Resurrecting the Preamp

[NickG]

This is an interesting discussion, and I don't wish to speak for Chris, but he betrays his feelings about preamps in the following comment embedded within the Weiss CASH List review (perhaps his thinking has been refined since):

 

"More and more audio systems consist of digital only sources and are less dependent on a traditional preamplifier. Digital to Analog converters with volume control have thus become increasingly popular. In 90% of audio systems this popularity (bypassing an analog preamp) serves the system well. It’s a rare occasion when inserting a preamp improves sound quality but it does happen. The volume control implemented in the Weiss DAC202 may increase that percentage to 99% because of its flexibility and superior design."

 

Certainly there are products being created with the idea in mind that the D/A conversion and need for a preamp is being challenged. Devialet, Peachtree, the NAD M2, Berkeley, Metric Halo, Weiss, and Benchmark are examples of gear that make it hard to say there is no case where any of these products don't degrade the sound when used without a standalone preamp. Classe is on the way, and I wonder if Grace uses lower quality parts in their m903 than their straight preamps?

 

I don't mean to suggest that those who prefer the sound with a pre in the chain are wrong about what they hear. But it seems that the idea may be more system dependent, rather than absolute. In the list of amps in the previous post, most of them are tube amps, perhaps some have too low an input impedance - but if a DAC has the same output impedance as a pre being used, that shouldn't matter.

 

Chris is not talking about situations where one might want to bypass the D/A conversion. Fewer products do that, and I have not heard much about how they perform. The Grace m903 does it and the Classe will do it.

 

 

 

[rom661]

All due respect to Chris but this is an area where he and I will have to agree to disagree. I'm not saying going preampless can't work well. But his 90% figure is hard for me to swallow.

 

Not real sure what you meant by your comment about the Classe (I assume you mean the CP-800) being able to bypass the DAC. I guess you are talking about devices not intended to act as a gain control for anything but the DAC. I had a CP-800 on hand for three weeks and it is a glorious preamp without regard for the DAC. I used both vinyl and my DAC8 balanced into and it works really, really well. However, I consider it a preamp with a DAC integrated into it, which I guess is your point.

 

It should be shipping before too long.

 

Rick

 

[Quest]

maybe i have a simplistic view.

 

no matter what, there is still a pre-amp in the chain. if it is within the dac then it becomes a question of whether the included pre-amp is good (to what level), and whether that performance can be bettered. no?

 

even when having a chat about the dcs debussy, the representor told me that while majority of the time people who buy it do not find an improvement by inserting their existing pre (better to run direct), but occasionally there will be people who find it better especially if they own a high end pre-amp. he also told me he is personally a 'pre-amp person'

 

funnily, the asia weiss representor also said something similar, that he prefers having a pre in the mix.

 

i get more of such views than otherwise, when talking to these people.. but of course, u can say that maybe they are trying to sell me more things.

 

[One and a half]

a tuner, tape, aux, phono input to go with that?

 

Pre-Amps are cool.

 

[PeterSt]

Would love for a DAC mftr. to design an excellent analog output stage that would allow bypassing a preamp.

 

and

 

no matter what, there is still a pre-amp in the chain. if it is within the dac then it becomes a question of whether the included pre-amp is good (to what level), and whether that performance can be bettered. no?

 

Well, no.

IMO.

 

To start with the latter quote, I see no reason why a "preamp" section within a DAC would improve. Ok, we'd avoid some interlinks and everything matters, but we better avoid ALL.

 

The latter implies referring to the first quote above, because that is allowed to do just that. So, an "output stage" which doesn't require a preamp. Think what a preamp actually does, and that it -apart from providing a decent impedance match between the DAC and main amps where the DAC itself does not- it gains - or merely attenuates (but it does both).

 

To do this well it needs a complete concept, or strategy if you like.

 

Ok, sorry to name a name which is not much sujective to me, but the Phasure NOS1 was explicitly created to operate without a preamp. It's the explicit advice to go without, not because it can't be used with, but because you'd be molesting sound all over. Or you could say : what I tried to make so well, is just thrown out in a whimp. A waste.

 

The NOS1 has an output impedance of 33Ohm (each pin). Not a big deal, if you only know what you are doing it for. But right from this point all the trouble starts ...

(sorry if this sounds like repeating to some)

 

At knowing that each means of attenuation destroys sound, there HAS to be a digital means that works OK. I won't explain how or what, but without that all is doomed again. So, I created that, and you could say it needs a complete software player. Looks overdone, but still part of the concept. And for those who don't know : a lossless digital volume, which *thus* prooves it doesn't molest. Didn't exist, thus had to be "invented", and lossless in this regard means that the attenuated "file" can be used to recreate the original. All relations kept. But, officially can be used only on 16 bit (redbook) material, and played back on 24 (or higher) bit DACs.

 

Still people want analogue volume controls, so when all was finished I tried. And tried.

And tried.

Believe it or not, it just can not work. It kills sound completely, and the measureing of whatever I all tried - you don't want to see it. And this is even with a 10$+ one resistor.

Small disclaimer : analogue volumes *can* be done, but in the domain of "voltage controlled" D/A chips. But since I don't like the chips which can do that, and the one I use can not, it's a period.

Side note : I bought everyting I could find including $500+ LDR modules, which would end up above $1000 for balanced operation, but it doesn't matter; it can't work.

 

Throughout the thread I read about TVCs and "passive" could do the job matter maybe. Well, it won't, because everything which smells like a transformer as an uneven frequency output ... better don't know it. This is not (only) about the cut off of high frequencies, but merely the impedance response of the transformer itself which reacts differently to different frequencies. Ah, what is the difference which capacitors and coils for LS XOvers, and in the end, just resistors.

 

So I gave up on any means of analogue volume control.

It is maybe not so easy to grasp what the audible difference can be, because -and it has been said in the thread a couple of times- most often (if not almost always) a filtering device like a preamp actually *will* let be the net result better than without. Well, only if we'd measure our chain with devices we can't afford in the first place, we'd see how wrong it actually is to apply such a filtering means.

That in the mean time we will be listening to the distortion of our main-amps, pricey interlinks and even (bit perfect) software is something else .... TO SOLVE.

 

The whole thing is way more complex than just these aspects, because it goes far beyond the subjects we want to know about. It dives right into the filtering of DACs being wrong (says - no, claims me) and as soon as the preamp is out, you are going to listen to *that*.

 

I'll stop here, with the (again) notion that we should listen to the "chain" which sounds best. This is undoubtedly different for everybody, because so many things are involved. But theoretically (I think, no statement this time) removing the preamp should be worse for most, because it just *is* not good. Think about this too. If things would be 100% good we'd be listening to musicians, and although we may get closer and closer to that, we know we don't. Why ? because things *are* wrong. Remove a filter like a preamp is, may unveil that. But YMMV of course.

 

Peter

 

PS: Some additional perspective maybe : From the output of the D/A chips to the output of the main amps I have exactly one resistor and one GainClone chip (and interlinks). Once one has it working like this, each next resistor matters, and it will relatively completely kill the good sound. Now look what's in your chain for resistors and even active devices, and try to interpret a. how bad that could be in the first place, and b. that adding a volume pot to it won't matter all that much anymore.

Less is really more.

 

[barrows]

While I agree with almost everything that you say above regarding "less is more" I feel it is important to point one detail out:

 

While you claim one resistor in the signal path (and for this part I assume you mean one series resistor, yes?, and that you are not including the power supply rails as being in the signal path), you then state that you use an IC for your gain stage. Well, IC anplifiers typically have quite complex circuits internally, including many resistors directly in the signal path, so by using an IC amplification chip, you actually have a quite complex circuit.

I understand that you tried to design a simple discrete circuit for the NOS 1, and found better performance from the IC, and am not making any comment on how the NOS 1 sounds (as I have not heard it), but to claim simplicity for an output stage which uses an IC amplifier is a little misleading.

 

Quest: Suggesting that a DAC with volume control has an "internal preamp" is not really correct. A preamp actually introduces many more stages where signal degradation can occur, herewith:

 

Typical DAC with preamp signal path:

 

DAC chip-I/V stage-analog output stage-interconnect to preamp-preamp input switching-preamp input stage-preamp attenuation stage-preamp output buffer-interconnect to amplifier.

 

Typical DAC direct to amp with digital volume control:

 

DAC chip-I/V stage-analog output stage-interconnect to amplifier.

 

As one can see, eliminating the preamp removes the following sources of distortion/noise: an interconnect and attending connections, an input switching stage, at least one (and sometimes two) active gain stages, and an attenuation stage.

 

If one were to make a DAC with an anlog volume control, the preamp would still add the input switching stage, an active gain stage, and an interconnect and connections.

 

I would like to see what Ayre could do with a Reference Series USB DAC designed to go direct to an amp, using their variable gain transimpedance (VGT) design (the VGT adjust output level by directly altering the gain of the circuit) used in the KX-R preamp, this could be:

DAC chip-I/V stage-VGT-interconnect to amplifier. This approach would eliminate the degradation of a digital volume control, and of an analog volume control. It appears that this approach could result in very high performance for those who have no need of input switching.

 

[Jim Smith]

I would like to see what Ayre could do with a Reference Series USB DAC designed to go direct to an amp, using their variable gain transimpedance (VGT) design (the VGT adjust output level by directly altering the gain of the circuit) used in the KX-R preamp, this could be:

DAC chip-I/V stage-VGT-interconnect to amplifier. This approach would eliminate the degradation of a digital volume control, and of an analog volume control. It appears that this approach could result in very high performance for those who have no need of input switching.

 

What Barrows said!!!

 

[Exeric]

While I think there is a lot of interest in eliminating the preamplifier for many people they aren't able to get the results they want without one. You have two basic problems to resolve in eliminating a preamplifier - how to handle the audio buffering, and how to handle the control aspects that the preamplifier does.

 

A lot of people have thought about extending the dac concept so it includes the preamplifier functions. But I think it makes a lot more sense to go back to the original concept of the integrated amplifier. Because the integrated amplifier has traditionally been seen as part of a mid-fi system people have been trained over decades to view it as second-rate. It doesn't need to be seen that way and a lot of the early hi fi tube integrateds are still highly prized. That is because the synergy is built into the things. You can still design it that way but the amp and preamplifier manufacturers want to maintain the culture of snobbishness about the inferiority of integrateds because they get to sell more stuff.

 

If you think about the sound of general amplification they have created an artificial

division at the point where the voltage gain changes to power gain. It is still a holdover from the lp that required huge voltage amplification before it even got to power amplification. Nowadays with relatively high level sources there is absolutely no reason for amp makers to maintain that division. It's artificial. Any good amp maker knows how to add the required buffering and small voltage amplification to their amp so that damage is minimized in the process. Instead they have just catered to a certain snobbish appeal to separates that was conditioned into people over decades during the lp era.

 

The power amps made today probably are inadequate to be driven by themselves. They are meant to be! All that is required to change is the psychology behind that snobbishness for manufacturers to go back to building good integrated amps. It makes a lot more sense to do that than try to combine the very different digital and analog amplification requirements into a dac.

 

[Exeric]

I think it makes the most sense to separate the features by division between analog and digital circuitry into separate boxes for the highest quality. That means having separate selectable digital inputs on the dac. Digital Volume control might be optional. It would feed an all analog integrated amp that has it's own selectable analog inputs and of course a volume control there is mandatory. That way you separate analog and digital circuitry as much as possible. There is going to be legacy analog inputs around for a long, long time so it doesn't really make sense to use only selectable digitsl inputs on the dac, especially if you are paying big bucks for an integrated amp.

 

There might be a further refinement of division of labor for the least cross contamination. That would be if one wanted to digitize analog sources. The adc for that could be considered just another single source input into the dac. You would most likely just use a card in a computer for that. You really have to be anal, like me, to worry about the best division of labor for highest quality for all these inputs and outputs. But I think there is a tendency to believe the status quo is the best way even though it just a result of conditions existing in the past that no longer exist today. (like mandatory LP source amplification).

 

[sandyk]

"But I think there is a

tendency to believe the status quo is the best way even though it just a

result of conditions existing in the past that no longer exist today. (like

mandatory LP source amplification)."

Just when you think you are home free because you have pensioned off your vinyl setup, they supply STBs where the level is

[Exeric]

Well, with the integrated circuits In the preamplifier section of present integrated amps you go back to the ingrained philosophy that an integrated is allowed to be crappy. Manufacturers should not be allowed to get away with that. It is just lazy thinking and poor execution based on an old fashioned paradigm that does not deserve to still exist. If one insists on having a seperate low level source that requires high voltage amplification it should be entirely separate, like a phono amp. It should be an optional amplification stage to get if it is required. Most people probably wouldn't need it. The way it is now to get the highest quality audio it is mandatory to buy a preamplifier and power amp. You actually can do a lot better by building your own combined unit if one knows some electronics. Tons of people do just that at DIYaudio.com. (not affiliated).

 

[4est]

Well, of course one can do better if they build their own stuff. Besides the expenses saved on commercial goods, the DIYer can tune their stuff as required specifically to the task at hand. All with the help of a large community if DIYers, and their knowledge base. Do not under estimate their knowledge either. The Phasure DAC for instance (excuse me Peter), is a fine example of what can be done creatively using some of the concepts kicked around in DIY community.

 

[Exeric]

I've learned a lot at that site. ;-)

 

[barrows]

some integrateds which are not as compromised as mentioned above. The Pass integrateds, now available as both the x .5 series 150 watter and the XA .5 series 30 watts of class A (and over 100 watts of class A/B) are good examples of well done integrateds, and there are others. An integrated can be a great option, as it reduces the number of gain stages, just like DAC direct: an integrated amp can be as simple as an input switching, followed by a voltage gain stage, the volume control, followed by the current stage to drive the speakers. With proper inplementation there is no technical reason why an integrated cannot perform as well (and the potential for improved performance is there) as separates.

I think more audiophiles might prefer separate power amps though, but maybe it is just me! As far as sytem set up goes, separate power amplifiers gives one maximum flexibility in component placement (amps near speakers).

 

[4est]

And this takes us back to separates again for flexibility. Using integrateds means possibly replacing the entire unit for speaker types.

 

[Exeric]

For active speakers I'd have to rethink what I just said. Integrated amps are not a solution there. I would still prefer the digital inputs going into, and selected in, the dac for reasons I said. It would not be difficult at all to use that dac as a digital preamplifier. The only proviso is that power amp manufacturers have gotten into this completely ridiculous habit of building ONLY to be fed by preamps. Once one starts looking at the amp design from a diy standpoint it really seems predatory on the part of the manufacturers to stop so arbitrarily short of making a complete amplification package.

 

Did you ever see that movie "the loneliness of the long distance runner". The champion stops one yard short of otherwise crossing the line in first place. That is how I see the big guns, we know who they are, in power amplifier design. Not all of them, just most. You "should" be able to completely satisfactorily drive any power amp from a minimally effective dac without a preamplifier. Again, I conclude most of them intentionally stop just short of that.

 

[blaine78]

Always prefer a good pre-amp than direct. Direct from DAC to power amp, always found it bit dull and too matter of fact. yeah sure it sounds cleaner, but also find it abit sterile. I think a good Pre-amp brings back the 'fun' and 'drama'.

 

[Exeric]

the amp builder wants you to need the preamplifier. He could easily build the amp so you wouldn't need the preamplifier. He did not so you would spend extra money on a new enclosure, new power supply, and new interconnects. Plus if he had optimized the design in one package it would even better than what you are now hearing.

 

[blaine78]

sorry that doesn't make any sense.

a power amp has to be used with a source with a volume.

i happen to prefer as many do here, a pre amp between a dac and power. it's a matter of taste in sound.

a power amp is just that, a pre amp is just that.

also, if you noticed my amp, it is a integrated amp with pre and power in the one chassis.

i've tried stand alone power direct with dac, i didn't like it , see above for last post.

Hi-Fi manufactures split out pre and power separately for 2 main reasons, dedicated power supplies with less interference from each other in the one chassis, and the ability to mix and match components with other manufactures.

 

[barrows]

I really think this attitude is a bunch of hooey:

 

"power amp from a minimally effective dac without a preamplifier. Again, I conclude most of them intentionally stop just short of that."

 

Manufacturers try and build what they think the market demands. The idea of a preamp/amp combination is a left over from the vinyl age, where preamps typically had inbuilt phono stages. It certainly is an advantage to have separate amp and preamp if a phono stage is included in the preamp, as the high gain of a phono stage (70 dB for MC) has no business being in the same enclosure as the large power supply required by a power amplifier.

With all line level sources, separates really make no sense any more, but there is a leftover feeling amongst audiophiles that separates will offer higher performance. This feeling is, technically speaking, in error. Many amplifiers have separate internal power supplies for voltage gain stage and current stage, just as many DACs have separate supplies for digital and anlog sections-there is no significant advantage to putting everything in separate boxes just to accommodate separate power supplies, especially with balanced circuits.

Manufacturers are not trying to sell additional boxes, they are trying to provide what the market demands.

Some audiophiles need a separate preamp to accommodate analog sources (or an integrated), some audiophiles want a preamp to pair with active speakers, some might need (properly buffered) multiple outputs to use in bi-amping arrangements, or with subwoofers. Some might want to go amp direct from a DAC. There are products available today in every category, to handle every approach listed above.

I do not feel it is an amplifier manufacturers responsibility to design his input stage to be super sensitive to handle a few customers who might want to go amp direct from a DAC with a wimpy output stage. Clearly, if a DAC manufacturer wants customers to be able to achieve top performance going amp direct, it is the responsibility of the DAC manufacturer to build a suitable output stage and volume control. Right now it is fashionable for DAC builders to suggest that one can gain an advantage by going amp direct, unfortunately, most of these same manufacturers have not done their homework on really getting their DACs to perform really well in direct mode. They "add" a volume control (which is really easy, as most DAC chips have this built in anyway) to their DAC and call it good without addressing getting the output stage to the point where it can drive virtually any amplifier.

 

 

[Exeric]

The argument I was making is that it is not a coincidence that dacs with volume controls don't seem to want to work direct into most power amps. Jim Smith was saying he had tried amplifiers driven directly by the dcs Paganini. He said the performance was weak. I'm here to tell you that a dac with an output impedance of less than 1 ohm over the audio spectrum is not wimpy.

 

Something is not correct here. If that is true, and I have no reason to believe he is prevaricating as he has written a book about getting good sound, then any logical thinking person must believe that it is the amp producer's fault. The reason big amp producers can get away with a situation where a 1 ohm output impedance is insufficient is because they are under engineering the power amp in order to sell preamps. That may not be the case for all manufacturers but because there are enough gullible souls who think It is the Paganini's fault they can get away with it. If audio consumers were more discerning they would know that if they buy a megabuck power amp that doesn't work direct from a Paganini then there is something rotten in

Denmark with the power amp. Amp makers, ESPECIALLY high end makers, know that they have customers with more money than sense.

 

[blaine78]

I will never buy brands that don't have a long running good reputation. I don't think ATC or NAD are being dodgy with their power amps. They are quite rock solid. It comes down to synergy in my situation.

and isn't that the whole point of this hobby, buying bits of equipment, listening and enjoying, trying other pieces to match your taste as your taste grows and possibly change. yes it is expensive, but if you have a passion for it, i don't see it being a waste if you buy sensibly that is. i don't regret any purchase on equipment to this day. some cables on the other hand, sigh.. but wont get into that.

getting a great synergy from the equipment you have is quite rewarding. I'm really not one for an 'all in one' box. i find no joy in that.

 

[Exeric]

Well, I like the idea of tuning ones system also, that is why I'm a pc guy (not as in politically correct), because there are more options like your suggestions in JRMC. And that tunability is fairly easy, fast, and relatively cheap. If I wanted to attain the same joy with regards to tuning amp/preamplifier combos I'd have to rob a different bank every week and go around in a full time disguise.

 

[barrows]

This is just plain wrong:

 

"Denmark with the power amp. Amp makers, ESPECIALLY high end makers, know that they have customers with more money than sense."

 

Just not true, period. I have not tried the the dCS units personally, so I cannot comment on them. I would note that Michael Fremer found the sound with the dCS Debussy run direct to an amp to be at least the equal of running the same system with his dartZeel (quite exotic) preamp in place. Having met Jim Smith, I certainly would not doubt his findings (with the Paganinni) in the systems he has tried.

I have tried the PS Audio PerfectWave DAC direct vs with preamp, and found it to sound great direct. This DAC has an output stage which was specifically designed to be able to drive power amps directly, I know because I worked at PS Audio during its development. As I recall the output impedance of the PerfectWave is 100 ohms per phase, so nothing special there. But the output stage itself is a fully discrete, FET input bipolar output design, running on 30 volt rails with very high current headroom and Jung style super regulators. On the other hand, my DIY DAC does not adequately drive my amp, eventhough the designer suggests that there should be no problem. Very few power amplifiers are that hard to drive these days, DAC designers just have to do a little more than run some low voltage/current opamps in their output stages, run off of weak power supplies, if they want to drive a wide variety of amplifiers properly.

 

 

[blaine78]

don't think i'll get back into the separate pre/power as very content with the integrated i have now, and in future if ever did upgrade it will be another integrated that performs aswell as separate pre/powers, it is possible.

i just think some DAC's with their volumes controls are just not up to scratch when plugging direct into a power.