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CGS28 Bleed and channel mutes

CGS28 Bleed and channel mutes

2015-06-25 by spunraddish

This should be my last question here for a bit, seeing as I've got the other 15 or so PCBs working on their own; I've built up my sequential switch, and it has some funny behavior. The clocking is perfect and the state address is mostly correct, but hte default state is backwards, though that may just be a wiring mishap. The direction change and inhibit input work perfectly.

Here are the issues;
Channel 1 bleeds into channel 2.
Channel 2's input is muted.
Channel 3 bleeds into channel 4.
Channel 4 is muted.
Channel 5 is fine.
Channel 6 bleeds into all channels a bit, but opens with the occasional distortion.
Channel 7 bleeds a lot into all channels.
Channel 8 bleeds a bit into channel 7.
The reset input doesn't work.

I've already swapped out the 072 and the 4051 that does the multiplexing, to no effect. The 4051 is the same manufacturer as the original chip, which I believe to be TI. Some channels fire better when in reverse direction.

I am also running this on +/-12V; any ideas?

Thanks,
Eric


Re: CGS28 Bleed and channel mutes

2015-06-25 by Ken Stone

Start with checking the voltages to the power rails of the chip. Make sure the -0.6 is working (-0.7 V is acceptable).

Ken
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On Fri, Jun 26, 2015 at 2:39 AM, spunraddish@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:

This should be my last question here for a bit, seeing as I've got the other 15 or so PCBs working on their own; I've built up my sequential switch, and it has some funny behavior. The clocking is perfect and the state address is mostly correct, but hte default state is backwards, though that may just be a wiring mishap. The direction change and inhibit input work perfectly.


Here are the issues;
Channel 1 bleeds into channel 2.
Channel 2's input is muted.
Channel 3 bleeds into channel 4.
Channel 4 is muted.
Channel 5 is fine.
Channel 6 bleeds into all channels a bit, but opens with the occasional distortion.
Channel 7 bleeds a lot into all channels.
Channel 8 bleeds a bit into channel 7.
The reset input doesn't work.

I've already swapped out the 072 and the 4051 that does the multiplexing, to no effect. The 4051 is the same manufacturer as the original chip, which I believe to be TI. Some channels fire better when in reverse direction.

I am also running this on +/-12V; any ideas?

Thanks,
Eric





--
Ken Stone otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>

Re: CGS28 Bleed and channel mutes

2015-06-26 by spunraddish

Hi Ken,

I've checked the mutliplexing 4051; I found that power is at ~ +11.25V at pin 16, and pins 7 and 8 are at -.69V. Pin 6 is at a steady 1.35V. Is that alright?

Thanks,
Eric

Re: CGS28 Bleed and channel mutes

2015-06-26 by Ken Stone

16, 7 and 8 are fine. Anything below 5V is fine on pin 6 when the INH input is low. When the INH input goes high (i.e. gets a gate input), pin 6 will go to something over 7V (12V?). It's a digital input,so the exact voltage isn't important.
Make sure your diodes are not backwards.
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On Fri, Jun 26, 2015 at 12:36 PM, spunraddish@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:

Hi Ken,


I've checked the mutliplexing 4051; I found that power is at ~ +11.25V at pin 16, and pins 7 and 8 are at -.69V. Pin 6 is at a steady 1.35V. Is that alright?

Thanks,
Eric




--
Ken Stone otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>

Re: CGS28 Bleed and channel mutes

2015-06-26 by spunraddish

I checked all the diodes visually, cross-referencing the circuit diagram to make sure there were no mis-markings, and of course there weren't. I did a diode test on each, and they all came back normal for 4148s.
What would cause this to run backwards (8-1) when this is wired "correctly" (maybe not) and what would cause the reset to malfunction? Hm, maybe the 074 is busted - tomorrow is another day.

Thanks for the help,
Eric

Re: CGS28 Bleed and channel mutes

2015-06-26 by Ken Stone

People are too quick to blame the parts. Usually it is a construction error.
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On Fri, Jun 26, 2015 at 2:22 PM, spunraddish@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:

I checked all the diodes visually, cross-referencing the circuit diagram to make sure there were no mis-markings, and of course there weren't. I did a diode test on each, and they all came back normal for 4148s.

What would cause this to run backwards (8-1) when this is wired "correctly" (maybe not) and what would cause the reset to malfunction? Hm, maybe the 074 is busted - tomorrow is another day.

Thanks for the help,
Eric




--
Ken Stone otherunicorn@...
Modular Synth PCBs for sale <http://www.cgs.synth.net/>

Re: CGS28 Bleed and channel mutes

2015-06-26 by spunraddish

Yes, construction error indeed - I found that the diode of channel 6 was not connected due to a lifted trace via continuity test, so now I have no more bleed from distant channels.

The problems that are still there are that channel 2 and 4's inputs pass no signal, but accept full bleed from the previous channels (1,3).

Channel 5 distorts the signal, now channels 6, 7 and 8 are mostly muted, with 8 passing signal occasionally and bleeding to 7.

Still no reset.

I know now that there was likely nothing wrong with the 074s. In these last two problematic projects I used .1uf polypropylene caps that I thought would give superior clocking performance, perhaps these were a poor fit.

Thanks,
Eric

Re: CGS28 Bleed and channel mutes

2015-06-29 by spunraddish

More construction error - I found that pin 9 of the 4051 multiplexer had another lifted trace, so now all channels work with very minimal bleed, though it's still there. Now off to find what is hopefully the final error that is not allowing the reset to work.

Thanks again!
Eric

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