Hi there, I've got an old Carlsbro PA amp, and despite it not being worth much as an amp I'd quite like to use it for the spring reverb. Only problem is the power amp section is knackered, and that's the only route the reverb seems to go through - going through the speaker output, slave and pre-out. All there is is a loud crackle when using these outputs with a very weak signal.
Since I have no need for the power section, I was wondering if any of you guys might be able to help me find a way of getting the reverb circuit to go through the aux output, that's of course if the power section being all but completely broken doesn't affect the power going through the reverb tank - although the entire preamp is running absolutely fine if the reverb isn't supposed to be routed that way!
There's no schematic but the circuits seem like they're possibly quite straightforward? I know these amps are cheap but it'd be nice to try and save it for some sort of use and try and get a bit of a better understanding of electronics while I'm at it. Beyond a few simple guitar and pedal solderings I've not done much.
Got a few pictures, but if there's anything else that'd be useful then I'll get more. Thanks for any help anyone can give!
Since I have no need for the power section, I was wondering if any of you guys might be able to help me find a way of getting the reverb circuit to go through the aux output, that's of course if the power section being all but completely broken doesn't affect the power going through the reverb tank - although the entire preamp is running absolutely fine if the reverb isn't supposed to be routed that way!
There's no schematic but the circuits seem like they're possibly quite straightforward? I know these amps are cheap but it'd be nice to try and save it for some sort of use and try and get a bit of a better understanding of electronics while I'm at it. Beyond a few simple guitar and pedal solderings I've not done much.
Got a few pictures, but if there's anything else that'd be useful then I'll get more. Thanks for any help anyone can give!
Relocated to PA systems, hopefully you'll get the answer you seek here.An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
You should be able to connect the pre-amp out to a separate amplifier. This should be the summed output of the 4 channels . If you send the signal (via the reverb button)from any channel you should get this with reverb at the pre amp out. The aux out is a separate route to an external effects unit or monitor. Sometimes the pre amp socket uses switching contacts to disconnect the path to the power amp - clean these and you might have a working amp.
Cool, I'll get it plugged into a speaker and see what it does. The crackling and loss of volume seems to be equal across all of the outputs after the preamp however, but I've got some contact cleaner that I've got for the pots on my bass so I'll have a go! What exactly am I looking out for do you know if it does have that switching?
If everything is a bit broken is there likely to be a simple positive/negative/ground from the preamp that could be soldered to a jack? The preamp and poweramp are 2 pretty tidy separated entities, attached to the front and back panels, and the wiring between them just clips together. Seems fairly straightforward if I know what's the power coming from the mains to the preamp, and what's the signal from the preamp to the poweramp (providing it's going there at a decent volume, not sure what sort of signal level is used to directly drive a poweramp...)
If everything is a bit broken is there likely to be a simple positive/negative/ground from the preamp that could be soldered to a jack? The preamp and poweramp are 2 pretty tidy separated entities, attached to the front and back panels, and the wiring between them just clips together. Seems fairly straightforward if I know what's the power coming from the mains to the preamp, and what's the signal from the preamp to the poweramp (providing it's going there at a decent volume, not sure what sort of signal level is used to directly drive a poweramp...)
Think I've fettled it! I've taken the signal to the poweramp and rerouted it through the footswitch jack. Not gonna get used, so I disconnected it from the rest of the circuit. Was quite buzzy initially, but seemed to be better when the earthing went back to the poweramp section as well as through the jack which is understandable, as usually you want as many groundings as possible as long as they don't cause any ground loop issues right?
All working fine, apart from the fact it seems to be hissing a little when the original wire from the footswitch connection isn't being used. The grounding got reattached to the aux inputs, where they were all linked together previously, but the hiss is there if the footswitch connection isn't used too.
Gonna solder it back on if there isn't another solution, but when it's not connected the signal is so much stronger and (aside from the ground noise) clearer. Is this just a natural trade off when earthing signals in some situations? That it compromises output for a clean signal?
A few pics of the horrible mess I've made below... (Lead free solder + not very hot soldering iron + no clips or any decent surface to solder on + not very good at soldering = this, it's all connected at least)
If those pictures don't load then try this
Carlsbro Marlin - Google Photos
All working fine, apart from the fact it seems to be hissing a little when the original wire from the footswitch connection isn't being used. The grounding got reattached to the aux inputs, where they were all linked together previously, but the hiss is there if the footswitch connection isn't used too.
Gonna solder it back on if there isn't another solution, but when it's not connected the signal is so much stronger and (aside from the ground noise) clearer. Is this just a natural trade off when earthing signals in some situations? That it compromises output for a clean signal?
A few pics of the horrible mess I've made below... (Lead free solder + not very hot soldering iron + no clips or any decent surface to solder on + not very good at soldering = this, it's all connected at least)
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
If those pictures don't load then try this
Carlsbro Marlin - Google Photos
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Firstly: you have disconnected the wiring from the footswitch socket. This would be designed to switch the reverb off/on remotely. Unless you have joined the wires that were switched at the footswitch socket - the reverb won't work at all and this could explain the hiss .
Next: don't really understand your description of your mod to the power amp wiring - have you taken the signal out (via the footswitch jack) to an external amplifier and speaker? This would likely cause a ground loop( if you havn't disconnected the ground on this signal path.)
If you plug a speaker in to the Carlsbros output , do you get anything (hum , crackles etc)
It's kind of hard to work out whats what from your pictures - remember the rest of us cant see the whole amplifier, or tell which socket is which from inside the amp!
And your right about your soldering! time to buy a new iron and some decent solder.
Next: don't really understand your description of your mod to the power amp wiring - have you taken the signal out (via the footswitch jack) to an external amplifier and speaker? This would likely cause a ground loop( if you havn't disconnected the ground on this signal path.)
If you plug a speaker in to the Carlsbros output , do you get anything (hum , crackles etc)
It's kind of hard to work out whats what from your pictures - remember the rest of us cant see the whole amplifier, or tell which socket is which from inside the amp!
And your right about your soldering! time to buy a new iron and some decent solder.
Yup it's a nightmare to work with, spent a bit of money on that thing too and it's never been hot enough.
The reverb is working perfectly, and I can eliminate the ground hum with the wiring how it was originally, just there is a hiss that is apparent compared to the aux out (not affected by whether the reverb is running or not). You're right though, it's the signal out I've taken that was running to the amp. The only reason I went for the footswitch initially was it was a jack I wasn't going to use, and thought that the earthing going to the poweramp might hopefully function in the same way as if it was going to the amp I'm using, not quite unfortunately!
It's not an unbearable amount of noise or anything, not when it's all earthed, the earthing going to the poweramp and elsewhere on the board seems to make very little difference. The background hiss is minor but a bit irritating, probably the same level as a pretty overdriven guitar amp, but like I say it's not happening on the aux out.
Main speaker outs, preamp out and slave outs all have the same low level and very loud crackling unfortunately. It was getting used as a bass amp and it died at a practice one day, was ages ago and I can't remember exactly what happened, but in the cases of a dead solid state isnt it usually a case of output chips or the caps dying?
There should be a picture of the front controls in the Google folder thing hopefully?
Sorry this is a bit of a difficult one, there's no schematic anywhere. Just a bit of a DIY project to see if I can use this unit for something rather then throwing it, the spring reverb is lovely now I've got it (sort of) working. Just need to work out how to earth it better while preserving the signal level..... Is there likely to be any complicated earthing once it's gone to the power amp that requires the signal out as well as the earth? If the signal is at line level I don't understand why it's not just going out of a jack that was disconnected from the rest of the board. I know very very little about the internal workings of amplifiers if you aren't guessed already, beyond don't touch the capacitors/output valves & transformer if you don't know what you're doing. Trying to use this as an opportunity to learn some stuff!
The reverb is working perfectly, and I can eliminate the ground hum with the wiring how it was originally, just there is a hiss that is apparent compared to the aux out (not affected by whether the reverb is running or not). You're right though, it's the signal out I've taken that was running to the amp. The only reason I went for the footswitch initially was it was a jack I wasn't going to use, and thought that the earthing going to the poweramp might hopefully function in the same way as if it was going to the amp I'm using, not quite unfortunately!
It's not an unbearable amount of noise or anything, not when it's all earthed, the earthing going to the poweramp and elsewhere on the board seems to make very little difference. The background hiss is minor but a bit irritating, probably the same level as a pretty overdriven guitar amp, but like I say it's not happening on the aux out.
Main speaker outs, preamp out and slave outs all have the same low level and very loud crackling unfortunately. It was getting used as a bass amp and it died at a practice one day, was ages ago and I can't remember exactly what happened, but in the cases of a dead solid state isnt it usually a case of output chips or the caps dying?
There should be a picture of the front controls in the Google folder thing hopefully?
Sorry this is a bit of a difficult one, there's no schematic anywhere. Just a bit of a DIY project to see if I can use this unit for something rather then throwing it, the spring reverb is lovely now I've got it (sort of) working. Just need to work out how to earth it better while preserving the signal level..... Is there likely to be any complicated earthing once it's gone to the power amp that requires the signal out as well as the earth? If the signal is at line level I don't understand why it's not just going out of a jack that was disconnected from the rest of the board. I know very very little about the internal workings of amplifiers if you aren't guessed already, beyond don't touch the capacitors/output valves & transformer if you don't know what you're doing. Trying to use this as an opportunity to learn some stuff!
Short solution, a.k.a. "Plan B"
Pull the reverb tank from the Carslsbro and build a simple standalone reverb.
Can be as simple as asingle TL072 plus a few parts.
Post all codes visible on the tank, a couple pictures, and measure both coils DC resistance , all this to properly identify it and be able to suggest you a proper drive and recovery circuit.
You´ll end with an independent "reverb "pedal" or rack unit usable anywhere.
In the long run, way easier than trying to go inside the broken PA head and back.
Pull the reverb tank from the Carslsbro and build a simple standalone reverb.
Can be as simple as asingle TL072 plus a few parts.
Post all codes visible on the tank, a couple pictures, and measure both coils DC resistance , all this to properly identify it and be able to suggest you a proper drive and recovery circuit.
You´ll end with an independent "reverb "pedal" or rack unit usable anywhere.
In the long run, way easier than trying to go inside the broken PA head and back.
Basically this:
1) these values are for Tube amplifiers (higher impedance) ; for general purpose "Rack Reverb" use reduce mixing resistors R38/R40 to, say, 22k each.
2) you will need a simple +/-15V power supply, nothing more complicated than a 12+12VAC 250mA transformer, 4 1N4002 diodes and 2 x 2200 or 4700 uF x 25V capacitors.
3) as is, this unit passes Dry (all the time) and Reverb signal (adjustable) and works between Preamp and Power Amp adding reverb to "everything".
If you want to use on an Effects Loop, add a switch opening the Dry path through R40 so you have only Reverberated signal, Effect Loops usually provide the Dry path.
Try it both ways, pick the one which works best for you.
An externally hosted image should be here but it was not working when we last tested it.
1) these values are for Tube amplifiers (higher impedance) ; for general purpose "Rack Reverb" use reduce mixing resistors R38/R40 to, say, 22k each.
2) you will need a simple +/-15V power supply, nothing more complicated than a 12+12VAC 250mA transformer, 4 1N4002 diodes and 2 x 2200 or 4700 uF x 25V capacitors.
3) as is, this unit passes Dry (all the time) and Reverb signal (adjustable) and works between Preamp and Power Amp adding reverb to "everything".
If you want to use on an Effects Loop, add a switch opening the Dry path through R40 so you have only Reverberated signal, Effect Loops usually provide the Dry path.
Try it both ways, pick the one which works best for you.
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