[sdiy] MN3007 Chorus Acting Weird

[Jacob Watters]

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 <http://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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