Problems with Space and Time Reverb

[GiulioGratz]

Hi, i just soldered the last pot in this reverb and tried it: it doesn't work (i'm not so lucky with the brick  ); i used a perfboard and the same components of the layout provided in this forum.

I have this problems:
when i mix some effected sound to the clean signal i get a bad percussive sound in the background ( ~80/100 bpm i think) and this sound becomes the main one if i turn the mix all the way up (gain > 1)...
if i play my instrument into the pedal with mix pot at max, i have a tremolo-like effect.
Other pots:
tone is ok;
reverb seems ok, but i can't understand so much... it seems a very suble effect;
regen: don't know;
delay: it works.
Tried with 3 different pt2399. Checked all the resistors and capacitors, and 7805 gives correctly ~5 volts in output.

After some minutes arises a very bad feedback that hides all the other sounds coming out from the effect.

Any idea?
Thank you very much

Ps: as always, sorry for my english! Cheers

[samhay]

Hi,

>when i mix some effected sound to the clean signal i get a bad percussive sound in the background ( ~80/100 bpm i think) and this sound becomes the main one if i turn the mix all the way up (gain > 1)...

There is something wrong in the wet - delay or reverb - section.
With the reverb at min you should have delay only in the mix. With reverb pot at max you should only have reverb, but the delay before you hear the effect will change with the delay pot. Does the delay pot change the tremolo effect?

>After some minutes arises a very bad feedback that hides all the other sounds coming out from the effect.
Does this happen with the mix at minimum setting?

I guess you used this layout?
http://www.diystompboxes.com/smfforum/index.php?topic=107226.msg995623#msg995623

It is quite tight, so there is quite easy to get a solder bridge or other short somewhere.
It would be helpful if you could give voltage readings on the PT2399, the power pins of the reverb brick - pins 1, 2 and 4 -  and both op-amps.

[GiulioGratz]

Ok, so the delay pot acts well... It does just that... Anyway the percussive sound is always at the same frequency, also changing the delay control...
Oh, yes: i used that layout... And unfortunately i'm far away from home (and from the pedal)... Thus i'll give voltages this week end! Thank you for the fast answer!

[samhay]

OK, that sounds like the reverb brick might not be very happy as the PT2399 must be working if the delay pot works.
If you turn the reverb pot all the way down, do you still get the percussive sound or do you get clean delay?

I should also check -
you are using a BTDR-2 brick?
And it is mounted on the solder-side of the board?

[GiulioGratz]

At reverb down i still get the percussive sound!
And i used btdr-2 vertical, connected to a female angular header soldered on the solder side of the board
Just thinking: pt2399 repeating infinitly the noise of the dc plug inserted into the jack? Could be a wrong value cap or res near the IC?

[samhay]

Yes, sound like it could be a problem with too much feedback into the PT2399.
This is unlikely to be a problem with cap values, so I would focus on resistor values - should be easy as they are almost all 10k - and solder bridges.
The other thing you can do is de-solder lug 2 of the regen pot. This is the feedback path, so with it removed, you should not get any repeats. If you still do, then you have a short/bridge somewhere.

[GiulioGratz]

Here i am. Voltages:

(2~6 means oscillating between 2 and 6)

DC   = 8.49

pots at noon, tone at max

7805 = 4.95

IC1:
1   1~8
2   1~8
3   1~8
4   0
5   1~8
6   1~8
7   1~8
8   8.49

IC2:
1   1~8
2   1~8
3   1~8
4   0
5   1~8
6   1~8
7   1~8
8   8.49

PT2399:
1   4.95
2   2.47
3   0
4   0
5   2.89
6   2.47
7   0~1
8   0~1
9   ~2.5
10  2.47
11  2.47
12  ~2.5
13  ~1.8
14  ~1
15  ~2.5
16  2.47

BTDR-2:
1   4.95
2   0
3   0.95~1.04
4   0
5   2~6
6   2~6

[GiulioGratz]

And this is the board...

[img=800x450]https://i.imgsafe.org/b8043b5.jpg[/img]

[Kipper4]

There seems to be an issue with the TL072s voltages typically I would expect them to be 4.5v.
DMM loading might be throwing them out. But 1-8v on the ins and outs seems way off.
Are your grounds good?

Schematic in this thread

http://www.diystompboxes.com/smfforum/index.php?topic=107226.msg973194#msg973194

[duck_arse]

And this is the board...

[img=800x450]https://i.imgsafe.org/b8043b5.jpg[/img]

GG - you can't have "=800x450" in your image tag opener. you can have "img height=450" or "img width=3000" for ex. also, any url that points to "https" will not show. appaently, the s in https means secure, as in we can't access the link. so, drop the s, and the numbers, and the result would be ......

[samhay]

There is something wrong with the Vref (half supply) voltage. This is set by the 2 x 10k resistors (R21,22) placed between the 2 op-amp ICs in this layout:
http://www.diystompboxes.com/smfforum/index.php?topic=107226.msg995623#msg995623
This is where I would start looking for cold solder joints, shorts and/or a resistor that isn't 10k.

However, with the voltages posted, I am not sure how it would manage to pass clean signal if all those op-amp pins are really floating betweeen 1-8 V.

[GiulioGratz]

Resistors and capacitors are ok (double checked). Resoldered some cold-like joints. There still is the percussive sound in the background, but at a lower gain.
Maybe my measures aren't so good i was really in a hurry! I'll measure voltages again. And i'll check Vref!
Thank you very much!
And thank you duck_arse i edited the post thounsand times, finally i left it ad it is now LOL

[samhay]

OK great, that sounds like progress.
It won't hurt to re-flow all the solder joins then test for continuity between things that both should, and should not, be connected.

[GiulioGratz]

Are there some differences in measuring voltages with instrument and out jacks plugged in?

[samhay]

If you are measuring DC, then it shouldn't make a difference. Does it make a difference?

[GiulioGratz]

It doesn't. Just thinking. Anyway, resoldered vref resistors and all is as it was before. Still the percussive sound.
The problem is that the effect is very strange, the wet sound goes away in the same time interval of the percussion... That's so bad, if i turn up the mix control i actually have a tremolo effect, only very strange because there is also the delay that makes some rhythm below the constant "tremolo"... 

Ps: reverbs are so painful  i've never been able to make work neither a chasm reverb (and i re-done the board 3 times in that case)

[ElectricDruid]

It doesn't. Just thinking. Anyway, resoldered vref resistors and all is as it was before.

If you've checked the Vref resistors and the capacitor and all those are ok, then something somewhere else is shorting out the Vref supply. You need to follow the Vref path around the circuit and see if you can see any shorts. Alternatively (or as well) find all the components that connect to Vref on the schematic, and then give them a good checking over.

Tom

[samhay]

If you now measure voltages on the op-amp signal pins  - 1-3 and 5-7 - are they still oscillating between 1-8 V?

If you turn the mix all the way ccw, do you get clean signal now?
What is your input - guitar or something else?

[GiulioGratz]

With mix all the way down i have perfectly clean signal and my inputs are guitar and bass.
I measured voltages some hours ago, if i remeber them right they were (stable) at vref (near 4.50 V).
But there still is what i described in my last post, so it wasn't the only problem, maybe...

[samhay]

OK, so your Vref must be sorted now as you won't get clean signal if it isn't.
I'm starting to think you might have a wiring problem - which is quite understandable.
If you leave the reverb brick unplugged - I note the socket - and set the reverb pot fully on (cw) you should not get any signal if you turn the mix pot fully on (cw).
If that checks out, what does the regen pot do to your tremolo effect?