Metropoulos Forum

Hello, is there alot to do with power supply caps and sustain, mainly on the high notes? Ive raised mine from 330uf to 390uf and my high notes don't seem to sustain much and pinch harmonics seem harder to do. Is there any correlation? Thanks

Hi sorry for a late response. I'm guessing your referring to the small electrolytic cap bridged by the 820ohm resistor on V1?

If so yes, the 330uf is over kill as it is. Its letting through a wider band of frequencies than is really necessary this can lead in part to flubby bass. Earlier Marshall designs ie; the bass circuit use a 220uf but some of the guys around here favour smaller caps to loose the flub.

So to answer your question if any thing I'd reduce the size of that cap not increase it. For my personal taste I like the standard 220uf or 330uf.

Hi, thanks for the reply. I was actually talking about the caps after the bridge rectifier from the power supply. I was wondering how manufacturers decide what size to use for those as i see alot of different values. Is there a formula using the power transformer specs?

There probably are calculations you could do but I'm not that clued up...

It all depends on how tight you want it to sound, lower filtering can result in power supply sag when its cranked or heavily overloaded with a pedal on the front end which is really cool if your into that sound.

With higher filtering the power supply will recover quicker so the sound will hold together and not collapse. Also cool if you want a tight solid together sound.

Lower generally sounds and more importantly feels more vintage.

Anything over 2x dual 100uf/100uf, 500v in series parallel is kinda over kill. To answer your question I'm not 100% sure but I think I have read somewhere that too much filtering can have a bad/ detrimental effect on the sound like what you have said is happening in your amp.

50uf/50uf in series parallel is my fave, kinda middle of the road I guess. Solid but it can give up the good when pushed.

32uf/32uf your in sag city... Also cool just depends on what you want. Others have different opinions but for me all the filtering affects the sound in a subtle way but its definitely noticeable but more importantly it affects the feel.

High filtering is hard edged and stiff, plenty of punch. Low filtering is a softer feel.

What amp is it that you are using? 390uf on the first filter cap is not a standard Marshall value and would make for a very stiff, unforgiving amp. As revolver1 mentioned, too much filtering can have a detrimental effect on the sound unless you are into hifi home stereos and such. They use much higher levels of filtering to accurately reproduce the very low notes that a home stereo would need to produce.

Whether or not your amp uses a tube rectifier or solid state diode rectification also plays a role in how much filtering you can have at the first node. Tube rectifiers have much lower limits on capacitance whereas an ss rectifier can work with whatever value you decide to use.

As above

330uF mains filtering is overkill in a Marshall, would never go higher than 100uF.

If it has valve rectifier 64uF is tops or you will kill a GZ34 in short order.

Just saw the replys. This amp is a rivera ktre. Ive went from stock 330uf up to 390uf down to 220uf back to stock 330uf. These caps are in series. 390s were awesome on the fast chugga chugga stuff on the low strings but when playing up high really felt stiff. 220 really sagged in the low string stuff but felt great on the higher notes especially for solos. 330 just seemed to be more balanced. I imagine theres some matching up to the power transformers when selecting filter caps.