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Cartridge loading explained

the thin end of the wedge

Gracias, tocayo.

Postby bauzace50 » 09 Aug 2006 03:11

Carlos Filipe,
goodness, tough act to follow! Thanks for exposing a useful tool and veil lifter. It is better to work from knowledge, and this takes one to that place. Thankyou.
Carlos Bauza (Tocayo, means two people with the same name).
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cartridge loading: grado RP

Postby bouquet » 09 Aug 2006 11:43

Tuning your cartridge loading does make a difference :
I 'am currently using a Grado RP with 45 mH/475 Ohm and diy-cabling with 47pF total capacitance. Amp-input has no additional C.
Calculations will give you an optimal loading resistance of 30,9K in stead of 47K.
Mechanical resonances of the Grado are not taken into account.

Thus I made the phono input resistance of my phono-amp switchable from 47K to 47K//91K=31K and 47K//39K=21K and listened.
31K did improve sound stage and depth without degrading treble.
21K improved it even more.
I will certainly not go back to 47K..!

Ron Bouquet
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Re: cartridge loading: grado RP

Postby carlosfm » 09 Aug 2006 15:55

bouquet wrote:...diy-cabling with 47pF total capacitance.


Hi Ron,

I think you are just counting with the capacitance of the interconect alone.
My diy cable has around 40pF capacitance.
The rest (~53pF) is the internal arm wiring, up to the female RCA outputs on my TT.

bouquet wrote:21K improved it even more.
I will certainly not go back to 47K..!


How dare you? [-X
They say 47K! :mrgreen:

Congratulations, you're on the right path. :-({|=

Btw I calculated 15K for a Grado Prestige series, same electrical specs as yours.
I don't own a Grado, so I can't try it.
The last judgement is always our ears.
You may want to try it.
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Postby Audie » 09 Aug 2006 17:49

carlosfm,

Thank you for your very informative posts, very clearly explained.

Proper cartridge loading is a necessary step in setting up a cartridge, and your information has simplified the procedure.

Now, you have spurred me into action - I have two tonearm leads that I need to shorten!

regards,

Audie.
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Postby bouquet » 10 Aug 2006 08:38

Hi Carlos,

I think you are just counting with the capacitance of the interconect alone.
My diy cable has around 40pF capacitance.
The rest (~53pF) is the internal arm wiring, up to the female RCA outputs on my TT.


My RB300 is rewired with 36 AWG PTFE ( teflon ) insulated copper-litze.
In fact it's made from a dead PC-mouse cable ; when you remove the outer sleeve and the screening you end up with very flexible teflon insulated wire. I used it in one straight line from cartridge to phono-amp
without any screening , each wire between arm and phono-amp inside another PTFE sleeving.
Thats's why the capacitance is so low : distance between conductors !
Total capacitance measured was ~47 pF including amp-input with cartridge disconnected offcourse.

Calculations : Ropt= 1/sqr ( L/C ) gives 30,9 KOhm for loading and a resonance of 109,5 kHz.
Where L = cartridge inductance ( 45 mH ) and C = measured total cabling cap ( ~47 pF ).
45 mH + 100 pF will give you 15K loading and 75,05 kHz resonance.
At the moment I'am just experimenting with different R-values for loading.
Capacitance should be as low as possible.
No screening !!


Regards

Ron Bouquet

I hate 47 K !
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Postby carlosfm » 10 Aug 2006 09:22

bouquet wrote:I used it in one straight line from cartridge to phono-amp without any screening , bewteen arm and phono-amp inside another PTFE sleeving.


Hi Ron,

Lower capacitance can be had without screening, but at least the signal and ground leads from each channel should be tightly twisted together, as soon as they get out of the arm.
Even then it may pick up (audible) noise, but depends of your environment.
Without a record playing, if you take the volume of your amp close to max. and you don't hear significant hum and/or strange noises (clicks, etc), it should be ok. A little hiss is normal.
Unshielded wire works for line level, which is not as sensitive, but for a TT I would not use it.
These days more and more gear is wireless, fluorescent lamps neaby should be avoided, and even mobile phones can put interference in sensitive audio signals. They work in a much higher frequency, but harmonics come all the way down to protrude with the audio signal, if unshielded cables are used for weak signals.

Anyway, for your cartridge, lower shunt impedance is better, down to 15K, base on 100pF total capacitance.
But in your context of such low cable capacitance, impedance can indeed be a little higher.
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Postby bouquet » 10 Aug 2006 10:36

Hi Carlos,

Outside the wires of each channel are firmly twisted indeed and only 20 cm long as the phono-amp is shelved right below the TT.
The phono-input is desensitizised for RF-signals by 2 V input capability and a RF-blocking choke as grid-stopper ; strange noises are in fact detected RF !
My TT is quit , very quit , without screening.
And no screening open's up the sound .
regards

Ron Bouquet

I hate 47 K's
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Postby carlosfm » 10 Aug 2006 11:16

That's great, Ron.

Oh, don't hate 47K, it can work with some cartridges. :mrgreen:
I have a Shure Pro-8 which sounds best at 47K.
The booklet doesn't spec inductance, this was by ear.

Some day i'll buy an inductance meter...
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Postby bouquet » 10 Aug 2006 12:16

Hi Carlos,

Be carefull , L-meters can destroy your cartridge as can R- en C-meters.

I've still 47K switchable on my phono-input.

regards

Ron Bouquet
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Postby carlosfm » 10 Aug 2006 14:21

bouquet wrote:Hi Carlos,
Be carefull , L-meters can destroy your cartridge as can R- en C-meters.


Yes, it must be measured with some caution, during a short period of time.

bouquet wrote:I've still 47K switchable on my phono-input.


Me too.
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Postby BenC » 11 Aug 2006 10:40

Hi Carlos,

Your post on cart loading opened up new directions for me! All the while I thought only MC carts need proper loading while MM cart loading stays at 47K ... I could now experiment with different MM loadings! ... Am thinking of taking out the 47K resistor in the MM phono input of my preamp and instead plugging an RCA Y-connector (one male --> two female plugs) at each of the RCA phono inputs ... one of the female input for the IC and the other one for the loading ... Am I in the right direction?

Thanks and more power to you!
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Postby carlosfm » 11 Aug 2006 12:06

BenC wrote:Am thinking of taking out the 47K resistor in the MM phono input of my preamp and instead plugging an RCA Y-connector (one male --> two female plugs) at each of the RCA phono inputs ... one of the female input for the IC and the other one for the loading ... Am I in the right direction?


Hello Ben,

Yes, you can do that.
Then you solder several resistor values on a bunch of RCA male plugs and you just exchange them.
Make some markings on each RCA male, with the resistor value.
Please power off the phono pre before changing RCA loading plugs.
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Postby bouquet » 11 Aug 2006 12:19

Hi BenC,

You don't need to remove the 47 k in your phono amp ;
just calculate the value that makes the wanted loading when parralleled with the 47 K and solder it in your RCA-connectors.
P.e. 100 k in parallel will give you 32 k loading ;
47 k in parallel will give you 23,5 k loading.

In most amplifiers you can't remove the 47 k at all because of DC-path :shock: .
If you want to remove it anyway , replace it with a larger value , like 470 k or 1 MOhm.

happy listenings

Ron Bouquet

I (sometimes) hate 47 K ! :lol:
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Postby carlosfm » 11 Aug 2006 15:34

bouquet wrote:You don't need to remove the 47 k in your phono amp ;
just calculate the value that makes the wanted loading when parralleled with the 47 K and solder it in your RCA-connectors.
P.e. 100 k in parallel will give you 32 k loading ;
47 k in parallel will give you 23,5 k loading.


Yes, but in some cases you may need more than 47K loading, and then you can't get that.

bouquet wrote:In most amplifiers you can't remove the 47 k at all because of DC-path :shock: .
If you want to remove it anyway , replace it with a larger value , like 470 k or 1 MOhm.


Ron, that is exactly the reason why I advised to power off the phono pre before changing the RCA plugs with the resistors.
Indeed, instead of removing the internal 47K resistors, one can replace them with 2.2MOhm resistors, which won't affect much the final value when paralleling with normal value resistors (under 100K).
The important is, the phono pre must not be powered on without any resistor from input to ground.

bouquet wrote:I (sometimes) hate 47 K ! :lol:


Aha! :mrgreen:
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Postby BenC » 14 Aug 2006 03:17

Hi Ron and Carlos!

Thank you for the great advice! The reason why I would like to take out the 47K resistor is ... i just wanted to lessen the math work when I use an MC cart. ... I figured, to get the resistor value for a particular loading I need, I just multiply the desired loading with 400 (am using a 1:20 step up) or 100 (if i use the 1:10 ratio) instead of doing the usual math. :oops: ... But because of your timely advice, I might go to the higher resistor value (1M or 2.2M) for safety reason ... and still be able to play around with the higher (than 47K) MM loading!

Thanks and more power to the both of you!
BenC

PS. Does the quality of the resistor have an effect on the resulting sound? Or can I just use any resistor and concern myself with just the (resistor)value? Thanks!
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