Maestro FSH-1 100k trimmer function ?

[petey twofinger]

question , i did a search , but came up empty handed ,

what is the function of the 100k trimmer ?





tonepad layout

http://www.tonepad.com/getFile.asp?id=138

[mth5044]

Perhaps biases the S/H?

[Mark Hammer]

Yes.  It introduces a bias voltage that is mixed with the S&H voltage to set the centre frequency.  The mixing node is at the emitter of the transistor that feeds the control voltage input on the OTAs.  The sampled noise voltage comes in via the 22k resistor, and the bias comes in via the 100k resistor.  You can actually make that trimpot a panel-mount control.  Just note that only part of the range will be useful.

[petey twofinger]

thank you , i noticed mark mentioned a parallel cap mod , that effects the "sampling frequency , was thinking i am going to try that , once i get it properly adjusted , i can mess it all up again . kicking myself for not building this sooner , as with all the info i harvested , it was not much of a challenge getting it fired up .

huge thanks to all who shared info on this one .

[Mark Hammer]

If its the mod I'm thinking of, it was a "droop" function.  The cap to V- after the gating FET holds the sampled noise voltage, and the FET after it provides a high-impedance input that serves to keep the sampled noise voltage stored in the cap, without leaking, as long as possible.  If one places a resistance in parallel with that storage cap, the stored voltage will leak out, at a rate determined by the resistance value.  Obviously, to yield an audible effect, the resistor has to provide more leakage than the FET does, but not so much leakage that the cap never gets to hang onto anything for very long.  I'd start with something in the 470k-1M range. 

When it works right, you get a step-like change in filter frequency, but the frequency quickly descends before the next clocked change.  The sound is like a kid's vocal imitation of a quickly firing "space laser gun" ("PEE-yooo, PEE-yooo, PEE-yoooo").  The "droop" rate needs to be different for different sample rates.  If the clock is set slow, the droop rate has to be slow or else you'll go to 0V in the storage cap before you've taken in the next sampled noise voltage.  If the clock rate is fast, too slow a droop rate and you won't hear the effect.  A pot can be okay, though a 3-position toggle with no-droop, fast-droop, and slow-droop setting can be fine too.

It's a neat effect with a pleasant feel, and very simple to implement.  Recommended.

[petey twofinger]

if i was correct ( the .05 cap between fet's q5 and q6 ) tried a 2m2 there , with the speed pot at 90 percent or higher , it reduced the effect drastically

today was auditioning many transistors , and quickly trying a few mods . i am getting a minute tick , but i am thinking it may just be a fact of life with this circuit , after  8 hours worth of substituting Q's . someone mentioned a 1458 being quieter than the 4558 thats in there for ic3 (osc) , we shall see . i am in no rush , no chassis , i have plenty of time to finalize this build .

thanks Mark .


( c9 @ https://www.generalguitargadgets.com/diagrams/fsh1apl.gif?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a )

[Mark Hammer]

The chip you use for the LFO should probably be a 358 or TL022, something low current.

Yes, that .047uf cap is the one, though I think 2M2 is probably a bit too high a value.  You'll find you need to tinker with the 10k noise trimpot and the 100k tuning trimpot to nail a nice range of filter movement that shows off the droop.

[petey twofinger]

 
Mark i did get the " peow mod " to function , it sounds exactly like the soundclick sample you shared . 1590 BB , the BB is going to read " bout to burst " , if i use it .
i also found a reduction in tick using the low draw op amp ( 358 ) .

i find at times it seems to get locked into a repetitive loop and almost sounds like a phaser , not so random . i will try different noise transistors . i also lifted a trace and cooked a jfett , attempting to solder the socketed parts in place / modding and getting chatty ... oh well . i was soo close !


i feel some of the pot values should be altered to provide better function over the area of sweep.

i have a concern , am i correct in assuming this :

in s/h mode , the only pots that effect anything are resonance and the rate or speed ( besides the 10k and 100k trimmer )

( i am externally mounting the trimmers , a 500 ohm with resistors padding the for the ten , and a 50k for the 100 . )

the attack , decay and depth pots on mine do not seem to effect any change when in sample hold mode .

when in filter mode they are extremely bunched up at one end of operation .

thank you for any assistance . i may have overlooked any sort of instructions or manual from tonepad , , but i get the feeling it is just the pdf .

[chemosis]

i dont understand why the envelope filter has no frequency control?? how do you change the frequency???

[chemosis]

so the 100k trimpot will act as freq controll for the envelope filter???i dont really care about the sample and hold function unless it can be altered into lfo.

[slacker]

Without modifying the circuit you can't set the frequency for the envelope filter, in "up" mode it will be at a low frequency when you're not playing and will sweep to a higher ones depending on how hard you play and the setting of the range pot, or the other way round in "down" mode. The trimpot sets the centre frequency for the S&H side only, it doesn't do anything for the envelope follower side.
If you want to control the starting frequency for the envelope filter you could permanently connect switch lugs A0 and A2. then the trim would affect the envelope follower as well as the S&H, you might need to tweak a few things to make it a useful control.

[chemosis]

i thought in i could change the overall freq of the envelope filter side via C3 and C5??? is there any other mods for the envelope filter side besides up and down or wet/dry blend. i love the EF side just wish it had a little more control. i dont even care if it messes up the sample and hold side

[chemosis]

the subdecay prometheus sounds very similar to the fsh-1 at times. is there anyway to make the fsh-1 sound a little thicker and lower like the prometheus?? what about changing c3 and c5??