TP16 - mass reduction and tweaking

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andy2424
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TP16 - mass reduction and tweaking

Post by andy2424 » 11 Mar 2019 10:27

Dear all,
I am trying to give the best shot to a Thorens TP16 thonearm. The official mass is 16.5g. I am confused and curious about a few things:
1. Does 16.5g include in the calculation the mass of the TP 60 headshell?
2. If one removes the back screw-in extra weight, does tonearm mass reduces to 16.5g - 5g = 11.5 (5g being the weight of the screw-in extra weight at the back)? That would make the TP16 a proper medium compliance tonearm even without further tweaking!
3. Has anybody noticed real sonic advantages in removing the (plastic) rotating VTF mechanism from the tonearm? Is the advantage (if any) the (a) additional reduction in mass, or (b) the elimination of undesired vibrations? I appreciate the idea, but ... is it a detectable improvement?

last question:

4. In the case if the TP16 and TP60, when calculating the resonating frequency, i.e. f = A/sqrt(C * mass), In calculating total "mass" should one add also the headshell: i.e. (arm + HEADSHELL + cartridge + screws) ? Many web-based pages do not ask you headshell info.
As in:
RF = A ÷ √ (M × C)
A = 1.000 ÷ 2*pi = 159.23
M = Total mass (arm + headshell + screws + cartridge)
C = compliance (at 10 Hz)

Obviously, including the weight of the TP60 in the calculation make a massive difference in the resulting RF. For instance consider a cartridge DL-110 which is 4.8g, which has a Compliance of about 14@10Hz (i.e . 8@100Hz). We have the following rather different scenarios:

Setting = [TP16 + TP60 + Denon DL110]

Case 1 (with Headshell in the calculation and no modifications to TP16)
M = 16.5+10+0.5+4.8 = 32.3 (that would be huge!)
RF= 159.23/sqrt(14*32.3) = 7.43Hz

Case 2 (without Headshell in the calculation + and no modifications to TP16)
M = 16.5+0+0.5+4.8 = 22.3 (very reasonable already)
RF= 159.23/sqrt(14*32.3) = 9.01Hz

Case 3 (without Headshell + tonearm weight diet)
M = 11.5+0+0.5+4.8 = 17.3
RF= 159.23/sqrt(14*32.3) = 10.23Hz


Thanks for your help
Best, Andy

tlscapital
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Re: TP16 - mass reduction and tweaking

Post by tlscapital » 11 Mar 2019 13:58

1. The effective mass of a tonearm is calculated without the headshell. Only the tube and if ever the connector is taken into account but not past beyond the bearing. All that goes past that point is part of the counter-balance/weight mass.

2. The resonance ratio of tonearm/cartridge is more of a ball park figure to "check" an eventual match or not so much likely. It does not indicate better sounding results as such if ever. Anything between 8 or 12 is considered acceptable...

3. To calculate the tonearm to cartridge resonance ratio, the headshell and all that is in it plus the effective mass of the tonearm tube/wand and all that is on and in it (adapter, ring, wires and dampening) upfront the bearing are accounted.

4. This should help choosing either a matching cartridge accordingly or a tonearm to fit the cartridge. And or finally to tweak the tonearm effective mass accordingly. This is done most of the time by enhancing it's effective mass I believe.

5. The TP16 tonearm is not renowned to have a lot of evolutive potential as such. Of medium effective mass, it can take lower compliant cartridges by adding extra weights on the headshell and counterweight. But to what "sonic" result ?

6. Tonearm sonic signature has to be taken into account when one is tweaking on his tonearm. I am not sure that enhancing, just like stripping down if ever, this tonearm effective mass will benefit it and/or the cartridge combination.

KentT
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Re: TP16 - mass reduction and tweaking

Post by KentT » 11 Mar 2019 14:54

Get a Ortofon OM 10, install it, balance it, set tracking force, call it a day. No modification necessary. Your arm is not built for a Denon MC, or get an older lower mass Ortofon MC or an Audio-Technica MC, which will work better with the arm you have. Other alternatives, get an armboard, and a medium mass arm and install it (cash outlay required and some labor)

andy2424
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Re: TP16 - mass reduction and tweaking

Post by andy2424 » 11 Mar 2019 16:08

@tlscapital, thanks for your help on the effective mass. That makes sense.
[Question: role of the counter-balance/weight mass]: certainly there must be a significant difference between a tonearm design with a very heavy weight closer to the pivot and one with a much lighter weight positioned further away from the pivot. Intuitively, shouldn't the second one (with less moving weight) be the preferred design?

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Re: TP16 - mass reduction and tweaking

Post by tlscapital » 11 Mar 2019 16:16

KentT wrote:
11 Mar 2019 14:54
Get a Ortofon OM 10, install it, balance it, set tracking force, call it a day. No modification necessary. Your arm is not built for a Denon MC, or get an older lower mass Ortofon MC or an Audio-Technica MC, which will work better with the arm you have. Other alternatives, get an armboard, and a medium mass arm and install it (cash outlay required and some labor)
Yes, I'd say seek another cartridge (medium toward low compliance) or fit another lighter (still medium) effective mass tonearm but that is all in all another project if ever.

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Re: TP16 - mass reduction and tweaking

Post by tlscapital » 11 Mar 2019 16:21

andy2424 wrote:
11 Mar 2019 16:08
@tlscapital, thanks for your help on the effective mass. That makes sense.
[Question: role of the counter-balance/weight mass]: certainly there must be a significant difference between a tonearm design with a very heavy weight closer to the pivot and one with a much lighter weight positioned further away from the pivot. Intuitively, shouldn't the second one (with less moving weight) be the preferred design?
The resonance induced by the counterweight is the issue De-coupling and dampening try to diminish that. To have the counter weight (no matter it's effective mass) close as possible to the pivot/bearing is also participating into that diminishment.

andy2424
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Re: TP16 - mass reduction and tweaking

Post by andy2424 » 15 Mar 2019 13:40

@KentT :

Thanks. I checked the Ortofon OM10. Its compliance numbers are
- Dynamic (Lateral) = 25
- Dynamic (Vertical = 15

The compliance of the DL110 is lower: 14 (@10Hz); officially 8 (100Hz).

It seems that the Ortofon should make things worse, not better? Using its vertical compliance of C=15 the resonating frequency should be:
f = 159 / sqrt[15 x (16.5g +10g + 0.5g + 5g)] = 7.27Hz

Am I missing something?
Thanks

Japi Roelofs
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Re: TP16 - mass reduction and tweaking

Post by Japi Roelofs » 15 Mar 2019 14:04

I used a Denon DL-110 on a stock TP16 tonearm, and it sounded fabulous. No modification was needed.

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Re: TP16 - mass reduction and tweaking

Post by user510 » 16 Mar 2019 20:10

My understanding has been that the rated effective mass of the original TP16 includes the head shell and all counterweights. Therefore if one removes the screw-in auxiliary weight at the counterweight end, that will lighten the overall effective mass of this arm. So too will it lighten the arm if one replaces the TP60 (heavy) head shell with a lighter head shell.
When attempting to calculate a particular arm/cartridge resonant frequency, which we can test using a test record, one adds cartridge, shims and fastener weights into the formula below.

rf = 159 / sqrt ((eff. mass + cart weight + fastener weight) * (compliance))

Above formula is taken from the Moerch tonearm website and has been in popular use for decades. Often times I've used this formula to predict a particular arm/cartridge resonant frequency and then will test the actual pairing using the HFN-001 test record using side 2 track track 2 that tests this on the lateral. In general I have found calculated predictions to be close to the reality of the actual tested arm/cartridge combination.


-Steve
PS: disclaimer. I'm no math geek. I just do essential shop math for figuring out geometry and will not get involved in any lengthy discussions on this subject because I can't. I just feed the numbers into the formula, operate the formula and then test the result. If the test result matches closely to the calculated prediction, it must be valid. m2c.

andy2424
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Re: TP16 - mass reduction and tweaking

Post by andy2424 » 19 Mar 2019 13:46

Hi.
So ... I eventually re-cabled the TP16 with a single run of Cardas 33awg Unipivot (lighter than the standard 33 cable). Removed the two plugs inside tonearm and shell, removed extra weight at the back.the idea, learned on this forum was to reduce interference and achieve a better RF by matching shaving g a bit the mass of the arm (I was initially working under the "Case 1" scenario above that suggested the arm was a bit too heavy.
Then mounted a Denon DL110.
Result 1. Very good.
However....
Result 2. ... the big surprise happened when I mounted the cartridge metal plate that comes with the Denon (which is 1.5g on his own, by the way). Wow, what a change! Beautiful resposnse across the entire frequency spectrum.
What's going on here?
Is the metal plate making the cantilever responding better by adding extra rigidity to the cartridge? Or, is it the effect of a better compliance match between cartridge and arm (that would imply that Case 1 must be incorrect)
Whatever it is, I love the result..
Thanks!
Andy

tlscapital
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Re: TP16 - mass reduction and tweaking

Post by tlscapital » 19 Mar 2019 14:18

andy2424 wrote:
19 Mar 2019 13:46
"Case 1" scenario above that suggested the arm was a bit too heavy.
Then mounted a Denon DL110.
Result 1. Very good.
However....

Result 2. ... the big surprise happened when I mounted the cartridge metal plate that comes with the Denon (which is 1.5g on his own, by the way). Wow, what a change! Beautiful resposnse across the entire frequency spectrum.
What's going on here?
Is the metal plate making the cantilever responding better by adding extra rigidity to the cartridge? Or, is it the effect of a better compliance match between cartridge and arm (that would imply that Case 1 must be incorrect)
Whatever it is, I love the result..
Thanks!
Andy
See there's good, better and in the happiest case; wonderful. Those Thorens headshell are sadly not the best things on earth I am afraid. If there where to be interchangeable, I am sure that trials and comparison with sturdier built headshells will have seen a lot of those TP headshells swaps for other design.

Anyway, yes this metal plate could have added some "rigidity" there but only some if ever. Likely more effective mass evidently but did you re-adjust VTF and anti-skate afterward or not ? And what about your VAT/SRA settings before and after if ever ? This changes (to be fiddle with some) can prove crucial IME.

andy2424
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Re: TP16 - mass reduction and tweaking

Post by andy2424 » 19 Mar 2019 15:44

@tlscapital,
Yes, of course, VTF kept constant at about 1.75g in both cases. (Otherwise adding the plate would squash the cartridge)

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