Foxx tone machine not enough volume

[JebemMajke]

Hello

I've built a Foxx tone machine, using this schematic



With a couple of mods.

47k resistor above q1 is a trimmer, 4,7k resistor bellow q2 is a trimmer, 15 k before q3 is a trimmer, and 47k before q4 is a trimmer.

Why?

Because I wanted to bias the pedal perfectly with all the transistors out there.

My pedal now has bc550C's, for the sake of testing.

But it doesn't have enough volume ...

my voltages are 2,2 ...7 .... 7 .... 7

Do you have any advice, except adding another volume up stage?

I like the fuzz and the tone, and the octave up, but there is just not enough volume.

[Mark Hammer]

Stick a 1k trimmer between the diode pair and ground.  Adjust to get a decent balance between appropriate limiting and volume.

[JebemMajke]

Ok

How about 100k vol pot?

[bool]

Try reducing the value of Q4's 1K5 emitter resistor.

Or throw the germ diodes away and use 4148's...

[Mark Hammer]

The diodes are there for the same reason they are there in a number of other octave-up units: to limit the level so that the octave can seem to "bloom" at the same volume, rather than only emerging after the note seems to die out.  Although the diodes do contribute a bit of distortion, 90% of the distortion comes from earlier stages in the circuit.  Trust me, it will still be plenty fuzzy even without them.  I suggest the trimmer to soften the clipping, but not so much that the quick-&-dirty limiter function is lost entirely.  You can certainly try silicon diodes.  It may get you what you want.  It will certainly allow for greater output level,  How much impact on the "bloom" that has remains to be seen.

[PRR]

> With a couple of mods. 47k resistor above q1 is a trimmer, 4,7k resistor bellow q2 is a trimmer, 15 k before q3 is a trimmer, and 47k before q4 is a trimmer.

That's more than "a couple". And some of them are pointless. Q1 RC is not critical (it is locked in NFB with Q2). Q2 RC and RE must be =equal= for octave action. Q3 RB2 and Q4 RB2 are not real critical as long as the collector voltages are in the 5V-7V ballpark.

[JebemMajke]

I read quite a lot on the topic of Foxx tone and ultimate octave and how different transistors worked differently. They all had fuzz and octave up, but the harshness of the sound or the lack of it was different from unit to unit.

I wanted an option to tweak all of them separately.

And q1 and q2 are some sort of fuzz face, q4 is an LPB-1, and q3 is very similar to hornby skewes treble booster, except for the caps.

For Q1,Q3 and Q4 that is how i bias those pedals, as for Q2 i just wanted to see the difference it can make.

[JebemMajke]

The diodes are there for the same reason they are there in a number of other octave-up units: to limit the level so that the octave can seem to "bloom" at the same volume, rather than only emerging after the note seems to die out.  Although the diodes do contribute a bit of distortion, 90% of the distortion comes from earlier stages in the circuit.  Trust me, it will still be plenty fuzzy even without them.  I suggest the trimmer to soften the clipping, but not so much that the quick-&-dirty limiter function is lost entirely.  You can certainly try silicon diodes.  It may get you what you want.  It will certainly allow for greater output level,  How much impact on the "bloom" that has remains to be seen.

I did this mod, and it sounds better. As for the bloom, i don't see any difference.

I guess I ll try it with a strat and see if there is a difference.

[Mark Hammer]

The octave is, in some respects, always there.  The problem is that all that harmonic content hides it.  So the octave always seems to come out of hiding after a note has been held for a bit, after the harmonic fog blows away.  The simple limiting effect of the diode pair holds the volume semi-constant, but contributes a bit of harmonic content of its own, via its clipping action.  The added series resistance reduces the clipping action a bit.

If you play into the circuit using a neck humbucker pickup, above the 7th fret, and with the tone rolled down, you may hear the octave sooner, such that it won't seem to bloom.  The added harmonic content of the single coils may require greater time for the harmonic fog to dissipate, in which case a "bloom" may be more apparent.