2. amps-preamps
  3. 163964-16222

First Watt SIT-3 preamp pairing advice

Hi There,

I have Nelson Pass's First Watt SIT-3 power amplifier. I am using a ~15 year old VAC (Valve Amplification Company) Standard Preamplifier with NOS Telefunken 12AU7 and 12AX7 tubes for the 2 stages. I am looking to upgrade the preamp and am considering the Passlab XP-12 or the Linear Tube Audio MicroZotl MZ3 preamp. My impression is that both preamps are fairly popular when pairing with First Watt amps. Anyone here have paired both these preamps with the SIT-3 and can provide impressions that might help me decide? If there is 3rd option that you like very much, I am all ears too. Thanks in advance for any advice.

Andrew
longinc

Showing 3 responses by vinpic

vinpic
34 posts
 
I have the mz2, a great preamp overall but not capable of driving the sit3 to its full splendor.  Dynamic range & bass mgmt arr simply not as good as higher gain pre-amps.  In my stable the VRossi L2i does a great job, the preamp section of a Lumin or Mola Mola dac is amazing as well (the latter set @6V)
vinpic
34 posts
 
Hi Longinc - using Cube Audio Nenuphars 92db 
a marriage in heaven with the sit3 🍾

vinpic
34 posts
 
For what is worth 2 notes I had stored in my files regarding the SIT3.  Hope it helps 

Regarding the SIT3, an important point to note is that it has an extremely low gain (for a power amp) of only 11.5 db. Power amp gains are typically in the mid to high 20s.  

Consequently it can be calculated that the SIT3 will require a single-ended input (it does not provide a balanced input) of about 3.2 volts to be driven to its maximum power capability of 18 watts into 8 ohms. If a digital source having a volume control is used without an active preamp it will almost certainly not be able to provide that much voltage, even with the volume control at max. And in many and perhaps most cases vinyl or other analog sources won't be able to do so even when used in conjunction with an active preamp.

I considered purchasing a SIT3 recently, but that factor made it a non-starter for my system. I went with a Pass Labs XA25 instead, which I have been delighted with.


Regarding the optimal ohm rating for the SIT3, the following is from Nelson Pass.

“The most popular impedance for the load is 4 to 8 ohms, which is the region where it measures best, and there is not a lot of difference between those two numbers. At lower, we see increased distortion, and at higher impedancethe distortion numbers don’t go up, but there is an increase in higher orderharmonics. It’s not a big deal, but you can play with this by putting some resistance across the speaker. Typically people play with resistor values from 8 to 25 ohms, and since resistors are cheap I recommend that you get several values to try. The type of resistor is not critical, but should be ratedat 5 watts or more.”

I have Avantgarde duo XD at 18 ohms. I use a Zu Audio 10 ohm resistor across my terminals to give the amp a resistance rating of 6.42 ohms calculated.

Works wonderfully.


More to discover