Cartridge loading comparison (long... very long)

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dougdeacon

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Cartridge loading comparison (long... very long)
« on: 6 Oct 2003, 07:47 pm »
Just FYI for John, maybe pointless/old news for everyone else.

I've had my new rig set up for for about a month now:
- Teres 265
- OL Silver w HiFi Mod (thanks to TWL on A'gon)
- Shelter 901 (half price from a guy who didn't quite like the bass!!!)
- BentAudio Mu, copper wired
I promised John a report when I got a chance to try different loads on the trannies, so this is it.

I'd been at 100 ohms from the beginning. This is Shelter's recommended load if running straight into a phono stage, but they also suggest 20 ohms if using a tranny. I didn't understand why there'd be a difference, but someone on A'gon explained it thus: a phono stage wants to see maximum voltage, a tranny wants to see maximum current. Loading the cartridge to produce whichever is needed should give best results. (Makes sense to me but what do I know? Comments?)

This person also opined that a typical MC cart outputs maximum current when loaded slightly above its own internal resistance. The 901's internal resistance is 14 ohms, thus the 20 ohm recommendation for a tranny. Is anybody still with me? Sorry for the endless post, but it's all new to me so I'm learning by writing it down. My DIY skills barely extend to tying my shoes!

The resistors John sent with the Mu's allowed me to choose 10, 19, 25, 38, 56, 75, 83 or 100 ohms, plus a bunch of higher numbers that wouldn't suit this particular cartridge. I was advised to avoid going below the cartridge's internal impedance, so I ruled out 10 and started with 19. This was near the value recommended by Shelter and as far from the familar 100 as I could get. I figured a big change would make it easiest to hear differences.

After 5 or 6 sides I had a good handle on it. At 19 ohms bass was deeper/stronger/tighter but treble was too light. Imagine the center of gravity of every instrument being shifted downward. Every tone was there but the higher frequency ones lacked weight. Low notes on the piano were fabulous. I could practically taste those fat, brassy strings vibrating, but high notes lacked that steely punch. Overall there was less air, shorter decays, less focus, etc., as you'd expect. This was great news, since it meant I had the sweet spot surrounded: 19 was too low, 100 was too high. On we go.

Once I knew what to listen for, 1-2 familiar sides were enough to get a fix on a particular load. My second attempt was at 38 ohms. Oops, too high. Lost the bass and the HF's were a teensy bit etched. (I say "lost the bass" but it was actually very subtle. Even at 100 ohms into the Mu's the Shelter 901 produces spectacular bass. Loading down to the right level just gave me the last 1-2%.) As a double check on the HF's at 38ohms, I fiddled with VTF. The Shelter 901 changes audibly if you deviate from the sweet spot by as little as .05g. In this test raising VTF even .15g didn't tame the HF's, so I knew the loading was too high. (Again, this HF etch was subtle, far less noticeable than the HF hash on any CD for example. Still, if one has the tools to approach perfection, why not use them?)

Back down to 25 ohms. Ahhh!!! That's the spot. 22-24 might be even better but now we're truly into the realm of recording variations. 25 ohms is where I'm going to stay. This magical rig just got a touch more magical. Reiner's 'Scheherezade' shimmers for one moment, explodes at the next and ravishes continuously. Bernstein's 'Rhapsody in Blue' truly rhapsodizes. Thanks to John for the wonderful transformers. I feel like Gollum with a fresh-caught fish! So tasty and wwrrrriggly!  :singing:

P. S. Please let me know if I didn't write enough!  :mrgreen:

John Chapman

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Cartridge loading comparison (long... very long)
« Reply #1 on: 7 Oct 2003, 02:13 pm »
Hello!

Thanks for posting this! I have been curious about the rather low load recomendation from Shelter when a transformeer is used. It just seemed lower then I expected but you did indeed end up quite low in value. Goes to show how you can dial in the sound with load swapping and that's why I wanted an easy way to swap loads on the MU enclosures. If it is a pain to swap loads I figured most folks would not bother with it and they would not end up optimizing the sound.

BTW - just got back from VSAC and it was a really great show! We used a Shelter 501 and it was a really great sounding cartridge. No wonder there are so many of these Shelters out there. About 1/3 of the tx103's I have sold in the last year seem to have ended up matched with Shelter 901's!

Many Thanks!

John Chapman
www.bentaudio.com