[sdiy] MN3007 Chorus Acting Weird

[Loscha]

I have the service manual with schematic.

https://drive.google.com/file/d/1pAKfI1DnXV6J5OV2YnYM8utkCj2drDS1/view?usp=sharing

On Sun, 16 Feb 2025 at 10:07, Jacob Watters via Synth-diy <
synth-diy at synth-diy.org> wrote:

> That makes sense. I didn't even consider phasing.
>
> Thanks again!
>
> *Jacob Watters*
> JacobWatters.com <http://jacobwatters.com/>
>
>
> On Sat, Feb 15, 2025 at 5:44 PM Richie Burnett <
> rburnett at richieburnett.co.uk> wrote:
>
>> A sinewave mixed with a time-delayed (phase-shifted) sinewave just
>> results
>> in another sinewave with different amplitude and phase.  So you mostly
>> just
>> perceive a variation in the intensity (volume) as you get
>> constructive/destructive interference between the dry and delayed signal
>> at
>> that one frequency.
>>
>> If you fire a saw or square into the Chorus effect there's a rich
>> spectrum
>> of harmonics and you hear that lush "swooshing" chorus effect as you get
>> constructive & destructive interference at all of the harmonic
>> frequencies
>> at different times during the periodic sweeping delay.  The movement in
>> the
>> resulting spectrum is much more complex and interesting to the ear.
>>
>> The delay time in cheap BBD chorus effects is also typically only 5ms or
>> thereabouts, so you need a reasonably high pitch input signal before you
>> get
>> much "beating" at the actual fundamental frequency of the note.
>>
>> -Richie,
>>
>>
>>
>> -----Original Message-----
>> From: Jacob Watters
>> Sent: Saturday, February 15, 2025 10:16 PM
>> To: Richie Burnett
>> Cc: SDIY
>> Subject: Re: [sdiy] MN3007 Chorus Acting Weird
>>
>>
>> You were correct! I used a square wave, and I could immediately hear a
>> normal chorus effect. I checked the scope, and I could see left and right
>> movement.
>>
>> I am curious to learn more - is this because the BBD circuit works on a
>> limited frequency range, and a low frequency sine is outside of that
>> range,
>> but the harmonics in a square wave are within the range? This would
>> explain
>> some of the unique character that people say a BBD has.
>>
>> Thank you so much!
>>
>> I am going to swap the rate trimpot for a panel mounted pot, and then
>> this
>> thing is ready to use :)
>>
>> Best regards,
>>
>> Jacob Watters
>> JacobWatters.com
>>
>>
>>
>>
>> On Sat, Feb 15, 2025 at 4:50 PM Richie Burnett
>> <rburnett at richieburnett.co.uk> wrote:
>> 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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>>
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