Zero Point SDX help needed

[soldersqueeze]

 Hey, I was wondering if anyone can advise me-
Just finished my ZPSDX, and I have delay, but the feedback pot goes into runaway feedback at around 9 o'clock   I'm also not convinced that my modulation is working... Apart from that it sounds nice, but there's clearly some problems. Checked all my values and solder work, seems good (I don't have a camera to prove it at the minute I'm afraid.
One point to raise is that I installed r45 by mistake and by the time I realised it was a bit tricky to remove, so I cut the trace on the back of the board connecting it to ground as I figured this removed it from the circuit. Could this foolish action be the cause of my woes? Or the b550c transistors I used?
Any help much appreciated as I suspect this pedal is awesome...

[madbean]

You did not need to cut the trace-- you could have just clipped one of the resistor leads. But, either way gives you the same result, which is to leave it off the circuit. So, I think you are good there.

To change where the FDBK pot runs off, you can increase R41 to a higher value. 9'ock seems kinda early though for that to happen.

The C suffix destination on the BC550 doesn't matter.

I can't really comment on the modulation until you provide a description of what's going on there. Is your LED lighting up with the rate control?

[soldersqueeze]

I didn't fit an LED- do I need to?
I just noticed Q2 was upside-down, but socketed. Flipped it, and now I get clean signal with no delays at all on any setting. Could I have killed something?

[soldersqueeze]

tried an led in there, it just stays lit no matter where you set the controls

[midwayfair]

Double check the values on all your pots. Like ... make sure you didn't use one of the 1M for the feedback pot and a 50K for the depth.

[madbean]

tried an led in there, it just stays lit no matter where you set the controls

What kind of voltages are your reading on IC5?

[soldersqueeze]

Double check the values on all your pots. Like ... make sure you didn't use one of the 1M for the feedback pot and a 50K for the depth.

I suspected this too, but the pots seem fine. A shame, because it would have been a nice easy fix  

What kind of voltages are your reading on IC5?

EDIT- info no longer relevant- see latest post

I thought as I was doing IC one I'd check them all, I have no idea what IC3 is doing with its life. Why would delays come through when q2 was the wrong way round but stop when i removed and flipped it?

IC1
1 - 4.6
2 - 4.6
3- 4.6
4- 0.0
5 - 4.6
6 - 4.6
7 - 4.6
8- 9.3

!C2
1 - 5.0
2 - 2.5
3 - 0.0
4 - 0.0
5 - 3.6
6 - 2.5
7 - 0.7
8 - 0.7
9 - 2.5
10 - 2.5
11 - 2.5
12 - 2.5
13 - 2.5
14 - 2.5

ic3

1 - 5.0
2 - 2.5
3 - 0.0
4 - 0.0
5 - 3.8 jumping to 4.0 and back
6- 2.5
7 - 0.0
8 - sits at 0.0 for 7-ish seconds then jumps to 4.5, settles to zero and starts again :s
9 - sits at 2.5 for 7-ish seconds then drops to 0.1, settles to 2.5 and starts again
10 - sits at 2.5 for 7-ish seconds then jumps to 4.5, settles to 2.5 and starts again
11 - 2.5
12 - 2.5
13 - 2.5
14 - 2.5

ic4

1- 4.6
2 - 4.6
3- 4.2
4- 9.3
5- 4.6
6- 4.6
7- 4.6
8- 4.6
9- 4.6
10- 4.6
11- 0.0
12- 4.6
13- 4.6
14- 4.6

ic 5
1- 8.2
2- 0.6
3- 4.6
4- 0.0
5- 0.6
6- 4.6
7- 0.6
8- 9.3

[soldersqueeze]

OK, I don't know what I was smoking when I checked this, but I had missed out r54 (modulation now working nicely), and I broke a solder joint removing Q2 from the board yesterday. Both of these now fixed, plugged her in, and now I think everything works except the feedback pot acting oddly and hitting runaway at 9 o'clock still. I'm checking all my values again seeing as I was clearly failing when this was assembled, but if anyone can point me at areas which could be to blame I would be very grateful indeed.

[madbean]

Go ahead and socket R41 and try higher values there. This will move the oscillation point forward with the FDBK pot. That point is slightly different with each mode setting, but a 10k-22k will make all the difference there.

[soldersqueeze]

Socketed and popped a 20k in there. It helped but I'm still not sure it's working correctly- I can get to about 12 o clock before deafening feedback in the first and second modes, and about 3 o'clock on the third and forth. Also, The repeats are about unity gain with the blend maxed- it that another problem I have?
Can you point out any key areas to triple check values?
Sorry for all the questions.

[midwayfair]

Socketed and popped a 20k in there. It helped but I'm still not sure it's working correctly- I can get to about 12 o clock before deafening feedback in the first and second modes, and about 3 o'clock on the third and forth. Also, The repeats are about unity gain with the blend maxed- it that another problem I have?

This all matches my build. It's normal for the feedback pot to work a little differently between modes -- it matters how much signal is filtered out with each instance.

[garfo]

D'you think it is possible to control the level of signal that it is sent before the repeats on each individual mode?
I love my sdx, specially the tape mode. I have increased the resistor that controls the feedback but even with that, when I'm on tape mode the repeats go into runaway oscilation very soon.

Socketed and popped a 20k in there. It helped but I'm still not sure it's working correctly- I can get to about 12 o clock before deafening feedback in the first and second modes, and about 3 o'clock on the third and forth. Also, The repeats are about unity gain with the blend maxed- it that another problem I have?

This all matches my build. It's normal for the feedback pot to work a little differently between modes -- it matters how much signal is filtered out with each instance.

[jimilee]

D'you think it is possible to control the level of signal that it is sent before the repeats on each individual mode?
I love my sdx, specially the tape mode. I have increased the resistor that controls the feedback but even with that, when I'm on tape mode the repeats go into runaway oscilation very soon.

Socketed and popped a 20k in there. It helped but I'm still not sure it's working correctly- I can get to about 12 o clock before deafening feedback in the first and second modes, and about 3 o'clock on the third and forth. Also, The repeats are about unity gain with the blend maxed- it that another problem I have?

This all matches my build. It's normal for the feedback pot to work a little differently between modes -- it matters how much signal is filtered out with each instance.

So how did this all turn out, I'm experiencing runaway oscillation the same way.

[jimilee]

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