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 Forum index » DIY Hardware and Software » YuSynth
ADSR V2 Sustain Always High
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Sebo



Joined: Apr 27, 2007
Posts: 542
Location: Argentina

PostPosted: Thu Jan 03, 2013 6:55 am    Post subject: ADSR V2 Sustain Always High Reply with quote  Mark this post and the followings unread

Hi:
I recently build my second ADSR V2, the first worked OK, but this one have some trouble. Attack and Release works OK, but sustain is always high no matter the position of the pot.
I measured the gate after Q2 and is OK, but the signal after Q3 is not right, if I understood right it should be a pulse/trigger, but I'm meassuring a constant high signal with some sporadic very narrow pulses going to 0V.
I changed Q3, C4 and R10 with no luck, looked for shorts or breaks, but everything seems OK.
I tought to try a smaller cap (1nF), but I don't know why isn't working as it should.

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yusynth



Joined: Nov 24, 2005
Posts: 1250
Location: France

PostPosted: Thu Jan 03, 2013 12:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

The behaviour you describe is normal, the signal at the collector of Q3 must be high with no gate and briefly go to 0V at the beginning of the GATE. The 555 is triggered by a falling edge.
Try and change the 555 that may be defective.

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Sebo



Joined: Apr 27, 2007
Posts: 542
Location: Argentina

PostPosted: Thu Jan 03, 2013 3:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've already changed the 7555 (2 times) and didn't help.
I found another suspicious behaviour:
The output is very low about 3V (I'm not sure but at the begining of my test I think it was 10V, but I'm not sure).
The voltage between R12 y P4 is changing with the gate, also the Voltage at the other side of R12, that is conected to +15 is changing a little, I can't found any shorts or anything that justifies that.

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Sebo



Joined: Apr 27, 2007
Posts: 542
Location: Argentina

PostPosted: Thu Jan 03, 2013 5:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Yves:
I found the problem, it was a short in the TL074 (in the LED circuit). It was har to find because was a short inside the socket.
Thanks a lot for the help.

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Blue Hell
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Joined: Apr 03, 2004
Posts: 20992
Location: The Netherlands, Enschede
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PostPosted: Thu Jan 03, 2013 6:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

I love these detective stories Cool

(Especially when they have a happy ending)

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yusynth



Joined: Nov 24, 2005
Posts: 1250
Location: France

PostPosted: Fri Jan 04, 2013 12:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Short in the socket, gee that was not an easy one to find Sebo !
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Sebo



Joined: Apr 27, 2007
Posts: 542
Location: Argentina

PostPosted: Fri Jan 04, 2013 7:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, and it was my fault, a little piece of copper from a multicore wire fall inside the socket, and when I inserted the chip gets trapped inside, I saw it by chance...
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Rolbista



Joined: Nov 17, 2012
Posts: 23
Location: Poland

PostPosted: Sun Jan 04, 2015 8:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi, I see this thread is now 2 years old, but I seem to have similar problem - attack and release work fine but decay and sustain are always at max no matter the settings (actually I don't know about the decay part because I can't hear it with sustain always up. Anyway, ADSR seems to work ok when I touch pin 5 on the 555. Also, someone on the Muff Wiggler also encountered this type of fault, here are the findings: (i hope he doesn't mind)

"That's what I thought at first. I have it in a socket. But I pushed it and pulled it and scooched it around to get it to seat properly in the socket and the pressure and the movement didn't work. It only worked when I actually touched pin 5. Orrr touched both of the leads from the cap. But it didn't work if I just shorted pin 5 to ground. I reworked the joints for the socket and for the cap and I still got the same thing. I changed the value of the cap and it was still the same.

It was something about my resistance to ground was the only thing I could figger...

I clipped a resistor to the leads from the cap and Voila! It worked! I tried a few different values and soldered it on and it works great hmmm.....

I'm not sure why. Maybe has something to do with a long power lead and the cap discharging... That's just a guess hihi It's the only thing I can think of It's peanut butter jelly time! "

Any ideas how to fix it? I mean there is no additional resistor at this point in the circuit.

*EDIT* Well, I soldered a 470K resistor in parallel to the cap beetween pin 5 of the 555 and ground and now everything works like it should, although I have a feeling that this resistor affected the Decay's pot action a little bit
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