Maintaining a "balanced" signal chain

[mikekars]

My understanding is that in a "patch cable" sort of signal chain one single leg that is not balanced will unbalance the whole chain.

I am wondering if this will also be true in my particular case.  I have  drive signals coming from a DR260 that  will go to several  amps.  So, for example, the low frequency signal out of the DR260 will go to a PLX3402 set to parallel inputs.  That PLX3402 will be daisy chained to a second PLX3402 also with parallel inputs.  Then that PLX3402 will be daisy chained about 40 feet vial xlr to a third and 4th PLX3402 (other amp rack near other speaker stack).

So if I use a TS patch cable between the first two amps does that unbalance the whole signal chain?  Or do the amp connections and their unknown internal wiring some how keep it balanced?

The reason I ask is I already have some short patch cables for this that are just the right size but they are TS, not TRS.  If all connections were just in the same rack I would probably not worry about it.  But I am making that long run to the the other stack with an XLR that will likely be run next to lighting and other power cables that could induce some noise. 

Or is it not likely to be an issue either way?

And a second question, will the DR260 output be able to drive all those amp  inputs (total of 4)?

 

 

 

[agedhorse]

 

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mikekars wrote:

 

 

My understanding is that in a "patch cable" sort of signal chain one single leg that is not balanced will unbalance the whole chain.

 

I am wondering if this will also be true in my particular case.  I have  drive signals coming from a DR260 that  will go to several  amps.  So, for example, the low frequency signal out of the DR260 will go to a PLX3402 set to parallel inputs.  That PLX3402 will be daisy chained to a second PLX3402 also with parallel inputs.  Then that PLX3402 will be daisy chained about 40 feet vial xlr to a third and 4th PLX3402 (other amp rack near other speaker stack).

 

So if I use a TS patch cable between the first two amps does that unbalance the whole signal chain?  Or do the amp connections and their unknown internal wiring some how keep it balanced?

 

The reason I ask is I already have some short patch cables for this that are just the right size but they are TS, not TRS.  If all connections were just in the same rack I would probably not worry about it.  But I am making that long run to the the other stack with an XLR that will likely be run next to lighting and other power cables that could induce some noise. 

 

Or is it not likely to be an issue either way?

 

And a second question, will the DR260 output be able to drive all those amp  inputs (total of 4)?

 

 

 

 

 

 

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Yes, in this case it will unbalance everything because of the way the inputs are configured.

The DR260 will be driving 8 inputs, not 4. The PLX paralleling occurs before the input amplifier. Yuo will have 8 x 20k (balanced) inputs paralleled, that's just about the practical limit IMO. Each side of the line driver will be driving about 1.2k.

[mikekars]

Thanks for the succint answer.  If driving 8 inputs is the practical limit of one DR260 output channel, then I am at that limit and should take some care with this.

If the amplifier is in bridge mode, will this also look like "2" inputs to the DR260 regardless of the parallel mode switch setting on the amp?

It appears that on the RMX and original PLX series the bridge mode and parallel input mode switches are independent.  But on the PLX2 series, switching to bridge mode turns on the "parallel input" LED indicator light automatically.

[dboomer]

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mikekars wrote:

 

So if I use a TS patch cable between the first two amps does that unbalance the whole signal chain?  Or do the amp connections and their unknown internal wiring some how keep it balanced?

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It depends on the circuitry used.  Some units have buffer amps thet will re-balance and some just parallel out what you put in.

 

I wouldn't worry much about it.  When dealing with a hot line level and a very short distance (assumed) running balanced doesn't make much difference except in drive level, which is just an adjustment you make.  Or as Andy points out, if you try to drive too many units.

[agedhorse]

Bridged mode would present 4 inputs to the dr260, but bridge mode may not be desireable for other reasons.

[Dogoth]

 

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agedhorse wrote:

 

Bridged mode would present 4 inputs to the dr260, but bridge mode may not be desireable for other reasons.

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My thoughts exactly. Bridge mode is entirely different than paralleled stereo inputs. Yes you would be driving less inputs but the output impedence scenario for the amps changes dramaticaly. The worst case of loading down the dr260 would probably be reduced audio quality (you MIGHT loose the output stage but it's doubtful). The worst case of loading down bridged amplifiers could easily be smoked amplifiers AND speakers (a far more catastrophic failure).

As agedhorse pointed out it's NEAR the maximum load for the dr260 (not beyond it). If you're really worried about it, get either a small distribution amp or a passive transformer/splitter device (with the latter you might loose some gain which can probably be made up for elswhere). You could even make the transformer impedence conversion at the beginning of the chain and end up balancing it all in the process.

Personaly I wouldn't worry about it.

My .02