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
mesch
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.
I think you're assuming that an XLR connection is inherently balanced and, if so, you're mistaken. If your preamplifier is not a true balanced differential preamplifier, it doesn't benefit from the gain of a balanced connection. Depending on the circuit, you may get some of the benefit of a balanced connection's  noise rejection, but you won't get the gain.

... 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....

... 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?

Yes, a design can certainly be implemented in that manner. Based on your findings, though, the preamp has not been designed in that manner in this particular case.

Best regards,
-- Al

That's because our ears do not equate doubling sound pressure level (6db voltage) to perceived loudness. We need to experience about a 10db increase to perceive "twice as loud". 
Ai, thanks again for your reply. I knew after making the comparison that the input stage on the Jolida pre's XLR was not configured to deliver the expected gain, I was not sure as to why, or if it was even possible. I know know the answer to both questions. As always, your reponse was both succinct and articulate.

Cleeds, I have never assumed  XLR connection to be balanced, particularly ones found on single ended gear. However, as I have found out from Al's response, it can be possible for a unbalanced preamp to to capture the additional gain supplied by a balanced source if it's input is configured to do so. This is likely not the norm however. 

Gs5556, I understand the 10dB  ~= 2X volume relationship, However a 6dB gain is substantial.

I should add that I was not troubled by the lack of a differential gain between the RCA and XLR inputs on my pre. If anything the 20dB gain offered by the Jolida is more than required for my system. I am over attenuating the signal. Should I consider having Jolida modify my unit I will ask if the gain can be adjusted. 

I Truly appreciate the education provided by many on this forum.
Thanks for the nice words, Mesch.

As an FYI, a commonly seen example of a preamp (or integrated amp or power amp) having a single-ended internal signal path while providing 6 db of additional gain for an XLR input compared to the gain provided for an RCA input, would be a solid state design which utilizes an "op amp" ("operational amplifier") integrated circuit configured to differentially receive the balanced pair of input signals while providing a single-ended output. That kind of an input circuit can be configured to provide 6 db of gain, zero db of gain, or any other desired gain within a wide range of limits, simply by changing the value of two resistors.

Best regards,
-- Al