Gates SA-134/MO-3638 Issues

[beatnik]

Good to see it finally up and running
The only issues with the wooden front panel is that you lose some shielding and also the components attached to it are not earthed.
This could potentially be a safety issue, for example if for any reason there is a fault in the mains toggle switch, and the lever becomes live, if it doesn't have a path to earth you'll get zapped. It doesn't happen often but I wouldn't take chances..
Another thing potentiometers can pickup noise if their body is not earthed. In a high gain circuit like this I imagine it could be an issue
I suggest fitting an aluminium panel behind the wooden one or alternatively ground the front panel components using large solder lugs.
Ah and you need a bigger knob ! And maybe an output pad to drive some hotter levels in the preamp

 

[13engrsapper]

For me the easiest is real time analysis of the amp. There's math, but I'm far slower at remembering what math and why. The quick math in my head says the other way is 12dB more feedback. If the current cap is sized for exact linearity, or even a bass bump, the more feedback the greater the bass bump, so the cap has to get correspondingly larger. In a simple case 220K to 110K is gonna be roughly 6dB more NFB. Double the cap size. All that makes the two versions of the amp look like a 12dB difference, roughly. There are frequently other associated factors that can skew this. The 0.5 of the other may have wanted totally linear bottom, with this one wanting slight bass boost.

I agree with EMRR and the real-time analysis. We've been doing this decades, with tons of decent test equipment, I recently caved and bought an old Rhode & Schwarz UPD Audio Analyzer... What a difference, no more one at a time tests requiring signal generators, o-scopes, bridging transformers, etc, no more all night math quizzes.... Plug it in and look at it... change something look at it again. The UPD allows you to change input and output impedances on the fly while your device is connected as well. Amazing what you can learn, and how fast. Math is great, and needed, as is my scope - But a modern real time setup is a HUGE help. In fact, if I had to get rid of it, I would probably just quit... it made it that much easier.

 

[andYz00m]

Good to see it finally up and running
The only issues with the wooden front panel is that you lose some shielding and also the components attached to it are not earthed.
This could potentially be a safety issue, for example if for any reason there is a fault in the mains toggle switch, and the lever becomes live, if it doesn't have a path to earth you'll get zapped. It doesn't happen often but I wouldn't take chances..
Another thing potentiometers can pickup noise if their body is not earthed. In a high gain circuit like this I imagine it could be an issue
I suggest fitting an aluminium panel behind the wooden one or alternatively ground the front panel components using large solder lugs.
Ah and you need a bigger knob ! And maybe an output pad to drive some hotter levels in the preamp

The pot is grounded to the star ground bar and the pilot light has plastic housing so wasn’t grounded to the chassis. I see what you mean about the mains power and it becoming live. I’ll address that.

So far, this thing is dead quiet and there is never any power to gear unless someone is there at the studio, so I’m not too worried about fire hazard with the power switch failing.

Definitely good points though to watch out for, thanks! While building the face plate, I was thinking… this is why people don’t usually do this… and yes I need a WAY bigger knob… haha.