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Old 8th May 2002, 10:43 PM   #1
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Default PCB for Aleph P 1.7 preamplifier

hi,

I founded the pcbs for the Aleph P 1.7 preamplifier at http://web.vip.hr/pcb-design.vip , and I would like to build it.

The design is really awesome and it looks unbeliveable,
but like you see there is no power supply on the pcb.
I talked to Kristijan (guy who designed pcbs), and he said that with separate power supply (in another enclosure) preamplifier would sound even better, if that's possible.

Now I am little confused, I tought that all wires should be very short, and with separate enclosure they will be longer than in the same enclosure - with preamp.

Can anyone tell me which way should be better, and why ?
Is it worth it to install power supply in separate enclosure ?





---
Strobo
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Old 9th May 2002, 12:14 AM   #2
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Using short wires for the signal is a good idea. For the power supply, it's a lot less critical. The power supply puts out DC, which is not particularly influenced by long runs of cable.
Putting the power supply in a separate location helps by reducing hum (picked up from the transformer), and various kinds of high frequency noise (emitted by the diodes in the rectifier, etc.).
It can be a nuisance when you want to move things around, though. Consider having a detachable cable between the power supply and the circuit itself.

Grey
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Old 9th May 2002, 12:38 AM   #3
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Exclamation Power Supply wiring

With the greatest respect, I beg to differ. The regulated supply and or filter caps should be very close to the circuit with short wires for low impedance and good regulation and stability. Isolation of radiated transformer noise is a good idea but other factors must also be considered. The line rejection is made worse by signal currents in the power supply creating voltages in the wire's series impedance. RF noise from the supply is not reduced since it is conducted by the wire. If this wire is not shielded more RF can be picked up by the cable. Power supply design is as important as "signal path" to how a circuit sounds. You do a great diservice simplifing this subject as can have great impact on the performance of a circuit.

H.H.
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Old 9th May 2002, 01:15 AM   #4
Evaas is offline Evaas  Canada
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Question how to solve all problems

So how do you build a better power supply? What if I put some large caps in the amp enclosure across the power rails in addition to the power supply caps? and how do you prevent the rf from being transmitted through the wire to the amp? I'm talking about an unregulated supply, so there's no feedback path

Evan
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Old 9th May 2002, 01:47 AM   #5
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Default Separate power supply

I am quite surprised that from all audio components only preamplifiers have separate power supplies (in general). This was maybe important when RIAA stages were part of the preamp, but now they are usually not and if someone needs phono preamp it's another separate box with it's own supply.
SS preamp circuits are not much different than power amps front end circuits. Yet those front end circuits are never separate from the amp (the only exeption I'm aware of is Coda amp) and they work quite happily in spite of the big toroid transformer inside the amp.
My impression is that separate PS for the preamp has only sense if there is not enough space inside preamp enclosure or the manufacturer wants to elevate the price of the product.
I have never seen separate power supply for CD transport or DAC (again the only exeption I know is Lab47) although those units are much more sensitive to transformer noise than simple preamp circuit.
I can say from my experience that power supply has very big influence on the sound (probably the same as the circuit itself). The same with wires. My suggestion is that it's better to do it in one box. But if someone wants to do it separately good idea is to put transformer, rect. bridge and some caps in one box and then the rest of the caps and active regulation circuit in the same box as the preamp. Also I recomment using split bobins transformers (not toroidals) and separate supplies for right and left channels.
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Old 9th May 2002, 02:04 AM   #6
Evaas is offline Evaas  Canada
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Talking one counterexample...

one example of amps, phono stages, & cdp's that use outboard power supplies is naim audio. In fact I think the only thing they make with a ps included is the integrated amp.

but I guess I'm hearing that you don't gain much by moving the ps to a separate box, and you could hurt some if done wrong.
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Old 9th May 2002, 02:19 AM   #7
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You just confirmed what I said. You could give me only one example. To tell the truth Naim equipment never caught my eye. It doesn't seem to be popular were I live.
If you shield supply of your Aleph preamp inside chassis I don't think it would be different than separate supply.
Although those boards look pretty big and you might not have enough space.
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Old 9th May 2002, 02:35 AM   #8
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Sorry if I was misleading above. I'm at work and have to fit my replies into spare scraps of time between doing other things.
My usual strategy is to have the transformer, rectifier, and bulk caps in one box, then regulation and more caps in the same chassis as the circuit.
Another nice trick is to use circuit topologies that inherently cancel out signal junk on the rails. A good example of this is a differential. The signal passed though the load resistors--one positive and one negative--cancel, leaving only a net DC drain on the power supply. If you can contrive an entire circuit that has only a DC draw, you've got a lot more lattitude as to what to do with the power supply, although I still tend to regulate things.
Note that a lot of regulator circuits aren't stable without a cap nearby and plan your layout accordingly.
Amps rarely have remote power supplies because of the current draw involved. It causes too much voltage drop through the umbilical. Smallish solid state amps are about all you ever see with remote power supplies. Class A and large amps are a whole 'nother ball of wax. Tube amps are a better candidate for this because they use more voltage and less current.

Grey
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Old 9th May 2002, 02:52 AM   #9
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Thumbs up Good Save Grey!

I agree with everything except I think that seperate supplies for amps are fine with the game plan you outlined. Even line level and power amps can pick up noise from the magnetic field from toroid transformers and AC wiring. My Aleph 3 measures more noise in one channel than the other due to closer proximity of one channels circuitry to the AC wiring than the other. Jocko once demonstrated a dramactic decrease in noise and improvement in sound on a Threshold amp by moving the unbolted toroid power transformer about 4 inches further from the amplifier circuitry. It suprised both of us how easy this was to measure and hear. There are also advantage in decoupling the transformer vibrations from the rest of the amp.

H.H.
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Old 9th May 2002, 03:25 AM   #10
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Probably the best solution would be not to use preamp at all. If you have enough gain what you need it for?
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