Bathtub Reverb - Issues

[SamuelG]

This is how I would add a deep switch, that way I could have it original or deep tone if I wanted to.
I would not mount C2 on the PCB, I would run 2 wires from the PCB holes for C2 to a DPDT switch and then mount the capacitors on the switch.
It would be a lot easier to change the caps on the switch if you want to keep trying different values.

There is a way to use a DPDT ON-ON-ON switch so you can have 3 different settings if you wanted Normal-Deep-Bass settings which I have used in the past, It gave me normal for guitar, deep for a deeper tone on guitar and Bass for Bass guitar.
If you would like to see it let me know, I would have to find it on my computer, I'm to tired now at 3.30am to look for it.
Cheers
Mick

EDIT: I couldn't help myself so I drew the 3 way switching circuit up in KiCad just to show everyone, I have been meaning to start a new thread just for mods and when I do I will place all this in there as well.

I was thinking about this mod for C2 in the Bathtub Reverb. C2 also isolates the Reverb module from the high plate voltage. Doesn't that mean all the mod caps should be rated for over 250V DC?

 

[SamuelG]

A suggested list available from Tayda

C1	470nF 630V	A-4849
C2	4u7F 400V	A-3338
C3	22uF 400V	A-3336

 

[Tassieviking]

If I did it on a HV capacitor I think I would add a resistor (2M-5M) to each extra cap to pre-charge it up to HV, I don't think the resistor will change anything tone wise but will help with pops and arching in the switch.
The caps would have to be HV caps just like they are paralleling.
I don't think you would need that much more capacitance, I would try with 22nF original, another 22nF for deep and a 100nF for bass.
I think it's try and see unless someone can run a sim on the circuit.

Coupling caps are not usually very big in valve amps, usually somewhere between 22nF to 100nF is very common.
https://www.ampbooks.com/mobile/amplifier-calculators/coupling-capacitor/

 

[SamuelG]

I think this is how I’ll wire it… just need to drill that extra hole in my BTR

 

[Tassieviking]

The resistors are in the wrong place, if you remove the resistors it will work fine. (just bridge them out)
The resistors would go from 2-5 and 2-6 on that drawing, they are not needed but I would put them in so the caps can sort of reach the right voltage level in case they are switched in.
I like to think they help to prevent any pops in the signal when you change the switch position, purely my speculation and not based on any tests.
The resistors are of a very high value so they should not make any difference in the tone of the circuit.

 

[SamuelG]

Thanks Mick

It’s taken me a few goes to get my head around how these resistors fit. It just felt weird “shorting” the switch even though it is with such a high resistance… I’m with you now.

With your 2P3T you have “Bass” labeled as C1+C2+C3 but drawn “Down” as C1+C3.

I suspect that the difference between 144nF and 122nF would be very little, if any, by the time the coupling cap has been increased from the stock value of 22nF.

I know I should try both, but I must confess that if C1+C2+C3 “works” I’m not sure I’d find the motivation to required to find out how much dropping from 144 to 122nF will make

 

[Tassieviking]

You are right that the Bass setting would be C1 + C3 only, I drew it up in the middle of the night and I did it fast so I made a mistake.
I like mistakes because you learn the best when you do it wrong, as long as no one gets hurt.
I picked up the 3 way switching from "PassinWind" on the TB forum, he used it on his onboard preamp design and then on the pedal as well.

 

[SamuelG]

Totally agree!
You’ve helped me a lot, my modded BassDude wouldn’t have happened without it.

 

[SamuelG]

Thank you very much for taking the time Tassieviking. You were right, it must've been a broken trace, after going through your trouble shooting guide, there was no continuity between the left side of R12 and the 2 pins on the right of the 10 pin link to the tube PCB. The jumper solved the issue.
Now, in the sound, do you have any suggestions to incorporate more low frequencies?

Just to let you know. I finished my build and it has exactly the same issue. So it looks like a fault in the batch.

I also used Mick’s suggestions re the Norm/deep/bass and can confirm the bass is preserved on the bass setting
Sounds good and the LED works!

 

[BisonG]

I finally had the time to implement this mod in my build and it works great! It's exactly what I was looking for to get back those bass frequencies when the reverb is engaged. I also like this pedal as a prramp and get nice saturation out of it when driving it hard. I tend to reduce the reverb knob to the minimum.but still can hear some reverb. Is there a way to bypass the reverb effect and leave the preamp only? Thanks again Mick!

 

[SamuelG]

I finally had the time to implement this mod in my build and it works great! It's exactly what I was looking for to get back those bass frequencies when the reverb is engaged. I also like this pedal as a prramp and get nice saturation out of it when driving it hard. I tend to reduce the reverb knob to the minimum.but still can hear some reverb. Is there a way to bypass the reverb effect and leave the preamp only? Thanks again Mick!

Hey Bison,
If you are looking for saturation and OD, I'd strongly recommend the Particle Accelerator PCB set from C2CE.
There is a known way of bypassing the eq if you want to mod it and then it's pretty much the old SushiBox Space Heater. It's what I use as my first drive stage.