Tone stack Mod for Bogen H30

[Stringbassfellow@]

Hello all! Trying to add a tone stack to a Bogen H30. Any suggestions on where I should put it in this schematic?

[Stringbassfellow@]

anyone? pleeeeeeeeeeeease

[nickb]

Sorry- I can't read that schematic at all. It's too small for me and It's not an amp that I'm familiar with. I see there is some kind of tone shaping going on in there but there are changes to the sch too.

Generally, you may need to add a recovery stage after the tone stack due to the losses.

[Stringbassfellow@]

Here's a link to the only schematic online I can seem to find:

http://i1117.photobucket.com/albums/...00Rremoved.jpg

[Stringbassfellow@]

I can see the tone circuit that's in it and have tried to put a tone stack similar to a Fender in line and around it, but it doesn't seem to do anything. I was going to make my next step a Baxandall circuit.

[Jazz P Bass]

Here is the schematic.

[Stringbassfellow@]

Mr. Jazz P Bass... YOU ROCK! Thank you!

[nickb]

I can see the tone circuit that's in it and have tried to put a tone stack similar to a Fender in line and around it, but it doesn't seem to do anything. I was going to make my next step a Baxandall circuit.

The tone shaping is part of a quite complex multiple (three) feedback path network. Just guessing, but it may be that when David Bogen first tried out his tone switches he got instability and started adding things to fix it - I really don't know.

IMHO, I think the safest and most flexible approach would be to leave all that as it and add a tone stack and recovery stage before the phase splitter V4. You could replace the 6SF5 with a twin triode like 6SN7 and use the second half for recovery - a voltage gain of 10 is all you need.

The other approach would be to replace the existing tone switch with some kind of tone shaping with variable controls. It could be made to work but I suspect it will get tricky.

[J M Fahey]

I would leave it as is.
Looks very interesting, it's quite original, I guess the tone shaping must be as radical as allowed by feedback stability and, besides, to me it's like having an unusual original colour '57 Strat (say peach colour or whatever) and sanding it down to paint it "white like Jimi Hendrix's" with a can of corner store bought spray paint.
Who needs just ***another*** boring Tweed copy?
Just sayin'.

[okcrum]

You could remove the switched tone stack completely. A Fender or other tone stack would go between the plate coupling capacitor of the second gain stage, and the grid of the tube from which you removed the old tone stack. It would have no effect in place of the existing tone stack. You'll need to raise that grid resistor to 1 meg or so - from what I can see it's 100k or something like that.