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
colopilot
28 posts
 
I have a Modwright SWL 9.0 and run it into a McCormack DNA 500.

It is a really fantastic combo. The Modwright has an output impedance of 600 ohms and it drives the 500 without any problem.
mdconnelly
133 posts
 
I had similar concerns when I first started looking at the McCormack amps. I've got an ARC SP9 preamp (tube hybrid) with GNSC ref mods that has a recommended load of 60k ohms, but it's output impedance is only 250 ohms. I was operating on the mistaken assumption that the ARC recommended load was reason enough to avoid 10k input impedance amps such as the DNA-500 or earlier DNA amps with Steve's balanced transformer upgrade. Bad mistake!

Fortunately for me, I sent Steve an email about this and received a similar response to the one he posted above. Since then I've replaced my Levinson 331 with a DNA-500 and it's working extremely well with the SP9. I am totally ecstatic about the changes the DNA-500 wrought in my system.
ar_t
165 posts
 
You can load the Jensen or Lundahl 1:1 transformers higher than 10K. You have to use a HF termination ("zobel") to get the FR correct. I do it all the time. The impedance is no longer flat if you do, but there is no such thing as a free lunch.
stevemcx
166 posts
 
True enough, Art, but the RC networks result in bandwidth limitations I do not care for. I find I prefer the sonics with a 10K load and no RC termination.

Steve M
fplanner2000
616 posts
 
I have a DNA-500 that works amazingly well with VAC preamps. I used to use a Standard LE and now have a Phi 2.0. The synergism is excellent and both Steve and Kevin (at VAC) were very helpful in explaining the impedence situation to me and assuring me that the impedences would work, especially with the Phi. The sound is, needless to say, very impressive as well.

(Steve - we need to talk when you get back)

Hope this helps.
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