Discussion in 'Turntables' started by mjw21a, Sep 18, 2018.
Need to look into some HM7’s.
Buy the transformers and DIY.
Considering it but on the other hand, I no longer have a drill press to do an enclosure properly. I'd want to do it up in a nice, slender aluminum enclosure I can hide behind the phono stage in the rack. I don't want more "junk" showing, in other words.
On the plus side, I can pick premium RCA connectors and wiring, and add my own switches for various things (grounding, high/low output, stereo/mono, etc.). I did find a kit from the Luhdahl distributor that isn't too badly priced--I just wish their standard option had switches vs. soldering jumpers for changing the ratios.
I've since ruled out the Hashimotos since they are too pricey.
BTW, I don't understand those SUTs that have captive interconnects. Seriously? That is why I passed on a Quicksilver I saw for sale. I don't want some interconnect of unknown quality, and not being able to replace it if the RCA connectors go bad.
HM7's are quite nice. May as well save $$$ and shoot for the moon.
Not to change your mind about pursuing a Hashimoto-based SUT, but I have the K&K SUT using Lundahl LL1931 transformers and it is quite nice. The kit includes switches between 1:8 and 1:16 turn ratios plus it has connectors on the board that allow loading resistors (or capacitors in my case). My only issue is the switches and loading location are inside the case. However, give the owner, Kevin Carter, a call as he was willing to do custom work.
I've been in touch with Kevin--he replied back this morning. I asked him a few questions re: loading and ratios I need for this all to work. I was looking at his Basic kits vs. the Premium, partly because the Basic has three loading options per transformer vs. only two. (I'm thinking about buying something flexible and future-proofed, as I likely won't have the ART7 forever.)
The issue with the LL1678 with a 30dB gain is that my eventual load (with 47kΩ) at the preamp would be too low for the cartridge (44Ω, where the cart wants 100Ω minimum). I could probably modify the phono stage, though, as I've found the load resistors in the schematic, and I can easily swap out one of the lower value resistors for a higher value. (The resistance is chosen via DIP switches in the preamp.) That is only if I stick to the 30dB gain. If I use the LL1678, I can use the 24dB gain (the middle gain setting), or go with the LL9226 and get 26dB as the maximum gain (out of three), both of which get me closer to the 100Ω value.
The Premium kits offer the LL1931 (your model) or the LL1941 (higher gain), with two gain choices. A little past my budget but not too bad, really. (Once I sell my unused phono stage, that might cover it.)
Excellent! You've certainly done more research than I did on the variety of products K&K can provide. I chose the 1:8/18dB - 1:16/24dB model as it got close to the loading I wanted for my current cartridges and it had the switches. For example the 1:8 provides a load that works for my Denon DL-103 even though the gain is a little low. The 1:16 yields a load of about 184 ohms which is close to what several of my other MC cartridges (100 to 150 ohms) need then loading resistors can be added to fine tune things. The 24dB gain is more than enough.
My nicer cartridges, Shelter 501II and Ortofon Cadenza Red, both seem to work best at 100 to 120ohms so I may look for a dedicated 1:20 transformer (e.g. Hashimoto HM-3 at 1:20 is 117ohms) for them.
Since they are a distributor for Lundahl, we can order just about anything from Kevin. That is good for the DIY side of things, or he has those two kits that offer a pre-built option.
May as well, it's to be a quite significant improvement over anything else I've ever tried. The closest to the performance of a HM-7 I've heard was previously the vintage Fidelity Research FRT-4. If budget can't quite stretch to a 7 that would be my choice. An extremely flexible stage in terms of gain, multiple tables/arms and the next best sounding SUT I've heard.
I'm not sure how seriously you should take Audio Technica's "100Ω minimum" recommendation. It would limit you to a maximum turns ratio of about 1:20, assuming a standard phonostage input impedance of 47k, but the cartridge has such a low output (0.12mV) that it could benefit from a slightly higher turns ratio.
The cartridge's coil resistance is 12 ohms and its inductance is only 8 microhenries, so I think the inductance is low enough to ignore for now. Here are a few figures for the load impedances and output voltages you would get with different turns ratios:
1:10 470 ohms, 1.17mV
1:15 209 ohms, 1.70mV
1:20 118 ohms, 2.18mV
1:25 75 ohms, 2.59mV
1:30 52 ohms, 2.93mV
1:40 29 ohms, 3.41mV
1:50 19 ohms, 3.66mV
1:60 13 ohms, 3.75mV
What's more important - the output signal level or the load impedance? Ultimately, what's really important is good sound quality, including a good signal-to-noise ratio. 1:60 would give you the best signal-to-noise ratio but I would be doubtful about the sound quality, not because of the low impedance seen by the cartridge but because it's so difficult to make a transformer with such a high turns ratio and good performance. I would expect a 1:20 transformer to give you much better performance than a 1:60 transformer, and the output voltage of 2.18mV should be enough to work with, particularly considering your phonostage has slightly higher gain than most mm phonostages.
I think you will always have to compromise with the ART7 because its output is so much lower than many other modern LOMCs but its coil impedance isn't particularly low. For reasonably hiss-free performance I think you would need a minimum turns ratio of 1:20. Is it worth going much higher than that? That would be a matter of speculation and you could only really know for sure by experimenting, but I wouldn't make the load impedance seen by the cartridge the most important criterion in your decision-making process.
Going from my experience I would say the range 1:20 to 1:30 is where you should be.
That is about what I came up with also.
I also have the option of lifting the 47k resistor in the phono stage and adding one in the SUT. (I've found the load resistors in the schematic of the phono stage.)
EDIT: I could also remove the 47k pair and one of the other resistor pairs connected to the DIP switches inside, and move the 47k pair to that position. That means I could still switch in the 47k if I ever needed it, but could completely remove resistance if I wanted to load it externally on a SUT. I just hate having to modify something that is factory original, even though I could restore it to stock form easily.
And some good shielding inside the box where the transformers are mounted.
I see in your sig you have the VTPH2A. I would be interested in hearing your opinions using the HM7 SUT into the tube MM stage of the VTPH2A (versus using the FET/tube MC stages of the VTPH2A only). I've had my HM7 for a couple of years but am still breaking in the VTPH2A.
I've never used the FET/tube stage in the Herron. I'll get to it.
I have zero shielding inside the box I use for either of the Hashimoto builds. Both very quiet.
Wouldn't a well-sealed aluminum box be the shield?
Twisting pairs of wires is also a good noise reduction technique (if the transformers are wired vs. pins for a PC board). Common mode rejection. Same thing used in twisted pair networking cable for noise rejection.
@edwyun Is that an Aleph in your avatar?
I don't know what your phonostage is and without seeing a circuit diagram I can't be sure exactly what those resistors do, put there's a possibility they don't just set the input impedance but also have some other function in the circuit. Be careful about removing resistors.
I really advise caution about taking Audio Technica's "100 ohm minimum" too seriously. If that involves using resistors significantly higher than 47k across the secondary of a high ratio step-up transformer, there's a good chance the frequency response will be affected. Lower load impedances tend to flatten the frequency response of a step-up transformer and extend the bass (though at the expense of mid-band gain). Higher load impedances do the opposite.
I have some initial impressions with and without the HM7. Will see how things pann out with more time.
@edwyun Is that an Aleph in your avatar?
Yes. Enjoy them very much.
The SUTs made by Hashimoto (eg, the Live! MC-907 that use the HM7s) use shielding inside the box.
Separate names with a comma.