Alpha/MKS left channel Chorus/BBD issue(w/ audio example)

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Overgear
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Gear: AX-73, S3000, MFC42, K5000R, K4r, K1, Nord 3R, MKS-50, Juno-106, JP-8000, CS-10, CS-15, TVS-1, PP SEM(x2), Rogue, Source, Pro-One, P-600, Mopho
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Alpha/MKS left channel Chorus/BBD issue(w/ audio example)

Post by Overgear » Tue Feb 23, 2010 6:58 am

My MKS-50 has a cycling/chirping noise in the left channel that is only present when the chorus is on. It appears to be the chorus lfo as it changes with the rate control...and, no, this isn't the typical Juno chorus hiss. I have seen(even here) other Alpha/MKS owners have this but I don't know if anyone has provided an audio example. So, here goes...

Example - I upped it 45db to make it clearly audible.

I messed with the rate for a couple of minutes but at about 20 seconds you can hear it at max/127. When it's going that fast, it creates a awful 10hz tone. Even at 80, if you play in the upper octaves, you will get a DC offset-10z tone. It kinda sounds like the lfo signal is overdriven in the left side

Has anyone had any experience with this or can tell from the audio where to check? I do have the service manual and I see the BBDs and associated circuits. I'm hoping for a nice little trimmer to adjust but I doubt it's gonna be that simple.

I have a track I really need it for that's got a lot of soft bits and the chirping is evident. Plus, I have to multitrack it - 3 times - because of polyphony. The chorus is essential to the sound. I've tried external choruses(including the CE-300) and it is just not the same. Any help would be greatly appreciated.

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Maschinengeist
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Re: Alpha/MKS left channel Chorus/BBD issue(w/ audio example)

Post by Maschinengeist » Wed Feb 24, 2010 5:01 am

Lemme check my service manual and I come back to you with possible hints.
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Overgear
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Posts: 111
Joined: Wed Sep 20, 2006 12:27 am
Gear: AX-73, S3000, MFC42, K5000R, K4r, K1, Nord 3R, MKS-50, Juno-106, JP-8000, CS-10, CS-15, TVS-1, PP SEM(x2), Rogue, Source, Pro-One, P-600, Mopho
Location: VA

Re: Alpha/MKS left channel Chorus/BBD issue(w/ audio example)

Post by Overgear » Wed Feb 24, 2010 6:09 am

Thanks!

Hoping everything is well with you, sir.

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