MP-1 Classic Noise Gate "stuck" at max values even when turned off

[Bret]

Hey everyone, new member, long time lurker.

I have an MP-1 Classic with an odd behavior - it seems that the noise gate is clamping shut even when it is turned off in the patch. It also ignores the threshold I set, whether turned on or off. I tried turning the gate on and setting it very low but that doesn't seem to work either.

When I'm on the Tube Clean setting, I have to strum very hard to get the occasional sound through, but the sound that does come through is crystal clear, clean tone, and as the notes fade it will mute. The same behavior is present on the Tube Brown and Tube Dist voices, but on Tube Dist with the gain up the gate is only active if I really let a note ring out for a while. Still, it very clearly sounds like an overly aggressive noisegate and since turning on/off the gate doesn't change the behavior of the amp, I'm inclined to think that's the problem.

I'm not afraid to pick up the soldering iron here, but I'm not really sure what I'm looking at on the schematic or what values I should check first. I'd love to get a few pointers on where to start here - thanks!

[rnolan]

Hey Bret, welcome and nice to hear from you, albeit I wish it were better circumstances.  I've not heard of this behaviour/problem before.  I tend to agree there seems an issue with the gate in/out, but more complicated, if that's all it was/is, then the threshold setting should work.  Can you select gate mode options (fader/gate), I use MP-2 and am assuming the gate is similar in the Classic where Gate mode is a hard gate and Fader fades the sound.  From what you describe, the gate is turned on and the threshold is set quite high and you can't change it.  A not so great (slight) work around is crank up all your drive settings and turn the master down, thus providing max signal to keep the gate open, although it's not a fix.  Also if you crank up the compressor, that will also increase the signal and help keep the gate open (but stuff your playing dynamics).

IIRC a new(ish) member Gregg was looking into the clamping circuit and its components for the MP-2 (again which I assume is similar if not the same), and maybe he can chime in with some ideas?  You can find Schematics here https://adadepot.com/index.php?topic=148.75.  I suspect the gate is either part of the compressor or maybe the chorus schematics?  I had a look and it's above my pay grade LoL.  Though it makes sense that the gate is before the chorus, just after the gain stage (so you don't chorus noise).

[Bret]

Thanks! Yeah - it's an odd behavior. I saw the other thread about gate issues and there were a few components listed there, so I'll start poking around that area this weekend when I have a chance.

Luckily the situation isn't too dire, since I have a regular MP-1 and MP-2 to keep me company while the Classic is out of commission.

The gate does sound quite nice on the overdrive voicing, since my standard MP-1 is a bit noisy in comparison. Ultimately if it comes down to it, I'd even be happy to just disable the gate entirely though so I can use the clean/brown voicings. I'll be sure to post if I can figure anything out, in case someone else encounters the same problem.

[Harley Hexxe]

There's no selection for a type of gate in the Classic, it's either on or off.

I've never heard of this kind of issue in the Classic though, this one is a first.

[rnolan]

Thanks Harley, that's good to know.  I thought it would be the same as the MP-2. 

Hey Bret, glad you have a couple of (very nice) alternatives.  Not sure how/if you can disable it.  Let us know if you work it out, better still fix it.  I'll PM Gregg to maybe have a look into it if he has time.

[Harley Hexxe]

I think Gregg would have to have one of these on the bench to trace the circuit and see what's up.

Still, I find this to be an odd issue in the Classic. But I digress, these are old electronics now and components do fail after enough time goes by.