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Line Level Technical Question

crosstownk

Howdy,

I'm in the process of installing a competition grade car stereo into a room in my house. It's not impossible but it isn't simple.

Basically, I'm installing a set up consisting of 3 amplifiers (high, mid and low) all fed by a digital sound processor.

Rather than use the car head unit (source), I'd prefer to use my home Pioneer receiver as the source to connect to the car DSP.

The home receiver has a line output of 200mV/1kOhm. The car DSP has an input of 500mV/22kOhm.

Will this work? Will there be any consequences?

All advice appreciated.

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ZENER

IMO ICE equipment has awful sound quality with regards to distortion and S/N figures. Another limiting factor is the power supplies you use to drive them but that's another story.

Short answer is yes, it should work. Most hi-fi components have an output level of 200 to 500 mV into about 10 to 47Kohms. You say the tuner delivers 200mV into a load of 1K, into 22K that level may be higher (less of a load). Worst case scenario is the volume of the amplifiers may need to be increased to compensate for lower drive signal. I'm guessing the 500mV figure is required for full output from the amplifiers.

Care to tell us the various components you're using for this setup ?

Ken

crosstownk

Thanks for the reply.

ZENER wrote: »

IMO ICE equipment has awful sound quality with regards to distortion and S/N figures.

Yes, this can be the case but with decent equipment the S/N ratio can be acceptable. The DSP I use is a noise culprit with an S/N of 85dB. It is noticeable between tracks or maybe during soft classical pieces but as I mainly listen to rock, it doesn't bother me.

ZENER wrote:

Another limiting factor is the power supplies you use to drive them but that's another story.

Agreed. A power supply is going to cost me around €300 to supply the current required. I'm also concerned about noise that any PSU will create.

ZENER wrote:

Short answer is yes, it should work. Most hi-fi components have an output level of 200 to 500 mV into about 10 to 47Kohms. You say the tuner delivers 200mV into a load of 1K, into 22K that level may be higher (less of a load). Worst case scenario is the volume of the amplifiers may need to be increased to compensate for lower drive signal. I'm guessing the 500mV figure is required for full output from the amplifiers.

Yes, I can adjust the amplifiers to compensate. The system is still in the car so I intend to connect the home receiver to the DSP input and see how it performs with the 200mV.

ZENER wrote:

Care to tell us the various components you're using for this setup ?

The components are between 13 and 15 years old but the sound in the car is excellent. I put the system together for sound quality rather than sheer volume. That said, it's also loud.

The in-car source is a Pioneer Premier DEH-P700R but as stated, I intend to use the record out function on my receiver in place of the Pioneer head unit.

The source is fed to a Pioneer DEQ-9200 Digital Signal Processor which is switched to Pro mode. The processor outputs to three individual amps. One for high frequency (Pioneer GM-620) which powers two Pioneer tweeters, the second is to a 4 channel mid range amp (HiFonics American Eagle) that supplies two sets of speakers. The speakers have different response curves. One set is mid-bass and the other set is mid range. The third amp (Pioneer Premier GM-X644) gets a mono signal from the DSP and is a four channel amplifier bridged to two channels. Each channel powers the two coils of a 12" dual voice coil subwoofer.

It might be perceived to be less hassle to buy a new stereo for the house but I love this system in the car and hopefully it will sound as good in the smallish room I plan to install it in. Time will tell..........

ZENER

Just to supply the Subs you'll need 60 Amps at full power !! Almost the same again for the HF section. I imagine the midrange amp will need to be as powerful so you're looking at about 150 to 180 amps at 12 volts to power that lot ! That will be one huge PSU to supply that lot ?! I imagine it'll hummmm like mad too. Unless the PSU is a good quality Switched Mode job then it will have poor regulation leading to poorer sound. A S/N ratio of 85 db isn't great but you shouldn't be hearing a noticeable hiss unless the volume is quite high or the specs are . . . wrong ?

The secret to all of this is the PSU IMO, it's where the top quality Hi-Fi amplifiers score against cheaper integrated or AV amplifiers, usually separate PSU for each channel to provide optimal stereo separation and staging.

Tempted to suggest a car battery connected across the supply rails to provide decent capacitance and smoothing at high loads but I imagine that won't go down well with anyone else living with you.

Of course the overriding question is . . . WHY ?!

Ken

crosstownk

ZENER wrote: »

Just to supply the Subs you'll need 60 Amps at full power !! Almost the same again for the HF section. I imagine the midrange amp will need to be as powerful so you're looking at about 150 to 180 amps at 12 volts to power that lot ! That will be one huge PSU to supply that lot ?! I imagine it'll hummmm like mad too. Unless the PSU is a good quality Switched Mode job then it will have poor regulation leading to poorer sound.

I don't think I'll need anywhere near 180 amps. Currently the system is protected by a 100A master fuse at the car battery. The sum total of all the fuses in the amps is 85A. I'm getting a loan of an 'Amp Clamp' at the weekend that I can clamp around the supply cable to the boot to measure the current being drawn. I'll use this as a guide before purchasing a PSU.

I'm looking at a few switch mode PSUs and may get two rather than one to keep humm to a minimum. I can locate the PSU in an adjoining room if necessary.

ZENER wrote:

Tempted to suggest a car battery connected across the supply rails to provide decent capacitance and smoothing at high loads but I imagine that won't go down well with anyone else living with you.

I want to avoid a lead acid battery in the house for lots of reasons but I like your thinking!

ZENER wrote:

Of course the overriding question is . . . WHY ?!

No logical answer comes to mind............except, maybe, the excellent sound quality that this system delivers in the car. Hopefully it replicates in the house - that's a question I just have to answer...................

ZENER

Certainly sounds like an interesting project and something I've seen a lot of comment on online. The why, I suppose, is purely a personal thing but I'm tempted to point out that the environment inside a car including the ambient noise levels is vastly different to that of a living room or bedroom in a domestic setting but you're already aware of that.

Going on the model numbers you've posted the 2 Pioneer amplifiers are rated at 600W each which equates to about 50 Amps each and that's not including the Eagle amplifier which is probably around the same. Granted you'll probably never run them at full whack but you'll still need to allow some headroom for transients like heavy bass kicks or loud vocal passages.

As for the ClAMP Meter, be sure it's one capable of reading DC. Sounds obvious I know but most clamp meters used by electricians use the transformer effect in order to measure the current so only work on AC at 50Hz with ranges extending up to 450 Hz for this Megger unit.

As the amplifiers are going to alter the current draw in an AC like way this type of meter may not be accurate. Also the frequency range of these AC meters is quite limited so measuring the current while the amp is playing, say, vocals above 300HZ may cause a misreading.

DC clamp meters use Hall effect devices to measure the magnetic field caused by the current flow through a cable but again the frequency of the current drawn through the cable is determined by whatever sound is being played by the amplifier and again may be inaccurate depending on the spec of the meter.

Very interested in seeing the final setup when you have it done !

Ken

Edit: You mention probably getting 2 Switched Mode PSUs, if you do be sure to isolate them from each other using diodes to prevent any issues if the output voltages are not exactly the same. Remember you'll need diodes capable of say 60 amps. this will drop the voltage available at the amps by between 0.4VDC and 0.6VDC. The PSUs will probably have a trim pot to alter the voltage output so you can compensate for this drop using that.

crosstownk

Thanks again, Ken.

You may have the specs wrong for one of the amps. The amp that powers the tweeters is a 2x 35W amp. A 600W amp for a pair or tweeters would be overkill. I built the system based on lower frequencies requiring more power. 2x 35W is adequate for tweeters.

If its OK with you, I may PM you on my short list of PSUs as you appear far more knowledgeable than me on this subject.

Yes, it's a personal project that may fail when it comes to the acoustic environment of a car vs a small room but I'm prepared to take that risk as I'm somewhat confident. The room I intend to use is about 2.5m x 2.5m and is a quiet, well insulated room and the most distant from my neighbour who I don't want to disturb.

Currently the system is still in the car. I need to sell the car ASAP as its taxed to September and passed its NCT last week but the system needs to be removed first. This will take a couple of weekends to complete. I hope to start the removal this weekend - weather permitting - after I perform some tests with the current consumption and 200mV output of the home receiver.

My next research topic is what size suitable cabinets to build for the mid range speakers..............

crosstownk

I tested the 200mV from the home receiver by connecting it to the DSP in the car.

I'll need more than 200mV as with the DSP at full volume, the sound is only barely audible. I think I'll use the head unit as the source and hope that its Aux In will preamp the 200mV signal.

ZENER

What's the make/model of the receiver you're using ? You mention using the "Record" output, is there no line level outputs available ?

Ken

crosstownk

I'm using a Pioneer SX-205RDS

https://www.google.ie/search?q=pioneer+sx-205rds&ie=UTF-8&oe=UTF-8&hl=en&client=safari#biv=i%7C2%3Bd%7CVDoE0Zs9H_PVJM%3A

I'm also considering one (or two) of these as a PSU. Any thoughts?

ZENER

If I was to go on the comments I'd look elsewhere but you're going to be pulling less than 60% of the rated power you might be ok. Tripping breakers at switch on is worrying though. Are there any other options ?

You'll need 10mm^2 cables for the Sub and Mid amps to ensure you don't get a compression effect from volt drop across smaller cables.

As for the receiver, not sure why you're getting such poor volume. Is there a true line level output (775mV) from the unit ? Record outputs tend to be lower level, is that what you're using ?

Ken

crosstownk

There's no line level output - just the two record outs for Tape 1 & 2.

I'm not too keen on the PSU mentioned above and I'm considering a combination of two of these - probably a 40A and a 30A. I'll split components across both PSUs accordingly.

Another obstacle is providing a permanent 12VDC supply the memory circuits of the DSP and/or head unit. A small wallwort will do the job but I assume I'll need diodes as the -12VDC will be shared with the high current circuit.

EDIT: I suppose I could use a relay to that isolates the wallwort when either of the high current PSUs are switched on.

dharn

Following this thread with interest, an other question occurs to me, you will have to build speaker enclosures, wont this have a huge effect on the sound of you system, so after getting all the electrics sorted you might be very disappointed, building speakers is surely an art in its self

ZENER

Nail on the head ! A dark art indeed and very expensive. Still, it is an interesting project but will require a lot of time and a bit more cash than a standard domestic setup.

I've been trying to find some decent PSU for this but at this type of current you're into almost industrial type units.

Aside from the low levels from the receiver how is the project coming along ?

Ken

crosstownk

crosstownk wrote: »

I'm in the process of installing a competition grade car stereo into a room in my house. It's not impossible but it isn't simple.

And this is proving to be the case!!!

I'm still undecided on the PSU but at the moment I'm leaning towards this one. Any comments guys? Reviews seem OK. Some ham radio dudes mention noise on HF but I'm not sure if this will trouble me.

Speaker cabinets are another consideration that I'm acutely aware of. I'm looking at building two truncated pyramid cabinets but I've yet to calculate the volume. I'll be putting the mid range and mid bass into the cabinets but each will be sealed from the other. A very good friend is an excellent professional carpenter who is well capable of building these cabinets to spec. His attention to detail is in excess of impressive so I'm confident he's the man for that job.

I spent the weekend so far removing the system from the car and all I have to show so far are cold and sore fingers!

I'm eager to order a PSU soon. I have given consideration to getting a variety of smaller PSUs so each unit will have a dedicated supply. However, I use an old VW Passat fuse box as the central electrics for the system with one +12VDC supply that feeds all units with supply power and also the remote turn on signal.

All input and potential problems/pitfalls appreciated. I want this to work so I'm willing to take the time consider all options.

crosstownk

3 amps (HF is upper left), DSP hideaway unit and dual voice coil subwoofer. All in the boot.

Same but alternative view of the amplifiers and DSP.

This view shows the VW Passat fuse holder and relay plate that I used as the central electrics for the audio system.

Now it's removed and awaiting a PSU and speaker cabinets for installation in the house...........

A slightly different angle.

Time now to order the PSU and hope Revenue don't shaft me........

crosstownk

A quick update in case anybody's interested.

The power supply arrived today and seems OK but I haven't put it under load yet. Voltage is adjustable and I intend to run it at 14.4VDC.

The speaker cabinets were built last weekend by my carpenter buddy who did a great job. Bass response from the mid bass speakers (with full range rather than crossover) is good. I haven't tested the mid range speakers yet as I don't want full range from the amp I'm using for test purposes to cause them to exceed maximum excursion. The cabinets were constructed based on the T/S parameters of the drivers with a bit of help from WinISD. Hopefully I'll get a chance to paint the cabinets at the weekend. I'm not concerned about the subwoofer enclosure as I'll use the custom built enclosure that was used in the car.

Next job is the wiring. I intend to use the VW Passat central electrics that I used in the car as it will provide adequate fuse protection for all components. I'll be mounting the three car amps on a wall so I need the wiring to look neat.

To date, the project is going well. My only concern for now is how well the PSU will behave under load but I'll know that in a week or two. I'm limited for now as the head unit is in for repair because the CD won't eject - a common fault with Pioneer head units due to a cracked PCB ribbon.

If anybody has any further observations or suggestions I'd appreciate them. I'm not rushing this as its difficult and I want it to be as right as it can be so any input you have is appreciated.

Thanks in advance.

ZENER

Would love to see photos of the MID enclosures ? You may get better efficiency from the Subs with a better designed enclosure as I think you'll be disappointed with the fidelity of the in-car ones. Far too small to pump the air required (for frequencies under 50 Hz) for good low down bass response with that sort of power in my opinion. Getting bass in the limited confines of a car is a far cry from a domestic living room, sealed environment - less decoupling from the cabinets and poorly tunes ports will all contribute to how they sound. Time will tell of course !

In a car you tend to fell the air pressure generated and the vibration of the bass (along with a slight delay) because the cabin is relatively small in comparison, translate that to a comparatively huge air volume of a living room and things change.

Be sure to use large diameter cables for the power to the amps, the amps for the Subs will need at least 10 square to ensure there is no voltage compression leading to poor reproduction.

Looking forward to your first audition of the system and lots of photos

this thread is on my favourites now.

Ken

crosstownk

Thanks, Ken.

I'll post a photo of the cabinets at the weekend. It's hard to find time during the week to do any real work on the project.

Your post echoes my concerns and reinforces my thoughts to date. I appreciate your input.

The cabinets will house both the mid-range and mid-bass speakers. The mid-bass enclosure is adjustable for internal volume to some extent. Both drivers will be subject to a band pass filter from the crossover but will have different HPF xovers for low frequency limiting. The mid-bass will xover at 80 or 100Hz at either -12 or -18dB/octave. The crossover on the mid amp will set the HPF of the mid-ranges higher at min 200Hz with similar slopes. Both will have LPF set at somewhere around 5kHz and I'll start at -6dB/octave. The tweeters will step in thereabouts with a HPF either -12/-18dB/octave.

The dual voice coil subwoofer will have its LPF set near or at the mid-bass HPF but I'll probably start with a slope of -24dB/octave to prevent it doing too much above 120Hz. From my previous in-car experience with this sub, I am expecting to have to attenuate it to avoid too much boom. I may end up needing a sealed enclosure rather than the current ported one.

I'm hoping that the DSP will allow some fine tuning as it did in the car. It offers full network crossover control with various cut-off slopes which will lend to lots of tweaking.

My main focus at the moment is to finish the cabinets before wiring the amps. I'll be using high quality cabling throughout. I removed the Bandridge speaker cable from the car and I'll have a few metres left over!

A lot done, a lot more to do

crosstownk

Some crappy iPhone photos of the cabinets progress and the PSU at 14.4VDC.

crosstownk

First problem encountered yesterday but I was expecting it to some extent and might yet get away with it.

I painted and finished the cabinets over the weekend and then put the mid-bass drivers in and drove them via my home Pioneer receiver.

For some reason, during the design process, I neglected the port Mach. Using the full range from the receiver, there is noticeable 'whistling' from the port.

OK, this is noticeable when full range is used to drive the mid-bass. It may not be as prevalent when the crossover HPF (min 80Hz) is employed as less air will be shifted. Hopefully I'll know more over the coming weekend. It's a nuisance but not a disaster. At worst it means I'll need to drill. At best I'll escape.

Notwithstanding the above, the sound from the mid-bass driver sounds excellent which is encouraging.

Still loads to do.

cnocbui

ZENER wrote: »

IMO ICE equipment has awful sound quality with regards to distortion and S/N figures. Another limiting factor is the power supplies you use to drive them but that's another story.

...

Care to tell us the various components you're using for this setup ?

Ken

Not all ICE equipment is inferior to it's domestic counterparts in distortion and S/N. In some cases it can be superior, but for the most part I would agree.

I have adapted car HiFi components for use as a secondary audio system for use with the TV and the result has been excellent.

It is pretty minimalistic and basic. Input is via a 3.5mm male headphone plug, which is usually parked in a socket with a lead to RCA connectors in the audio-out of the the TV. By unplugging the jack, it can be used as a 2 channel system with an iPod, phone or any source with a 3.5mm headphone socket .

The input lead connects to a Nakamichi EC-200 active crossover which allows for the crossover FQ to be selected and for the low/hi output gain to be adjusted. THD is less than 0.003% and S/N is greater than 105db

Apart from the speakers, this is THE critical component. I previously had a Kenwood crossover that did the duty. It malfunctioned after many years and I replaced it with the Nak and could kick myself for not having done so at the outset. The difference in quality and performance was like night and day. A hiss I had always thought was from the PSU just went, leaving silence and the overall sound quality improved significantly.

The crossover feeds two Nakamichi Power amps - a PA-300 and a PA-400M. The former delivers 75W into 4 ohms - two channels. THD is 0.003%. FQ response 5Hz-50KHz ±1db. S/N ratio is better than 115db. The latter amp is 140W into 4 ohms - single channel. THD is 0.002%. FQ response 1Hz-70KHz ±1db. S/N ratio is better than 110db. All specs are at the rated outputs.

Not too shabby for 'ICE' components.

The PSU is a DAIWA variable voltage unit rated at 30A. And mana from heaven - it has a knob on the back to allow you to adjust the speed/noise of the cooling fan.

Speakers are ICE components in custom enclosures.

Manual volume control of the rig is it's achillie's heel.

crosstownk

cnocbui wrote: »

Not all ICE equipment is inferior to it's domestic counterparts in distortion and S/N. In some cases it can be superior, but for the most part I would agree.

I have adapted car HiFi components for use as a secondary audio system for use with the TV and the result has been excellent.

It is pretty minimalistic and basic. Input is via a 3.5mm male headphone plug, which is usually parked in a socket with a lead to RCA connectors in the audio-out of the the TV. By unplugging the jack, it can be used as a 2 channel system with an iPod, phone or any source with a 3.5mm headphone socket .

The input lead connects to a Nakamichi EC-200 active crossover which allows for the crossover FQ to be selected and for the low/hi output gain to be adjusted. THD is less than 0.003% and S/N is greater than 105db

Apart from the speakers, this is THE critical component. I previously had a Kenwood crossover that did the duty. It malfunctioned after many years and I replaced it with the Nak and could kick myself for not having done so at the outset. The difference in quality and performance was like night and day. A hiss I had always thought was from the PSU just went, leaving silence and the overall sound quality improved significantly.

The crossover feeds two Nakamichi Power amps - a PA-300 and a PA-400M. The former delivers 75W into 4 ohms - two channels. THD is 0.003%. FQ response 5Hz-50KHz ±1db. S/N ratio is better than 115db. The latter amp is 140W into 4 ohms - single channel. THD is 0.002%. FQ response 1Hz-70KHz ±1db. S/N ratio is better than 110db. All specs are at the rated outputs.

Not too shabby for 'ICE' components.

The PSU is a DAIWA variable voltage unit rated at 30A. And mana from heaven - it has a knob on the back to allow you to adjust the speed/noise of the cooling fan.

Speakers are ICE components in custom enclosures.

Manual volume control of the rig is it's achillie's heel.

Hey - well done on getting it all up and running!

I'm almost there, I have the system mounted and wired for power and sound. All that remains to do is hook up the PSU and the head unit that I collected from the repair shop today. Hopefully the coming long weekend will see it in action.

Thankfully, both the head unit and DSP/crossover share the same remote control for basic functions - real tweaking has to be manual but I have an extension lead for the DSP dash controller which is about 7m long so at least I can tweak from the listening position!

dharn

Any more pictures of the speakers

crosstownk

dharn wrote: »

Any more pictures of the speakers

I'll post some over the coming days.

I finished the wiring tonight and fired it up. It sounds incredible without much tweaking but it does need tweaking.

I started with Drifting Away by Insomnia and got good response. I cranked it up and the ammeter on the PSU showed peaks of 50A. I went outside to put the bin out and see how much sound was 'escaping'. It all sounded quiet enough except for the buzz from the bass coming from the soffits!!!! The bass is also very noticeable in my feet through the floorboards.

Then I stuck on Sunset Boulevard - The Lady's Paying - which sounded excellent but it peaked at almost 70A :eek: I've the PSU at 13.8VDC but will wind it up to 14.4VDC once I'm happy that all is well. The additional voltage will hopefully add to the overall sound.

I've more tweaking to do and I also need to sort out the change over relay for memory back up for the DSP and head unit but I'm not sure of what back up supply to use. More research.

So far it's working and sounding better than I expected. The mid amp gets hot quickly at high volume so I may need to employ some cooling or place the amp horizontally rather than its current vertical.

crosstownk

A quick pic. I'll sort out grilles/covers for the speakers at a later date. I also need to have my carpenter buddy construct a housing for the head unit and DSP that are on the shelves in the photo.

crosstownk

The system is up and running a couple of weeks and I'm happy with the sound from it. HF caused me hassle as it wasn't loud enough in the mix but I increased the HF amp gain today and it seems better. If I'm not happy with it after a few days I'll have to reduce the Mid amp gains. That won't be an issue as the system is way to loud to run at full volume so I can afford a bit of reduction. The subwoofer is awesome. If I crank up the volume to max, I can hear the bass frequencies 4 doors down!

Anyway, I've a little problem. I use a changeover relay to switch between the main PSU and a smaller one that I use for memory backup on both the head unit and the DSP. When the main PSU is switched off the voltage slowly decreases over 6 or 7 seconds. The relay doesn't changeover until the voltage drops to approx 3 volts. The head unit looses its memory but the DSP is unaffected - thankfully, as the DSP requires a lot more settings but its a pain to have set up the head unit each time.

What can I do to either make the relay changeover sooner and/or cause the voltage to drop more rapidly? I was thinking of putting a bulb or some other load to cause the voltage to drop quicker.

Any suggestions?

EDIT: Temporary solution. If I simply switch the main PSU off while the system is powered up the voltage drops quicker and the head unit retains its memory. I can live with this but would prefer to power it down before switching the PSU off because when I turn on the PSU the next time, the system springs to life instantly. Plus the speakers pop and crackle when I switch the PSU off.

ZENER

How fast does the change-over need to be to avoid losing the settings ?

What about using the relay as a changeover but with its coil powered from the main switch ? That way when the power is switched off the relay switches over connecting the auxiliary PSU to the radio tuner.

The changeover should be quite fast hopefully keeping the memory intact ?

I can pm you a drawing if I'm not explaining it properly.

Ken

crosstownk

ZENER wrote: »

How fast does the change-over need to be to avoid losing the settings ?

The closer to zero the better but 3 seconds should do the job.

ZENER wrote: »

What about using the relay as a changeover but with its coil powered from the main switch ? That way when the power is switched off the relay switches over connecting the auxiliary PSU to the radio tuner.

The coil is powered by the main switch. The problem is that when the main switch is powered off the voltage takes some time to drop. The 6 or 7 seconds is enough to cause the head unit to loose memory.

ZENER wrote: »

The changeover should be quite fast hopefully keeping the memory intact ?

I would have thought so but the PSU voltage drops slowly after power down.

ZENER wrote: »

I can pm you a drawing if I'm not explaining it properly.

Please do. Just to be sure we're on the same wavelength (which I think we are)

Thanks, Ken.

ZENER

I take it the relay coil is powered from the output side of the large PSU ?

What if the coil was powered from the smaller PSU ? With this PSU on a switched socket, when the switch is flipped to on it would energise the coil in the relay - disconnect the main power from the large PSU and immediately change over to the smaller PSU which could be either switched via a contact in the relay or via a diode to the STANDBY connection on the Head Unit ? The changeover would be milli-seconds in duration.

It will mean using a relay with higher rated contacts to carry the current from the large PSU to the amplifiers.

I'll draw something up tomorrow and PM you. I'm sure there's a way to have the whole thing on one mains switch too. Leave it with me.

Ken

ZENER

Could you try something for me ? With the main PSU turned off and the standby PSU on can you check if the REMOTE out from the Tuner has any voltage on it when you try to turn it on ?

Ken