Need help fast - Unbalanced Preamp to Balanced Amp

If your "balanced amp" is "fully balanced," meaning that its internal signal path is entirely balanced, and both its red and black speaker terminals are actively driven (as opposed to the black terminal being grounded internally), an rca-to-xlr adapter or adapter cable is not a suitable solution. It would probably result in 75% of the amplifier's power capability becoming unavailable, because only one side of the balanced signal path would be driven with a signal.

I have used this transformer-based converter in voice recording applications, and for that purpose at least it has proven to be completely transparent sonically. It's spec sheet is at http://www.artproaudio.com/downloads/specsheet/dti.pdf. It can be purchased here. They appear to be having a special sale on it, and when you add it to the "shopping cart" you will see a much lower price than the $60 that is initially indicated. I don't know how its sonic quality would compare to the results you would get from the active (powered) unit Kal suggested.

If you really want to do it right, although at several times the cost, call Jensen Transformers and have them help you select one of their "Iso-Max" units. Also, see their technical white paper on interfacing of unbalanced and balanced equipment:

http://www.jensen-transformers.com/an/an003.pdf

BTW, NEVER connect two outputs of any component together, via a y-adapter or otherwise. In this case it would most likely have no effect, as Kal explained, but in other situations it could result in damage. On the other hand, connecting two inputs together, to a common signal source, will not cause damage and will usually (although not always) give good sonic results.

Regards,
-- Al

Almarg has completed my thoughts. The transformer-based ARTS and, especially, the Jensen units are superior on paper. I have no hand's-on experience with any of them as I have used only Cardas or Kubala-Sosna cable adapters when necessary.

Kal

Thanks guys. I didn't mean to highjack the discussion, as I'm not the originator of the thread, but I do have an interest in the topic.

For those who might be interested, here's my actual situation. . .

I'm waiting on delivery of a pair of Maggie 1.7's. I thought I would use my very good sounding Rowland Concerto Class "D" integrated with internal phono. However a friend let me try a DIY SS Class "A" 45w amp that is based on a Nelson Pass design. As good as the Rowland sounded, I fell in love with vocals thru the DIY amp. Hard to beat Class "A" for midrange purity.

With this in mind, I thought I might purchase either a Pass XA30.5 or XA 60.5 mono's to go with the Maggies. My room is small (12'x 14'x 10') so I shouldn't require a huge amount of power for them to play at satisfying levels for my usual jazz, blues, female vocal listening. A stereo XA30.5 might be all I need. The heat wouldn't be as big a factor vs the mono's either.

I'm currently using a custom Placette RVC (unbalanced) that has 2 inputs. My Squeezebox is connected to one input via a PS Audio PerfectWave dac, and I'd like to use the phono of the Rowland thru the 2nd input. Unfortunately the Rowland only has balanced connectors for it's output, thus the need for conversion.

Not knowing whether I'll keep the Rowland or not, I'd rather not spend a lot of $$ on cabling at this point. Almarg & Kal have provided several alternatives for me to explore. I thank them and everyone else who has provided suggestions. Hopefully I will discover something that works and is relatively inexpensive.

If you use an adapter, sometimes you can wind up with a hum because the adapter is not grounding the unused input.

With a balanced amp you have a non-inverted input and an inverted input that is part of the XLR connection. If the RCA to XLR adapter is only using the non-inverted input, often there will be no connection on the inverted input. This can leave you with some hum, and often less gain.

To correct this, open up the XLR side of the adapter and have someone (if you can't solder) connect pin 1 of the XLR (ground) to the unused connection (often pin 3, which is the inverted input).

This will get rid of the hum and the amp will have normal gain.

It would be better to have a cable that does the conversion rather than an adapter, as there are less connections.

If you go the transformer route as mentioned above, place the transformer as close as you can to the preamp can keep the cable to it short. Then run the balanced cable from the transformer to the amplifier- this cable can be a lot longer than you are used to with single-ended, and you will not have to sink as much cash into it for it to sound right.

The transformer will have some artifact; although the Jensens are very good I find they reduce bass impact and liveliness, so if your cable can be short from the preamp to amp I would go with the adapter rather than the transformer.