Jon, you need to help complete the equation. I would have to assume that you are using a phono pre that has adjustable input impedance. Are we talking moving magnet or moving coil?
Phono cartridges have circuits which consist of coils of wire. These coils have electrical resistance and inductance parameters which make them sensitive to resistive and capactive loading created by the tonearm wiring, interconnects and circuitry of your phono pre. Cartridge manufacturers will generally specify the proper load resistance capacitance with your particular cartridge.
The cartridge will obviously present the flatest frequency response curve when the manufacturers load is observed. Improperly loaded cartridges will in fact exhibit frequency response dips and peaks like you describe along with emphasized surface noise.
To complete this equation thoroughly you really should consider the following factors;
The capacitance per foot of your interconnects,
The capacitance of the internal tonearm wiring,
The load components inside your phono pre.
Often this information is specified but you may find that it is not optimum for your cartridge. Many designers put way too much capacitance in their preamps disregarding (it would seem) that the tonearm wiring contributes to this amount.
A couple of general rules of thumb. With moving magnet, the higher the capacitance, the higher the degree of (as you put it) "muffling" of the sound. As an example, a moving coil cartridge should be hooked into a phono pre set at an impedance level approx. 2.5 times the impedance level of the coils of the cartridge. The impedance of the input of a step up transformer should be the same or slightly higher than the values of the coils of the cartridge.
Does this help or did I just confuse matters worse? |
the cartridge is a koetsu onyx. i've rewired my tonearm w/ cardas 33 ga Cu. i'm experimenting w/ phono interconnect using the sound of guitars i know or own as reference. currently i'm closest w/ modern audio design "pearl" altho i'm still switching between the mad, some purist audio design phono cable & some homemade cable w/ extruded 5 9s silver & eichman plugs. the phonostage is a retubed mar modded melos ps 1 gold.
altho i've read that koetsu' are supposed to run into 100 ohm loads, i seem to prefer a 390 ohm load i have avail. since there is no " factory" documentation on koetsus and there are varying opinions on the net, how do you determine 2.5x the impedance level of the coils?
i'm also confused about impedance. it looks to me as if my controls select resistors of increasing value and i've encountered threads that refer to " resistive" loading and i've assumed that i was selecting an "obstruction" to the flow of current. does a resistor generate a frequency specific "impedance" because the coils oscillate around a null point? is that all it takes to move from resistance to impedance?
as i look at this it occurs to me that perhaps i need a primer in electricity. is there a concise reference i should know before sending out threads like this?
thanks for your patience'
jon |
Jon, Love your analog, Huh? I love ya like a brother already.
I am going to attempt to address your response paragraph by paragraph, but I really hope that some of our Audiogon brothers/sisters pipe in and help us out.
First: Do you know the capacitance/ft. of the Cardas 33 ga. tonearm cable?
Second: I'm sure that you realize that the capacitance/ft specs are probably all over the place between the five 9 silver, the M.A.D., and Purist Audio cable. What have you finally settled on using, and what is the capacitance/ft?
Third: You are probably preferring a 390 ohm load on your 100 ohm preferred Koetsu because of the capacitance of your wiring (whatever that capacitance may be?)
Fourth: I am sure that one way or another, SOMEONE professionally representing Koetsu could provide you with the coil impedance levels. Personally? I would pissed if they couldn't.
Sixth: Quite honestly? I can't tell you what load components are used in your pre, or what values they are, as I am not familiar with the unit. HELP on this one fellow Audiogoners!
Seventh: (And I'm not sure on this one) In theory, a resistor/array could generate a frequency specific impedance, but I don't know circuit design thoroughly enough to provide you with a specific configuration. HELP on this one too fellow Audiogoners!
Eighth: Back in my days of E/M design/packaging we used to have what was considered the "Electronics Bible" that was somewhat similar to the "Machinery's Handbook" or the "Mark's Standard Handbook For Mechanical Engineers". I still own both of the aforementioned, but the "Electronics Bible" escapes me (Too many drugs). Audiogoners. HELP! Audiogoners.
Last, There are some very intellegent (and some not so intellegent) contributors to this site who I'm sure can help us out here. Hopefully some will pipe in and contribute to this thread.
This much I can do: If you were to provide me with the following info, I could perform some calculations and give you some hard numbers to work with.
Give me your cartridge output, I could calculate the optimum gain of your phono stage.
Give me the phono stage sensitivity specification, and I can calculate the db gain of your pre.
If we know the gain and the maximum output, we can then calculate the maximum input overload. We will then calculate the maximum cartridge output that the pre can properly amplify without distortion.
Oh, for the love of music......Ed. |
The cartridge acts like a curent generator i.e. it trys to put out the same current no matter what the load is.
Using the equation V = I x R (voltage = current times resistance) it is clear that as resistance goes up with a constant current, the voltage will go up. The phono stage amplifys this voltage so the bigger the load resistance, the higher the output.
I'm not sure what you mean by attack distortion, but as a general rule, the high frequency energy will increase as the load resistance is increased. |
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. |
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.
|
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? |
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. |
Bombaywalla, thanks for the correction. I'll try to remember that a coil of wire moving in a magnetic field can't, sorry I mean "CANNOT put out any current whatsoever." Presumably, you learned your electronics from a better school than I. By the way, I recommend you avoid getting too close to any electric power generation equipment, just as a precaution. |
Bombaywalla, Yes, The "magic" number is actually an RIAA derivative. It is a number generally used as an established "benchmark". It works not only at the line stage levels, but also commercial remastering from analog to digital format.
Based on remastering with the current commercial CD recorders in use, the actual recommended value is 300mv, as 300mv is what would be required to attain a 0db recording level with the recorder's level controls set at max. How RIAA actually arrived at that number? I can't tell you. But I would guess that SOME type of standard needed to be established.
The 325mv figure that I use, allows for a small working margin. Lord knows sometimes we need it.
Now if we could only find our original poster of this thread. I think he may be sitting back reading all of this and thinking, "Don't these guys have a life?"
Can you blame him? Ed. |
Jameswei,
I stand corrected!
I realized this a bit after I hit the "submit" button. Writing too late @ night crosses wires inside the brain! |
duh.
out w/ flu a few days but as i try to wade thru this, i fear i may have tried to return too soon.
i think my koetsu has an output of 0.6mv. i believe my melos phonostage offers 54 and 78 db of gain, i use the lower output since even that provides a higher level than my cd player. i am clueless about the capacitance of my various "phono" cables, altho i may have some documentation on the purist; they are all 1m. length.
i think i'm finally clear on the importance of the capacitance of the phono cable & preamp, altho i'm not yet clear on how to solve it, but i'm still struggling w/ the resistance/impedance issue: primarily i see now because of ignorance of fundamentals. i've got the electrons moving d/t the coil over magnet assembly. does increasing the value of a resistor to ground force more of those electrons to the tube grid? is this the formalism for increasing the load on the cartridge?
thanks,
jon |
Hi Jon, I had that nasty flu a couple of weeks back. I'm STILL feeling the residual effects. Hope you're feeling better.
I'm confused. I looked up the Koetsu Onyx on the Elusive Disc website. It states that it has an output of 0.2mv. Is this cartridge offered with an "optional" ouput of 0.6mv also? Is the information I am being provided incorrect?
The difference between those two figures is somewhat significant. A 0.2mv output would require an optimum gain of 64db vs. 55db gain with an output of 0.6mv.
If your Melos is providing you with either 54 or 78 db of gain, you could now understand why you are using the lower output setting. A 0.6mv cartridge output would work almost perfectly with your 54db phono gain stage setting as (by the numbers) it would actually require 55db. You are really not going to get any closer than that. BUT, if it is in fact a 0.2mv output, it would also explain why you are experiencing the sound characteristics you described in your original post.
I think now you can see why I use my little calculations/formulae. THEY WORK! It helps to take all of the guess work out of these equations. They allow you to make a more accurate selection of cartridge/phono pre right from the very start or, in the very least, give you a closer approximation of where you need to be. (Measure twice, Cut once)
If you could, recheck your cartridge output. After that has been firmly established, we can then address the capacitance/operation issues. |
my koetsu is an old onyx( 5 yrs) w/ an output of 0.6 mv. the 0.2mv output is for the new platinum coils.
altho it seems counterintuitive to me that increased resistance should lead to increased output, i guess that's why they call it ohm's law instead of ohm's clever idea or the like. since it appears my taste (&/or hearing loss) lead me to a peaky output preference (altho it seems to me brighter & "airier"), am i doing anything destructive to the suspension of my cartridge running it into 390 ohms?
i should add how much i appreciate this forum. i can't guess how many years it would take me to make any sense of this material without the expert & experienced help available here.
thanks,
jon |
Jon Re; Onyx cartridge output. That would explain it.
And No. The suspension of your cartridge would be unaffected by load and is not considered adverse.
And, it's been a pleasure, Ed.
Happy Listening. |
