Ic big muff Keeley psi vs original op amp thoughts

[aaron323]

I am looking to use the 510k/47k and 50k pot values from a Keeley psi in the op amp big muff instead of the 560k/62k and 10kohm potentiometer just before the sustain control.

Any thoughts about this or should I stick with original big muff values?

[Keppy]

The Keeley values should get you probably-imperceptibly more max gain, and maybe-noticeably less min gain, with no impact on frequency response in the audio band. Even side-by-side, the differences are probably inaudible unless you have the gain at min or max. I say use whichever values are more convenient.

[antonis]

50k Sustain pot value will alter succeeding stage gain for any pot setting other than its extremes..

e.g. for 10k pot set at 50% rotation (neglecting R8 IC1B output impedance) equivalent parallel resistance set in series with R9 (8k2) is 2k5, so total resistance in gain formula denominator is 10k7..
For 50k pot set at 50% rotation, equivalent parallel resistance set in series with R9 is 12k5, so total resistance in gain fomula denominator is 20k7..
Regardless of next stage NFB resistor value (I suspect it is the "standard" 470k), next stage gain is halved..

P.S.
I refer to NEXT stage gain and not to IC1B one, for which what said by Keppy is true and correct..

[duck_arse]

p.p.s. - welcome to the forum posting.

[antonis]

p.p.s. - welcome to the forum posting.

So you dare to call us mannerless, don't you..??

[Keppy]

Antonis is right, I didn't notice the next stage is an inverting one. Thanks for the gentle correction. That doesn't change the max gain, but to paraphrase him it changes the perceived taper of the pot, leaning towards lower gain when not maxed. It should still work just fine for you.

[aaron323]

Thanks guys for the input  .. looks like I need to do some studying in my spare time. I have also been pointed in the direction of sallen key / mfb filters but I'm not sure that does anything to the perceived gain?

[aaron323]

So long story short a 62kohm resistor is not too common here, I have 47k, 56k or 68k to choose from so it's not going to change the gain a great deal? The pot will change it more than the resistors?

[PRR]

> The pot will change it more than the resistors?

That's what it is for? (within limits)

Also:
https://www.amazon.com/Kookantage-Tolerance-Resistors-Assortment-Certificated/dp/B098BKR447
https://www.amazon.com/Guanruixin-Resistor-Compliant-Respberry-Projects/dp/B07SFKCX6W
https://www.amazon.com/BOJACK-Values-Resistor-Resistors-Assortment/dp/B08FD1XVL6
https://www.amazon.com/AUKENIEN-Resistor-Electrical-Resistors-Assortment/dp/B09CZ6XGP6
https://www.ebay.com/itm/165484057958

[Keppy]

So long story short a 62kohm resistor is not too common here, I have 47k, 56k or 68k to choose from so it's not going to change the gain a great deal?

The 56k or 68k makes about a 10% difference to the gain of that opamp stage, which is not a big deal.

[antonis]

a 62kohm resistor is not too common here, I have 47k, 56k or 68k to choose from

If you have E12 series resistor values availiable, place 2 X 120k resistors in parallel and earn peace of mind..
For an ideal result, make a parallel combination of 2 X (56k+68k) series resistors..!!

[aaron323]

The 56k or 68k makes about a 10% difference to the gain of that opamp stage, which is not a big deal.
[/quote]

If my maths is right it looks like the Keeley non inverting op amp stage has a gain of 11.8 and the ic big muff gain of 10. So using the 560k and 56k I will get a gain of 11.

[antonis]

I still don't get the point of discussion..

If you're looking for the "perfect" setting replace R7 with a 100k pot (wired as variable resistor), or a 10k pot in series with a 56k resistor and walk in peace of mind..

[ElectricDruid]

"Perfect" is a state of mind, not a gain setting, Antonis!!

[antonis]

But mind DOES set, doesn't it..??

[aaron323]

I still don't get the point of discussion..

If you're looking for the "perfect" setting replace R7 with a 100k pot (wired as variable resistor), or a 10k pot in series with a 56k resistor and walk in peace of mind..

I just hate desoldering pcbs so thought I'd try get it as close as I can to the original circuit with the parts I have available.. just being fussy, 

[iainpunk]

this thread reminds me of a post on 4chan that resonated with me:


cheers

[duck_arse]

this thread reminds me of a post on 4chan that resonated with me:


cheers

4chan - tolerance. irony?

I disclaim that I've never been to forchan, nor know anyone that has been to forchan, nor know of anything that may or may not have happened at, by, or to fourchan.

[edit :] I lie. willienillie used to tell me stories of when it was good.

[iainpunk]

you only get to see a tiny bit of 4chan in mainstream media, mostly /pol/ (politically incorrect) and /b/ (random, kind of the main page) but its filled with different boards and each has its own topic, from cars /o/ to manga /a/ and from DIY /diy/ to flash games /f/. they've done some pretty epic things, like finding locations of ISIS training camps through the stars in the background of propaganda video's, wishing a veteran happy birthday, putting a russian kid through college, getting pedo's killed and playing capture the flag against Shia LaBeuf

although the site is somewhat homogenous in culture, theres great diversity of opinion. derogatory terms are used throughout, but every demographic gets it equally.

i used to spend hours every day on 4chan, mainly /pol/ /diy/ and /r9k/. stay away from /mlp/

cheers