Thoughts on passive preamps.

Any thoughts on passive preamps? Anyone experienced with passives? Given proper compatibility, transparency is said to be one of their main virtues. The reason I ask is I want to switch to a tubed preamp, and was hoping to gain a degree of forgiveness in my system. As it stands, it is fairly hard on your average recording.

 

Thanks Steve.

 

I agree with Steve, IMO they never seem to display the sonic "advantages" that they are supposed to offer over actives.
The preamp is the "heart" of the system and plays a very big part in determining the sound quality. I have used everything from all SS to all tube systems and, no matter what amp be it SS or tube, I find that a tube driven preamp offers smoother , warmer and "tailorable" sound as compared to an SS unit. I have actually sold and gone back to the same model tube pre three times. Each time I came back my reaction was " Wow, this sounds like music again.

 

I would not dismiss the strategy of the passive preamp without auditioning.

There are many well respected audiophiles who have chosen to use this method. There have been some interesting approaches recently, with the Placette, EVS attenuators, transformer volume controls etc.

Since the output of the average CD player is ridiculously high, no gain is required by the preamp. Impedance matching is important, and if this is done correctly I can't see why the passive method cannot be excellent.

I have a BAT VK-50SE preamp.

Regards,
Geoff

 

I tried this method. The sound was thinner than with a preamp. I went back to a tube preamp and I am much happier.

 

I agree. I have an LW-1 passive that takes a (sealed) black box approach to impedance matching. Most of the arguments both ways are plausible, yet I feel the need to explore the effects of a tubed pre. I wish I could afford the BAT.

 

Dumb question time.

When you are referring to a "passive" pre-amp are you in fact speaking of a line-stage pre-amp? Would my SS Classe' with both an MM and MC stage be considered "passive"?

 

semi-dumb answer

The Classe is most likely an active linestage. Passive refers to the absence of gain stage(s) in the preamp. That is one of the reasons impedance matching and cable length are important between the power amp and source. My passive doesn't even require AC power. It relies on the output of the cdp and the relative efficiency of the power amps for the signal to pass through without degradation, i n addition to its on secret scheme for impedance matching.

I just sold my Silver Audio Appassionata ICs and have put the LW-1 up for sale as well. I want a tubed pre. Must set aside for some Telefunkens...

 

Passive would consist of an attenuator that would act on an unamplified input signal. The phono preamps are active and are required to bring the output levels of the phono cartridges up to line level voltage at which point they would be outputted along with other input signals fed into the preamp with no further amplification. For instance a CD player should have an output of approx. 2v. A passive preamp would pass those 2v on to the amp if the volume pot was wide open (no attenuation). The volume pot would be used to lower the signal into the amp to the desired listening level.

On an active preamp the signals inputted are then amplified. This can be be very wide ranging with most SS preamps nominally putting out in the 1-2v to maybe 10v before clipping or overloading the signal. A tube preamp can sometimes be capable of outputting far higher signals 40V to 50V or more not being unheard of. The output voltage has to satisfy the input sensitivity of the amplifier it is feeding. In other words an amp needs a required amount of input signal in order to attain its full rated output.
Hope I didn't make this too confusing.

 

I used to employ a Reference Line Preeminence One passive with a SS Sunfire amp - it was a good match. The same passive sounded horrible with my SET amp. Comes down to system matching, I suspect.

 

what is meant when there is a tube pre amp with a "phono stage" included? is that volume control? someone explain this passive and active thing to me in greater detail please. i have never used a pre amp before so i have very little knowlege on it. enlighten me.


and also, when using a pre amp, do you actually run the pre amp through the phono input into the regular amp?

 

Check out

http://www.getplugged.com/ha_learn/GPHALEARNSUBTOP_380581.html

for answers to your questions.

 

I think a passive preamp is an excellent choice IF:

1. You're happy with the rest of your system.

2. You don't require remote control.

3. You don't require more than a minimal cable run between your sources and your preamp, and your preamp and your amp(s).

4. You're listening to one or two sources, in stereo, with no processing or tape loops required.

Judging from your statement that your system is "fairly hard" on your recordings, I don't think inserting a passive preamp is the way to go.

Passives tend to clean up the sound, presumably by removing another layer of circuitry from the playback chain, leading to a clearer, airier treble and sometimes a loss of bass (though this may be a reduction of bass distortion). But I've never heard anyone claim that a passive "softened" their system's sound.

One possible way way to test the likely effects of a passive on your system (assuming it's CD-based) is to use the variable outputs on your CD player, if you have them, and run those directly into your amp. (Hopefully you haven't been using the variable outputs AND an active preamp.) Do NOT run fixed outputs directly into your amp.

After turning everything off and then unplugging it, swap cables, make sure the variable outputs are all the way down, plug everything back in, and fire the system up. Carefully bring the variable outputs up to your normal listening level. Now just relax and listen.

If you don't think the sound improved at all, you're very unlikely to enjoy a passive preamp, whose effects are likely to be "more of the same" on your system. If the CD player direct connection wasn't satisfactory, you need to upgrade something else in your system.

 

I have found passive pre amps to have the following limitations:
Smaller sound stage
Lacking in depth in the sound stage
Lower dynamics

On the plus side, I have observed:
On a good passive preamp, no greater inner detail can be found

All said and done, think a good active stage (tube or SS, which ever flavor is yours), offers almost as much clarity and detail. This is of course on more expensive pre amps. I like my dynamics and sound staging, so at least for now, I pass on passives.

 

There are three types of passive circuit elements - resistors, inductors and capacitors. You can't call it an amplifier if it is passive. A "passive preamp" is an attenuator at best. It does not amplify so shall not be called a preamp.

 

Right. I labeled it preamp as an expedient to facilitate a quick and simple understanding of its functions, sans gain stages of course. Although this is not absolutely correct in a theoretical sense (as you have pointed out), it is common usage in most audio discussions. The LW-1, btw, has two line outs, a tape loop, and a selector switch that controls four inputs. It is more than an attenuator.

 

thanks for the link. it didnt answer all of my questions though. for instance, you hook up a turntable into the rca inputs of the preamp, and then run the outputs to phono inputs of the regular stereo amp?

i did a little searching and found this tube preamp for $300 made by a guy who works pretty much by himself in canada under the name space-tech. i've read quite a few good things about it, saying it competes with units far more expensive. anyone have any experience with this outfits pre amps?
the name of the unit is QA-001. it has 2 rca inputs and 2 rca outputs and volume control knob. forgot the link but you can find it on yahoo if interested. would this be considered a passive pre amp?

 

trilogia,

If your pre does not have a phonostage you obviously need a stand-alone version. Once all the equipment is in place hook the ICs and ground (if applicable) from the tt into the phono input, then run some ICs from the phono output into the preamp (like aux, - whatever is left).

As for space-tech - he makes some good stuff - but he ain't all that cheap... Decware makes some cool SET amps and intergrated models (the basic Zen SE84 sounds wonderful with properly matched and efficient speakers) and runs $500 - no pre needed unless you have more than one source (sometimes you can just get a quality switchbox).

Also take a look at ASL - they make a nice triode/pentode integrated for under $800 and some cool mono block push pull amps for around $225.

I am sure all this will generate more questions than answers - but isn't it fun?

Here are the links:

http://www.decware.com/tubes.htm

http://www.divertech.com/antiquesl.html

Happy hunting,

 

My apology. An attenuator with selector switches and tape loops. But it still doesn't amplify. I wasn't try to pick a fight with you, pigmode. But lot of confusion may have come from the inaccurate term "passive preamp" which is generally accepted in the audio press.

 

someday I would like to see a web site where they said "our product doesn't stand up to the more expensive gear". I guess I won't hold my breath.

I have spent a fair amount of time stressing over the passive v. active (I won't get into the degradation of the English language by marketing types rant) scenarios and I have decided not to get an active preamp.

Everyone fuddies around with sonic degradation issues, and if that doesn't get you, the FUD factor of 'impedance matching' which is invisible and consequently easy FUD (Fear, Uncertainty, Doubt) material.

I was wondering if somehow, by having a passive in my system, I was missing out on some obscure yet significant musical content. I spent most of a long weekend recently with my system simplified to the following: Theta Miles -> Wireworld Atlantis II -> Laurel IIs -> Klipschorn -> My mind, via my ears.

The Theta has analog domain volume control.

I listened to all kinds of source (well CD source) and was, in a word, intoxicated by the sound all weekend long. I found no fault whatsoever in this setup. Someone earlier mentioned:

Smaller sound stage
Lacking in depth in the sound stage
Lower dynamics

as indicators of bad passive performance. I found none of these things to be true.

I am adverse to spending four figures on a 'good' active preamp just to find out what I have alledgedly been missing.

Of course, YMMV. Not everyone here is privledged enough to own the wonderful stereo components that I have.

 

No problems Paul. It's a misnomer that I have learned to accept.