Power amplifier regulated power supplies

[RobHolt]

Good or bad idea?

Some companies such as Naim revert to fully regulated supplies for their bigger and more expensive amps, while others such as Exposure use (used?) it in all amplifiers. Cyrus power and integrated amps go regulated when you add a PSXR.

I can think of one quite important reason not to use them - limited dynamic headroom.
In a conventional PSU the output under dynamic conditions can exceed the steady-state by a considerable margin.

Any view on the potential positives?

 

[Richard Dunn]

Good or bad idea?

Some companies such as Naim revert to fully regulated supplies for their bigger and more expensive amps, while others such as Exposure use (used?) it in all amplifiers. Cyrus power and integrated amps go regulated when you add a PSXR.

I can think of one quite important reason not to use them - limited dynamic headroom.
In a conventional PSU the output under dynamic conditions can exceed the steady-state by a considerable margin.

Any view on the potential positives?

It depends if your primary purpose is to deliver voltage or current. Regulation is better for voltage delivery, where as a nice big VA unregulated supply has a freedom to deliver current in the short term by not being regulated. And it depends how tight the regulation is, for power amps it can be too tight. Power amps are looking for low impedance supplies not necessarily voltage clamped supplies.

Swings (reg) and roundabouts (unreg) - as a kid I always prefered roundabouts and I still do.

Though I reg all things like dac or phono unit supplies because its a different compromise.

Remember a power amp is not one amplifier, it is a series of gain stages that have different supply needs. Some basically voltage gain, some voltage and current in about equality, and the output stage almost entirely current gain. Now one thing I have been meaning to try, but it means building higher current and voltage regs than I do at the moment, so haven't tried it (yet). The nva amp circuit can be split supplied so the input voltage stages could be seperately supplied and reg-ed and even perhaps the drivers, but I think maybe my ones draws too much current and are better off without it.

And remember what a regulator is and does, it is just a (usually unity gain) DC amplifier used to supply the voltage rails to an AC amplifier.

 

[Dave Simpson]

Sort of a thread crap but what makes one preamp *emphasize record surface noise more than others? Is it insufficient overload margins in the first stage or something else?

*the ticks and pops seem louder and last longer on some preamps vs others. I'm sure the "last longer" bit is my imagination but...

 

[RobHolt]

Sort of a thread crap but what makes one preamp *emphasize record surface noise more than others? Is it insufficient overload margins in the first stage or something else?

*the ticks and pops seem louder and last longer on some preamps vs others. I'm sure the "last longer" bit is my imagination but...

On vinyl, yes could be input clipping prompted by a loud transient such as a scratch.
Overload margins a HF can certainly be erm, marginal on some designs.

 

[Dave Simpson]

I found it an odd attribute when I switched from American preamps to a British unit years ago-completely unexpected in other words. I didn't think it would be the bandwidth limiting since there's not much information beyond 20K to corrupt (or so I thought) but the British unit seemed quieter and less reactive to record noise.

 

[Richard Dunn]

It is caused by current or voltage clipping.

In voltage clipping the signal hits the rail.

In current clipping the rail is pulled down to hit the signal.

This causes the transient to ring.

 

[Dave Simpson]

Front end overload caused by cartridge signal vs an issue with insufficient power supply rails (or the former causes or combines with the latter making matters worse)...correct Richard? Pardon my ignorance with electronics....

 

[Richard Dunn]

Front end overload caused by cartridge signal vs an issue with insufficient power supply rails (or the former causes or combines with the latter making matters worse)...correct Richard? Pardon my ignorance with electronics....

Vinyl scratches and debris in the groove can literally make the cart try to take off, the transient in those low signal terms is enormous. If you don't have sufficient headroom on the rails, far more than is normally deemed necessary, you will clip. I use plus and minus 24v so I have a 48v swing so the phono amp copes very well. But remember there is very little current delivery from the cartridge so there are surprisingly high current demands on the circuit to meet this transient, so your normal Walmart plug type supply just runs out of instant current ability and the rails are pulled down dynamically on the transient.

So you need far bigger power supplies than convention would dictate when just considering the steady state signal. Plus the circuit design considerations require more than convention would dictate, but I don't want to go into too much detail.

This is simplistic as there are many other considerations to take into account.

 

[Dave Simpson]

Thanks-that's a perfectly understandable explanation for someone like me with zero electronics knowledge.

 

[Tenson]

I switched from unregulated to regulated on a power amp that already had very good PSRR and it got noticeable quieter. That is, it went from a tiny bit of background noise to none at all.

I think bass got a little more grippy, but actually my plan eventually is to use them just for mid and treble in an active design.

The amps are Greg Ball's SKA GB150. Interesting to hear your thoughts on that design Richard, since it is a little different to many.

The unique topology eliminates the Vas stage which compromises conventional designs, instead employing positive feedback to achieve highly linear and very high first stage gain. Then a complementary 300MHz Class A buffer drives the MOSFETs with only feedback lead compensation for excellent stability with all loads.

 

[nando]

Richard have you ever played with choke regulated psu's if so what is your opinion,
nando.

 

[Richard Dunn]

Richard have you ever played with choke regulated psu's if so what is your opinion,
nando.

No, and no opinion.

 

[nando]

thanks, i

 

[Richard Dunn]

As I say best regulation for me is enormous overkill power supplies.

I have the Mk3 TDS monoblocks up and running at last. Input and current mirror is running on a 500va, drivers are running on 650va, outputs on 1000va. 4300va per amp pair I love big toroids.

I suppose I shouldn't say how good it is blah-blah-blah. But any of you who want to come and listen in Epping are welcome.

And surprisingly they have only twice overloaded the consumer unit on switch on and taken out the trip (once for each monoblock), I thought they would do it everytime, but it seems only first time, as long as there is some residual charge in the caps it just dims the lights for a moment.

 

[RobHolt]

Bet those are heavy?

And surprisingly they have only twice overloaded the consumer unit on switch on and taken out the trip (once for each monoblock), I thought they would do it everytime, but it seems only first time, as long as there is some residual charge in the caps it just dims the lights for a moment.

I've just finished servicing an Old Musical Fidelity P170 for a chap.
Thats a dual mono beast with a pair of large toroids - possibly 500va each - into 4 x 22k uf caps.
That makes a nice loud mechanical 'boing' at switch on accompanied by a slight flicker of the lights.

Yours must dim the whole street!

 

[nando]

that's nothing like richard i love big toroids, john done my friends nu-vista 300's not only the psu weight a ton but when i switch it on here to try it trigered the fuse box and lights went dim, question for him was where is the step up power on from stand by to full on? answer: no need just put 30 amp fuse in the box, hence a hefty elec. bill, wife no happy, sound very happy.