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

KenL,

I'm not sure whether or not the Pass XA series amps would be good matches for a passive volume control, because of the XA's relatively low input impedance (20K unbalanced, 30K balanced). Although I note that Stereophile's measurements indicate that those impedances are "constant across the audio band," which will help matters. You should probably raise that question in a separate thread if you decide to pursue that possibility.

As you may be aware, the XA30.5 is considerably more powerful than its rating suggests, and JA's measurement in the Stereophile review was 195 watts into 4 ohms (although the amp leaves Class A operation at considerably less than that).

The Maggie 1.7's sensitivity of 86db/1m/2.83V corresponds to 83db at 1 meter for 1 watt input into its 4 ohm nominal impedance. 195W will result in about 106db at 1 meter. Given that for planar speakers volume levels fall off relatively slowly with distance, that strikes me as reasonable in relation to your small room dimensions and music preferences, assuming that the spec is accurate.

As far as interfacing the balanced output of the Rowland to the unbalanced input of the RVC is concerned, my suggestion would be to have a custom cable made up which connects xlr pin 2 to the rca center pin (assuming the Rowland conforms to the USA convention of pin 2 non-inverted and pin 3 inverted); xlr pin 1 to the rca ground sleeve; and leaves xlr pin 3 open. If you were to use a standard adapter, that would most likely ground pin 3, which would mean that the Rowland's output signal on that pin would be shorted to ground. Most equipment can tolerate that, but some cannot. Check with Rowland on that point if you would prefer to use an adapter.

If you want to consider a transformer instead of an adapter cable, my instinct with gear of that caliber would be to go with a Jensen. Although for the price at which B&H is currently offering the ART DTI, there is essentially no downside to experimenting with it.

Regards,
-- Al

Ken, re Energizer's nice offer, keep in mind as I indicated earlier that commercially made xlr-to-rca cables (and adapters) in most cases have pin 3 shorted to pin 1 (ground). I would not use that cable on an xlr OUTPUT without first checking with Rowland.

See this thread for an example of a problem that was caused by doing exactly that, albeit with relatively inexpensive equipment.

Also, I don't know how similar your Rowland is to the Continuum model that is currently listed on their website, but for that model, at least, it describes the xlr output as being "high current." That most likely means it has low output impedance, which will mean that the device driving pin 3 will be forced to supply LOTS of current if it is shorted to ground.

Regards,
-- Al

is this what you have in mind of each of your single channel transformer has one input for RCA and one output for XLR?

Dob, yes there would only be one rca cable for each channel, connected between the preamp output and the input side of the transformer. And of course one xlr cable for each channel, connected between the output side of the transformer and the power amp input.

As Mitch indicated, for an "input transformer" the xlr cable should be very short, less than 2 feet iirc.

Jensen's site indicates that before ordering it is usually best to speak with them directly, for help with model selection and other guidance.

Best regards,
-- Al

Hi Ralph,

See the following datasheet, and the note near the bottom of page 1 of the user manual for the PI2XX (the unit shown has balanced inputs and balanced outputs, but a similar model can be ordered with unbalanced inputs):

Datasheet: http://www.jensen-transformers.com/datashts/pi2xx.pdf

User Manual: http://www.jensen-transformers.com/datashts/pi2xx_usr_man.pdf

Note that the recommended load impedance range is 10K to infinity. And that the output impedance of the transformer at 1kHz, with a 600 ohm source impedance connected, is very high at 4.65K, of which 1.9K is dc resistance.

Given the very high output impedance, it would seem to make sense that cable capacitance should be kept very low, to avoid high frequency rolloff. That would apply whether the output is balanced or unbalanced.

Your comments appear to be applicable to output transformers, such as this one, which as explained in this application note will not perform as well in terms of cmrr as will an input transformer.

Best regards,
-- Al

Hi Mitch -- Assuming you are referring to the LAMM LL2 Deluxe, you've most probably seen JA's measurements, which indicate an output impedance rising to 3.3K at 20Hz. A phone call to Jensen sounds like it would be in order, to ask them what effects that would have.

Best regards,
-- Al