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Output transformers - which model?

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Hi,
I have a few questions regarding the use of output transformers that I hope you will respond to:
I would like to use a Behringer DCX 2496 as a digital crossover for my 2-way hornsystem in order to play around with different crossover frequencies and slopes . Thus, the chain of components will be:
Philips DVD963SA (digital out) => AES/EBU input of the Behringer => 4 analog outputs (LOW, left and right, and HIGH left and right) connected to two stereo power amps.
In order to control the volume I will use a 4-channel attenuator between the Behringer and the power amps.
My power amps are very sensitive to ground loops and I have heard that transformers can be use to eliminate ground loops effectively, so now I consider using tranformers between the volume control and the Behringer.
Just to add further information, the power amps are semi-digital ICE-power based amps from Acoustic Reality (the one for bass have an input impedance of 8 kOhm and the one for the mid/high section has an input impedance of 55 kOhm). I intend to cross somewhere between 150 and 300 Hz.
However, I know nothing about output transformers. So here are a few questions:
1. The advantage (as I understand it) of using transformers is the elimination of ground loops. Are there any disadvantages of using transformers in this application � except that I will have to buy them of course:-)? And what will they do to the sound?
2. Will the impedances vary accross frequency when using transformers?
3. Which transformers from Lundahl would be the best to use for my application?
I thank you a lot in anticipation and hope to hear from you!
Regards
Peter

Follow Ups:

Re: Output transformers - which model? - KevinC 20:34:27 06/28/05 (3)
Lots of interesting stuff here.
If you are going to use a transformer to break a potential ground loop, then normally you would use a 1:1 transformer large enough to handle the highest signal level at the lowest frequency of interest. What maximum signal level do you anticipate at the output of your crossover needed to drive your amps?
I am not sure what a transformer will do to the sound in your situation, because I have never used one in a similar situation. However, I can say that I like what transformers do sonically when they are used to couple stages together that can benefit from their properties.
Within the audio band, a properly chosen transformer will not casue variation in impedance with frequency.

Kevin Carter
K&K Audio
www.kandkaudio.com
- Re: Output transformers - which model? - pk 07:06:18 06/29/05 (2)
  Hi Kevin,
  Thank you very much for your reply!
  You wrote:
  > What maximum signal level do you anticipate at the output of your > crossover needed to drive your amps?
  Well, I must admit that I can not answer this question very specificly, but I can tell you this: At the moment I do not use a Behringer, but a conventional preamp with a built-in fixed-value active crossover. Besides the crossover function the concentional preamp only acts like a "buffer" with 0 dB gain in the line stage, and this is surely enough to drive my amps.
  So, zero gain is ok. As far as I know the Behringer should not add any gain by itself, so I assume that the situation is similar to the current one using a conventional preamp.
  I further intend to use either the adjustable level controls from the Behringer or fixed analogue resistors (should be better) at the output of the Behringer in order to match the levels between "high" and "low".
  I can see that I am not very specific, but I hope that this is sufficient to provide a specific suggestion between the different output transformer models.
  I thank you again and hope you can help me further! Thanks!
  Regards
  Peter
  - Re: Output transformers - which model? - KevinC 09:34:37 06/29/05 (1)
    A transformer like the LL1690 is good for up to about 4V RMS at 20Hz. The smaller LL1544A will manage about 1.8V RMS at 20Hz. These are my favorite choices. However, you might consider a larger leap into improvement by removing the op-amp output stage entirely and tying the transformers directly to the voltage outputs of the DACs in the Behringer. One customer has done this and was very enthusiastic about the improvement.
    
    Kevin Carter
    K&K Audio
    www.kandkaudio.com
    - Thanks a lot for your reply, Kevin! (nt) - PK 23:47:31 06/29/05 (0)
      Regards
      Peter

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