ECHO Base build - complete but a little distortion

[Michael Allen]

Fired this up and after a little debugging (pots wired backwards causing unreal feedback) got it to work this evening. I think I'll really like it but I'm getting a little distortion on the repeats. It doesn't sound like the original note is being distorted, but the first repeat and successive sound like an overdrive pedal.

Voltages look good for the opamps. The audio opamp have 8.93V supply and 4.93V on all pins (except ground). PT2399 looks good too. About 2.4V on 9-16 with a 4.93v supply. The opamps are OPA2134. I threw them in cause I had them and figured they would work quietly, is there some characteristic that could be causing some distortion? Like the existing circuit doesn't bias them right?

Since the first note isn't distorted I don't know what to aim for, but I don't think its the PT2399 that's causing all the distortion.

Any ideas?! And awesome circuit!

[slacker]

Is the bypassed sound Ok? If it is then I don't think it can be the opamps, because the clean sound goes through them as well as the delayed sound.
Your voltages look fine, if you want to check them, I posted my voltages in the original thread.
http://www.diystompboxes.com/smfforum/index.php?topic=60662.msg498824#msg498824

On your layout, which looks great by the way try double checking the resistors on the right hand side of the PT2399, If any of those were the wrong value then it could be overloading the PT2399.
Check the wiring of the feedback pot as well because that could cause problems if it was wired wrong. I take it you've got lug 1 grounded?

Hope you get it sorted.

[Michael Allen]

I think it was my amp/cable causing some distortion. Not a problem now.

However.... I'm getting a weird power issue. Power seems to cut out almost entirely (and short the power supply) and then come back, every 5 seconds or so. It doesn't seem to have anything to do with the position of the controls. Goes away if I take the PT2399 out of the socket.

Any ideas? It wasn't doing this when I was first debugging it.

[slacker]

Sounds like a dodgy cap to me or an electro the wrong way round. If removing the PT2399 solves the problem, then I'd check the 47uF electros off pins 1 and 2.

[cobra94]

Hi Guys,

I just wanted to chime in and confirm both Slacker's circuit and Michael's pwb layout.  I finished it over the weekend and after debugging the same "reversed wired pot" issue the circuit came to life (it hit me around 1am in bed, the wife was not pleased with my "That's got to be it!!!"  ).  I changed the 20K feedback limiting resistor to a 90K (didn't have a 100K handy) and it made the feedback control more usable (extended range) before the oscillations set in.

All voltages correspond to slackers posted values so that was a great help.  What could be useful is relative pot settings for the sound clips (e.g. depth 9 o'clock, level 12 o'clock etc.) this would just be added confirmation that our circuit is performing as the original.

The last issue I have to look into is that I don't hear the effect of the "mod speed" pot unless the level pot is almost maxed (boosting the wet signal).  I put a scope on the LFO and saw the triangle wave form so I know it's working.  I'll have to stop playing with it long enough to reopen it though and that's going to be hard. 

Great job gentlemen!!!

Cheers,
Peter

[slacker]

Thanks for the report.

I agree 20k is probably too low for the "feedback" resistor, I've been meaning to change mine for something bigger. When I built it originally I deliberately made it so some of the settings were probably more extreme than anyone would want. My idea was to live with it for a while to see what settings were useful and then tame some of the extremes, never got round to it though.

Not sure what your modulation problem might be, the modulation should be obvious at all delay levels. Some of the chorus sounds do need the level turned up, but the more extreme vibrato and tape delay type effects should work where ever the level pot is set.
I'd check that the mod depth pot is wired correctly, lug 1 should be grounded, which isn't shown on Michael's layout.
Also check the orientation of the BC560/2N5087 especially if you've used a 2N5087 because it needs to be the opposite way round to the BC560.

[cobra94]

Hi Ian,

I'll probably end up going higher on the resistor, 100K was my starting point but I don't really want it to oscillate until maxed.

I believe the pot is wired correctly but I will check it this evening.  I did use a 2N5087 (reversed it accordingly) and I have a few extras, would the gain of this transistor be a factor?  I'll also have a look after the level pot and make sure the 2 10K's are correct.

I can't help feel the issue is with the LFO, the depth effect is noticeable with the level @12 o'clock but I don't hear the vibe until the level is past 2 o'clock.

[slacker]

Are you running it off a powersupply or a battery, because the LFO doesn't seem to work too well on batteries once the voltage starts dropping.
I don't think the gain of the transistor should make much difference. From the datasheets 2N5087s are pretty similar to BC560s, so they should be fine. Having said that I haven't tried a 2N5087 but other people have reported that they work fine.

[Michael Allen]

Replaced the electros and same problem.

I used 100R resistors for all the 220R resistors. Could this cause issues?

[slacker]

I used 100R resistors for all the 220R resistors. Could this cause issues?

Shouldn't do.

If removing the PT2399 stops it then, it could be a bad chip, have you got anything else you can try it in? Otherwise I'd check for shorts around the PT2399. Might be worth checking the voltage on pin 1 of the PT21399 socket with it removed to make sure it's getting the full 5 volts.
It's probably worth checking around the voltage regulator as well, it doesn't get hot or anything does it?

[cobra94]

I'm using a power supply so I don't think sag is a problem and I agree with you on the transistor gain (not an issue).  I really want to see what is happening at the level pot (signal level) first.

Mike, I have two PT2399's and when swapping them in my rebote 2.0 I do notice one distorting considerably more then the other.  I think these chips are a little more sensitive than most so it could be the cause.  What if you put a load resistor across the V+ and gnd pins in the 2399 socket and see if the short reappears.  At least you'll know if another component is the real cause.

[Michael Allen]

Man I am at a loss on this one...

I've tried several PT2399s and same results with each of them.

If I put a small (100r) resistor across the power rails of the PT2399, the power fades out, fades in and blinks a few times. Then fades out, fades in and blinks some more, in a cycle.

I've replaced all the electros, actually took all of the electros, caps and diode off the power power rails and still get the power cutting out.

I've disconnected the LFO section and still get the power cut out.....

[slacker]

Weird. If putting a load across the PT2399s power pins causes the problem then it means it's something to do with the 5 volt regulator, because that powers the PT2399. It also provides bias voltage for the opamps, but that won't draw much current which is probably why it's OK when the PT2399 is removed.
I'd try replacing the regulator, or at least check the components around it.

[DimebuGG]

I don't why they're complaining on this unit where actually its a fine build.

[gigimarga]

Where i can found a PCB for this delay in PDF format?
All i see are images and i don't know what are the correct dimensions when i try to print.

[DimebuGG]

I made my PCB in pdf which is taken from Junkworks design since it is gif