Alpha Juno 2 VERY noisy chorus needs repair help - diyAudio
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Old 24th November 2010, 02:06 PM   #1
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Default Alpha Juno 2 VERY noisy chorus needs repair help

Recently i bought this unit cheap knowing a few things needed repairing (skippy dial fixed by resetting the synth, uneven velocity fixed by cleaning, presumably weak battery but works ok) .
All of them fixed easy but I created a new one:
A noisy chorus circuit!

The noise can be described as digital noise/silence shaped with a square wave 50% / 50% timeframe (drrrrrt / silence / drrrrt / silence...). The noise increases with CSR RATE, but goes away if bellow ca 70 value.
If I sett CSR RATE value low, play a note and increase CSR RATE it plays correctly. But if i play a new note with the now high setting it will distort the sound.

VCF and VCA LFO is not touched by this error.

The unit is fairly clean and shows no obvious signs of shorts or defect parts.

Any help here?

I have the 20 page service manual available if requested.
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Old 24th November 2010, 04:07 PM   #2
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Join Date: Nov 2004
Location: NCR
hi there trondl,
my initial response was going to be check the connections, clean the potentiometers, but I see you've already done that.
I am starting to wonder if maybe it's a capacitor problem, an old electrolytic might be leaky, something like that.

You know what? post this on in the geekslutz forum. I think you'll have a good time there and better luck.


Trans-directional-servo-logamp non-zerocrossing autogain compressing thingamajig
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Old 24th November 2010, 06:37 PM   #3
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thanks gain-wire.
now posted on gearslutz
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Old 25th November 2010, 08:44 AM   #4
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
If the chorus is adding this, get the scope on it. Chorus is generated in a variety of ways, but it involved phase shifting. SO if there is a bad stage in a bucket brogadee, or whatever, it should be visible. What does this distortion look like on a screen?
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Old 25th November 2010, 01:39 PM   #5
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Don't have access to a scope but this is how it sounds on CSR RATE: 127 and dropping towards 0 value after 5 seconds. Note that this is recorded at very high volume and is not very audible when played at normal levels.
Attached Files
File Type: zip ju2 chorus noise csr rate (274.6 KB, 3 views)
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Old 10th December 2010, 03:00 AM   #6
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Location: Texas
Have you ever heard any effect that was NOT noisy? By noisy I mean compared to having nothing between the instrument and the amp. If you have I would like to buy it.
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