet and need to finalise footswitching design which might change it anyway.

Here's the block diagram.


Will post more as I go.

Rgds,
Paolo.

Patricide

Ok personally I understand none of that. Id be very interested to hear how it sounds though cause the sounds your going for would be pretty similar to what im after myself.

A7X

I hope you post updates and pic's Cant wait to hear this man good luck.

spoonbadger

Sounds very interesting man, but sadly it means very little to me .

Here's a question, do you have any idea where i could learn about this kinda stuff. I'd love to know about amp circuitry .

A7X

Theres many places. This website explains a few things and has loads of links and is generally pretty cool ha www.beavisaudio.com see wat ya think.

Quattroste

I was the person thinking about trying to organise an Amp Building project and finding a place to meet each week etc. My job has since changed and I doubt I'll have the time to do this now. It's still something I would like to but it wont be any time soon.

Please post pics each week and show progress. The amps functionality sounds great so far, but i have to admit a lot of the detail goes over my head.

A7X

Also I was wondering if you have schematic drawn out? I would love to see it.

Paolo_M

Guys, thanks for the encouragement!!

Spoonerbadger (and anyone else interested): Could I suggest that you start with the DC chapter of Fundamentals of Electrical Engineering and Electronics. It's available online for free download as a html help file here http://www.vias.org/feee/. Without a basic DC understanding, and possible some ac, it'll take you much longer to read through any amplifier technical article and really understand it. Following that, Jack Darrs book on amplifiers is also available for free download here http://www.pacificrecone.com/JackDarrBook.html and it's a great primer for both valve and SS amps. I've a bunch of other website links and book references that I'll post as I go.
It can be very easy to get bogged down and confused in all the detail but try and remember that the primary function of any amplifier is to vary the amount of electric current flowing through a loudspeaker from a DC power supply, by using your guitars signal as the control mechanism. This is like how you use your hand to control the amount of water flowing from a tap by using the hand valve, and it's exactly why vacuum tubes became known as valves.
Despite all the complexity assosiated, it's basic action is this simple so try to keep it at the back of your mind.

A7X: I've schematics for each of the blocks drawn on various sheets of paper. I'll post an overall schematic once finished. It'll probably be missing some componant values assosiated with the tone circuits, not because I'm super secretive or anything, but because I plan to try different values in each spot until I'm happy with the tone. I had a look at the Beavis Audio site and there's some great info on there but the guy seems to be as daft as a brush!! :pac:

A7X

Paolo_M wrote: »

Guys, thanks for the encouragement!!

Spoonerbadger (and anyone else interested): Could I suggest that you start with the DC chapter of Fundamentals of Electrical Engineering and Electronics. It's available online for free download as a html help file here http://www.vias.org/feee/. Without a basic DC understanding, and possible some ac, it'll take you much longer to read through any amplifier technical article and really understand it. Following that, Jack Darrs book on amplifiers is also available for free download here http://www.pacificrecone.com/JackDarrBook.html and it's a great primer for both valve and SS amps. I've a bunch of other website links and book references that I'll post as I go.
It can be very easy to get bogged down and confused in all the detail but try and remember that the primary function of any amplifier is to vary the amount of electric current flowing through a loudspeaker from a DC power supply, by using your guitars signal as the control mechanism. This is like how you use your hand to control the amount of water flowing from a tap by using the hand valve, and it's exactly why vacuum tubes became known as valves.
Despite all the complexity assosiated, it's basic action is this simple so try to keep it at the back of your mind.

A7X: I've schematics for each of the blocks drawn on various sheets of paper. I'll post an overall schematic once finished. It'll probably be missing some componant values assosiated with the tone circuits, not because I'm super secretive or anything, but because I plan to try different values in each spot until I'm happy with the tone. I had a look at the Beavis Audio site and there's some great info on there but the guy seems to be as daft as a brush!! :pac:

I look forard to having a look through them. That second link you gave is exactly what I've been looking for thanks.

Ha yeah . I think there is three guys and a load of outside people supplying info, but i think they try to put things in laymans (dunno how to spell it) terms. They have a link to a forum called www.diystompboxes.com and I dunno if you would be bothered but they'd love to see something like this.

Anyways I really can't wait to see how this goes for ya.

All the best.

Yakult

This could be a very interesting thread. Cant wait to see how it turns out

spoonbadger

Paolo_M wrote: »

Guys, thanks for the encouragement!!

Spoonerbadger (and anyone else interested): Could I suggest that you start with the DC chapter of Fundamentals of Electrical Engineering and Electronics. It's available online for free download as a html help file here http://www.vias.org/feee/. Without a basic DC understanding, and possible some ac, it'll take you much longer to read through any amplifier technical article and really understand it. Following that, Jack Darrs book on amplifiers is also available for free download here http://www.pacificrecone.com/JackDarrBook.html and it's a great primer for both valve and SS amps. I've a bunch of other website links and book references that I'll post as I go.
It can be very easy to get bogged down and confused in all the detail but try and remember that the primary function of any amplifier is to vary the amount of electric current flowing through a loudspeaker from a DC power supply, by using your guitars signal as the control mechanism. This is like how you use your hand to control the amount of water flowing from a tap by using the hand valve, and it's exactly why vacuum tubes became known as valves.
Despite all the complexity assosiated, it's basic action is this simple so try to keep it at the back of your mind.

A7X: I've schematics for each of the blocks drawn on various sheets of paper. I'll post an overall schematic once finished. It'll probably be missing some componant values assosiated with the tone circuits, not because I'm super secretive or anything, but because I plan to try different values in each spot until I'm happy with the tone. I had a look at the Beavis Audio site and there's some great info on there but the guy seems to be as daft as a brush!! :pac:

Brilliant!.Thanks paolo!.

'Got me some coffee, some zeppelin and i'm ready to learn this stuff :pac:.

fish-head

Deadly buzz!

Watch out for any deadly buzzes though. Don't be getting fried.

freshcream

If this works for you I might copy it.

good luck with the project I will following this thread very closely

Paolo_M

Lads, made a folder for the pics on photobucket so the first post doesn't seem to work any more.

Anyway here's my latest bits and pieces:

The workspace, needs a bit of a tidy :pac:


The power amp schematic, some values will probably end up changing but here's what I'll start with


The power supply, I haven't allowed for any channel status LEDs and I'm not sure I want to. I reckon if you cant hear what channel your on then the amp isn't that great in the first place. May end up putting them in for aesthetic purposes. I'll probably end up with more filtering on the preamp, probably a RC per stage.


The original block diagram


Still working on the preamp, componant layout, front/rear panel design and none of the parts have arrived yet.

Here's a really cool site that give you free circuit simulation and lets you fool around with the values so you see how everything flows without running the risk of killing yourself.
http://www.falstad.com/circuit/index.html
Book reference would be How to Service Your Own Tube Amp by Tom Mitchell and gives great info in a simple to understand format for the technically minded or interested guitarist. I found it really helpful.



I should warn that if you don't feel confident that you know what your doing then don't go poking around a live amp.;)

A7X

Thanks for posting up the schematics man. Love reading them. I hope u update us alot about this if its not too much trouble for you. I really can't wait to hear it. Also Thanks for all the links and refrences tht u posted they're a great help.

Eoin Madsen

I'm bored today, and far away from my music making facilities.

Let's nerd out some. :pac: What kind of tone stack are you going for? And cathode follower, or plate fed? I see gain stages after tone which suggests the latter, I think? And are you putting in an effects loop? I've been having a lot of thoughts about effects loops lately.

Paolo_M

Eoin Madsen wrote: »

I'm bored today, and far away from my music making facilities.

Let's nerd out some. :pac: What kind of tone stack are you going for? And cathode follower, or plate fed? I see gain stages after tone which suggests the latter, I think? And are you putting in an effects loop? I've been having a lot of thoughts about effects loops lately.

Think I'll stick with a standard BMT, but I'll have the Res and Pres control too when engaged.
Let's get real nerdy!! :pac: Personally, I think cathode followers have no place in a guitar amp. Fender copied their design from an RCA manual which had one included and then Marshall copied Fender etc.etc. so a lot of guitar amps have one now.
What good is low ouput impedance when your gain is only .97ish? With a plate connected tonestack, sure you've a much higher output impedance driving it, but you can have gain up to 60 which more than compensates for any signal loss. It's probably not a great idea for Hi-Fi but who cares, guitar amps thrive on non linearity. Mesa or Peavey don't seem to have had many complaints anyway!!
Was thinking of an effects loop alright. If I do go for one it'll be partially SS :eek:. I'm toying with the idea of using a source follower to drive it then using one of my 6 gain stages as a recovery. I'd have to be a bit cleverer how I use the stages though. I want to keep the amount of stages shared by each channel to a minimum so I don't have to comprimise tonally. May end up using SS recovery as well and have it by-pass switchable. I don't really use a lot of effects anyway. The other balls is I'd need a seperate LV tranny but it looks I'll be using one anyway for the switching, I'm not sure there'll be enough juice in the heater to do it.

Eoin Madsen

Low voltage is always the thing that trips me when I start thinking about relays. An extra transformer is probably the least disruptive way. You going to go transistor or magnetic for the switching?

I don't think I'm nerd enough to argue with your ts logic, but I have to say, my ears have quite a fondness for the various Bassman derived Marshall with their cathode follower tone stacks. The actual tone control is not great though. Something I might do at some stage is make a fixed circuit to emulate a 1959 tone stack with everything at 5 (and maybe try to lower the overall gain loss), and then add a completely different eq on top of it. I was thinking something crazy like the filter stage of a Pultec eq. :pac: More likely to do it for a bass amp though, I think, or something with a fullrange cab.

My inclination for an FX loop would really stem from wanting to have the option to add a dynamics processor or EQ. I wouldn't be huge on effects anyway. Well... maybe a chorus. Evidence does seem to suggest that an SS loop fares better in terms of non-colouration. But definitely something you want to be fully bypassable.

I have an amp in progress that I haven't touched in about six weeks.

Paolo_M

Eoin Madsen wrote: »

Low voltage is always the thing that trips me when I start thinking about relays. An extra transformer is probably the least disruptive way. You going to go transistor or magnetic for the switching?

I don't think I'm nerd enough to argue with your ts logic, but I have to say, my ears have quite a fondness for the various Bassman derived Marshall with their cathode follower tone stacks. The actual tone control is not great though. Something I might do at some stage is make a fixed circuit to emulate a 1959 tone stack with everything at 5 (and maybe try to lower the overall gain loss), and then add a completely different eq on top of it. I was thinking something crazy like the filter stage of a Pultec eq. :pac: More likely to do it for a bass amp though, I think, or something with a fullrange cab.

My inclination for an FX loop would really stem from wanting to have the option to add a dynamics processor or EQ. I wouldn't be huge on effects anyway. Well... maybe a chorus. Evidence does seem to suggest that an SS loop fares better in terms of non-colouration. But definitely something you want to be fully bypassable.

I have an amp in progress that I haven't touched in about six weeks.

I'm going to use good old mechanical relays, sub milisecond switching is not high on my priority list, my foot can't move that fast anyways :pac:. Good design will minimise any popping....hopefully.

The cathode follower tone stack thang is really a result of the DC coupled stage that almost always comes before it. Because of how the bias settles, the upgoing part of signal get's fairly heavily clipped producing loads of creamy even order harmonics, mostly 2s and 4s.
Have a read of the DC Cathode Follower section on here http://www.valvewizard.co.uk/, I think you'll enjoy it .

Agreed on SS and colouration of tone. The extreme linearity achievable (with all the FB etc.) is actually a good thing in a loop to get it as transparent as possible. I'm only considering the loop because I don't want a tuner up front and I occassionly use chorus and delay. The plan is guitar => wah, modded of course :pac: => amp

What are you building amp wise? Where are sourcing parts?
I found this place stocks good parts (axial coupling caps, sprague atom and JJ filters, got some chassis punches from them too) http://www.bluebellaudio.com/.

Eoin Madsen

I'm loosely building the output stage of a P1 extreme with a Marshall 1959 style preamp. I got a chassis a couple of years ago from Nik at Ceriatone that I never got around to using (he powder coated it gloss white instead of matt black - I have no idea how - and I didn't get off my ass and strip it etc until the end of last year). I've got the preamp part of the board done, mostly vishay resistors (from Metroamp) and sozos. I drilled the chassis for the transformers over Christmas. The PT is a Danbury I got from ampmaker.com, rated for 160mA at 275V/190V and 3A. I got some axial filter caps from turretboards.com when I was getting parts for my Champ last spring. I think I need to go buy some power resistors, but I'll probably just go in to Maplin for them.

The OT... I still can't remember the place I got it from. (In the UK, and they were a pain in the ass to get responses from. They had some maplin project amp from many years ago on their site, and the URL was something convoluted... I must dig up the emails). It's a Danbury rated for 10W, with 5kR or 2.4kR taps into 8R. And it has an ultralinear tap. I'd like to run the whole thing into a wedge-shaped sealed or possibly ported 2x8, if I can find somewhere that will make one.

I got a line output transformer from Sowter, which may or may not feature. I'm provisionally planning to put in a KT88 and use the amp as a low watt bass amp.

I think most of my alpha pots and misc are from Metroamp. There's a box with a whole lot of them in it. I also have a bunch of orange drops from smallbearelec.com, and every flavour of sozo that I got from sozoamplification a couple of years ago. John at Sozo was good enough to post the caps for the price of posting an envelope of capacitors, rather than insisting on a minimum charge courier like a lot of places seem to. Ampmaker in the UK was also notable in that respect.

I have a few F&T 50+50s I got from Metroamp back in '04/05. The one I checked earlier still meters about 46uF on each side, but I'm concerned they may have expired from sitting in a box too long. Also sitting in a box awaiting a future project I have planned are a pair of Heyboers for a 100watt Marshall.

More parts than built projects by a long shot.

Thanks for the links.

Paolo_M

Eoin, I'm using the same PT for my project!! Your project sounds cool, now get off your ass and finish it, or you'll end up like Gaudi!! :pac: Seriously I'd love to see pics as you go.

Latest update:

Here's a schematic that I've mocked up using a cool, free (even cooler) package called Express PCB http://www.expresspcb.com/. There's no values filled in, partly because it took ages to draw out that much and the Ireland match was on, and partly because they'll be changing once testing begins again so I didn't really see the point. I know what the starting values will in my head anyway, their written on scraps of paper!! I'll be using pots for some of the critical tone shaping resistors and tweaking until I hit "the spot", then measuring them out and installing that value as a fixed resistor. I realise that I'll probably need additional voltage dividers to stabilise the amp and stop it squeeling like a pig but I'll figure that out as I go.
The power supply is missing obvsiouly, that's another days work!!
I said I'd make up a mock company name for the project, sure f*ck it, why not?



Anyway Ampmaker mailed to say their stuff is on route, undrilled chassis, wooden cab, trannys, sockets and various nuts and bolts. The Bluebell componants should be in late next week.

A7X

Paolo_M wrote: »

Eoin, I'm using the same PT for my project!! Your project sounds cool, now get off your ass and finish it, or you'll end up like Gaudi!! :pac: Seriously I'd love to see pics as you go.

Latest update:

Here's a schematic that I've mocked up using a cool, free (even cooler) package called Express PCB http://www.expresspcb.com/. There's no values filled in, partly because it took ages to draw out that much and the Ireland match was on, and partly because they'll be changing once testing begins again so I didn't really see the point. I know what the starting values will in my head anyway, their written on scraps of paper!! I'll be using pots for some of the critical tone shaping resistors and tweaking until I hit "the spot", then measuring them out and installing that value as a fixed resistor. I realise that I'll probably need additional voltage dividers to stabilise the amp and stop it squeeling like a pig but I'll figure that out as I go.
The power supply is missing obvsiouly, that's another days work!!
I said I'd make up a mock company name for the project, sure f*ck it, why not?



Anyway Ampmaker mailed to say their stuff is on route, undrilled chassis, wooden cab, trannys, sockets and various nuts and bolts. The Bluebell componants should be in late next week.

Without sounding like a huge noob, lol I was wondering how the switches such as your crunch switch make a difference.

I mean the components that the switch will be connecting to ground are already connected to ground, so to me it looks like your just adding another way of getting there.

The only thing that i can think of that makes sense to me is that it will mean that less current will be going through the resistor that connects the cap to ground. Is that the point or am I wrong. I'd love if you could help me make sense of this. lol Sorry about the noobyness.

Paolo_M

If you leave the resistor unbypassed the gain of the stage is lower. Bypassing it with a capacitor allows you to increase the gain. Selecting the right value of cap you can boost certain frequencies (or not). By connecting the cap to ground through a resistor it effectivley removes it from the circuit. The switch then bypasses the resistor bringing the cap into play.
The reason for using the resistor in the first place instead of just switching the cap to ground is to avoid a great big thump sound when you switch it on.
If I work the stage gain out right, this switch will let this channel have two modes; clean and crunch.
Hope that helps explains it.

A7X

Paolo_M wrote: »

If you leave the resistor unbypassed the gain of the stage is lower. Bypassing it with a capacitor allows you to increase the gain. Selecting the right value of cap you can boost certain frequencies (or not). By connecting the cap to ground through a resistor it effectivley removes it from the circuit. The switch then bypasses the resistor bringing the cap into play.
The reason for using the resistor in the first place instead of just switching the cap to ground is to avoid a great big thump sound when you switch it on.
If I work the stage gain out right, this switch will let this channel have two modes; clean and crunch.
Hope that helps explains it.

Yeah man thanks, That has helped clear it up more for me.

ClutchIt

Is anyone else ever baffled by how expensive tube amps are? I mean there is no way a tube amp would cost the same to manufacture as a: TV / HiFi / Fridge / Wash Machine / Dish Washer etc etc,. Yet they charge us about 3-4 times the price.
Really Wierd.
I know you're prob thinking supply and demand and is something to do with it but a large company like Fender could easily charge about €500 for a 2x12 combo and still make a large profit. They is screwing us methinks!

Voodu Child

ClutchIt wrote: »

Is anyone else ever baffled by how expensive tube amps are?
I know you're prob thinking supply and demand and is something to do with it but a large company like Fender could easily charge about €500 for a 2x12 combo and still make a large profit. They is screwing us methinks!

Tube amps are available at all costs. Including 2x12s for €500 :pac:

A7X

voodoo_child wrote: »

Tube amps are available at all costs. Including 2x12s for €500 :pac:

Me thinks more often than not its the name and the added reliabilty that goes behind the expensive price tbh.

Eoin Madsen

ClutchIt wrote: »

Is anyone else ever baffled by how expensive tube amps are? I mean there is no way a tube amp would cost the same to manufacture as a: TV / HiFi / Fridge / Wash Machine / Dish Washer etc etc,. Yet they charge us about 3-4 times the price.
Really Wierd.
I know you're prob thinking supply and demand and is something to do with it but a large company like Fender could easily charge about €500 for a 2x12 combo and still make a large profit. They is screwing us methinks!

I was less baffled after I started buying parts. They're not cheap, and there isn't enough of a market any more for all the components to be made (to decent spec) in the one giant inexpensive place. I mean, paying 2k+ for an amp head, someone is definitely making a larger profit than is warranted. But €500 for a 50w head... the transformers will be cheap, even if the profit is fair.

Paolo_M

Quality valve amps will be more expensive to manufacture than SS amps due to their nature. You can use similar manufacturing techniques to Dell and Apple et al to lash out a load of SS amps real quick, it's just not possible to do this with valve amps. If you take the business point of view; they're two very different markets. The SS amp market tends to be "stack 'em high, sell 'em cheap" and are large volume, low margin items. Valve amps tend to be lower volume but accordingly higher margin. I don't believe there's a cartel or anything, and it's a competitive market.
From my point of view I've dropped the gut's of a grand so far on parts, though a lot of that is tools like hole punches, oscopes, proper iron etc.
The parts just assosiated with this amp will still come out close to €600 and good few hours will go into it.

Anyway first delivery from AmpMaker arrived today.

Rest of the gear will be here in the next few days.

Really can't wait to get stuck in!!
Will have to get rid of that jack on the power transformer and put a proudly in it's place.

ClutchIt

Oh yeah, I know they're more expensive to make than SS but I was comparing them to Fridges, washing machines and dish washers which are still about 35-40% the price of a good tube amp.
Ever try buying the parts for a f**king washing machine ?
Cartel it is.

Paolo_M

ClutchIt wrote: »

Oh yeah, I know they're more expensive to make than SS but I was comparing them to Fridges, washing machines and dish washers which are still about 35-40% the price of a good tube amp.
Ever try buying the parts for a f**king washing machine ?
Cartel it is.

This is starting to turn into it's own thread within a thread...:pac:
I work for a large PLC manufacturer and I believe the business models are similar in the amp industry from what I've read.

Firstly you've manufacturer Fender, Marsh etc. Due to large volume sales of SS amps Marsh et al can forward order their componants, pre assemblies etc, in vast bulk orders. The fact that their agents are tied to certain volume targets allow them to do this without much risk. Valve amps are much slower sellers and they do not risk such vast forward ordering. Because of this the unit cost is lower even ignoring the actual cost of manufacture.
Then you've the agents/disctributors. Again SS amps are large volume sellers so they don't mind fill their warehouses with the stuff as they know it'll move quickly. Because of this they can operate at a reduced margin. Valve amps again are much slower and there is a risk involved as they may have racks full of stuff not moving for weeks at a time. Therefore they have to operate at higher margins.
Finally you've the stores. The same theory as above applies and so their cut is higher on valves amps. All of this means that you, the consumer, will pay more for a quality valve amp than a SS model.
Dishwashers, fridges etc.etc. fall into the SS amp category where they sell in large volumes and move quickly and therefore all the middle men and manufacturers can afford to operate at lower margins, meaning cheaper prices.
I can assue you that if Hotpoint or whoever only started selling 20 units a month in Ireland the prices would shoot up instantly.

Mmmm, building a washine machine, I think I've found my next project!!

spoonbadger

Paolo_M wrote: »

This is starting to turn into it's own thread within a thread...:pac:
I work for a large PLC manufacturer and I believe the business models are similar in the amp industry from what I've read.

Firstly you've manufacturer Fender, Marsh etc. Due to large volume sales of SS amps Marsh et al can forward order their componants, pre assemblies etc, in vast bulk orders. The fact that their agents are tied to certain volume targets allow them to do this without much risk. Valve amps are much slower sellers and they do not risk such vast forward ordering. Because of this the unit cost is lower even ignoring the actual cost of manufacture.
Then you've the agents/disctributors. Again SS amps are large volume sellers so they don't mind fill their warehouses with the stuff as they know it'll move quickly. Because of this they can operate at a reduced margin. Valve amps again are much slower and there is a risk involved as they may have racks full of stuff not moving for weeks at a time. Therefore they have to operate at higher margins.
Finally you've the stores. The same theory as above applies and so their cut is higher on valves amps. All of this means that you, the consumer, will pay more for a quality valve amp than a SS model.
Dishwashers, fridges etc.etc. fall into the SS amp category where they sell in large volumes and move quickly and therefore all the middle men and manufacturers can afford to operate at lower margins, meaning cheaper prices.
I can assue you that if Hotpoint or whoever only started selling 20 units a month in Ireland the prices would shoot up instantly.

Mmmm, building a washine machine, I think I've found my next project!!

oooOOOOOoooo,someone's on speaking terms with marsh :D.

Paolo_M

Made a big decision on the build. During detailed layout and design work I found that, while all the componants would fit as measured in the 18W chassis, it would make future modding and tweaking more difficult. It's only when I started fitting the componants in mock fashion that I realised just what little room there would be to maneuver.
As this is a first design/build from scratch I decided that building a great sounding, two channel amp would be enough of an achievement to start with without adding the additional complexity. The next project, if this one is successful..., will be the original design with a 6V6 output stage in a full sized 100 Watt chassis.

As a result I've reduced the spec as follows:
Shared tone stack for both channels
No more vol and solo controls for each channel
One preamp valve less, dirty channel shares two of the clean channels gain stages now

Schematic
Here's the revised schematic, had to use a coil symbol for the heaters as I couldn't find the proper heater symbol..:o


Amp title
Dirty Blue is the working title for the amp as it will go from Vox chime, to big ballsey blues overdrive, right through to dirty rotten, face melting metal.
If anyone wants to lend me a better title I'm all ears.

Grounds and noise reduction
Have decided on elevated heaters, and a mix of star and bus grounding.
All power supply grounds will be starred and the preamp and controls will have their own bus ground back to the star point. The safety earth will have it's own chassis connection point to comply with electrical regulation, though I'm not sure I have to for personal use. All signal carrying wires will be shielded at the source end.
Anyone into this will find these links interesting http://www.aikenamps.com/StarGround.html, http://www.geofex.com/Article_Folders/stargnd/stargnd.htm

Layout wise I'm shooting for this


and hopefully avoiding this


Next steps
Just completing the layout drawings now, will post when complete and will be cutting the chassis at the weekend, hopefully.

Paolo_M

Not as much progress made this weekend as I'd hoped. :mad:
Componants and chassis tools still haven't arrived...
Still, it left plenty of time to "celebrate" the rugby.

Did get to finalise the, to scale, chassis layout diagram, ignore the tipex

This is an absolutley essential excercise for anyone thinking of building an amp. You can really get a feel for the amp layout, how the lead dress should be, where best to route the cables, wheher componants are gonna fit ok etc.etc.
Matroamp and Ceriatone et al are cool because they provide these diagrams for you, but unfortunatley "yours truly" here decided none of the kits were exactly what I wanted so I had to go and do my own...
The squiggly lines are supposed to represent twisted wires.

The drilling template, to scale, for the turret board


Will probably get ahead and drill and stake the board later.
Since I took the picture I've spotted one dot missing on the left...:mad:
I deliberatle rearranged the right side of the board on the drilling template as it was slightly cramped around the power resistor, not sure if it's clear on the layout but the power resistors are in red with the 1 W carbon films in yellow.

This is a cool troubleshooting website for anyone with a valve amp and a good amount of electrical knowledge.http://www.geofex.com/ampdbug/ampdebug.htm. Be careful, once again, if you don't feel confident in your abilities to do any of these checks then save yourself the hassle, shocks, burns etc. and take the amp to a tech.

funkydunkey

great ol' post. hope you get loads done the weekend. enjoying following your progress. I am looking at building something around 5-10watts. something like a champ-style design. have been looking around online for parts. how do you find ampmaker? i contacted them about getting a package put together but to be honest they seemed faiirly uninterested. have you had any luck getting parts from them?

Paolo_M

Ampmaker were sound with me anyway. I know Barry was mad busy and had stopped doing the kits during Jan and Feb while he was still trying to meet the xmas backlog.

On Ampmaker: The OT arrived yesterday

It measures out fine for ratio etc. but it's fairly unbalanced. There's 98 ohm for one anode to CT and 76 ohm to the other. I guess I'll wait to hear how it sounds, but I may end up upgrading it. There's no end bells available for these either which is a bit annoying.

Got the turret board drilled and staked. The empty holes are for mounting.


Unfortunatley I'm having supplier problems. I ordered 20 X 1N4007 rectifier diodes from Maplin in a hurry as I'm taking a week off work next week to finish this project and didn't have any 4007s left. Here's what arrived...

They were in stock, they just made a "delivery error". Even four would have built the damn bridge!! :mad:

Bluebell Audios stuff only shipped out yesterday, even though everything was "in stock and ready to go" a month ago when I ordered.

Anyways 'nuff giving out.
Here's a bunch of amp related book recommendations for you.

Another recommendation is to just buy a damn kit clone of your favourite amp and don't bother with your own design!!

On the brighter side, I have this in for service

It was built in the '70s by a Marmac who were based in Sligo. I was talking to the guys who designed it the other day. They still work in Joe O'Neills in Glenamaddy but Marmac has ceased to exist a long time now since "the transistor amps came along". Those are original Mullard EL34s.
When I look at that power transformer (wound by Marmac themselves) compared to the one for my amp build I can't help thinking of that scene in Crocadile Dundee; "That's not a power transformer, this is a power transformer!!"

Paolo_M

Bluebell gear is now not due until next week...:mad:

These delays have given me a lot of time to think/re-think my circuit design.
Re-read a lot of the books and done a lot of circuit analysis on my "ideal tone" amps; Vox clean/crunch, Plexi gain, Soldano/Mesa face-melt. Here's yet another revised schematic. Reckon I could write a book on the AC-30, SLO, Super Lead, Mark IIc etc. at this stage!!
.

Check out this guys page http://www.freewebs.com/valvewizard/. I've used his load line plotter .xls extensively. There's also a bunch of great articles on there explaining how each amp section functions.

Got some of chassis drilled, and "dry fitted" the transformers and turret board.
Decided not to risk damaging by work bench so I used the kitchen table instead!! :pac:

Really seeing the benefit of being so precise with a template and double checking everything. Every hole was within a mil of where it should be, and it's easy to widen a pilot hole to full size in the "right direction".

My apprentice has been a great help!!


Also have ordered an empty American 18mm pine 2 X 12 cabinet from Tube Town. Ordered up a V30 and G12H30 for my rock/metal cabinet. Got the tolex and glue for my chassis box from the same place.
Will also build a "vintage blues" 2 X 12 cabinet with a greenback and maybe a bulldog. That's for another day...

Gigging in DeBarras tomorrow night and on the rip(ish) for Paddys weekend so there'll be nothing done 'till next weekend.

punchdrunk

paolo
looks feckin deadly so far!
who are you getting to paint the chassis?
how much were the ampmaker trannies? cheaper than sowter/mercury mags?

best of luck!

Paolo_M

Cheers punchdrunk, I'll use silver undercoat and laquor coat the chassis myself. May get proper face and rear plates made up if the amp turns out well, plexi-glass has the best tone from what I've heard!!
The transformers were around the same price as the hammond equivalent. Mercury tends to be more expensive 'cos they are fitted out with majic mojo inside.

Bluebells gear arrived yesterday...at last.


Here's the hole punches, and they are the jawb. Absolutley essential for anyone punching their own chassis.


Sad to say I got up at 6am this morning to get started, I think I may have a problem....
Got front rear and top of the chassis drilled, punched and dry fitted.
Everything fits pefectly.


The front panel controls are from left to right:
Input jack

Channel switch = This brings in an extra gain stage to go from clean to crunch/overdrive.
On top of it is the bright switch which works on both channels.

Gain pot
Above it is the gain boost switch. This kicks in yet another gain stage for face melt madness. It works on the overdrive channel only.

Next up is the bass, mid and treb controls. Above the bass control is a bass shift switch to remove some low end on the overdrive channel for a more Van Halen type tone.

Next is the master volume.

Then you've the resonance and presence controls. Above them is a three position switch. Centre off = no feedback like a Vox or Marshall 18 watter. To the left will have more feedback so that the amp stays tight when the master is set low and to the right will be for when you're playing flat out.

Finally you've the stand-by, power and pilot light.


The back panel goes:
IEC jack, mains fuse, HT fuse, Solid state or Emulated valve rectifier switch, Class AB to Class A switch, "Single ended" switch, Pentiode or Triode switch and the 8 and 16 ohm jacks.


Next steps are to remove the blue protective film. Paint and coat the chassis and get wiring.

Eoin Madsen

Looking good. I think I was going to bed around the time you were getting up. :pac: How did you make the hole for the IEC socket, incidentally?

I sprayed my chassis with a nice matt black metal paint, but some of the corners flaked off. I probably should have researched the painting thing first.

Paolo_M

Eoin Madsen wrote: »

Looking good. I think I was going to bed around the time you were getting up. :pac: How did you make the hole for the IEC socket, incidentally?

I sprayed my chassis with a nice matt black metal paint, but some of the corners flaked off. I probably should have researched the painting thing first.

Cheers Eoin,
Ampmaker sell a blank chassis with two IEC socket holes predrilled on either side at the rear of the chassis.

I'm going for a silver/chrome metal paint with two coats of clear laquor, hopefully that'll keep the flakes, dings and rust away. Not sure that herself would approve of having all the anodizing kit in the house, but maybe some day...:pac:

How's your project coming along? I'm interested to see how your tone-stack works out.

I noticed that Mesa are filing for a patent on a single ended switch for the Lone Star Special. Wonder how p*ssed of they'd be if an Irish guy had filed for the European patent first? No-one seems to have patented or implemented the Class switching idea either, Mesa patented Simul-Class which is a different thing. Suppose I'd want to build it and make sure it works first!!

Paolo_M

Apparently 24 hours is not enough for laquor to dry, despite what the instruction say/claim.

Applied two coats of primer, left for 24 hours, fine sanded/cleaned, applied two coats of metallic paint, left for 24 hours, fine sanded/cleaned, applied two coats of laquor and left for 24 hours.
Touch testing the side and it seemed to be fine.
Brought the chassis up to the "workshop" to start mounting the hardware and found I had left a number of finger marks and dents/fudges in the process. The stuff hadn't dried properly.
My heart sank, WHAT THE F*CK, AHHHHHHHHHHhhhhhhhhhhhhh!!!!!!!!!! :mad:
I've done DIY stomp boxes before so kinda' knew what I was doing but this didn't happen before.
I guess the larger surface area etc. takes longer to dry and harden properly, this is a "small box" size chassis.
Spent a couple of hours before work yesterday morning and most of yesterday evening removing the paint work to start again as to do anything else would make a further botch job of it. Still not quite finished. :mad: :mad: :mad: :mad:

Moral of the story just so anyone else can avoid it:
I'd reckon you'll need to leave the final laquor coating to dry for at least 48 hours, preferably longer (I'll be leaving it three to four, the final day sitting on a shelf in the hotpress. Feck the smell, she'll have to live with it!!), before you can start working on it.

Based on this little episode I'd say it'll be the middle of next week before I can start the wiring.

Of all the skills required to design and build an amp from scratch, so far patience is the one I'd say that is by far the most important. Be warned....

Eoin Madsen

Preparation of chassis/enclosure has to be the single biggest pain in the ass when it comes to amp diy, imo. Electronics and high voltages are a cinch by comparison.

punchdrunk

this thread is great,getting some great tips here as i'm thinking of building one of these soon

http://www.tangible-technology.com/tubes/1566/1566.html

alot of the chassis work will be the same story as paolo_m and eoin are going through,

thanks lads for making the mistakes for me :pac:

funkydunkey

a quick question for ye there. the sheet metal punches...is there any great advantage to using these over a drillbit? also, what size punches would i need?

Eoin Madsen

They're essential for the valve sockets. It's quite difficult to get your hands on a drilling machine that will hold the shank of a 30-ish mm drill bit. I really wouldn't want to be drilling that hole in any case - you'd have to step it a bunch of times, and you'd have to go really slow with the big drill so as not to mash your chassis out of shape (and be careful not to scald yourself off it at the same time). And then you'd have to go around the hole a few times with a file.

There's really nothing to recommend a drill for a hole in metal over 15mm. :pac:

Paolo_M

+ 1.
I've found that trying anything beyond 8mm, the size for most pot bushings, with a drill bit will make unholy, burry mess and you'll probably damage the chassis while you're at it.
With the punches, you drill to 8mm, then use the 9.5mm or 12mm punch for carling switches and jacks. If you need bigger holes for filter caps clamps (33mm) or valve sockets the 12mm punch hole will be big enough for the 33mm hole bolt.
It's way easier and way, way neater.

I'll have more progress updates shortley. Some of the board is populated and the chassis is in the shed with the laquor coat drying, again.

Paolo_M

Chassis looks a bit better now...:pac:


Got some wiring done.


Good bit of the board is complete. Obviously I'll tidy it up, straighten ground wire etc. once it's complete and tested.


That's it for now, gonna kick back with a beer or two happy with the days work (got the lawn mowed and front door handle fixed too!! )

boycey

Paolo_M wrote: »

That's it for now, gonna kick back with a beer or two happy with the days work (got the lawn mowed and front door handle fixed too!! )

Loving this thread Paolo, cant wait to see (and hear if you're into your home recording) the finished product.

Good to hear you got that front door handle working, I'm guessing your doorbell has been souped up to 5.1 valve driven surround sound:pac:

Paolo_M

Here's the latest progress pics

The left most one is from Sunday. The other two are from yesterday.

The amp now has heater power to all valves.
Power supply is wired as are the first three gain stages, power amp, gain control and channel switching.
Everything measures out fine and operates correctly.
I even threw some signal in the input and followed it through the three gain stages with the oscilloscope. I'll put some of those photos up if anyone wants to get really nerdy!! They show how the signal get more and more clipped by each stage and you can watch it happen using the gain control to push it more or less.
The Class, triode and valve rectifier emulator switches and channel switching is all working well.
Just have the tone-stack, feedback and phase-inverter wiring to finish.

If I was starting again I'd use pre-tinned, solid-core cable instead of stranded. Stranded is great for small, intricate jobs like guitar wiring, mods, building amps into bean cans etc. but I reckon solid core is the job for buildiing valve amps from scratch.
I also found that using DPDT miniature switches for channel switching is very hard work, wiring wise. You can see the small space you have to work in and mistakes are easily made by accidentally shorting cables...I know this from experience...:rolleyes:
Next time I'll use SPST minis wired to a relay mounted on it's own board.
The above experience really highlighted the value of the scope when fault finding. I had the problem found and corrected very quickly, whereas I'd have been arsing around with a multi-meter for ages trying to find it before.

The empty 2 X 12 also arrived today from Tube Town

along with the tolex and tolex glue for the amp head box. The tolexing is something I've never done before and can't find much info on so it should be fun.

Here a useful web-site that I've refered to a fair bit http://www.el34world.com/.
http://www.amptone.com/ is also a good site for general amp.

How does eveyone do home recording?
I have a Beta SM57 and a laptop. Any advice on the best way of doing it?

Eoin Madsen

Looking good. I've made an embarrassing amount of progress in the last few weeks (none at all... although I did fix the problem with the champ I built about 6 months ago).

Paolo_M wrote: »

I have a Beta SM57 and a laptop. Any advice on the best way of doing it?

Get some kind of preamp, even if it's just a little 2 channel mixer, and then use a jack (or whatever output) to minijack cable to plug into the laptop input. You want to hit the computer input at some kind of line level - computer "mic" input is about as bad as they get.

Get in pretty close with the mic, SM57/Beta 57 tone gets pretty thin and nasty at any kind of distance. I usually start with a close mic perpendicular to the front of the cab and aimed right between the cone and the "dust cap", around 6 cm from the grill cloth. From there, it's a matter of moving position, distance and angle to get the best sound. High frequencies are stronger towards the centre of the speaker. High end also falls off at angles off-axis to either diaphram - the mic or the speaker cone.