sometimes, --more-- effective mass does the trick.....

Posted by user510 on December 18, 2004 at 02:14:21

I've been listening to this Expressimo RB250 / Shelter 501 II combo for what seems like ages. I just had it aligned with a protractor, its vta tuned by ear and was pretty happy. Nicely detailed sound, hard to characterize any particular trait since the setup seems to change it's tonal character with each new record. That's working good, I thought.

BTW, the table is a Teres 145. The all acrylic job with the shot loaded platter.

Anyway, the other day I thought maybe the arm/cart could use some additional tuning. I had never been able to get it to successfully track band 8, side one of the hfnrr test record without at least 'some' buzzing. That's the anti-skate track / torture test. Track 9 was out of the question. So I thought to try some things to maybe improve this score. Watching the lateral and vertical arm/cart resonance test I saw a lateral resonance of 11-12hz. That's good, but the vertical was clearly resonating the arm/cart at 14-hz. That's a bit high, I thought.

The Rega arm has a effective mass rating of 11.5 g and the Shelter cart, stiff little bugger that it is, has a rather non-compliant compliance of 9.....or so someone says. Maybe the compliance is really stiffer than 9 or the rega arm is lighter than 11.5g, but it began to bug me that the vertical resonance was above the desired range ( 8 - 12 hz).

What to do...? Well I thought to add some mass out over the cartridge where it will have maximum influence on the effective mass of the arm/cart system. Looking through the scrap bin I found some 1/64th inch thick lead sheet. I cut a thin strip about 1/4 inch wide in a length to match the circumferance of the arm just before the head shell end. Using black electricians tape, I wrapped the thin lead sheet around the arm, at it's neck, tightly with the tape. No other arm wrap was used.

After resetting vtf, back to the recommended 1.8gram for this cartridge I ran through the tracks on the test record again. This time vertical arm/cart resonance was happening at the upper end of 12-hz. The lateral resonance was wiggling the arm/cart at 9-10hz. Now I had both figures within the recommended ball park. Time to try those anti-skate tracks again.

This time, with a little adjustment made to the anti-skate dial on the rega arm, I was able to get a clean tone with no buzz of any kind through track eight. Track nine is still a fail,loud buzz but the arm/cart tracks through....noisily. Who passes track 9 anyway...!

Long story needs to get shorter so I'll wrap it. Listening test reveal a different tonality with the arm/cart adjusted this way. Overall, it's warmer. Still highly detailed but the highs have more warmth. Low frequencies are still tight but fully extended and with substantial kick and weight. No real gains made to the low frequencies but the highs and mids are certainly less....shall we say...bright...?

Another observation is to watch the needle drops going into the lead-in grooves on various records. Much smoother this way. Watching the cantilever actually display a small amount of compliance where before it was obviously......a stiff little bugger.

Seems like a move in the right direction.

-Steve

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Topic - sometimes, --more-- effective mass does the trick..... - user510 02:14:21 12/18/04 (16)

Re: sometimes, --more-- effective mass does the trick..... - Headshell 08:54:38 12/18/04 (11)

And what if you change to a heavier cartridge? - garth 02:37:48 12/19/04 (5)

Re: And what if you change to a heavier cartridge? - Headshell 02:53:01 12/19/04 (4)

Huh? - garth 03:02:17 12/19/04 (3)

Re: Huh? - Headshell 12:12:52 12/19/04 (2)

Jan, you make no sense. Give it up. - garth 13:48:37 12/19/04 (1)

That's your opinion. Do you have concrete theoretic considerations? - Headshell 23:01:40 12/19/04 (0)

Re: sometimes, --more-- effective mass does the trick..... - user510 11:48:39 12/18/04 (4)

Re: sometimes, --more-- effective mass does the trick..... - Headshell 12:34:20 12/18/04 (3)

Re: sometimes, --more-- effective mass does the trick..... - user510 15:36:00 12/18/04 (2)

Re: sometimes, --more-- effective mass does the trick..... - Headshell 02:14:53 12/19/04 (0)

Re: sometimes, --more-- effective mass does the trick..... - Headshell 00:55:11 12/19/04 (0)

Have tried this experiment with the HiFi Mod as well? - Dan_ed 06:36:57 12/18/04 (1)

Re: Have tried this experiment with the HiFi Mod as well? - user510 11:56:32 12/18/04 (0)

The heavyweight lowers the effective mass of the arm. - garth 06:04:48 12/18/04 (0)

This is a great post - jefe 05:14:10 12/18/04 (0)

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