Preamps can color sound considerably. Surprising?

@antigrunge2 Can you find it for your specific DAC?

In the example I gave above, one would likely be better off to adjust the DAC’s output level much lower, and then a passive pre would be cranked around louder.

I suppose those with a passive pre and a DAC with adjustable output level, could do this at home and tell us if there is a difference or not?

A DAC without the output level adjustment should not be as good (if all else was equal)…

@holmz 

my Dac is an Antelope Zodiac Platinum with a relay based attenuator and an output impedance of 56 Ohms unbalanced into my Wavac EC 300b power amplifier with an input impedance of 100kOhms. Hard to see where the problem might be with a 200x span. I’d love to try Ralph Carstens ClassD monos on balanced; this raises the Zodiac’s output impedance to 112 Ohms for his 100kOhms input impedance. Most problems discussed around attenuators deal with marginal situations, which on modern designs to my knowledge are rare. Your last sentence only applies to digital attenuation, which is lossy.

That is super low output impedance, compared to a CD player or other sources with 600-1000 ohms.
It is the stuff in ~1k ohms or the 10k ohms range that would then get knocked down 40dB (or maybe it is 20dB in both volts and impedance… so one goes from 1k ohm to 100k ohms, and trying to drive the amp with a 100 k ohm input impedance.

A 112 ohms output impedance going through an attenuation of -40dB should be 11,2 k ohms?
It is probably better to run the knob at -20 and knock down the DAC by -20dB to get to -40dB.
 

Your last sentence only applies to digital attenuation, which is lossy.

I am running an RME, so I knock my DAC down by 10-15dB just to get the DAC and the other sources to be about the same, which are 4 RCA sources and 2 XLR sources. It seems OK, but I could see knocking down 6 bits off of 16 would be a problem. Especially if only 12-13 bits were in action.

We will see what @atmasphere says, but half the reason I post is to get corrected if my thinking is off… but I think/believe I have this right.

My Tortuga passive and has plenty of power, punch, clarity and detail. Width is nicely presented and depth too.

I use a 1/2 meter  Audience IC that goes to a Modwright phono stage from the Tortuga.

I am using 1/2 meter Kimber KCAG IC`s from the Tortuga to my ATI 3002 amp. The ATI feeds a pair of Revel F52`s. 

I use a 1 meter pair of Zu IC`s into a Dayton Audio SA 1000 subwoofer amp which powers a Revel Ultima Sub 15 subwoofer. I have 3 other subs in the mix too.

This is my recipe for a very satisfying, enjoyable sounding system.

This works well and It will play as loud as you would ever want.

Try a Tortuga passive, you might be pleasantly surprised by what you hear 👍 

Am I right in saying that most digital devices are designed to have low output impedance?

@antigrunge2 

No. They are likely deigned to have good sound and or good performance (which are not always the same...). Some have tube outputs and are designed to have as low an output impedance as the tube will permit... at any rate, low output impedance isn't usually the goal although its usually desired.

One of the main reasons we've sold line stages over the last 25 years and right to this day is that analog volume controls often outperform digital volume controls. With an active preamp you then set up the DAC to have the volume all the way up so there is no resolution lost, and then control the volume with an analog control.

The problem with a passive is the volume control is a series element with the output impedance of the source. This means the source impedance is raised quite a lot insofar as the interconnect cable between the passive control and power amp is concerned (and also as far as the power amp is concerned).  So controlling the interconnect cable, even if the control is 10KOhms is a lost cause. That is why passives are so susceptible to interconnect cable interaction.