Regulate the psu of a power opamp with a similar power opamp?

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Regulators are opamps, as I learned up to now.

So: why not regulate the psu of an poweropamp with absolutely the same opamp?

I think about a LM3875, 3886 or whatever amp, with an psu, regulated with exactely the same chip, therefore the same behaviour.

But: I am not an EE and therefore, it would take me many hours studiyng a new topic.

Maybe, out here in the world, someone could pick up this idea and show some draft of an possible regulation circuit, using a power opamp?

Maybe, this could start the next step, in gainclone evolution?

Franz

P.S.
Maybe, in the different datasheets of the poweropamps, there is a suggestion for an regulator? But I dont remember...
 
It can be done. The biggest issue is typically cost. Also, there is much "talk" about having a supply that can deliver more than the amp wants.

There are a number of regulators that use opamps with a transistor at the output for current gain. Just Google it.

If you go to the Analog Devices or TI web sites and look at IA app notes you will see opamps used as regulators for strain gauges.

Try it, see what happens.
 
So: why not buffer the input of an poweropamp with absolutely the same opamp? (or LM1875)

I saw a thread about setting up a LM3875? with a OVERALL gain of one.

I think, this is not the same: LM3875 are not designed to use with unity gain. I have an amp setup like this, and it is not a good amp. Too much feedback!

No, the regulator should work exactly like the powerstage. The same gain, the same currents.

Franz
 
Hi Franz,

You can't use the LM chips to make a regulated PSU, because they are only stable at gains of >10.
They were made for audio.
The good news is, of course you can do it with the OPAs.
OPA541 would be the only choice, as the 548 and 549 are limited to +/-30V max. PSU voltage.
 
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Hi Franz,

Franz G said:
I think, this is not the same: LM3875 are not designed to use with unity gain. I have an amp setup like this, and it is not a good amp. Too much feedback!

I realise that the LM3875 is not stable with a gain <10, but the thread I was referring to, was using a LM3875 as a unity gain preamp (a buffer). They did this by using a 1:10 voltage divider on the input and then a gain of 10. So the OVERALL gain was 1.

I can't find the original thread but I did find a similiar one.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=26330

More information on this topic:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=22936
 
You know, guys, I am living, because I can dream.

Somewhere at the internet, I read an information about an DNM Stereo Amp, using two additional redundant power stages, same gain, same load (I know, this is another problem, as loudspeakers are a complex and not a linear load) as the real power stages, just to regulate the psu.

O.K., it was an advertisement.

But why not follow this idea? With power chips, this is not to much luxurious, to build redundant power stages. And the little bit heat of the needed output resistors: for me this is not a problem, if it is sounding good. :D

Maybe, someone could pick up this idea? When not, just give me some time...

Franz
 
Franz G said:
Regulators are opamps, as I learned up to now.

So: why not regulate the psu of an poweropamp with absolutely the same opamp?

I think about a LM3875, 3886 or whatever amp, with an psu, regulated with exactely the same chip, therefore the same behaviour.

But: I am not an EE and therefore, it would take me many hours studiyng a new topic.

Take a look at the chart depicting the frequency and phase response of the LM3875 -- compare it to the AD825 -- the '3875 just isn't the same league in terms of performance.

I think that you would find a simple regulator circuit based upon a TL431 and a pass transistor (look at Elso's Kwak-clock power supply) to be much better than trying to bootstrap an LM3875 or LM3886 to provide the same functions. Simpler, less expensive, less real estate consumed and a demonstrated body of knowledge.

But I still want someone to demonstrate why an LM3875 or LM3886 amplifier should be regulated. You still burn watts which could be added to your musical enjoyment.
 
But I still want someone to demonstrate why an LM3875 or LM3886 amplifier should be regulated. You still burn watts which could be added to your musical enjoyment.

Because, even the LM3875 and the LM3875, having many regulators inside, are needing some peak current power.

And the trannies are too slow (no, not to slow, but they decrease voltage if some current is needed from the chip), or you take a real big one.

So, you need big caps.

Here in this forum, you can follow the fact, what too big caps can do to chipclones.

So, regulating a chipclone is an undisputed advantage for me. If it is easy and cheap, of course.

And dont forget: the regulators are working like secondary fuses: they avoid too much current.

So, why not regulate a psu for chipclones, as we are not industry, calculating costs x mio?

Franz
 
Jocko Homo said:
Where's Phred when you really need him.............?

Jocko


Yeah, we seem the only two guys missing him.
Why don't you guys use a BIIIG transformer that has 1% regulation making any electronic regulation superfluous.......
This kind of "stiff" powersupply will surprise your ears.
I tried electronic regulation in my own small amp and it sounded constricted and dynamically "flat" compared to straight from the transformer.
 
Pedja said:
Hi Jack,

I’ve found fascinating your posts about usage of regulated supply in GC during last year or something. Does this topic dominate in your dealing with GC?

Btw, how does the demonstration you are searching for should look alike?

Pedja

I just haven't heard anyone demonstrate why it should result in a better product. In the interim, the regulator is just dissipating heat needlessly.
 
You can lead a horse to water...........

If your amp has high PSRR, unlike those of us who insist on making open-loop amps, Elso's suggestion sounds better.

(Not a pun, but hey, it works!)

Regulated PSUs for the output stage frequently don't work out as nice as you would think that they would. Just like Elso said.

And I like regulated PSUs........

Usually.

Jocko
 
Re: You can lead a horse to water...........

Jocko Homo said:


And I like regulated PSUs........


Jocko

Regulation has its place, a very big place --

From what I have read, regulation helps in those cases where the amp has poor PSRR, and in cases where frequent clipping are going to take place -- with an Overture amp the chip is going into protection mode as this (clipping) takes place.

The regulator has its own set of feedback compensation equations, it's own pratfalls. I don't think you put an off-the-shelf regulator in without also looking at the performance with a phase-gain meter -- seeing how the entire supply responds to a pulse or noise on the power line, dramatic changes in load, etc.

Of course, this is why I built the power supply test bed -- just putting the finishing touches on it now. We will get to the bottom of this.

By the way, just testing here on a Sunday afternoon -- the electrical noise in the lab is much, much, much lower than a typical workday.
 
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