Need some help with Diezel VH 4

[whomeno]

Built from this Vero. I have sound ,every thing seems to work fine except when I'm not playing I'm getting squealing if I turn gain above 7. I used sheilded wire for in put and out put. I checked for bridges between the traces all parts placement. do not know what to look for now





Schematic





My board









Voltages 12 v in
7660S
1- 10.55
2-5.27
3-1.5mV
4-4.9
5-  -10
6-1.69
7-7.14
8-10.59

2134
1-1.3mV
2-1.4mV
3-1.4mV
4-9.88
5-.3mV
6-.3mV
7-.3mV
8-10.41
TL074
1-.9mV
2-1.1mV
3-.1mV
4-10.41
5-2.5mV
6-34.8mV
7-37.8mV
9-8.77
10-1.3mV
11-9.88
12-1.2mV
13-.4mV
14-.4mV

[ElectricDruid]

The TL074 has got no proper negative power. That's the first thing that leaps out. Pin 11 (-ve supply) is virtually the same as pin 4 (+ve supply).

[whomeno]

what should the -ve be?

[antonis]

what should the -ve be?

Pin 11 (-ve supply) is virtually the same as pin 4 (+ve supply).

[whomeno]

I traced the -v from 7660s to the 74 pin 11
7660s pin 5 is -10.05 the 74 pin 11 is -9.89
is this the right voltage?
voltage in is 12v

[whomeno]

rechecked all resistors, caps, links placement. why would i be getting the wrong -V

[antonis]

You should use a LM2940CT-10 (not 12) for 12V IN..!!
(you do need at least 1.5V dropout voltage for regulator good working state..)

As it is, you get UNREGULATED 10.59VDC on pin 8..
(meaning that in any case of IN power dip or load increase you'll get respective voltage dip..)

e.g. Supposing 12V IN and 10.6V OUT, dropout voltage is 1.4V..
For 11.8V IN, OUT voltage will be 10.4V..

[whomeno]

would it help to run it at 18v in

[antonis]

Any power higher than 13.6V (up to 26V) should be fine..

https://www.ti.com/lit/ds/symlink/lm2940-n.pdf?ts=1689934046970

edit: I presume layout designer should have a 9V or 10V regulator in mind when setting IN supply to +12/18V..

[whomeno]

ok 18 in at 74 pin 11 -11.56  pin 4 12.05 it did not seem to make a differance

[antonis]

it did not seem to make a differance

You mean, it keeps squealing..??

If so, plz post a more crisp schematic of your particular layout..!!

[whomeno]

that made it worse going to 18 v now I can't get to 6 before I could get to 7

[whomeno]

It goes through a 10R resistor. could I change that to get it

[ElectricDruid]

ok 18 in at 74 pin 11 -11.56  pin 4 12.05 it did not seem to make a differance

That seems better to me. Now you've got the positive supply properly regulated, and the 7660 which is generating the negative supply is clearly working too. We'd expect slightly less than 12V on the negative because those voltage multiplier chips aren't 100% efficient, so -11.5V from +12V is about right. So that's all good.

The new schematic is a huge improvement, so thanks. The other one was too small to read.

What are the remaining problems?

[antonis]

If so, replace LM2940 with a 5V regulator and walk in peace..

More seriously now, verify no external interference..
If squealing persists, start to raise the values of NFB caps..
(C6, C13 and definitely C10..!!)

P.S.
Could we see some pics of your build..??
(wiring included 'cause it might be the main suspect and duck_arse will slap our hands at any minute..)

[whomeno]

I took c 10 47pf out and put in a 100pf. no noise at all now. thanks

[blackieNYC]

What does the 110k resistor across the crossover/gate(?) diodes do?  Partial signal bypass or a blend? Does it make the shutoff a little less abrupt?