need help... stupid voltage divider question

[pinkjimiphoton]

this one hasn't come up.... for me... before, really.
of course i am a monkey with a breadboard and no real knowledge
but a decent ear for distortions

so i'm building one of these things again. i love messing with this circuit...




added pots fpr mixing the levels of the two fuzzes, gain, biasing etc and some cap and diode swaps... two in34's in series in the rectifier is a real nice sound...

but i don't wanna have to run it on a charge pump, and certainly not two 9 volt batteries.

i've had issues with charge pumps every time. always a bit of a whine.,.. can't "hear" it but can tell its there. also don't wanna deal with a daughterboard and all that crap.

i mean, looking at this, it SHOULD be able to run off a dang 9 volt battery, right?

well, it does..... and fairly well, tho when it runs out of voltage it does some  crazy amusing octave jumps and bizzarre arpeggiations, particularly if ya turn the tone control on your guitar off, which triggers a really fun instability thats ridiculously synthetic sounding...

took a couple minutes of head scratching to realize i could run it off a simple 9v with a simple voltage divider and be done with it.

so i made one with two 10k resistors,  which worked admirably. got the negative voltage running at half voltage where the two resistors meet, ground and hot.

but i was wondering cuz i really know nothing of the science involved or the math, if i want it to run better, should i go with a higher resistance in the divider?

i mean, at 10k/10k it runs ok, but hard to bias in to the real sweet spots..

so if i make the divider with larger value resistors, will that increase the available current to run the thing on? or will the increase in current lead to a decrease in voltage?

i really don't know how that works... my gut is trying me to try two 100k or even 1 meg resistors, but i figured i'd ask in hopes someone could educate my dumb @#$%ian ass on how best to use these and when in some way a 3 year old could understand so MAYbe i have a chance?

or am i completely off base and clueless like i think i am?

appreciate the advice!!! thanks!

from the last debacle with this thing:

https://www.diystompboxes.com/smfforum/index.php?topic=117278.0

make it a a2k pot for the octave. works better

[ElectricDruid]

Ok, so you're converting a bipolar power supply circuit to use a single supply like the majority of pedals use.

10K/10K should be ok for the midpoint "virtual ground", but you should add a decent cap from that midpoint to -V. Try 47uF or so.

Given that we're moving to a single supply, I might be inclined to separate the Fuzz 39K/820R and Struzz 1K/1K dividers from the op-amps with a capacitor and then take the bottom end to -V (power supply ground) rather than the midpoint virtual ground. That said, it should work going to the virtual ground, but I'd prefer not to have so much stuff connected to it in a single supply circuit.

For the 39K/820R, 100n is ok and gives you a rolloff below 40Hz. For the 1K/1K, the cap has to be much bigger (~2.2uF) or the resistors need to be larger. Why not use a 10K/10K instead? Then you could use a 220n with no problems.

The input is separated from the circuit's bias by that 1uF cap, but the output has no such separation, so a (at least one) cap is required somewhere. You could do that after the Fuzz/Struzz dividers, or you could do two caps before (as I suggested), but you need one or the other or you've got a hideous thump of 4.5V hitting your output.

HTH,
Tom

[pinkjimiphoton]

Ok, so you're converting a bipolar power supply circuit to use a single supply like the majority of pedals use.

10K/10K should be ok for the midpoint "virtual ground", but you should add a decent cap from that midpoint to -V. Try 47uF or so.

i will try that bro. at this point, there's ZERO power supply filtering, just a 9v snap tacked on the board. so should i add a cap to the positive side as well?

Given that we're moving to a single supply, I might be inclined to separate the Fuzz 39K/820R and Struzz 1K/1K dividers from the op-amps with a capacitor and then take the bottom end to -V (power supply ground) rather than the midpoint virtual ground. That said, it should work going to the virtual ground, but I'd prefer not to have so much stuff connected to it in a single supply circuit.

as i have it wired, they are going to the actual ground .  i have the half voltage coming off the junction of the two 10k's, and the top to+ and the bottom to - on the battery.
i had thought about tieing that to the mid point but it seemed better to leave to the "actual" ground.

For the 39K/820R, 100n is ok and gives you a rolloff below 40Hz. For the 1K/1K, the cap has to be much bigger (~2.2uF) or the resistors need to be larger. Why not use a 10K/10K instead? Then you could use a 220n with no problems.

its already built lol, thats why!! i DID add a cap... but just one.. get to it in a minute

The input is separated from the circuit's bias by that 1uF cap, but the output has no such separation, so a (at least one) cap is required somewhere. You could do that after the Fuzz/Struzz dividers, or you could do two caps before (as I suggested), but you need one or the other or you've got a hideous thump of 4.5V hitting your output.

yeah, i put a 100n cap in series with the output of the two different sections, literally inline between s3 and s2. kill two birds with one cap that way. <and the preexisting holes worked out well>

when all was said and done, hacked in a b50k for the fuzz, and a a2k for the struzz level pots, and a b100k as a normal output volume after the 100n output cap.
also tried a c1m for the gain, but its a waste the way its wired, so gonna just go a1m instead.

also hacked in a 1m trimmer in place of the 680k bias resistor on q1, changed the snubber down to 100p from 560,  and a 10k bias pot for q1 to be able to tweak it in.
input cap i bumped up to 2.2u, and made the series resistor into the first chip 10k instead of 8.2k.

quite a bit of molestation here sounds pretty good

HTH,
Tom

helps a lot. thank you!! but still, my question.... would i be better off, do you think, with higher value resistors for the power supply voltage divider? would it be a little more stable?

or should i just go break out the bb and mess with it more?
[/quote]

[Fancy Lime]

Hi Jimi,

the voltage divider for the virtual ground needs to be capable of keeping the virtual ground voltage the same despite opamp "a" pulling charge from it. The smaller the resistors are, the easier it can do this but the more it will drain the battery. How much the opamp pulls out depends on the opamap but you'll probably be able to use 100k/100k without any difference and can save some battery life.

What this thing is in essence is a half wave rectifier in "fuzz" mode and a full wave rectifier in "struzz" mode. I have messed with those a bit and found (after a suggestion by Mark Hammer who, as usual, had done the same thing long before) that the full wave rectifier sound sounds much better when followed by clipping diodes to ground. Just a suggestion that may be worth exploring.

Andy

[PRR]

[pinkjimiphoton]

Hi Jimi,

the voltage divider for the virtual ground needs to be capable of keeping the virtual ground voltage the same despite opamp "a" pulling charge from it. The smaller the resistors are, the easier it can do this but the more it will drain the battery. How much the opamp pulls out depends on the opamap but you'll probably be able to use 100k/100k without any difference and can save some battery life.

What this thing is in essence is a half wave rectifier in "fuzz" mode and a full wave rectifier in "struzz" mode. I have messed with those a bit and found (after a suggestion by Mark Hammer who, as usual, had done the same thing long before) that the full wave rectifier sound sounds much better when followed by clipping diodes to ground. Just a suggestion that may be worth exploring.

Andy

hi andy,
thanks man, i actually grok'd that! i was wondering if bigger resistors would work better.
i settled on the 10k ones i had put in last nite.

paul, thanks man! i will file that away with my stuff!! i seem to revisit this cct from time to time.

anyways, this is what i ended up with.

i found adding a 2.2n cap from pin 2 of u1 to ground really makes the octave jump out in a spitty chewy way that is positively delightful, and tracks most of the neck. so i added that to the switch to choose fuzz or struzz.

i didn't try the diodes to ground trick this time, i don't think it really needs them.

i used an old metal can lm301 for u2, and for u1 used a ca3140ez which i had kicking around and never tried <i often buy a couple weird chips when shopping to try out for shits n giggles>... that combo can be fairly devastating. the 301 really smooths it all out, and the 3140 is very sensitive to guitar knob twiddles.

i changed a couple of the resistors around q1 to trimmers to mess with... found i could improve the fuzz a little that way with a bias trimmer, and changing the 680k feedback resistor to 1m gave enough leeway to play with a few different chips.

gave a little more output at the expense of a little gain in the feedback loop of u1, and went with a 50k fuzz volume pot. instead of going with the 2k octave volume pot i had initially tried, i settled on 100k... lets me get the octave as loud as the fuzz now. finally, added a proper output cap... apparently the output of the chip has a cap or caps built in? i dunno..., 100n seemed right. and i gave it a master volume, 100k.

gave the fuzz a little more gain with a smaller e to ground resistor, and decreased the snubber from 560p to 100p.  that helped.

now, you can actually turn down your guitar and it cleans up nicely, even in octave mode.

gave it a more normal power supply. first time i ever did this like this, believe it or not
in this case, basically a voltage divider made up of 2 10k resistors and a 33uF cap. i was surprised when it worked i really hated the dual battery/18v/chargepump thing. this sounds better at 9v imho!

anyways, this is where i ended up at. it seems to sound pretty good, the octave part works well and the fuzz is much improved. levels can now be mixed properly, and i don't wonder if random dc is gonna blast thru and cook something.

hint: if ya want absolute madness, omit all the power supply filtering and turn your tone knob off. suddenly it thinks its an autowahfuzzoctavearpegiator noisemaker that reminds me a lot of the ugly face.

pic:




i think that freekin chip is possibly the best sounding chip i ever tried in a distortion.

https://www.renesas.com/us/en/www/doc/datasheet/ca3140-a.pdf

you can drive it to .5 v below the negative rail, super high input impedance, mosfetty goodness, low power consumption and a lot of other cool stuff way above my paygrade. check it out! i just looked it up, now, of course. probably had it for years.