Inline passive attenuators, should I bother?

[Matias]

Actually the +1 dBu is the lowest analog reference level on the RME, using it allows to reduce the amount of digital attenuation if you have too much gain in the amp.

My mistake, you are right already using the lowest gain. So yes, using an inline attenuator should do the trick with the current amp. Or sell the amp and buy one with adjustable gain.

 

[gvl]

My mistake, you are right already using the lowest gain. So yes, using an inline attenuator should do the trick with the current amp. Or sell the amp and buy one with adjustable gain.

Another option is to buy very inefficient speakers

 

[gvl]

Personally - in that circumstance, I'd fit attenuators. But I'd build my own into the XLR interconnect.

Yeah, this is what I should do. Is there a recommended schematic for balanced ?

 

[antcollinet]

Yeah, this is what I should do. Is there a recommended schematic for balanced ?

(Open invite : I'm cobbling this together as I go so feel free to check my work, and correct if necessary.


I would use a simple U-pad as illustrated by the blue resistors in the sketch. (R1x2 and R2). It should be installed at the amp end of the interconnect.

The red resistors represent the output impedance of your Dac, and the input impedance of your amp.

It simplifies things if you assume the balanced signal is fully balanced (V- is exactly equal to the inverse of V+). In this case R2 can be considered as two series resistors whose value is R2/2 - with the mid point connected to earth.

Then for each half of the balanced pad, you have Rout in series with R1, forming a simple resistor divider with R2/2 in parallel with Rin

If we assume Rout = 100ohm, and rin = 47K, and that we want say 30dB of attenuation.

We also want R2 to be large compared with Rout (to reduce load on the DAC) but we want R2 to be low compared with Rin (makes Rin insignificant in the attenuation)

30dB is aprox a ratio of 1:30 (Co-incidentally). So if we choose R1 to be 10Kohm and R2 to be 2x (10K/30) we won't be too far away - say 680ohm for R2.

So we have Rout+R1 = 10100, and we have R2/2 = 340 in parallel with 47K = 338ohm.

Attenuation will be 338/(10100+338) = 0.032 = -29.90dB


Feel free to adapt for the specific I/O impedances of your DAC and Amp (though if similar to the estimates above probably no need to worry) and the attenuation you want to achieve.