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- I’m not sure if I’ll find the help I’m looking for here but I figure it’s worth a try. I have built a point to point modified muffin with tone tweq eq. I included the clipping mods, hpf, lpf, tone bypass and tone tweq and everything wirks great other than the tone tweq. When I switch off the bypass mode the only effect I get from the eq circuit is a volume drop from pin 2>1 of the tl072 corresponding with the 300k feedback resistor. When audio probing I get no change in tone anywhere within the circuit and the pots make no change. I have traced all my connections visually about a million times and gone over the schematic just as many times. I’m at a total loss and would love any advice you can give. Thanks guys
Not sure why I shrunk those pics. These are bigger
I can imagine the many hours you have already spent on this. Without a GPCB board to examine, I can only make these suggestions:
Use the schematic to verify every connection. Measure the power at every pin on the TL072 Use an audio probe to trace the signal into the TL072 and through each section of the opamp.
This was truly an ambitious endeavor. I hope you can see it through to success.
Thank you Wilkie. I’m getting 4.31 at pin 3 and 5 where the voltage divider comes in but I got .001 or something like that everywhere else. I’ve already replaced the chip once because I thought maybe I’d burned it. I have successfully used op amps with point to point in the past with no trouble as well as tons of transistors. What voltage should I be expecting?
By the way, pins 4 and 8 are clipped as the schematic shows no contact there.
Thanks again for any feedback that may help me get to the bottom of this.
I finally figured out my mistake. The op amp in the schematic doesn’t show pins 4 and 8 so I omitted them. I finally looked back at the power section and saw those numbers to +/- there. Eureka. Thank you.
As you’ll know Ollie
You definitely need pins 4 and 8 for power and ground
Just for future reference as you saw IC pins are usually shown in the power section of the schematic where you’ll see a small V- 4 and V+ 8 indicating dual op amp power pins obviously a small 4 and 7 and 4 and 11 for single and quad op amps
Definitely a silly thing to miss but now it won’t happen again. I’ve only recently started learning about the inner workings of op amps. The journey continues.
Did you miss the fact that Barry has the ToneTwEQ board on sale for only $1.85? That might have saved you a bunch of time adding it to your Muffn.
You must have the patience of Job. Happy to hear you worked it out! Great work!
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Not sure why I shrunk those pics. These are bigger
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