jfet shunt trem cap value help

[duck_arse]

(click, click for full size.)

here see what's on my breadboard at the moment, tremming up a very, very clean storm. it is based on a dissection of the Tremface by RG at geofex. the addition of the linearising resistors R10 and R11 maintain a very clean envelope, shaped as tuned by the bias trim. however, with no signal they also add an lfo whumpa-thumpa in the output at unacceptable level. so the C6 cap is added, and pretty well fixes the problem.

the questions: how is the value of C6 calculated, against what other parts values? 10nF works, 680nF works, but I dunno what it needs. 150nF? 330nF??



and - with R7, R8, R9, is the output level going to load-down further than I want at the first sign of a less than optimal following load? should I just add an emitter follower, and call it 'buffered'? is there any obvious parts [R17] could be dumped from the design?

thanks for looking.

[PRR]

> how is the value of C6 calculated

I would think "against 1Meg", and 0.01uFd may be ample, even less since it is a distortion balance and deep bass distortion may not matter. OTOH how many pennies would you save with 0.002uFd?

[antonis]

<off topic on>

Does Rate LED work OK, in the mean of Q3 set fully saturated..??

<of topic off>

[duck_arse]

> how is the value of C6 calculated

I would think "against 1Meg", and 0.01uFd may be ample, even less since it is a distortion balance and deep bass distortion may not matter. OTOH how many pennies would you save with 0.002uFd?

ah-Hah! but - against audio or against lfo? I'm using that rig for the nice envelope shaping it gives.


[off]

rate led winks well enough on breadboard, if not full flash flash. I was quite pleased with myself, working that part out.

[off/off]

[antonis]

against audio or against lfo?

Isn't LFO audible..?? 

[duck_arse]

thumpy audible without the cap, yes. [I realise not audible, but the output shows thump on the cro.]

[duck_arse]

for antonis - looks like still some room.

[ edit :] I added some decay-to-faster envelope today.

[antonis]

Very narrow room margins, I'd say..