cool reverb apart from switch spdt 'pop' issue

[slacker]

As an experiment Rob, try guitar straight into mixer compared with guitar through just the buffer into mixer. See if you get any significant volume and tonal changes, if you do it suggests the mixer is at least part of the problem. If not I'm officially stumped.

[deadastronaut]

hi mike , i tried the fet buffer in front of the reverb, distortion was fine with reverb on/off...but clean with reverb on/off the same issue..


@ian: i'll try that now...

ok just tried the buffer on its own into mixer...and yes the vol increases a good amount with the buffer on compared to bypass...

out of curiosity i tried the buffer into my roland micro cube on a clean , and it was fine...hmmmm...yay!!!..

then i run the distortion and reverb into the roland cube and that was fine too....on/off clean dist...fine yay!!!...

soooo...the problem was my ''out'' all along, as in my mixer...wtf?. . ive never had this problem before!!!!...how would  i  go about curing that?...

[samhay]

Didn't realise the reverb section had gain. Cool.
You could appropriate the op-amp used to buffer Vb (nice touch, but probably not essential) and stick it after the volume knob as a non-inverting buffer.

Oh, and I still think you should pull or increase R11 as it should be dropping your dry signal quite a bit.

[deadastronaut]

hi sam;  tried the R11 mod..sticking a 1M lifts the level a bit....33k is about unity.

as for your opamp suggestion...got a diagram of what you mean?...i'm a dumbass.

[mth5044]

He means take your Vb off of R1/R2/C3 junction and use the opamp IC1a as a buffer after the volume pot. The buffer would be this guy here:

[samhay]

Yes - mth5044 beat me to it. However, that adds to the parts count and is a bit messy. I just realised that IC2d is a differential amplifier - interesting idea - and so much of what I was saying about unity gain is not quite right. The 33k R11 is probably going to work just fine in this case (although 1M will too).

If you want to stick with the op-amp output buffer, you might be better off using an inverting op-amp with a pot in the feedback loop to give you your level control. You could remove the 1uF cap and level pot, add e.g. a 10k resistor to the (-) input of an op-amp and put a 10k or bigger pot in the feedback loop. The 1u cap then goes on the output and you have a low-impedance buffer/volume control. I think this will work, but I am starting to realise that there are a few things going on in this circuit that I had not considered, and there are probably a few more I haven't yet.

[slacker]

Glad you got it figured out Rob even if the answer wasn't what you wanted. If it's the same mixer you mentioned in your D.I box thread then according to the manual the line inputs, I guess you're using those, have an input impedance of 10k Ohms. This will seriously reduce the volume from your guitar and roll off treble, this explains why you get the volume boost and extra brightness switching the reverb on. It probably also explains the volume drop with the dirt pedals, the input impedance will interact with the pedal's volume pots and depending on the size of the pots and where they're set it will mess with the volume.

You might not have noticed it before because with dirt or boost pedals or anything that significantly alters the tone, the issue would be masked, by whatever the pedal is doing and you can just crank the pedal's volume up to overcome any loss. Pedals with always on buffers like the Boss or the Echo Base would also hide the problem.

[deadastronaut]

cheers ian, great explanation,  so yeah it was mixer all along....mystery solved...cheers guys!.

i'm interested to see how it behaves  with the DI  now....

so for the record on here,

the reverb is good to go, without the 33k/4.7n.....and the volume really... ...though when the bright switch is on (which is still cool, ) there is a bit of a jump in vol.....

but i'll have a tweak around that switch (through my amp )..not mixer.

[Jdansti]

I told you it was good!!!

BTW-Time to change the message icon to smiley face. 

[deadastronaut]

ok...

[R O Tiree]

Rob, if you let me have the revised schem I can see whether I have to fab a new board or just insert jumpers/nothing depending on what's changed.

[deadastronaut]

Hi mike, and everyone...

heres the schemo, i removed the 33k/4.7n...adjusted the switch resistor to ground to 8.2k,  2.2k was a little fierce imo..and had a big leap in vol too...

i removed the vol pot as its pretty redundant now...unless there is a way of making this louder?. which would be nice, but its fine as unity without the vol pot anyway..i'm just a fussy sod..

i also stuck a 1M pulldown on the out, as it popped when on/bypassed otherwise.

so here it is..

[armdnrdy]

Since you removed the volume pot....why don't you put a proper tone control pot in it's place. I was going to make that suggestion a while back but....you seemed to be enamored with the idea of a volume control on a reverb unit.

[deadastronaut]

hi larry,  i'm just going to leave it as a 3 knob version now, that'll do me fine.

cheers for all your help guys... 

now lets build this bugger!!!

[samhay]

Cool - it's on the list.

Nice job Rob.

[deadastronaut]

^ yeah its well worth a build for sure...this will be on my setup for a long time i reckon.

[Jdansti]

hi larry,  i'm just going to leave it as a 3 knob version now, that'll do me fine.

cheers for all your help guys... 

now lets build this bugger!!!

Will there be a @#$%ing bass knob?

[deadastronaut]

hi jon, nope, but there may be a kazoo mode switch..... for

bwrrrrrr....bwrrrrr..........bzzzz....brrrwrwwwrw....zzzzz....type sounds...

always handy...

[Jdansti]

 

[quad]

Hi,

Any progress on the build?