Just a quick power supply capacitance question

[Nuuk]

OK, while we are waiting for pictures, please tell us what speakers you are using with this amplifier!

[markiemrboo]

Originally posted by Nuuk
OK, while we are waiting for pictures, please tell us what speakers you are using with this amplifier!

Celestion 7's (the original ones not MKII, if that matters) at the moment. They're 8ohm "nominal" is all I know. Tried looking for proper specs on the drivers, but they're unlabelled so.... I couldn't find anything. I am guessing they would work OK on an unregulated supply though...

[Nuuk]

I am guessing they would work OK on an unregulated supply though...

Well . . .

[markiemrboo]

Originally posted by Nuuk


Well . . .

Is that a "well.... why not try it "? Or a "well..... it possibly won't work "?

I was intending on trying to wire it up unregulated tomorrow, with a separate transformer for the preamp and it's regulator. This configuration will just about all fit in the case.

[Nuuk]

If it wouldn't work, I wouldn't encourage you (or anybody else) to go ahead.

So yes, give it a try. Get the amp working and then try a pre amp. At least you will have something to listen to while you work on those regulators. Depending on the synery with your speakers, you may not bother with the regulators!

[BWRX]

markie, when you made your voltage measurements were the outputs of the regulated supplies connected to anything?

[BWRX]

There is a problem with the schematic in this post.

Let's break it up into parts so it's easier to see what's going on. Look at the positive rail regulator circuits first. The regulators share the same input voltage and return nodes but their output voltages may be independent of each other. This is important because the positive linear regulators have an NPN pass transistor inside that is used to regulate the voltage at the output.

Now, look at the negative rail regulator circuits. They also share the same input voltage and return nodes but they also share the same output node because their output nodes are connected to return nodes of the positive rail regulators. Any difference in output voltage between the two negative rail regulator circuits will cause currents to flow and make the lower side regulators dissipate a lot of heat (what you saw markie).

To make this split rail positive regulator circuit work you need 4 bridge rectifiers (2 on each secondary) to isolate the "virtual" grounds of the two regulator circuits.

Refer to the attached schematic if you prefer a visual explanation.

Cliff notes: Notice how the inputs, returns, and outputs of both negative rail regulators are tied together. That isn't kosher.

[markiemrboo]

Originally posted by Nuuk
If it wouldn't work, I wouldn't encourage you (or anybody else) to go ahead.

So yes, give it a try. Get the amp working and then try a pre amp. At least you will have something to listen to while you work on those regulators. Depending on the synery with your speakers, you may not bother with the regulators!

Ok cool, cheers. I'm back listening on the old Cambridge Audio A5 while I mess about. It certainly seems to sound quite different...

I think I will move the preamp in to a separate case after all, after a bit of thought. Seems like a better / easier idea really, as I can complete the power amp and even use it while building the preamp.

Originally posted by BWRX
markie, when you made your voltage measurements were the outputs of the regulated supplies connected to anything?

BWRX, good question. No, as it goes there wasn't. I was too scared of blowing up opamps given the simulation results. Should I test with 'load resistors', one between +ve and ground and one between -ve and ground presumably? I simulated this and it was, unfortunately, no different.

[markiemrboo]

Originally posted by BWRX
There is a problem with the schematic in this post.

Let's break it up into parts so it's easier to see what's going on. Look at the positive rail regulator circuits first. The regulators share the same input voltage and return nodes but their output voltages may be independent of each other. This is important because the positive linear regulators have an NPN pass transistor inside that is used to regulate the voltage at the output.

Now, look at the negative rail regulator circuits. They also share the same input voltage and return nodes but they also share the same output node because their output nodes are connected to return nodes of the positive rail regulators. Any difference in output voltage between the two negative rail regulator circuits will cause currents to flow and make the lower side regulators dissipate a lot of heat (what you saw markie).

To make this split rail positive regulator circuit work you need 4 bridge rectifiers (2 on each secondary) to isolate the "virtual" grounds of the two regulator circuits.

Refer to the attached schematic if you prefer a visual explanation.

Cliff notes: Notice how the inputs, returns, and outputs of both negative rail regulators are tied together. That isn't kosher.

BWRX, thank you so much for looking at things and taking the time to debug and explain this for me! It seems like you can see what I see, but actually properly understand it and explain it a lot better than myself.

This certainly explains why one channel was getting so much hotter.

Presumably then, if I were to use three regulators (edit: three regulated split supplies i mean...) off of one transformer, (one per channel for the power amp, and one for the preamp) I would just as easily be able to achieve this by using three bridge rectifiers on each secondary, right? If so, you've just made my day! I was totally bummed out that I couldn't get it to work properly!

[BWRX]

The attached schematic is the correct way to make two regulated split rail supplies from a dual secondary transformer using 4 positive linear regaulators.