Having a pot(stepped pot, etc.) on the output of the dac is a bad move, as you'll be driving your cables from a high impedance source.

I would suggest using some sort of level control with the sub amp, not at the source.

But can the attenuator go between the digital board and the line stage board?

I'm inquiring for my mastering studio. I can already control the volume digitally from the computer. But, I believe that every DAC that I've ever plugged directly into my amp causes a loud popping noise when I switch sampling rates. It is basically the sound of my amp trying to send the speaker coils across the room, and it is quite a concern. That's why I've always used a passive, buffered "preamp" in my signal chain, to attenuate the analogue signal. But, it is unbalanced. I would like to build a DAC with a balanced output that I could run, safely, straight into my amp, and control the volume of it and the sub, which is on the separate SE output, simultaneously.

Well, actually I am looking to use this with a different DAC board. It is a piece of gear that hooks up via firewire and has great conversion, but it has a transformer I/V stage that colors the output, making it less suitable for mastering. So I'm hoping someone can answer my specific question. Can I use a stepped attenuator to control the volume of the output for both the balanced and the SE of the Legato?

This brings up another question. Are there no DIY firewire DACs?

It's a Texas Instrument PCM1794.

So what if it went from the Legato's balanced outputs to the stepped attenuator, and then of some kind of buffering circuit, and then a separate Ballsie Lite board to run the sub?

I can't seem to find the output impedance of the I/V stage.

Great! But, to clarify...

Are you saying that, everything aside, in order to use the DAC with the I/V stage, I have to change resistor values?

Or, are you saying that if I change the resistor values, I may not need to use buffers?

Thanks!

I may do that in the future. But, in the meantime, how do I order version 1 of the Legato kit (and does that version work with LCBPS kit)? And just so I don't mess anything up, could you give me the resistor numbers for those as they are on the schematic?

Thanks for the help!

Edited by user Wednesday, November 17, 2010 9:59:20 PM(UTC)  | Reason: Not specified

Thanks again for all of the help. I sort of changed the plan and simply wish to use the balanced output to go to another unit.

I took my best guess at which resistors to change, but I'm not sure I got it right. I can't get the trimmers to bring the input to 0 V. I think I messed something up. I would really appreciate knowing exactly which resistors to change.

Thanks!

Edited by user Wednesday, March 2, 2011 9:07:31 AM(UTC)  | Reason: Not specified

Hi,

My first post here as I am recently discovering this site. I did a search here for "passive attenuator" and this post seems to have some information useful to me. I,m not sure I understand everything discussed in this thread but I do understand some of it.

I'm also interested in adding a buffer to the output of my 48 step balanced passive attenuator preamplifier. It's value is 5k and is connected to the input stage of my power amplifier using short cables. The input side of the attenuator is being fed from the balanced outputs on my DAC. Due to remodeling and having to relocate my equipment, power amplifier, I will have to place the power amplifier roughly 20 or so feet from the attenuator and this creates a problem. So my thoughts are to put a buffer, using short balanced cables, in line between the attenuator and buffer and then on to the power amplifier using the longer run of cables. Would The IVY III Balanced Linestage or The Legato 3.1 Discrete Balanced I/V Stage work well for this application with little or no alterations to their original design?

Thanks,
Ron

Having looked into this a great deal since starting this thread, the term "balanced passive attenuator" doesn't say enough about its configuration. Some attenuation networks maintain constant impedance at their input and output, such as a T-pad. Whatever the configuration, your power amp is likely to buffer the balanced inputs to maintain a high common mode rejection ratio. Otherwise, it at least has some network that will even out the impedance of the hot and cold inputs. There could even be an exception to that, if your amp uses a symmetrical balanced bridged configuration, and doesn't actually have a differential amplification stage (very unlikely). Since your are running a balanced signal, you probably have nothing to worry about.