How much capacitance can I add (upgrade) to the amplifier's PSU?

[Dave]

A 500VA transformer for a 100W A/B amplifier.

Yup, I did miss that.

You can work out the loading for ordinary listening levels of audio program material.
It is not a bad approach to engineering. It is experience. Stop being pedantic.

I still disagree with this. A circuit should be able to handle any reasonable user input (reasonable being cranking the volume knob to the maximum, not shoving a 10Vpp signal into the input) without the risk of self-destruction.

[CJay]

I really do wonder what advantage the OP hopes to gain from making these changes, I'd love to know what make and model of amp it is to see if I can track the changes and work out what the manufacturer achieved by making them too, looks like there's a schematic available so it could be an interesting exercise.

[Brumby]

I really do wonder what advantage the OP hopes to gain from making these changes...

That's the question I would like to see an answer to, as well.

[kris2ff3r]

I really do wonder what advantage the OP hopes to gain from making these changes, I'd love to know what make and model of amp it is to see if I can track the changes and work out what the manufacturer achieved by making them too, looks like there's a schematic available so it could be an interesting exercise.

The next version of the amp had 20 watts more, a total of 120W.
How ever the schematics is almost identical, with a few changes (including two more output transistors).. And three times the capacitance (60000µF).. As I said the 100W ''edition'' had only 20000µF.. Yes there is a difference, but I still don't get that it should be big enough to 3x the power supply capacitance of the 100W amp.

There is no schematics available. I only have them available since I worked in the same company that made the amps, but I didn't work in the engineering section

[drussell]

Adding a bit more capacitance isn't going to make the amplifier more powerful.  It is still going to clip at the point set by the circuitry.  It will still output the same maximum 100 Watts.

It might potentially improve the transient response on large peaks a little bit, though, especially if you're driving a very low impedance load...  You might get a bit more solid bass "punch", for example.  Probably not much, though.  The manufacturer chose 20,000 uF for a reason, however, if you think it seems a bit anemic you can always try it and see if you like the result. 

It is virtually impossible for it will blow anything up but it will likely not make a noticeable difference and might actually make any power supply diode noise worse, as floobydust pointed out, but I don't think you'd hear that either with a change of 20,000 -> 30,000 uF.

[Zero999]

I really do wonder what advantage the OP hopes to gain from making these changes, I'd love to know what make and model of amp it is to see if I can track the changes and work out what the manufacturer achieved by making them too, looks like there's a schematic available so it could be an interesting exercise.

The next version of the amp had 20 watts more, a total of 120W.
How ever the schematics is almost identical, with a few changes (including two more output transistors).. And three times the capacitance (60000µF).. As I said the 100W ''edition'' had only 20000µF.. Yes there is a difference, but I still don't get that it should be big enough to 3x the power supply capacitance of the 100W amp.

There is no schematics available. I only have them available since I worked in the same company that made the amps, but I didn't work in the engineering section

120W is hardly any more powerful than 100W. I doubt most people would be able to tell the difference. It certainly isn't worth the extra capacitance and transistors.

[Kleinstein]

20000 µF is already enough capacity for a 100 W amplifier - that is at least with normal 4 or 8 Ohms speakers.
Adding more would reduce the voltage ripple but increase the current ripple. With modern, not too bad amplifier one would not notice a difference as neither of both can be heard. To much capacitance can cause problems like noted before - likely not yet at 50% more.

A 500 VA transformer for a 100 W amplifier is rather large. Assuming 50% PF and 50 % amplifier efficiency, it could deliver 125 W continuous. Amplifiers for private use are more the opposite way around: like a 50 VA transformer for a 100 W amplifier.

[Simon]

Ah yes, the audiophiles' fascination with excessive capacitance and using two FWBs where one will suffice.  Now how was I expecting that...

Tim

Stick to the topic, or find a different post...

Maybe listen to the advice you are being given, from what I can tell you still can't explain why you want to modify a unit that has been designed "just so", what do you know that the manufacturer does not, if you do know more than the manufacturer then I suggest you share that before you go around telling very experienced members to get lost, unless of course you don't actually want help......

[kris2ff3r]

We'll see how it goes...

As the schematics states; there are two sets of rectifiers, one for the + VCC, and one for the -VCC. Both rectifiers has it's own secondary winding.
Meaning the VCC+, and the VCC- are not the same winding and therefore each rectifier only ''work'' with 10000µF, and not the whole 20000µF supply for the channel(?).

I am not an electronics engineer so correct me if I'm wrong. I only work production and the amp is not mine either.

The owner requested the bigger cap source. I said I could do the upgrade, but I want to consult with the pros here first, don't want to mess up he's amp.

[Simon]

Well if you have that resistor in series then clearly there was a concern, if you really have to change it then if your increase the capacitance by 50% you should do the same to the resistor. But really why bother, unless the amplifier is suffering at high volume then why change the caps ? If you get 50% more caps in the same space they will be 2/3 the quality, you will have things like increased ESR which is unlikely to cause a problem here (if anything help) but it just demonstrates how pointless the exercise is.

[drussell]

If you get 50% more caps in the same space they will be 2/3 the quality, you will have things like increased ESR which is unlikely to cause a problem here (if anything help) but it just demonstrates how pointless the exercise is.

Not necessarily!

There have been major advancements in capacitor technology.  Depending on the age of this amplifier, far, far better capacitors (both performance and physical quality, longevity, etc.) may be available in the same or smaller package than the originals.  Most certainly if you compare typical, older 60s, 70s, 80s capacitors to those manufactured today, you will find huge performance increases in a smaller package.  It would be nice to know what amplifier he's talking about and the age of it, of course, though...

If the amplifier is reasonably old the caps have probably started to degrade at least somewhat from their original performance specifications anyway.  If there is any question as to their performance currently it is most certainly justified to be replacing them, and I would do the same thing as the OP is asking.  I would put in a somewhat larger-value, better quality capacitor if I could fit in in the space for this application.

Why all the hate for the OP's amplifier owner's request?  It seems to be a perfectly logical and valid course of action to me.  It is probably exactly what I would do if I were replacing the main filter caps in an older amplifier.

[Simon]

Yes that is true if they are old capacitors but information has been vague. I don't quite see the point of increasing the capacitance unless necessary.

[kris2ff3r]

If you get 50% more caps in the same space they will be 2/3 the quality, you will have things like increased ESR which is unlikely to cause a problem here (if anything help) but it just demonstrates how pointless the exercise is.

Not necessarily!

There have been major advancements in capacitor technology.  Depending on the age of this amplifier, far, far better capacitors (both performance and physical quality, longevity, etc.) may be available in the same or smaller package than the originals.  Most certainly if you compare typical, older 60s, 70s, 80s capacitors to those manufactured today, you will find huge performance increases in a smaller package.  It would be nice to know what amplifier he's talking about and the age of it, of course, though...

If the amplifier is reasonably old the caps have probably started to degrade at least somewhat from their original performance specifications anyway.  If there is any question as to their performance currently it is most certainly justified to be replacing them, and I would do the same thing as the OP is asking.  I would put in a somewhat larger-value, better quality capacitor if I could fit in in the space for this application.

Why all the hate for the OP's amplifier owner's request?  It seems to be a perfectly logical and valid course of action to me.  It is probably exactly what I would do if I were replacing the main filter caps in an older amplifier.

Thank you, the amp is made between 95-97 I believe.

[Simon]

ok so you can cram some more capacitance in, but has the owner reported an actual problem ? once upon a time diodes would be supplied with a maximum capacitance rating they could work wih for this very reason, hence your 20 ohm series resistors, this kit was well thought out, but apparently the owner knows more than the designer. Just make sure you apply gold coloured sticky sheet to the outside and charge him 100x the actual price of the caps and you will be ok oh and you will have to come up with a bit wank word for the new technology you have applied, do that and he will be happy

[drussell]

Yes that is true if they are old capacitors but information has been vague. I don't quite see the point of increasing the capacitance unless necessary.

Does it really matter why the amplifier's owner wants to change the capacitors?

The original question was whether a (somewhat) moderate increase in capacitance would have any potential downsides and what those potential downsides were.  I find that to be a perfectly valid question regardless of the original motivation.

Just my $.02 CAD, YMMV... 

[Simon]

Well given the protection circuitry it will probably be ok, but it is worth the OP understanding that you can't just do this and no it's not a case of more is better but more is pointless. As the protection circuitry is in place it will limit the peak current so adding more will likely be ok, given the fact that the designer went to such pains to design the thing right in the first place clearly a very well thought out value of capacitance was put in. The resistors are probably also to stop the traditional pop sound you get when powering an amplifier up (soft start ? ever heard of that OP?) and in this case may save your bacon if you decide to just add capacitance. like i said, wrap gold foil around them and charge the guy and arm and a leg, he will probably not bat an eyelid and have better bragging rights about his system

[drussell]

ok so you can cram some more capacitance in, but has the owner reported an actual problem ?

Why does it matter if there is currently a "problem" or not?  This wasn't a repair question.  The owner wants to change the capacitors.  Maybe he's going to install it into a permanent installation and doesn't want to have to worry about component life for another 20 years.  Who cares why?  That is a completely different conversation.   

once upon a time diodes would be supplied with a maximum capacitance rating they could work wih for this very reason,

Most certainly!  Especially tube rectifiers with capacitor input rather than choke input filters, you most definitely don't want more than the recommended capacitance on the rectifier (typically about 20 uF for a small receiving-tube sized rectifier) or you'd blow the daylights out of it in short order.

This amplifier presumably has one or more beefy bridge rectifiers which can easily handle more surge than they were previously handling and it even has soft-start.  He's not going to be blowing up rectifier diodes adding some more filter capacitance in this case.

hence your 20 ohm series resistors, this kit was well thought out, but apparently the owner knows more than the designer. Just make sure you apply gold coloured sticky sheet to the outside and charge him 100x the actual price of the caps and you will be ok oh and you will have to come up with a bit wank word for the new technology you have applied, do that and he will be happy

Maybe the owner is after audiophoolery and maybe not.  The original question, though, wasn't whether there was some audible benefit from increasing the capacitance and we have no idea why the owner wants to do it, it was whether it would work or not.

Replacing 20 year old electrolytics isn't some kind of insane, crazy idea, especially if they have been in constant service!  That is reasonable maintenance philosophy, IMHO, and going from 10,000 to 15,000 uF is also reasonable from an engineering perspective.

[kris2ff3r]

Jesus Christ.. And you wounder why I tell you to stick to the topic?

And where do you find the 20ohm series resistors? Or other protection circuitry? Do you mix up different posts?
And if I know what slow start is.. I said that the amplifier has a slow start circuitry with a 20 ohm resistor. But not in the power supply it self, or did I misunderstand you?

[Simon]

You said there was 20 ohms and a bypass relay and you posted a diagram about the time you started to tell people to get lost and I started getting reports. The guy you told to get lost was probably the most qualified to answer your question but apparently you know it all.

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[drussell]

And where do you find the 20ohm series resistors??

He's talking about the 20 in the soft-start circuit.

There is no need to mess with that, will be fine at 20 .

[kris2ff3r]

You said there was 20 ohms and a bypass relay and you posted a diagram about the time you started to tell people to get lost and I started getting reports. The guy you told to get lost was probably the most qualified to answer your question but apparently you know it all.

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Seriously?
''Ah yes, the audiophiles' fascination with excessive capacitance and using two FWBs where one will suffice.  Now how was I expecting that... ''

You're right. Best answer I ever got..

Anyway, I do consider the case closed. Thank you all for your input (On topic of course)...
I will check up those rectifiers. But they are no longer in production.. Don't know what will be most like the RS603

[Simon]

Well now that we have more information than your original post yes it is unlikely that adding more will do harm but very certain that it won't help much, I don't know in which year diodes with huge surge capabilities came about but if this was out of the 80s or earlier the answer would be a definite no, if you had not been so hasty in your dismissals of a light jibe Tim may have written you an essay in reply and left you in no doubt.best thing to do when you join a forum is not to jump on the difensive too fast. No question here is too stupid to ask but when you are clueless a bit of humility helps you go far as genuine people readily share knowledge on here if those asking are with bothering with.

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[kris2ff3r]

Well now that we have more information than your original post yes it is unlikely that adding more will do harm but very certain that it won't help much, I don't know in which year diodes with huge surge capabilities came about but if this was out of the 80s or earlier the answer would be a definite no, if you had not been so hasty in your dismissals of a light jibe Tim may have written you an essay in reply and left you in no doubt.best thing to do when you join a forum is not to jump on the difensive too fast. No question here is too stupid to ask but when you are clueless a bit of humility helps you go far as genuine people readily share knowledge on here if those asking are with bothering with.

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I'm truly sorry, it that was never my intention to be rude, or on defence. I do appreciate all input regarding the case, but there was a lot of ''not necessary, why on earth would you do that?'' - The same ''stupid audiophiles'' song.

I never asked this question for super audio conditions. I asked them because I would like to know more about the electronics

[Simon]

No one here holds a grudge. It is often easy to assume something will have a simple answer. My boss does that a lot. He thinks that because I don't have any qualifications he can do as well as I can, the result then is that he comes back from visiting a customer overseas and had to make a second trip to take me with him, but strangely when you put the guy that designed it and the guy that miswired it all together they work miracles.

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[drussell]

People need to always remember, too, that English is not everyone on this forum's primary language.  A simple difference in the way a question is phrased can elicit completely different responses.  I wonder how this thread would have gone if the original question were more like:

"I need to replace the main filter capacitors in XYZ audio amplifier.  The originals are 10,000 uF.  What are the potential pitfalls of using a 15,000 uF part to replace them?"