SUT DUT

[edwyun]

So I have two SUT devices under test - the Bob Device's Sky30 (using Cinemag blue label Sky30 transformers) and the Sound Tradition Live! MC-907 (using Hashimoto/Sansui HM7 transformers). As both trannies have 15x/30x turns ratios, I should be comparing apples to applies so to speak in this comparison to follow in the coming days. Operationally, the only difference is that the Sky30 has a ground lift switch. Nice touch.

Stay tuned...

 

[edwyun]

First note - 15x/30x turns ratios aren't always the same. The Sky30 is specified as providing 24dB/30dB of gain at 15x/30x while the HM7 is specified as providing 23dB/29dB of gain. Perhaps this takes into account insertion loss.

 

[vonclod]

What cartridge are you testing with? I need to find a SUT for a Supex SD 900, a friend recommended Hashimodo.

 

[doctor fuse]

What phono preamp are you using? I was exploring SUTs, but my knowledgeable audiophile friend urged me to get a Benz-Micro PP1 that came up for sale at a decent price. I am still curious about how it would compare to a preamp and SUT.

 

[Blue Shadow]

Fortunately that 1dB difference may not be the only difference, but it might be just enough to make the louder one seem to be the better one, that old hi-fi store trick.

This could be interesting to learn the results.

 

[edwyun]

What cartridge are you testing with?

Dynavector 20x2L. Because the recommended loading for the cart is >30 Ohms, I am using a parallel resistor with the SUTs to get it to about 80 Ohms.

What phono preamp are you using?

Lehmann Audio Decade.

Fortunately that 1dB difference may not be the only difference, but it might be just enough to make the louder one seem to be the better one, that old hi-fi store trick.

Agreed. So I will have to match levels with the preamp to account for this.

 

[edwyun]

Fortunately that 1dB difference

I also think that the dB difference measured at the SUT outputs will result in a greater dB difference after the signal passes through the phono stage/pre.

 

[rothwellaudio]

The turns ratio is really the only reliable figure and as long as the two transformers have the same turns ratio they should have the same "gain" (baring things like coil resistance). The "gain" figure isn't really gain in the same sense as it would be with an active amplifier. A turns ratio of 1:15 would give you a gain of 23.5dB, but only if the source impedance (ie cartridge coil impedance) was zero or the load on the transformer was open circuit.

I suspect the discrepancy between the figures for the two transformers mentioned is simply due to manufacturer rounding up the figure to nearest whole number and the other manufacturer rounding it down.

 

[rothwellaudio]

Dynavector 20x2L. Because the recommended loading for the cart is >30 Ohms, I am using a parallel resistor with the SUTs to get it to about 80 Ohms.

I wouldn't recommend using the 1:30 setting with that cartridge as the turns ratio is unnecessarily high. I would recommend the 1:15 setting. Assuming a 47k load at the input of the phonostage the load seen by the cartridge will be 209 ohms, which is >30 ohms, just as Dynavector recommend. There's no need to make the cartridge drive a lower impedance load, but if you really want to there are two possible options: a resistor in parallel with the transformer's primary winding or a resistor in parallel with the transformer's secondary winding. The former makes a lot more sense to me though you will find plenty of advice online advocating the latter.

 

[rothwellaudio]

What cartridge are you testing with? I need to find a SUT for a Supex SD 900, a friend recommended Hashimodo.

You need a turns ratio of about 1:20 for that cartridge, or maybe 1:25. I think 1:20 would probably be better because, as a general rule, lower turns ratios give better performance.
The MCL that I sell would work with the Supex.
http://www.rothwellaudioproducts.co.uk/html/mc_step-up_transformer.html

They are available in Canada through Tri-Cell Enterprises:
https://www.tricellenterprises.com/

 

[edwyun]

I suspect the discrepancy between the figures for the two transformers mentioned is simply due to manufacturer rounding up the figure to nearest whole number and the other manufacturer rounding it down.

You're probably right. Tonight I will measure voltages from the outputs of the SUTs. Then I can level match for the testing.

I wouldn't recommend using the 1:30 setting with that cartridge as the turns ratio is unnecessarily high. I would recommend the 1:15 setting. Assuming a 47k load at the input of the phonostage the load seen by the cartridge will be 209 ohms, which is >30 ohms, just as Dynavector recommend. There's no need to make the cartridge drive a lower impedance load, but if you really want to there are two possible options: a resistor in parallel with the transformer's primary winding or a resistor in parallel with the transformer's secondary winding. The former makes a lot more sense to me though you will find plenty of advice online advocating the latter.

Agreed. I am using both SUTs at the 15x settings. Having used the 20x2L for a while, I know it works best with a setting in the 60-120 Ohms range in my setup. I did try the SUT's without any parallel resistor on the secondary side (e.g., at 15x and loading at the standard 209 Ohms) but it was a bit too bright. Hence, I use a 30 KOhm parallel resistor to get the loading to 81 Ohms. The Decade makes doing this real easy because it has a custom slot to add resistors.

 

[edwyun]

There's no need to make the cartridge drive a lower impedance load, but if you really want to there are two possible options: a resistor in parallel with the transformer's primary winding or a resistor in parallel with the transformer's secondary winding. The former makes a lot more sense to me though you will find plenty of advice online advocating the latter.

I do have some shielded RCA plugs that I soldered resistors into. I guess I can try them in parallel on the primary side. As I said though, the Decade has a custom slot for easliy adding a parallel resistor on the secondary side, so that I what I am using. It may be interesting to see if there is any audible difference with adding a parallel resistor on the primary side.

 

[rothwellaudio]

It may be interesting to see if there is any audible difference with adding a parallel resistor on the primary side.

Yes, that would be interesting. Use about 130 ohms in parallel with the primary to get an 80 ohm load on the cartridge.
The load seen by the cartridge will be the same as before but the load seen by the transformer will not. I'd be interested to know what you think if you try it.

 

[marcmorin]

The load seen by the cartridge will be the same as before but the load seen by the transformer will not. .

makes the most sense

 

[edwyun]

Using the AP analogue test LP, 1kHz test tone, I measured the average voltage over the 2 minute track and got the following results (the Decade phono pre was set for MM, 46dB gain, with 30 KOhms parallel resistor):

Sky30:
- 15x:
-- measured at the SUT outputs: 8.789mV
-- measured at the preamp outputs at preamp unity gain: 0.7484V
- 30x:
-- measured at the SUT outputs: 17.232mV
-- measured at the preamp outputs at preamp unity gain: 0.9024V

HM7:
-15x:
-- measured at the SUT outputs: 4.372mV
-- measured at the preamp outputs at preamp unity gain: 0.4666V

30x:
-- measured at the SUT outputs: 8.692mV
-- measured at the preamp outputs at preamp unity gain: 0.7874V

I will level match at the preamp outputs for all listening sessions with the SUTs (In the midst of several hours of listening to the MoFi pressing of Rush - Permanent Waves LP).

Edit - it seems the best I can do for level matching is within 0.22dB.

EDIT EDIT - see below for proper test results. The above results were not taken under correct testing conditionss

 

[vonclod]

You need a turns ratio of about 1:20 for that cartridge, or maybe 1:25. I think 1:20 would probably be better because, as a general rule, lower turns ratios give better performance.
The MCL that I sell would work with the Supex.
http://www.rothwellaudioproducts.co.uk/html/mc_step-up_transformer.html

They are available in Canada through Tri-Cell Enterprises:
https://www.tricellenterprises.com/

Thanks, I figured at some point I would ask you.
I do have a Luxman 8020 but it's designed to work with a Denon, I was thinking the impedance wouldn't match up.
I will be looking into your SUT.

 

[bobins08]

I wouldn't recommend using the 1:30 setting with that cartridge as the turns ratio is unnecessarily high. I would recommend the 1:15 setting. Assuming a 47k load at the input of the phonostage the load seen by the cartridge will be 209 ohms, which is >30 ohms, just as Dynavector recommend. There's no need to make the cartridge drive a lower impedance load, but if you really want to there are two possible options: a resistor in parallel with the transformer's primary winding or a resistor in parallel with the transformer's secondary winding. The former makes a lot more sense to me though you will find plenty of advice online advocating the latter.

Can you explain why you prefer to put load on the primary?

 

[edwyun]

I listened to the first side of the LP for several hours, going back and forth between the Sky30 and the HM7. While I did notice some differences, a lot of it was nuanced and slight (as opposed significant) differences. It was also subject to a few minutes of downtime to switch SUTs. This was not a DBT.

On the Sky30, the soundstage was wide and deep. The image and location were nicely rendered. In my setup, the image was very slightly forward of the speakers but well placed. Air around the voice and instruments was excellent . I could easily locate Geddy's voice and bass, Alex's guitar and Neil's various drums and cymbals in the 3D space. As expected, Geddy's voice had a nice edge and crispness to it but there seemed to be a touch more of sibilance. The bass and guitar had a lot of good detail and harmonic structure to their sound. The bass and guitar were easily separable in their duets. The bass was very full and deep. The percussion was well defined.

On the HM7, the soundstage was wide and deep similar to the Sky30, perhaps a bit wider. The image and location were nicely rendered as before. The image was neutral or slightly laid back of the speakers with the HM7. Air around the voice and instruments was excellent as before. I could locate the voice and all the instruments as before, but I could locate them a bit better in space, especially when localizing the drums circling across the soundstage. Interestingly, in comparison, now the Sky30 seemed a bit etched as if it had a slight bit more of HF energy than the HM7 (there was a little less sibilance with the HM7). The detail in the instruments was there and the HM7 had great sonic texture and separation of the bass and guitar in their duets. The HM7 had a slightly more rounded heavier bass but not boomy.

In sum, both sounded great - especially the soundstage, dynamics, liveliness, and musicality - and both had a very realistic presentation. There was an ease to the sound from both SUTs but the HM7 seemed a slight bit more realistic and smooth without being lush or colored. Perhaps because the HM7 did not have that slight edginess that the Sky30 had. Some caveats though - (1) I have used the HM7 longer than the Sky30 so it may be that I am more familiar with, and thus subconsciously prefer, the sonic signature of the HM7, (2) my system tends to be more on the neutral but revealing side, so the Sky30 may be too much of a good thing, and (3) in matching levels as best as possible, the Sky30 had a 0.22dB gain advantage.

(Next, some Jazz or Classical).

 

[rothwellaudio]

Using the AP analogue test LP, 1kHz test tone, I measured the average voltage over the 2 minute track and got the following results (the Decade phono pre was set for MM, 46dB gain, with 30 KOhms parallel resistor):

Sky30:
- 15x:
-- measured at the SUT outputs: 8.789mV
-- measured at the preamp outputs at preamp unity gain: 0.7484V
- 30x:
-- measured at the SUT outputs: 17.232mV
-- measured at the preamp outputs at preamp unity gain: 0.9024V

HM7:
-15x:
-- measured at the SUT outputs: 4.372mV
-- measured at the preamp outputs at preamp unity gain: 0.4666V

30x:
-- measured at the SUT outputs: 8.692mV
-- measured at the preamp outputs at preamp unity gain: 0.7874V

I will level match at the preamp outputs for all listening sessions with the SUTs (In the midst of several hours of listening to the MoFi pressing of Rush - Permanent Waves LP).

Edit - it seems the best I can do for level matching is within 0.22dB.

The HM7 seems to be giving almost exactly twice the voltage of the Sky30. That implies that the turns ratios are mislabelled and the two transformers do not have ratios of 1:15 and 1:30. The Sky03 at 1:15 is giving the same voltage as the HM7 at 1:30, so at least one of the transformers is mislabelled. Without knowing the signal level going into the transformer it's impossible to say which one is right and which one is wrong.

 

[rothwellaudio]

Thanks, I figured at some point I would ask you.
I do have a Luxman 8020 but it's designed to work with a Denon, I was thinking the impedance wouldn't match up.
I will be looking into your SUT.

According to the specs I found ( https://audiomaniacy.pl/index.php?topic=434.150 ) that transformer has a turns ratio of 1:10, which is a bit on the low side but you would get away with it. Its specs say "optimum primary impedance 20 ~ 40 ohms", but I wouldn't worry about that too much because it really means there's sufficient primary inductance to cope with a 40 ohm source impedance. Your cartridge's impedance is much less, so there'll be more than enough primary inductance to cope with it. That's good. The downside is that "more than enough" primary inductance means more turns of wire, therefore more coil resistance and more inter-winding capacitance which could compromise the top end of the frequency response.
Anyway, it's certainly worth trying that transformer with your cartridge. It's not a complete no-no.