Cross-Channel Amplifier Interference when using a Taylor A/B/Both Switch Box...?

[timfitz63]

Wasn't quite sure which sub-forum was more appropriate for this post, but...

I've got one of those Taylor A/B/Both Switch Boxes (which have apparently now been discontinued by Taylor).  I picked mine up a little over a year ago, about the time I got my T5-C1.  As I recall, it seemed to work fine then, at least when pairing my brother's VOX AC4 and Fishman Loudbox Mini amplifiers.  Then it got stored away for a while.

After moving back to Texas from a long-term work site in Kentucky, I hooked mine up in my recently-purchased house, paring my newly-acquired AC15C1 and my Loudbox Mini.  Immediately, I noticed that there was an very obvious and objectionable cross-channel interference/feedback/hum/buzz coming from either amplifier whenever they were paired through the A/B/Both Box -- particularly on the selected amplifier.  The instrument could still be heard over the amplifier, and the switching functions of the A/B/Both box seemed unaffected; there was just a bad humming noise in the background...

I'll spare all the details of the troubleshooting effort that ensued, but suffice it to say that I determined that neither amplifier seemed at fault; both sounded very clear whenever used independently.  This seemed also to eliminate power supply issues (all the outlets had been tested for proper polarity/grounding during the pre-buy inspection for the house), interference from surrounding appliances and lighting, sunspot activity, etc.  But I tried other wall outlets anyway; no difference.  Either amplifier also would clear up whenever the other amplifier was disconnected from the A/B/Both circuit (i.e., the cord leading from the box to one amplifier was unplugged, either from the box or the amplifier, but the second amplifier remained connected through the A/B/Both Box).  I also tried pairing other amplifiers I own as well (a Fender Mustang II and the Taylor ES amplifier that came with the BR-V), in various combinations; the results were unchanged.  I tried more physical separation between the amplifiers; no joy.  About the only thing I didn't do was buy new cords to connect everything (I'm using RapcoHorizon G1S-10-I 10-ft. patch cords running from the box to each amplifier, and a RapcoHorizon G1S-15-I 15-ft. patch cord running from the guitar to the box -- all cords seem to work just fine when connected between the guitar and any amplifier directly).

I contacted Taylor customer service and described all this to them; after they scratched their heads a bit they had me send the A/B/Both Box back to them.  They checked it over and told me it was functioning correctly.  But when I tried it out last night after receiving it back, the outcome was the same:  the cross-channel humming was still there...

Anyone else experienced this?  If so, any solutions?  I wonder if the signals (either audio or electrical) need to be filtered or balanced better.  But I'm grasping at straws here...  The A/B/Both Box isn't much more useful to me than a doorstop at the moment, though, so any suggestions are appreciated...

[3dognate]

Try lifting the ground on one amplifier by using one of the 3 to 2 prong adapters... you may be introducing a ground loop.

You can also cut the ground connection on one of the t/s cables running from the A/B/Y box to one of the amps to lift the signal ground rather than the amplifier's ground also...

A ground loop would be my first suspect... and first thing I'd want to rule out.

[timfitz63]

Try lifting the ground on one amplifier by using one of the 3 to 2 prong adapters... you may be introducing a ground loop.

You can also cut the ground connection on one of the t/s cables running from the A/B/Y box to one of the amps to lift the signal ground rather than the amplifier's ground also...

A ground loop would be my first suspect... and first thing I'd want to rule out.

Thanks, I'll look into that.  What would be the easiest way to check for the existence of an electrical ground loop before spending $50+ on a purpose-made correction device like Hum-X?  And would both amplifiers need something like Hum-X to correct a ground loop problem, or just one of them?

I guess I'm not savvy enough about electronics/electrical equipment to know how the audio connection would create a ground loop in the equipment when they're both plugged into a grounded outlet...  But then I read this on Wikipedia:

... Low current wiring is particularly susceptible to ground loops. If two pieces of audio equipment are plugged into different power outlets, there will often be a difference in their respective ground potentials. If a signal is passed from one to the other via an audio connection with the ground wire intact, this potential difference causes a spurious current through the cables, creating an audible buzz at the AC mains base frequency (50 or 60 Hz) and the harmonics thereof (120 Hz, 240 Hz, and so on), called mains hum...

So at least now I've got a better idea of what may be going on... I DO know, however, that ground loops are very bad in aviation, though...

[timfitz63]

Well, you called it "3dognate!"  Not having a better option handy to troubleshoot an electrical ground loop, I reasoned that I could just plug both amplifiers into the same wall outlet (one in each receptacle) and that should put them on the same grounding potential.  Low and behold:  no cross-channel hum.

So unless there's a better option, I'm off to get me a Hum-X.  Still would like to know if it's necessary to have one or two of these things to correct the problem on different power circuits; they're kind-of pricey gizmos for what's essentially a glorified tron-herder...