Passive linestages, preamps

[davetroy]

I've done some searching on Audioholics.com and have seen almost no discussion of passive linestages and preamps. Is there a reason for this? Has anybody out there had any experience (negative or positive) with passives? I'm a bit surprised by the lack of conversation about them on this forum because good passives seem to be considerably cheaper than good actives.

 

[furrycute]

Well, theoretically, a preamp's only job is volume control. So a good passive preamp is just as good as any active preamp. But I have tried a couple of passive and active pres. For whatever reason, the sound always sounded thin, indicating a lack of bass, in the passive configurations when compared to the active configurations. And I have no idea why that was the case.

 

[highfihoney]

Ive had a passive in my rig's before & wasnt none too happy,furrycute nailed what i would describe as thin sounding music,im a big fan of preamps with tone/balance controls so passive's & most audiophile preamp's dont sound right to me.

 

[Ampdog]

Whew!!

That is an accusation and a half! (Meaning not to contradict it - I have little experience of such commercial products, but these things should be "transparent".)

Firstly not to be pedantic but a passive pre-amp is one of those irritating misnomers. It should be a passive or active control unit. A pre-amplifier means per definition that there is amplification.

This description is also to my mind more accurate of its purpose. With respect, Furrycute, a control unit should not only control volume, although that certainly is the main purpose. I don't want to start the whole debate again on this thread (has it been done elsewhere?) but there is well-motivated use for also some form of tone compensation, input level equalisation, and sub/ super audio filtering.

Just the briefest motivation: We can perhaps accept that tonal correctness is looked after on the CD (though it is often clear that that is not the case) so tone controls should not be necessary. But what about room acoustics? What reaches the ear is mostly no longer what is on the CD. It could be said that three-way tone compensation is far from ideal; sure. But it is better than nothing. And please, let us not have the comment that tone controls degrade the signal. When set at zero compensation, they have (or should have) no audible effect. This has been tested to death.

Sub and super audio filtering is also fraught with argument, but it can be shown that signal products in inaudible regions can cause objectionable artifacts - filters are cheap and simple enough these days.

About transparency, the above members' experiencers are serious. Where are folks cutting corners? I would like to see such circuit diagrams. Not to boast; just for the record, because I am familiar with it, in a fairly extensive transistor pre-amplifier I use 12 transistors plus controls (per channel), and folks claim that quality is indistinguishable from a straight wire. (To be complete I must add that the transistor count includes an RIAA phono stage.) At pre-amp signal level this is not a particular achievement.

So what is happening? Why the audible effect?

(Furrycute, I would agree that "amplification" with the output levels of most CD or DVD players is not necessary. My own device provides for line inputs of 150mV from other devices, but perhaps overdone. No argument there.)

 

[highfihoney]

Whew!!

That is an accusation and a half! (Meaning not to contradict it - I have little experience of such commercial products, but these things should be "transparent".)

Firstly not to be pedantic but a passive pre-amp is one of those irritating misnomers. It should be a passive or active control unit. A pre-amplifier means per definition that there is amplification.

This description is also to my mind more accurate of its purpose. With respect, Furrycute, a control unit should not only control volume, although that certainly is the main purpose. I don't want to start the whole debate again on this thread (has it been done elsewhere?) but there is well-motivated use for also some form of tone compensation, input level equalisation, and sub/ super audio filtering.

Just the briefest motivation: We can perhaps accept that tonal correctness is looked after on the CD (though it is often clear that that is not the case) so tone controls should not be necessary. But what about room acoustics? What reaches the ear is mostly no longer what is on the CD. It could be said that three-way tone compensation is far from ideal; sure. But it is better than nothing. And please, let us not have the comment that tone controls degrade the signal. When set at zero compensation, they have (or should have) no audible effect. This has been tested to death.

Sub and super audio filtering is also fraught with argument, but it can be shown that signal products in inaudible regions can cause objectionable artifacts - filters are cheap and simple enough these days.

About transparency, the above members' experiencers are serious. Where are folks cutting corners? I would like to see such circuit diagrams. Not to boast; just for the record, because I am familiar with it, in a fairly extensive transistor pre-amplifier I use 12 transistors plus controls (per channel), and folks claim that quality is indistinguishable from a straight wire. (To be complete I must add that the transistor count includes an RIAA phono stage.) At pre-amp signal level this is not a particular achievement.

So what is happening? Why the audible effect?

(Furrycute, I would agree that "amplification" with the output levels of most CD or DVD players is not necessary. My own device provides for line inputs of 150mV from other devices, but perhaps overdone. No argument there.)

Hi ampdog,i know you addressed your post to furry cute but after reading it i dont get it,i understand what you wrote but in what contex,you mentioned "cutting corners" can you please explain.

 

[Nuglets]

Whew!!

Firstly not to be pedantic but a passive pre-amp is one of those irritating misnomers. It should be a passive or active control unit. A pre-amplifier means per definition that there is amplification.

If there is no amplification there is no sound. A pre-amplifier mean there is an amplifier in it, it means by definition "before the amplifier". Maybe my interpretation of what you meant is wrong but that is what I got out of the statement. Now I have never heard of an Active or Passive pre-amp so I'm going to do a bit of research on the topic but I'm going to assume that either one needs an amplifier after it. Basically what I'm getting at is that I see no misnomer in calling it an active or passive "pre-amplifier".

 

[PENG]

If there is no amplification there is no sound. A pre-amplifier mean there is an amplifier in it, it means by definition "before the amplifier". Maybe my interpretation of what you meant is wrong but that is what I got out of the statement. Now I have never heard of an Active or Passive pre-amp so I'm going to do a bit of research on the topic but I'm going to assume that either one needs an amplifier after it. Basically what I'm getting at is that I see no misnomer in calling it an active or passive "pre-amplifier".

Ampdog was saying that a passive unit does not amplify the signal therefore should not be referred to as a preamp. In the case of a passive control unit, the power amp only will do the amplification.

You can also argue that there is nothing wrong with the term passive preamp because the thing actually allow you to reduce the signal so it does amplify the signal but it does it in a negative way.

 

[davetroy]

Ampdog was saying that a passive unit does not amplify the signal therefore should not be referred to as a preamp. In the case of a passive control unit, the power amp only will do the amplification.

You can also argue that there is nothing wrong with the term passive preamp because the thing actually allow you to reduce the signal so it does amplify the signal but it does it in a negative way.

Meaning that you've had negative experiences with passive linestages?

Also, passive preamp seems to me like a reasonable label: it's a preamp in that it comes before the amp, right?

Anyway, I recently experimented by taking my integrated amp out of the equation and playing my CD player (with no volume control) directly through my amp, and the results were extremely positive: clearer separation of instruments, no loss of bass, much higher volume than my normal listening level. I'm hoping that substituting a passive linestage (or volume control) for the integrated will result in equally positive results, but I don't know for sure. Which is why I posted this question.

 

[wire]

Meaning that you've had negative experiences with passive linestages?

Also, passive preamp seems to me like a reasonable label: it's a preamp in that it comes before the amp, right?

Anyway, I recently experimented by taking my integrated amp out of the equation and playing my CD player (with no volume control) directly through my amp, and the results were extremely positive: clearer separation of instruments, no loss of bass, much higher volume than my normal listening level. I'm hoping that substituting a passive linestage (or volume control) for the integrated will result in equally positive results, but I don't know for sure. Which is why I posted this question.

Can i ask
What are the brand names of your equipment .
I take it you are using your Integrated amp ( bypassing the Amp section ) as a Preamp then running to your Power amp for tone and volume controls , maybe i read it wrong ?
There are alot of Pre Amps out there ( new and Used ) , all sound different .

 

[Seth=L]

I believe he meant a cd player connected directly to an amp, dangerous for unsuspecting speakers.

Passive "attenuators" do not amplify, they only allow more of the output of the source to be utilized untill max volume is reached at which point the input is maxed.

The experiment that davetroy did illustrates what the max volume would be on a passive attenuator with that source.

 

[mtrycrafts]

Well, theoretically, a preamp's only job is volume control. So a good passive preamp is just as good as any active preamp. But I have tried a couple of passive and active pres. For whatever reason, the sound always sounded thin, indicating a lack of bass, in the passive configurations when compared to the active configurations. And I have no idea why that was the case.

Passive preamp have or can have very high output impedance as its volume control is usually it, hence it is not a good way to connect components with the same or higher output impedance as the input is. Certainly can have an effect on frequency response.

 

[davetroy]

Can i ask
What are the brand names of your equipment .
I take it you are using your Integrated amp ( bypassing the Amp section ) as a Preamp then running to your Power amp for tone and volume controls , maybe i read it wrong ?
There are alot of Pre Amps out there ( new and Used ) , all sound different .

My integrated is a Rotel 1062. CD player is a Rotel 1072. Amp is a McCormack 0.5. Speakers are Vandersteen 2ce Signature. It was just a test that I ran for about 30 minutes, using Ravel's Bolero (because it starts out so softly, thereby limiting the chances of damage to the speakers). I would never bypass the integrated (which I'm using as a preamp) permanently, nor would I try this test with any other piece of music. Yes, the main purpose of the test was to check volume level of the CD player. Yes, I'm aware that preamps sound different, but that's the point. I don't think I want the preamp to color the sound.

 

[highfihoney]

I'm aware that preamps sound different, but that's the point. I don't think I want the preamp to color the sound.

This is where i ran into problems every time i tried to go passive,i tried 2 different passives & on several occasions ive taken amps that i have with their own gain controls & hooked them up with either a mcintosh cdp i have that has internal volume or a dynaco tube model cdp with internal volume.

In all cases i ended up with different results depending on the recording,some recordings sounded ok,some sounded great but most recordings had sound ranging from weak & thin to flat out terrible,alot of what i heard could be contributed to room conditions & the mix or recording quality but it became quickly aparent to me that going down this path would lead to an endless search for perfect audiophile recordings & limit my play list.

I think that in the end going passive or bypassing a pre all together causes more problems than what its worth & causes people to have very short lists of music that they keep in rotation where with more flexible systems with full function preamps you dont need to listen to "famous blue raincoat" all the time to have a wonderfull sounding rig.

 

[davetroy]

This is where i ran into problems every time i tried to go passive,i tried 2 different passives & on several occasions ive taken amps that i have with their own gain controls & hooked them up with either a mcintosh cdp i have that has internal volume or a dynaco tube model cdp with internal volume.

In all cases i ended up with different results depending on the recording,some recordings sounded ok,some sounded great but most recordings had sound ranging from weak & thin to flat out terrible,alot of what i heard could be contributed to room conditions & the mix or recording quality but it became quickly aparent to me that going down this path would lead to an endless search for perfect audiophile recordings & limit my play list.

I think that in the end going passive or bypassing a pre all together causes more problems than what its worth & causes people to have very short lists of music that they keep in rotation where with more flexible systems with full function preamps you dont need to listen to "famous blue raincoat" all the time to have a wonderfull sounding rig.

Which passives have you used?

 

[Biscokid]

I am currently building a transformer based passive pre. I have heard great things about them such as the Promethius TVC and the Bent TAP. FWIW MOST intergrated amps are basicly a passive pre and a power amp combined. Very few have active linestages.

 

[wire]

My integrated is a Rotel 1062. CD player is a Rotel 1072. Amp is a McCormack 0.5. Speakers are Vandersteen 2ce Signature. It was just a test that I ran for about 30 minutes, using Ravel's Bolero (because it starts out so softly, thereby limiting the chances of damage to the speakers). I would never bypass the integrated (which I'm using as a preamp) permanently, nor would I try this test with any other piece of music. Yes, the main purpose of the test was to check volume level of the CD player. Yes, I'm aware that preamps sound different, but that's the point. I don't think I want the preamp to color the sound.

Have you thought about a Pre from McCormack , I see that they made a Passive Pre . ( you probably look at it already )

 

[highfihoney]

Which passives have you used?

The first passive i had was a pretty cheap model from creek then i ended up with an expensive model from placette,both were the darlings of the audiophile mags.

 

[PENG]

My CD player has a volume control button on the back plane. It sounds a little better when I connect it directly to the power amp.

 

[davetroy]

Early returns on Promitheus TVC

Just thought I'd give an update since I started this thread a while ago. I've now spent about a week with a Promitheus TVC (made by a small Malaysian company; costs about $420). System is a Rotel 1072 CD player, McCormack DNA 0.5 power amp, Vandersteen 2ce Signature speakers. Observations so far: No loss of bass. In fact, the bass might be a little tighter. No thinness. There seems to be less of a harshness to the sound from many CDs, especially acoustical (classical, opera). I say it sounds less electrical. My wife says it sounds less harsh. I'd say it sounds more real, although I emphasize that I have not A/B'd it with my previous pre (actually a Rotel integrated acting as a pre). The maker of the TVC says a hundred hours of break-in are required; users on Audio Circle say 400 hours. I don't believe any of this because I can't imagine what there is in a passive to break in! So I'm expecting nothing to change, which is fine. What has changed, strangely, is that I had to move one of my speakers in because the soundstage shifted.

Placebo effect? Maybe. The TVC is doing exactly what I'd hoped it would do.