Pork Barrel: substantial boost when engaged

[spaceboss]

Hi folks, I was wondering what I should do next.

If anyone has any IC  voltage readings for MN3007 9v or 15v (same problem either way), perhaps that would be a good next step?

(1) Project Name: Pork Barrel

(2) General description of the problem: I'm getting a substantial ice-picky boost when the effect is engaged.  I guess that it is possible that this is normal for the effect, but it seems both unpleasant and severe. This is most obvious when adjusting the trimmer. There is no non-distorted setting without the massive boost and treble accentuation.

(3) Steps that you have taken to try to resolve the issue:

A) I started with both the road rage and depth mods and went back to 9v and no depth mod in order to reduce the variables.

B) I replaced all of the ICs.

C) I took a digital picture and blew it up and double checked all of the resistor codes, IC orientation, diode orientation, transistor orientation, and electro capacitor orientation.

D) Checked all capacitor values and double checked the transistor numbers.

E) Checked for solder bridges and reflowed the whole board.

(4) List any substitutions you used for parts/values

I have not made any substitutions.

I suspect that the problem could be in the area that amplifies the effected signal as the board passes un-boosted audio without effect when the trimmer is turned fully counter-clockwise. Unfortunately I'm not good enough with schematics to know where that would be-or if I'm on the right track or not. The transistors are cheap tayda transistors and perhaps they are out of spec if they are involved in the amplification.

Any help would be much appreciated. I've pretty much exhausted what I can do on my own at this point. If it would be useful I could grab IC or transistor pin voltages.

Happy Thanksgiving weekend.

All the best.

James

[stecykmi]

try removing R27. this will eliminate the chorus signal from the output. if it's still loud, you know the problem is in the dry signal or the final gain stage based around IC1B.

[spaceboss]

Thanks, I'll give that a shot tonight.

I also found some IC voltages posted by Lace Sensor a while back, so I will post mine and compare my readings with his as well.

James

[spaceboss]

Hello again.

I removed R27, and with no effect there is no boost/icepick. So I guess I should isolate the final gain stage around IC1b (I'm not 100 percent sure where this is).

My IC voltages are (taken pre-resistor removal):

JRC4558D (minor fluctuations)
1  5.64   8  9.48
2  5.65   7  5.51 - 5.58
3  5.64   6  5.62
4  0       5  5.64

TL062CP
1  0 -8          8  9.48
2  4.69-4.8    7  3.25-6.97
3  2.81-6.87  6  4.79-4.86
4  0              5  4.69-4.85

3101 (minor fluctuations)
1  9.38   8  .62
2  4.79   7  2.9-3.3
3  0       6  8.17-8.4
4  4.83   5  .27-.37

3007 (minor fluctuations)
1  9.37   8  4.58
2  4.82   7  4.58
3  4.84   6  4.78
4  .62       5  0

If this sheds any light on anything for anyone, let me know. For reference, these were lace sensor's numbers from long ago:

TL062
1 - 0-6.7 / 2-5 fluctuating
2 - 3.8 / 3.8
3 - 2-5 / 4-5 fluctuating
4 - 0 / 0
5 - 3.6 / 3.8
6 - 2.1 / 3/5
7 - 1.8-5.2 / 3-4 fluctuating
8 - 7.3 / 7.6

4558D

1 - 4.6 / 4.8
2 - 4.7 / 4.8
3 - 4.7 / 4.8
4 - 0 / 0
5 - 4.7 / 4.8
6 - 4.7 / 4.8
7 - 4.7 / 4.8
8 - 7.4 / 7.8

MN3101

1 - 7.4 / 7.6
2 - 3.8 / 3.9
3 - 0 / 0
4 - 3.8 / 3.9
5 - 0.3 / 0.3
6 - 6.5 / 6.6-6.7
7 - 2.45 / 2.4 - 2.6
8 - 0.5 / 0.5

MN3007

1 - 7.3 / 7.6
2 - 3.8 / 3.9
3 - 4 / 4.1
4 - 0.5 / 0.5
5 - 0 / 0
6 - 3.7 / 3.9
7 - 4.2 / 4.4
8 - 4.2 / 4.4

Again insight on what to look at next would be helpful. Cheers.

James

[spaceboss]

At the risk of conversing solely with myself... 

1) Are the voltages that I posted in line with what one would expect for this pedal?
2) Would transistor voltages help anyone identify any issues?
3) If I'm looking at IC1b, what should I be looking for there (I assume 1b is those components that connect are linked to pins 5, 6, and 7 of the JRC4558. Does Q3 play a role in the amplification? If the HFE is on the high side, could that be my culprit?

Thanks again, I know folks here busy, any help is appreciated.

James

[LaceSensor]

the voltages look fine to me.
Mine were a tad lower as I was testing witha  battery putting out about 7.5-8v

Try changing Q3 and see what happens. is it correctly oriented?

[spaceboss]

Yep, Q3 was correctly oriented, but swapping it out fixed the problem! That'll learn me for not socketing transistors in every build.

Thanks stecykmi  for point me in the right direction, and Lace for the heads up on Q3.

A beer on me, should our paths ever cross.

James

[LaceSensor]

Awesome. Do yourself a favour and run this at 15v too, much better.