Gain into my preamp from DAC


I am using a Bryston BDA-1 DAC into a Jolida Fusion Tube preamp. The output of the DAC is 4.6V via 'fully differential balanced' (Bryston terminology) XLR and 2.3V via unbalanced RCA. I understand that this is to be expected. Both DAC outputs can be used simultaneously, however I geberally use the XLRs to the Preamp and the RCAs to a headphone amp.. 

When I compare output volume between the XLR and RCA inputs of the preamp there is no difference. I would have expected 6dB greater gain via XLR . I understand that the preamp is not balanced.

Please elucidate as to this finding. Thank in advance.


mesch
Not sure how one 'geberally' uses anything, however understand it to be very difficult :-).
If your preamplifier is not balanced, then you won't get higher gain on the  XLR inputs because it's using them single-ended.
Hi Mesch,

That kind of result is not unheard of, and two possible explanations occur to me:

1)The balanced input of the preamp is processed through a stage which receives the balanced pair of signals differentially, converts them to a single-ended signal, and in the process intentionally introduces a 6 db gain reduction, perhaps for the purpose of matching the gains provided for the single-ended inputs.

2)The circuit in the preamp which receives the balanced pair of signals just processes one of those two signals, in single-ended fashion, and ignores the other signal.

A means of distinguishing between those two possibilities would be to connect the RCA output of the DAC to the XLR input of the preamp using an RCA-to-XLR adapter. The adapter would route the signal on the center pin of the RCA connector to pin 2 of the XLR connector, while grounding the other signal pin of the XLR connector (pin 3).

If doing that results in the same volume as when an XLR cable is used, for a given setting of the volume control, it would point to explanation 2. If you hear essentially nothing when you do that, it would also point to explanation 2. (That result would occur if the preamp utilizes the signal on XLR pin 3 and ignores the signal on pin 2). If the volume is 6 db less than when an XLR cable is used, it would point to explanation 1.

Best regards,
-- Al

Cleeds, I am not sure that the input portion of a single ended device can't be configured to accept both signals from a balanced device when connected via XLR such that the 6 dB gain is enforced. This was one aspect inherent to my question, and as mentioned, I remain unsure of this. 

Al, I was hoping you would chime in on this, and as always you did not disappoint. Regarding explanation 1), is it possible that the 6 dB gain can be maintained while the conversion from balanced to single ended is accomplished, as opposed to a designer wanting to maintain equal gain across inputs? Regarding the two possibilities, I do not have the required RCA to XLR adaptors, however I am planning on asking Jolida as to their XLR input and with the information provided I am better positioned to formulate my questions to them. Thanks!