[sdiy] SOLVED RE: AX60 Voice Issue

[gregory zifcak]

To be honest, I don't fully understand the schematic, but I'm guessing the transistors are part of a muting circuit? I ended up just probing the signal flow at various points and narrowing it down that way. Bypassing TR2 restores normal behavior. I'd be curious to hear insight from someone who understands the circuit.
In other news, I took the opportunity to put a resistor in series with the resonance pot to limit the voltage to a range closer to what's recommended in the CEM3394 datasheet (2.5v vs. 4.13v). Now I get a very smooth response, with self-oscillation when the slider is at about 95%, instead of the typical 40%. Makes the synth feel much less angry. I got the idea from this analysis: http://www.youtube.com/watch?v=B5ikCDzhFRA


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>> Subject: Re: [sdiy] SOLVED RE: AX60 Voice Issue
>> From: tom at electricdruid.net
>> Date: Tue, 28 Aug 2012 20:42:54 +0100
>> CC: synth-diy at dropmix.xs4all.nl
>> To: zifcak at hotmail.com
>>
>> How's that work then?
>>
>> By which I mean; how does a blown transistor in the chorus circuit come to generate the symptoms you reported?
>>
>> (Just curious)
>>
>> Thanks,
>> Tom
>>
>> On 28 Aug 2012, at 18:57, gregory zifcak wrote:
>>
>>>
>>> blown transistor (TR2) on the chorus board.
>>>
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>>>> From: zifcak at hotmail.com
>>>> To: synth-diy at dropmix.xs4all.nl
>>>> Date: Mon, 27 Aug 2012 16:55:48 -0700
>>>> Subject: [sdiy] AX60 Voice Issue
>>>>
>>>>
>>>> Hey all,
>>>> Strange behavior from this AX60:
>>>> In split modes 2-4 and 4-2, all voices work. I can simultaneously hear 6 pitches when I hold 6 keys. the balance slider functions normally, mixing between the two patches.
>>>> In single mode and in split modes 6-0 and 0-6, only voices 5 and 6 are sounding. I can hear the other four faintly in the background. I have checked the CV going to the VCA, and it's a consistent 4v across all CEM3394s.
>>>> The signal paths for the mixed voices are split into two groups; 5 and 6, and 1 thru 4. What I don't understand is why all voices would be present in split modes but not in single mode.
>>>> Any ideas?
>>>> Service manual can be found here:http://manuals.fdiskc.com/flat/Akai%20AX-60%20Service%20Manual.pdf
>>>> Thanks in advance,Greg
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