Just a quick power supply capacitance question

[t.]

Originally posted by markiemrboo


Do note that *individually* they work fine, I have never questioned this. It is only if I try and run them all off of a single transformer "in parallel", as in my drawing, they don't.

Have you specifically done this and it has worked, or are you speaking only of a single supply?

Like I said before I built all three of those supplys on the diagram thats on DD.http://www.diyaudio.com/forums/showt...21#post1111121
I started with the simple single one first to see if I liked the results then tried the pair of regs run from the single transformer then upgraded to a pair of transformers

[markiemrboo]

Originally posted by t.


Like I said before I built all three of those supplys on the diagram thats on DD.
I started with the simple single one first to see if I liked the results then tried the pair of regs run from the single transformer then upgraded to a pair of transformers

I am willing to bet that if you tried lowering the voltage of one of the supplies, on the same transformer (as the "second diagram" shows), so say you had one supply giving +-30v for both channels of the power amp and then a +-15v supply for a preamp) you would see what I am seeing...

[t.]

Originally posted by markiemrboo


I am willing to bet that if you tried lowering the voltage of one of the supplies, on the same transformer (as the "second diagram" shows), so say you had one supply giving +-30v for both channels of the power amp and then a +-15v supply for a preamp) you would see what I am seeing...

I've built several amps since building the LM338 so no longer use it anymore.

So is the pair of dual regs for the amps ok and its just the pre amp regs causing problems?

[markiemrboo]

Originally posted by t.

So is the pair of dual regs for the amps ok and its just the pre amp regs causing problems?

No. It seems to me that even with just dual regs they only "appear" to work ok, and measure as you expect, because they're outputting the same negative rail voltage by design (why would you want to have the left channel running at a lower voltage than the right channel?). Thus, you can't see that the negative rail isn't adjusting (regulating?) like it should be.

I could still be wrong of course. I even *hope* I am wrong... but I doubt anyone will believe what I am saying until someone with a tad more respect and knowledge also tries it and reports their findings. I also doubt anyone really cares enough and/or has enough spare time to indulge in such an activity

[AndrewT]

Hi Markie,
each pair of regs is independant from each other pair.

The outputs are connected to amplifiers that are independant from each other.

There can be no interaction on the -ve output of one pair that affects the -ve of another pair, unless there is a connection or mis-wire somewhere.

How about that pic that someone else suggested.
The system will work from a common transformer.
Give us a chance to help you.

[markiemrboo]

Originally posted by AndrewT
[B]Hi Markie,
each pair of regs is independant from each other pair.

The outputs are connected to amplifiers that are independant from each other.

There can be no interaction on the -ve output of one pair that affects the -ve of another pair, unless there is a connection or mis-wire somewhere.

Well, as I said... I checked the wiring multiple times. It was exactly as the picture I drew.

Would you be able to work from a simulation, given that I am seeing the exact behaviour the simulation gives? I can post SWCAD III files if you like, though I am using two "sine wave" voltage sources to 'simulate' the two secondary windings of the transformer.

How about that pic that someone else suggested.
The system will work from a common transformer.

Give us a chance to help you.

As I said, I hope I am wrong. I apologise if I am coming across like I don't want help or anything. Of course I do....

[t.]

I give up!
I'd suggest you stick to a circuit you understand more how it works, sorry but like I said I've built all three of those circuits on DD and all measured fine on a load.
I never run a pre-amp from the same supply as the amp section, instead I'd run them separate from a lower voltage transformer

[markiemrboo]

Originally posted by t.
[B]I give up!

This is a shame

I'd suggest you stick to a circuit you understand more how it works,

After Andrew explained it a page or two back, I thought I understood how it worked. As far as I understood it, the 'negative rail' was "actually" 0v, and the regulators created a virtual / floating ground (i'm not so sure of the terminology) ?

I was confident it would work and I should ignore the simulator results, but... it didn't. So now I don't understand why it doesn't work.

sorry but like I said I've built all three of those circuits on DD and all measured fine on a load.

I built the "second diagram" and it measured fine too.

I never run a pre-amp from the same supply as the amp section, instead I'd run them separate from a lower voltage transformer

I would too, except I don't have enough space to do that... unless I go with an unregulated power amp supply, then I think I might be able to make it all fit.

[t.]

Just post a picture of the one causing problems both top and bottom , its about the only way to figure out what the problem is

[markiemrboo]

Originally posted by t.
Just post a picture of the one causing problems both top and bottom , its about the only way to figure out what the problem is

I can't post any actual real-life pictures. I'm still waiting for my digicam to be returned from RMA.