386 strange Volume findout

[richon]

I was playing with my breadboard testing a 386 based pedal....   it has an BAXANDALL EQ right after the 386 (pin5) and the output pot (the volume pot of the Baxandall) is 500K....


the strange thing happends when playing with the Volume pot.....

at 6 (volume position) or less the pedal sounds good but then on 7 and on 8 it seems that the sound or the EQ changes how it behaves....   

i know that with 7 or 8 it has more output than unity....  but it changes a lot how the distortion sound...  like it got a bumb in the distortion grain, better and tighter bass notes...  no so much highs and mids right one...

but with the volume on 6 it sounds ok, but not that SPECTACULAR...


how or why could I explain this behaviour?

[richon]

Could it be a matter of IMPEDANCE??

howcome would the Volumen Pot change so much the sound (without moving another pot of the pedal)

[richon]

seems like writing here give me ideas to check and solve the problem by myself 


I found that the output of the Baxandall didn't have a cap before the Volume/Level pot...  so maybe this is what it needs to make the EQ less interactive with the rotation of the Volume/Level Pot.

any thoughts?

[petemoore]

  Introducing a cap as DC blocker also introduces it as a possible filter element when in signal path.
  Otherwise caps and resistors or pots generally cause some possibly noticable reaction in the other, sometimes easier to stick a big 'ol cap than to satisfy any reading uncertainty here, + toward OA, - toward ouput which'd be nearer ground in standard NPN fuzdistorter 16v/10uf would make something much smaller value in series with it [like one of the TC caps] the dominant value of the two.
  Perhaps there's no DC path to influence bias of an active stage [causing upset], because the TC has DC blockers at all possible paths.
  Basic info for not having an actual look at 'it.

[richon]

this is what i have....

the Cx cap is "NOT" there (jumper) ..... so this is the cap i think could be missing to solve the problem...  right? (maybe a 100nF cap so it doesn't act as a filter with the volume pot (at least not eating any usefull frecs)

[richon]

as obsesive as I am....

after looking again at the schematic I found , that not using the Cx the Volume Pot interacts with the Treble Pot changing the value of it (so changing the highs of the sound)

now, would a super big Cx Cap stops this interaction between Volume Pot and Treble pot?

[petemoore]

  Looks like Cx was marked this way because it is the final HP filter, attenuating LF's if Cx value is small enough to impede noticably the frequency sent to it.
  It also blocks DC of course, and can be made large enough to be inconsequential to the bass output.
  Without it it looks like a maze of wiper setting possibilities in which the V and treble interact.
  It should be a simple matter of de-jumpering between two pot lugs, and substitutin'serting ''+10uf-'' or something between .1uf and 22uf.

[Gurner]

I'm curious why you're using a 386 (audio amp), in a config that would be more suited to a generic opamp?? (is this part of an overall schematic you're using from elsewhere?)

If you put the volume control *before* opamp/LM36 it won't interact with the bandaxall (but you'll still have level control), IMHO whatever follows on from your bandaxall will likely impact its performance.

[richon]

before the 386 are some gain stages so to keep the sound I'm looking for I can't have a LEVEL pot before the 386.

(After the Volume comes the output jack)

Maybe I'll try a 1uF or 10uF to keep the bass un-afected on the output...  and keep the interaction to cero (hopefully)

PS: the drawing was mine, this is why I did put the "Cx".

PS2: maybe i'll test further mods as beside the volume , the highs were changed very subtle but in a very pleasent way when the Volume Pot rotates.