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polmuaddib

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Hi everybody,
I need help making an XLR input on a regular single end amplifier. Since regular cable adapters wouldn't work, I decided using a transformer and already got the general purpose Lundahl 1588. I saw that they use them in some high end amplifiers.
The reason I need XLR input is for rejecting hum and grund loops that occur in my system. There is no way to track the source of ground loops, so I beg you not to suggest something like that. I also bought the 1588, so I would ask not to suggest other transformers.
Now, here is a schematics of Lundahl and there are three applications that they suggest. There could be others, I suppose, but the one I need is just the conversion of balanced signal to unbalanced without creating a hum or ground loop.
I was thinking of using Parallel-parallel connection (1 : 1) for low loss isolation application, where I would connect pin 6 to XLR hot (2), pin 9 to XLR cold (3) and leave XLR ground (1) floating while on the other side I would connect pin 1 to RCA positive and pin 4 to RCA ground.
Questions:
1. Do I need some resistor, and what value, somewhere? (please, specify where)
2. Since I am hoping for the best SNR connection, would other connection work better, like Phase splitting for 1 : 1+1 input?
3. What about ground from Lundahl (pin 8) and XLR ground (1 and sleeve)? Do I connect all to the chasis of the amp, or only Lundahl ground?

1588.jpg

I thank you for all the suggestions. I know this is not a small ask and I really appreciate the help.
 

somebodyelse

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https://www.jensen-transformers.com/wp-content/uploads/2014/09/Audio-Transformers-Chapter.pdf
Sections 2.1.2 and 2.2.4 seem most directly related to your situation.

I think what you probably want is series input and parallel output, with the shield connected to the RCA ground and a very short low capacitance cable between the transformer output and the amp's RCA input. This provides the step down to better match the high level signal usual on balanced outputs to the more sensitive single ended input. The short, low capacitance cable is needed to avoid roll off of high frequencies. I'm no expert though, so someone with more experience may know better.
 

Ricardus

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Per Lundahl over at Lundahl is super helpful and a very nice guy. A company I used to be technical coordinator for met with him some years ago at NAMM to work a deal to carry his products. If you email Lundahl with your specifics he will very likely answer the email himself.
 
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Ricardus

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Thanks. That's a good idea.
In fact, 3 years ago I was working on a vacuum tube mic preamp project and had some transformer questions, so I emailed Lundahl and Sowter, and Per replied, and Brian Sowter replied. They're very helpful.

Let us know what he says. He might have a different transformer recommendation, too.
 
OP
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polmuaddib

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Yeah, I am not buying a new transformer. This LL1588 was very expensive and it needs to be put to work:). I bought it because I saw it used in many high end amplifiers and know that it can be used for that purpose. I didn't count on being more versatile, though.
I sent an email and i will let you know when the reply comes.
Thank you.
 

Ricardus

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Yeah, I am not buying a new transformer. This LL1588 was very expensive and it needs to be put to work:). I bought it because I saw it used in many high end amplifiers and know that it can be used for that purpose. I didn't count on being more versatile, though.
I sent an email and i will let you know when the reply comes.
Thank you.
If need be you could sell those 1588's on GroupDIY no problem.
 
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