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the19thbear
Joined: Apr 19, 2007 Posts: 150 Location: denmark
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Posted: Fri Feb 22, 2013 1:10 am Post subject:
Jupiter 4 pitchbend problem |
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Basically i cant get the offset right, to do octaves pitchbend. No matter how i position the pitch bend sensitivity pot, i cant get the pitchbender IC to output (via Pin7) equal plus/minus voltages when moving the actual pitch bender knob to its two extreme settings.. Its always +2,5/-1,8 (just an example) and never, say, +2,5/-2,5. On the audio side of things, that means that i cant get a normal pitch one octave down/pitch one octave up, its always a perfect octave up, when i pitchbend to one side, and then less than an octave down when i pitch bend to the other side... I already change IC1, but no cigar. Could C1 and C2 be the problem?
The PSU is right and the pot is getting +/-15v.
Thanks! Last edited by the19thbear on Tue Feb 26, 2013 5:43 am; edited 2 times in total |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Fri Feb 22, 2013 11:26 am Post subject:
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I would assume it has to do with some interaction between the two sensitivity pots and the op amps up at the top, but I can't really make out the schematic very well. Do you have a larger size you can attach rather than putting in line? |
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bubzy
Joined: Oct 27, 2010 Posts: 594 Location: United Kingdom
Audio files: 64
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Posted: Sat Feb 23, 2013 1:22 am Post subject:
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have you tried buffering the "bend signal" before you split it out to the two trimmers before the op amps at the top? _________________ _Richard_ |
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the19thbear
Joined: Apr 19, 2007 Posts: 150 Location: denmark
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Posted: Sat Feb 23, 2013 2:37 pm Post subject:
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Thanks alot for suggestions. I reuploaded the image now.
The thing is, this circuit is showing the pitchebender schematics from a jupiter 4 that i am restoring, and it has worked earlier, i just cant seem to find out whats wrong. On the schematic you can see that you can select the pitch bend pot to modulate, VCF, VCA and VCO. Just ignore that part.. since the schematic is so simple i can only see that IC1 could be bad...
Here is what i have checked:
-Checked plus/minus 15v på IC1 -OK
-Checked plus/minus 15v on both sides of pitchbender pot. - OK
-swapped IC1: 4558- OK
-Check pins 7 på IC1 and see if i have equal plus/minus coming out when adjusting the bend sensitivity and pitchbending to either side= Impossible! (im guessing i have to get, for instance +5v when doing positive pitch bend and -5v when doing negative pitch bend in order to get an octave. - It changes when i vary the sense pot but its always offset wrong. A full octave up and say, half an octave down.
Any suggestions? Its just so dead simple that even I understand it... but it still doesnt work.
Thanks again! |
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bubzy
Joined: Oct 27, 2010 Posts: 594 Location: United Kingdom
Audio files: 64
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Sat Feb 23, 2013 5:24 pm Post subject:
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Is there a reasonable way to disconnect that pitchbend input and measure whether it is what you expect *before* you get to the pots up at the top?
I'd think if this worked once before that would be a good thing to know before modding the circuit. That said, i agree with Bubzy's circuit as a way to isolate the sections of the circuit.... |
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the19thbear
Joined: Apr 19, 2007 Posts: 150 Location: denmark
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Posted: Mon Feb 25, 2013 1:31 pm Post subject:
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Ok. I spent the last 2 hours trying to get at this thing...
As you can see from the original diagram, the 100k pot (the bender) is a dual thingy..
It has 4 terminals. Pitchbend up i can adjust via "bend sens" pot, and pitch bend down i can adjust via the screw inside the pitchbender (see attached picture).
The 2 pots influence/offset each other making it very hard to calibrate it.
I have been adjusting and adjusting for about an hour, but its impossible to get it to be completely equal. Sometimes it is, sometimes it isnt.. because of the mechanical part of the pitchbender (an old spring that determines the exact position where the pitchbender will snap back too.... And when i have adjusted the octaves to be 95% correct, i have to screw in another screw to hold the pitchbender in place, and that sets the whole thing off. ( because you have to hold the whole thing tight and that somehow offsets the calibration - again.. this is caused by moving parts - moving them tiny bits.
Will buffering in any way help with this? What IC would be good? Im a newbie when it comes to electronics, and i cant really see what it will help here. Or can i connect a pot somewhere around the buffer and do easy calibration from there? (after i have screwed in all screws etc - so i dont offset the whole thing - i'll just calibrate it afterwards via the new pot).
Is that possible? I would be more than happy with a 97% correct pitchbend - the last uncertain 3 percent will be caused by the old spring i think.
Thank you SO much!!!!!! |
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the19thbear
Joined: Apr 19, 2007 Posts: 150 Location: denmark
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Posted: Thu Feb 28, 2013 8:16 am Post subject:
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bump |
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the19thbear
Joined: Apr 19, 2007 Posts: 150 Location: denmark
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Posted: Mon Mar 04, 2013 9:59 pm Post subject:
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Anyone? |
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bubzy
Joined: Oct 27, 2010 Posts: 594 Location: United Kingdom
Audio files: 64
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Posted: Wed Mar 06, 2013 10:36 am Post subject:
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if its a resistance difference, you could find out what the difference is and pad one out with an additional resistor. although this isnt a perfect method, it may give you a more usable range. just a thought. additional buffering isnt going to do you much good, as if you have used the mod i suggested along with the original circuit, theres already enough buffering happening.
other than that, you may want to just try with a "normal" potentiometer, and see how you get on. _________________ _Richard_ |
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the19thbear
Joined: Apr 19, 2007 Posts: 150 Location: denmark
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Posted: Sat Mar 09, 2013 9:20 am Post subject:
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thanks alot! |
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