2. amps-preamps
  3. 1268737214

Who is using passive preamps and why?

Seldom has there been any discussions on passive preamps in the forums and although my experience with them has been limited I have found them so far to be very enjoyable and refreshingly different. They seem to fall into their own category, somewhere between solid state and tube. Finding a preamp that is satisfing has been difficult. Some active solid state preamps can be very good but they seem to inject grain to some degree in the upper registers and some tube preamps are not too far behind. So far I think they should at least be matched up with an amp that has sufficient gain which is often overlooked. Which passives are you using and with what amp? Why do you like them?
phd
herman
2,242 posts
 
hmmmm, can't find where I said 10K was a good match. Which original example are you referring to?

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clio09
3,353 posts
 
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.

Reviewing my response I see that my point was not clearly stated. What I meant was that in your example it would be obvious to me based on my own personal criteria that an amp with 10k input impedance would not be a good match for a passive. I'm not saying that you a stating otherwise. I understand you were just using the numbers to illustrate an example, which is of interest to me and why I was wondering about the formula you used to come up with the calculation.
pubul57
3,712 posts
 
Herman, if the impedances and cable capacitance are right, so that a tranformer doesn't really solve a problem, wouldn't a resistor based passive, like my Goldpoint, perform better than a TVC, especially in terms of bandwidth? Anthony?
pubul57
3,712 posts
 
I once did have the Placette RVC and then tried the Placette Active, and what I notice was more articulate bass, I now wonder if the issue was the the RVC simply has too low an input impedance to be optimal in my setup - but it sure was transparent.
herman
2,242 posts
 
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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