[sdiy] MN3007 Chorus Acting Weird

[Jacob Watters]

Thank you so much! I will keep this on file.

On Sun, Feb 16, 2025, 6:32 a.m. Loscha <loscha at gmail.com> wrote:

> 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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