2. amps-preamps
  3. 1075728615

TVC vs. active pre?

I'm using a Bent Audio NOH in my system, and love the sound - it's detailed, open, dynamic, coherent, musical and very immediate.

Whenever I talk to amp designers however, the universal preference seems to be for active preamps. My feeling is that if there are no interfacing issues between the pre and the power amp (sufficient voltage drive, no impedance or capacitance problems) that an active pre can't "add quality" to the signal. As far as I can tell, an active preamp provides buffering and gain. Absent any need for these, I don't see what benefits it can provide.

Is my assessment incomplete? Are the recommendations for active preamps simply based on the avoidance of potential interfacing issues in unknown systems?

I understand that a good active may beat a poorly implemented passive, but given good design/build in both situations, what would it take for an active to beat a good passive, especially a TVC? And specifically, has anyone gone from a TVC to an active? If so, what were the system issues that prompted the change?
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Showing 1 response by atmasphere

atmasphere's avatar
atmasphere
11,574 posts
 
The job of the line stage in a preamp is to similtaneously provide volume control and also control the effects of the interconnect cable. A depressingly large number of preamps (especially tube preamps) fail at this task. Passive volume control systems are usually even worse when it comes to the latter task, though often better at the former.

The concept of the TVC is nice in that one should be able to have both a good volume control as well as cable control, but in practice the effects of the transformer are quite noticeable and the difference in sound from one volume control setting to another (which is a problem that plagues passive units) is still there.

The only way to get around the buffering (to interface to the cable and load) issue in a passive is to build the volume control into the amplifier. This is not always practical, as one is still stuck with the fact that the quality of the control remains critical. Good volume controls (usually some form of multiposition switch) are fairly large; semiconductor style controls (often used in remote volume controls) don't as yet sound right.

'Right' is a relative term; the more transparent your system the more these comments will make sense.
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