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DIY Bassman: driving me nutz!

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7/28/1999 1:19 PM

DIY Bassman: driving me nutz!

I have a strange problem with this 5F6 bassman clone. (Along with the standard distortion troubles...) With a guitar plugged into just one input, the volume controls for both channels affect the volume of the output to about the same extent, as if they were running in parallel. I have checked and rechecked my wiring several times, but I'm stumped by this. Could my distortion troubles be related to this, for instance if the two channels were acting as two gain stages? This is my first project, and I'm happy to get any sound at all, this early in the game, but I'd appreciate any ideas from out there. Thanks!

7/28/1999 2:38 PM

Benjamin Fargen

Moss man,

It sounds like you have each set of your input jacks wired to both grids (pin 2 & 7) rather than one set per grid on the 12AY7. The normal channel should have one wire running to pin 7 and the bright channel should have one wire running to pin 2.

If this is the case it very well could be the cause of your distortion problem. I believe 12AY7's are easily overloaded (especially by gain pedals) and in that configuration you would be driving both triodes simultaneously with one input signal. This signal would then be continuing on to both volume pots.

Double check the input jack(s) to grid wiring again and keep us posted.

Benjamin.

7/28/1999 2:46 PM
Farrow	Also keep in mind that the voulme controls on 5F6A Bassmans (and JTM-45 type Marshalls!) are quite INTERACTIVE. Turning up "normal" has an effect on "bright," and vice-versa. Double-check your grid connections on the first tube, but you'll never get them wholly independent. Farrow http://surf.to/pharaohamps

7/28/1999 3:39 PM
Benjamin Fargen	Farrow, Point taken.......I have zero experience with either circuit in person.....only on paper. I assume this is due to the fact that both 100K plate resistors are tied together at the plate supply?.....there must be some signal bleed from one path to the other. Benjamin.

7/28/1999 4:23 PM

You could have been right. The volumes do interact a bit but it’s not as much as Mosrite man’s. It’s not because the 100k resistors are tied together at the plate supply. There will be no interaction at that point because it’s connected to ground with a BFC so it’s AC ground. The interaction will be through the 270k resistors in series with the vol wipers. As you adjust chan 1 vol you change the potential divider resistance to ground seen by chan 2 vol so chan 2 volume will also change a little.

Dave

7/28/1999 5:53 PM
mosrite man	Thanks a million, guys. I'll double-check these connections and let you know what happens, as soon as I 'm finished with the chores the wife has cooked up for me...[:} Thanks again!

7/28/1999 6:18 PM
Benjamin Fargen	Dave, I see.....Thanks for the clarification and explanation! Benjamin

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