Trying a BAT VK-P5 with a Step up Transformer

I'm going to crack open a VK-P5 next week, making sure all its 10 tubes are all ok. I recently bought a step up transformer to try with it.

The story below is my journey on why I went this way.

The VK-P5 sounds good, but I feel it can be better. It has mixed reviews. Some negative, mostly bland. But I know it sounds good. I want it to be great.

Mike Fremers review here was not complimentary -“velvet-fog”

He described it as "Produces A Luxurious, “Velvet Fog”, which I read as a backhanded remark.

He used a .2mV output Transfiguration Proteus with a 1 ohm impedance. To me, that may have been too weak for a preamp 50dB of gain. I believe tubes like to be driven. They dont shine just barely at cruising speed. Carts also shine the best when they are properly loaded. The VK-P5's lower load setting is 100 ohm.

I also found someone who had success with the VK-P5 using a K&K set up transformer.

His impression - "the sound is fantastic (necessarily reflecting the contribution of the Dynavector Te Kaitora cartridge, of course). The bass, if anything, is even more extended than with the Clearaudio; and the mid-bass is "richer" and fuller, but no less well-defined. The Clearaudio's strength is in the midrange (try any acoustic piano record!), but this is ever-so slightly more present and palpable. There is a qualitative difference bewteen this and the MM playback, which is that the MM seems to emphasize the leading edge of transients, whereas the MC has more "sustain" in its playback."

I got a Rothwell MC-1 280 ohm set up transformer that produce 22 db gain to attach my Dynavector 20x2L that puts out 0.28mv. I am going to tone down the output of the phono pre from 50 db to 44 db using the internal pot to produce a total of 66db gain with the SUT.

VK-P5 will be set at 47k ohms and 150pf capacitance using a user capacitor slot in the pre. The MC-1 Special will end up giving my Dynavector a 282 ohm load, with a 0.2% db reduction in output. I expect the system to put out a total of 65-66db gain.

I used the math shown here -

47kohms / 5ohm squared = 1880 ohms

5 ohms / (1880 ohms + 5 ohms) = 0.002db gain reduction

The Dynvector sounds great at 100 ohms. Its sound pretty good at 1000 ohms. I do not expect 280 ohms to be an issue.

Pretty excited to get this system running. 10 tube phono pre with 66db gain. I do not expect to be disappointed.

It'll take a couple weeks giving some free time.
You can always send it back to BAT for a refresh if things ever get uninspiring. Being what it is, I can't see how that can happen.

Whoever bought  this was probably happy camper.  Seems like decent price. The current P12 is $13k!
I got the VK-P5 for 1150, which I think was a great deal.

My main ppre is a Sonneteer Sedley which has been great.

Excited to do some testing and listening.
$1150 is a fair price.

My phonostage has 60db, and I was   about to try a .25mv. cart(AT ART9XA) I played it safe with a .4mv instead.

My phonostage is tubed as well. All tubed-rectified/active gain-no step up. Things get extra hissy in quiet passages when the volume knob gets cranked,so getting more juice out of the cart is paramount. Enjoy.

I received the step up transformer and tried it on my Sonneteer Sedley to begin with.

It was hard to figure out what it did and if the playback had improved any. The difference became apparent when I used my db meter to level match the test. I set the volume at 77 db gain average and heard the following:

1) I was able to discern a ringing sound in the mids and highs that was not apparent to me before. It evidences itself as a smidge of harshness.
2) With the ringing diminished, more detail became apparent, and at the same average spl, the min and max spl had a wider range
3) mid bass also improved. highs were less bright.

The overall all effect is not really an improvement of the frequency response, but a refinement of the sound. Its that much more pleasing and sweet with the base being more pronounced. The refinement also allowed a little more detail and some new sounds to come through. Not a whole lot, but observable. I have some screechy and tinny sounding vinyl records that were really quite acceptable after running it through the SUT. Interesting.

I'll be trying the new preamp next week.
Also notice a dramatic reduction groove / tracking noise between tracks. Also, the click from switching off power to the motor disappeared. 
Interesting results.

I once  took a Zesto Allaso for a test drive. Plugged into the MM input of my Fosgate .I was curious to hear the difference (if any) between passive and the active gain.

While I did appreciate a smidge more of quiet when blasting something, I had to concentrate to hear what type of difference in SQ there was. Very subtle level of overall reduction of "organic/real"(best way I can describe it) presentation? Maybe a cartridge specific thing. I didn't  have an exotic LOMC-just used a AT ART9 .5mv. 

Maybe a different story with another cart? Perhaps one of those real low ->.3mv, fancy builds?         
So my Sonneteer Sedley (SS) preamp is making a come back. In trying a lot of configurations, the Sonneteer Sedley with the DV cart combinations and permutations I'm rating below.

BEST - DV on SS set for MC 50 ohm load and 10pf capacitance
VERY GOOD - DV on SS set for MM with 47K on load and 147pf capacitance. Transformer in between.
GOOD - DV on SS set for MC at 100 ohm and 10 pf capacitance (great but has some slightly perceptible ringing)

When Im done refreshing the BAT preamp, going through the tubes, I am putting in a 50 ohm setting (user option with open pins inside) and a 150 pf option.

I will be comparing the DV on the BAT on MC, 50 ohm/100ohm at 100pf. And Also the DV on the BAT on MM with the transformer set at 47Kohm and 150pf with the transformer.

I am also looking at purchasing a Hana SL to try out. The DV has been with me for about 5 years and could use a substitute. The Hana will be a perfect match for the transformer, at least on paper.

Thanks for keying me onto this. I think I have figured out a path to try.

First, I believe I have found a resource that agrees with my findings. My Dynavector 20x2, 5 ohm 2.58mv cart, doesnt sound as good with a 280 ohm load with a transformer vs. being loaded at 100 and 50 ohm load using my phono preamp. I hear positive things, but over all, its not the best setting.

Here is the resource - "A typical MC cartridge will sound somewhat “lightweight” when it is loaded too lightly (load impedance is too high) and will sound somewhat dull when the load impedance is too low."

That said, I reached out to Andrew at Rothwell and he confirmed my computations and gave me some information that allowed me to understand the MC-1 much better. I used three primary resources to figure out my next move.

I need to get the SUT to present the right load to the cartridge.

I studied up on the science and formulas using Rothwell's site -

K&K provides a schematic how to load the SUT so that it presents my desired load to the cartridge.

I reverse calculated the way my MC-1 is built so that I can compute the load resistor I am going to use in the schematic from K&K using MH-Audio's SUT Guide -

I arrived at the following conclusion. The MC-1 presents a 280 ohm load with a 20 and 258 turns of wire on the primary and the secondary. Or thereabouts, the exact ratio is 12.9.

The nonlinearity of the impedance transformation gets a little complicated. The impedance differs by the square of the turns ratio. For a 1:12.9 (22dB) step-up, the impedance is transformed by a factor of 167. That is, with the secondary loaded by 47k ohms, the primary reflects what appears to be 280 ohms to the cartridge.

The question now is what resistor should you put in parallel with the 47k phono stage to change the loading to 50 ohms? I used the following formula:

First get the SUT impedance presented to the phono preamp with the MC on the SUT - (Transformer Ratio^2 * Desired Loading) = (12.9^2 * 50) = 8320 ohms

From there, you can get the Resistor load using this formula 1 / (1 / Desired Loading - 1 / Phonostage) whereby 1 / ( 1/8320 ohms - 1/47Kohms) = 10.1 Kohms

I verified my calculations using this site -

Soldering a 10.1 Kohm resistor to the output of my SUT, with the phono preamp set at 47Kohm will present a 50 ohm load to my cartridge.

You can also put the parallel resistor on the primary side, but then the value is the above divided by the turns ratio squared.

Ive got a few resistors incoming to modify my SUT. I am hoping I am able to keep the sweetness of the SUT's sound, while retaining the brilliance of the cartridge.

Man, I havent done this much analysis and math since school