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In Reply to: I've gone back to active posted by Charles Hansen on April 10, 2006 at 08:17:18:
>On the other hand a top-quality active preamp will give a bigger soundstage, more space around each instrument, more drive and pace, and more low-end authority. And a top-quality active gives up nothing to a top-quality passive (except for price).>Is it an impedence matching issue?
Additional low level amplification that's needed?
How can an additional active circuit improve the sound? It seems counter-intuitive.
I always thought simpler was better.
Follow Ups:
< < I always thought simpler was better. > >I did too. But "listening" is a much better way to evaluate sonic performance than is "thinking".
When our only product was the V-3 power amp (which you reviewed back then), we developed it by using a DAC with a variable output and no preamp. There was just a potentiometer inside the DAC box, with a buffer stage to drive the cable. This sounded very good.
In an effort to improve the sound we ran the fixed outputs into a stepped attenuator that plugged directly into the input of the amps. They were little boxes with a 12-position rotary switch and some Vishay resistors. There were no extra cables, nor any issues with driving cables. This sounded better still.
Finally we made fixed attenuators that consisted of rhodium-plated connectors back-to-back with two resistors soldered in place. Again, these plugged directly into the power amp with no extra cables, but now there were no switches and we could use our favorite resistors. This sounded unbelievably good.
When we made our first preamp, it was with some trepidation, because we figured there was no way that all that circuitry and switching and volume controls could sound as good as two resistors directly soldered to rhodium-plated connectors.
We were wrong.
I think the main reason that people like passive preamps is because there are so many bad sounding active preamps out there. (This is true of even some well reviewed units.) I'll take a mediocre passive over a mediocre active any day of the week. But a good active sounds better than the best passive.
...which was why.Some years ago when I was using a Rowland Coherance One preamp, Emmanuel Go of First Sound, IIRC, brought by his Reference One Passive for me to review. It sounded great and blew away the Rowland.
That was one of the best preamps during the early 1990s but I'm sure there are many more advanced ones now - 15 years later.
Today, I use a Wadia CD player (with a digital volume control) connected directly to my amplifiers. Many others are using similar set-ups or passive attenuators and no line stage.
I'm wondering if an active preamp has an advantage, theoretically.
It's like asking why different cables sound different. As far as standard electrical theory goes, they should all sound the same. But they don't. So people come up with hand-waving explanations that may or may not have anything to do with reality.It's the same with active preamps. I can't really offer any a priori reasons why they should sound better. But they do. So one can make hand-waving explanations based in 20-20 hindsight. I can make some of those too, but I have no idea if they are correct. I'd rather not bother making handwaving explanations. The bottom line is that a *good* active preamp simply sounds better.
As far as your listening experience goes, you are about 10 years behind the times. Wadia was able to set up a strong dealer network in the '90s simply because of the phenomenon you described. They would go to a dealer, ask to hear their best system, and then replace the source and preamp with a Wadia. The Wadia would typically "blow away" the dealer's existing front end, largely because most solid-state preamps of that era had a lot of sonic problems (even many of the expensive ones).
But I can pretty much guarantee you that if you put a (in no particular order):
Audio Research Ref 3
VTL 7.5
Ayre K-1xe
CAT SL-1 Ultimate Mk IIin your system that the overall sound would improve significantly from what you now have. (And a manufacturer of variable output CD players would have a pretty tough time selling them to a dealer that carried one of the above preamps.)
As an aside, I would also bet that if you could repeat your comparison of the original Rowland Coherence One against the First Sound passive that you would find some areas where the Rowland was better. I'm sure that the First Sound was more open and transparent, which may have suited your system at the time, so I'm not surprised that you preferred it. The best of today's active preamps allow you to have your cake and eat it too.
Mr. Hansen should include one more component in his list of distinguished preamplifiers: the conrad johnson Act II. I was using the Placette passive preamp before the Act II arrived two weeks ago. (I never touch the volume control on the dCS Elgar Plus DAC; I'm told it degrades the sound, so run the DAC wide open.) Now that the cj has broken in, my reaction is definitely WOW! It even beats my old CAT Ultimate. Anyone who thinks all active preamps are a negative has simply never heard a really good one.
In a system that had no gain issues and supposedly no impedance matching issues, the Placette Active just plain blew away a Placette passive - the active was much more dynamic and lively, and had a bigger soundstage.
Yeah I have heard good things about that Placette active. That, an Ayre or perhaps a Tom Evans would maybe make me think about going away from tubes in a preamp (then again maybe not).
rw
Well here's the funny thing. In most active preamps you are first attenuating the signal coming in and then amplifying it again. So is it the gain or is it the voltage and current stability regardless of the dynamics that give the active its advantage?? I don't know, maybe someone attenuates the output in their design.Perhaps this is the problem with passives then is that the output is attenuated and this robs the dynamics of the signal. An active preamp nearly always attenuates before the amplification.
be attenuated then amplified? If one "extra" gain stage is good, why not more? Why not piggy back two preamps? First attenuate then amplify then attenuate then amplify again?rw
...mostly just more confused.The problem is that you are thinking about the system and not listening to it. By *only* employing thinking, you are starting from the wrong place, so it is not surprising that you are reaching the wrong conclusion. In other words, if all an active preamp does is "attenuate and then amplify", then it would make sense to add dozens of them to get even better sound. Clearly this is an absurd conclusion.
But if you start by listening, you find that an active preamp *does* improve the sound (as so many other comments in this thread testify to). So the correct next step is to think about it and try to come up with a theory as to why.
Here's one possible explanation: all passive preamps have a relatively high output impedance, while all active preamps have a relatively low output impedance. We are typically talking about 2 orders of magnitude (100x) difference here. One could logically conclude that cables and/or power amps sound better when driven by a low source impedance.
This would also avoid the absurd conclusion that dozens of active preamps in series would sound better than a single one. This would also explain the comment in this thread that the active Placette (passive + buffer) sounds much better than the passive Placette.
Is this the real explanation? I don't know. But it is plausible, and it doesn't lead to absurdities.
I'm not a techie geek who only grasps what has been proven via DBT or ABX. I have heard some excellent preamps such as the C-J ART II, Burmester 808, VTL 7.5, etc, but not in systems that would otherwise support merely using attenuators.We are typically talking about 2 orders of magnitude (100x) difference here.
With my main system, the factor is six and a third: 4000 ohms vs. 600 ohms driving 137k ohms. Likewise, my GamuT source is 4 volts driving a 1.3 volt sensitivity amp. As has been suggested before, my experience suggests the relative success is highly system dependent.
I will continue to use my ears as the primary criteria. Thanks for your comments.
rw
I'm not quite following you. You are presumably using VTL MB-450 amps. The passive preamp is apparently a DACT stepped attenuator of unknown value. I'm unclear as to what active preamp you are using, and also what sonic differences you found between the active and the passive.I guess what would be relevant would be the result of your listening tests of (say) the DACT stepped attenuator versus (say) the CJ ART2. I have not done this specific comparison, but I would imagine that the CJ would give better overall sonic results in most systems. And at the same time, I'm sure that the DACT would give very good sonic results in many systems and would be far and away a better value.
As an aside, please note that an active preamp will have a constant output impedance, regardless of the volume setting. On the other hand a passive will exhibit a variable output impedance that depends on the volume setting. For series attenuators (such as the DACT), the highest output impedance (ie, maximum interaction with cables and power amp) will be 1/4 of the input impedance, and is achieved at a volume level that is 6 dB below maximum. (This is typically in the range often used for listening.)
I'm unclear as to what active preamp you are using, and also what sonic differences you found between the active and the passive.I still use an Audio Research SP-9 MKIII for use with my vinyl source where the gain is required. I found the attenuators offered more resolution and stage width.
I use 10k attenuators with the GamuT CD-1 having a 75 ohm output impedance. I downloaded the spreadsheet they provide to indicate HF roll off at the various attenuation levels. With my system, it is non-existent at any gain setting.
...and is achieved at a volume level that is 6 dB below maximum. (This is typically in the range often used for listening.)
Except for some very low gain sources like Telarc recordings, I usually run the attenuators around -12 to -14 db down.
rw
I'm not surprised that there are some noticeable sonic advantages to your DACT attenuators compared to a $1600 (if I recall correctly) preamp. This is consistent with what I wrote earlier in the thread, because for relatively low priced preamps, passives will give more bang for the buck.The problem is that a cheap volume control can limit the ultimate performance that is available from a preamp. On the other hand, most passive preamps use high quality stepped attenuators of one form or another. You don't usually find a high quality stepped attenuator in an active preamp until you spend thousands and thousands of dollars.
without the need for as many gain stages. Both John Cooledge and I have been using attenuators in our less than megabuck systems to their best advantage. Even Harry Pearson is coming around to that notion with the introduction of the exceptional ASR Emitter integrated amps. They are quite unconventional with their three chassis-battery powered line stage approach.Decades ago, I thought Sao Winn had a great idea with his strain gauge cartridge eliminating one very critical and expensive stage. I see no practical reason today why high output digital sources need attenuated gain stages. Let's build a 500 horsepower motor governed to 100.
rw
...and I wish I owned one AND an MET1!Anthony, thx for your info.
Quite right of course-- it is an Act 2. My computer is at work; so far I have avoided having one at home, so have trouble remembering names or numbers of my components. Verdi, Elgar, Purcell no prob., but the dCS P8i CD player-- that one took a long time to store in my aging head.
I don't know what the 'A' means, but the 'CT' means composite triode.
Thank you jeffreybehr for the info re the ACT2 preamp. Now that I know what the CT stands for, I'll ask Lou Johnson about the A. Spent a pleasant afternoon with him at his factory some time ago; a very nice guy, and that over-sized garage of his in Fairfax turns out some of the best equipment in the world. But if you acquire an Act2, be patient. After two weeks, I was ready to dump it and go back to the CAT Ultimate. And then, suddenly, in the course of two evenings--WOW! Figure 150-200 hours to break in those Teflon parts.
...said it's more like 500 hours on the teflon-capped pieces before they get to maybe 90% of 'done'.I just ordered an MET1 and I'm so excited I can hardly stand it. It should arrive early next week.
The ACT2 and the CT5 use the big teflon-film caps, while the CT6 and the MET1 use the very-good-sounding 'styrene couplers they've been using (and evolving) for years. Tor says 50 hours on these 2 pieces before they're 90% broken-in.
(nt)
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