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JoeMorris
Joined: Apr 26, 2009
Posts: 161
Location: Brighton
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 Posted: Tue Jan 05, 2010 8:03 pm Post subject:
Please help poor rookie with ADSR headaches! |
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Hi all,
I've built a couple of MFOS ADSRs as part of an all-in-one semi-modular +/- 15v synth setup, of which I have the midi interface & oscillators up and running so far, and I can't get EITHER of them to work! I've been looking at them all day, and it's driving me slightly bonkers, so I thought I'd see if anyone could help... long shot, but you never know..
I'm tracing a gate signal all the way up to the TL082 U-1a pin 3, but don't really get the deal after that (I'm still learning)... I've checked all the parts and soldering and all looks fine to me, with both boards the same too (of course there could be a mistake i've duplicated and haven't noticed, but I have checked thoroughly). . but I get no output whatsoever on the output jack no matter what settings I twiddle.
Has anyone else come across any problems in their adsr assembly that might at least give me a starting point as something that could have gone wrong?
Any ideas extraordinarily welcome.
thanks
Joe |
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RF
Joined: Mar 23, 2007
Posts: 1502
Location: Northern Minnesota, USA
Audio files: 28
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| Posted: Wed Jan 06, 2010 11:29 am Post subject:
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Can I assume you are building on the PC boards Ray sells?
The TL084 (U5) is oriented different from all the other IC's - check that..
Check the output jacks for correct wiring... same for all the pots and switches.
Check for proper voltage, (plus and minus) on each IC.
Do you get any output when you use the manual gate button?
Start with those - and we'll go from there...
Good luck!
bruce
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"I want to make these sounds that go wooo-wooo-ah-woo-woo.”
(Herb Deutsch to Bob Moog ~1963) |
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JoeMorris
Joined: Apr 26, 2009
Posts: 161
Location: Brighton
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| Posted: Wed Jan 06, 2010 2:52 pm Post subject:
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| Quote: | Can I assume you are building on the PC boards Ray sells?
The TL084 (U5) is oriented different from all the other IC's - check that..
Check the output jacks for correct wiring... same for all the pots and switches.
Check for proper voltage, (plus and minus) on each IC.
Do you get any output when you use the manual gate button?
Start with those - and we'll go from there...
Good luck!
bruce
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Thanks ever so much for your reply bruce. After a few more hours troubleshooting I'm still not getting to the root of the problem.
I have checked the TL084 orientaton - that is fine (I am using a TL074 which i gather is fine?).
I have meticulously double checked every component value and orientation and touched up all the solder points wth a brief tip of the soldering iron just in case of bad joints.
I have double checked all of the off board connections - all fine.
I have checked all the power rails on the chips and they are all getting power as per the schematic. (+15v/-15v for the opamps, +15v for everything else)...
The one development I have had - i hadnt added the manual gate before, now i've added one and it DOES trigger the envelope! So at least I know that the envelope itself works. It just isn't being triggered by the gate or trigger inputs for some reason. One thng i did notice, is that when i measure the gate signal voltage at the tip of the jack from the MIDI interface itself when it isn't plugged in I get a 5v signal, but when i plug it in to the socket and measure the tip solder lug, or the gate node on the board, I only get a 2.3v signal. I don't know if this is relevant.
So I'm basically at my wit's end here, with such a simple pcb! doesn't seem fair.
Could i have some duff chips?
joe |
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RF
Joined: Mar 23, 2007
Posts: 1502
Location: Northern Minnesota, USA
Audio files: 28
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| Posted: Wed Jan 06, 2010 3:55 pm Post subject:
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Hi Joe -
Try a higher voltage gate.
I think this needs just over 2 volts gate level - and you are pretty close to that...
Next - try a trigger input..anything?
If that's not it, check the components just to the right or below U1a on the schematic. Hang in there - you'll find the problem.
bruce
_________________
www.sdiy.org/rfeng
"I want to make these sounds that go wooo-wooo-ah-woo-woo.”
(Herb Deutsch to Bob Moog ~1963) |
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RF
Joined: Mar 23, 2007
Posts: 1502
Location: Northern Minnesota, USA
Audio files: 28
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| Posted: Wed Jan 06, 2010 4:05 pm Post subject:
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Gate voltage level.
I just checked on of my MFOS ADSR's - and it took just a skosh under 2.5 volts to trigger it.
bruce
_________________
www.sdiy.org/rfeng
"I want to make these sounds that go wooo-wooo-ah-woo-woo.”
(Herb Deutsch to Bob Moog ~1963) |
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JoeMorris
Joined: Apr 26, 2009
Posts: 161
Location: Brighton
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| Posted: Wed Jan 06, 2010 4:15 pm Post subject:
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ok one step forward at least - so i tried it with a trigger output from my drum pads and that worked...! so the trigger in does appear to work.
but i just dont understand for the life of me why the gate output doesnt work...
my midi gate output is 5v which should be more than enough, but as i say for some reason it drops to just over 2v by the time it reaches the pcb, anyone got any bright ideas why that could be... could be something to do with my problem i guess.... |
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JoeMorris
Joined: Apr 26, 2009
Posts: 161
Location: Brighton
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| Posted: Wed Jan 06, 2010 4:17 pm Post subject:
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| sorry just saw your message - wonder why my gate voltage is dropping so much before it hits the board then? |
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RF
Joined: Mar 23, 2007
Posts: 1502
Location: Northern Minnesota, USA
Audio files: 28
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JoeMorris
Joined: Apr 26, 2009
Posts: 161
Location: Brighton
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| Posted: Thu Jan 07, 2010 7:33 am Post subject:
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Thanks a lot for all your help RF -
My midi interface - an Oakley MidiDAC - actually has a mod option to increase gate output from 5v to 15v - and this seems to work fine now! still surprised the 5v out isn't enough to trigger it, but it works, and that's all that matters!
Unfortunately it's a case of two steps forward one step back, as the v/oct driver on my oscillators seems to have gone down - unconnected i'm sure... but always seems to be the case!
Still, the envelope is running which is fantastic! cheers. |
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