[richs]

My Sig. 30 is arriving today. I'm very excited to get home for work (I bought it on Audiogon, but don't worry Vinnie, my purchase let some other lucky soul by the Sig 70's). 

I need to switch between two inputs, so was considering buiding by own switching device,  but I came across the Promitheus TVC passive pre-amp.  It's getting rave reviews in a long thread over on Two Channel Audio.  Its seems a virtue of this device is that it lowers impedance (and lowers it more as the volume decreases). Given that my dac has an output impedance of 50 and Sig 30 has an input impedance of 20, would this be a good pairing.  Note that I'm driving Gallo Ref 3's (which are not especially easy for the Sig 30 to drive), I also listen at fairly low levels (75-80 dbs) in a pretty small room).

Thanks in advance for any thoughts.

Rich

[Vinnie R.]

Hi Rich,

Glad to hear that you are finally getting a Sig 30 for your Gallos!

The output impedance of your dac is probably 50-ohms.  The input impedance of the Sig 30 is 20 kohms (20,000 ohms).  This pairing will be fine and I personally would not use a TVC in between the two.  Just feed your source to your switch, and then to the Sig 30.  Keep is simple.

Note that I'm driving Gallo Ref 3's (which are not especially easy for the Sig 30 to drive),

It'll drive them, you'll see 
I heard this combo for myself, and since you are in a small room and don't really crank it up, you'll have no problems. 

Keep up posted!

Vinnie

[GHM]

Vinnie I'm curious..could you put a bypass switch(amplifier direct) in the Sig 30s or 70s? So other preamps can be used without the extra wiper or attenuator in the path.

[Vinnie R.]

Vinnie I'm curious..could you put a bypass switch(amplifier direct) in the Sig 30s or 70s? So other preamps can be used without the extra wiper or attenuator in the path.

Hi GHM,

No and the main reason is that Sig 30 was voiced with the DACT CT2 in the path.  I have tried it direct (no DACT) and it does not sound like it should.  The impedance of the DACT ties in with the input stage, so I do not want it bypassed.

The other reason is because many preamps have high gain and get too loud too quickly, so the built-in DACT is a way of setting the gain of the Sig 30 so you can get the most useable range of volume control out of your active preamp. 

I state this in the Sig 30 User's Guide:

Your Signature 30 can be used with an active preamp in front of it (for input source selection purposes, extra gain, or added “sonic character”).  If you are using an active preamp, we highly recommend that you set the precision volume control of your Signature 30 to a setting that will allow you to achieve the most useable range of your preamp’s volume control.  Doing so will also lower the noise floor of the active preamp/Signature 30 combo. 

In other words, setting the Signature 30’s precision volume control to MAX is NOT always the best solution when using an active preamp…especially one with a lot of gain.

Hope this helps,

Vinnie