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Old 7th May 2005, 09:24 PM   #1
pjpoes is offline pjpoes  United States
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Default using audio isolation transformer

Ok, I may be using these wrong, I may be completely off, but I had some of those transformer coupled balanced to single ended converters. I took them apart and pulled out the transformer in order to attempt to install them into a cd player I have, which causes my stereo to buzz whenever its installed. I thought these might stop the buzzing. The wires on one side are Black and white, and yellow and red on the other. To simply test them, I hooked RCA's on both ends, with a short length of wire, and installed those as the interconnects. My first attemp simply wired one side to a set of rca's, and the other side to another set, and hook it up. This worked, didn't sound all that bad either, though I haven't really listened extensivly, but it signifigantly reduced the output. Since these probably aren't 1:1 transformers, this may simply be the way it is, but I also have never used such devices, so I might be using them wrong. Anyone know the correct way to do what Im trying to do, I basicly am trying to make a cheap transformer coupled output stage by hooking these to the output of my cd player.

I have this feeling the ground should not go through the transformer, is this correct. I understand how to hook them up to convert single ended to balanced, but what about keeping it single ended on both ends. I do have a balanced preamp, so I could attempt that as well.
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Old 7th May 2005, 09:49 PM   #2
dhaen is offline dhaen  Europe
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To check whether they're 1:1 or not, just switch the inputs and outputs. If their 1:1 the level should be the same both ways. You can also get a clue by measuring the DC resistance, as they often use the same gauge of wire for primary and secondary.

The likely reason for your level decrease is that your RCA's probably have a 1K ohm source impedance. You'll need transformers with a lot more turns to match this.
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Old 7th May 2005, 11:57 PM   #3
pjpoes is offline pjpoes  United States
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thanks, They aren't 1:1 I dont believe. They also didnt do what I wanted, though I used them differently than before, which might explain why.

I hooked them up so that the positive runs through a wire on one side of the tranny, and out the other. I then tied the other two wires on the tranny, one from each side to the ground of the interconnect, but left the interconnect ground intact, sort of bypassing the tranny I guess. This is essentially how it was hooked up to do the XLR conversion, accept that one side of the tranny is hooked to the second phase of the wire, instead of back to the rca ground. The result was a huge increase in output, but also an increase in the hum and noise.

I have seen this used to replace an opamp in the output stage before, and is probably a better way of doing it, as it would probably reduce some of that noise, But I have a feeling that the Hum will only go away when I find out where it is, and eliminate it.
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Old 10th May 2005, 06:30 AM   #4
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From what i can understand you have DI transformers that transforms a line-level to microphone-level? If so they are certainly not 1:1 transformers.But anyway..
Transformers should never be close to other transformers without a good magnetic shield to isolate them.
So maybe there is some other transformer, mains for instance, that induces hum and noice in the signal?
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Old 10th May 2005, 12:25 PM   #5
pjpoes is offline pjpoes  United States
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well my next closest transoformer that could be incuding this hum is about 10" above it in my rack, its a potted and encapsulated one in my preamplifier.

Actually, I dont know how I never tried this before, but I found whats causing it, or atleast part of it. When my TV is hooked up to my dvd player, it causes me system to hum. Its currently hooked through the component output, so I have three largish RCA's about 12 feet long running between my tv and dvd player. I suspended them over the power wires that run along the ground, so I can't see that being the problem, though it could be. The TV and stereo are hooked up to the same wall outlet, but different outlet strips. The TV does not have its own ground plug, but could it still have a different ground potential, and be causing this. Should I attempt to ground the DVD player and tv to the same point, maybe attach some chassis screws together with a run of wire?
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Old 10th May 2005, 12:56 PM   #6
pooge is offline pooge  United States
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If you removed the transformer from its shielded housing, you are going to pick up noise. Keep it in its housing.

Check here for a trouble-shooting guide:

You may also need an isolator for your TV. A ground loop could be caused by the antenna ground. Get a 75 ohm isolator for the antenna. As a quick and cheap arrangement, you could hook up baluns back to back, connecting the 300 ohm leads together.
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