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In Reply to: RE: Passives posted by jrdoe on May 03, 2016 at 18:16:37
IMHO, the MAIN advantage of a passive is transparency and possibly lower noise but many SS linestages are extremely quiet these days.
That being said, there can be disadvantages to passives. You have to be much more careful in choosing the other components to be used in a passive setup. You might gain transparency but I've heard some passive setups sound dynamically dull, sterile, and thin.
Basically you want a source with a robust signal output and higher than normal voltage swing can be very beneficial. As an example, the Cary CDP that used I in my passive setup provided 3vrms output which is higher than typical. My amp didn't require a lot of drive to reach full output power, and my speakers were somewhat sensitive.
So in the end, I was able to achieve excellent transparency, maintain great dynamics, and the sound wasn't sterile, thin, or anemic. I was also able to keep the passive about midway in it's range so it wasn't turned all the way up or nearly all the up. I still had plenty of room in both directions.
These critical component matching issues are key to a great sounding passive setup, and not nearly as critical when using an active linestage.
The Best Sounding Passive Setup I Ever Had
Placette Passive with a network of relay switched discrete precision resistors & the Cary CDP source.
Follow Ups:
I agree with Abe, a passive volume attenuator will work best with a high output source and amplifiers having high input impedance, such as 100K ohms or higher.
I have a Goldpoint unit here as well as Endler attenuators, both of which are resistor controls.
I have also had the Chapman Bent unit here (Acoustic Imagery JaySho) and I agree there are some equipment matching advantages the TVCs have over the resistor units but, to me, the resistor units sound more "real."
However, compared to the many active preamps I have owned, all of the passives resulted in the "dynamically dull, sterile, and thin" sound Abe described, to some extent.
My nirvana came with a buffered zero gain unit constructed by Steve McCormack at SMc Audio. Being buffered, the preamp controls the cables and drives anything, and the zero gain works well with my high'ish output Metrum DAC (4V). The volume control uses Audio Note Tantalum resistors, which sound very nice.
Another preamp I really enjoyed was the 6dB gain Tom Evans Vibe with pulse, which uses a DACT attenuator with SMD resistors.
The days of needing high gain preamps are pretty much gone for those of us using digital sources since most of those have outputs of 2V minimum to as much as 6V and amplifier sensitivities are typically in the 1-1.5V +/- range for full output.
As long as you maintain a a proper impedance match there really is not much need for a traditional preamp.
Again matched properly!
If you try matching with a lower impedance amp it will be very bright and edgy. Not a nice thing. Too high and things get bloated. But that could be what you want?
charles
I feel passives that use a transformer don't have the problems that resistive passives have
Alan
Unless the transformers are VERY good, I have found TVCs to be less transparent than a resistor based passive and even many good active preamps.
The only nearly invisible volume control I have tried is a shunt volume control, which passes the signal through only 1 resistor and the pot is shunted to ground.
The Luminous Audio Axiom works really well IF your source has a really good output stage. It won't do wonders with wimpy opamp outputs.
Its hard to convince the TVC lovers other passives are worthy. Resistive types are much more dependent to proper equipment suitable for passives. Id bet a sizeable percentage of people who have tried passives dont really have the ideal gear scenario for it.
ET
I had the same Placette Passive years later in another setup and it didn't work out. tI sounded a little thin and dull.
TVCs may be less finicky with the surrounding equipment choices (I haven't tried one personally to experience it) but one of the BIG advantages of the Placette (to me anyway) is that it has a 128 step remote volume control. Maybe they exist in a TVC but I don't know of any with fairly small discrete volume steps like the 128 steps in the Placette.
Yes I have the same one and like the many steps.
ET
"...but I don't know of any with fairly small discrete volume steps like the 128 steps in the Placette."
I think you're right.
My AVC has only 25 steps, 2db each, but I have never felt like I was "caught between steps".
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Morricab hits it right with his comments in my experience.
I have been using two preamps on and off for the last decade or so. A DIY SET single stage VT137 triode preamp with stepped DACT volume pot and a Sonic Euphoria autoformer volume control (SE).
In terms of tonal balance, they are virtually identical. I think the SE is slightly more focused sounding, VERY slightly less noisy (my VT137 preamp is VERY quiet four an active, tube preamp, a requirment since I use 100db+ effiecient horns) and I never have to turn it off or on.
My active VT137 preamp sounds bigger (wider, deeper soundstage), has more "air" or a sense of room accoustics where the recording occurred, actually sounds more transparent (that always get me, how can an active preamp sound more transparent than an autoformer Which is basically a long wire?) and has better bass (deeper, bigger, more). I like both sounds.
I have experiemented with many resistive based passives and agree that they are more transparent than my SE and probably a bit more than my VT137 pre but they always sound dryish, strangly lifeless and ultimately somewhat boring. I can run my PS PWD II dac straight into my amps without a preamp and I get that same sound as with a resistive passive preamp (the sound is detailed, transparent, fast) but ultimately somewhat fatiguing and lifeless.
With passives you are listening to more of YOUR amp. The review of music sound quality is more a reflection of your amp when it comes to passives.A good passive will use a very transparent resistor. So it will offer almost nothing to the actual signal.
Edits: 05/05/16
Nice post. I have not had this issue with my passive (Placette) I have an ideal scenario with a source that is rated 2.53 VRMS @50 ohmsand amps that require a volt with 100K input impedance. I bi-amp with my passive. I think the best case is that with your passive you must still be able to overdrive your amp or amps fairly easy. Ive seen a few passive set ups and most could not.
ET
Thanks. I have a pretty good setup for passive preamps too. PS Audio PWD II has a stout output section (is actually designed to work well without a preamp) and low output impedance, my amps have ~100k input impedance. My phono preamp also has tons of gain (~70db with SUT) but output impedance is a bit higher than it could be.
I used to have problems with just too much gain in my system, my preamp volume control was never above about 4-5 clicks. I ended up going from a highish gain 3-stage SET to a much lower 2-stage SET amp setup and that works great. I can basically use pretty much all of my volume control now and it maxes out at levels MUCH higher than I can tolerate.
Straight out of the DAC (without preamp) or using a resistive based passive preamp might be the most truthful and accurate setup but perhaps it is too revealing and I find it somewhat fatiguing in the long run, so I prefer the slightly more "euphonic" and dynamic sound I get from my active preamp or my autoformer preamp.
The impudence doesn't drop as much (at all?) when you turn up the volume, though i think you still need to be careful about getting the impedance ratio between the digital source and the amplifier, even with a TVC.
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