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Plexi Marshall 50's: 50uf vs. 32uf

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5/1/2003 6:56 AM
Mike	Plexi Marshall 50's: 50uf vs. 32uf In regards to Plexi 50 watts, what's the word on the two variations, 50uf vs. 32uf filters. I know plate voltage, etc., would be lowered with 32uf's yielding a possible "browner" sound. Most Plexi's I've encountered have 50's. Adverse effects on XFMR's? Sweeter tones? Any opinions? regards, Mike

5/1/2003 9:31 AM
Chris ( CMW amps )	Hi Mike The 50uFs will give more/tighter bass and the 32uFs are a little more spongy . If you do have both values at your bench I suggest trying both values so you can experiment with that . have fun building & tweaking ! Chris

5/3/2003 7:32 PM
LFOscalator	The 32's will give more sag -- meaning a spongier sound. Marshalls tend not to be designed to be spongy so it doesn't surprise me that most plexi's use 50's to tighten the sound. So, if you want a truer Marshall-like sound, go wth the 50's. LFO

5/7/2003 8:28 PM

I totally disagree tonewise in the non-MV Marshalls. I also didn't notice any difference in B+ based on 32ufs, 50 ufs, or 100ufs in my amp.

The higher uF filters don't necessarily "tighten" bass. They give more bass, true, but this to my ears doesn't necessarily mean "tighter". The 32ufs yeilded the "tightest" bass in my 50 watt marshall clone. They also yielded a much more complex and open midrange.

The 50ufs and especially 100uf (only on the plates, screens and PI, didn't try it in the preamp) sounded bassier but boomy. Tightness in the bass, in this case, meant less boominess and more midrange relative to bass, which sounded tighter. Kind of like the difference between a 6L6 and a EL34, or a Marshall 412 vs. a Marshall 410 - in both cases the former has more bass but the latter, to my ears, sounds "tighter" in the bass because it is more controlled.

Now, with a high gain preamp, the bigger filters really paid off for tight thumping bass. But not with a Marshall SL preamp in my amp. I am totally sold on the 32 ufs for non-MV Marshalls. I think the 50 ufs LCRs were probably used for years in Marshalls due to availability, not for any tonal reason.

5/6/2003 2:10 PM

I'm not sure why the plate voltage would change, it didn't in my Marshall when I switched from 50uFs to lower values. In this particular amp, with the smaller filters the amp sounded better to me. Before, either the bass was killing you or the treble was slicing your head off or both. If you turned down the bass it got too thin and if you turned down the treble it got too muffled. With the smaller filters, the bass and treble just seemed "more pleasant". Now I can have a lot of bass (if I want) or a lot of treble (again, if I want) or both and it still sounds good. Hard to describe and it very well could be my imagination. In my case, it is a 50 watt Plexi with the filters as follows: 100uF (both sections of an LCR can paralleled)-40uF-20uF-20uF-10uF. If the noise went up after the swap, it wasn't enough for me to notice.

Matt

5/7/2003 5:38 PM
LFOscalator	When you say the plate voltage did not change, did you make your measurement when the amp was idling or under heavy load? From a practical standpoint, I would think you would only see a change in PV under extreme load with smaller cap values. But I never made these measurements for a Marshall for different PS caps so I don't know what actually happens.

5/7/2003 6:53 AM
Mike	Interesting stuff, thanx guys. I do have some around, just need to take the time to A/B a little... regards, Mike

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