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

[kris2ff3r]

Hi
I am thinking of upgrading the capacity on my power amplifiers PSU.
The Amplifier is a dual mono 100w A/B Design using a capacity of 20000µF per channel. I was thinking of upgrading to 30000µF, by changing the two 10000µF caps with 15000µF (in each channel).
If I'm not mistaken a power supply can't be too big, so this should not be a problem? I could in theory change it to x000µF's
Or will it do some things worse?
These are the caps for the VCC supply.
Will the VDD work as well? It's 4400µF, and thinking of upgrading to 6600µF, using two 3300µF, instead of the standard 2200µF's

[DrGeoff]

Why? What do you hope to achieve?
Is there a problem with ripple in your current power supply?

[IanB]

Precisely. Why do you think this would be an "upgrade"?

[kris2ff3r]

This has nothing to do with my (or others) personal preference. I hope to achieve a bigger power supply.
I'm simply asking if it would be a problem

[DrGeoff]

This has nothing to do with my (or others) personal preference.
I'm simply asking if it would be a problem

It may be.
The discharged capacitors appear as a short circuit at switch on. So the rectifiers must be able to handle the expected peak current at this time.
Once it settles down it should be OK, just check the switch on transient.
Also, it will take longer for the capacitor to discharge through the bleed resistor, so allow for that when tinkering.

[Ian.M]

Precisely. Why do you think this would be an "upgrade"?

+1.

Aluminium foil, paper and electrolyte is a lot cheaper than copper or silicon power devices.  Also electrolytic caps typically have quite a high tolerance range, so tend to be over-specced in the first place to guarantee the minimum capacitance required. The way to bet isn't that the OEM skimped on the caps as they are far far more likely to have cut corners on the transformer, output devices and/or heatsink.

If you are unlucky and the output devices  or their heatsinking are marginal, stiffening the power rails by increasing the bulk capacitance may push them over the edge into destructive overload and failure.

Also, for linear supplies, increasing the bulk capacitance decreases the conduction angle of the diodes in the rectifier, increasing peak currents and thus radiated and conducted EMI as the suppression components aren't designed to handle the higher pulse currents..   Other system components or the earlier stages of this amplifier may therefore pick up more 100Hz hum and RF impulse noise masking any improvement you may expect from reduced output stage rail ripple.

[kris2ff3r]

This has nothing to do with my (or others) personal preference.
I'm simply asking if it would be a problem

It may be.
The discharged capacitors appear as a short circuit at switch on. So the rectifiers must be able to handle the expected peak current at this time.
Once it settles down it should be OK, just check the switch on transient.
Also, it will take longer for the capacitor to discharge through the bleed resistor, so allow for that when tinkering.

I forgot to tell that it looks to be some sort of series wiring, with ground in the middle. See attached for the schematic.

The amp has a slowstart circuit, not sure how ''slow'', but it starts very fast (way under a second).
When the amp is turned on, it starts with a 20ohm resistor wired directly to the primary side of the transformers.
When the slowstart timeup is done, the relay kicks in and there is ''no'' resistance from mains to the transformers

[ejeffrey]

This has nothing to do with my (or others) personal preference. I hope to achieve a bigger power supply.
I'm simply asking if it would be a problem

Maybe I am not understanding what you are asking for, but adding capacitors does not make a power supply bigger in terms of higher load capacity, assuming the supply was designed properly in the first place.  For that you need to upgrade the transformer.  You might also need more capacitors.  Increasing capacitance by itself will reduce ripple but also can have problems mentioned above.  Given the relative cost of transformers vs. capacitors, I agree it is unlikely someone would build a linear power supply and not put enough capacitance to get the maximum power from the expensive transformer.

[T3sl4co1l]

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

Tim

[kris2ff3r]

This has nothing to do with my (or others) personal preference. I hope to achieve a bigger power supply.
I'm simply asking if it would be a problem

Maybe I am not understanding what you are asking for, but adding capacitors does not make a power supply bigger in terms of higher load capacity, assuming the supply was designed properly in the first place.  For that you need to upgrade the transformer.  You might also need more capacitors.  Increasing capacitance by itself will reduce ripple but also can have problems mentioned above.  Given the relative cost of transformers vs. capacitors, I agree it is unlikely someone would build a linear power supply and not put enough capacitance to get the maximum power from the expensive transformer.

That's exactly what I think, it it too small. In the later design they used 60000µF in the powersupply.
I think the manufacturer noticed it was to small. I don't know if the supply is too small, I haven't meassured ripple.

It's really an easy question; can I upgrade the capacity in the powersupply without breaking anything, or  introducing new noise, or other unwanted parameters (as mentioned by Ian.M).

[kris2ff3r]

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...

[DrGeoff]

That's exactly what I think, it it too small. In the later design they used 60000µF in the powersupply.
I think the manufacturer noticed it was to small. I don't know if the supply is too small, I haven't meassured ripple.

It's really an easy question; can I upgrade the capacity in the powersupply without breaking anything, or  introducing new noise, or other unwanted parameters (as mentioned by Ian.M).

Yes, you can add more bulk capacitance to the simple unregulated power supply.
It will, most likely, have no audible effect at all.

[Dave]

No, you can not just add a shitload of capacitance to a power supply.

Excessive capacitance means that the current spikes through the rectifier are going to be shorter and have a much higher in amplitude (the same amount of charge needs to be transferred in a shorter amount of time).

So where's the problem?
Higher RMS current on the windings, so hotter windings.
Odd current harmonics introduced to the mains, interfering with pretty much everything.

Unless the capacitors need replacement (bulging, high ESR, reduced capacitance), leave them be.

[IanMacdonald]

Will not make one iota of difference to sound quality. If you make a wiring mistake though it might just result in smoke and empty pockets.

Functionally, a regulated PSU would make more difference to quality at the expense of small loss of output power.  Reason manufacturers do not regulate is 'specmanship' - Using unreg rails for the output stage gives the highest possible peak output power from a cheap PSU. 

[kris2ff3r]

Or maybe the power supply ripple rejection of the amplifier is high enough that a few volts of 100/120 Hz ripple will not make much difference to the noise level? I do not believe regulated power supplies for class A/B amplifiers are particularly common.

True, only regulated power supplies on A/B amplifiers I've seen is in preamps, but that's a different story.

So far I have one saying it shouldn't be a problem, but not necessary either
And one saying ''I can't add a shit load of capacitance''. - The plan was to increase the capacitance with a third (total of 30000µF). stock is 20000µF, not sure if you think it's too much.. Or should be okay?

The powersupply is NOT regulated. For the VCC, it's only a bridge rectifier, and the capacitors (in series, with ground in the middle).
There is one 500VA transformer for each channel. Please see the schematics in one of my posts above

[IanB]

It's really an easy question; can I upgrade the capacity in the powersupply without breaking anything, or  introducing new noise, or other unwanted parameters (as mentioned by Ian.M).

Easy questions don't necessarily have easy answers. If it was an easy question you wouldn't be coming here asking for answers. You would already know the answer yourself. (It's an easy question, right?)

[CJay]

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...

Umm, rude much?

Yes, you can add capacitance, no it might not work as others have said.

You say the manufacturer changed the design for later versions, are you sure it was only the capacitance they changed?

Can you be absolutely sure they didn't fit a heavier bridge, change that slow strt circuit, the transformer, any number of other 'small' tweaks?

Does it sound good now?

What are you trying to achieve that makes you believe extra capacitance would be the answer?

[DrGeoff]

No, you can not just add a shitload of capacitance to a power supply.

Excessive capacitance means that the current spikes through the rectifier are going to be shorter and have a much higher in amplitude (the same amount of charge needs to be transferred in a shorter amount of time).

So where's the problem?
Higher RMS current on the windings, so hotter windings.
Odd current harmonics introduced to the mains, interfering with pretty much everything.

Unless the capacitors need replacement (bulging, high ESR, reduced capacitance), leave them be.

Except the OP is not proposing to add a "shitload". Only raise it by 50% of its original value per rail.
The bridge will be already quite large with regards to peak forward current, probably in excess of 50A.
The 500VA transformer already has a soft start circuit for inrush current mitigation, which will also cause initial slow ramping of the capacitor charge.
The load on the transformer is not constant and, unless the unit is being used in a nightclub, unlikely to be reaching anywhere near its rated output power.

It is highly unlikely that any of the potential problems described here will have any audible or other effect on the OP's equipment. The initial values for the capacitors were probably chosen at random to be as big as they could fit in the enclosure anyway.

Too many whiny children here.

[Zero999]

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...

Umm, rude much?

Yes, you can add capacitance, no it might not work as others have said.

You say the manufacturer changed the design for later versions, are you sure it was only the capacitance they changed?

Can you be absolutely sure they didn't fit a heavier bridge, change that slow strt circuit, the transformer, any number of other 'small' tweaks?

Does it sound good now?

What are you trying to achieve that makes you believe extra capacitance would be the answer?

They probably took offence to the word audiophile. Heck I probably would have used a more derogatory term.  Hence why I've kept out of this thread.

Yes, adding capacitors won't improve the sound quality. My guess is it won't make any difference. It could cause more heating in the transformer and rectifier, as mentioned above, so don't do it.

[kris2ff3r]

Thank you all for your great minds

I never  ment to be rude to anyone here, but please stick to the topic.
This tread is only about the different parameters I can expect from such a change in the powersupply.
I do see most here think it's unnecessary (maybe it is)...
Talking about how unnecessary it is, was not the point.

Again, thank you all for your input, and DrGeoff for answering my actual question

[Zero999]

Thank you all for your great minds

I never  ment to be rude to anyone here, but please stick to the topic.
This tread is only about the different parameters I can expect from such a change in the powersupply.
I do see most here think it's unnecessary (maybe it is)...
Talking about how unnecessary it is, was not the point.

Again, thank you all for your input, and DrGeoff for answering my actual question

The trouble is people have minds of their own and the forum has its own rules set by a team of administrators and moderators. When you create a thread, you don't get to decide what's acceptable and what is not.

[Dave]

Except the OP is not proposing to add a "shitload". Only raise it by 50% of its original value per rail.

While I agree that the word "shitload" is excessive for a 50% increase, your previous post seemed to imply that you can just freely increase bulk capacitance without consequences.

Yes, you can add more bulk capacitance to the simple unregulated power supply.

Did I misinterpret your words?

The load on the transformer is not constant and, unless the unit is being used in a nightclub, unlikely to be reaching anywhere near its rated output power.

The way I understand it OP wants to increase the output power of his current power supply, which implies that he is already loading it to the maximum and wants more out of it.
Relying that a use case is unlikely to happen is a pretty bad approach to engineering. Reliable designs always have safety margins.

[Zero999]

Yes, if more power is required, then a transformer with a higher current rating is required. Unfortunately, that won't increase the volume by itself. A lower impedance speaker or more speakers in parallel should be connected to the amplifier, assuming it's capable of driving a lower impedance load. If the amplifier's output is distorted due to clipping, then increasing the voltage and current rating of the power supply will work, but the amplifier will need to be able to withstand the higher voltage and current.

[DrGeoff]

Except the OP is not proposing to add a "shitload". Only raise it by 50% of its original value per rail.

While I agree that the word "shitload" is excessive for a 50% increase, your previous post seemed to imply that you can just freely increase bulk capacitance without consequences.

Yes, you can add more bulk capacitance to the simple unregulated power supply.

Did I misinterpret your words?
You didn't read them in context with the first post I made outlining the possible implications of such.
The OP clearly specified what they wanted to do.

The load on the transformer is not constant and, unless the unit is being used in a nightclub, unlikely to be reaching anywhere near its rated output power.

The way I understand it OP wants to increase the output power of his current power supply, which implies that he is already loading it to the maximum and wants more out of it.
Relying that a use case is unlikely to happen is a pretty bad approach to engineering. Reliable designs always have safety margins.

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

[floobydust]

I find increasing filter capacitance is audible, it does affect an amplifier's fidelity.
But it's not the mains ripple you are reducing in the hopes of getting better sound. This is counter to most intuition.

Adding filter capacitance can make things sound worse... if the amplifier does not have proper grounding because you are increasing the peak ripple current. This shows up as more 2xmains (100/120Hz) hum occurring and head scratching because the smaller filter capacitors were quieter.
Rectifier reverse-recovery time is also longer with higher peak currents, you'll need to consider snubbers across the rectifiers to reduce RFI.

It is the (rail's) 1/2 wave audio ripple under load, that adds intermod distortion, poorer channel separation.
Some audio power amps have poor PSRR and say 10kHz ripple can make it through the internals. It's not just 100/120Hz happening there.

Power supply rail noise scope picture by Bonsai; taken from hifisonix.com Ovation Power Amplifier 150W at 8ohms.