Combo mods? e.g. adding speaker cab functionality.

[kiat]

Have you modified your combo? Maybe bypassed the speaker or bypassed the amp or something else? Please say if you have.

Yesterday I added speaker cab functionality to my old combo that had gotten really awkward to work with. Below is the story behind it and what steps I took with this etc, in case you're interested in doing the same or similar, or just want to see what the inside of a Bloc80b looks like!

# The background

I've in old Traynor Bloc80b that has miraculously been with me since new, despite 20+ home moves and life's ups and downs. For the past 7+ years it had been making very loud snap, crackle and pop noises, always when turning off and sometimes when any of the pots sere moved. It was unpleasant for everyone. I couldn't risk it at a gig.

So I decided to see if I could reuse it as 15" speaker cab but without losing any existing functionality. A few howtos showed just removing the internal speaker cable from the amp and routing it to an external amp via a jack, but it solved only part of the problem.

The solution is very straightforward, I did it in a couple of hours, because I had to find all the right tools, etc but realistically it's a half-hour job.



# The details

The solution basically involves adding a special kind of jack socket to the combo, which switches the amp from onboard to external simply by inserting an external speaker cable.

Parts:
* Switched Jack Socket (Neutrik NYS215 Stereo 6.3mm PCB)
* Speaker Cable (Red & Black 2.6 x 5.2mm 6Amps)
* Soldering kit
* Tools

Red wire to the socket terminal the jack tip (positive). Black to the barrel (negative). Make sure you have the default terminals connected to the onboard amp.

Actions:
0. Remove the combo from power
1. Cut cable from internal amp to speaker
2. Extend speaker cable with new
3. Drill hole for back
4. Install the new switching jack
5. Solder the existing amp cable to the jack
6. Check that works with power on and a bass connected to the existing combo input jack.
7. Power off
8. Solder the now extended speaker cables to the other side of the switching
9. Repeat the check with your bass to external amp connected via speaker cable to the new switching jack socket.
10. If this works, you're done, so replace everything and add some kind of sign what this new jack does.

Tips:
* take pictures so you can recall the existing layout and to make posts like this!
* cut the wires close to the speaker, so that you have enough internal amp cable to route to the interval amp.
* be careful with the soldering iron and don't touch any other wires with it that you don't intend to.
* I had a connection block, but a Wago or splicing the speaker cables, whatever works

And fixed the peeling Tolex while I was it with this German cobbler glue - the glued parts have to be hammered for maximal adhesion! Thought it might work on this solid state combo and it has. Would have needed to find something else if it was a valve amp!

 

[Mike Caldwell]

I would also look at getting your amp checked out, not a lot there, could be a simple fix.

 

[Redbrangus]

It looks like a tidy-enough mod. I'll only offer that the switch in the switching jack isn't really rated to handle the power of the amp output -- its designed for signal level switching. It will probably work fine, at least for a while. If you do have a situation where the speaker isn't working with the onboard amp, that's the first place I'd look for failure.

 

[kiat]

I would also look at getting your amp checked out, not a lot there, could be a simple fix.

Thanks, the next town has a guitar shop with a valve amp repair specialist, that apparently can fix amps with replaceable components. I'll be taking it there soon.

It looks like a tidy-enough mod. I'll only offer that the switch in the switching jack isn't really rated to handle the power of the amp output -- its designed for signal level switching. It will probably work fine, at least for a while. If you do have a situation where the speaker isn't working with the onboard amp, that's the first place I'd look for failure.

I'd like to take precautions. What could go wrong with it, overheating? It's metal and plastic - mechanical with no electrical components.

 

[agedhorse]

The internal switching contacts can fail, they aren’t rated for that kind of current.

It’s also important to be sure that the speaker jack is isolated from the chassis (your jack is isolated but many are not). Some amps do not use a ground referenced power amp output and grounding it through the jack to the chassis may destroy the amp.

 

[mexicanyella]

The bassist in a college friend’s punk band used to use an 80-watt Yorkville like that one, cranked way up, and that amp seemed to take it in stride, and be audible amongst the pounding drums and distorted Marshall guitar amp melee. I have not seen one of those since then.

Cool project idea; I would second the suggestion of getting the internal amp checked out in case it’s an easy fix, but even with that working perfectly your mod seems like it could lead the way to some fun amp/speaker combination experiments.

I’ll be interested to hear how that switching Jack works in that configuration; I’ve wondered about trying a similar mod to a Peavey guitar amp I have, so it could power a bass cab in a pinch if my bass head ever goes down for repair.

Edit: I’m looking at your photos, and “Kövulfix” (is that the adhesive you used?) is one of those words that seems to defy pronunciation by English speakers!

 

[Redbrangus]

I'd like to take precautions. What could go wrong with it, overheating? It's metal and plastic - mechanical with no electrical components.

As @agedhorse said, the switch part of the jack can fail at the contact point -- a small amount of the conductive surfaces just burns away due the overcurrent. Technically, I guess you could say it's overheating, but it's a miniscule amount and confined to very small area -- there's no need to be concerned about it not being safe. And to be honest, it probably wouldn't be too much of a problem. You aren't likely to be inserting or removing the jack while there's signal present, so you will be avoiding the 'switching under load' situation that would greatly exacerbate this issue.

I'd strongly advise you to be sure the combo amp is unplugged from the power source if you're using it as an extension speaker. And again, as Andy said: be sure you don't use this speaker rig with an amp that employs bridged output topology like many of the modern Class D amps do.

 

[Mike Caldwell]

I'd strongly advise you to be sure the combo amp is unplugged from the power source if you're using it as an extension speaker. And again, as Andy said: be sure you don't use this speaker rig with an amp that employs bridged output topology like many of the modern Class D amps do.

Yes, for a brief moment the tip of the jack would be connected to first the ground of the amp and then to + output of the amp till the contacts would open. With the isolating jack and the amp unplugged it would be ok.

As for 1/4 inch jacks on high power speakers.......the first series of JBL SR cabinets used 1/4 input jacks that also did the switching between full range and bi-amp. I work on many of those converting over to Speakon and if needed putting in a heavy duty switch to select between full range and bi-amp.

 

[bobcruz]

As mentioned already, a switching jack can briefly connect the plug to the combo's amp when plugging it in or unplugging it. If the external or internal amp is powered on when this happens, the amps can be destroyed. This could also happen if the plug is only partially inserted or becomes that way when in use. To avoid these pitfalls, it would be better to install two regular, nonswitching jacks, wiring the combo's amp output to one and the internal speaker to the other. Then make a short jumper cable (using speaker wire, not a pedal board patch cable) to connect the two when you want to use the combo as a combo. The jumper would have to be physically unplugged to use the internal speaker with another amp, so there is no danger to either amp. Just be sure to carefully label which jack is which since plugging the external amp into the combo amp side would be a disaster.