VCLFO - All working apart from sine output

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mumblinstevedubya
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VCLFO - All working apart from sine output

Post by mumblinstevedubya » Sat Feb 02, 2013 7:19 am

Greetings all!

Just got the VCLFO up and running with everything working apart from the Sine output.

Have check all connections and nothing obvious. :hmm:

Any help appreciated please

Thanks

Steve

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Synthbuilder
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Post by Synthbuilder » Tue Feb 05, 2013 5:29 am

Have you got a 'scope?

If so check pin 7 of U2. That should also be the sinewave output. If it is then the output is either broken somewhere or shorted.

What's the voltage, with respect to ground, at pin 2 and 13 of the THAT340? It should be zero on both. If not check the resistor values of R45 and R51.

Tony

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mumblinstevedubya
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Post by mumblinstevedubya » Tue Feb 05, 2013 7:21 am

Thanks for the reply Tony.

I will check this out when I get home.

I have a scope but no probes at the moment :bang:
Is there another measurement I can take on U2?

Thanks

Steve

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Synthbuilder
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Post by Synthbuilder » Tue Feb 05, 2013 10:19 am

mumblinstevedubya wrote:Is there another measurement I can take on U2?
Not really because it should be an AC signal there. You could just check that the output of U2 is not at one of the rails, ie. approx 13V or -13V. That would indicate a problem with either the op-amp, the THAT340 or the resistor values around the THAT340. Or a solder short somewhere around there.

It's always a worth a quick measure of resistance from the output socket's signal lug to its earth lug. Do this with the power off. If it's a short, ie. less than 10R, that will be your problem.

Tony

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mumblinstevedubya
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Post by mumblinstevedubya » Tue Feb 05, 2013 2:32 pm

Problem solved.

2 x 20k resistors had unsoldered themselves from the board and jumped back into my parts draw.

Or maybe I just neglected to put them in..............

:oops:

Thanks for help

Steve

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