2. amps-preamps
  3. 1140406847

Preamp impedance mismatch with McCormack DNA2

I recently purchased a McCormack DNA-2 with an SMC Rev.A mod. The amp currently has a 100K input impedance, however I am sending it back to Steve for some additional mods including the Jenson balanced transformer upgrade, which would change the input impedance to 10K. I am currently running direct out of my Reolution Audio Opus 21 cd player, but would really like to add a tube preamp. I am finding that alot of tube preamps are typically ( on paper ) not suited for driving a lower input impedance. However, what is on paper and what is reality are often two different scenarios. I would appreciate some suggestions on some balanced tube preamps that may work well with this amplifier. I don't live in an area where there are dealers so trying several at home is not possible. At least with some suggestions it will help narrow my search and the amount of traveling I will have to do. Thank you for all the help.

Darrin
rhythmace4218
rhythmace4218 OP
53 posts
 
I have talked with Steve McCormack. He was very helpful,and advised to look at preamps with a 1000 ohms or less output impedance. I have read many reviews on several balanced preamps and even though they may may have an output impedance substantially lower than 1000 ohms at 1khz. However, the output impedance drastically rises as the frequency falls. I realize this is normal, but almost all the reviews make mention of mating the preamp with an amplifier with an input impedance of at a minimum of 20-30K. I noticed that the DNA-500 also has a low input impedance of 10k. Maybe I could get some useful feedback from some DNA-500 owners as well. Perhaps I should skip the Jenson upgrade. Does anyone have any experience with this particular Jenson transformer upgrade from SMC? Is it worth it? Thank you

Darrin
bgrazman
226 posts
 
I'm having great luck with a Supratek Syrah preamp and the SMC Platinum version of the DNA 0.5.

Before the Supratek was an ARC LS-7 (also tubes).

The amp came into the system unmodifed... I had the Rev. A work done and lived with it a few years and just a few months ago went for the full monty. Have only seen the results get better & better.

I would also second albertporter's comments--Steve has always steered me in the right direction.

happy listening,
clio09
3,353 posts
 
A Joule Electra LA-100 MkIII has an output impedance of 600 ohms and according to Jud Barber will drive an amp with as low as an 8k input impedance rating. They show up used here for less than $2k, otherwise near $4k new.

Space Tech Labs is a good option as well. I have been looking into them for their passive preamp and Albert is more than willing to customize one for me based on my equipment specs.
kr4's avatar
kr4
3,672 posts
 
I have used the Sonic Frontiers Line-2 and Line-3 preamps with the balanced line input on my DNA-1 Rev. A very successfully.

Kal
mitch2
3,922 posts
 
Ditto what Kal says, the SF Line 2 and 3 SE both sounded great with my DNA500, however they both have quite low output impedence for tube preamps, below 100 ohms in the case of the Line 3. Steve's answer is the conventional "amp input should be at least 10x the pre output" guideline, which I suspect will be fine.
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