What Effect on Gain and Tone of Mix Resistors (270K vs. 470K

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What Effect on Gain and Tone of Mix Resistors (270K vs. 470K

Postby PCollen » Mon Nov 13, 2006 11:14 am

Seems to me there would be slightly MORE gain with 270K mix resistors than 470K. And then, if playing through the BRIGHT channel, rolling the NORM channel volume up would increase effective V2a grid-to-ground resistance and therefore increase signal level to V2a giving more signal gain through the pre-amp.

Comments ...?
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Postby Billy Batz » Mon Nov 13, 2006 4:36 pm

Just changing a 470k series resistance to 270k doesnt really change the percieved drive that much. Mostly just high end. The same way rolling down the tone takes away drive but way more subtle in this instance. The larger factor would be the reduced resistance from the bright channel to the normal channels ground like you said. With the normal volume on zero it would seem like less drive. But if you keep the normal channels volume up a bit, it negates taht difference a good deal and then it mostly seems to change the tonal character of the amp more then effect any drive/gain amount. I assume you have or will try it? I just jumper in 2 470k's in parallel with the 2 470ks with mini jumper cables. You can always replace just the bright channel with a 270k but I dont think it makes much of a drive difference and it helps to seperate the interactiveness of the volumes which isnt a huge deal really. I didnt think enough of it one way or another to bother changing it.
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Postby shakti » Mon Nov 13, 2006 5:51 pm

Seems to me that a bright channel with 270k is proportionally less bright than one with 470k, at least in my limited experience. Makes sense, since the cap would have less effect the lower the value of the resistor.
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Postby Billy Batz » Mon Nov 13, 2006 6:58 pm

If you use a cap, yeah. I guess most people do. Its hard for me not to automaticaly turn back to my own experimentations which, most of the time I dont use a mixer cap, even tho I happen to now.
Last edited by Billy Batz on Mon Nov 13, 2006 7:21 pm, edited 2 times in total.
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Postby Brentsp » Mon Nov 13, 2006 7:02 pm

shakti wrote:Seems to me that a bright channel with 270k is proportionally less bright than one with 470k, at least in my limited experience. Makes sense, since the cap would have less effect the lower the value of the resistor.


I built a single channel plexi spec with a PPIV MV. The mixer is a 270k and a 470k to ground. It does give it a bit more drive and with the PPIVMV the PI overdrives a bit to and gives me quite a bit of gain for a plexi spec. Heres a clip http://www.soundclick.com/bands/songInf ... ID=4659769
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Postby PCollen » Tue Nov 14, 2006 9:03 am

[quote="Billy Batz"]Just changing a 470k series resistance to 270k doesnt really change the percieved drive that much. Mostly just high end. The same way rolling down the tone takes away drive but way more subtle in this instance. .[/quote]

Billy: Did you consider changing the Bright Ch mixer cap when changing mixer risistor values. I think this must be done to maintain the same 'roll-off' that the cap and mix risistor perform: F = 1/ 6.28 x R x C.
Assuming a 270K/500p start point, I think you would have to reduce C by half, to about 250p to keep things equalized.
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Postby Good Guest » Sat Nov 18, 2006 5:20 pm

Wasn't that one of the many changes to a transitional plexi.....they switched from 270k mixer resistors with a 470 pf to a 470k mixer but didn't change the cap?

1.25 khz compared to 720 hz = Big differance in tone.

Perhaps they used a 330pf on the 270K makeing an even bigger differance 1.78 khz.

More research must be done on this. I remember the hendrix marshall on ebay that marshall bought to model the new hendrix amp..it had 270k mixers. Can't remeber the cap tho.
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Postby Billy Batz » Sat Nov 18, 2006 11:09 pm

It was a 500p. I dont think Ive seen more then a single marshall that had something other then 500p (or 470p/556p etc...) or none at all.
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