[sdiy] MN3007 Chorus Acting Weird

[Richie Burnett]

Try testing it with a sawtooth or square waveform.  With just a sinewave you 
can only really get amplitude modulation, especially if the test tone is 
quite a low pitch.  And that could sound like panning if you alternately get 
constructive interference on one side and destructive on the other side of 
the stereo image.  With a bright saw or squarewave at a decent pitch you 
should be able to hear some periodic detuning or at least some "phasing" 
between the dry and the chorused waveform edges.

-Richie,



-----Original Message----- 
From: Jacob Watters via Synth-diy
Sent: Saturday, February 15, 2025 9:35 PM
To: Richie Burnett
Cc: SDIY
Subject: Re: [sdiy] MN3007 Chorus Acting Weird


I am testing it with a sine wave from a signal generator. When I look at a 
scope, I only see vertical movement. When I listen with my ears, I only hear 
panning.

I found this photo of the service manual. It's difficult to read the exact 
values, but maybe someone familiar with the IC will be able to tell how it 
should be functioning. The BBD part is in the rectangle at the bottom with 
the "DC 1/2" label.

https://rvb-img.reverb.com/image/upload/s--wzg-Dhdj--/f_auto,t_supersize/v1669410662/zuo0v17w68dkc6c0n99s.jpg

Jacob Watters
JacobWatters.com



On Sat, Feb 15, 2025 at 4:28 PM Richie Burnett 
<rburnett at richieburnett.co.uk> wrote:
What input signal are you testing it with?

-Richie,


-----Original Message----- 
From: Jacob Watters via Synth-diy
Sent: Saturday, February 15, 2025 9:17 PM
To: SDIY
Subject: [sdiy] MN3007 Chorus Acting Weird


I am repairing a Yamaha KM602 mixer, which has a builtin MN3007 circuit. The
chorus circuit behaves a bit odd. Instead of being a modulated delay that
causes a pitch shift, it seems to behave like an auto-pan circuit. The sound
level increases on one side, while decreasing on the other, and alternates
back and forth. It is labelled as CHORUS on the front panel, so that is not
the behavior that I expected.

Is this normal, or is something wrong with the circuit?

I tried finding a pdf of the service manual online, but I was unsuccessful.
Does anyone have the service manual and can provide some input as to how the
circuit should work?


Thanks for your help!

Best regards,

Jacob Watters
JacobWatters.com





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