PEAVEY Bass preamp Distortion(Fuzz) Section - Help extracting e making a pedal

[nego_veio]

Hi,
This is my first contribution to the forum.
I Have the schematics of a Peavey f 800 b bass preamp that have a one-knob-distortion in it. I know this amp for a long time, its "distortion" have a full and rich bass response and a beautiful and extreme fuzz in it. I searched for this schematics for a long time, now i found it and i want to extract the fuzz section off it, eliminating the rest of the components to make this simple and powerfull bass distortion, like in the preamp.
I have plenty experience in making pedals, i have made from overdrives to phase shifters, so making the pedal would not be a problem.
But i have some difficulty in extracting the distortion secton from the preamp schematics, i'm not good at that and i don't have that experience. And i'm here asking for some help.
In case someone is interested, i'm here sharing the schematics with you.
Please, i would aprecciate this help so much.
Thank you.
PS: Sorry about my bad english, it's not my native language.

[Boogdish]

I'm still pretty new at this stuff, but I would try to get it inbetween the pair of .01 coupling caps separating the section from the input and from the first EQ section:


This is not taking into account power supply, since the schem you posted was 24v.

[nego_veio]

what about the power supply?
what i would have to change to use a 9v power supply?

[nego_veio]

anyone?

[Mick Bailey]

Can you post the link to the full schematic?

[superferrite]

I am going to be of no help, but I encourage you to proceed!  My friend has of of these Seventies Peaveys and they have a really nice distortion for bass--one that NEEDS to be put in a stompbox.

[dxm1]

How about this for a start?



If you have the power amp schematic, see what voltage mystery point 'P' connects to.

[nelson]

Nice redraw, I would say there is no added benefit of keeping the distortion switching section - Q5 on the schematic above. I would remove that transistor and connect the 2K7 resistor from the clipping diodes straight to the wiper of the dist control. I would also change the "volume" control which is actually a blend control to something more akin to the blue box blend control, Up the value of the pot and place say,  4k7 resistors either side of the pot. I would keep the treble bass and middle controls (I imagine they are important to the fuzz 'performance in the amp, and add a volume control at the end. I would also change it to 9v.

[nego_veio]

sorry, i don't have the power amp schematic.
Mick, I already posted the full pre-amp schematic.
dxm, thanks for that. sorry, but what is "IJR"?

[nego_veio]

how about this for the power supply?
http://www.geofex.com/circuits/+9_to_33.htm

[Mick Bailey]

sorry, i don't have the power amp schematic.
Mick, I already posted the full pre-amp schematic.
dxm, thanks for that. sorry, but what is "IJR"?

Can't see the link on this thread - am I missing something? Browser is Firefox

[nego_veio]

sorry, i don't have the power amp schematic.
Mick, I already posted the full pre-amp schematic.
dxm, thanks for that. sorry, but what is "IJR"?

Can't see the link on this thread - am I missing something? Browser is Firefox

Mick:
http://img413.imageshack.us/my.php?image=f800bvx4.gif

[Mick Bailey]

There is a fair bit of tone shaping in the circuit after the distortion section which will contribute to the overall sound. This is before the equalizer stage. My feeling is that the distortion section on its own may be disappointing.

[nego_veio]

There is a fair bit of tone shaping in the circuit after the distortion section which will contribute to the overall sound. This is before the equalizer stage. My feeling is that the distortion section on its own may be disappointing.

i agree. do you think that i can go just before that 4.7k resistor, or i will have to include that 3 transistors in the end too?
and what about that P point? i just have to connect the two P points and thats it?
that you all for your help. i'm going to try this schematic next week and i hope to post nice results here.

[dxm1]

Ok, here is another stab at it. Everything up to the EQ section. Still using a charge pump to get 18V. This thing is approaching the complexity and component density of a Dr. Boogey.  I'm not sure a Peavey simulator is worth it...

http://i176.photobucket.com/albums/w196/pbody_pics/misc/PeaveyBassFuzzMod.jpg

IJR means 'Input Jack Ring', a wire connected there switches the 3906 and hence the 9V power.

[Mick Bailey]

You certainly need to include the transistors before the tone stack. Referring to dxm1's schematic, you may get away with taking the output straight off C21 for stompbox use.

[nego_veio]

where exactly is the sound distorting in this?

[Mick Bailey]

Most of the distortion will come from the clipping created by the pair of back-to-back diodes.

[JB872]

Old thread but I'd also like to see the Festival 800b distortion circuit in the form of a pedal. I know there was some question about the schematic for the power amp section.....I think this might be what your after?

http://www.gjelberg.no/files/peavey_super_festival_800module_schematic.pdf

[Gus]

Like Mick Bailey posted
Looks like diode to ground clipping softened up a little with resistance in series with the diodes and the EQ section after this will change the sound

Two transistor voltage gain into an emitter follower direct coupled.
Note the feedback from the EF to first emitter the gain control is in parallel with the first emitter resistor and cap to ground.
The foot switch turns on the transistor connection the wiper to ground to change the gain to where the wiper is set.
The volume shorts the output to ground at min setting.

I would guess an noninverting opamp gain stage powered by 24VDC into a cap then clipping diodes with a series 2.7k+470ohm to ground then a cap to a volume control might sound close for the distortion section