Catch 22

[angrykoko]

There is a note about using a 25ka volume pot instead of the 100K

I have both handy and was wondering if anyone did the mod and if it was worth doing?  Or is it saying it's a better setup if your using the pedal as more of a boost?

Also, I'm assuming the note means simply soldering a 18k resistor across lug 2 & 3 (on the schematic) and I can still use a board mounted pot?

I hate to miss out on good mods 

[GrindCustoms]

The idea is to use a A25K pot and reduce it to A10K like what is originally used in a Timmy, it brings the overall resistance lower but mainly change the behavior of the Taper, bringing unity gain at noon instead of around 2 oclock. Mod is appropriate for all useage.

[angrykoko]

Thanks Rej,

I thought the A10 on the bom was a typo which is where I got the A100K (from schematic)... so I thought we were reducing from 100K.

It makes more sense now with your explanation, thanks a ton!

Just gave it a try.. I really like it.   Box it up tomorrow if I get time.

Thanks again.

Koko

[dannoceti]

So do you need to add the 18k resistor with the catch 22 board?


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[angrykoko]

Not if you use the A10k volume pot like the bill of materials states.

You do only if you want to use an A25k pot like the mod states.

[dannoceti]

Not if you use the A10k volume pot like the bill of materials states.

You do only if you want to use an A25k pot like the mod states.

Okay thanks, I think I'm going to build it with the mod so I will order the 18k resistor. All the caps are non polarized film except the 3 electrolytic polarized right? I was confused because the BOM has C3 and C6 as "non- polarized". Aren't C1-C6 just film caps and C7-C9 polarized electrolytic?

Also does anyone know the differences in ic2 choices or are they just for power and don't affect the audio?

Last question, did anyone just use the Timmy ic (JRC4559)? Curious why a different ic was used?


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[angrykoko]

Not if you use the A10k volume pot like the bill of materials states.

You do only if you want to use an A25k pot like the mod states.

Okay thanks, I think I'm going to build it with the mod so I will order the 18k resistor. All the caps are non polarized film except the 3 electrolytic polarized right? I was confused because the BOM has C3 and C6 as "non- polarized". Aren't C1-C6 just film caps and C7-C9 polarized electrolytic?

Also does anyone know the differences in ic2 choices or are they just for power and don't affect the audio?

Last question, did anyone just use the Timmy ic (JRC4559)? Curious why a different ic was used?


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Yes C3 & C6 are film box caps.  The are noted as non polarized because caps up around 1mf and higher are typically electrolytic but these are box caps.

I used the jrc4559 but I haven't gotten around to trying anything else.
Was there anything on fsb about the different ics ?

Koko

[dannoceti]

Not if you use the A10k volume pot like the bill of materials states.

You do only if you want to use an A25k pot like the mod states.

Okay thanks, I think I'm going to build it with the mod so I will order the 18k resistor. All the caps are non polarized film except the 3 electrolytic polarized right? I was confused because the BOM has C3 and C6 as "non- polarized". Aren't C1-C6 just film caps and C7-C9 polarized electrolytic?

Also does anyone know the differences in ic2 choices or are they just for power and don't affect the audio?

Last question, did anyone just use the Timmy ic (JRC4559)? Curious why a different ic was used?


Sent from my iPhone using Tapatalk

Yes C3 & C6 are film box caps.  The are noted as non polarized because caps up around 1mf and higher are typically electrolytic but these are box caps.

I used the jrc4559 but I haven't gotten around to trying anything else.
Was there anything on fsb about the different ics ?

Koko

Okay that makes sense, thank you. I haven't looked at FSB but will check it out!


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[angrykoko]

Oh and ic2 is the charge pump to get the circuit running at 18v

I used the icl7660Scpa, I think it was less expensive at mouser for it was why.

[paulc]

Not if you use the A10k volume pot like the bill of materials states.

You do only if you want to use an A25k pot like the mod states.

Thread necro...  sorry about that, but I've not really dug around this board much in the past.  The 25ka/18k resistor volume change is not about making a 25k pot  a 10k value.  The resistor is wired from input to wiper, and not in parallel with the whole pot.  This was just to come up with a tweaked taper that would put the voltage divider at -12dB at 50% rotation for unity gain at that setting.  Both the 25ka and 10ka pots put unity at about 2 o'clock with all the boosting bunched up from 2 to 5 o'clock.  Linear taper pots had it around 9 o'clock which was a horribly jumpy taper.  This is based around a +12dB zero gain setting, so once the gain is turned up it gets thrown out the window and really doesn't matter.