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
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.
cmach
197 posts
 

I have used a CJ Premier 17LS and am now using the CJ CT-5.
Both worked without a problem.

Cmach
hiend2's avatar
hiend2
453 posts
 
Impedance Matching plays a large role in preamp/poweramp matching. More then i had any idea of. System is a Mini max tube preamp with a output impedance of 1200ohm. Amplifier is a rogue zeus input impediance of 100,000 ohms I think.
The zeus has 2 sets of RCA inputs. A normal high impedance input and A "low impedance input" Via A input transformer.
The Low Z input completely Blows the normal High impedance away in sound but there is a noticable Blur to the sound from the input transformer. After hearing the diffrence between the 2, Im making it a PRIORITY to match preamp/poweramp impedances very close as possible.
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