DB delay not working

[taviii]

Hi! I have finished this deep blue delay today and im not getting the effect to work.
First time i plugged it just got a low volume hiss and some squealing.
I searched the forum for something similar and came across the need to bridge leg 3 and 4 of the pt2399.
I did it and now the effect sounds clean like a bypassed signal, no delay, and neither of the 3 pots seem to affect anything.

I'll leave a picture of the schematics I've used and the builted board








I've looked the board for shorts between the traces or some mistake but i couldn't spot any.

I substituted some resistor values
360k original / 350k
180korginal / 182k
5.1k original / 5.6K

Also the 100uf cap used is rated 10v

Anyone could possible help me know what could be wrong? I'm trying to get a multimeter to check pin voltages.

[anotherjim]

I can't see much -  we do need voltages.
One thing is the voltage regulator pins the right way around? The big regulators are opposite to the small plastic one it's designed for.

[taviii]

The big regulators are opposite to the small plastic one it's designed for.

I was aware of that and im pretty sure i put it the right way.
5v are going to pin 1 of the pt2399.

Soo i finally bought myself a multimeter😂

Input: 9.85v (wall power adapter)

Pt2399
1-5.1
2- 2.54
3- 0
4- 0
5- 2.8/3.75 oscillating
6- 2.57
7- 0
8- 4.6 decreasing to 0?
9- 0.86/2.7 osc
10- 2.5/3.5 osc
11- 2.54
12- 2.54
13- 2.54
14- 2.54
15- 0.06
16- 2.6 decreasing to 0 again

Tl072cp
1- 3.9/4.3 osc
2- 4.4
3- 4.4
4- 0
5- 4.4
6- 4.5
7- 4.5
8- 9

7805
In- 8.95
Ground- 0
Out- 5.1

Guess my values are messed up. I checked the board for shorts and scratched in between traces with a razor blade but keep getting the same result.

[anotherjim]

First problem is the PT2399 pins 15 & 16. Pin15 is an output and should read 2.54. Pin 16 is an input, but it should be biased from pin15 (via x2 10k resistors) and have about the same voltage.
With power off, you should be able to read 20k ohms between those pins of the PT2399. You have an SMD part in an adapter - are you sure its pins are soldered down ok?

[antonis]

Too much excessive solder all over the neighourhood..

[duck_arse]

is pin 7 of the pt2399 shorted to ground?

[taviii]

found a bad trace going to pin 15, now is reading correctly, here are the new voltages:
1- 5.1
2- 2.5
3- 0
4- 0
5- 3.26
6- 2.54
7- 0.58
8- 0.60
pin 9 to 16 read 2.54

pin 15 and 16 are good now, but i keep getting a clean signal.

is pin 7 of the pt2399 shorted to ground?

both pin 7-8 are going to ground thru some 100nf ceramic capacitors. should i try to conect them directly to ground?

you should be able to read 20k ohms between those pins of the PT2399. You have an SMD part in an adapter - are you sure its pins are soldered down ok?

it now reads 20ohms between pin 15-16, and i also checked the ic and the adapter pins for continuity and they are all correct.

[duck_arse]

going to ground through a cap is exactly what the circuit requires. your voltage reading of 0V at pin 7 suggested that it was shorting to ground, as in not going through the cap. as you now have a voltage there that is not 0V, it suggests no shorting. [I can't find a circuit with voltage measures for those pins on a PT2399, so can't say if your measured indicates good, bad or other.] don't be tempted to go shorting pins to ground willy nilly - do as your schematic tells you.

it now reads 20ohms between pin 15-16

20 Ohms, or 20 kilo Ohms?

[anotherjim]

Pin 7 volts low was probably in response to the input problem.

I would suggest audio or scope probing to see if audio is passing through the delay chip. Audio in at pin15 and out at pin12 and pin14. You might disconnect the 22k between the 2 op-amps to cut the clean sound so if you can then hear audio from the output, it must be coming from the delay.

[taviii]

20 Ohms, or 20 kilo Ohms?

20k ohms

Pin 7 volts low was probably in response to the input problem.

I would suggest audio or scope probing to see if audio is passing through the delay chip. Audio in at pin15 and out at pin12 and pin14. You might disconnect the 22k between the 2 op-amps to cut the clean sound so if you can then hear audio from the output, it must be coming from the delay.

Did the audio probe.
Pin15 is getting clean signal
Pin 12 clean signal maybe a little delayed
Pin 14 kind of works. Delay pot works weirdly and if turn it up and strum a note it comes out of the amp with delay but I've got no repetitions.

I cut out the 22k resistor and still got the same

[anotherjim]

Cutting out the 22k wasn't going to fix it, just helps to focus on the PT2399. Now you know the PT2399 has a delayed output, you could put the 22k back, but I'd leave that until you have repeats working.

It seems like the basic delay is working. Turning the delay pot should sound like a tape recorder speed effect on pitch.

Do you have a circuit schematic that matches the layout you built? This helps to find our way around the circuit.
I'd also suggest reading this...
https://www.electrosmash.com/pt2399-analysis

[taviii]

thank you guys for your patience

It seems like the basic delay is working. Turning the delay pot should sound like a tape recorder speed effect on pitch.

yes, it sounds exactly like that. the other two pots doesnt make any change on the sound, or at least for my ears.

Do you have a circuit schematic that matches the layout you built? This helps to find our way around the circuit.
I'd also suggest reading this...
https://www.electrosmash.com/pt2399-analysis

nice read, lots of info, i dont have any electronics background and some concepts are hard to grasp.

i will try to draw my layout, i just crowded the components a little bit because my perfboard was a little smaller than requested.

[anotherjim]

Well, here's a schematic (circuit diagram) of the same kind of thing...

When you have this, we have part ID numbers (that 22k is R4).
If you find a board layout only and there's no matching schematic - walk away and find one that does!

[antonis]

I'd also suggest reading this...
https://www.electrosmash.com/pt2399-analysis

<Off-topic ON>

Am I missing something or it's just a typo..??



<Off-topic OFF>

[anotherjim]

I think the figures are a typo. Timing of that cap is going to be much shorter anyway? The transistor base will clamp the cap voltage at about 0.7v. It doesn't have to wait to reach 5v. I hate seeing that circuit. Shouldn't there be another resistor between cap and base? As drawn would make sense to me with a MOSFET, but not a BJT.
I think I've seen a BJT version with an emitter resistor providing a safe minimum current out of pin6, and that would make more sense.

[antonis]

 

No Jim, don't go so deep..

Just  noticed that  for 1 sec time constant, it needs to have a product of  1X10⁵ X 1X10^-5..

No involvement with 4 (or 5) x RC charging constant or Vbe voltage drop..
(which, BTW, absolutely true & correct said..)

[taviii]

Delay is working know thanks to you guys! Sound very nice.

I've got a bad trace going from pin 14 to feedback section so thats why i wasn't getting repeats.

Update. I have been using the pedal for the last hours and i think i have a problem with latency when the delay pot is half-way or full. I have a huge gap between my pick attack and the sound coming from speakers with the delay at full.
There are many reviews of the ddb on youtube an none seem to have this problem.
Any idea on what might be causing the latency?

[anotherjim]

Sounds like you don't have dry sound going through, only the delay. Did you put that 22k resistor back?

Runaway feedback is a recurring problem (pun intended) with any delay with a feedback circuit. Because too much signal is stored in the delay memory, it will always be too late to turn the feedback down.
You could reduce the feedback by increasing the mix resistor from the feedback pot to the PT2399 input (R15 in the Sea Urchin version).