Solid State Guitar Amp Forum | DIY Guitar Amplifiers

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!

Looking for some guitar speakers with a bit of a mid scoop, definitely around the 400-500hz range where electric piano has a fair amount of mud, and a nice extended treble without too much upper mid harshness. Want something that's not too fizzy with overdrive, but considering a pedal with a clean blend so can keep the overdrive in the midrange with clean top & bottom end for better clarity, so hopefully extended highs for clean tone won't translate into fizz for overdrive! The most promising things I've seen are in the Jensen Jet range, as alot of them have that dip in the lower mid-midrange, and they also have a good power handling for my 200w LabSeries L11. Anyone got any good suggestions?

Awesome, glad to hear I don't have to do any more rooting around in there! Was enough of a task to clean the casings up, very dusty and gimey! Will check the pots to see if they're scratchy and clean them when it's next open if needed, because that's obviously a little bit more straightforward!

Yeah it was my concern that they may hold similar voltage, given their placement & size I assumed they fulfilled a similar role to power valves but wasn't too sure. Would I just measure whether they've bled or not across the screws, is it that straightforward? Need to get a ohmmeter first to be honest as I don't own one yet! Not sure I've used one since secondary school... They're rated on the parts list as being 3000uf 100v, but I don't know if parts are overspecced in that regard, because I know next to nothing about power amps or supplies.

Thanks again!

On another anxious note, the thing is apparently set up for 230v, with mains in the UK being 240v, will that matter much at all? Slightly less concerning, is the thing has a fan as well as a heatsink, assumably at lower volumes this being connected won't matter from a cooling perspective (it's so stupidly bloud I very much doubt it'll get used anywhere near the top of its headroom). But if it's taken out the circuit will it affect anything else to do with the power section, or will it simply be drawing less power?

Cool, thanks for that guys. Is there any other suspect parts that could be causing the noise I mentioned? The best way I could describe it is almost like a  It's very much seems to be related to how much the power section is trying to output. How hard the preamp is driving it, and the preamp overall is fine. Tested that by digging in and messing with the channel volume and the preamp output (which seems to have a very very weak signal or something isn't quite right with that either? The preamp seemed to be sending enough to drive the power section the 1st time I used it because the volume control unsurprisingly had an absolute ton of headroom).

*Before I've even posted edit* I've just went upstairs to power it up to refresh my memory on the sort of noise it was making and it's fine! A few random crackles again which I put down to the pots and stuff (maybe?) but no evidence of it at all now. Strange! I was doing a bit of soldering to try and get that old reverb socket out so don't know if something had stayed very hot and sounded horrible as a result? Not sure! Anyway just tested with a bass and no problems! Sounds ace. Definitely still getting it a full service however!

Just out of interest however. How worried should I be about the filter caps if I was to remove them to get at the poweramp? I know they're not things to be treated carelessly but I'm worried about any stored charge and generally removing them and screwing them back in again! There's no way I can get at this reverb socket properly without moving them.

Thanks again!