Preamp impedance mismatch with McCormack DNA2

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,

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.

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

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.

Hello all -

Please note Darrin's reference to the DNA-500. He is correct when he says that it has the same 10K input impedance as the DNA-2 *after* adding the Jensen input transformer. This is also the same input circuit used in any of my SMc Audio monoblock amps (but *not* the same as the original McCormack Audio DNA-1 monoblocks) or any SMc Audio amp upgrade with balanced inputs. I believe there are several members here who have the DNA-500 (or my monoblocks, or my amps with balanced inputs) and their experience should be valuable.

I usually design my amps with a 100K input impedance for maximum compatibility, but using the Jensen (or Lundahl) input transformers forces a shift to 10K (at least for the 1:1 types I prefer). It would be nice if I could offer all of the advantages of the transformer input topology along with high input impedance, but I feel strongly that the strength of this approach more than outweighs this small disadvantage. Using these transformers allows me to simplify my input stage somewhat, and provides a “brickwall” filter against DC and RFI – without the need for blocking capacitors or additional filters. Like many audiophiles, I used to look askance at the use of transformers, but I must say that I have become very fond of them. Used properly, I feel they offer a lot of advantages, and their main drawback is high cost.

I know that many owners of these amps are using tube preamps happily. I haven’t made a list (apparently I should!) but I have heard quite a few mentioned: C-J, ARC, ART, Sonic Frontiers, VTL, Rogue Audio, just to name those that jump to mind. Most of these have output impedances in the several-hundred-Ohm range, but I’m pretty sure that none of them exceed 1KOhm. I have even heard one person say that they tried the DNA-500 with a Hovland HP-100 and liked what they heard, despite the Hovland’s high output impedance (over 2KOhm, I believe). While I would not recommend this combination as a good impedance match, it is interesting to hear that at least one person liked it. Of course, solid-state preamps should work fine, as well as buffered “passive” designs and some transformer-based volume controls (TVCs).

It would be great to hear from owners of these amps about their experience with various preamps. I’ll make a point of noting the models people have used successfully ;-)

Best regards,

Steve McCormack
www.SMcAudio.com