Recommendation for what values to start with for post-OD treble bleed mod?

[itsgiusto]

I'm almost done with my Ceriatone OTS FM (Dumble #102 clone). I've been worried that it'll be just a tad too bright, so I'm adding two mods:
1. switchable bright cap on master volume via push-pull pot (in addition, I lowered bright cap value from 68pf to 47pf)
2. post-OD treble bleed

The point of the treble bleed as opposed to the switchable bright cap, presumably would be to get it so I don't have to switch the bright cap on and off in order to get a sound that works for both the OD and clean channel, since the treble bleed only affects the OD-channel.

In this thread someone posts this schematic showing their treble bleed mod:


It looks like a good place to start, except for two things:
1. I don't think I have room on my faceplate to put a 500k pot
2. I want the bleed to be entirely switchable, so that I can switch it to where the mod is completely out of the circuit.

With that, I think I'm going to try a variant like this:


The switch would be an ON-OFF-ON so I could switch the treble bleed entirely out of the circuit.

So my question is, what would be useful values to start with for the resistor and the two caps? I know I'll have to iterate later, but what would be good values to get me into the ballpark? I was thinking maybe 150k, 1nf, and 500pf.
Or would it be better if I did a variant in which I have two separate resistors I'm switching between, and only a single cap, which would make it closer to having a pot, like the original mod above? This would look something more like this:

[professormudd]

I do not have any technical advise to offer, but I wanted to mention that I noticed you have a couple of threads for this build. I am not a mod or anyone important, but I feel compelled to mention that you might be better off having a single thread for your build and ask all of your questions related to it in there. I did the same thing as you at first; making new threads for every question. But it cluttered up the board, and I got better responses after I consolidated anyway.

[itsgiusto]

I do not have any technical advise to offer, but I wanted to mention that I noticed you have a couple of threads for this build. I am not a mod or anyone important, but I feel compelled to mention that you might be better off having a single thread for your build and ask all of your questions related to it in there. I did the same thing as you at first; making new threads for every question. But it cluttered up the board, and I got better responses after I consolidated anyway.

Thanks, but my questions have not been anything specific to my build, nothing about debugging, etc, which would require continuity between my questions in order to answer. I'm more wanting to pick people's brains with small questions about various Dumble-y topics, and how things are typically done, what people often use for various mods, each pretty distinct from each other.

[dbharris]

I think if you play around with a low pass frequency calculator, you will be able to see what effect the original circuit has and then decide what 2 options you would like to have. Of course, once you play the amp you might want to change this more.

If it were me, I would build a stock amp. Let it burn in and get to know it for a month before making any deviations from the schematic.

-Dan

[itsgiusto]

I think if you play around with a low pass frequency calculator, you will be able to see what effect the original circuit has and then decide what 2 options you would like to have. Of course, once you play the amp you might want to change this more.

If it were me, I would build a stock amp. Let it burn in and get to know it for a month before making any deviations from the schematic.

-Dan

One thing I'm very unclear about is how the resistor in series with the cap would affect the cutoff frequency. Unfortunately all of the lowpass frequency calculators only have the cap going to ground, not both the cap and resistor.

[Smitty]

I'm using 390P and 100K in a 124. Keep in mind all amps sound bright by themselves and more balanced once you get up on stage and in a mix. I remember how bright Robben Ford sounded live the last few times I saw him. I think 102 is supposed to be bright. A bright on clean switch is another good solution to the issue of balancing clean and OD treble balance.

[dbharris]

This blog may be of interest to you https://mimmotronics.com/blog/uncategor ... c-filters/. In particular what they call the Type III filter. Somebody can correct me if I am wrong (I have no EE background) but you would take into account the 150K resistor and then the shelf filter, that output feeds the ratio pot.

-Dan