Linear, regulated power supply (for a phono stage or preamp)?

OK, let's assume that a linear PS (+24v DC only) consists of:
1. a power transformer with, say, one 24v secondary.
2. a diode bridge to rectify the AC - producing 24 x 1.414 = 34v DC
3. and a regulator/smoothing section ... to produce a nice smooth +24v DC supply.

Assuming I want to provide +24v DC to the L & R channels without them interacting with each other ... my options seem to be:
a. have a completely separate PS for each channel - ie. including #1, #2 and #3, above for each.
b. two PSs consisting of #2 and #3, above - but sharing the one secondary.
c. or taking two regulator/smoothing circuits off the output of the one diode bridge.

Option a. seems to me to be completely OTT - and entirely unnecessary.

My Qu is ... is there any advantage in going with b., above - rather than just c.?

Thanks,
 
A good voltage source has an output impedance of very near zero. As long as you don't exceed the current capability of the supply, connecting the left and right channels to the same supply will not produce any interactions. Otherwise C.
 
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If you use a good regulated supply, the crosstalk will be negligible to begin with, but if you want complete peace of mind, separate the supplies using two RC cells, for example 10 ohm + 1000µF; you could even go one step higher and add a 1mH inductor to the resistor. If you opt for the right inductor, its self-resistance might replace the resistor.
If you get the layout/wiring right, this should provide you with 150dB+ of separation. Is it enough?
 
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The physical circuit layout is just as, and maybe more important than what you are concerned about. And as mentioned, any well designed regulator will minimize any channel to channel interaction. For best results I recommend using any of the newer generation of low noise, low drop-out regulators.

Mike
 
While "a" might be tempting, at some point you are going to connect the grounds together. Like Ylli wrote, if your regulator is up to the task it will be more than good enough. Go for "c" if you feel better about it. And you will always have to care about what Mike wrote.

KISS. But watch your back...
 
A good voltage source has an output impedance of very near zero. As long as you don't exceed the current capability of the supply, connecting the left and right channels to the same supply will not produce any interactions.

Sure, that's the theory - but I discovered something a couple of years ago when I tried to power 3x DACs (for my 3-way active system) from a single LPS. I unfortunately was plagued by a high-pitched whistle/whine from the spkrs.

After a lot of head-scratching as to what was causing this ... I disconnected one DAC from the shared PS - nothing changed. So I then disconnected the 2nd DAC - so the PS was only powering one DAC.

Result ... the whine/whistle went away! (y) So I bought two more PSs - giving each DAC its own separate PS.

It's this experience that caused me to ask my question.

Otherwise C.

Thank you for the confirmation - that's what I had thought. :)

If you use a good regulated supply, the crosstalk will be negligible to begin with, but if you want complete peace of mind, separate the supplies using two RC cells, for example 10 ohm + 1000µF; you could even go one step higher and add a 1mH inductor to the resistor. If you opt for the right inductor, its self-resistance might replace the resistor.

Thank you - yes that's certainly an option ... but not really any easier than just having individual reg circuits.

The physical circuit layout is just as, and maybe more important than what you are concerned about.

Agreed! (y)

For best results I recommend using any of the newer generation of low noise, low drop-out regulators.

Mike

I prefer to use an emitter-follower based regulated PS designed by Hugh Dean. (AKSA amplifiers).

Go for "c" if you feel better about it.

Thank you for the additional confirmation. (y)

And you will always have to care about what Mike wrote.

Sure! (y)

No channel separate psus. That is unproved nonsense!
One psu for all.

Please see my comments at the start of this post.

Try to use the psu of the pre or power amp.

Naim proved over 40 years ago that powering a preamp from a separate PS (the 'HiCap') sounded much better than powering the preamp from the power amp's PS.
 
Sure, that's the theory - but I discovered something a couple of years ago when I tried to power 3x DACs (for my 3-way active system) from a single LPS. I unfortunately was plagued by a high-pitched whistle/whine from the spkrs.

After a lot of head-scratching as to what was causing this ... I disconnected one DAC from the shared PS - nothing changed. So I then disconnected the 2nd DAC - so the PS was only powering one DAC.

Result ... the whine/whistle went away! (y) So I bought two more PSs - giving each DAC its own separate PS.

It's this experience that caused me to ask my question.
So:
1: your psu was not up to the task
2: your layout/wiring was not good
3: (one of) your dac's was faulty (or badly executed)
 
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So:
1: your psu was not up to the task
2: your layout/wiring was not good
3: (one of) your dacs was faulty (or badly executed)

Sure - one of those is certainly a possibility.

However, when I gave each of my DACs its own PS (and made no other changes) ... the problem went away. :)

So, as my option "c." seems to be feasible ... I will no longer try to share components - or channels - between the one PS. (y)
 
I'm thinking the "best" would be something between a and b. Have a single transformer with two secondaries, each secondary powering a channel. This gives ground isolation without having to use two transformers.

I've thought of this for a power amplifier as well, using a transformer with four secondaries to make two +/- supplies, one for each channel. Connecting the grounds together is optional.