Bassdude mods and pulldown resistor question

G

Gritdog

New member
I’m going to build the Bassdude and thinking of some mods that are plexi inspired (but slightly less aggressive) and some which provide a middle ground.

Plan is to install switches on:
- C5 (coupling cap): ~22n, ~10n, 4.7n
- C6 (bright cap): 100pf, ~250pf, ~390pf
- C8 (cathode bypass cap): ~220u, ~5u, 1u

I’ve built 2 C2CE tube pedals and can follow directions but I’m beholden to Google and the forums for any mods... I found a diagram for an on/off/on switch with the capacitors wired onto the switch but there’s a few things I’m not sure about. IMG_4294.png

1. Whether I need pull down resistors and if so how I wire them (where I connect them and how to ground them).
2. Where I should locate the switches in the enclosure. I thought there might be enough room under the back of the pcb but I’m not sure. Otherwise perhaps up near the jacks.
3. If I add a 330k resistor to ground on R12 (to mimic the load of the second channel / reduce gain which aligns with the amp), how I ground this. And tbh whether this is even worthwhile.

Any help would be greatly appreciated! Also welcome any comments on the mods above or any other experience!

Cheers!
 
I take it you want the Bassdude to play guitar on, I usually adapt the circuits to suit a Bass guitar more but there are some mods described in "The Mod Squad" thread I started.
The mods you describe all sound ok to me if you want to make the sound brighter with less bottom end, I believe I mentioned turning a Bassman into a JTM45 in post #6 in the Mod Squad thread.
You might want to put sockets in for the caps so you can swap them easier so you can experiment more, but if you are going to place the caps on switches it is fairly easy to swap them anyway.
Make sure you use 630V caps for all replacements of C5, and remember if you parallel caps you add the value together. Ie. 4.7nF + 10nF =14.7nF
I always place the switches between the jacks, and if you are going to drill or have the box drilled place the jacks as low as you can to make more room for the switches.
There is no room between the PCB and the front of the box for switches, maybe some slide switches would fit but not any toggle switches.
I would not bother to place a resistor to ground on R12, there is a gain knob that can reduce the signal to 0 right in front of R12 so just use that, if you really need to reduce the signal then use a tube with lower gain to make that happen.
T

Thread 'The MOD Squad'

This Thread is for any and all mods that people want to share, I love modding circuits if I can make it more useful to me.
I especially like to add deep switches and Bass switches along with Bright switches so I can use the pedals for Bass and guitar.
I like to use the Tube calculators on the Ampbooks.com website, there is also lots of great info to read on their pages.

Guitar Amp Circuit Design Calculators

www.ampbooks.com www.ampbooks.com
And I also use the online tone stack calculator a lot...
 

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That’s great advice, thanks!

Do you have advice on whether I need pulldown resistors and how I should wire them?

I did see that thread, thanks. The other interesting difference between this bassman circuit snd the 5F6A and the 60s Marshalls was the V2 cathode. Seems this circuit has 22u and resistor whereas those other amps have just the resistor. I’m running out of switches so I might socket that cap to experiment and possibly the cathode resistors given those values on subsequent circuits were all invariably higher but I doubt that makes enough difference to bother.

And, yep building to play guitar.

Cheers
 
What exactly do you mean by "pull down resistors" ?
If it is to reduce any pops when changing the switches then I think the best way is to pre-charge all the un-used caps to the same voltage they they will be charged up to when in circuit, I usually do this on high voltage caps with a high value resistor around 1M to 2M.
The resistance is high enough to not affect the tone but it lets the caps all reach the same voltage.
On the picture you posted above I would use 4 x 1M resistors, link the left side of the switch with a resistor between C1 to C2, another resistor between C1 and C3 and then do the same on the right side.
When the voltage in the caps all reach the same voltage there should be hardly any noise when using the switch.
 
Yeh that’s I meant, thanks. Just to confirm, I’ll attach each resistor to the leg of the caps you mentioned? (or I guess even the switch lugs at those points?)

Sorry I thought that was the right term after some trial and error googling.

Thanks for your help.
 
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