Bob Cordell Interview: Power Supplies

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AndrewT

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I reckon "dynamic headroom" is a measure of the "badness" of an amplifier.
i.e. a power amplifier that delivers 28Vrms into an 8ko load and delivers 27Vrms into 8r0 load and delivers 26Vrms into 4r0 is quite good.

An amplifier that delivers 32Vrms into an 8k0 load and 30Vrms into 8r0 load and collapses to 26Vrms into a 4r0 load has great dynamic headroom but will probably sound much worse than the first when driving speakers.

Both amplifiers can legitimately be labeled as 169W into 4ohm amplifiers.
 
TonyTecson

TonyTecson

Member
Joined 2003
I reckon "dynamic headroom" is a measure of the "badness" of an amplifier.
i.e. a power amplifier that delivers 28Vrms into an 8ko load and delivers 27Vrms into 8r0 load and delivers 26Vrms into 4r0 is quite good.

An amplifier that delivers 32Vrms into an 8k0 load and 30Vrms into 8r0 load and collapses to 26Vrms into a 4r0 load has great dynamic headroom but will probably sound much worse than the first when driving speakers.

Both amplifiers can legitimately be labeled as 169W into 4ohm amplifiers.
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and i bet that the first one has a heavier transformer than the second case.....
 
A

Adrculda

Member
Joined 2009
Tony said:
and i bet that the first one has a heavier transformer than the second case.....
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Most newer amps are cheaply built on a boat or in a sweat shop with surplus materials and are nothing special. I had a friend over that has been in high end audio for quite a while ( i serviced a few of his amps for him ) and after a few changes to my own cheapie he was amazed what improvement it made.
Still though I'm overhauling the power supply in it as its weak.
Originally had 300VA EI core with 5600uF capacitance at 35V rails...
Now, 750VA EI core with 8700uF capacitance at 45V rails :)
Also replaced output devices and now looking at a biasing circuit as from Yamaha it self biases via tempco :s
 
jan.didden

jan.didden

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AndrewT said:
I reckon "dynamic headroom" is a measure of the "badness" of an amplifier.
i.e. a power amplifier that delivers 28Vrms into an 8ko load and delivers 27Vrms into 8r0 load and delivers 26Vrms into 4r0 is quite good.

An amplifier that delivers 32Vrms into an 8k0 load and 30Vrms into 8r0 load and collapses to 26Vrms into a 4r0 load has great dynamic headroom but will probably sound much worse than the first when driving speakers.

Both amplifiers can legitimately be labeled as 169W into 4ohm amplifiers.
Click to expand...

Generally spoken people regard more dynamic headroom as better. It also depends on how you spec it. If spec an amp for say 100W in 8 ohms but give it 54V 'soft' rails, on music it can peak well above 100W equivalent, so it has good dynamic headroom meaning it can deliver peaks of MUSIC much better than the 100W spec suggests.

jd
 
A

Andre Visser

Member
Joined 2007
janneman said:
Generally spoken people regard more dynamic headroom as better. It also depends on how you spec it. If spec an amp for say 100W in 8 ohms but give it 54V 'soft' rails, on music it can peak well above 100W equivalent, so it has good dynamic headroom meaning it can deliver peaks of MUSIC much better than the 100W spec suggests.

jd
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Perhaps so if you don't care about sound quality, as AndrewT also suggested.
 
A

Andre Visser

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Joined 2007
janneman said:
Sorry, I don't see the connection? Don't you like it if your 100W amp can process peaks of say 150W equivalent without clipping? Or is there something else I miss?
jd
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My experience is only that a stiffer supply normally result in better sound quality.

I would rather listen to an amplifier that sound good and clip at 100W (which I doubt you will reach with a good supply anyway) than one that can 'process peaks of 150W equivalent without clipping' but lack in sonic quality. As I see it these amplifiers make for 'impressive specifications' while driving 8 Ohm resistive loads but please don't connect speakers to it. :)

André
 
jan.didden

jan.didden

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Andre Visser said:
My experience is only that a stiffer supply normally result in better sound quality.

I would rather listen to an amplifier that sound good and clip at 100W (which I doubt you will reach with a good supply anyway) than one that can 'process peaks of 150W equivalent without clipping' but lack in sonic quality. As I see it these amplifiers make for 'impressive specifications' while driving 8 Ohm resistive loads but please don't connect speakers to it. :)

André
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Ahh, those anecdotes 'but it sounds better'. Never can win there. Never learn anything there either ;)

jd
 
A

Adrculda

Member
Joined 2009
Andre Visser said:
My experience is only that a stiffer supply normally result in better sound quality.

I would rather listen to an amplifier that sound good and clip at 100W (which I doubt you will reach with a good supply anyway) than one that can 'process peaks of 150W equivalent without clipping' but lack in sonic quality. As I see it these amplifiers make for 'impressive specifications' while driving 8 Ohm resistive loads but please don't connect speakers to it. :)

André
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True, but i noticed that with larger capacitors, they tend to get lazy on the current delivery and have a muddy bass.
I went from 2 x 14000uF to 6x 8700uF ( installed today ) and the difference is night and day !!!

On another side note...
When designing a power supply please give yourself extra 15-20% of your operating voltage when selecting caps. This will give you a longer service life and give you more possibilities for a transformer upgrade if you ever choose to.
 
TonyTecson

TonyTecson

Member
Joined 2003
but i noticed that with larger capacitors, they tend to get lazy on the current delivery and have a muddy bass.
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could be because of light power transformer used, changing to a heavier one should improve it....

sometimes you can get away with bigger caps, but then the power transformer should liekwise be bigger in a sense that it should have better regulation.
 
A

AndrewT

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Joined 2004
janneman said:
on music it can peak well above 100W equivalent, so it has good dynamic headroom meaning it can deliver peaks of MUSIC
Click to expand...
my point that seems to be missed is that Dynamic headroom can never be classed as good.
Dynamic headroom is an invention of manufacturers of low quality amplifiers that try to impress us with numbers of no sound quality value.

Dynamic headroom is a measure of the badness of an amplifier, not it's goodness.
 
jan.didden

jan.didden

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AndrewT said:
my point that seems to be missed is that Dynamic headroom can never be classed as good.
Dynamic headroom is an invention of manufacturers of low quality amplifiers that try to impress us with numbers of no sound quality value.

Dynamic headroom is a measure of the badness of an amplifier, not it's goodness.
Click to expand...

The real reason why Dynamic headroom is a Good Thing is that that 100W in 8 ohms is purely a marketing spec. Nobody in his right mind will drive an amp continuuously to deliver 100W in 8 ohms; you can't even find music for it (except some old AD/DC stuff perhaps).
With real music, you'r doing well if the avarage is 10W. That means that the power is there only for the peaks. And which ever way you crumble the cookie, an 100W amp with a stiff supply clips before the 100W amp with the soft supply with a couple of extra volts headroom does. The better sound quality (of course all things except that supply stiffness being equal) comes from the last amp; it simply clips less.

jd
 
Bonsai

Bonsai

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"my point that seems to be missed is that Dynamic headroom can never be classed as good.
Dynamic headroom is an invention of manufacturers of low quality amplifiers that try to impress us with numbers of no sound quality value.

Dynamic headroom is a measure of the badness of an amplifier, not it's goodness. "


I am currently working with a customer who produces audio componenet systems. The power supply (standard transformer and caps) is rated at 300VA, and the IC based power audio amplifer at 100W into 4 Ohms per channel. On the front of this system is a sticker that proudly proclaims '4000W Peak Music Power' . I asked the engineers what this means. They could not tell me.

I long for the good old days when manufacturers had to (or jus t did out of honesty) quote RMS power into 8 and 4 ohms.

We measured the above product on our AP system, and indeed, it is a 100W RMS into 4 ohms amplifier - but that is all.
 
mr_macgee

mr_macgee

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Joined 2008
Bob Cordell said:
This thread is definitely about classic so far, but the thread has also included issues of grounding. I think there may have been a couple of posts awhile back that involved smps, and I don't think anyone would object to a discussion involving smps. A couple of power amplifier companies, for example Halcro and Chord, assert that smps have sonic advantages in high-end gear. Many others would strongly disagree and argue the other way.

Bob
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Rising from the grave an old post (2+ yrs) in this thread but curious what the opinion is at present? Has SMPS made any inroads over classic or has the anecdotal evidence and opinion swung the other way?
 
mr_macgee

mr_macgee

Member
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Bob Cordell said:
Here's a new topic to consider: power supply quality.

We constantly hear about people installing Black Gate capacitors, or Shottky diodes, or better bypasses in power supplies and getting startling sonic improvements. Often, we hear about better bass. I believe in putting good power supplies in power amplifiers, but often I've wondered what the mechanism is for improvement in sonics.

Sure, the power supply sags during a bass transient. Sure, we want to keep EMI off the supply lines. But if the rails don't sag to the point where the output stage doesn't clip or run out of headroom, why should there be a difference? After all, source-follower and emitter follower output stages have quite good power supply rejection. If we can take the amp up to nearly full power into a 4-ohm load without seeing any 120 Hz artifacts on the output, why should there be a sonic effect?

But there is a lot of anecdotal evidence that there is. Is this just a mystery of life in audio, or is there a mechanism to explain this?

Maybe the quality of the supply and its variations and stuff on it matter to the earlier stages in the amplifier, like the input stage and the VAS. But these stages require much less current, and it should be much easier to filter them or even regulate them. So if we just supply the earlier stages with exceptionally clean and stable rails, will we no longer see a big benefit from improving the main rails beyond stock? Maybe otherwise-very-high-quality amplifiers just don't pay enough attention to the rails for the input and driver stages?

I don't know. What do you guys think?

Bob
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I would also like to know after almost 3 years of discussion in this thread about power supplies has there been any new solid rules/guide lines that the majority in this forum agree on that should be followed when designing/implementing a new classic power supply?
I would like think with all this brain power over the past 3 years, 800 comments and 16 pages of writing that someone can come up with a nice summary. I'm sure it can be very useful for new and old members. I've enjoyed reading what I can but 16 pages is a lot to go through.

Bob, I would like to say thanks for starting up this thread with good questions; It's been a great and useful discussion. Cheers!
 
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