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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Delayed Modulation, with no release.
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Europanaut



Joined: Apr 04, 2014
Posts: 46
Location: Nanaimo, BC, Canada

PostPosted: Sun Mar 29, 2015 12:42 am    Post subject: Delayed Modulation, with no release. Reply with quote  Mark this post and the followings unread

Hello!

After many successful MFOS builds in a row (thanks to Ray's great documentation, not due to my barely-adequate skill level), I've come across an anomaly.

I've just finished the Delayed Modulation Module. The modulation part works great, and the gate/trig attack seems fine so far, but the release doesn't work at all. I'm triggering from a J-wire keyboard, using Ray's single-buss keyboard circuit (which works well with my other envelope gens).

I've tried both gate and trigger, but once the modulation starts, it won't stop.

I'm running 15v, and have implemented the appropriate changes to the circuit, as described on Ray's site.

Any suggestions on where to start my troubleshooting process, or what the likely culprit might be?

Thanks!
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Skrog Productions



Joined: Jan 07, 2009
Posts: 904
Location: Scottish Borders
Audio files: 103

PostPosted: Sun Mar 29, 2015 6:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Smile

Do the usual visual checks at the wiring around the pots area & pcb circuit soldering points in that area too , also check the zener diodes are keeping the A/R levels around + & - 5V with your multimeter.

Although I have this pcb ... I've not built it yet (hoping to build soon on my 12V system)


Dave.

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Europanaut



Joined: Apr 04, 2014
Posts: 46
Location: Nanaimo, BC, Canada

PostPosted: Sun Mar 29, 2015 3:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Dave,

I've measured Z1 and Z2.

At the striped end (cathode?) Z1 is showing -.78v. The other end is showing -5.74v.

At the striped end of Z2, I'm getting -.78v. The other end is showing 0v.


What should I be expecting from these test points?


Thanks again!
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Europanaut



Joined: Apr 04, 2014
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Location: Nanaimo, BC, Canada

PostPosted: Sun Mar 29, 2015 8:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, the plot thickens.

The module DOES appear to be working correctly. Sort of.

I measured the gate voltage, at the Gate In of the module, when receiving gate voltage from the keyboard (which works fine on everything else), and I've made some interesting observations.

Gate in from keyboard - no key pressed: -1.32v
Press key: +12.75v, modulation starts.
Release key: -1.27v, modulation does not stop.
Remove cable from module: -13.25, modulation stops.

When modulation starts and stops, all attack and release functionality works 100%.

So the module CAN work properly, but is not "releasing" unless I physically unplug the cable.

The same results occur if I run it from the gate out on the sequencer. It's like the module needs to be pulled down at zero, rather than requiring -12v.

Again, any suggestions?
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elmegil



Joined: Mar 20, 2012
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PostPosted: Sun Mar 29, 2015 9:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

So first of all, those voltages sound totally normal. When you have a keyboard plugged in, generating no gate, it's holding that point at ground. So you have ground then 10k then 200k, then -15V. 1/20 * -15V = -.75V if everything is perfect. You're pretty close to that, within tolerance of your resistors and your supply voltage, I'm guessing.

This is the second time recently I have been reading about Ray's EGs not cutting off when an actual signal source is plugged into them, and it's the same basic circuit in this case. The other one was a SL Mk II -- more inputs, but the same structure with the FET and NPN.

Honestly, my bet is the FET. A 2N5457 is supposed to cut off entirely at -0.5V, and you're getting lower than that (at least I think so; you should measure at the junction between the 10K and 200K resistors, which is also the gate of the FET).
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Europanaut



Joined: Apr 04, 2014
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Location: Nanaimo, BC, Canada

PostPosted: Sun Mar 29, 2015 9:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks elmegil.

I get 15v at the G of the 5457, with no gate signal applied.

Being new to this, what should I expect at that test point?
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elmegil



Joined: Mar 20, 2012
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PostPosted: Mon Mar 30, 2015 6:56 am    Post subject: Reply with quote  Mark this post and the followings unread

If you have a ground signal at the jack, you should have -.75V or so at the gate of the FET, I believe. I don't have one to validate that.
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Europanaut



Joined: Apr 04, 2014
Posts: 46
Location: Nanaimo, BC, Canada

PostPosted: Tue Mar 31, 2015 7:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:


Honestly, my bet is the FET.



Just tried a quick 5457 replacement. No change.
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Europanaut



Joined: Apr 04, 2014
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Location: Nanaimo, BC, Canada

PostPosted: Wed Apr 01, 2015 12:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks to help from Ray, I swapped R2 for a 120k, and it's working. As I work through the calibration, I'll report back if there are any further changes to the circuit.
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Europanaut



Joined: Apr 04, 2014
Posts: 46
Location: Nanaimo, BC, Canada

PostPosted: Wed Apr 01, 2015 1:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Here's the output of Mod Out, set to sine, low range.

Does it seem a bit messy? I have nothing to compare to, so maybe this is normal?


Posted Image, might have been reduced in size. Click Image to view fullscreen.
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