cartridge loading ?

Jwblaschke,

Since u r using a Koetsu, are you also using a step-up xformer either ext. or built-in? If I had to guess, I'd say you are. If the Koetsu is 0.4mV output, then you need 60dB TOTAL of gain in your phono section i.e. phono pre & step-up. This 60dB number is valid down to 0.15mV output.

The resistor loading provided to the cart. is a resistor to GROUND! Thus it is not in the signal path & thus does NOT divert any music signal into itself. That is why there is no attenuation of the music as you keep going higher (to 1K Ohm).

Intuitively, the coils in the cart. form an inductor. This inductor also has a DC resistance. It has to 'cuz it is (very fine) coiled wire, which, by Phyiscs, will DC resistance. This DC resistance is usually stated by the manuf. - 13 Ohms or something like that. You do not want to load down the music signal as it comes off the cart into the phono pre hence Buscis2 suggested an impedance 2.5X. I have found that 10X is usually much better. Thus a 100 Ohms phono pre input is OK for a cart. DC resistance of 10 Ohms IFFFFFF you are *not* using an MC step-up. I'll come back to this later.
Further, the capacitance of the interconnect + that of the phono pre creates a cap to ground. Now, you have a low-pass filter where the -3dB corner is set by the phono pre load resistor that is in parallel with the cap. By selecting the correct value load resistor you can shape this low-pass filter's freq. response to suit your listening preferences. In general, too large a load resistor creates an amplitude peak just before the filter rolls off & this creates an emphasis on the high freq. Some prefer this & it *appears* that you are one such person. That's just fine - chose a load to suit your preferences. OTOH, too low a value cause in-band attenuation & the sound becomes 'lifeless', 'dull', 'no sparkle', zero dynamics', etc.

If you are using a step-up, then observe what ratio you are using in the step-up. Say, that it is a 1:5 step-up. Thus the impedance is xformed by 5-square, i.e. 25, to the side of the cart. Usually, the way to use a step-up is to RETAIN the 47K default load in the phono pre & add, IN PARALLEL, some resistance (to ground again) so that the cart. "sees", the correct impedance. Manuf. suggested imp. is a good starting pt. & you can fine tune from there.

Supposing you retain the 47K default imp. & use NO add'l resistance, then the cart. sees 47K/25 Ohms. I don't have a calculator handy so do work out the Math. If you add another 47K in parallel (either solder it on or use the provided load binding posts), then the net imp. will be 47K in parallel with 47K, which is 47K/2. Then, this is xformed to the cart. side as (47K/2)/25. This is the final imp. the cartridge sees.

In general, the amt. of cap. in your interconnect plays a vital role in the sonics as it part of that filter. The biggest contributor to the total cap. should be the phono pre input stage only. That is why you see many people having very short interconnects from cart. to pre &/or step-up to pre.

Usually people do not approach this issue as stated by Buscis2 in his 2nd post as it gets hairy very quickly! Just ensure that your interconnects are not of the high cap type & that they are only as long as needed.

Long post, I know. Hope that it helps you. FWIW. IMHO. YMMV.

Let me get this straight. When you decrease the resistance at the phono preamp, the volume should go up? That's what I observe with my setup. This is called "loading" the cartridge. When the resistance is lowered, the cartridge is required to put out more current to drive the phono preamp (just like a low impedance speaker is a more difficult load to an amp). The burden, or load, is GREATER when the resistance is lower. If the cartridge is able to do this, the volume should go up. Eventually, the cartridge runs out of power and the sound deteriorates. Is this what you observed?

Bombaywalla, Thanks, I was hoping SOMEONE else would help out with this. My approach does get a little hairy, BUT it is very thorough. With the correct calculations, the numbers don't lie.

Also, I found after locating the specs on the Koetsu Onyx, that the output is actually 0.2mv @ 1khz/5/cms, vs. 0.4mv as you stated with an output impedance of 5 ohms, and a recommended loading of 5-100k ohms.

A 64 db gain would be optimum for a 0.2mv output. This calculation is based on achieving a 325m V rms output @ 5 cm/s.

I offer this info not in the spirit of disagreement, but in the spirit of clarification.

Now let's just hope that Jon is not so disgusted that he went out and purchased a CD player. :>)

Thanks again for your contribution Bombaywalla, Ed.

Jameswei,

Don't know where you learnt your electronics but a phono cartridge is a PASSIVE device. It has nothing in it but a wound coil of wire & some magnets. It CANNOT put out any current whatsoever even if it tried to! All it can put out is a VOLTAGE. As already stated by Herman, the VOLTAGE put out by the cartridge is FIXED! Nothing under the Sun can make it increase (it can decrease as the cart. ages & the magnets decrease in their strength but this would happen over several yrs, maybe 10s of yrs).
If the volume is increasing by decreasing the resistance @ the phono pre, I suspect that the resistance (in the input stage of the phono pre) is part of an electronic ckt. that is sets the voltage gain of that ckt. Decreasing it could increase the gain of that ckt. Hence the volume increase. If I have wrongly assumed this & the resistance you are talking about is the resistance you add/take-away externally, then there should be NO change in volume i.e. It doesn't make any sense that the volume changes w/ change in ext. resistance.
Hope that this clarifies.

Buscis2: Cool! I accept you output voltage numbers of the Koetsu. I only GUESSED at the output level as I have no pesonal experience w/ this part. cartridge. I would suspect that 60dB total gain would be sufficient but if your experience shows 64dB is better, then, so be it. I suppose that achieving 325mVrms @ the phono pre is a "magic" number to get max. gain from the pre onwards (to the speakers)?? i.e. it is the max. input to the line-stage of the preamp?

If the phono pickup is open circuit, (disconnected from the preamp, or with a very, very high input resistor) it will produce voltage. Since the circuit is open no current will flow. Motion of the stylus is resisted only by its mechanical compliance.

If the phono pickup circuit is closed by a reasonable resistor value (say 47K) the voltage will cause current to flow. The current is dissipated in the resistor and that is power. This power is generated by the pickup, and power generation requires that work be done. In this case the work is the force that the stylus exerts against the electromagnetic force generated by the current flowing through the pickup coils in the pickup magnetic field. The stylus becomes less compliant. Thus, the loading resistor in the preamp affects the mechanical properties of the stylus, with obvious impact on sonic characteristics.

The pickup is a pretty wimpy generator and can't put out much current. When the resistor value is lowered, and more current is drawn, the pickup voltage will decline. When this happens the sound volume will decrease. This is from a purely electrical point of view. I suppose that the changes of stylus mechanical characteristics might counteract the electrical effects over some small range of resistor values. You can be sure that when the resistor value goes to zero, current will be maximized, but it will be very quiet.