critique my circuit?

[antonis]

are there any resources where i can learn how to calculate the input and output impedances of a stage?

Beware of what you wish for..!! 



P.S.
Op-amps, MosFets & JFETs will follow with much more simplicity..

[duck_arse]

what should i be looking out for?

garbage ai posts from garbage ai posters and spammers, not to put too fine a point on it.

[thunderaxe]

what should i be looking out for?

garbage ai posts from garbage ai posters and spammers, not to put too fine a point on it.

is that what that was? i see that the account only has a single post, but what purpose would that serve for an AI bot?

[antonis]

what purpose would that serve for an AI bot?

Showboating via generaly accepted rules of no particular impementation..

e.g. EQ doesn't interfere with distortion stage, not even for pots extreme settings..

[duck_arse]

ai only knows to take a post like your own, regurgitate it "in its own words", and add something useless or obvious. then the poster sneaks back in and adds a spam link or hides a spam sig, like that.

[thunderaxe]

!!!..DON'T PUT GARBAGE TO Vref..!!!

i'm designing the PCB right now, and i made sure to route it so that lugs 1 of VOLUME & CLEAN (which use VREF as signal ground) are on a separate track than any of the VREF-as-bias-voltage connections, and that they hit the filter cap before anything else. the VREF-as-bias-voltage connections hit the voltage divider resistors first.

so it basically goes:

(VOLUME & CLEAN)<--->filter cap<--->voltage divider resistors<--->bias voltage connections

do you think this is helpful, will it make any difference at all?
furthermore, if it is helpful, do you think i could do what i was suggesting above, and skip C6, tying that signal ground to the signal ground side of VREF instead?

[antonis]

do you think this is helpful, will it make any difference at all?

No..

[thunderaxe]

well okay. it sounded good on the breadboard with VREF just as one big pool and i'm doing a vero prototype right now which is also like that so we'll see how it sounds

[antonis]

Just place Vref cap negative plate as close as physicaly possible to PS ground..

I've posted AN-581 in my post #5

[thunderaxe]

okay, so before i get my PCBs printed i wanted to build a prototype to test the circuit in an actual stompbox, so i made a hack job of the original circuit on its PCB and the tone section, clean buffer, and output stage on vero. it's ugly, but it works. except for one thing -- with the VOLUME and CLEAN pots turned to zero, where there should be silence, instead there is a fizzy, extremely high-passed ghost of the distorted signal still in there. turning CLEAN all the way up, which should sound identical to the bypassed sound, instead sounds like the bypassed signal with a superimposed fizzy version of the signal.

at first i thought this might be because using VREF as the signal ground was polluting VREF, but it doesn't matter where i ground lugs 1 of VOLUME & CLEAN to, including giving them their own dedicated cap directly to power supply ground, that fizzy ghost signal is still in there. lifting them from ground entirely makes the signal jump to full volume, which is to be suspected. with no audio signal running through the pedal, lifting the grounds brings in a lot of white noise.

at one point i suspected that maybe all of the wires criss-crossing my circuit as a result of my hack job meant that some of them had become microphonic, but lifting them up and away from the circuit board and placing a piece of steel between them and the circuit board made no difference whatsoever. i would have expected at least a little fading in and out or some kind of audible change as i moved the wires if it was because of that.

removing the wire from lug 2 of VOLUME to the output stage (how the distorted signal enters the summing amp), however, made the fizzy ghost signal almost entirely go away. it's still in there in the tiniest amount if i really listen for it but about a hundred times quieter. good enough for me. obviously that isn't a fix though, just an attempt to isolate the problem.

any ideas on what might be happening here?

[antonis]

Could you plz try to diconnect both CLEAN & VOLUME lug 3  from GND (or Vref) ..??
(pots setting shouldn't matter a lot but try for about equal setting..)

[thunderaxe]

EDIT: my original post wasn't entirely accurate. it's corrected here:

when lug 2 of VOLUME (distorted signal) is still connected:
-with no audio signal running through the pedal, when lugs 3 of both pots are grounded, it is silent.  lifting them away from any kind of ground brings in a lot of white noise.
-with an audio signal running through the pedal, when lugs 3 of both pots are grounded, there is a fizzy, very high-passed signal remaining even when both pots are turned to 0. lifting lugs 3 from any kind of ground makes the signal jump to full volume. at that point i can't tell if the fizzy signal is still in there because everything else is so much louder. in fact,
-with lugs 3 grounded, when turning up the VOLUME (distorted signal) even a little bit, i can't tell if the fizzy ghost signal goes away or just gets incorporated into the distorted sound in a way that i can't tell if it's there or not.

when lug 2 of VOLUME is disconnected, 99% of the fizzy signal is gone, regardless of whether lugs 3 are connected to any kind of ground or not, and there is no white noise. with CLEAN turned to 10, there is no difference in the sound between grounded or not.

[thunderaxe]

okay, so some strange results using my audio probe, but they're making me suspect the problem actually is microphonic wires:

with lug 2 of VOLUME disconnected from the next stage, lugs 1 of VOLUME & CLEAN grounded to power supply across their own 100uF cap, and VOLUME set to zero: there is no signal coming from lug 2 of VOLUME, as it should be, because it's shorted to ground across the pot set to zero. but even the wire going to R19 in the next stage has the ghost signal in it, just significantly quieter than it was at the output of the pedal with the wire connected to lug 2. moving this wire around changes the volume and quality (amount of treble etc) of the signal, which is what makes me suspect it is the wire being microphonic. taking the audio from the pedal output, it is the same volume and exhibits the same behaviour, which makes sense because it's just being buffered/unity-gain amplified by the output summing stage. connecting the wire back to lug 2 makes the signal disappear from the wire (but not the output), which also makes sense because now the wire is grounded across the pot.

taking the audio from the pedal output, as mentioned above, with the wire disconnected from lug 2 there's a very faint ghost signal in there, but reconnecting the wire to lug 2 makes the ghost signal much louder, very audible (but still much quieter than the full distorted signal at full volume which is why i'm still calling it a ghost signal), the way it was when i first started posting about this problem. this confuses me -- why would reattaching the wire, which grounds it and makes the signal disappear from the wire, make it much louder at the output? does grounding one end of the microphonic wire(s) allow them to function better as a microphone?