VRG CV

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welhamc
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VRG CV

Post by welhamc » Thu Jan 11, 2018 8:34 pm

Hi Muff

It appears that the down CV on my VRG isn't working as it should be... For instance with the VRG set to LFO mode and the up and down controls set to about equal so that the LED is nicely pulsing red and green, connecting an LFO to the DOWN CV input modulates the VRG's LFO output with modulation of the DOWN CV pot so that the LFO stutters between red and green before slowly lighting up on either colour. However this is not replicated with the UP CV controls when the LFO is connected to the UP CV jack.

Ive double checked the connections between the jacks and the PCB and theres no problems there - where else should I check for the culprit?

However I also noticed the arrow between UP CV and DOWN CV on the front panel - is what I described how the module should function normally? Ie is the UP and DOWN modulation linked - it seems like their jack connections are connected together on the main PCB

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Synthbuilder
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Re: VRG CV

Post by Synthbuilder » Fri Jan 12, 2018 4:26 am

welhamc wrote:... is the UP and DOWN modulation linked.
Yes. The DOWN CV input is normalised to the UP CV input. So any CV inserted into the UP CV input will also go to the DOWN CV input. Simply move the DOWN CV pot to its middle position if you wish to have no modulation of the down time.

Inserting a jack into the DOWN CV will override the normalised connection.

Tony

welhamc
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Post by welhamc » Fri Jan 12, 2018 12:12 pm

Thanks for the reply Tony - I suspected that they may be normalised together. Do you have any ideas on why the UP CV controls do not affect the VRGs output though? As I mentioned the DOWN CV controls work perfectly when a CV is inserted to the DOWN CV jack.

Since the UP and DOWN controls are normalised together a CV into the UP CV jack should also affect the DOWN of the VRG, but this isnt so on my unit - the CV into UP does not affect either CV pot. I have checked for continuity issues between the UP CV signal and NC tags and the main board but didn't find any problems.

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Synthbuilder
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Post by Synthbuilder » Fri Jan 12, 2018 3:49 pm

Have you checked continuity between the tip of the jack plug at the free end of an inserted patch cord and pin 3 of UPR on the main board? This will check whether the signal is getting from the patch cord to the VRG's circuitry. This can be broken when the tip connection socket is failing to mate properly with the inserted jack.

I'm not sure what else it could be if the signal is getting through from the DOWN CV socket but not from the normalised connection.

welhamc
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Post by welhamc » Fri Jan 12, 2018 6:46 pm

Yep I tried the connection between an inserted patch cord tip and pin 3 and there was no problem there - I may try swapping out the TL074 at U5 to see if thats the issue

welhamc
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Post by welhamc » Fri Jan 12, 2018 6:57 pm

Alas - swapping out the TL074 at U5 had no effect... Pretty stumped

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Post by Synthbuilder » Sat Jan 13, 2018 7:47 am

welhamc wrote:Alas - swapping out the TL074 at U5 had no effect...
I don't think it's that part of the circuit. You earlier mentioned that the UP CV has no effect on either the down speed or the up speed. This, along with the fact that the DOWN CV does work, suggests the signal isn't getting from the CV input to the main board properly.

Maybe it's getting to pin 3 but there's a break in the connection somewhere after that. Do you get continuity from pin 3 to pin 6 - both on the main board?

Have you got a scope?

Tony

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