Mix'n'match wireless

[sandall]

I got caught out at a festival on Sunday when they asked "by the way, can you add in a battery system for the Dog Show?" - no problem; charged car battery, 12v amp, couple of horns on sticks, throw in a spare Trantec hand-held & make up a 2.1mm coax to croc-clips lead for the receiver - all radiomic receivers will work off 12v, won't they?

 

Wrong!! - with the battery reading 12.3v every one I tried (including an S3500, clearly marked "12-18v" on the back) produced a very low, horribly distorted output at anything above a whisper. Exactly the same results back at base next day. I had assumed they used 9v regulators, but obviously not.

 

I've got loads of other kit (including old Audio Ltd sets with the 5-pin DIN connectors), some of which MUST work off a battery, but it's all belt-pack stuff (I used to do a lot of musicals), & I really don't want to give the dog-show man a G2 because he's bound to break the switch, & they won't want to pay for the repair.

 

So, my question is - has anyone tried mixing Trantec hand-helds with Audio, Shure or AT receivers, & if so was the companding & deviation near enough to get away with in a not very quality-conscious situation?

 

I'm talking VHF here, as apart from G2s (which I don't want to use) all my hand-helds are Trantec S.1s, S.2s or S3500s.

 

 

[pete10uk]

I've powered numerous radio receivers, both vhf and uhf, cheapo and sennheiser g series, from batteries over the years and can't ever recall an issue.

 

I have also personally mixed uhf tx and rx's as long as long as the frequency's have matched they have been fine, I've seen cheap vhf mixed but can't recall brands eta but they seemed to be as fine as any other vhf.

[paulears]

I actually have a rack of Trantec receivers and regularly use them with Sennheiser hand held and the companding mismatch actually works quite well, a very gentle compression. The other way around can give high volume use ops a hard time as the expansion the other way means feedback can be tricky to manage. Not had as much success mixing Shures and Sennheisers - sounds a bit thin and weedy? Not sure why.

[Lamplighter]

 

Wrong!! - with the battery reading 12.3v every one I tried (including an S3500, clearly marked "12-18v" on the back) produced a very low, horribly distorted output at anything above a whisper. Exactly the same results back at base next day. I had assumed they used 9v regulators, but obviously not.

 

 

 

I have just checked a Trantec S3.5 Mine works satisfactorily down to 9.0 dc at which point the internal 10 volt regulator is showing 8.4 v out. At this setting 800 Hz tone at peak deviation is not visibly distorting and a music signal with the yellow peak light occasionally flashing sound fine.No strange noises when audio source removed. I suspect that your problem lies elsewhere in the system.

The 10 volt regulator only needed 10.4 volts to provide its 10v output so operation from a 12v battery should not be a problem.

Brian

[sandall]

I suspect that your problem lies elsewhere in the system.

 

Quite right Brian. The (TOA) amp only has 1 balanced I/p, on a 5-pin DIN, which I didn't have a cable for, so I was using the unbalanced jack inputs. Running off a battery obviously creates an earth loop, as roughly when the audio kicks in so does a loud farting / fast motor-boating noise (the threshold varies with the receiver model). A transformer or DI would presumably have solved the problem, but that's one for the hindsight department.

 

Good point about not all systems using companding, Paul. When I have a bit of time I'll get out all the hand-helds & non-matching receivers & have a play.

[Simon Lewis]

... Running off a battery obviously creates an earth loop, as roughly when the audio kicks in so does a loud farting / fast motor-boating noise (the threshold varies with the receiver model). A transformer or DI would presumably have solved the problem, but that's one for the hindsight department.

 

I suspect that's not an earth loop issue but more RFI? Motorboating is usually due to parasitic low frequency oscillation? Can you can try again using the the balanced input?

 

 

 

[DrV]

If you were running both the radio Mic and the amp off the same 12v battery then the problem is most likely to have been due to poor regulation of the battery voltage. This in turn could have been due to excessive internal resistance of the battery and/or the supply wiring. Solutions would be separate batteries, a bigger battery with lower internal resistance, thicker wires and wiring the supply in a star configuration direct from the battery terminals. Best solution would be separate batteries - a car battery for the amp and something like an NP7-12 for the Mic.

 

As Simon says, motor-boating is low frequency oscillation and very often caused by supply rail regulation issues.

 

Dave

[Modge]

thicker wires and wiring the supply in a star configuration direct from the battery terminals.

I have seen much PA suckiness* caused by undersized wiring running stuff at 12v via an inverter.

 

 

*technical term. I'm a lampie.

[sandall]

If you were running both the radio Mic and the amp off the same 12v battery then the problem is most likely to have been due to poor regulation of the battery voltage.

 

As Simon says, motor-boating is low frequency oscillation and very often caused by supply rail regulation issues.

Dave

I called it motor-boating?, but more like a 2-stroke at moderate run-speed. Yes I was using a (2-pointed) star connection for power, with reasonably thick cables for the amp, & the battery was a rock-solid 12.28v, though I didn't have enough hands to check if it dropped at all at nasty-noise time, so you could be right. On the other hand the unbalanced connection would almost certainly be grounding the audio cold pin, hence my thoughts of an earth-loop - the balanced input worked perfectly, at all levels.

 

I did think of using an inverter, but the term "modified sine-wave" always frightens me off.