Who is using passive preamps and why?

"seldom any discussion" ????????????

This has been debated to death. Do a search on passive and you will find hundreds of threads about this topic. I can't imagine anything will come up in this thread that hasn't been stated many times before.

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Paul is correct. Those who dismiss them as wimpy and lacking dynamics and bass simply don't know what they are talking about. That may have been their experience with them but that isn't the fault of the passive, it is the fault of the people trying them with other components they weren't well suited for and not knowing enough about the principles involved to solve the problem. Hook up a high impedance source to a low impedance passive into a low impedance amp and you get wimpy. Do it right and you get world class sound.

Here is the ugly truth about about preamps...the volume control inside all of them, active or passive, is a passive device. It is either an inductive voltage divider like a TVC or a resistive voltage divider like a potentiometer or stepped attenuator, but they are all passive. An active preamp adds a buffer stage so it mates well with a wider variety of equipment than the voltage divider by itself. If you choose wisely as Paul states, paying close attention to the source that's driving it and the amp after it then you don't need that buffer and you get glorious results with world class dynamics and bass. In fact, it is better than an active because you've taken out an unneeded gain stage.

Active preamps are for those who can't figure out what it takes to integrate a passive into their system, their source can't drive the amp loud enough so they need more gain, or they simply are trying to use a passive with components they will never work well with. Yes, you limit your choices for other components but there are plenty out there that mate beautifully with a passive.

Like I said earlier nothing has been said here that hasn't been said before.

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I completely agree that some components demand that you use an active preamp and such systems are capable of superb performance, but I think perhaps you missed my main point. The main point of my post was that it is not the passive volume control causing the problem some experience, it is trying to use it with the wrong components.

Let me try again. ALL systems consists of some source of an electrical signal, usually a DAC chip or a phono cartridge these days, followed by a series of active devices that eventually amplify the voltage to a level sufficient to drive the speaker. At some point in this chain of amplifiers you must include a passive volume control. To keep it simple let's concentrate on a system that only plays CDs.

The most common way to do this in a high end system is to have some amplification inside the source which amplifies the DAC chip output up to around 2V. That feeds an active preamp which may or may not amplify the voltage but contains at least a passive volume control and a buffer. That is followed by an amp that further amplifies the voltage and can supply enough current to drive the speaker. There is nothing magical about putting the volume control where it is. It could be in the CD player, it could be at the input to the amp, or if the output of the CD player is robust enough and the amp input is benign enough so the buffer isn't needed it could be put in a separate box between the CD player and the amp which we call a passive. My point is if you blame wimpy sound on a passive it means you don't understand what I stated above.

How about this? I don't have a preamp of any kind. I'm using Pure Vinyl software which controls the volume in the digital domain using 64 bit math. I modified the source so the DAC chips are connected directly to the input triode tubes of my amp through a 1:1 transformer followed by 2 more triodes. In case you are interested they also just release a version called Pure Music which doesn't include the vinyl functions.

Check it out http://www.channld.com/pure-music1.html

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Pubul57, the engineers among us can give sound scientific reasons why resistors should outperform transformers just as they can explain why transistors should outperform tubes. However, there is a large contingency out here who swear by these supposed inferior devices. My personal experience with a PLacette confirms that a resistor based device can be excellent as well as the TVCs. One problem with the Placette's is their 9K impedance which poses a problem for many systems.

If interested in a TVC check out Jeffrey Jackson's work.

http://www.jeffreywjackson.com/Passive_Aggressive.htm

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Rrog, just because you tried numerous times doesn't mean you ever tried a combination that was suitable for the purpose. There is absolutely no reason a source component can't have an output stage that is capable of driving an amp directly and many do. Having a 7 Volt output is only part of the story since it could also have a high output impedance and therefore be incapable of properly driving a low impedance passive and/or amp. No disrespect intended but statements like yours which fail to properly explore all of the facets involved and dismiss topologies which are proven to work when properly implemented only add to the confusion of those who are trying to get the big picture.

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Pubul, I see your point, they do have limitations, or perhaps better put they require careful implementation, but that could be argued for just about anything. After years of experimenting I've found that a couple of stages of triode amplification and very high efficiency speakers is what floats my boat. I would venture to say that if more people heard one properly implemented they would agree. This type of system is a perfect candidate for a passive pre.

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I prefer the sound of an active preamp because it sounds like music.

Rrog, once again a dogmatic statement that fails to take into account all factors. If you want to say you've never heard a passive that sounds like music then it appears that would be true, but I guarantee you they do in the right system as many have stated in this thread. Are you saying you have golden ears and all of us, and there are many thousands, who prefer passives in their systems don't hear well?

Pubul, attenuate means to reduce or weaken so any volume control whether resistive or inductive is an attenuator. For some reason you usually see that term with stepped resistor controls and not with TVCs but they are both attenuators.

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no, no, no, no, no, no, no, no, no, no, no, no, no, no, no,

I'm not angry.

Passionate? ok

Tired of seeing people declare absolutes in a world with so many variables? ok

After so many years on these forums tired of seeing the same things debated over and over and over? ok

But I'm not angry. Amused perhaps after seeing the same preposterous statements repeated over and over (like passives are wimpy) but perhaps frustrated would be a better choice as it frustrates me that there are people like Phd who come here to learn and they get responses about passives that are so far off base that they are worthless at best and at worst scare the uninitiated away from a topology that could be the answer to their quest.

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Even with the volume turned all of the way up the CD player is loaded with 33K ohms and the Zout of your player is only 50 ohms, a ratio of about 700:1. Conventional wisdom says at least 10:1 with higher better and no benefit beyond 100:1. I think 10:1 is a bit low but you are in a very good place. I would be tempted to try a Placette or a transformer control with those ratios.

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Rrog, If you want to say that the overall gain structure of the system must be considered then, yes, in some systems you do need the extra gain you can get from an active so the factors you listed which have to do with how loudly it can play do need to be considered, but that is true no matter what. It isn't something to consider only when you hope to use a passive. Having a system with so much gain that you can barely turn up the volume control is a problem just like turning it all the way up and it not being loud enough is a problem. To say your list is something to consider with a passives and not saying it is something to consider when building any system misses the point and is misleading, they are factors to consider with any preamp since either scenario (too much or too little overall gain) can be achieved with a passive or an active if the rest of the system has too much or too little gain.


Other than how loudly it can play and how much drive to the amp it takes to get there, the factors you mention have nothing to do with whether or not a passive will work well...speaker impedance? In fact you left off the most important factor; the ratios of source output impedance, passive impedance, and amp input impedance.

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Rrog, I'm sorry if you felt insulted but I was merely pointing out that your post had nothing that was exclusive to passive preamps. Everything you mentioned pertains to any system. I didn't point this out to insult you. I brought it up because your post didn't have anything that pertained to a debate about the pluses and minuses of passives vs. actives and it would be easy for the uninitiated who read it to falsely conclude that it did.

Again, I'm sorry if this offended you, but turning it into a pissing contest doesn't help anybody who is reading this and wants the facts. This debate will never move forward as long as you continue to latch on to some small piece of what I say and try to build a case around it. Example, you asked

What would you rather have? A system that hardly plays above a whisper at full volume or a system that plays loud at 9 o'clock?

I didn't say either one was a good choice. I said you could get either one with either a passive or an active if you didn't build the system correctly. I want neither one nor would I accept it. I've constructed my system so it plays near maximum volume with the volume all the way up. That's the way it should be.

You also stated

To say the requirements for passive and active are equal can be misleading to the unsuspecting Audiogon member reading this forum.

I never said that. In fact if you look through my posts I said that they require careful system matching, actives will work well in more situations than passives will, and that passives are not suited for all situations. How did you go from that to all requirements are equal? What I did say, and this is the whole point of my last post, is that you have to consider the same factors in regard to system gain when you talk about either one. That doesn't mean they have the same requirements. When you build a race car you need to be concerned about safety, reliability, handling, gas mileage, and many of the same factors you consider when you buy a car for commuting. Even though you consider the same factors it doesn't mean they have the same requirements.

You also stated

Let's take your incredibly high efficiency speaker out of the equation and replace it with a medium to low efficiency speaker leaving everything else the same. Now what do you have?

You once again are clouding the picture by focusing on just one facet of the equation, this time my speakers. Of course if you kept everything the same in my system and substituted low efficiency speakers it would be a problem. I could substitute a preamp that has 30 dB of gain and cause problems, I could substitute a source that had a much higher output and cause problems, and the possible ways to screw up the sound are endless. I picked a gain structure that complements high efficiency speakers because that's what I have. If I had low efficiency speakers I wouldn't build it with flea powered SET amps and low gain. Your whole premise of changing speakers is silly and has nothing to do with the debate..

Finally, as for my inexperience, I'm not sure how to answer that. It appears you consider yourself to have some experience but your incomplete answers that draw false conclusions and your use of convoluted logic would say otherwise. Why else would one bring speaker impedance into a discussion of passive vs. active preamps? Since you brought it up I'll run with it and say you are simply out of your league in this discussion. I started in this hobby in the sixties and I've put together good sounding systems using all manner of solid state as well as tube electronics including Conrad Johnson, Avantgarde, VTL, BAT, Aesthtix, Lamm, Mark Levinson, Naim, and Theta to name a few using all manner of speakers including B&W, Magnepan, Soliloquy, Wilson, Alon, Lowther, and others. I've experimented extensively with all types of room treatments and tweaks including many manfactured and DIY cables. I've built both active and passive preamps. I taught electronics in an associate degree program for 10 years, in my current system I built my woofer amps from scratch, the mid/tweet amps from kits and modified their power supplies, built the bass horns, and modified the output circuit in my DAC so it bypasses the active stages. That doesn't mean I know everything but I do understand the concepts involved in this matter. I have clearly and logically described what they are and why they matter. Since you continue to misconstrue what I say and latch onto small snippets instead of discussing the underlying concepts this discussion is pointless.

Good day

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From a measurement standpoint resistors should beat transformers, but an awful lot of people claim they like the sound of the transformers better. My opinion is either one can sound very, very good if properly implemented and this is one of those issues where it comes down to personal preferences.

I tried a Placette in a system before I was biamping and it sucked the life out of it. I talked them into building me one that had an input impedance of 100K instead the stock 9K and it sounded wonderful. I compared it to some Slagle transformer units and to tell the truth couldn't say say which I really preferred, leaning a bit to the transformers but they were both very good. Now that I biamp I don't use a preamp as I control the volume via digital processing in Pure Vinyl software.

I know, not much help but at this point I think you need to try both and see which you prefer.

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hmmmm, can't find where I said 10K was a good match. Which original example are you referring to?

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Pubul, the output voltage isn't the issue, just about any CD player has enough voltage to drive any amplifier to full volume. The problem occurs when the CD player output impedance (Zout) is too high compared to the load it sees which is a combination of the input impedance (Zin) that it sees from the passive and the amp.

Many passives have a Zin of 10K or less and this is further reduce by the Zin of the amp. At full volume they are in parallel so a 10K passive and a 10K amp would result in a 5K load for the pre. That is problematic for many CD players and phono stages no matter how much voltage they can generate with no load applied.

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Clio, I wish they would allow pictures so I could post a drawing, but you are looking at a series-parallel circuit with the Zin of the amp in parallel with part of the passive. When the volume is all of the way up the whole passive is in parallel with the amp Zin so you use the math for parallel resistors. In my example they were both 10K so it is 1/2 of the 10K. With the volume close to zero it rises to about 10K. and falls as the volume goes up.

Pubul, yes, on paper the resistor is better but many ears say differently, If you look at the results with test equipment in the audio band it is pretty much a wash anyway. What measures better does not always sound better.

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Can't argue with your math but I think there is a simpler way to look at it, something I should have brought up before. You need to consider 2 factors.

To make a match first look at ratio of source Zout to amp Zin. Convention says 1:10 minimum, I say closer to 1:100 is much better. In Pubul's case with 50 Zout and 100k Zin he is way above minimum at 1:2000.

Then pick a passive as low as you can get away with. At full volume (worst case) the combination of amp Zin and passive should be at least 10X source Zout but let's go with 100X. Pubul's 50 ohm source should see at least 5K so a 10K passive looks to be a great match. A 10K passive in parallel with the 100K amp is 9K.

For the reasons your math points out going with a passive much greater than required can cause problems just like going too low with too low being worse. That's why you see Placette building 9K passives. In Pubul's case many would argue a 50K pot is too high.

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big caveat, I've never tried this but those who's ears I trust, like Dave Slagle and Jeffrey Jackson tell me performance is compromised when you go with transformer ratios in TVCs that exceed 1:1. In other words trying to get voltage gain from a transformer volume control deteriorates the sound. No proof from my end but these guys have yet to steer me wrong.

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Agreed, in that case it is. I was looking at the bigger picture. I'm not sure where that falls into the equation but according to ears I trust they say best is

.....autoformer at 1:1 or less

.....then autoformer with a small amount of voltage gain

.....then true transformer at 1:1 or less

It is wild conjecture on my part but logically following that sequence a step up followed by a pot would seem to be the next lower desired configuration.

I'll probably never try it but it would be an interesting experiment.

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