Ever perform a preamp bypass comparision test?

Sean, your result would seem to maybe indicate that the attenuators in both your preamp and your DAC are of roughly the same quality (I take it that you normally run the fixed outputs from the DAC and use your preamp for level control). Have you ever done the comparision I describe above, using the feed from either the DAC's fixed outputs, or from the variable outputs set to a constant comfortable level? That would tell you what the contribution is from the preamp alone.

(FWIW, it seems from the lack of response to this and previous posts I've made along these lines, that not too many other members are interested in trying to do this kind of isolation testing on their gear. I'm a little surprised, to tell the truth - I find it fascinating and informative, but maybe I'm just a freak! :-)

You're not a freak. In some ways, what you propose is threatening to some of our core beliefs as audiophiles. There was a thread not too long ago about which component is most important, and many people weighed in with preamp. At times, I must say I agree with that. But it's also fundamentally irrational if you believe that the job of the preamp is to switch and attenuate (and maybe add gain). The mainstream audiophile press has steadfastly avoided seeking the truth on this matter and us sheep audiophiles have followed suit (not singling anyone out). It's scandalous, really.

On the other hand...What is frustrating is that a great preamp can make a system sound more like music even through it may well flunk the bypass test. It is adding to the sound--how else can we explain it?--yet doing so in a way that is musically compelling.

Zaikesman: I have done exactly as you stated. Sorry if i did not make that clear. I ran the fixed outputs from the DAC into the preamp and then fed that into the amp. I then switched over to the variable outputs of the DAC which directly drove the amp via the DAC's built in stepped attenuators. I could tell no difference between the variiable of the DAC fed into the amp in "direct drive" mode and the line level out of the DAC feeding the preamp which fed the power amp. This tells me that the preamp is either extremely neutral or that the stepped attenuators are "coloured" in a manner that is exactly the same as the preamp in question.

The "straight wire bypass" device that i was talking about allows you to actually put another preamp, power amp or both in SERIES with your existing "reference system". It comes with a device that allows you to gain match the system so there is no difference in volume. You can then manually switch between just your "reference components" or your references with the other components placed in the signal path to see if there is a difference. You can set up the switching device so that you can see if all of the components are active or you can do it in a blind and random fashion. If you can hear the difference with the "test components" switched in, they are either "coloured" or you are experiencing loading problems with the specific gear in question. Sean
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I have a quicksilver line stage that I have done a simple mod on- I have taken the leads from the tape in jacks and unsoldered them from the tape switch and soldered them in parallel with the output of the attenuator, so I have both an active on one output and a passive on the other, all using the same exact switches and attenuator.
I have never seen much sense to a preamp being an improvement, after all, all we really need one for is to switch between sources and volume control. Why pay big money for something that is suppossed to do as nothing as possible, why not do nothing in the first place?
There is another side to the argument that says a matching devise of some sort is nessessary for the best sound evan though a passive may work. while of corse we all know this is system dependant, and obvious because different components have different input and output qualities, there seems to me to be much more to this, and I find it intreguing.
Needless to say, I find the passive more transparent, (but realize that the quicksilver is not supposed to be the most absolutely transparent preamp possible). The passive does not seem to always go as deep in the bass as the active does, and while it may seem that the extra depth that the active does is due to either the effect of gain, or the fact it is tubes, I'm not convinced that it is artificial. The deepness that I am referring to is not just more bass that is always present, but rather deep bass that it seems is suppossed to be there when the program calls for it.
And also, I find that sources that are suppossed to be good for driving a passive and not good for for a passive (due to the output impedences) don't seem to be following the rules. My theta cd player seems to benifit more, or suffer less from a passive, while my micheal yee phono amp which has the lowest gain of all my sources, seems to benifit the most going passive.
Also, amps that I have tried this with that I would think would benifit from an active stage due to thier input impedences sound better with the passive, both a pse studio IV (50 ohms) and a hafler dh-200 (33 ohms). No loss of high frequencies at all. This seems to be true no matter how much I have to crank up the volume to drive them.
These have all been with only 1 meter interconnects, and I have yet to try long ones, and I plan on trying more amps. All of my comments have been thinking only of transparency, or what I am believing to be accuracy to the signal, but I am not really sure if while at the same time I am losing information and details going passive, that the active is not the most accurate to what the signal is intended to be. The quicksilver is neutral, I can say that, and right now I am enjoying the option of going either way. I'm on the fence.

We're still on slightly different pages here Sean, so maybe it is me who's not being clear. What I am suggesting is to stay with one set of outputs from the DAC (could be either one - the variable ones could be useful for achieving an overall volume that doesn't blast away the subtle differences, but once it's set, leave it there and treat it as fixed), or to use any other source. The idea is to focus on what *the preamp* is doing to any line-level signal it gets. To do this, you have to maintain the same interconnects and I/O jacks, and just swap the output leads on the preamp from the active, normal ones to passive, direct ones like processor bypass. That way, you can compare the sound with and without the effects of the preamp's gain and attenuation stages, while keeping the connections and cables constant. To do this, you must set the volume control on the preamp to unity gain, wherever that may be. What you are describing is comparing the sound of your DAC's attenuation to that of your preamp's, which is a different comparision, and one that only matters for that particular source component (it does tend to confirm that your preamp must have a quite transparent gain stage and jack complement, as well as your interconnects being very fine, since you're losing one set when you go to the DAC's internal volume control, and as we theorized above, it could mean that the two attenuators behave very similarly, but your test does not isolate the preamp or maintain all the other variables as constants - it's a legitimate and useful test, but a different test nonetheless).