Passive Stage preamp vs Active Stage Preamp


As you all probably know lots of integrated amp designs (solid state) exersise the passive preamp part design which are basicly either transformer or a high quality potentiometer and simple input circuitry.
Many of us know that most of the CD players have a sufficient enough output voltage to feed the power amp (from 1V upto 3V) Same thing with DACs. Analogue phonos are able to produce the same kind of outputs.
The input sensitivity of power amp <=500mV
For somehow I've been experimenting with loaned WADIA No 15 DAC with variable output that has just a passive potentiometer and connected a variable output directly to my Bryston 3b-st. The result was deeper soundstage and details vs. setup through Bryston 11b preamp. The only drawback was that the volume range is much smaller than with preamp.
Can anyone summarize all advantages and disadvantages in using passive preamps vs. active?
Does it make a sence to try a passive stage preamp in my current solid state setup which is Theta Data II -> EAD DSP700 ->...
and analogue J.A. Michell GyroDec -> Delphini phono ->...
and ending with Bryston 3b-st?
Also if such exists, describe an importance of using active stage in tube setup.(Impedance matching?)
marakanetz

Showing 1 response by 6bq5

You have one false statement in your subject paragraph: "Analogue phonos are able to produce the same kind of outputs." The output from a cartridge is very depandant upon the design, Moving Magnet, Moving Coil, etc.; the output ranges from ~0.2mV - ~1500mV. While the output as voltage may be suficcient to drive some amplifiers ( from the high end of the scale) you are forgetting the issue of Phono Equalization. The output from a phonograph/turntable MUST be equalized for the signal to be balanced music. There are many curves, but the RIAA is the only one used today for new recordings. There are primarily two means of effecting this EQ: the first is an Active EQ circuit, where the signal is amplified as it is EQ'd, the second is Passive. THe traditional problem with a passive design, is that the EQ will drift as the gain device (vacuum tube or transister) changes gain; thus the EQ can/will drift over time. Additionally the input "load" that most cartridges like to see is 47K Ohm, Not what most line level inputs like.

Using a passive pre-amp for line level ( CD, Tunner, Tape, etc.) can get you "closer" to the music, and there are many purists who have one source connected directly into their amp. This should not be done w/ a phono input!. But the down side is that most avtive pre-amps provide a level of protection for the downstream devices, which is lost in a passive unit. If you have considered balanced inputs, you will not be able to use a passive pre-amp.

The choice comes down to your listening preferences and system habits. if you feel that the reduced control allows you to hear more and that is OK, then get rid of the pre-amp. If the Phono is your primary source, you will need some type of Active Pre-amp.
Good luck