Transistor Superladder VCF Linear input

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terjewinther
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Transistor Superladder VCF Linear input

Post by terjewinther » Mon May 01, 2017 2:31 pm

I have the old Transistor Superladder filter, the triple-width panel, and a PCB from June 2004. The filter is working great and sounds good.

Should LIN CV input be able to handle negative CVs?
I ask because given a triangle LFO (positive and negative going) or an inverted envelope the filter gives off a clear thud when the CV input goes negative (both going from zero to negative and from negative to zero). Various settings of the lin CV input pot makes no difference, unless it is so low almost no CV comes through, of course.

All the other inputs handle negative CVs with no problem at all, and positive-going CVs in the LIN CV input works perfectly as expected.
I search the docs, but there was no mention of this, not anything to calibrate (the CV goes through an input pot anyway).

This has been my main filter for years, but I have never used the lin CV with negative CVs before, so it is only now that I discover this.

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Synthbuilder
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Re: Transistor Superladder VCF Linear input

Post by Synthbuilder » Mon May 01, 2017 2:51 pm

terjewinther wrote:Should LIN CV input be able to handle negative CVs?
Only partly. Any LIN CV more negative than -2V will stop the filter dead. :deadbanana:

Tony

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Re: Transistor Superladder VCF Linear input

Post by Synthbuilder » Mon May 01, 2017 2:56 pm

terjewinther wrote:Various settings of the lin CV input pot makes no difference, unless it is so low almost no CV comes through, of course.
But reading that does suggest that R82 is the wrong value. It should be 100K. Which means that -2V would indeed stop the audio from the filter but only if the LIN CV pot was up full. At half way point it would need around -4V to kill it. If any negative voltage is killing the audio then R82 would have to be very low.

Tony

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terjewinther
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Re: Transistor Superladder VCF Linear input

Post by terjewinther » Tue May 02, 2017 2:44 pm

Synthbuilder wrote:
terjewinther wrote:Should LIN CV input be able to handle negative CVs?
Only partly. Any LIN CV more negative than -2V will stop the filter dead. :deadbanana:

Tony
Aha! OK, will have to check that. If that is indeed the case, then it is working properly.

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terjewinther
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Re: Transistor Superladder VCF Linear input

Post by terjewinther » Sun May 07, 2017 12:52 pm

Synthbuilder wrote:
terjewinther wrote:Should LIN CV input be able to handle negative CVs?
Only partly. Any LIN CV more negative than -2V will stop the filter dead. :deadbanana:

Tony
You are so right! Tested it today, and indeed anything lower than -2V and the filter is completely silent. Thanks!

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