Minnow voltages

[Robusto]

Hello,

I have been trying to build a Minnow. My first attempt had a few issues, so I started over with a new PCB. One of the issues was that the +8 and -8 were reading +9 and -9. On this new board I decided to start by just populating the power section, and I still have the same problem. What could be causing this? Does that 1 volt matter? It must or it wouldn't be designed like that. Any ideas?

 

[DailyDovetails]

Do both areas read 9 volt or do legs 6 and 11 of IC 3 read lower than legs 4 and 8 of the TL072?

Edit:corrected pin

 

[Robusto]

Do both areas read 9 volt or do legs 6 and 9 of IC 3 read lower than legs 4 and 8 of the TL072?

LM13700
6 -6.32v
9 0v

TL072 1
4 0v
8 +7v

TL072
4 -3.5v
8 +7v

My supply voltage is 9.46v until I connect it. When connected it drops to 7.3v. Is that normal?

 

[PJS]

Your voltages are not making any sense. Make sure you are numbering the pins correctly - also for the LM13700 it is pins 6 and 11 that are relevant for this.

 

[Robusto]

Your voltages are not making any sense. Make sure you are numbering the pins correctly - also for the LM13700 it is pins 6 and 11 that are relevant for this.

View attachment 73657

Well, I am passing signal through the effect now, but it doesn’t seem quite right. The S/H is really slow even when turned up all the way.

LM13700
6 -6.3V
11 +6.65

The op amps are both -6.55 on 4 and +7 on 8.

There’s something weird with the voltage coming in I think. As before, supply is 9.45V until I connect it and then it drops to to 7.29. I’ve checked all the power section parts again and they are all installed correctly. It has to be something to do with low voltages since the S/H is voltage controlled, but I don’t know what else to try.

 

[PJS]

Have you gone through the process of calibrating the trimpots?

 

[darwin999]

@Robusto -
Any chance you have a sufficiently large current draw that's loading down your voltage supply - either your external supply or the 1044?
1044's output voltages can shift noticeably even with 10mA current draw, and shift by ~1V for every ~25mA (very roughly).
Try measuring the current in the circuit to see if this is a possibility.