Howdy friends!
So I recently attempted to build a dirt baby, and I'm having an issue. What I get is no direct signal; just one small, very quiet, very dark repeat, but that's it. The speed of the repeat is affected by the delay time, the modulation works (as does the vibrato/chorus switch), and the trim does affect the volume of the repeat. So that's encouraging.
I have checked all of my voltages which I will list below. They all look to be right in the ballpark and seem appropriate given that this is the latest dirtbaby PCB. I've checked over my solder work using my super nerdy jeweler's visor, and I do not find any bridges, no missed points, etc. I made sure to isolate the pots from the PCB with double sided tape. I've double checked my electrolytic cap orientation, and the only value sub I have done is 30pf instead of 27pf in C2. You will see that that one is soldered on the opposite side of the board as it would normally be. The reason for this is that I was attempting to find a 27 pF cap, and continued populating, however those have been tough to source. Otherwise all stock.
The only thing I am thinking is that either that substitution is a much bigger deal than I thought, or, more likely, I may have gotten the LED polarity wrong for D2. I have the flat side on the left (the square pad), and now that I think about it, I think it should be oriented with the flat side toward the flared graphic on the PCB. If this is wrong, I'll fix it first before doing the ol' audio probe.
I have no problem digging in and pulling that out, question is, would that cause the issue I'm having here? Does it have to be a diffuse red led as opposed to a clear one?
In the interest of full disclosure, while I am always in the rock before box mode, with this, I did sorta "half" box it, as I really wanted all the pots to be straight in the enclosure when I soldered them to the PCB. This is to alleviate an issue I've had where I solder the pots in and then they end up a little or a lot crooked. That said I did so with a purpose and with my eyes open, and I've taken it out and am now attempting to trouble shoot. My pedal doesn't work but at least the damn pots are straight!!! ;)
Voltages as follows, 9.6 v power supply:
IC1:
1: 1.66
2: 3.11
3: 3.10
4: 0
5: 4.55
6: 4.59
7: 4.51
8: 9.51
IC2:
1: 5.08
2: 2.55
3: 1mv
4: 0
5: 2.93
6: 2.54
7: 1.09
8: 0.74
9-16: 2.55
Ic3:
1: varies
2: 4.72
3: 4.3-5
4: 0
5: 4.72
6: 4.74
7: 4.5-5
8: 9.47
IC4:
1: 4.6
2: 4.61
3: 4.18
4: 0
5: 4.42
6: 4.63
7: 4.63
8: 9.5
Regulator:
1: 9.5
2: 0
3: 5.07
Verified the voltage coming in is correct.
Thanks!!! :)
Yes you definitely want to reverse that led. You can simply try without. If use one you should use a green one though, it does make a (slight) difference
Hope you get it sorted! It's a great delay. I prefer mine running at 18v
Well, I tried reversing the polarity of the LED, and it's exactly the same either way. Hmmmm. Guess it's audio probe time. Still if anyone has any ideers I'm all ears. :)
Quote from: ElCapitan on November 03, 2018, 12:23:36 PM
Well, I tried reversing the polarity of the LED, and it's exactly the same either way. Hmmmm. Guess it's audio probe time. Still if anyone has any ideers I'm all ears. :)
Nope, sorry don't have much time, but I did have a look at your board and voltages, everything looks quite fine... check your soldering, and yeah, an audio probe is really good to check that kind of problem.
Maybe try to swap the audio opamps too (don't bother about the lfo section), and the PT2399
Figured it out sorta. R25 had a 470k resistor instead of a 470 ohm. Thought That did the trick, but after a couple minutes playing it after boxing I stopped getting any dry signal. I unboxed it, thinking maybe there was a short, but nope, same issue. I probed the blend pot and it's wet on all three pins. I'm kinda at a loss where to go from here. Any suggestions?
Now that you reversed the LED check pin7 again on the PT3299. Are you getting closer to .7v?
The LED does make a difference - a green (or yellow) diffused seems to work best. Its purpose is to prevent the input of the PT from clipping. It does make a subtle difference but the effect will certainly work without it.
As to why you are losing dry signal -it's a stumper. The dry signal part is very straight, going through that initial gain stage then to the blend pot. Considering your description of the problem here's what I would do: if your dry signal is dying after a couple of minutes, then take some voltage reading right after it dies out. Specifically check all the voltages on IC1. We want to see if it is losing power somehow.
Yep, now I'm getting .74 at pin 7 on the pt2399. Ic1 voltages are normal. I can't seem to get the dry to reappear sadly. Would you suspect the blend pot given that the dry doesn't show up on any of its legs? I dunno kinda just spitballin'.
Check your soldering, it doesnt look ideal in some places. Check especially C4, R5, the blend pot. The dry path is very simple: Input, C1, R2, IC1B, C4, that's about it!
That did the trick!! Just replacing my tip and reflowing a few spots was all it needed. Been working for about an hour now, just in time for band practice. Thanks much!!
Great, glad you got it working! Enjoy!