Yes, the standard 47K mm input on the SP14 should work fine.
Added an SUT...not sure I understood this
I just added a Denon AU-320 step-up transformer in between my AT-OC9XML cart and my ARC SP-14 preamp. I am glad that the (relatively quiet) hum that had been present before is now gone...and I mean gone...since that was what motivated me to add an SUT.
However:
I sort of expected that I would also experience a noticeable increase in gain. Specifically, using the 40-ohm (10X) tap, I would have expected maybe a 6-8 dB increase in volume, and more with the 3 ohm tap. I am not hearing that, and in fact am getting the opposite effect. This means I actually have to peg the volume control if I want to achieve 95 dB levels at my listening position, something I rarely, but still occasionally, do.
Also, I removed the 22-ohm loading resistor upon connecting the SUT. I noticed previously that a 40-ohm loading still had the cart sounding pretty bright. But with no loading and using the 40-ohm tap, things sound natural. I sort of expected I was going to need to add a 40-ohm resistor (at the tonearm) to achieve the same loading.
All of this confuses me; I'm happy so far with the sound yet perplexed. Perhaps some good Samaritan here will be able to explain why I am hearing what I am hearing. in the meantime, I'm just going to enjoy my quieter background.
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- 86 posts total
@noromance the SP14 does not have an MC setting. The expectation was that one would either just crank up the gain or use SUT or headamp. @jasonbourne52 I wish I had someone else in my orbit with an SUT to borrow, but my audio clan is very anti-vinyl, so no joy there. It's good to know my expectations were not crazy. The AU-320 has a built-in cable for output, and maybe I can find someone who can solder in a set of jacks instead, since the cable is pretty generic. |
@dweller the SP14 has a built-in phono stage. |
You absolutely need to ensure you’re loading a SUT at 47K. Any less load resistance than this, and you’ll start throwing away gain, as well as encouraging other distortions. Your talk of 40 ohm, 22 ohm resistors makes me nervous you’re adding a heavy load to the SUT. If the SUT ratio is chosen properly for your cartridge, then 9 times out of 10 the natural reflected load from the SUT directly into a 47K ohm MM input works out "fine", with no need for additional loading on its primary or secondary. |
What mulveling said. There is only one correct way to terminate the SUT, with a 47K ohm load (or higher in some rare cases for special reasons) across the secondaries and input to an MM phono stage. With a SUT that has a 1:10 turns ratio (like yours), this will have the cartridge "see" a 470 ohm load, which is OK for 99% of LOMC cartridges. It's really simple. Don't overthink it. The cartridge likes to see a load impedance that is at least 10 times its internal impedance or greater. Your cartridge has an internal impedance of 12 ohms, so you are fine with a 470 ohm load. (Greater than 10X ratio is acceptable.) The load seen through a SUT is equal to the value of the phono load resistance (47K ohms) divided by the square of the turns ratio (10-squared = 100). Hence the cartridge sees 470 ohms (47,000/100). Your cartridge puts out 0.4mV at the standard stylus velocity. So the MM phono stage will see 4mV, which is perfect for driving any typical MM phono stage. |
- 86 posts total