SOLVED Special Overdrive question.

[Allthumbs]

I've built a fuzzdog Dumb Lloyd that is very similar. The difference that I can see is the tone pot on the Special is 20k instead of 25 k.

My build has a problem with the tone pot in that it's muffled until about 8.5 then it's sweet around 8.5 to 9.5 then it's shrill t 10. Tight sweet spot and lots of unusable space. I like the feel of it so I may either mod mine to the Special's specs or start over with the Special.

Does the difference of the tone pot have any bearing on the problem I'm describing? Had anyone built one of these and can verify it works correctly? modding it to the Special shouldn't be any trouble......

 

[phi1]

You’d get some difference between 20k - 25k, but it likely wouldn’t be a huge improvement in the usable range.

I would try a W taper pot (either 20k or 25k). This tone control section is like a tube screamer, but with a different cap (100n). A TS performs much better imo with a W taper pot. When I built my TS with a B taper tone pot, the response was very flat from about 9 o’clock to 3 o’clock or so. Changing to a W made it much smoother.

So, assuming you have all the other components right,this change should open up the range you like from 8.5-9.5 to more like 6-9 (roughly speaking).

EDIT: come to think of it, 20kW should give you a slightly better range than 25kW, so I’d shoot for that if possible. But regardless, the w taper should help a lot.

 

[Allthumbs]

You’d get some difference between 20k - 25k, but it likely wouldn’t be a huge improvement in the usable range.

I would try a W taper pot (either 20k or 25k). This tone control section is like a tube screamer, but with a different cap (100n). A TS performs much better imo with a W taper pot. When I built my TS with a B taper tone pot, the response was very flat from about 9 o’clock to 3 o’clock or so. Changing to a W made it much smoother.

So, assuming you have all the other components right,this change should open up the range you like from 8.5-9.5 to more like 6-9 (roughly speaking).

EDIT: come to think of it, 20kW should give you a slightly better range than 25kW, so I’d shoot for that if possible. But regardless, the w taper should help a lot.

thanks much.

 

[Allthumbs]

Curious to know if an even smaller value pot would do more to expand the range. I have the W25k and not doing so much. I've gone through the schematics of both the PedalPCB and the Fuzzdog and they seem to be extremely similar. I have a W10k to try.

Could be I just don't really like the effect

 

[phi1]

Bummer the W25k didn't expand your range enough. I'd hesitate to just drop a 10kC in though.

The tone pot does 3 things:
#1. When turned down, it rolls off more treble.
#2. When turned up, it increases the gain of that op amp (which cuts bass, so it sounds like it boosts mids and highs). The Accent knob also controls the gain of this stage.
#3. The pot changes the frequency where bass is cut at that stage, as the pot is turned up, the cutoff frequency gets higher

If you use a smaller pot, you risk having more treble rolled off by #1, which could somewhat counteract the treble gained by #2 and #3 using a lower pot. Although with it being a C taper, it might still get you the expanded range you're after.

Here are a few other ideas. (I've not tried them, so it's all based on theory, so definitely experiment)
-If it's really just more range on the treble side that you want, you could try to get a 20kC or 25kC
-Use the 10kC, but do not connect lug 1. This means you won't have the action of #1 that cuts treble when the pot is down, so you can use the full range of the knob to control the treble boost.
-You could experiment with C9 (from Fuzzdog schem) (100n). This will affect the frequency where bass is cut (or think of it the frequency where mids and treble start to boost). It interacts with the tone pot via function #3 above.
-You could reduce C5 (Fuzzdog schem). R8 and C5 form a treble cut (low pass filter) before the tone knob, cuttingfrequencies above 723Hz (F=1/(2piRC)). If you reduce C5, you will cut less highs before the tone pot, and that might help you dial in the sound you prefer.

 

[Allthumbs]

This is a lot of great info. Thanks so much for taking the time.

I'm sorry but I'm an idiot. I soldered another B25k in there thinking it was a W25k, got confused in my haste and messy situation here. I'll go back and try again.

Still, this info helps me a lot and does not go unappreciated. The Fuzzdog pedal could serve as a base for learning to do these mods to see what happens. I've heard good things about the Dumbloid pedal so if it does pan out I see a PedalPCB version after I figure it all out. Curious about that one, too as I;ve been searching for good low gain sustaining type boosters, this one seems to do that

EDIT: The actual W25K pot does the magic. Now the sound is much better, nice mid hump, plenty of good tone travel in either direction a a few clicks. Still ultra shrill at the top and mud bottom at the low end. Thinking of doing the same W25k to the Accent pot as suggested previously.

Next will be the C5 mod to see. as it stands the tone if very open and lively, low volume feedback and thick gain.

thanks again

 

[phi1]

You’re welcome, glad the 25kW is working good.

For accent, don’t use W taper, use C or A depending on where you want more tweakbility (I’d guess A). On the tone pot, W works well because both sides of the pot (lug1-2 and lug2-3) happen to benefit from the nonlinear taper. But for accent, only lugs1-2 are used. So if you don’t like linear taper, then W would give you an extra dead spot at one of the ends.

 

[Allthumbs]

perfect. thanks again

 

[piapium]

Where did you find w25k if I may ask?

 

[Teddeeh]

Also. With a w25k pot (like i did for the c150k)
Open the pot up and scrap away some of the outer track.

THIS IS A BIT TRICKY SO BE WARNED!!
You need a multi meter to check resistance, but i scraped away some out track on a c100k pot to make a c150k, and i did the same with a w20k pot to make a w25k.
sounds odd i know. But trust me, a lower value pot, remove some of the black track inside and the resistance goes up.

A Pot wont fall apart the second you open it up, try with some from your junk pile to practice if unsure.
Now you can make most pot values. Ive mixed pots too.