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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
pubul57
3,712 posts
 
Maybe, but my CD player puts out 4volts in high setting, I would think that would drive anything without any help from a preamp. Impedance matching I get, "drive" seems to be a strawman as far as dynamics.
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almarg
9,670 posts
 
I can understand frequency abberations due to impedance matches, but why would a passive ever be any less dynamic?
One explanation which I suspect underlies those perceptions in many cases would be upper treble rolloff caused by the high output impedance of a passive preamp interacting with cable capacitance that is excessive in relation to that output impedance.

Upper treble rolloff would result in dull and sluggish transients, which very conceivably may create the subjective perception of reduced dynamics.

Regards,
-- Al
herman
2,242 posts
 
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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pubul57
3,712 posts
 
Herman, does the 50kohm of my attenuator address that issue, or does it cause problems on the other end into my 100kohm amp load?
herman
2,242 posts
 
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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