Since convential wisdom dictates that tube pre amps prefer higher impedences, & you inhabit a dealer barren area, you`re in a lose lose position. YMMV. |
Steve McCormack would be an excellent source for the answer to your question. I have known Steve for nearly 30 years, a very bright guy who will answer without any bias.
This is a natural since he's doing work for you. |
Check out this preamp http://www.space-tech-lab.com/SP-QA-111-BAL-SP.html . Albert at Space Tech.Labs can custom design to meet your needs. Very Very nice preamps. |
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 |
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 havent 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 Im 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 Hovlands 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. Ill make a point of noting the models people have used successfully ;-)
Best regards,
Steve McCormack
www.SMcAudio.com |
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. |
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. |
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. |
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 |
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. |
I have used a CJ Premier 17LS and am now using the CJ CT-5.
Both worked without a problem.
Cmach
|
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. |
I have a Cary SLP 2002 tube preamp and would recommend it highly if you can be patient and find one used. It is a low impedance design from what I understand. It uses 6922 driver tubes and 12AU7 buffer stage tubes and is a fully balanced design, with a fully regulated power supply. The output impedance is 480 ohms, so it should mate well with 10K input impedance amps.
The sound slots nicely between typical warm tube preamps and very neutral preamps. The huge amount of tube rolling options allows one to further tune the sound to personal tastes.
Cary Audio are very helpful. Call them and speak to them about any questions.
I have found through experience that with the same speakers, a change in the preamp offers the the biggest change to the sound of my system.
Good luck
kw........ |
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