Aquaboy DX weird voltages

[dondougie]

So I populated my ABDX with MN3008's running at 15V with a Road Rage. IC3 is normal voltage- and signal wise, but I'm getting 14V at pins 3 and 4 of IC4. The cancel trimmer seems to do nothing, but i checked it out of the circuit and it works fine. Something up there around R28 - R30 seems suspicious, but I already redid the solder joints and checked for bridges. Any suggestions?

Thanks in advance
Andre

[Scruffie]

Hm, that is odd, check the values of R25 to 29.

Voltages on Q3?

And the cancel trim isn't a very dramatic control so it's not surprising you don't seem to notice much, you'd probably only see its effect on a scope.

[dondougie]

Hm, that is odd, check the values of R25 to 29.

Voltages on Q3?

And the cancel trim isn't a very dramatic control so it's not surprising you don't seem to notice much, you'd probably only see its effect on a scope.

Thanks for your reply!
Well, the resistors are correct, but I don't know about q3:

C 14.47V
B 13.9V
E 13.4V

[Scruffie]

Try swapping IC3 & 4 and see if it's the BBD or the board.

Oh hang on a minute, I just see you said you tested it OUT of circuit and it worked fine, I thought you said the pedal was working fine.

In that case, what are the voltages on all the pins? I wonder if there's an issue with your bias trimmer, if the bias is too high, the outputs will be high.

[dondougie]

I swapped the ICs and one of them doesn't work and has the same high pin 3&4 voltages in the IC3 spot. And I thought I would have a new delay by the end of the weekend 

I'll order some new BBDs and try this again, thanks for your help!

[dondougie]

I got the new chips and it works! The only problem I have now is self oscillation at about half of the feedback pot with t1 at min. Do I have to lower r13/14 or is it another resistor? I have 47k in for both right now.

[Scruffie]

Great!

Check for near half supply on Pin 7 of the NE570, you only adjust R13 & 14 if this is not the case.

To decrease feedback, increase R39.

[dondougie]

Thanks for your help! I went up to an 82k for R39 and it works perfectly now with T1 set to half! I like this much more than my MN3205 Dirtbag, though some of the magic is already there. Now I can only hope that the 3005s I have on order are real, and that it doesn't take too long before the new Dirtbag comes out 

[dondougie]

ok, boxed it and now there is a lot of clock noise starting at half delay time, even in bypass (I used a 1776 relay bypass board). Wiring is kind of a mess right now, with the road rage right between the switch and the output jack, otherwise the orientation is the same as in the build doc. Would shielded cable from the out jack to the switch board help?

[Scruffie]

ok, boxed it and now there is a lot of clock noise starting at half delay time, even in bypass (I used a 1776 relay bypass board). Wiring is kind of a mess right now, with the road rage right between the switch and the output jack, otherwise the orientation is the same as in the build doc. Would shielded cable from the out jack to the switch board help?

It might help...

You say it's kind of a mess, if you want to get rid of the whine, tidy it 

But the Road rage is a possible source of noise so extra protection such as shielding certainly can't hurt... you may have to relocate it in the enclosure though, I couldn't say.

[dondougie]

So I checked the wiring and realized that I haven't grounded the enclosure  damn those fancy insulated jacks  now everything works as it should, thanks again for your help!