FF with extra diodes 4 compression. How to make it work??

[brett]

Hi. 
I was thinking of making a fuzzface compress and sustain more.
First I added a diode between the input and the base of Q1, as in Joe Davisson's Antiquity fuzz.
[url][http://www.diystompboxes.com/analogalchemy/pedals/antiquity.html/url]
Then, for extra compression, I decided to put a diode between the collector of Q1 and both the 33k resistor (5.6k in JD's Antiquity) and base of Q2 (ie for diode compression).  The idea was that the first diode compressed positive excursions of the signal.  The diode on the collector of Q1 should have compressed the negative excursions of the signal.  The diode was a 1N4148 and the orientation was band to the collector of Q1 (so it was forward biased).

Q1 hFE was about 100 and Q2 hFE was about 130.

The sound I got was a modest, buzzy fuzz.  It did have some synth-like overtones (octave up??).  But I wasn't after that.  The gain was really low, so I'll go back and try MPSA18 or 2N5089 transistors.

Any helpful ideas?
Thanks

[bluesdevil]

Try using mpsa13's for both spots with 4 germanium clipping diodes (2 pairs in opposite directions) at the end of circuit, like here:
http://aronnelson.com/gallery/album03/buzz_tone
Not sure how it will react in an exact  fuzzface circuit, but in this particular circuit it sounds great... maybe worth a try?

[MartyMart]

May be worth repeating but using Ge diodes ( lower forward current ... )
And perhaps higher hfe trannies would help,  5089/MPSA13/18 ?
I do like using diode pairs to ground at the end of a FF, but there is a
serious tone/distortion change then ... a "softness" control is nice ( see FAQ )
and can reduce the effect of the diode crunch sound.

MM.

[Joe]

FWIW, the diode trick doesn't work in a PNP circuit, if you're trying to do that.

[brett]

Hi.
It's an NPN circuit (BD139s).
NB The diodes are not for clipping, they are forward-biased in the opposite direction to signal "flow", and provide compression.
The Ge diode idea seems good.  It should throw the bias out less.  (previously I was down to 4k on the collector of Q2 to get 4.5V).
I'll also try MPSA18s or even MPSA13s.
thanks