I'm going to build my own RIAA pre-amp. It will be fitted inside the turntable. My MM cartridge (Ortofon 2M Red) specifies the load capacitance as 150 - 300 pF. Am I better of aiming for the low side (150 pF), the high side (300 pF) or something in the middle? Besides the tone-arm's cable capacitance (some 20 - 30 pF, I presume) I can dial in any capacitive load I want. Which is preferred, or is this a matter of personal (audible) taste?
It has a quite big impact on the frequency response above 10 kHz or so. If you have a good test record, you could try measuring what gives the flattest response. I would guess that the best value is somewhere in the middle of the range.
There are people on this forum who experiment with non-standard loads (different resistance and different capacitance), for example @Nick Sukhov and @billshurv and @Hans Polak For some cartridges, they get better results than with the manufacturer-recommended load.
There are people on this forum who experiment with non-standard loads (different resistance and different capacitance), for example @Nick Sukhov and @billshurv and @Hans Polak For some cartridges, they get better results than with the manufacturer-recommended load.
You can always add capacitance, but it’s difficult to remove if you find you need lower…
Being a huge fan of Audio-Technica MM, I would personally suggest trying to have the absolute minimum input capacitance possible on anything you build. This requires looking at tonearm cabling and internal wiring as well… however it’s quite worth it in my experience.
Being a huge fan of Audio-Technica MM, I would personally suggest trying to have the absolute minimum input capacitance possible on anything you build. This requires looking at tonearm cabling and internal wiring as well… however it’s quite worth it in my experience.
I use pin sockets for certain devices in preamps, put them in your PCB. You can now install whatever capacitance for trial and error and tune the sound to your ear and system without unsoldering and soldering. When you find the perfect value, solder it to the socket.
You are highlighting a serious problem of the whole MM industry. Technically, it is quite clear that the optimum capacitance to achieve flattest frequency response must and will be known to the manufacturer and it will have +-10% tolerance or so.
But they don't publish it because in real world application the loading situation is often ill-defined. So they just tell us what they think is tolerable range of loads.
General rule is the larger the capacitive load the lower the peak resonance frequency will be and the stronger the peaking.
If your ears have aged already and drop off quickly above, say, 12kHz or so then a lower and stronger resonance (like at 15kHz) might sound better than a higher and weaker one which would be the target young fresh ears with 18kHz++ response might prefer.
Scroll down for 2M Red measurements with 210p load:
https://www.audiosciencereview.com/...o-cartridge-measurement-library.46108/page-15
The rise is significant, a lower capacitance will give a flatter response. What you prefer is always a matter of taste, of course, you'll have to try and see. I like elwood625's pin socket idea.
https://www.audiosciencereview.com/...o-cartridge-measurement-library.46108/page-15
The rise is significant, a lower capacitance will give a flatter response. What you prefer is always a matter of taste, of course, you'll have to try and see. I like elwood625's pin socket idea.
Thanks to everyone for their valuable input. I would have also guessed that somewhere in the middle would be the preferred loading capacitance, but seeing that my hearing only still goes up to 12,5 kHz, I will make provisions so I can try everything from the bare minimum up to the middle.
Once my build is complete, I will show it here, so MarcelvdG can see how his design worked out, and I can hopefully tell you whether I could hear any difference in loading capacity.
Once my build is complete, I will show it here, so MarcelvdG can see how his design worked out, and I can hopefully tell you whether I could hear any difference in loading capacity.
Flat frequency response means flat (and horizontal too) phase characteristic. And that translates into good reproduction of the musical transients, no "ringing" after the sharp pulses etc. So, no matter your hearing ability, it is advisable to have 20Hz~20kHz within the documented/standardised margins.
The termination is very important and don't believe the manufacturers recommendation. The cartridge and load form a two-pole low pass filter. What you have is shown in the illustration. You have a zero at zero because the cartridge won't produce DC and a zero at infinity because the cartridge does not have infinite FR and two poles. You know that if the Q is 0,5 or less the poles are on the negative real axis and you won't have any overshoot or ringing. It will also never reach steady state so you need a little higher Q than 0.5. You also know that if the Q is over 0.707 you get a resonant peak in the FR. I see that very often in the FR plots for cartridges. Now, a Q of 0.577 gives you a Bessel alignment filter and Bessel filters have a phase linear response and the best transient response. The formula for the Q is given on page 411 of the old Radiotron Designers Handbook and is approximately Q=Rl*SQRT(C/L). You have to include the tone arm wiring capacity too.
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I was told by someone named "Adam Smith", that "free market" and other such stuff exists, and every thing that has demand will be produced in good quantitiy...
You would think that the Ortofon's of this world could give the required information for a proper design. That's very normal in an engineering and development environment. As it is now, you can only come to some form of approximation, and only properly if you have a test-record. Anyhow, I'm plowing on with my build. The parts have been ordered, including a surplus of input C's. Luckily, my hearing is not that good anymore.
Thanks @rayfutrell
The electrical data of the Ortofon 2M Red cartridge are specified as:
L = 700 mH
r = 1k3
With the below I've calculated the system electrical Q for different capacitive terminations at a 47 k load resistance.
Recommended load by manufacturer: 150 - 300 pF
C = 150 pF -> Q = 0,68
C = 300 pF -> Q = 0,96
For Q = 0,57 (0,56) -> C = 100 pF
So, for an optimum electrical Q, I would need a total capactive load of 100 pF // 47k.
So, do Ortofon specify a higher C-load to make-up for a falling F-response? Since my hearing only extends to 12,5 kHz, it seems to me, I should aim for a total load of 100 pF.
Sometimes you read to exclude the input C altogether.
With a tone-arm capacitance of 30 pF -> Q = 0,31. That sounds way underdamped.
The electrical data of the Ortofon 2M Red cartridge are specified as:
L = 700 mH
r = 1k3
With the below I've calculated the system electrical Q for different capacitive terminations at a 47 k load resistance.
Recommended load by manufacturer: 150 - 300 pF
C = 150 pF -> Q = 0,68
C = 300 pF -> Q = 0,96
For Q = 0,57 (0,56) -> C = 100 pF
So, for an optimum electrical Q, I would need a total capactive load of 100 pF // 47k.
So, do Ortofon specify a higher C-load to make-up for a falling F-response? Since my hearing only extends to 12,5 kHz, it seems to me, I should aim for a total load of 100 pF.
Sometimes you read to exclude the input C altogether.
With a tone-arm capacitance of 30 pF -> Q = 0,31. That sounds way underdamped.
The resistance of the cartridge itself has more effect than you would think. The assumption that the effective series resistance of the cartridge is constant over frequency is far from the truth.
In the table below, R is the effective series resistance and G the shunt conductance of a Shure V15-III, calculated from measured impedance magnitude and phase data.
In the table below, R is the effective series resistance and G the shunt conductance of a Shure V15-III, calculated from measured impedance magnitude and phase data.
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If I could find a beryllium cantilever cartridge I would promise not to eat, drink or breathe it.
I posess three such cartridges, but they are really old, their cantilevers are solid berillium rods rather than conical tubes...
😢
😢
Taking in all information, I come to the conclusion that using the provided L/R data from the manufacturer is not sufficient to come to any meaningful load capacitance calculation. So, it's back to the manuf. recommendation, and listening. Thanks for the clarification.