cool reverb apart from switch spdt 'pop' issue

[deadastronaut]

no idea..

its strange how it cuts the tails quickly...but smoothly fades off...as if a volume pot is being turned down.

its the turny down bit thats bugging..


meanwhile a little vid demo, i couldn't resist it,..

[samhay]

If you increase the value of the resistor to the FET's gate, does it behave any differently?

[deadastronaut]

nope.

tried from 100r-4.7M

[slacker]

and a max of < 1/2 for the wet ( 100k/220k + whatever voltage divider effect we have between the feedback and reverb pots).

I think you're looking at it wrong, R19 and C5 are connected to vref as far as signals going in the + input are concerned so the the gain for the feedback signal is 3 1+(R6/R19), assuming the R19/C5 combo lets though all frequencies of any interest. This is ignoring the divider effects of the feedback pot etc.
When you close the switch, for the feedback signal, the gain from the opamp drops to one, so the overall gain is 1/3 of whatever it was with the switch open.

My previous idea suffered the same problem to a lesser extent, the gain of the feedback signal went down in bypass.

This setup but with something like my original resistor switching idea should work better because then the gain will go up in bypass. 

[samhay]

slacker - you're quite right.


Edit - I think the easiest solution might be to do something a little different. Of course, I may be wrong yet again.

If we go back to the original plan of shunting the dry signal to ground, we can run the feedback into the (-) input of the op-amp via an inverting op-amp stage so that, hopefully, we don't have the phase issues we had earlier. We can appropriate the Vref buffer op-amp.

[deadastronaut]

i'm lost...again .

[deadastronaut]

This setup but with something like my original resistor switching idea should work better because then the gain will go up in bypass.  

which setup?...where am i?...arghhhhh....

this?.
http://www.diystompboxes.com/smfforum/index.php?topic=101126.msg939858#msg939858

[slacker]

On my phone so can't post a link. The feedback thing I posted in post number 363 but replace the fet switch with the resistor version I sent you at the start of this crazy adventure. Hope that makes sense.

[samhay]

Sorry to leave you hanging - have a couple of spare minutes now.

This is what I had in mind:

(if you don't want to use the FET swtich, then slacker's 2 x 4k7 resistor divider to ground should work too).

[samhay]

Oh - and nice demo Rob.

[deadastronaut]

cheers guys...

arghhh another opamp..

gonna need a bigger boat.. breadboard.. i'll squeeze the bugger on and give it a go....

[samhay]

nope - look again. I used the op-amp you were using to buffer Vref, which I don't think is mission-critical.

[deadastronaut]

ahhh gotcha..

[deadastronaut]

well....tried it. with strange results.

the overall reverb is not as full as before...

the feedback pot becomes a kind of  'delay time' pot,  when turned fully anti, it goes into a tight slapback delay, and borders on oscillation too....but defo not reverb.

the other end of the pot is reverb, but like i say its not as full reverb as before.....

[samhay]

It might be loading the brick down a pinch, so you could try increasing the 220k feedback resistor. You could try 1M feedback resistor and 1M feedback pot, which will also give you unity gain out of the new op-amp.
Not sure why it would be causing a slap-back effect unless there is really weird phase issues. Did you use the optional caps?

[deadastronaut]

just tried that,  the oscillation is really bad, its like a boomy bass distortion, nothing like normal reverb decay...totally unusable.

and has cut the fullness of the reverb..

tried optional caps/in out too..


heres a clip...of the range to show you what i mean..   1M POT fully right ....then 12 o'clock...then fully right.....nasty.
https://dl.dropboxusercontent.com/u/7464107/nastyverb.mp3

[samhay]

Yup - dark and then overdriving the brick.
You probably want a feedback resistor at least 2x the value of the feedback pot to prevent the clipping, so I'm not suprised about the clipping. The 470n cap should be cutting some of the bass from the feedback, but you may need to drop this value quite a bit.

However, with the feedback gain at 0 (ccw I guess) does it sound different than having no feedback loop at all?

[deadastronaut]

However, with the feedback gain at 0 (ccw I guess) does it sound different than having no feedback loop at all?

yeah its not the full lush  reverb/decay as we had before...its like its cut it in half (limited)

[samhay]

With the feedback ccw, there should be no feedback, as there should be no output from the new op-amp. Does this sound the same if you then disconect the feedback (e.g. pull a jumper to the new op-amp)?

[deadastronaut]

with feedback ccw i get a little reverb..

if i pull jumper from fb pot 3  to pin 1 it oscillates madly (in that dirty way)

if i pull jumper from fb pot 1+2  to pin 2 i get a quiet fuzz..