cool reverb apart from switch spdt 'pop' issue

[samhay]

Sorry - not sure which op-amp pin 2 belongs to.
I'm trying to determine whether the new op-amp is affecting the feedback-less reverb, so what happens if you remove the connection between the 10k/10k pot junction from the brick and the 100n (if there) or feedback resistor?
If that doesn't change the way the reverb sounds without feedback, then we should be able to tame the frequency response and gain of the feedback op-amp to hit the sweet-spot where the feedback just causes osciallation.

[slacker]

Have we ever tried just sending the feedback back into the input of the brick? Stick a resistor from pin 8 of the opamp to pin 3 of the brick so the opamp isn't connected directly to it then feedback from output of brick through caps and pot into input.

[samhay]

^Have we ever tried just sending the feedback back into the input of the brick?

Nice idea. The 10k input impedance of the brick may load down the reverb pot if we don't split the outputs, but otherwise it should work - it work's in my design anway. ..

[deadastronaut]

ok, i'll try that..in for a penny etc..

so resistor between pin 8 - brick 3..  (value?) ..

then out from the 2x 10k's ...100nf...220k...100kpot...100nf...then goes too ?..

[slacker]

(value?) ..

Dunno, try 10k for starters maybe. May need to diddle with it to find a suitable value, might also need to increase the gain from the opamp to keep input signal at a good level.

then out from the 2x 10k's ...100nf...220k...100kpot...100nf...then goes too ?..

I'd take it straight from one of the outputs of the brick, probably ditch the 220k for starters or make it something much smaller, we've got no boost in the feedback loop now, out from 100n from the wiper of the pot goes to pin3 of brick.

[deadastronaut]

out of curiosity whats the difference with 5/6 outs?.

[deadastronaut]

righto, i tried that, with varying values ,  however its cutting the reverb fullness + overall decay length again...arghhh...

[samhay]

I think we are forgetting to account for the mojo.

I'm a bit lost as to where you are now - what have you got on the breadboard at the moment?

[deadastronaut]

i went back to this version to get it working normally again,  and it had the best feedback with good controllable oscillation.

but still open to ideas..

[samhay]

OK - interesting to hear that shorting the op-amp gain worked the best.
If you want to try to get more feedback in tails, you could try and short R13 at the same time as you short the op-amp feedback loop. This is fairly large kludge, but might just work ok - in this case, you just need to put a second FET switch parallel to R13 to give it a try. If the feedback is then too loud, a series resistor to the FET might help.

[therealfindo]

cool, wasn't the oscillation done by changing 33k to a 22k?..IIRC.

68k ?

^ thats what i did

I used 68k as per the PDF.. could that be why the Osc switch seems to have no effect for me? Should I change the resistor to 22k?

[deadastronaut]

^ yes. 22k.


@sam hold on, that schemo isn't quite what i have i think...

[therealfindo]

hmm.. I've swapped it, but still not noticing the Osc switch making any difference, and especially not like in Chromesphere's video...

[deadastronaut]

^ drop it to 10k then..should oscilate like a bugger..   (btw there is no 68k in my layout.)

which layout/pcb?..

[deadastronaut]

right i went back to the drawing board with this just so i knw where i am and works fine, , i kept the  wet/dry/ and kept the fet switch.

(the fet switch when off is letting a little reverb through though..)  when on everything is fine and lush reverb again..with great feedback/decay

now lets try and nail this tails bugger...



(@realalfino: th 22k ocillates like hell. just confirmed it ok.)


edit:  when i switch  the tails (led off) it decays pretty well...but still have a lot of reverb. just not as much as when led on. 

[therealfindo]

^ drop it to 10k then..should oscilate like a bugger..   (btw there is no 68k in my layout.)

which layout/pcb?..

This one: http://www.diystompboxes.com/smfforum/index.php?topic=101126.msg917324#msg917324

[samhay]

Does a 1M resistor from the FET side of C5 to Vref help kill the reverb in tails mode?

[deadastronaut]

hi sam, been busy...

tried that 1M, still has verb though..

[samhay]

I know there was issues with the tails not working as intended,  but did slacker's groundin between 2 x 4.7k resistors idea work any better than the FET switch in terms of killing the dry signal?.

[deadastronaut]

morning..


http://www.diystompboxes.com/smfforum/index.php?topic=101126.msg938234#msg938234

same as this you mean, ..and just take the join of the 2 x 4.7ks to ground.?