All P-channel Regulator For TSSA Split Supply?

[Jay]

What is the problem of using the same transistor regulator for both positive and negative supplies?

Mosfet complementary pairs rarely have good complementary characteristics, but such regulator as attached is rarely used. Why?

[Osvaldo de Banfield]

No problem if well designed, but in the title there is a mistake, you are showing N channel.

[Nico Ras]

Hi Jay,

personally I will only regulate the front end and driver stage of the amp, it makes for a far less problematic design and the end results remains excellent. Besides you do not create another heat source.

[Jay]

Originally Posted by Osvaldo de Banfield

No problem if well designed, but in the title there is a mistake, you are showing N channel.

You're right it's N-channel. I was thinking about Positive-channel.

With bipolar we can choose many fast device, and the level of complementary is high (NPN and PNP match well). Not so with mosfet. Even with smaller mosfets.

[Jay]

Originally Posted by Nico Ras

Hi Jay,

personally I will only regulate the front end and driver stage of the amp, it makes for a far less problematic design and the end results remains excellent. Besides you do not create another heat source.

I have used this regulator for single ended circuits with very good result (may be because it doesn't really regulate well). And I haven't seen circuits not improved with this. Yes, many top/successful class-A amps use it.

Actually, instinctively I prefer to regulate the front end only, especially if the bias is not so high (here it is 2A). The problem is then the front end will have lower voltage (unless 2 secondaries used), which is not suitable here (I mean no success try in my case).

And I have prepared to use high bias with TSSA. It has a very good chance to be the best amp. It outperforms F5 in almost all area. Where this excels is in power (that's why I prepared for high bias). F5 cannot go high power without excessively increasing distortion (read: F5 Turbo), but TSSA can.

[Samuel Jayaraj]

The 2 N-channel MOSFETs would required to be closely matched, to prevent current-hogging.

[Jay]

Originally Posted by Samuel Jayaraj

The 2 N-channel MOSFETs would required to be closely matched, to prevent current-hogging.

Yes, thanks. I think you're right.

IRFP460 is a 20A 250W device. No problem with using only one device for any class-A amplifier. By paralleling I'm looking for better trans-conductance, not power handling.

Correct me if I'm wrong, I'm not worry with destruction due to thermal runaway, because one device is capable of handling all the heat.

What I'm worry about is the unbalance transconductance between positive and negative rail. I simulated 1 mosfet on the positive rail and 2 mosfets on the negative rail, and the result is much much worse than just using one mosfet for both rails. So I guess I will stick with using only one mosfet per rail.

[RNMarsh]

[/QUOTE] Actually, instinctively I prefer to regulate the front end only, especially if the bias is not so high (here it is 2A). The problem is then the front end will have lower voltage (unless 2 secondaries used), which is not suitable here (I mean no success try in my case).

And I have prepared to use high bias with TSSA. It has a very good chance to be the best amp. It outperforms F5 in almost all area. Where this excels is in power (that's why I prepared for high bias). F5 cannot go high power without excessively increasing distortion (read: F5 Turbo), but TSSA can.[/QUOTE]

The most important thing about regulation is to keep both rails at the same voltage. It does not matter very much if the absolute value changes... as long as both supply voltages change by the same amount. This can be assured by placing a very large value capacitor Between the + and - supply rails. Differential changes will be cancelled. This is especially useful in power amplifier output stages. I have been doing this for almost 20 years.

-RNM

[Jay]

Originally Posted by RNMarsh

The most important thing about regulation is to keep both rails at the same voltage. It does not matter very much if the absolute value changes... as long as both supply voltages change by the same amount.

If what you meant by "both rails" are positive and negative rails, I think it depends on the amp design. Doesn't matter for me if one rail is lower than the other if the amp doesn't care about it (like in many cases).

Originally Posted by RNMarsh

This can be assured by placing a very large value capacitor Between the + and - supply rails. Differential changes will be cancelled. This is especially useful in power amplifier output stages. I have been doing this for almost 20 years.

I have done this also, simply based on listening test.

NP, if I'm not mistaken, mentioned the effect of this capacitor (from -V to +V) is increasing the effective capacitance (thus better filtering)?

What I have seen is that the effect of this capacitor can be positive but can be also negative. But...

I just simulated this and indeed it has good effect, thanks.

[RJM1]

The problem that I see with this arrangement is that the negative rail and the negative regulated supply do not share the same ground.