-
BLACK FRIDAY SALE!
20% off all PCBs - No coupon code required - Valid through 12/01/2024
Components and sale items excluded
Tommy 3 on/off/on mod
- Thread starter roro701
- Start date
swyse
Well-known member
The switch on the tommy is functionally an on-off switch, switching in a 360 ohm resistor in parallel to increase the gain, and a 220nf capacitor to add bass back in because the 360r resistor changes the filter. With the bass pot on maximum the timmy really doesn't lose much bass in the lower gain setting.
Here the green lines are the low gain mode and the purple are the high gain mode, with gain and treble at noon, level at maximum and sweeping the bass pot.. As you can see on the low gain mode you don't lose much bass. If you want to increase the bass, I'd try changing c4 to a larger value. It might not be terribly pretty to fit a 2.2uf capacitor there, but this would be the effect if you did.
Feral Feline
Well-known member
OR...
You could add a cap and resistor to an on-off-on switch for SW2.
Centre is off, of course and then you'd have C9a & R12a flipped one way and R9b & R12b switch flipped the other way.
You'd want to breadboard it to see if it's worth the trouble, as it may be too subtle of a difference to warrant doing so. If it is subtle, you could push the values of cap and resistor so it's less subtle, but that may not necessarily sound great.
I'd still socket C4 if doing the SW2-mod
You could add a cap and resistor to an on-off-on switch for SW2.
Centre is off, of course and then you'd have C9a & R12a flipped one way and R9b & R12b switch flipped the other way.
You'd want to breadboard it to see if it's worth the trouble, as it may be too subtle of a difference to warrant doing so. If it is subtle, you could push the values of cap and resistor so it's less subtle, but that may not necessarily sound great.
I'd still socket C4 if doing the SW2-mod
swyse
Well-known member
I believe you need to find the pads that don't correspond to anything. Either the top or bottom pads on the switch will connect to the 360 ohm resistor and 220n capacitor, then the other will connect to nothing. What I'd personally do is solder the added components right to the unused switch lugs on the top of the board once you get the switch in place. In the corresponding row for the resistor and capacitor and bridge it to wherever it needs to go, either vref for the capacitor or the negative feedback loop for the resistor. The website photo may not show the final traces for the circuit board, but I'd try probing these locations first and see what connects to the resistor R12, then whatever one DOESN'T I'd use for the next step
If you bridge the switch on the cap side of it to leave the capacitor the same at 220n and just switch the resistor for a 1.2k, when in parallel with the 3.3k you'll get 880 ohms and the 259nf from the parallel capacitor, so at minimum bass settings you'll end up with a cut off around 700hz, which is pretty close to the 720hz of the tube screamer, that with the treble control might give you the mid hump you're looking for.
This is how I'd do it, putting the resistor right next to R3 and the capacitor, then run the loose lead to whichever part of the switch corresponds to nothing. You could do this on the underside if you wanted as well for a cleaner look, but it would be a bit more tedious to experiment if you didn't like the result and wanted to change.
Okay, if you can bear with me I’d appreciate that, I admit to being a little dumb
I socketed c4 for later and I have this, the 1.2k resistor is on the same place as r3 and I figured that the empty lug is that bottom left. Is this what you’re saying?Attachments
Feral Feline
Well-known member
Looks pretty good to me. If it tests well and you like that value, I'd then shorten the leads on that extra resistor as much as possible — lest it act as an antenna for noise/RF (despite being shielded in an enclosure, it might still be a radio/noise beacon).
Good thing Swyse is involved — beyond a simple corner frequency using the J. Orman's online calc, I'm not so great at figuring out the values needed to get specific frequencies.
Good thing Swyse is involved — beyond a simple corner frequency using the J. Orman's online calc, I'm not so great at figuring out the values needed to get specific frequencies.
Oohhh gotcha, I have a 220n cap jumping it right now
Feral Feline
Well-known member
The jumper-wire you’ve got going from the DPDT’s lug 4-to-6 …
I’d lay it down to the right (plenty of room there) so it’s out of reach of lug 5, the lid, and everything else it could short on.
I’d lay it down to the right (plenty of room there) so it’s out of reach of lug 5, the lid, and everything else it could short on.
Gotcha! I’m gonna do that after I replace the switch, I think I got a too cheap of a toggle switch and it died on me
Feral Feline
Well-known member
Desoldering switches is not a fun time.
Mind the heat on the new switch, take it easy and allow plenty of time between soldering each lug for the thing to cool down.
I've cooked good switches 'cause of bad solder (couldn't have been my *ahem* technique!
) — whatever, I applied too much heat for too long.
Mind the heat on the new switch, take it easy and allow plenty of time between soldering each lug for the thing to cool down.
I've cooked good switches 'cause of bad solder (couldn't have been my *ahem* technique!
) — whatever, I applied too much heat for too long.More than likely this is itDesoldering switches is not a fun time.
Mind the heat on the new switch, take it easy and allow plenty of time between soldering each lug for the thing to cool down.
I've cooked good switches 'cause of bad solder (couldn't have been my *ahem* technique!
I prolly broke it
