PT-80 analog sound

[tomas1808]

Hi,

I built a PT-80 delay pedal a couple of months ago, and after a lot of testing I'm having some doubts with the delay response of my unit. The problem is that the amount of repeats is exponential to the volume of the guitar. Meaning, if I play the guitar gently i get 2 repeats, but if i play it loudly i get 8; both with the feedback control set to the same level.

I know that its logical that given a quieter source the repeats will fade sooner, but in this case it seems a little bit too extreme. I have other delay pedals (Rebote 2.5, MemoryBoy) and they don't have this problem.

I just wanted to know if anybody is having this problem, and this is normal PT-80 behavior, or if this is just a problem with my specific unit.

Thanks!

[wavley]

Maybe a tweaking of the compander might be somewhere to look, it certainly makes a difference in the repeats of an RE-501 space echo when you adjust the compander.

[Galego]

Mine doesn't do that. I tried to play the guitar gently, to use clean and distorted sounds, and it always repeats the same number of times. Sometimes the last one is barely audible, but that's it.

[tomas1808]

Ok thanks a lot for the answers. I'am glad that its a problem, as it means that it can get fixed! Any tips on how to adjust the compander? Or should i just look for mistakes in its general vicinity?

[tomas1808]

Ok, after some time I decided to tackle this problem again, and see if I can fix it. I'm almost certain that the problem is the compandor, and so I did some research on it.

First I tested all the voltages on the IC's of the circuit, and compared them to the ones posted on GGG. They all were almost identical, except for pin 1, 10 and 16 on the compandor. The difference in voltages was still pretty small, but they were the only ones that stood out.

Here are the comparisons I got between the real values and the correct values posted on GGG:

• Pin 1 I got 0.76v against the 1v from GGG
• Pin 10 I got 6v against 6.6v
• Pin 16 I got 1.25v against 1v

I know the differences were pretty small still, but they were the only ones that were larger that 5%.

Pint 1 and 16 connect to the react caps so I thought they might be the problem. I took them out and tested them on my DMM but they seemed to be of the correct value.

Also I modded the PT-80 in order to add modulation as posted here: http://www.diystompboxes.com/smfforum/index.php?topic=60662.msg572620#msg572620 so that could be another source of problems.

Well if anybody has any idea on what could be the problem please let me know!

[runmikeyrun]

Try taking your modulation mod out of the circuit (unsolder a component or two) and see if the problem goes away. 

[tomas1808]

Try taking your modulation mod out of the circuit (unsolder a component or two) and see if the problem goes away. 

Thanks, will do!

[tomas1808]

Tried desoldering the oscilation circuit but the problem remains unchanged 

I re tested the voltages and got some interesting results though:



So the compandor seems to be somewhat near its theoretical values, but there seem to be some differences with the PT2399 IC. I dont really know what I'm even looking for here, so if anybody has any tips on what I could work on next to solve this, I'd be very grateful.

[anchovie]

Pin 5 is Clock Out, so it's a fast waveform rather than DC voltage. Nothing to be gained from measuring there. Pins 7/8 don't have much of an explanation in the datasheet, I don't think their DC voltage is critical.

I think that your DC voltages prove that the ICs are performing. How they are performing is determined by the resistors and caps connected to them. You should check that the passive components are the right values and both legs go to the right places.