Turtlerock Forum

i've got all the answers now. footswitch connects as per :

[img] http://www.sewatt.com/files/sewatt/R8%2 ... ck_144.jpg [/img]

thanks very much to the sewatt posse for resolving my question - http://www.sewatt.com/node/16115#comment-153566

chris.



ok. so i've got the EVJ open and ready.

http://www.diycustomamps.com/images/sch ... _schem.pdf

here's my plan -

emulate fender 'high' input :
R1 change up to 1Mohm
R2 change down to 22k

done. easy so far.

now - to put a high gain footswitch on :
R6 - bridge via a new rear 1/4" TS socket to footswitch

simple? i can't find anyone else having modded an EVJ for footswitch gain boost. but it seems evident enough.
i tested the footswitch, and it's a simple TS 1/4" open / close spst the same as a toggle switch.
i thought i could simply do the same as the spst toggle for gain boost -
run hook up wire from either side of R6
to tip/ring of a TRS socket (using the shield earthed out the signal),
and then switch b/w R6 and jumper
- switch off sends signal through R6, switch on allows signal to jump the 1M load.

didn't work.

whaddya think? if i had a spare two-pedal footswitch, i'd try putting gain on one and high boost on the other (via 100pF cap on the open C3 terminal) . . .

chris

perhaps the idea is that the footswitch takes that R6 C1 loop out of the equation entirely - ie it makes a break in that path when hi gain is switched on, rather than just bypassing R6.

Dunno, though, never done it.

yeah - that might be it. but i can't find anything further on the vjh mods pages . . . all they detail is to jumper R6.

unfortunately, the mods i have done seem to have induced microphonocy (?high pitched squealing) in the tube when the gain is past 2am. It didnt seem to be the R1 increase to 1M or the R2 decrease to 22K.
Last night, i disconnected the TRS socket for the footswitch by left the wires running off the pcb - insulated, of course. hopefully the microphony is just due to that.

i do like the gain mod, and when i could wind it all the way without the high pitched squealing the added gain on the input worked great for me.

hey astro - how'd you go with yours?

I've had....fun....with mine.

I'm actually not modding a VJ, I acquired the chassis, speaker box and transformers for nix and have been building a P2P single ended amp in it using a EL34 for the output. It's somewhere between a Champ and a VJ. Have a look at www.turretboards.com for details, its the "Fenderish Octal" build.

I've also tried to implement a few mods by picking and choosing some ideas floated on the VJ page of the single-ended forum www.sewatt.com Check it out if you haven't already, it's the best VJ resource on the net. I think some of the ideas you're floating there mfdu have been covered on that forum.

Bizarrely, I got mine built and running, but the Princeton style tone circuit was not doing the right thing. When I pulled it out, the whole amp stopped and that's where I am. I spent ages trying to isolate the problem, strangely it appears to be in the heater filament wiring (I get the 6.3A off the power trannies heater secondary, but when I connect that to the tube pins the voltages go all weird, then when I tie it to ground via 100R resistors it goes nada). I started to get a little frustrated with it, so I put it aside for the moment as when I get frustrated I get impatient, which is not a good trait to have around those voltages :shock:

thanks - i'll see what i can pick up on sewatt.

good luck with your build - sounds like a bit of a poopies.

we'll chat.

c.

ok. so the high pitched squealing was just because i'd left two insulated cables attached to the pcb, one either side of R6. these acted as antennae. lucky me. so they're gone, and the amp sounds wonderful and creamy with the increased gain via changes to R1 and R2.

still researching how to implement a footswitch gain boost - http://www.sewatt.com/node/16115#comment-153497

cheers,
chris.