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Shelter + BentAudio loading: field test

If anyone cares (if you do, see your doctor) I spent last Sunday playing with different impedance loads. Am I livin' or what?!

System:
- Shelter 901, 0.5mV, 14 ohms internal impedance
- BentAudio Mu stepup transformers, wound for 20dB gain
- c-j PV-11 preamp with MM phono stage, fixed 47kohm load

These trannies have a VERY neat feature. John Chapman uses Stephens & Billington TX-103's and adds a pair of small binding posts across the secondaries. You can swap resistors in about 5 seconds to load at any value you choose, or leave the posts open for a load of 47Kohms (or whatever your phono stage provides). Not quite as sexy as the Aesthetix Rhea's remote-controlled loading, but infinitely flexible and a lot less than $4K. John included 15 pairs of resistors so I had lots of choices. Yum!

I had (mistakenly) been loaded at 100 ohms for the first month while I broke in the new rig, fine tuned VTF, VTA, etc. Shelter recommends 100 ohms only when going straight into a phono stage, 20 ohms for a tranny.

Having discovered my initial error, I swapped in the 19 ohm pair of resistors for my first test (closest I had to 20). After 4-5 sides of familiar material I had a good handle on it. Bass was slightly better than before (hard to believe) but HF's were too lightweight. All the tones were there but there was no impact at the top end. Low piano strings vibrated with a delicious, brassy growl, but middle to high piano strings just lacked that steely punch. On we go...

Twl likes his Shelter loaded at 40 ohms so I tried the 38 ohm resistors. Nope, a bit too high for my system. The bass was slightly weaker and the HF's took on a very slight etch. Fiddling VTF and VTA didn't remove the etch, so I decided it must be the loading. Next...

Back down to 25 ohms. AHH!!! Clean and solid tonality from top to bottom, more air, tighter imaging and a harmonic rightness to everything. Brubeck (Time Out) and the Julliard Quartet (Bartok #4) are more life size and physically present than ever. I think the "perfect" load for my system is probably around 23-24 ohms, but 25 is very, very close.

This assortment of resistors cost $15, so they were a very cost effective upgrade. (Second best ever I think. Twl's HiFi Mod is still the all time champ, even at full retail!)

BTW, another good feature of BentAudio's transformers is that the secondary windings are extended straight out of the can and terminated with RCA's. This eliminates an interconnect, an RCA connection and two solder joints. If you need stepups, I highly recommend these.

No affiliation, etc. etc. Just singin' in my brain!
dougdeacon
dougdeacon OP
3,338 posts
 
Romy,

Great post, thank you for the tip. I don't know what resistors BentAudio uses, but I was actually thinking of buying a few pairs of Vishays to give values right around my discovered sweet spot of 22-25 ohms. You're recommending RN, which I assume is another brand name/manufacturer (right?) Any experience with RN vs. Vishay? If you haven't guessed, I'm no engineer! :)

Since I haven't tried other resistors, I naturally haven't noticed a, "distinct upper mid-range acceleration and a slightest more then necessary paunch (punch?) at HF". If the Roedersteins do this, more neutral resistors would probably be optimal at a somewhat higher load. Any guess how much higher vs. my present 22-25 ohms, just so I don't have to try a zillion pairs?

FWIW, I don't think anyone would call our present sound "bleached" or "boring", but who knows. We've never heard another high end system, so we're groping our way forward step by step.

TIA,
Doug
dmailer's avatar
dmailer
235 posts
 
After going back and forth between 36ohm and 50ohm I have settled on the 50ohm setting for my Shelter 901, Bent Audio, Trumpet combination . In my system the 36ohm seems to take too much of the leading edge transients out. The 50ohm setting is more open and not as closed in. I am sure that the setting one uses is all system dependent as well as personal taste. The rest of my system is Redpont TT w/ Kuzma Reference arm, Lamm LL2 line stage, Lamm ML1 amps, and Vienna Acoustics Mahler speakers. On audio asylum I read a post regarding resistors saying that the nude Vishays were the very best. Has anyone tried these and know where to obtain them?
dougdeacon OP
3,338 posts
 
Dmailer, thanks for the update. I'm sure you're right about the "best" setting being system dependent. Your Trumpet/Lamm electronics are certainly very different from my c-j stuff.

It may also be listener dependent of course. My partner has not heard the system since I "reloaded" it. He's more sensitive to leading edge transients than I am, and may well prefer a higher setting than the 25 ohms I preferred. Of course he also likes powerful bass, so who knows?!

I echo your call for resistor sources and advice. Anyone?
bombaywalla's avatar
bombaywalla
1,958 posts
 
OK, guys, I have been reading this thread & also Romy's fruitful comments (!).

I have a question for all of you: how does the quality of the loading resistors make any difference at all to the sound?

The loading resistors are connected between the phono input & GROUND or step-up xformer secondary output & GROUND. Thus, the loading resistors are *not* in the signal path. There might be some shunt signal current (coming from the cartridge) flowing thru these loading resistors to GROUND but the other end of the resistor is not connected to the phono pre in. These resistors *should* not affect the sound at all. Are you guys just going over-board selecting high-grade resistors for simply no reason?

You can see this on Jim Hagerman's website where he has explained cartridge loading. Notice that the loading resistor is connected to ground (in parallel with the load capacitance, which represents the phono pre input capacitance + interconnect cable capacitance).
Any *useful* comments would be appreciated.
dougdeacon OP
3,338 posts
 
Romy's post was actually about the best I've seen from him. Love and kisses his way!

I personally have no clue if the quality of resistors used for tranny loading would or "should" be audible. Perhaps we just have lingering audiophilia nervosa. At least this outbreak of the disease will be cheap to treat and limited to a few wacko's with stepup trannies!

Lew Johnson of c-j heard audible differences when he changed non-signal path resistors in their Premier and ART preamps. He can't explain why, but it's been confirmed by other listeners.

The designers of Dmailer's Redpoint TT and my Teres both hear audible differences between electrical components in the motor control circuits. That's a good deal further from the signal path than a phono load resistor. I don't think they know why either.

What fun would all this be without a few mysteries?
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