PRE CR (EQ, Dist preamp) by FEEDBACK [Pcb update]

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jschussler
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Post by jschussler » Sat Nov 16, 2019 12:04 pm

Hmm. Now I have power over the entire board, but at pin 4 of the two IC sockets it's reading 23v. Don't really understand how I can have more than 12v there....

And needless to say, the module's not passing audio at this point.

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jschussler
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Post by jschussler » Sat Nov 16, 2019 6:02 pm

Ok. Bad power supply.

New power supply, and I have 11v at the correct places on the ICs. Now I'm really puzzled at the lack of output.

How would I know if the ICs were fried?

(Sorry, I'm a noob at this)

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Post by jschussler » Fri Dec 06, 2019 1:48 am

Took some readings from around the board, here's what I'm seeing:

Image

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jschussler
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Post by jschussler » Fri Dec 06, 2019 1:59 am

Interesting tidbit: I swapped the ICs because I wasn't getting any output from the bottom one. It clearly has volts on the ins, but nothing on any other pins. The top one does have volts on the outs as you can see.

Swapping made no difference (the bottom IC in the top position does output volts, so it seems fine), so it's not a problem with the ICs. I'm trying now to figure out why the bottom IC could get power but not output anything....

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Post by strat-1 » Fri Dec 06, 2019 2:31 pm

jschussler wrote: I'm trying now to figure out why the bottom IC could get power but not output anything....
Do you have an oscilloscope ? I think you will not find the solution only with voltage measurements.

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Post by jschussler » Sat Dec 07, 2019 2:18 am

strat-1 wrote:
jschussler wrote: I'm trying now to figure out why the bottom IC could get power but not output anything....
Do you have an oscilloscope ? I think you will not find the solution only with voltage measurements.
I do, yes. What should I be looking for?

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Post by strat-1 » Sat Dec 07, 2019 3:19 am

jschussler wrote: I do, yes. What should I be looking for?
Probe the pin1 of U1 for us to see if you have signal passing through the transistors.

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jschussler
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Post by jschussler » Sat Dec 07, 2019 8:18 pm

Should I probe with just the bottom board connected to power, or with the entire module assembled and signal patched to the Input?

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Post by SphericalSound » Sat Dec 07, 2019 10:25 pm

With both assembled and connected and some signal patched too

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Post by EATyourGUITAR » Sat Dec 07, 2019 11:54 pm

take an output from a VCO and patch that to an input while everything is turned on. then you need to probe around the PCB with the jack tip on a patch cable with the other end going to your outs module or your attenuator or your mixer, headphone amp etc... you should be able to probe the module input before the first semiconductor. you should hear the VCO. then follow it in and out of the opamp. follow the signal path till it stops and you hear silence or low volume from an opamp output. where the signal can not pass will indicate the failed semiconductor.
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Post by strat-1 » Sun Dec 08, 2019 10:11 am

jschussler wrote:Should I probe with just the bottom board connected to power, or with the entire module assembled and signal patched to the Input?
Feed a 3Vpp (voltage peak-peak) 440Hz Saw into the input.
This circuit have high gain at input, so feeding a 8Vpp or 10Vpp signal at input, will overload the input to the op-amp. In this case you will not have a nice saw on the oscilloscope.

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jschussler
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Post by jschussler » Sun Dec 15, 2019 10:33 pm

(Sigh)

Found the problem. Not a component issue, though:

- There's a jumper at the very bottom of the board. Isn't discussed in the build guide, but it's shown in the picture of the module on page 13, so I put it in and installed the jumper.

Turns out, doing that cuts off any sound output. Take off the jumper, all is well.

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Post by strat-1 » Tue Dec 17, 2019 1:54 pm

jschussler wrote:(Sigh)

Found the problem. Not a component issue, though:

- There's a jumper at the very bottom of the board. Isn't discussed in the build guide, but it's shown in the picture of the module on page 13, so I put it in and installed the jumper.

Turns out, doing that cuts off any sound output. Take off the jumper, all is well.
That is not a jumper it is an alternative output on the back of the board.
If you install a jumper there you short the signal to the ground.

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Post by jschussler » Wed Dec 18, 2019 1:00 am

Ah. You may want to add a note about that in the instructions so future assemblers can learn from my mistake....

It sounds excellent, btw. Really happy with this, the BK, and the Chorus....

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Re: PRE CR (EQ, Dist preamp) by FEEDBACK [Pcb update]

Post by wavejumperr » Mon Feb 10, 2020 3:59 am

Any word on when this will be back in stock?
wigglers are a modular synth's way of making another modular synth

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