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Schematics and Layouts / Lab series L11 - can anyone see where the distortion might be coming from?
« on: January 10, 2021, 07:48:46 AM »
Hey guys, was just wondering if someone might be able to track down some OTT distortion I'm getting from the 2nd channel of my Lab Series?
The thing needed some attention after I'd got it and it was putting out a really inconsistent signal on both channels (although there was slot of noisy drive on the 2nd channel still) and I took it to a tech. I'd re socketed the reverb input/out from the board as it had all been disconnected. The tech managed to fix the power amp issues and there was now the ton of headroom you'd expect from a well made 70s 200w solid state amp. There was a weird feedback when you turned the master up, but so much volume that didn't matter.
Both channels now worked fine, but the connection to the reverb & distortion circuit had now been severed, reattaching it there was very very little volume from either the reverb or dry elements, and a really over the top clipping from the dry signal still present. Pretty much had to have the channel volume barely on to have lower gain clipping but nothing clean at all, although you could tell the signal sounded alot richer for going through that bit of circuit, as the sound is quite sterile without. Could live without it maybe as I can get round the reverb issue by splitting the signal and going through the footswitch, but that's predictibly noisy even with some signal boost from an EQ pedal, and also gets some nasty clipping when there's overdrive unless I really really full the signal (I know spring tanks get a LPF/HPFed signal to my knowledge, but it really doesn't sound right.
Got a new CA3094E for the distortion circuit, and the dry volume is better but not great, and there is now an increasing high/upper mid distortion signal that gets introduced as the master is turned up. The reverb however is now at a decent level with very little noise. I've messed with the distortion trim pot and that merely goes from very very distorted to extremely distorted. There is some breakup without the connection made to the circuit like it was when I got it back from the tech in a bit more of a controlled manner, just the overall signal seems like it'll be a tad warmer when it's working like it should, and the reverb sounds awesome.
Any ideas would be very appreciated! I can't find the listing from when I bought it, but they had mentioned that they had some unconfirmed reports it had belonged to some 80s metal band at some point, do not sure what might have been messed with!
The thing needed some attention after I'd got it and it was putting out a really inconsistent signal on both channels (although there was slot of noisy drive on the 2nd channel still) and I took it to a tech. I'd re socketed the reverb input/out from the board as it had all been disconnected. The tech managed to fix the power amp issues and there was now the ton of headroom you'd expect from a well made 70s 200w solid state amp. There was a weird feedback when you turned the master up, but so much volume that didn't matter.
Both channels now worked fine, but the connection to the reverb & distortion circuit had now been severed, reattaching it there was very very little volume from either the reverb or dry elements, and a really over the top clipping from the dry signal still present. Pretty much had to have the channel volume barely on to have lower gain clipping but nothing clean at all, although you could tell the signal sounded alot richer for going through that bit of circuit, as the sound is quite sterile without. Could live without it maybe as I can get round the reverb issue by splitting the signal and going through the footswitch, but that's predictibly noisy even with some signal boost from an EQ pedal, and also gets some nasty clipping when there's overdrive unless I really really full the signal (I know spring tanks get a LPF/HPFed signal to my knowledge, but it really doesn't sound right.
Got a new CA3094E for the distortion circuit, and the dry volume is better but not great, and there is now an increasing high/upper mid distortion signal that gets introduced as the master is turned up. The reverb however is now at a decent level with very little noise. I've messed with the distortion trim pot and that merely goes from very very distorted to extremely distorted. There is some breakup without the connection made to the circuit like it was when I got it back from the tech in a bit more of a controlled manner, just the overall signal seems like it'll be a tad warmer when it's working like it should, and the reverb sounds awesome.
Any ideas would be very appreciated! I can't find the listing from when I bought it, but they had mentioned that they had some unconfirmed reports it had belonged to some 80s metal band at some point, do not sure what might have been messed with!