Help to tune a Gristleizer!

[gigimarga]

hello,

i just finished to build a gristleizer (http://gaussmarkov.net/wordpress/circuits/gristleizer)...but when i'd tried to fine tune it i found some problems:

1. using the offset pot i couldn't set at 0V the output tension of IC3 (as i read in http://rubidium.dyndns.org/cag/pdf/gep.pdf)
2. if i biased it with the DP4T in some position (some wave form), in other position it will sound strange (misbiased)...especially on the triangle wave form when i have a volume drop too
3. big question: the gristleizer must to sound distorsed or not (mine sounds both - depending on the bias trimpot position)
4. how can i slow it at half (i think)?...i don't like the settings that seems to be a ring modulator...i want to sound more like a tremolo

thanks a lot!

[stobiepole]

I found that using a MAX1044 circuit to provide the +9 and -9 volt supply from a single battery also made biasing much easier. Did you use an oscilloscope to tune VR2 for a triangle wave? If not, I wouldn't worry about getting VR3 to 0V exactly - best to play with it by ear (and it might take some back-and-forth fiddling).

I pulled the trimpots that made the most interesting changes to the outside of the box. then it's just a matter of finding sounds you like...

Chris

[gigimarga]

ok...thx for your answers...but two questions still remains:

1. the gristleizer must to sound distorsed or not (mine sounds both - depending on the bias trimpot position)
2. how can i slow it at half (i think)?...i don't like the settings that seems to be a ring modulator...i want to sound more like a tremolo...what can i do for this: modify the speed pot value (double or shrink?) or modify the value of C1 (double or shrink?)

thx a lot!

[Paul Perry (Frostwave)]

Make C1 bigger to get the oscillator slower.
And I would have thought, that it was perfectly natural for the output to be very distorted at some settings of the bias trimpot. part of the fun!
And I expect ther eis some interaction between the 'shape' and 'offset' controls, that might be the cause of the volume difference.
It's a pretty rough circuit, after all (but, not knocking it!!)

[gigimarga]

i didn't find 2N3819 and i replaced it with a BF245B...it's ok or it's better to use a BF244 instead?

[Paul Perry (Frostwave)]

The thing with fets is, even if they are the SAME part number, the cutoff voltages vary a lot from one to another.
So it might be worth trying a few different ones.