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I've been trying to use a online calculator for cartridges and it requires a known inductance.
Loading requirements of a mmc is.
100pf
47k
Anyone know what the typical pf of a beogram 8002 is? That is tone arm + cables to the phono preamp.
Inductance of a mmc2?
Someone said it would be hard to have a pf close to 100 since many phono preamps are 100 not including the TT and cables.
Seems B&O would have designed a low pf into the TT because its meant to use mmc carts.
I guess a high pf can cause a peak in the higher frequencies. If its 20khz no biggie as I won't hear it.
this helped me to get my head around the subject
http://www.gspaudio.co.uk/blog/phono-cartridge-loading-capacitor_post78.html
to answer your questions
1) Anyone know what the typical pf of a beogram 8002 is? That is tone arm + cables to the phono preamp.
the DIN standard of 1973 which B&O faithfully followed was 80pF for the cart and tonearm (you can measure lots of arms like the Technics and Denons and find this 80pF value was very common in the seventies and eighties.
the DIN standard of 1973 mentions 300pF a lot when considering the overall capacitance from the cart to preamp ( including the 220pf inside the preamp), so in an ideal world, you would have 80pf ( for the MMCx cart and tonearm) 20pf for 30cm of interconnect ( very short, shorter the better) to the preamp and the normal 220pF value that most preamp manufacturers build to.
2) Inductance of a mmc2?
my SMMC2 is 190mH per channel (as confirmed by Peter at Soundsmith)
3) Someone said it would be hard to have a pf close to 100 since many phono preamps are 100pf not including the TT and cables.
in my experience, by far the majority of phono pre's are setup to the standard 220pF, some more expensive pre's are now setup to use 100pf
http://www.gspaudio.co.uk/jazzclub-phonostagepreamp.htm
4) Seems B&O would have designed a low pf into the TT because its meant to use mmc carts.
no, B&O used the DIN standard of 80pF for the capacitance load on the TT ( well actually the arm and the mmc cart) , I have measured the arm on a Begoram 5000 with an MMC2 cart and it was 83pF, but maybe my Maplins MultiMeter was not supremely accurate enough, or the tolerance on the 5000 TT was out a bit, but not too far off anyways. I will do the same test soon on my 7000 and 8002 :-)
5) I guess a high pf can cause a peak in the higher frequencies. If its 20khz no biggie as I won't hear it.
the peak resonance you refer to (Hagerman loading calculator ) is nothing like 20kHz, it refers to the normal Moving Magnet bump around 10 to 13kHz, if you take the Soundsmith moving iron design of the SMMC2, the pH value is 190pH per channel ( = 380pH ) now put this into the Hagerman calculator along with the standard DIN value of 300pH capacitance you will see the resonance bump value of 15kHz
when people talk about 20hz to 20kHz, that’s just a convenient estimation. Good hearing is 28hz to 16kHz. Great hearing is 25hz to 18kHz., and exceptional hearing is anything lower than 25hz and above 19kHz.
the pitch of your average dog whistle is 20kHz, and maybe some young children can hear this pitch – but I would be very surprised to meet an adult over 30 who can hear 20kHz ( Golden Ears )
fortunately for me I cannot hear anything much anything above 15kHz with my 54 year old years, and my 15 year old daughter can only just about hear the 19kHz, and once or twice the 20kHz wav files using the test below
http://www.noiseaddicts.com/2010/10/hearing-loss-test/
Thanks, I copied the text here in case that link goes dead.
Phono Cartridge Loading Capacitor 07 March 2014 - by Graham Slee
Inductance (L), resistance (R) and capacitance (C), when all placed in parallel with one another, form a resonant LCR 'tank' circuit.
As frequency increases, so does the inductance - it becomes more 'resistive'. As frequency increases, the capacitance becomes less 'resistive'. At some high frequency a point will be reached where the combination of inductance and capacitance resonates - it will produce a large peak or 'spike' in the frequency response. The resistor however, dampens the spike - reduces its amplitude (its height). When balanced up nicely you get an up slope to a particular frequency, followed by a down slope - both slopes being equal.
The rate of rise and fall is 6dB per octave. When this circuit is used as the input of a phono preamp, the inductance is the phono cartridge - it's also generating the electrical signal which is the music. The capacitance is made up of the arm cable wiring capacitance, plus a real capacitor in the input of the phono preamp. The resistor (quite often 47k) is a real resistor (or combination of values) also in the input of the phono preamp. The response graph you would see from this particular LCR combination would not be rising, peaking and falling, but will be flat, followed by a peak, and then followed by a down slope twice as steep, or -12dB per octave. How come it's different?
That's because of the equalisation in the phono preamp. If we know the inductance and the capacitance, we can work out the frequency where it slopes down. This frequency is where the electrical output is designed to start falling - the upper end of the phono cartridge frequency response. There is a simple physics formula for this... ƒR = 1/ 2pi sqrt LC Classic values are 500mH for a MM cartridge, and 200 pico farads for the total capacitive load. This gives a frequency of 16 kHz, which was considered excellent when hi-fi was defined as anything having a frequency response of 30 Hz - 15 kHz. So, how come MM cartridges have a frequency response reaching higher than 16 kHz? Well, from what we know, and we know that physics tells us it can only go to 16 kHz, it must be something other than being electrical - it must be mechanical. Therefore it has to be likened to a 'tuning fork', and the stylus assembly must therefore mechanically resonate to basically 'cheat' the response.
Going back to the electrical physics, we can see that by varying the cartridge inductance and load capacitance, the high frequency turnover point can be changed... For example, if the inductance were to be 400mH, the high frequency turnover will rise to nearly 18 kHz using the same 200 pico farad capacitance load. If it were to be 600mH, it would become 14.5 kHz. By reducing the capacitance to 150 pf it would become nearly 17 kHz. Because the vast majority of cartridges are 1] made to work with existing tone arm wiring capacitance plus phono preamp input capacitance - and that can add up to 200 - 300 pico farads, the sensible MM manufacturer will choose to make the cartridge inductance close to 500mH - plus or minus a little, and 2] because the output is closely dependant on ampere-turns - how many turns of wire there is - it will follow that for a range of say 2mV to 10mV output, it's going to end up as being in the region of 500 mH. As most tone arm cables plus internal wiring measures around 100 pf and most phono preamps use 100 - 200 pf, the total capacitive load is 200 - 300 pf.
The manufacturer knows what the electrical high frequency limit it is going to calculate out at. He will therefore tune the mechanical resonance to reach as high as he can get it. The question that usually gets asked is "what will happen if I use a cartridge specified for 400 - 500 pf into a phono preamp specified as having 100 pf input capacitance?". Well, first you need to add the tone arm wiring and cable capacitance - that will be around 100 pf, making the total load 200 pf. Then you have a difference of 200 pf. You can either try it like that and you may like the sound, and if you don't you either need to add capacitance, or buy a phono preamp with different capacitive loading switches (but remember switches can go resistive through corrosion - they don't last forever). You can also use an extension cable on the tone arm cable to increase capacitance.
But at what frequency do these differences take place and will you actually hear them? After all, the peak is damped by the resistance (the 47k). The frequencies are mostly going to be above 10 kHz with peaks or troughs of up to 2 dB. It is going to be very difficult for anybody in his/her 30's to clearly hear much higher than say 16 kHz. It is going to be quite hard to tell the difference 2 dB is going to make.
The thing that could influence what you hear may be psychological - that being the specification said one thing and the phono preamp said slightly different. Now that could be the breaking point...
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I got caught up in this in the beginning but after testing a several amplifiers, TTs, cartridges. It really did not make much difference to my ears. Which makes me thing the psychological aspect of the equation is probably a large factor in this. When you get in the 15K+ range little changes are not going to be heard by most people. I'm 50 so my days of great hearing are behind me.