Tube Amps / Music Electronics
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|8/4/2005 4:27 PM|
||High Freq. Tone Stack Cap, What are Y'all using?|
I haven't had alot of luck with mica's.. brite, but lacking that chime of the old Fenders, etc.
What's in your brew?
|8/4/2005 4:52 PM|
hey Bill (is that you asking on the PP bbs too?). Not to give you a hard time for cross posting but if it's about Marshall brightness, I've had luck with rolling it off using shielded wire on the grids. You know how some people describe their Marshall as bright enough on the br.ch. and too dark on the normal ch.? That's how mine is now. I think the answer is 1) roll off highs some 'til it sounds the way you want, and 2) (probably) make sure there aren't any oscillations. 1) should help prevent 2) though. The whole idea of shielded wire "ruining the tone" that you see sometimes, pretty ridiculous IMO. Or at least it depends on what someone is trying to accomplish.
|8/4/2005 6:57 PM|
I'm using a mica to no ill effect in my fenderish amp. But I know what you mean about the way the can sound. Mesa uses a ceramic for the treble cap. Most custom builders use mica. Not sure what Fender used. Ceramics sound kinda gritty to me. Maybe try a standard film type. I've thought about experimenting with a polystyrene cap in for the treble. You'd have to decouple with a film cap first (.1uf probably) then into the polystyrene cap. They don't come in a high enough rating to decouple with them.
|8/4/2005 8:46 PM|
Hi Dai and Chuck,
Yep, that's me.. As my Pop used to say, "When fishin, use as many poles as the law allows"..
I was a bit nervous about using the "F" word over there, and in this instance it is about my Plexi clone. My Tweed Super clone uses one of the NPO ceramic 330pf's I mentioned on the other site, and it sounds nice. Chuck, I've read about ceramic's being gritty before as well, I don't know if the NPO style helps this or not, I know the silver-face Fenders used Y5P's.. For those who missed the info I had at Plexi Palace, my Plexi clone presently has old Sprague polyester caps in the mix resistor bypass and treble tone stack, and the high frequency is as bland as peanut butter without salt. The Spragues replaced Mica's that were way to brittle.
I'd dismissed polystyrene's because of the low voltage and tiny leads, hadn't thought about using a higher rated cap in front of it!
I'll try the 330pf's in both the mixer bypass and tone stack ( with a 51k stack resistor in place of the 33k ). I've got a slew of 1 watt CF resistors and 1/2 watt cc's coming from Antique Electronics, I'll be replacing the present metal film's with the CF's A'la Marshall as well. I should say I'm real close to the Plexi tone, voltages are spot on, she's clean and articulate up to 5, then a great grind slowly develops there on up ( She's bloody loud as well ), I'm just trying to refine that high end.
FYI, A Marsten 784-128 will be tried out in place of the Drake 784-139 that currently lives in the amp. If there's an improvement ( Hard to beat the Drake, but Brian's 25% off sale was too good to pass up ) the Drake will be up for sale..
|8/4/2005 9:32 PM|
My Tweed Super clone uses one of the NPO ceramic 330pf's I mentioned on the other site, and it sounds nice.
I believe that NPO refers to the temperature characteristics of the ceramic cap, along with X7R, Y5V, Z5U and other ratings. Just mentioning that...
There are a lot of Fender amps out there with ceramic treble caps that sound great. In some cases the added clarity of a mica cap (one interpretation of its sound qualities) is good. I like changing the reverb mixer cap with mica, too, since all of the sound on the reverb channel goes through that little cap and resistor. [Not relevant here... ]
The issue brought up here regularly is that mica caps often do not work well in Marshall amps, which thrive on the "graininess" of the ceramic caps (again, one interpretation).
BTW 330pF is a great value for a treble cap! A little more balls than the traditional 250pF cap, but not as over-the-top as a 470-500pF cap.
|8/4/2005 10:13 PM|
"BTW 330pF is a great value for a treble cap! A little more balls than the traditional 250pF cap, but not as over-the-top as a 470-500pF cap."
Just the point I was going to make, IMHO the actual cap value makes more difference than the type.
|8/4/2005 10:28 PM|
IMHO the actual cap value makes more difference than the type.
In this case, you are probably right but there are some circuits in which the type of cap will have a bigger influence on the sound than the value. Like in a Marshall 2204 [see the MVP schematic here] there is an RC network going into the 3rd stage with a 470k resistor in parallel with a 470pF cap. On one of my 2204-influenced amps I added a rear panel switch to select between a mica and a ceramic 470pF cap, and the difference was very noticeable. The "graininess" of the ceramic cap gave it a softer sound, which smoothed out the preamp distortion. With the mica cap the distortion was a little bit sharper and not quite as musical. Or so it seemed to me... YMMV
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