seperate chassis for power supply

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i am thinking about building my first amp soon, i havent thought much about it yet though.

I want to make an intergrated amp, but with a seperate power supply and having each channel be its own mononblock. Sort of like the Mark Levinson No32 with the "dirty box" and "clean box" Would this have any siginifigant sonic advantages, I know the seperate chassis would add a lot to the costs of it, would that money be more wisely spent purchasing better parts?

Any designs out there to recommend? i am wanting around 200 watts class A. I was looking modifying the aleph 2's to increase there power output. How would i do this? high voltage? more transisters?

Also any help on control circuts would be greatly appreciated. I dont want a fancy display or anything, just basic input switching and volume control.

thanks alot,
So long as you put the power supply filter caps in each monoblock, it should be fine. I'm doing the same thing in my system. That is, 5 monoblock ESP 3A amps on a 2kW tranny. Although, now I'm looking at a switching design with HV outputs to directly drive ESLs.

Woops, I forgot-- you'll also want separate bridge rectifiers for each monoblock, and because of that, you must have filter caps for each monoblock anyway. Not necessarily inside each monoblock, though.

Putting the filter caps as close to the audio circuit as possible (inside each monoblock) will filter out the noise the wire going to the power supply with gather. Any long wires in audio circuits will inevitably pick up your favorite classical radio station, not to mention long wires are the playground for runaway oscillations.

To tell you the truth, because I was told it is a good idea to put the filter caps as close as I can to each audio circuit, I have never observed the effect of doing otherwise. =)

Short Antenna Wires

Altaic, the RF pickup is a function of the length of the connecting wire and the impedence loading the wire.
The psu caps will function as a dead short to any signal induced into the wire, so for power supply feeds RF pickup will not present as a problem.
If the inductors suggested as above are included in the amplifier cabinets, then you should not ever have a problem.

Regards, Eric.
so should i build the psu as in the design and just add more caps into the monoblock, or can i get away with less caps in the psu? How much will the capcitance or inductance of the wire affect the amp? Should i try to make the wires as short as possible, say 5 or 6 feet?

Joined 2002
I don't have direct experience with the following idea, and there may be a reason why it wouldn't be a good idea that hasn't occured to me, but here's my thought.

If the bridges were to be placed in the amplifier cabinets, the connection between the main PSU (now just the transformers and primary circuitry) will be the secondary AC. This can be cabled to each amp cabinet without a problem and rectified as soon as it enters the mono blocks. This would also isolate the transformers and their associated magnetic field issues from any DC lines. This being an integrated amp (kind of a contradiction in concept), the PSU cabinet would also house the pre-amp transformer and its secondary AC would be cabled to the pre-amp unit.

Maybe someone can shoot some holes in this idea. It's just a concept at this point. I don't know of it ever being done this way before.

Rodd Yamas***a
My design goal is to keep the audio signals as pure as possible (i know its quite generic, but thats what i'm aiming to do)

my options were to make a pre amp/ possibly with an external power supply, and then seperate monoblocks, this would require 4 chassis to do, Also part of the signal would still be exposed to the transformers (in the monoblocks)

My reasoning is if i take an "integrated amp" and seperate the power supply and channels as much as possible, this will improve the quality greatly, this is just a complete guess for now, and i'm hoping to experiment with it.

Like i say my electonics experience is fairly limited so i am wanting to modify an existing design. Any ideas on were to start from would be much appreciated. My goal is to get 200 watts class A output.
Rodd, you'd want to keep AC as far from inputs as possible, otherwise there will be lots of noise on the inputs. If you have the bridge rectifiers in each amp enclosure, you have to make sure all power wires are kept away from input wires. It's easier to put all of the bridge rectifiers in the psu enclosure and not have to worry about it.

i was wanting to put the rectifiers in the psu box

Would there be advantages to doing 2 seperate psu's withing the psu chassis, or would monoblock amplifer section provide sufficent channel seperation?
Nelson made a recent comment that caps should be in both the outboard psu and in the ampplifier enclosure, and large value series inductors between.

What role does the inductor play in this? more generally, what is an inductor used for anyways?

thanks for all the help so far,
CLC Supplies

At work I have an old high-end Akai amplifier that used to have an internal switchmode power supply, whose parts are no longer available.
I used an old rack mount case and fitted two transformers each with seperate secondaries, 4 bridge rectifiers, and four capacitors.
This gives 4 fully independant supplies that are wired to the amplifier box by 4 fig8 cables.
All earth commons are in the amplifier box and none in the psu box.
This works really well, and is probably a bigger current rated supply, although same voltage as the original.

Putting an inductor in series with each supply line forms a CLC supply.
The inductors act as energy stores in addition to the capacitors, and further keep any HF junk out of the amp, and gives smoother power rails.
I have not tried this, but expect it to be very worthwhile.
If Nelson says it is good, well then it is very likely to be so. :)

Regards, Eric.
If the bridges were to be placed in the amplifier cabinets, the connection between the main PSU (now just the transformers and primary circuitry) will be the secondary AC. This can be cabled to each amp cabinet without a problem and rectified as soon as it enters the mono blocks.

The large charging current pulses could be a cause of radiation. You'd normally want to keep these lines as short as possible for that reason...

They are also large in value (compared to the nominal DC current draw). If this is meant to be a 200W class-A effort, that would worry me! What sort of connectors would you use?
i'm planing on using neutrik speakon connectors

there rated at 25 amps contionous, that should be enough, right?

Would placing all the caps in the amp chassis help the radaition problem?

Wouldn't this cause the power cables to pick up alot of interference?

I'm starting to think that the best idea would be putting caps on both sides, possibly inductors?

As for the wires what would be the best way to shield them? Coaxial? litz config?

Has anyone had experience with external ps's in preamps, i'm curious if the DC is only problamatic at high currents.

I'm probably going to be bumping the power down to 100 watts, for practicailty reasons :( Possible the x100 i've been seeing posts about.

thanks for all the help so for,
The current pulses occur between the mains TX and rectifier, and the smoothing caps. So, I would put the caps in the PSU box.

I would agree with others here - make sure that you've got some good quality low-ESR capacitors close to the power amplifiers for decoupling. These won't draw current in sharp pulses, so avoiding the current-induced interferrence.

RF pickup is avoided by careful decoupling - small-value caps connected between the rails and ground or chassis. The best place to do this is on the back of the Neutrik connector in the amplifier chassis, if practical...

Too be honest, I'm not sure if this would be much of a problem in practice. I've got a good empirical technique for testing this - call your cellphone, and then wave it near the kit!

Not sure what sort of cable you'd use. I'd worry more about conducter size rather than screening...

considering your idea to use Speakon Connectors, I'd rather suggest to use Neutrik's "PowerCon" connectors. Much too easily those connectors might get mixed up, and I'm afraid your speakers would not like your PSU's output!:D
BTW: I'm using Speakon since 1 year or so, and I'm going to change all my speaker connections to that by the time. SpeakOn's are rugged and VERY reliable, even in "bad" environments like stage or so.

Good luck for your project!
Distant PS

If you are placing the PS and Amp in separate boxes, you can use an octal female socket on the PS derriere and an octal male on cord to the power supply. Consider using a pair of the inter-connects for a safety interlock.

In my single chip amps, where there are a couple amps ganged together, I use PC style connectors for the power. These aren't expensive and the user can make sure that they are always plugged in correctly ("polarized") by snipping the right plastic bits. I use the 6 connector headers and connectors. They will handle 7 amps/250 VAC. It helps if you have a crimper to use these.
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