Audio Isolation Transformers

[Steve Mac]

I purchased this:
Jensen Transformers
Anyone have experience with them?
Actually this brings up an interesting question you gents may have an opinion on. Originally I wanted a pro amp with balanced inputs. But I also wanted Class A solid state. Well I bought an amp without balanced inputs...long story short. But now I'm wondering if this wasn't such a bad idea. Rather than incur a differential input stage in a power amp...not that they can't be designed well...but leave the amp alone and use an audio transformer instead. My thinking is that done properly this is a better solution because not only do you get the common mode riff raff noise off your back but you also close the door on hi frequency noise because the transformers roll off. You gents must know this...opinions? Are there better products than this that will properly convert balanced to unbalanced? Thanks...

[bfish]

Need more info Steve. Your amp is unbalanced input and the source is...?

Added;
While all xfmrs offer isolation, a dedicated isolation xfmr typically has a 1:1 ratio. Xfmrs in conversion boxes are step-up or step-down, depending on which way they're used.

Converted systems only offer the advantages of balanced systems on the portion that's entirely balanced, so what's on the unbalanced side of the conversion device is still subject to all the stray "riff raff" your environment has to offer. Common mode (rejection) is the good property of balanced connection that keeps the "riff raff" where it belongs, out of the signal, thus holding the noise floor down.

Balanced connections only protect themselves, and can't clean up or remove unwanted noise that entered the signal path previously at another location, say, from your source components to the pre. While xfmr rolloff can help remove the inaudible spectrum components, it's only first order, and can be done more effectively in other ways. Xfmr rolloff is on both ends too, with many of even the best starting to dump at 30Hz on the low end.

Still, if you have to convert, what you got is as good a way as any, and Jensen makes some pretty good stuff. Spending any more yeilds diminishing return.

<font color="#FFFFFF" size="1">[ April 23, 2008 09:24 AM: Message edited by: bfish ]</font>

[Steve Mac]

Originally posted by bfish:
[QB]Need more info Steve. Your amp is unbalanced input and the source is...?

<font size="2" face="Verdana, Helvetica, sans-serif">balanced!

I read your comments...thanks.
I need to experiment with placement of the amps.
My gut feeling is that some noise is also induced from the ss amps' power transformers. So maybe I can't set em all pretty like I want.

[Steve Mac]

here's a link to the specs:
http://www.jensen-transformers.com/datashts/pc2xr.pdf

[bfish]

"balanced"

That's what I presumed from your description, but the "Audio Isolation xfmr" heading suggested other possibilities.

The Jensen unit specs are good, though they reveal the LF peak weakness and rolloff typical to all physically small xfmrs. No way around it, and they've done a good job of making it a minor issue.

In general, I wouldn't look to the unit to be of help in lowering your noise floor, as it merely eliminates one of several potential sources of ground loops.

Assuming you've no noticeable 60 or 120 Hz buzz, the power supplies shouldn't be an issue as they're not in the signal path. Broadband hiss (thermal noise) on the other hand, which rapidly becomes more audible with increases in speaker efficiency, is a fairly common issue, and harder to deal with. The constant conduction of class A amps leads to higher overall operating temps, which increases the thermal noise of all affected components. I'd consider cooling your class A's as the primary factor in placement, for longevity as well as noise. Comparing the noise level (preferably with a VOM or scope) of a completely cold system at startup to that of a hot system will easily reveal thermal noise issues.