cool reverb apart from switch spdt 'pop' issue

[deadastronaut]

normal bypass is fine...when on there is full reverb /  then bypassed no reverb.

tails switch on : no reverb when feedback is turned down.....but reverb when fully on..

tails switch off: no reverb.




(make the feedback pot 100k/470k/1M?) instead of 22k.

[samhay]

You could try taking the feedback from lug 3 of the "reverb" pot instead, that will solve the problem but I don't know how it will change the sound and feel of the effect.
You could also connect pin 1 of R13 to the junction of the R17 and R18 instead of to the opamp's input, this will kill the feedback in bypass solving the problem but you might not get much in the way of tails with no feedback.

1st option. Your feedback is now only wet signal. This might sound significantly different. You still get feedback in tails bypass.
The feedback pot will now be parallel to the reverb pot, so you may have cross-talk. Making the feedback pot bigger may help with this. Or not. I would only change it if it is objectionable.

2nd option. Your feedback is still the original mix of wet and dry, but you now kill it in tails bypass. This will reduce the tails you here, and may defeat the purpose of having tails. Or not.

I guess that if the tails sound ok when feedback is off, then I would go with option 2. If not, then try 1.

[deadastronaut]

morning...yawn...stretch...yawn....sip of coffee.

sitting here making lots of new breadboard jumpers....yawn..

i may as well just breadboard this up, and go from there..as i'l end up with a butchered pcb anyway..

i'll leave off the hi/lo switch as i know thats fine..

my breadboard is true bypass anyway, so it may make it easier for trying out 'tails'  options (depending on the 3pdt switch wiring of course) without loads of wires flying everywhere too...

and i'll try that fet switch lark out ..i take it the fet drain is to the left?.

i'll get it up n running as per my schemo, then try the fet switch out. ....(and try out the wet/dry mix too)

[samhay]

^ i take it the fet drain is to the left?.
That should work.

If you go down the FET switching route, then you can add another FET switch that sorts out the feedback problem. When you have feedback off in tails mode, do you get a decent amount of tails just from the reverb brick?

[deadastronaut]

^ i take it the fet drain is to the left?.
That should work.

When you have feedback off in tails mode, do you get a decent amount of tails just from the reverb brick?

...its a fair bit less ...but still there.....


got it all on breadboard all working fine ....

now to try the fet...

[deadastronaut]

ok, tried the fet switch..(j201)

the led goes on/off...

when led is on, i get full reverb..

when led is off i get reverb but not as full as when on...

no tails in true bypass though..

[samhay]

Sounds like the FET is not fully closing. A large pull-down resistor from the source to ground might help. Otherwise, do you have any other FETs?

[deadastronaut]

with a j201 the led goes off fully.. (tried 1M-4.7M source to ground)


tried a 2n5457, led didn't go fully off..

tried a 2n5485, led fully off..

when led is on i should get tails?..or off?..

excuse my dumassness but i'm not sure what that fet switch is supposed to be doing?..

[samhay]

The FET is essentially an SPST. When the gate is pulled high, it is on. The LED is just an indicator that the gate is getting 9V. Not sure why it didn't turn off with the 2n5457.

[deadastronaut]

ok, gotcha..

i just read this from merlin, so it should work...hmmmm....maybe if i lose the 10k before the fet...and increase the 22n to 100n as in his schemo...

http://www.valvewizard.co.uk/smalltime.html

edit, tried it no joy,...

[bluebunny]

Not sure if this helps or hinders, but when I built my Small Time (exactly according to Merlin's schematic - and from which I nicked the FET switching nugget a couple of pages back), I noticed that the J112 was passing just a teeny bit of signal, even when "off".  LED was definitely off, but if you "Townshended" the guitar, then you heard a very small signal leaking through.  Not had the opportunity to investigate, though - it's since been sold to a mate...

[deadastronaut]

cheers marc,

i'm getting quite a lot of signal through when switched though...without 'townsending it'   .hmmm..

when led is on..i get full reverb..

when led is off i still get reverb, just not as full...but there...

[samhay]

FET switches can get a bit leaky with large signals - yours is not staying off.
You could try a BJT instead, but make the 1k gate/collector emmiter a bit larger (10-100k). This isn't very HiFi, and probably won't completely turn off either, but it might play better with bigger signals.

Otherwise, did you try taking the feedback to the junction of the 2 4.7k resistors instead of to the op-amp (-) input?

[deadastronaut]

this is the schemo ive breaded..
http://www.diystompboxes.com/smfforum/index.php?topic=101126.msg938031#msg938031


BJT.. collector base emmiter wired like the fet?.

[samhay]

^BJT.. collector base emmiter wired like the fet?.

yup. RG suggested it a few threads ago, and I have used a bit since then. It can work quite nicely.
http://www.diystompboxes.com/smfforum/index.php?topic=103934.msg929532#msg929532

The suggestion to take the feedback to the junction of the 2 4.7k resistors instead of to the op-amp (-) input was made assuming you still have yesterday's PCB populated. Did you end up canabalising it?

[deadastronaut]

yep..butchered

ill try that tranny thing then...will be later as i have stuff to go do...

cheers sam.

[deadastronaut]

well i'm back on it...

tried the (various ) BJT to no avail..

i wonder why the fet switch isn't turning fully off...hmmm..


(btw i tried the wet/dry mix...very nice indeed, thats defo going on it. pure verb and no dry.. )

[samhay]

^i wonder why the fet switch isn't turning fully off

This is a known problem with FET switches.
R.G (I think) has written a nice explanation of why large signals can cause JFET switches to leak, but I can't find it at the moment. In general, think about what happens to the drain and source voltage relative to the gate when you put a large varying signal across it...

[deadastronaut]

heres what i have on the fet.. (switch)

D 4.55

G 0.05

S 1.85

[slacker]

Is the source side towards the 22n cap? If it is you need to add a resistor from source to VB, the drain and source both need to be referenced to VB.