[dubkarma]

In a system separate from the one in which I use the BCD-1 I'm using a transport with a Benchmark DAC-1 (at least until I save up for a BDA-1!). I want to match the output level of the DAC-1 with the 4.6 Volt output of the BCD-1's balanced analogue outputs.

The DAC-1 manual specifies maximum output levels, "at 0 dBFS," of the balanced analogue outputs not in volts, but in dBu, as follows:

+29 dBu with internal attentuator off
+19 dBu with attentuator set at -10 dB
+9 dBu with attentuator set at -20 dBu
-1 dBu with attentuator set at -30 dBu

The factory setting is -20 dBu and can be changed by moving four internal jumpers. To my ears, this setting is much the same as the fixed setting of the unbalanced analogue outputs, which Benchmark does specify as 2 volts.

So, how do I translate dBu into volts so I can level-match the outputs of the DAC-1 with those of the BCD-1? (The DAC-1 also has external miniature trimpots that can lower the output within each of the above settings.) I'd prefer to have the internal attentuator in the "off" position, because it offers by far the lowest output impedance of the four balanced settings (60 ohms). But I don't want to overload the balanced input of the BP-25 preamp I'm using with the DAC.

Assistance from the technically literate much appreciated.

TIA,

Joel

[dubkarma]

Sorry for wasting your time, folks. I found the answer to my question at:

http://www.sengpielaudio.com/calculator-db-volt.htm

4.6 volts RMS = 15.47 dBu.

So I can set the internal jumpers at 0 attentuation and use the external trimpots to dial down from +29 to + 15.5 dBU.

Cheers,

Joel

[NewBuyer]

...The DAC-1 manual specifies maximum output levels, "at 0 dBFS," of the balanced analogue outputs not in volts, but in dBu, as follows:

+29 dBu with internal attentuator off
+19 dBu with attentuator set at -10 dB
+9 dBu with attentuator set at -20 dBu
-1 dBu with attentuator set at -30 dBu

...I'd prefer to have the internal attentuator in the "off" position, because it offers by far the lowest output impedance of the four balanced settings (60 ohms)...

Glad you found your answer.

By the way: The DAC1 manual states that balanced output impedance using the -30db pad is better still at only 43 ohms, and to my ears this setting also sounds the best too (I use the variable output, I haven't needed/tried the calibrated output).

Like you, I'm very interested in auditioning the BDA-1 against the DAC1 PRE...

[dubkarma]

"By the way: The DAC1 manual states that balanced output impedance using the -30db pad is better still at only 43 ohms, and to my ears this setting also sounds the best too (I use the variable output, I haven't needed/tried the calibrated output)."

Do you mean the DAC1 Pre manual? I've got the DAC1 manual (Revision L) in front of me as I type: for the -30 dB attenuator setting it gives an output impedance of 160 ohms. Having said that, I've often wondered if there's typos in this section, because for the -10 dB setting it gives an impedance of 1600 ohms and for the -20 dB setting an impedance of 500 ohms!

(I use an active preamp, so the variable output isn't appropriate.)

[NewBuyer]

"By the way: The DAC1 manual states that balanced output impedance using the -30db pad is better still at only 43 ohms, and to my ears this setting also sounds the best too (I use the variable output, I haven't needed/tried the calibrated output)."

Do you mean the DAC1 Pre manual? I've got the DAC1 manual (Revision L) in front of me as I type: for the -30 dB attenuator setting it gives an output impedance of 160 ohms. Having said that, I've often wondered if there's typos in this section, because for the -10 dB setting it gives an impedance of 1600 ohms and for the -20 dB setting an impedance of 500 ohms!

(I use an active preamp, so the variable output isn't appropriate.)

It is interesting that both manuals for DAC1 PRE and DAC1 USB identify balanced output impedance of 43-ohms for the -30db pad, but the original DAC1 (non-PRE non-USB) says 160-ohms as you correctly state.  I hadn't noticed the discrepancy until you pointed this out to me here.  Perhaps an engineering change occurred since the original version of the DAC1?  Now you've got me wondering too. 

I can't find the output impedance spec for the BDA-1 (or BCD-1) by contrast, but with the Bryston discrete output stage I'm sure it is nice and low.  I can't wait to try it. 

[dubkarma]

I've read in other forums that the DAC1 USB and DAC1 PRE also use different output opamps than the DAC1. But enough of such talk in the Bryston AudioCircle!

So far, the BCD-1 is giving my separates, which retail at about four times its price, very serious competition.