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! :-) |
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). |
Basement, I'm not completely sure about this, but I think most preamps place the volume attentuator after a gain stage, so it might be that taking an output straight from the attenuator bypasses the output stage, but is not totally passive. The loss of bass when you run in this mode could very well be due to the interaction of the volume pot's output impedance with the load presented to it by the amp and interconnects when the normal output impedance-lowering buffer stage is not present.
I'm a little confused by your fifth paragraph, but maybe you put 'passive' in some spots where you meant to write 'active' (also, your phonostage is actually going to possess the highest voltage gain of any of your source components, although not probably the highest output voltage). In the next paragraph, I'm sure the input impedances you refer to on your amps must be K-ohms, not ohms, but again, it would be bass frequencies which would be rolled off if the input impedances were too low, not the highs (it's cable capacitance which can roll off the highs.) Help me out here Sean if I've screwed up any of this! |
Drubin, what I've noticed in my tests is more of a subtraction from the sound than an adding to it, which I guess is good sign in theory. For instance, piano can lose a little of its sparkle and percussive incisiveness, rendering it just a little veiled in comparsion. Stand-up bass loses some heft and definition, becoming less pitch-precise and more rubbery. On the other hand, some sounds do seem to gain unwanted artifacts; a half-opened hi-hat cymbal sounds more like two pieces of metal clashing against one another when listening to the DAC straight, but when the preamp is inserted, the sound becomes more akin to indiscriminate white noise - could this be the result of added intermodulation?
That's my SS preamp, though; with my tube preamp, there are losses to be sure, but you do notice right away a certain subtle tonal quality (which I like to characterize as 'sunny') is lent to the whole presentation. It can be attractive once you get used to it, but that is certainly something which is added, probably low-order harmonic distortion, and I don't know how it can be considered to make the result sound 'more like music'. This preamp definitely sounded more like music than my older cheap SS preamp that departed long ago, which was grainy, shrill, and flat in comparision, but it doesn't IMO improve on the straight feed from a quality DAC. |
JC, I appreciate your input, but I think you may have read some things into my post that I did not intend. I am not trying to make a case for running direct, and I do realize that my preamps (list prices about $1,800 to $3,000) are not SOA. Neither are most folks' preamps, and neither do most folks want to run direct or passive. I am also not trying to solicit advise concerning my own preamp situation in particular with this thread, which is why I'm leaving out the make and model info, since I don't want my comments taken out of context.
My post is just intended to explore the notion of employing a bypass test to look at preamp performance, and to see if other members have had experience with this kind of procedure and what their results may have been. In my own case, where I feel confindent that my DAC, at least, is just as capable of driving my amps' inputs as my preamps, I admit I am skeptical of the notion that a preamp could not only fail to cause *some* signal degradation, but could actually make the sound 'better'. I acknowledge that I don't have epxerience with the best preamps, but rest assured that I have no intention of removing the preamp function from my system. I just want to know exactly what it's doing. |
Jetter, need I reiterate for you that this is *not* a product review? This post, if I do say so myself, actually delivers on the promise implied by its title line, should you choose to click on it - something that other post you refer to did not (as of right now, mine is still the only response to that three-sentence 'review', which should be some indicator of how worthwhile it was). If you have some pertinent criticism of my post here, then please, by all means contribute it. (And if you care to see how I do write a product review, you know how to find that too.)
Drubin, I just want one control center in my system, without having to go around back and pull wires all the time, and with the gain I sometimes require to listen at higher levels. I realize there is always, at least in my own opinion, going to be some sonic tradeoff for this convenience. I know I wouldn't be the first audiophile to have ever concluded that a preamp is basically a necessary evil. :-) |
First question: I'd want to spend time doing this test in order to learn about my preamps and what they are doing, not only in comparision with each other, but to the unadulterated source.
Second: Of course not.
Third: Not true. It's passive resistive volume controls and long cable runs that source outputs may (as opposed to "usually") not interface well with, not amplifier inputs in most cases. |
Before I respond, let me say up front that I truly appreciate AV_specialist's interest in this thread if it is sincere, but either I am missing something or I need more explanation or justification of his seeming position, so here goes:
1) Umm...Duh! That's kind of the point of the test. (It's actually input switching, not "output switching".) Please go back and reread my description of the test and why I set it up the way I did if you did not pick up on this.
2) You show me the source component with an output stage incapable of driving a typical 1m or 2m cable run into an imput impedance of at least 20K ohms with least 1v to 2v, and I'll show you a source component that can't 'drive' a preamp any better than it can a power amp. Almost any digital player, DAC, or separate phonostage made will provide a low enough output impedance with enough voltage to interface with a typical amp input. Almost all amps (excepting some pro-type gear) will provide high enough input impedance, voltage sensitivity, and gain to be driven by a such a typical source. Of course, for listening you may desire more or less gain, but in general, unless you are restricted to employing very long interconnect runs or use a very low-gain amp, almost anyone could do my proposed test at unity gain and get instructive results. (In fact, even in the case of a setup where the interface was clearly disadvantaged by not employing a preamp, the results would still be equally instructive as far as ascertaining the effects of the preamp. Whether the results are in favor of the preamp or not doesn't negate the value of the test itself.)
AV_specialist, I don't mind being critically questioned, but I don't see what you're trying to get at. Either you're just trying to poke at me for the amusement of it, or you haven't really read carefully what I've written above. Why don't you just come out and tell me your agenda here? You obviously are in some way 'against' the test procedure I've outlined, but I have no idea why. I mean, if you simply prefer not to try this, then don't - but that wouldn't explain your coming on this thread to challenge me (your perfect right to do, and which I welcome), so I must assume you take a greater interest in this subject than merely not caring to bother with it.
If I had to guess why or what that agenda is, then I would suppose this: I believe many audiophiles tend to recoil at the idea of tests such as this because they don't really want to be made aware of the implications of the results. I am not saying that control over attenuation, switching, output buffering, or overall gain is unimportant in a system. I am not arguing against the use of active preamps. I use them myself, and will continue to do so as far as I can see. I do not normally listen to my system without a control center in the loop, and I have not owned a passive volume attenuator (yet). If I were to try one, I have no doubt that it would also suffer in comparision to the sound of the straight source, but not at unity gain as in my test, since that would involve zero attenuation, unlike an active preamp (for whatever that's worth).
But I do not for a second believe that putting the source signal through additional stages of gain and attenuation can in any way "improve" that signal, necessary as those factors may be for system control. However, it is true that a preamp may change the signal in ways that an audiophile could find pleasing, but without some sort of reference, the listener will never know for sure how to attribute those characteristics. The reference could be the sound of other preamps, and that is valid and is often done, but I am suggesting that the reference also include the unprocessed sound of the source itself, because that is the real baseline for determining how intact a preamp is capable of transmitting the input signal.
None of this means that other methods for controlling overall gain (volume) or driving long cable runs will necessarily be superior to a good preamp - they often won't be for any given source component or system layout. It also doesn't mean that in some situations, a preamp may not fortuitously balance out some sonic characteristic of a source component, amp, speakers, or cable, but complementary colorations do not equal transparancy to the source. That preamps exist at all in these days of all-digital rigs and stand-alone phonostages is mostly for ease of system configurability and convenience of control. They are no longer a necessity in the same way a power amplifier is. The saying "The best preamp is no preamp" didn't come into existence for no reason.
You can claim none of this really matters since we are not actually going to listen to music without our preamps in the loop in most cases, and that point is perfectly true as far as it goes, if that is all you are saying. But I think audiophiles ought to be much more skeptical of claims made by manufacturers or in reviews suggesting that XYZ preamp is going to confer all these wonderful properties upon the sound of your system. The best that we can actually hope for is that a preamp do as little harm as possible, while at the same time providing the most good in return when it comes to system flexibility and control.
I advocate that audiophiles would do well to learn more about what their preamps are really doing in their own systems, and remain unconvinced by any protestations from technically aware folks who ought to know better than to argue against the potential worth of performing a simple home test. Such preampophiles will often have a proprietary interest in maintaining preamp fiction, which in turn can lead to the fiction about source components needing all kinds of help in order to interface with amp inputs, when in fact it's cables and passive attentuators they may in fact have difficulty interfacing with. (And on that last item, it's as much [or more] the output impedances and insertion losses of passive attenuators creating difficulties for amp inputs and cable runs, as it is their input impedances creating difficulties for source components, that can cause them to suffer in comparision with active preamps. Despite those potential problems, many audiophiles still report better results using passive attenuators, given appropriate conditions, so I take all the Chicken Little hoopla about the dangers with a large grain of salt. I still want the availability of extra gain myself however.) A little personal knowledge about the performance of one's gear should be nothing to act scared of.
P.S. - If you have problems with what I am saying here, you should click on my threads and read my post about a test setup for looking at DAC performance and the effects of upsampling as implemented in an upsampling-switchable DAC. You ought to love that one... |
AV, you continue to totally miss the point. I have tried to be as clear as I know how about what it is I'm testing for here and why, so unfortunately there is nothing else I can say to you. Maybe if you read through the thread again, slowly, you'll catch on. And/or simply try the test for yourself and the light will dawn. Otherwise all I can comment on, is that you and I can't actually disagree about something if you don't understand what it is that you're taking exception to in the first place (and I doubt that if you did, we would really be in disagreement as much as you seem to think). Happy listening! |
Jb0194, I am clear that you prefer the sound of your system with your new preamp in place, rather than your previous one or the passive device you allude to. It is not surprising that your new custom preamp would sound better than one you describe as "modest". As for the passive attenuator, it would interesting to find out more about what type of device this is, and the context of its usage in terms of sources, amps, and cable runs. Two questions: Can you be more expansive and specific about what the "more compelling" differences are? And have you actually tried a bypass comparision such as I propose with any of the three units?
Jayme, although I don't believe that either of the preamps I used in my test was 'garbage', and also have never felt during normal use that what I hear from those preamps is 'garbage' (I've owned worse before), I don't disagree that it may take a larger preamp expenditure than I have made (can make?) to greatly ameliorate the situation I describe using my units, and I basically stipulate that much in my thread-head post. |
I guess I would describe it as "Something in/Something different out", whether that something is garbage or gold. A person is allowed to prefer the differences conferred upon the output by the preamp. And I acknowledge that whatever signal degradation is caused by the preamp, it might still be less than the degradation caused by an electrical mis-match between the source, cables, and amp input when running direct, or by some type of passive attenuation device, depending on the system context. My main point is that the only way for an audiophile to know any of this for sure, in their system, is to go ahead and perform the bypass test. |
