Presence knob on 6g3?

[cminor9]

I am working on my next build, a 6G3. Since this amp has a feedback loop which is very similar to the one on the 6G4-a, I was thinking of copping the presence circuit from the 6G4-a so I can add a presence knob on the 6G3.

Look at
http://ampedia.redbeartrading.com/da..._6g3_schem.gif
and
http://ampedia.redbeartrading.com/da...g4-a_schem.gif.

Very similar feedback loops/phase inverters. I'd think the presence control would translate well to the 5G3. Any reason this might be a bad idea or a waste of time?

[MWJB]

Use a 5K presence pot in the 6G3 circuit, with the 1500 nfb load resistor.

[cminor9]

yeah, ok...thanks! I might give that a whirl.

[dwhutchens]

I'm working on one of those now. Or at least thats what it began as. Just one channel without the tremolo. The presence control works well. I haven't settled on the pot value yet. I think I have a 25k in it now. I've been chasing ghost notes for a while. See my thread:

http://music-electronics-forum.com/s...ead.php?t=8887

David

[cminor9]

I'm working on one of those now. Or at least thats what it began as. Just one channel without the tremolo. The presence control works well. I haven't settled on the pot value yet. I think I have a 25k in it now. I've been chasing ghost notes for a while. See my thread:

http://music-electronics-forum.com/s...ead.php?t=8887

David

Yeah, saw your thread. Your thread made me consider doing the 6g3 in the first place. I was gonna do a 5G9 but ultimately decided that was a bit too close to my 5e3 and I wanted something sufficiently different but with trem.

One channel, eh? That sounds interesting. On a 5E3 no way would you want to drop the other channel. On a normal 6g3, are the two channels interactive? It looks like the trem work on both channels. I guess I am trying to figure out what I'd lose by dropping the other channel. I don't want two channels if the two channels are the same thing.

[cminor9]

Well, I just finished my 6G3, built with the presence circuit largely borrowed from the 6G4-a. I played it for a few hours with and a few hours without. Gotta say, I am not a fan of of the presence control here though I love it on other amps. It adds nothing of value, just some icepickieness. Even when turned all the way down it affects the frequency response. I could put a switchable pot on there, but I don't think I'll bother. Glad I haven't ordered a faceplate!

[The Kirbster]

I'd sure like to add a presence knob to the normal channel of my Bassman Ten. I'd get all my hight from the normal channel, then roll in channel 2 to fill in the low end! No drilling, though...I'd rather wire it in, adjust it, wrap it in some kind of insulator & leave it inside the chassis than drill it.

I don't know how to do it. I DO know how to drain the caps, though. Anyone willing to walk a newbie in Arkansaw thru this?

[tubeswell]

I'd sure like to add a presence knob to the normal channel of my Bassman Ten. I'd get all my hight from the normal channel, then roll in channel 2 to fill in the low end! No drilling, though...I'd rather wire it in, adjust it, wrap it in some kind of insulator & leave it inside the chassis than drill it.

I don't know how to do it. I DO know how to drain the caps, though. Anyone willing to walk a newbie in Arkansaw thru this?

FWIW You'd be better off starting a new thread than trying to get attention a the tail end of some old thread where nobody much looks.

Anyhow take a look at the Bassman 10 schematic 1972-1982 "Silver Face" Bassman 10 . You will see a 100R resistor to ground on the NFB loop (which runs from the OT secondary through the 820R resistor back to the bottom of the tail resistor in the long-tail pair). To make a presence control, you need to replace that 100R resistor with something like a copy the brown Bassman presence control circuit, but scale the values to reflect the overall 100R resistance of the existing 100R resistor in the Bassman 10 NFB loop (which, according to my off-the-cuff math, is something like a 250R pot in series with a 20uF cap, all in parallel with a 100R resistor AFAICT). Others might have some different views, especially as this is just based on a hunch about where to start. You might need to experiment a bit and tweak the values until it works right.