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Is a passive transformer based line isolator with 600 ohm in/out impedance suitable for use with an AVR?

Qbd

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I’m in need of unbalanced to balanced converters, and I’m looking at passive transformer based solutions.

I have a Denon X4200W, which is an AVR with normal RCA pre-outs

My use case is AVR->Subwoofer (long cables that do exhibit slight hum with RCA cables) and AVR->power amp (horrible hum with RCA->XLR adapters, though I still have some cables coming that need to be tried).

From what I can tell, transformer based solutions that can handle sufficient voltage (1.5 V or more) are not too common. One option I’ve found is the Palmer LI 02. The only problem that I can see is that it has a 600 ohm input impedance, which is AFAIK much lower than what is common for power amps used with AVRs.

Is a 600 ohm input impedance a problem though? Can it harm the AVR, or cause any problems with audio quality?

Alternatively, are there other solutions more suited to the task?
 

Cbdb2

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You might not need a transformer. There are other ways to get rid of ground loops. Are you sure the AVR to amp cables are right? If you still need a transformer Jensen makes some of the best audio transformers and they make many different kinds, there website has a ton of great info on transformers, ground loops, and wiring balanced to unbalanced connectiond etc.

Start here:

https://www.jensen-transformers.com/application-notes/
 
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Grumpish

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I’m in need of unbalanced to balanced converters, and I’m looking at passive transformer based solutions.

I have a Denon X4200W, which is an AVR with normal RCA pre-outs

My use case is AVR->Subwoofer (long cables that do exhibit slight hum with RCA cables) and AVR->power amp (horrible hum with RCA->XLR adapters, though I still have some cables coming that need to be tried).

From what I can tell, transformer based solutions that can handle sufficient voltage (1.5 V or more) are not too common. One option I’ve found is the Palmer LI 02. The only problem that I can see is that it has a 600 ohm input impedance, which is AFAIK much lower than what is common for power amps used with AVRs.

Is a 600 ohm input impedance a problem though? Can it harm the AVR, or cause any problems with audio quality?

Alternatively, are there other solutions more suited to the task?

Possibly a ground loop problem, does any of that kit have a ground lift switch? Or possibly try cables with the screen disconnected at one end.
 

sergeauckland

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I’m in need of unbalanced to balanced converters, and I’m looking at passive transformer based solutions.

I have a Denon X4200W, which is an AVR with normal RCA pre-outs

My use case is AVR->Subwoofer (long cables that do exhibit slight hum with RCA cables) and AVR->power amp (horrible hum with RCA->XLR adapters, though I still have some cables coming that need to be tried).

From what I can tell, transformer based solutions that can handle sufficient voltage (1.5 V or more) are not too common. One option I’ve found is the Palmer LI 02. The only problem that I can see is that it has a 600 ohm input impedance, which is AFAIK much lower than what is common for power amps used with AVRs.

Is a 600 ohm input impedance a problem though? Can it harm the AVR, or cause any problems with audio quality?

Alternatively, are there other solutions more suited to the task?
Transformers are what I use, with no problem. An excellent solution.
Firstly, the 600 ohm issue is a non-issue with HiFi equipment. All it means is that the transformer has enough iron in its core to be able to drive a 600 ohm load. You will be driving a high impedance, probably 10kohm or above, so the transformer will be very happy even at the lowest frequencies where core saturation takes place.

Secondly, pretty much any 1:1 transformer will handle more than 1.5v. The ones I use handle 8 volts (+20dBu) down to 30-40Hz with very low distortion. The Palmer you linked to also handles +20dBu, so more than enough.

The only downside to transformers is cost, the transformers I use (Sowters) are around £80 per channel. The Palmer is a little cheaper, but still a lot more expensive than the sort of £10 line isolators available on eBay, but will be a lot better, and be transparent in use.

If you have the budget for the Palmer unit, go for it, it will work properly, and transparently.

S.
 

DVDdoug

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The only problem that I can see is that it has a 600 ohm input impedance, which is AFAIK much lower than what is common for power amps used with AVRs.
It's OK (and common and normal) for a low-impedance to drive a high-impedance so the power amplifier-side is no problem.

It's the load on the AVR's preamp outputs that could be an issue. It doesn't seem ideal but my guess is that you'd be OK. Solid state electronics tend have low output impedance "by nature" and a transformer "reflects" the impedance so a higher impedance on the secondary results in a higher impedance on the primary. With no load on the secondary you have an inductor (which has lower impedance at lower frequencies) and again I'd guess the impedance is higher than 600 Ohms with no secondary load (or with a power amp on the secondary).

I have a bias against transformers in the audio path because they have limitations and it's "hard" to make one that works over the whole audio range. But that's just a bias... Jenson makes good ones and if it solves the hum problem of course that's a good thing!
 

polmuaddib

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What do modern AV processors use to convert unbalanced signal to balanced XLR output? Some opamps? Because there are no more true balanced processors made anumore (not in normal price range, at least). How does AVP solution compare to Transformers?
I think Amir measured Jensen trasformer and it was ok.
But, if you want to buy transformers for more surround channels, then might as well buy Marantz AV7705.... right?
 
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Qbd

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Thanks for the input everyone. So I take it that the 600 ohm input impedance rating shouldn’t be an issue at least.

Possibly a ground loop problem, does any of that kit have a ground lift switch? Or possibly try cables with the screen disconnected at one end.
I have tried lifting the ground (AVR -> RCA cable -> RCA-to-XLR adapter -> XLR ground lifter -> Hypex MC502MP amp). It did remove quite a bit of noise, but still lots remains.

But, if you want to buy transformers for more surround channels, then might as well buy Marantz AV7705.... right?
Yeah I am contemplating the AV7706 as a «cheap» processor instead of spending 100’s of $ on transformers, but it’s still pretty expensive even though it is perhaps the cheapest processor available.
 

EB1000

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The Jensen isolators works great w/o any audible degradation. I use the ISO MAX to isolate the NAD C658 from my Yamaha AVR.
 
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