Preamps can color sound considerably. Surprising?

@charles1dad it has been some of covered in a few places…

In theory and on paper, the passive approach should be more invisible/transparent, more out of the way.

In theory it starts to barf when the passive is doing more control.
Running “wide open” the passive is essentially a wire.

Remember that the passive pre is attenuating both voltage as well as impedance.

The pros and cons from my list:

• A high output impedance source = con
• Low output impedance source = pro
• High input impedance amp = pro
• Low input impedance amp = con
• High listening levels = pro
• Low listening levels = con
• Low sensitivity speakers = pro
• High sensitivity speakers = con
• High gain amp = con
• Low gain amp = pro

So the worst situation is driving some highly seniors give horns, at low volume through an amp with high gain from a high impedance source.

The volume is then cranked around anticlockwise, and the passive is attenuating the already high output impedance of the source to become tens of hundreds of kohms. 
 

If it is less sensitive speakers listen to at higher volume then the passive does not attenuate nearly as much.

If we add in ICs with high capacitance or inductance then we get a filter.
At that point it is often better to have a preamp than a passive, when the passive is trying to go very low… and it’s better to run a passive if it is doing very little attenuation.

@atmasphere,

many thanks for answering, a really helpful contribution. Am I right in saying that most digital devices are designed to have low output impedance?

@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.