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Messages - SwamiRob

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Thanks for the help! It's been so long since I've really used one that I forgot that they can be used with an active circuit (of non-lethal power ratings that also won't destroy the thing obviously haha). The supply was dead so got a new one, simple enough. All the wiring & fuse seemed fine, so I can only assume that the actual transformer had died maybe? Way above my level of understanding to mess with that anyway.

Hey guys, just wondering if anyone could point me in the right direction of ways to do pretty basic tests on gear? Specifically whether something's mains input is working correctly? I've got an old Alesis compressor which uses an unusual mini jack style plug w/ DC, and compatible supplies are hard to find. I've got a power supply for it and also a noise gate from the same series which is also not working. Is there any straightforward way of using a multimeter to see if there's a break in the circuit that deals with taking mains power? I imagine this could be more straightforward on the power supply then either of the units! Thanks for the help!

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 -

*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!

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!

Sorry should have been a little clearer, this is for a Rhodes/Wurli style electromagnetic piano. After something that is bright relatively speaking for guitar drivers, I'm well aware there's not gonna be any 10k coming out of them in any meaningful amount, and wouldn't want it either, especially not with a load of overdrive going on!

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 thanks again, it most certainly has a substantial heatsink too, I've been told/have read in many places that they were pretty well made bits of gear.

I did try the patching solution by the way, it doesn't seem to solve the weird noise issue, and it seems to be quite intermittent still. However it does seem to result in a slight volume & clarity boost (I tried to volume match and it seems to sound nicer with it in. Did try it a little bit earlier and this horrible noise seems to occur when going direct into the power amp with a signal hot enough to drive it properly.

Gonna have a bit more of a look when I'm off night shifts from tomorrow morning. And gonna see if I can't get this bloody reverb working!

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?

Awesome, will give that a go. Are these filter caps likely to be on my death certificate of I unscrew them? And if I do how much of a pain are they to get back in? Also is it worth going over everything with a soldering iron for dry joints etc, or is it not worth it if there's no obvious reason to do so even if the thing is a little old?

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!

Amplifier Discussion / LabSeries L11 power section repairs & spares
« on: July 20, 2020, 10:48:42 AM »
I've picked up a pretty battered L11 off eBay that I'm trying to get working for some electric piano. Was working ok other then the odd little sputter when I first got it (it was listed as probably needing a good service), when giving the thing a good clean out previous to it the reverb send/return socket has all the pins snapped off, and the reverb tank has a hook kissing off the transducer. Other then that it seemed to be able to get some decent volume without any problems other then the little random bits of noise that kept coming out that I figured could also be dirty pots. Second time I plugged it in to a 4ohm bass cab totally forgetting that it's 8ohm. Didn't use much volume but this time it sounded awful at anything other then minimal volume (until I worked out what I'd done...) making a horrendous farting noise. Same deal when I unplugged it and went it into a 8ohm speaker.

Not sure if the filter caps were ready to fail anyway and that's put them over the edge, or I've messed up some other element of the power section? Never ran an amp on the wrong impedance and don't know much about what it can damage, didn't think at all at the time as I'm so used to SS stuff being rated for at least as low as 4ohms.

I think I remember seeing that some obscure company makes output chips that are compatible with these (although my limited knowledge of output chips is that they tend to blow as quickly as a fuse and not gradually fail), but I'm a little concerned that there could be alot of components that are t going to be very easy to replace.

As a little aside if this ever gets revived to working condition - can anyone tell me a bit more about the compressor? The -/+ sides of it, is the plus side an upwards compression sort of effect/a downward expander/both/neither?

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