Valve Amplification Company Signature SE preamplifier Manufacturer’s Comment

Editor: Thank you for the thoughtful review of the VAC Signature SE preamplifier. We are grateful that Robert J. Reina found the Signature to be "the most significant audio product I've ever hooked up to my reference system."

With regard to John Atkinson's concern about the low-frequency measurements of the moving-coil phono stage, with the Signature SE's MC input, the selected load resistance is reflected through a transformer designed specifically for the particular traits of MC cartridges. Many active electronic signal generators bog down when confronted with this sort of load at low frequencies, such that the test equipment may operate outside of the assumptions of its designers and yield incorrect readings. However, using an external known resistance (10 ohms, for instance) to make the measurement and monitoring both sides of the resistance, the generator's distress can be observed, and one can confirm that the input impedance of the Signature MC phono stage does not fall dramatically and is responsive to the load switch at 20Hz.

If, as one sweeps frequency during test, one does not watch the generator's output but watches only the voltage at the output of the known test resistor, one will conclude that the preamp's input impedance is falling, when in fact the generator's output is falling. If the test system has its own internal "known" resistance (as does the AP SYS2722 at 20 ohms minimum), this problem may go unnoticed.

The reported measurement of 36 ohms input impedance at 20Hz likely represents the signal generator's difficulty coupling to the preamplifier, possibly due to interactions between the reflected load and the AP's own output transformers. These problems do not occur with actual MC cartridges.

JA also notes a slight rise in moving-magnet input impedance at low frequencies. We are unable to duplicate this result with our Agilent test system or with the external resistance method, and there is nothing in the circuit design to account for a rise. The small impedance drop at 20kHz is, of course, due to the 100pF MM termination (loading) capacitance.

Three other measurement notes:

1) JA is correct: The traces of 60 and 180Hz signal are due to stacking the audio and power-supply chassis on the test bench; we recommend greater spacing in normal use.

2) A slight channel imbalance can occur over time due to tube drift; incorporating feedback would tend to suppress this, but in our experience would limit the sound quality.

3) The difference in nominal MC load vs the chassis markings is due to the SE's input transformer having a slightly different turns ratio than the regular Mk IIa's transformer (1:8 vs 1:10). We will address this, but in practical terms, JA is right: Use the setting that works best with your cartridge.

Thank you again for the interesting and thorough review. And Robert? You're right: You really should hear the Statement instruments!—Kevin Hayes, VAC/Valve Amplification Company

Unfortunately, the review sample of the VAC preamplifier had long since left my lab when I received Kevin's Comment, otherwise I could repeated MC-stage measurements along the lines he suggests.John Atkinson

Valve Amplification Company
1911 North East Avenue
Sarasota, FL 34234
(941) 952-9695

Allen Fant's picture

Where is RR going?

John Atkinson's picture
Bob Reina died at the end of March. See This was the last review he wrote.

John Atkinson
Editor, Stereophile

TNtransplant's picture

Hi John - maybe this has been litigated in the past, but this one is fresh in my mind after seeing Kevin Hayes reply in the latest print issue.

Personally feel that Manufacturer comments should be appended to the online versions of reviews, especially if the reply is more substantive than a general 'thank you' and makes a valid point about the review itself.

I realize this may take extra effort, and perhaps providing comments and follow-ups might not be feasible for archival postings, but in my mind would certainly represent journalistic best practice.

John Atkinson's picture
TNtransplant wrote:
Personally feel that Manufacturer comments should be appended to the online versions of reviews...

It's now included in this Web reprint of the VAC review.

John Atkinson
Editor, Stereophile

TNtransplant's picture

I have no connection whatsoever to VAC but had read the review as well as comment and felt appropriate.

I'm in the midst of considering some upgrades to my system and in re-reading back issue reviews have realized that many of the most informative are from Robert Reina. His voice will be missed.

volvic's picture

Read this review several times knowing it was RR's last. In fact went back to past issues to re-read his older reviews. So long Robert J. Reina your Stereophile subscribers and Hi-Fi community miss you.

brian_pdx's picture

1) You mention the "pass through" for video on the VAC. How exactly would that be hooked up? If you wanted could you hook up HDMI connectors and if so how? For those of us who would like a 2 channel system in a place where video would be handy even if it isn't surround sound. 2) Speakers, as you know better than I, perform differently with different preamp/amp combinations. The difference is even more with tubes vs. transistors. Or so they say. Some "experts" say you should not use electrostats or planars with tubed equipment. True or not true? I now this is a challenge but recommending types of speakers rather than brands or models you would use with these reviewed products would be helpful to your readers. Thank you.

BruceH's picture

The level of after sales service from VAC is abysmal, I have been trying for months to get information from VAC regarding a replacement transformer for my VAC Auricle Pre. I have tried contacting them directly and through the local import agent and in all cases I have been totally ignored.
Too many boutique manufacturers fail to deliver on after sales service - if you sell a Rolls Royce product then you should have Rolls Royce service, unfortunately VAC deliver No Service which makes my VAC Auricle pre just a piece of land fill

VAC's picture

Dear Bruce:

Ironically, this message was called to our attention just one day after your parts were dispatched via FedEx. We strive to provide excellent service for our products, and to answer within 24 working hours the several hundred e-mails we receive daily. In reviewing the communication trail with you, we see several times where replies were sent but which did not seem to get through to you, as sometimes happens due to spam filters and so forth. Communications with our importer in New Zealand worked more smoothly, and we are grateful for his assistance.

The VAC Auricle, the last of which was produced around 11 years ago (yours was exported to Australia in 2005), was our entry level preamplifier, priced under $2,500 US, and a delightful component, well worth repairing and using for decades to come. Yours is the only known case of a failed power transformer, as you have diagnosed it, and that part was not available. To serve you rather than abandon you, it was necessary to fabricate a new transformer assembly (two transformers, mu metal shielding can, etc.), and regrettably that took some time. These were dispatched via FedEx on 25 March, along with a few other parts that we think should be replaced as a preventative measure to ensure that you do not experience further problems.

We apologize for the time this took to achieve, the evident glitches in e-mails, and the frustration you have felt. There are more than 10,000 VAC manufactured audio components in the world, and we actively support them all, with the sole exception of the 23.1 CD transport of 1994 due to the unavailability of the laser assembly. Hopefully you will not require service again, but, if you do, will we do our best to improve on this experience.

Best regards,
Kevin Hayes, President, VAC