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High Output Preamp for First Watt SIT-3?

I'm new to the audiophile world and recently purchased a First Watt SIT-3 with Magnepan .7s.  I have a Mytek Brooklyn Bridge for streaming, though I prefer to play vinyl with my Mofi Ultradeck.  The Mytek serves as the phono stage (69dB gain for MM?), and I don't use a preamp;  the Brooklyn is connected directly to the First Watt. 

I understand that the SIT-3 is only 11.5 dB of gain, and that's extremely low compared to most amps.  I like most everything about the system except for the fact that I have the Mytek maxed out volume-wise many days.  Certain LPs are cut quieter, and I wish I had more power.  There are times streaming where the Maggies aren't getting to their sweet spot.  I realize the Maggies are a lower sensitivity speaker. 

What should I look for in a preamp to fully drive the SIT-3?  Eventually, I'd like to replace the phono stage instead of relying on the Brooklyn.  Is there a tube preamp featuring a phono stage with sufficient output to drive my amp in the $4k range?  Otherwise, I'm eyeing the Modwright PH 9.0 and a linestage preamp, realizing that this will probably be costlier.  I'm looking for a warm sound, not analytical but engaging. 

Any help is greatly appreciated.  I'm a working musician with a basic understanding of related electronics but little experience in this world. 

murphbass
joeinid's avatar
joeinid
658 posts
 
@charles1dad 

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.

vinpic
34 posts
 
Hi. I used to own a sit-3 and had similar issues with the pre-amp. The best match I found is the COS Engineering D1 dac/preamp. Maximum output 8V (most pre-amp do 2-3V) and 0db gain. It’s one of the best dac I’ve ever used too. PM me if you wish to sell your SIT3 or are interested in knowing more about the COS D1.
charles1dad's avatar
charles1dad
10,236 posts
 
Hi joeinid,
Thanks for posting that detailed explanation per Nelson Pass. Given atmosphere’s comments I wondered if thi applies to the S.I.T-3 (up to a certain point). In your case you prefer the sound with less than your speaker’s 18 ohm impedance load.

My speakers are 14 ohms and my amplifier seems to thrive with this high impedance. No doubt that this likely varies amongst amplifiers.
Charles
almarg's avatar
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almarg
9,670 posts
 
While it won’t matter in the case of @joeinid ’s 107 db speakers it’s probably worth mentioning that the SIT-3 won’t be able to provide much power into an 18 ohm or other very high impedance, regardless of whether or not a resistor is connected in parallel with the speaker.

For example, based on the amp’s 18 watt/8 ohm and 30 watt/4 ohm ratings it is probably capable of supplying something like 22 watts into the 6.42 ohm load he mentioned, corresponding to a 10 ohm resistor paralleled with his 18 ohm speaker. In that case, though, most of the 22 watts would be consumed by the resistor, and it can be calculated that only about 8 watts would be delivered to the speaker.

It’s a different story altogether in the case of @charles1dad ’s Coincident Frankensteins, which are optimized for high impedance speakers and I’m guessing would not need a resistor to provide good sonic results and close to rated power even with an 18 ohm load.

Best regards,
-- Al

joeinid's avatar
joeinid
658 posts
 
@almarg

I totally agree with your assessment. Thank you for posting.

In my case, even 8 wpc is a lot for me.

It’s true that I’m wasting or throwing away power for the sake of keeping the SIT3 in its happy zone. So far the SIT3 is my favorite solid state amp on my Avantgarde although I enjoy others, just not as much.
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