Please help me understand the WSG schematic

[dashbad]

Hi There,

I have done multiple searches but couldn't find what I was after. Apologies if this has been asked before.

I'm trying to understand the second part of the WSG circuit after all the oscillator outputs have been summed. Is the 741 just acting with the resistors and caps to form the filter or is there anything else going on here?

I am having an issue with my build where I am seeing the correct oscillator output signals but seeing nothing at the summing point marked 'ODD' on the schematic.

I can get a signal on the oscillator side of R2, R5, R21 and R22 - but I get no signal at all on the other side of these resistors. (I realise it is supposed to be attenuated but I see nothing. If I try to check the resistance of these resistors with the battery connected they appear to have infinite resistance yet when I remove the power I see the correct 1 MOhm for each one.

Can anyone help? It sounds like a short but I can't see any issue with the wiring or soldering? Could I have fried my 741 or caps? Would this cause this issue.

Would appreciate any help.

[slacker]

If you're getting nothing on the junction of C1 and R10 then it probably means you've got a short. Either R10 is shorted or the right hand side of C1 is shorted to ground. Try removing C1, as that takes everything to the right of it out of the equation which will make it easier to debug. Then see if you can get a signal on the junction of the 1M resistors and R10. I would double check the value of R10 as well just in case you've used a 100ohm or something by mistake.
Once you've got a signal at that point reconnect C1 and take it from there.

Posting the voltages on the LM741 would probably be helpful.

Welcome to the forum

[dashbad]

Thanks for the help - it's very useful.

I've established that the issue is not with the filter circuit. I've disconnected C1 and I'm having the same issue.

I double checked all the oscillator output pins and I'm getting the signal I expect though the zany frequency pot (R13) has to be turned up high in order to get an audible signal - this occurs for both voices though so am assuming it's deliberate. (I don't have a scope so I can't test a signal <45 hz or so)

In terms of DC voltages I see 4.2 V on all osc output pins and at the left hand side of the 1MOhm resistors. The chip is powered and grounded correctly. All resistor values are also correct. I see 17mV DC on the other side of the 1 MOhm - but no oscillator signal.

When power is applied to the circuit I measure the 1MOhm resistors as having an infinite resistance which I believe is a clue but I can't seem to work it out. I read R10 correctly regardless of whether the battery is attached.

Do you have any other ideas? I have had another once over of my panel wiring but nothing incorrect seems apparent.

Thanks

[RF]

[dashbad]

Ok - thanks. I've checked the pcb thoroughly and have cleaned it with alcohol to ensure there are no invisible

So I've managed to 'temporarily' resolve this by removing the grounded end of R10. With this flying free I get the summed oscillator output and my filter works fine. In fact - I get some pretty weird and wacky sounds from the output

As soon as a connect R10 to ground I get no osscilator signal at the ODD point again. This leads me to believe there is something wrong with my ground but everything else is working fine and I've checked all the connections again and again

What is R10 for....? Why not leave it unattached?

[RF]

[dashbad]

Yes. Well 989 Ohms to be precise