Quick Cab Question!

Beecher

Okay! My cab has finally arrived to finish my rig, cept I only just got to open it now (wine reception in college led to one thing, which led to another etc etc and its now 1:30 in the morning). Anyways its 16ohm parallel with 2 inputs, so do I put 8 ohms into the 2 inputs (2 x 8 =16) or 16 ohms into the 2 inputs (My power amp has an 8 ohm left/right output and a 16ohm left/right output)

Edit: Also, Can I just run through 1 input on the cab or do I need to use both?

Beecher

Okay this sucks, Internet research has thought me that I can run a lower ohm head into a higher ohm cab, Ill just lose output power and headroom, so to be safe I used the 8ohm output of the head into the cab. No sound! ARG (yes I am using speaker cables etc). Now the front the of the power amp has 2 fuse sockets, both 160mAM power tube fuses. Theres a little red light above them and the right one is lit, and when I touch the head of the input cable the light gets brighter! Is this supposed to happen or is the fuse gone? Afaik all the tubes are fine.

Edit: I swapped the two fuses around and now the other one is lighting up, so it def looks like a broken fuse I JUST WANNA ROCK!!

Ancient1

Emm....best to wait for Eoin "Amp Surgeon" Madsen...

Rustar

Beecher wrote:

Okay this sucks, Internet research has thought me that I can run a lower ohm head into a higher ohm cab, Ill just lose output power and headroom

You sure about that? I'm no expert at this myself, but I understood it to be that if you had a 4ohm head you could plug it into 4 or 2, but not 8.
So an 8ohm head could use 8,4, or 2. So you should be ok if you use the 8ohm output from the head and the cabs are 8,4, or 2. Not sure what's going on with the dual inputs on the cabs though....

feylya

4 ohm head into 4-16ohm cab. I think it just has to have enough of a load. Having less of a load means BOOOOMMMM!

Beecher

I think ive figured the impendance for this anyways, one input is used for the signal from the poweramp @ 16ohms, the other input is for another 2x12. Ive re-fused the poweramp but all im getting now is a hum from the poweramp (not the speakers) when I though the head of a cable, and turning on the distortion of the pre-amp distorts the hum. :eek: ARG :eek:

Edit: Now when I plug my guitar in I can hear it but the sound is coming from the poweramp, not the speakers! ARG!

Edit Edit: Now I know why it wasnt working:



Tada, the sockets arent connected to the speakers! Which means ive prob be running my poweramp without a load on it which sucks! Im not happy :mad:

Rustar

Glad you fixed it! I'm still waiting for that Eoin Exposè on input impedances though......

Beecher

Cheers Rustar, Just finished wiring up the speakers and it appears to work (my poweramp apparently has 2 transformers, one for each side, and ive only run the left without a load so im not sure if its okay, but the right one is fine). Sounds awesome, expect a review with soundclips and pictures tommorrow.

I hope Eoin does do an expose, I keep hearing opposite opinions about mismatched impedences and which one is harmful!

Edit : Just cranked the gain there on it! MMMMMMMMMMMMMMMMMMMMMMMMMM

Doctor J

Rustar wrote:

You sure about that? I'm no expert at this myself, but I understood it to be that if you had a 4ohm head you could plug it into 4 or 2, but not 8.
So an 8ohm head could use 8,4, or 2. So you should be ok if you use the 8ohm output from the head and the cabs are 8,4, or 2. Not sure what's going on with the dual inputs on the cabs though....

Nope, that's the quick way to make your amp go on fire without use of matches or a lighter. It's the other way around.

Cabs must always be equal to or have a higher ohm rating than the power amp.

Karl Hungus

Now that you're sorted...

Beecher wrote:

Okay! My cab has finally arrived to finish my rig

What's the rig? :v:

Paladin

Im not Eoin but I work for Analog Devices designing amplifiers (among other things) so I think I would trust me on this kind of stuff (I wouldnt hire my lazy ass though).

If you mismatch impedences its not necessarily the end of the world, but it is not recommended for a few reasons.

Firstly, the one you are worried about, blowing things up...

If impedences are matched, and a poweramp can give more power than a speaker is rated for, then speaker can be blown up.

If the poweramp is rated for 8ohm, and you attach a 4ohm speaker, then you will be putting more current through it then you would a 8ohm speaker. This means more power (incidently, power is proportional to resistance X current²). Therefore a 100 watt rated 4ohm speaker can be blown by a 100W amp rated for 8ohms. However if you dont crank it up full it wont necessarily blow it up. But it could!

Going the other way round, attaching a 16ohm speaker rated for 100W to a amp rated at 100W for 8ohm, it will not be blown up.

Also remember the basic rule connecting speakers, parallel decreases the impedance, series increases.


The other more subtly reason that you should match impedences is that the signal may be slightly distorted if it is not matched. This may or may not be audible. Arguments between audiophiles and others often ensue
Anyway, just match them

Beecher

Karl Hungus wrote:

What's the rig? :v:

Guitars -> Boss CS-3 Compressor -> Boss DD6 Delay -> Morley Power Wah -> Engl 620 Rackmount Tube Preamp -> Alesis Quadraverb Rackmount (Great Chorus/Reverb plus it has input and output level knobs so it makes up for me not being able to use my attenuator) -> Engl 830 Rackmount Tube Power Amp -> 2x12 Cab With Celestion Vintage 30's.

Best thing is besides the cab its all second hand off ebay (even got new JJ tubes thrown in with the poweramp and preamp) and cost me pretty much under a grand, the wah being the best deal at 12 squids :v:

Edit: Will have pics and soundclips tommorrow, im only after finishing screwing the cab and poweramp back together.

Rustar

feylya wrote:

4 ohm head into 4-16ohm cab. I think it just has to have enough of a load. Having less of a load means BOOOOMMMM!

Doctor J wrote:

Nope, that's the quick way to make your amp go on fire without use of matches or a lighter. It's the other way around.

That's the problem with having a pointy head like mine, you can't tell whether it's on forwards or backwards!
:v:

Karl Hungus

Beecher wrote:

Guitars -> Boss CS-3 Compressor -> Boss DD6 Delay -> Morley Power Wah -> Engl 620 Rackmount Tube Preamp -> Alesis Quadraverb Rackmount (Great Chorus/Reverb plus it has input and output level knobs so it makes up for me not being able to use my attenuator) -> Engl 830 Rackmount Tube Power Amp -> 2x12 Cab With Celestion Vintage 30's.

Best thing is besides the cab its all second hand off ebay (even got new JJ tubes thrown in with the poweramp and preamp) and cost me pretty much under a grand, the wah being the best deal at 12 squids :v:

Edit: Will have pics and soundclips tommorrow, im only after finishing screwing the cab and poweramp back together.

Sounds mad. I be that would be a force to reckon with,

Eoin Madsen

Everyone can relax, I'm here now...

Rustar wrote:

You sure about that? I'm no expert at this myself, but I understood it to be that if you had a 4ohm head you could plug it into 4 or 2, but not 8.

No, it's actually the opposite. The head should be lower than the cab or equal. 4 ohm head, 4/8/16 ohm cab. But preferably 4 ohms. 8 ohm head, 8/16 ohm cab, but preferably 8. Having a lower impedance load can kill your valve output transformer, power FETs etc. They basically overheat from too much current.

There's no advantage to using two outputs from the same amp into one cab, and it does confuse the impedance issue, so I'd advise you not to do it. And never plug two amps into the same cab. The second jack is for linking another cab in parallel.

There's very little risk of blowing speakers with an impedance mismatch in a guitar amp, the speakers are almost always rated for more power than the amp can put out.

I gather it's less of an issue with solidstate amps, but in a valve amp, a mismatch changes the reflected impedance on the valve plates which does alter their behavior. Absolutely everything changes the sound in some way, the only issue that's really debateable is whether it's better or worse.

SirLemonhead

Post a picture of the rack

It wasn't me!

I agree. Today is the day and the day thou shalt post pictures of that mighty rig.

Beecher

Okay! Only got one piccy on my laptop (will take more and sound samples when I get home)

Karl Hungus

Madness. I'd seriously love to hear how that sounds.

SirLemonhead

Nice. That older Engl preamp model. How much did you pick that up for?

And where did you get the rack case, and how much? I'm looking to get one myself, but need one deep enough to hold a rack poweramp.

Any plans for those last 2 empty slots in your rack?

Beecher

MasterOfSolos wrote:

Nice. That older Engl preamp model. How much did you pick that up for?

And where did you get the rack case, and how much? I'm looking to get one myself, but need one deep enough to hold a rack poweramp.

Any plans for those last 2 empty slots in your rack?

Got the preamp + poweramp + case off Ebay together for I believe 520 euro a few months ago! The preamp is amazing though, has less channels than the current Engl lineup but has more tubes in it Have seen them go on Ebay for 200 euro buy it now, well worth getting, it really can cover anything from Mahavishnu Orchestrea to Dream Theater to Morbid Angel!

The case is an AAC Economy case, can be got from Musik-Produktiv quite reasonably. The 2 slots will be filled eventually, probably a Korg DTR-1000 racktuner and im not sure what else I really need, im quite satisfied with the tones but im sure ill find something I want!

Beecher

Karl Hungus wrote:

Madness. I'd seriously love to hear how that sounds.

No probs, Heres a linky. Its just part of a dragonforce song, I was just messing around with recording/micing my amp with cubase today so I can start getting involved with the recording/collaboration forum. Gain is only at 5 for the whole recording, you'd want to hear it 10!

feylya

How did you record that? Mighty impressive sounding!

Beecher

feylya wrote:

How did you record that? Mighty impressive sounding!

Amp is recorded through an SM57 into an Audigy 2 with the KX drivers into Cubase (I always meant to upgrade the Audigy 2 but with the KX drivers im getting 2ms latency and a decent recording sound and 2 audio ins so im leaving upgrading it for a bit.

Drums are from Groove Agent (got it off ebay for 20 squids!) and the piano is a free vsti called 4front (will post in Recording/Collab free resources section).

feylya

What interface do you have between the SM57 and the Audigy? Is it just plugged in straight?

Beecher

feylya wrote:

What interface do you have between the SM57 and the Audigy? Is it just plugged in straight?

A cheap Behringer 6 track desktop mixer (for mic interface)

feylya

I've been looking at getting myself one of these in the future

http://www.thomann.de/thoiw6_behringer_mic100_tube_ultragain_micpreamp_prodinfo.html

Just to test it out along with a SM57.

Beecher

Im currently using this, but for recording a guitar/vocals on their own the MIC100 would be far superior. Behringer make some great stuff, just build quality tends to let them down (to turn on 48v phantom power I press the 48v switch on, to turn it off I press the switch off, then unplug the mixer! Its ridiculous and its a fault in all of them, not just mine!). I'd totally say go for it, these days you can get some great results for very little money!

Edit: Perhaps a bargain hardware guide should be made for the home recording/collaboration forum?

feylya

Well, I won't be getting it for a while. I've my eye on a few other things first and I have to get paid too :v: