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Schematics and Layouts / Re: Lab series L11 - can anyone see where the distortion might be coming from?
« on: January 10, 2021, 08:20:21 AM »
Diagrams here, the disconnection to take the distortion circuit out is at O104 on the board layout. Bit confused by which chip it actually wants as there's reference to a CA3094, CA3094A AND CA3094AE in various bits of documentation, although from what could find it's just to do with voltage tolerance? Also confused about why that connection been severed takes the distortion out the circuit, as it seems to be split into 2 at that point and the distortion part is in the master section with the compressor (which still works regardless). I don't know a whole load about electronics however!
Also some pics here which I couldn't upload - https://photos.app.goo.gl/N4gUPZDWYLUg4khj9
*EDIT* Just had a mess with it again now, and the distortion circuit actually IS engaged when that O104 connection isn't made, seems to make a subtly quite nice difference to the tone when the trim pot is adjusted for maximum gain. Unless it's very low key I don't hear any breakup though, just makes the master more sensitive so don't know if the improvement in hearing is due to improve S/N ratio? It does seem to make a difference to how the 2nd channel clips when the disconnected wire is reconnected.
I've also tried disconnecting the reverb tank just in case I'd wired that incorrectly when I put the new connectors on that, however it makes no difference. So I'd be guessing the problem seems to be in the 2nd channel preamp somewhere but I'm a bit out of ideas now!
The only thing I can really think of now is the wire going from Ch2 has 2 connections, however the shielded part of it doesn't make much difference when it's connected. Says it goes straight to an earth as far as I can see on the schematic, but don't know if it's because something is broken and it's not having a proper earthing effect, or it's so noisy that the earthing effect is barely audible. Can't really imagine this has anything to do with it however!
Also some pics here which I couldn't upload - https://photos.app.goo.gl/N4gUPZDWYLUg4khj9
*EDIT* Just had a mess with it again now, and the distortion circuit actually IS engaged when that O104 connection isn't made, seems to make a subtly quite nice difference to the tone when the trim pot is adjusted for maximum gain. Unless it's very low key I don't hear any breakup though, just makes the master more sensitive so don't know if the improvement in hearing is due to improve S/N ratio? It does seem to make a difference to how the 2nd channel clips when the disconnected wire is reconnected.
I've also tried disconnecting the reverb tank just in case I'd wired that incorrectly when I put the new connectors on that, however it makes no difference. So I'd be guessing the problem seems to be in the 2nd channel preamp somewhere but I'm a bit out of ideas now!
The only thing I can really think of now is the wire going from Ch2 has 2 connections, however the shielded part of it doesn't make much difference when it's connected. Says it goes straight to an earth as far as I can see on the schematic, but don't know if it's because something is broken and it's not having a proper earthing effect, or it's so noisy that the earthing effect is barely audible. Can't really imagine this has anything to do with it however!