Why do preamp sections in DACs SUCK Abysmally compared to good preamps?

opus112

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Not noise, more specifically current loading.

I jumped a step or two in my reasoning. More current loading makes for more signal-dependent noise on the power supplies (due to circuits not operating in SE classA). The greater the noise on the PSU the more gets into the signal at the output. So more noise is a direct function of additional current demand.

SMPS supplies with fairly high carriers and residuals tend to cause the "etched" sound we know to be familiar. But many manufacturers using them have effectively reduced them down to very low levels. I get no trace of it, say, from an MSB DAC.

Its possible to tame switching supplies' noise. Just that there's no incentive to do that (filters are expensive to add) when the supply's intended for some purely digital piece of kit like a PC.
 

Folsom

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Current loading can cause imbalance, which may mean more current induced noise (at least I call it that, it's more like a lack of mutual cancelation that can amplify noise, but that's harder to explain to people). It's easy to understand what this can do by using say unequal sized wires to make a phono cable. You'll get enhanced audible noise from the turntable, even if it's shielded. Does other noise come? Probably, I'm sure you're right, but the current induced noise is highly audible especially without music playing (and needle on disc, spinning). But as I was saying, it can be fun, too, in the correct places. Bon Iver's For Emma, Forever Ago is a blast when he's projected huge (it also doesn't have HF sounds). This is exactly the reason I think coaxial cables sound like **** for phono, and exaggerate all of the turntable noise... in order to avoid a minor amount of negligible RF.

As valuable as this information is, it's not always real world practical because there's so many complications standing in the way of taking advantage of a system free of such issues, and hence this very topic.
 

Al M.

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Yes that helps a lot - the dynamics issue is about the output current demanded by the next component in the chain. Tube poweramps can have input impedances well over 100k and such impedances cause little or no degradation to perceived dynamics in my experience. They would need short and/or low capacitance ICs though to maintain the ease of drive.

Ok, thanks, that's what I thought. My tube poweramps have an input impedance of about 100k.
 

Folsom

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I've found the closers you get SS gear to being current compliant the closers to tubes it will sound for many qualities.
 

asiufy

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Not noise, more specifically current loading. But you're correct that depth isn't necessarily as obvious, but depth has a lot to do with speakers too.

SMPS supplies with fairly high carriers and residuals tend to cause the "etched" sound we know to be familiar. But many manufacturers using them have effectively reduced them down to very low levels. I get no trace of it, say, from an MSB DAC.

As you shouldn't, as MSB uses linear supplies :)

MSB's built-in preamp is also fully analog, so no "chopping bits" there, unlike most of the other DACs with volume control. It's basically a passive attenuator, with a single op-amp for the extra gain, if you need it. There's also one built-in analog input (with more as an option), so it really works as a full-fledged preamp.
 

morricab

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Been reading through this thread and thought I would add what I have found.

I have found that good preamps add a robustness and drive to the sound and often far more powerful bottom ends to a system than driving the amps direct from the DAC. I have heard that this is even true for some DACs with rather superb output stages like the ones from Lampizator.

Now, why should this be the case. Well, one of the main reasons I can see is power supply. Most good, high end, preamps are designed with VERY robust powersupplies. Often they have either a large unregulated supply, heavily regulated supply or both large and well regulated. Also, the output impedance is often (but not always) less than a few hundred ohms. I have yet to try a DAC that has a power supply as good as what I have seen in the likes of NAT, Audio Research reference, BAT, Allnic etc. Perhaps the Aries Cerat Kassandra DACs would do the job (although I don't think they have level adjustment) and maybe some top AN DACs (again are they level controllable?) or top Lampizator could do as well as a good preamp but the majority of DACs have opamp outputs with well regulated but small power supplies.

One can argue that an amp with a high input impedance wants to only see voltage and while on paper I would be inclined to agree, in practice this seems to not sonically cut it. I find driving even integrateds with a proper preamp to act as a "buffer" to my sources (even though my preamp is not at all a buffer by design) often works better even though it adds another stage (it is a unistage design, kind of like CJ ACT) but it has a large, dual mono, fully tube rectified and regulated high voltage supply. I heard this effect clearly when reviewing "passive" devices as well then inserting an active preamp always boosts the dynamics.

Now, a friend of mine has a Lampi GG and he has found that feeding that into a Bespoke Audio transformer based "preamp" sounds better than the Lampi on it's own and better than the NAT Symmetrical he had before (that he also found to drive his amps better than the GG alone). He said it is the only such passive he has found that in all ways betters top actives.
 

bonzo75

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Now, a friend of mine has a Lampi GG and he has found that feeding that into a Bespoke Audio transformer based "preamp" sounds better than the Lampi on it's own and better than the NAT Symmetrical he had before (that he also found to drive his amps better than the GG alone). He said it is the only such passive he has found that in all ways betters top actives.

Does he have the Symmetrical or the Magnetostat. And I thought he preferred it directly from the Lampi over the NAT recently, before the bespoke came in?

Anyway - I think it is a preference. I have tried it with two friends when I had the Jadis. The Jadis gave more weight, body, and coloration, but without it was faster, cleaner, more neutral. Two of them preferred it without, I preferred it with. I did the same experiment with the Magnetostat SE and the Magma SE (the special editions are way more expensive than the normal Magma and Magnetosat), and findings were similar. I also then did the same experiment with a friend's higher end Shindo. Same findings.

So, whether one prefers it directly or not is quite a preference thing. Another Lampi user sold off his Wavac PRT1 because he prefers it direct. I like to play with external preamps as well, so when I upgraded from B7 to GG I had the inbuilt pre taken off. The voltage on the Lampi can be customized for your power amps (3v or 5v, etc), I think, which I never did.
 
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paul79

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IME, when you get a really good preamp in the chain, comparing direct from DAC sounds smaller and the artists are more ghostly instead of full bodied. With every DAC I have tried at least, and using my preamp.
 

Folsom

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One can argue that an amp with a high input impedance wants to only see voltage and while on paper I would be inclined to agree, in practice this seems to not sonically cut it. I find driving even integrateds with a proper preamp to act as a "buffer" to my sources (even though my preamp is not at all a buffer by design) often works better even though it adds another stage (it is a unistage design, kind of like CJ ACT) but it has a large, dual mono, fully tube rectified and regulated high voltage supply. I heard this effect clearly when reviewing "passive" devices as well then inserting an active preamp always boosts the dynamics.

If your preamp is active, it is always a buffer by design. Otherwise it's only there to add noise to the signal (and no one does that).
 

morricab

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If your preamp is active, it is always a buffer by design. Otherwise it's only there to add noise to the signal (and no one does that).

This is a misuse of the term buffer. A buffer is normally understood as an active device without any gain that is acting as an active way of providing a good impedance match while also being able to deliver some current. An active device that has gain is generally not considered to be a buffer even though it might still provide impedance matching to some degree or another. My preamp has a high gain single stage that is not followed by the usual cathode follower buffer circuit.

Most tube and transistor circuits are not buffers as they have gain. Opamp buffers are also with a gain of 1 (or less). Preamps were originally to provide high gain for low output phono cartridges. Often that WOULD be followed by a buffer. Today there are still many designs with buffer output stages but there are many that are not.
 

Folsom

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I would say they all have buffers, with or without gain. It's the modern parlance. Some have better impedance buffering, all provide some current.

But preamp implies volume and source selection. A solo buffer would have neither. We say active or passive preamp, and actives have buffers with or without gain.
 

opus112

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Now, why should this be the case. Well, one of the main reasons I can see is power supply. Most good, high end, preamps are designed with VERY robust powersupplies. Often they have either a large unregulated supply, heavily regulated supply or both large and well regulated.

I concur, its pretty much all about the power supply. Even if the output stage is running in classA then, unless the output transistor is configured as a shunt (which is very rarely seen) or the output stage is fully balanced, the output current is going to modulate the supply rail. Opamp modulation of the supply rails is far higher in frequency because they operate in classAB and hence the currents from each rail look like rectified AC with the same sharp corners.
 

morricab

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I would say they all have buffers, with or without gain. It's the modern parlance. Some have better impedance buffering, all provide some current.

But preamp implies volume and source selection. A solo buffer would have neither. We say active or passive preamp, and actives have buffers with or without gain.


I refer you to wikipedia:
https://en.wikipedia.org/wiki/Buffer_amplifier

As you can see the article in wikipedia explicitly states that buffers are unity gain. Circuits that are not unity gain may or may not act in a buffering capacity depending on the design of the circuit (some gain circuits have relatively high output impedance and therefore do not really meet the criteria) but it is commonly accepted that a circuit that is defined as a buffer has a unity gain and its purpose is transformation. In that sense it is an active version of what transformers can do.


Whether or not a buffer circuit is a preamp or not depends completely on whether or not the designer has decided to stick input selection and a volume control (resistor or transformer or even transistor) in front of the buffer circuit. It has nothing to do with being a buffer. A good example of a buffer based preamp is the Audion preamps. These are simply cathode follower buffers with unity gain. Most sources don't need the gain in a voltage sense but badly need the current increase. Most preamps today have WAY too much gain for modern sources. The exception being a low output phono cartridge mated to insufficient gain in the phono preamp. Then a main preamp with extra gain might be quite beneficial in terms of dynamics and ultimate volume level. However most of the time, at least with sensitive speakers, it results in too much noise, hum and insuffcient range on the volume control. I run into this with my NAT preamp, which has over 20db of gain.

So, you can maintain your parlance but it is not in line with currently accepted definitions and only creates confusion among those who are not clear on what the differences in circuits are.
 

Sablon Audio

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Now, a friend of mine has a Lampi GG and he has found that feeding that into a Bespoke Audio transformer based "preamp" sounds better than the Lampi on it's own and better than the NAT Symmetrical he had before (that he also found to drive his amps better than the GG alone). He said it is the only such passive he has found that in all ways betters top actives.

It might be that the galvanic isolation of the Bespoke TVC plays a part in this finding. I believe our mutual friend was using the +6db gain setting also.
 

Folsom

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So, you can maintain your parlance but it is not in line with currently accepted definitions and only creates confusion among those who are not clear on what the differences in circuits are.

Except you just repeated exactly what I said. All active preamps have a buffer (of varying degrees, as poor impedance will demand more current, but none the less have more available than straight wire), but not all buffers are preamps. Preamps are anything with a volume and source selector, active or passive, and a solo buffer has not volume or source selection. Any active preamp, or buffer, may or may not have gain.
 

morricab

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Except you just repeated exactly what I said. All active preamps have a buffer (of varying degrees, as poor impedance will demand more current, but none the less have more available than straight wire), but not all buffers are preamps. Preamps are anything with a volume and source selector, active or passive, and a solo buffer has not volume or source selection. Any active preamp, or buffer, may or may not have gain.

Umm, no I did not say all active preamps have a buffer. Many use a buffer (i.e. A follower UNITY gain) circuit after the gain stage but some do not, like my NAT Plasma or the CJ Art/ACT, BAT REX, Audible Illusions M3a etc. A circuit with gain is not considered a buffer and usually do not have very low output impedances, which is why you sometimes see a transformer coupled output from to match to the receiving load.

Again, a buffer is specifically a circuit with a gain of 1 that is acting as a matching between a high impedance on one side and needing a low output impedance on another. The typical tube circuit would be a cathode follower or White cathode follower.
 

Ken Newton

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The answer to your question can be much more complicated than it might at first seem. There's no inherent reason why a DAC's analog output amplifier subsection must sound inferior to that of a dedicated preamp unit. Perhaps, the first thing to recognize is that, generally speaking, DACs are probably the most technically diverse single component in the playback chain. They are comprised of the most distinct subsections, at once spanning the digital, mixed-signal and analog domains. Among those function blocks are DSP including digital filters and noise-shapers, low phase noise clock generators, low distortion D/A quantizers, wide-band I/V converters, and analog image-rejection filters before even getting to the output preamp blocks.

Consider the extra design time and expertise required to integrate all of a DAC's subsections into a musical whole. Within any given set of cost, time, and technical expertise constraints there are going to be compromises in a DAC versus those same constraints for a dedicated preamp unit. Vendors who can leverage an in-house expertise with dedicated preamp units then have an advantage on that subsection of a DAC. I think it more than coincidental that it has before been observed that musical sounding DACs often seem to be produced by vendors known for their musical sounding preamps.
 
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Legolas

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Maybe I can chime in. I have an Audio Note DAC 5 which is basically an M5/M6 pre-amplifier with a digital board. It has tube regulated power supplies and transformers on the output. The output impedance is less than 100 ohms. Even though it has the standard 2V output I find it powers my Passive preamplifier to power amplifier just fine. I used to use an Audio Note M3 pre-amplifier but real sided it didn't need it. It sounds faster and more transparent without. Bass is still big and deep, everything is spot on.

My power amplifier is a Plinius SA-103 150 Watt class A and Zingali speakers which area 96db efficient, and I seem to have plenty of volume. At 12'oclock the police would be knocking on the door....
 

Legolas

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IMHO most of the time theoretically nothing to do with buffering in a technical sense - the output of most DACs can perfectly drive the IC cable and power amplifier. The preamplifier simply manipulates the signal, in some cases making it more realistic for some people.

I have just written in another thread about the DCS Vivaldi:

I have now played with several amplification systems using it, and although when used with solid state amplifiers I preferred it going through a tube preamplifier, when using powerful tube amplifiers I was not so sure any more - there is a freshness and immediacy in the direct mode that brings instruments directly in your room in the direct mode. But still a lot to learn about this great system


And sorry, no high-end product is perfectly neutral ...

I have come to think the same over the years. I went tube pre for that very reason, then later tubed DAC.
 

Legolas

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Back on topic.

201106160017189073.jpg
IMG_7411.JPG :)
Here is my DAC 5 and an M6 pre-amplifier for comparison. I believe the main difference in the design of these units is the amount of step-down on the output transformers. But the M6 at 12 o'clock would be super loud, I would guess my DAC would roughly equal that line level. If I play music at 1'oclock or more on my Passive, the neighbours would be banging on the door. To get a passive system to work well it needs the output impedance to be low on the DAC, the current supply to the line stage needs to be good, and the tube or solid state stage needs to be able to handle the interconnects i.e. capacitance aspect. My interconnects are 1.5 meters from DAC to Passive to Power amp inclusive. Also the Power amp needs to have roughly a 20 times impedance of the output. If there is an impedance mismatch the bass can vanish and it can sound tipped up. I have bass in spades, so it must be close to the ideal match? Not by design I must say. With my Audio Note pre in the chain it sounded slower and a bit too heavy for my system.
 

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