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PostPosted: Mon Dec 12, 2016 2:58 pm 
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Bottle Rocket

Joined: Mon Dec 12, 2016 2:04 pm
Posts: 4
First off, thanks for all the comments on this board -- you guys have all helped me tremendously through the years for all kinds of issues!

Short version: I think I need a stereo Y-cable for speaker-level loads, anybody know of a cable manufacturer that makes those? Cabinet has a single, TRS 3-conductor input jack. I’ve looked but haven’t found any matches for a rather odd question. Apologies if this is answered somewhere and I just missed it but I’m hoping to get some help from you signal wiring guru’s. I’ve scoured the internet but have yet to find anything similar. Long version follows.

I’m using a Triaxis/2:90 into a 16-ohm Marshall 1960 Classic 4x12 cabinet with 16-ohm 25-watt greenbacks. That cab has been re-wired as an 8-ohm stereo cabinet so it works fine with the 2:90 or my Mesa 20/20. Since the cab has only a single input jack, I’m currently using 2 speaker cables from the 2:90’s left and right channels and running that into a simply Y-cable, basically an insert cable per the engineer that re-wired the cab. The Y-cable has 2 female mono TS inputs to a single TRS male output.

I’ve been a little worried about some sounds I’ve been hearing from my amps so I started doing some research into speaker-level wiring vs. instrument-level cables. I asked some cable manufacturers about getting me a speaker-level Y-cable but they’re not familiar with anything like this. The connections have been this way for 15+ years without any obvious issues but I decided to look for a REAL speaker-level Y-cable. The cable manufacturers I spoke to were really helpful but had no idea how this type of setup was configured, nor did they have any type of what they termed "3-conductor" speaker wire. Makes sense, but is this all that unique? Maybe so...

I started questioning whether or not I was saying something wrong and I couldn’t remember how the engineer had re-wired the cab. So I finally opened it up to figure out the mystery -- it's using a single stereo input jack so I borrowed some ideas from a few sites to create my own drawing of the jack and the wiring to help explain things (mostly for my own sanity).  

As for the original wiring, fortunately I'd kept a drawing from 1998, no idea how I found that but I pulled out an old box with connectors and diagrams and I'd saved a sketch of the BEFORE setup.  Again, the cabinet is a standard Marshall 4x12 16-ohm cabinet that was previously wired up as in this first image (16-Ohm Mono), that is, if my drawing is correct.  I think that's called Series / Parallel but again I'm not a wiring expert. If image is missing the URL should work:

https://app.box.com/s/kmk6vvcps86dhg5ga4w52ik4p8qzryvg
Image

The stereo amp I use had no 16-ohm out so by re-wiring the cabinet the way he did, the engineer was able to achieve an 8-ohm stereo cabinet.  I remember us talking about re-wiring but we didn't want to cut the wood and change the single input jack to a wider "dual input" so I guess he used a single TRS jack in a creative way -- I think it's basically configured internally like a Y-cable as well where the TRS jack has split the signals -- there's a small image of what I believe was done in the top right of the first image below.  He used the TIP and RING connectors to drive the positive speaker posts and wired the SLEEVE connector to all the negative posts on each of the 4 speakers like in this image. Again, if image is missing the URL should work:

https://app.box.com/s/zijywhevpm8t8kcs2ep7dzce0w0mdfp9
Image

After the change, I run two normal speaker cables (nice, big 12 gauge), one from the Right and one from the Left 8-ohm 2:90 outputs (picture on bottom right) into a simple insert Y-cable to transforms the two TS male 1/4" speaker cable inputs to a single TRS 1/4" male output used to plug into the speaker cabinet's single TRS input jack.  It's absolutely is working as a stereo rig -- I have clear left channel and right channel separation through the top and bottom left and top and bottom right.  It's nice and loud and there seems to be no obvious signal dropoff.

But it's that "simple insert cable" that causes me concern. I'm worried about running it like that using the "insert" Y-cable rather than real speaker cables built for large amp loads. Given that it seems to work today, do you all have any concerns other than my own that this setup work be OK long term? 

BTW, I also have a Mesa 2x12 that I've used with both the 2:90 and the 20/20 but I'd like to use this Marshall 4x12 as well. Any other options without trying to re-wire again? Other thoughts or concerns on how this thing is wired up?


Last edited by AustinGymrat on Tue Jan 03, 2017 9:42 am, edited 7 times in total.

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PostPosted: Mon Dec 12, 2016 3:04 pm 
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Bottle Rocket

Joined: Wed Nov 09, 2016 9:07 am
Posts: 7
Will help - but can´t see pictures or drawings

ReidarNikolai


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PostPosted: Mon Dec 12, 2016 3:20 pm 
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Bottle Rocket

Joined: Mon Dec 12, 2016 2:04 pm
Posts: 4
Sorry, tried using IMG tags but I guess that didn't work -- changed to URL's for now but I'll try to post differently.


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PostPosted: Wed Dec 14, 2016 7:15 am 
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Mark III

Joined: Sun Aug 16, 2009 9:44 am
Posts: 347
Location: Melbourne, Australia.
Man, regardless of how you are wiring up your cab, you definitely need your cable to be rated for speaker load. Insert cables will over heat and burn out - possibly even causing the outer cover to catch fire. You are pumping heavy wattage into this thing, don't risk it. Insert cables are ok for a quick test, but time to get a proper speaker cable now. You might have to wire them up yourself if you can't find them anywhere.

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PostPosted: Thu Dec 15, 2016 9:30 am 
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Bottle Rocket

Joined: Mon Dec 12, 2016 2:04 pm
Posts: 4
Thanks ando, definitely agree. At this point, as bad as I hate to do it, I'm leaning towards re-wiring using a new jack plate, shouldn't be that hard but I need to understand how much power the new cabinet would handle.

I'm looking at this part: https://www.tubesandmore.com/products/jack-plate-plug-and-play-monostereo

The original cabinet wiring had it as 100-watts at 16-ohms. If I re-wire using this plate and take the suggestins in the attachments on that page (and I have 25-watt greenbacks rated at 16-ohms), it looks like a Stereo Parallel setup where each of the two inputs would be rated at 8-ohms. That works perfectly with the Mesa Boogie stereo power amps but any idea of the power ratings with that type setup using those 25-watt greenbacks? Would each side be then rated at 50-watts?

And now I have to figure out how to do some woodworking to expand cabinet opening, sheesh...


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PostPosted: Fri Dec 30, 2016 12:42 am 
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Bottle Rocket

Joined: Mon Dec 12, 2016 2:04 pm
Posts: 4
OK, I didn't get any other feedback here but a few of the cable manufacturers responded to some questions I had -- pretty much everybody agreed that the wiring I had done years ago was not optimal and could cause damage to the amp. The insert-cable solution (while working, per se), was called into question by everybody I talked to and their concerns aligned with my own.

I eventually ordered the Jack Plate part I mentioned above and rewired it all over the past few days. It was stressful as I expected, but not all that hard. The worst for me was cutting a square in the wood back of my Marshall cabinet which I did using a jig saw -- I practiced 3 or 4 trial runs on cardboard and thin wood pieces just so I didn't screw it up. The measurement labels provided in the Jack Plate drawing download were a bit off but the drawing itself was sized perfectly, go figure. So I ended up cutting that out and making a wood mold, then I practiced the cuts over and over before tackling the wood in the cabinet.

The final solution wiring solution I've drawn up from THEIR configuration as follows -- NOTE: The BLUE color in my final drawing is actually the WHITE wire from the Jack Plate wiring, hard to draw a WHITE wire on a WHITE background, so just imagine the BLUE wire as WHITE:

https://app.box.com/s/s1iqkye1hpo7beo3jo7r7ym6pnkb13ww
Image

Everything works perfectly BTW: the Stereo amp plugs in just fine using the 8-ohm stereo inputs (NO insert cables!!!) and stereo effects such as ping-pong delays can be heard beautifully bouncing between the left (2) speakers and the right (2) speakers. For those of you unfamiliar with Stereo cabinets, those that I've owned from Mesa Boogie have the bottom and top LEFT speakers wired together and the bottom and top RIGHT speakers wired together -- that same wiring configuration is what I have now with this Marshall cabinet.

BTW, this Jack Plate provides the following configurations, so it seems extremely versatile:

* 4 ohm mono
* 8 ohm left + 8 ohm right stereo
* 8 ohm left only mono
* 8 ohm right only mono
* 16 ohm mono

I also tested the 8-ohm mono (left-only), worked seamlessly. Then I set up my stereo amp sending the RIGHT channel to the 8-ohm mono of this 4x12 and the LEFT channel to my 2x12 Mesa Boogie Rectifier cabinet (also 8-ohm). That also worked great -- 6 total speakers in action and talk about nice stereo separation for any stereo effects, wow, just move the cabinets to the far corners of your room and sit near the middle of the cabs, unbelievably great sound.

So I guess my dilemma is now over and I hope never to revisit anything like it. A big thanks to those responding here and to the cable manufacturing folks -- especially Mike Hart of Seismic Audio Speakers. He went out of his way to answer a number of rather idiotic questions from me while offering his best advice over numerous emails, much appreciated!


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