Sakellogg, what actually happens is that I usually design a circuit topology, try it out in my home lab, then I send a schematic to Asia, where they take my initial offering and 'tart it up' with a nice case, power supply, automation, protection, etc. and release a prototype back to me for evaluation. In a few instances, I did NOT actually listen to the prototypes, but just measured them with a combination of HD, IM, and Spectrum Analysis, looking for certain 'errors' such as higher order odd harmonic distortion, noise, etc. Then, with a few changes, I release it for production. I then let the MARKETPLACE tell me if it is a 'classic' or a 'dog', I have made a few of both.
In building the JC-3, it was a little more involved. I had to design it and send it to my long time associate, Carl Thompson, for layout, then get a test board from him to stuff (usually with the available components in my lab, but sometimes like with some the IC's I had to special order), test it, and give back to Carl any mistakes either he or I made. Then a 'final' board is made, instructions are sent to Taiwan as to how to make the board and what parts to use. It is ALWAYS difficult to get people to use the 'right' parts, they really want to save a few pennies, wherever they can, and this can destroy the sound quality of the product, so I have to be watchful. In the JC-3 case, it was not so difficult, because they already made the JC-2 preamp, so they had good resistors, connectors and capacitors on hand, in stock.
Still, several revisions had to be made: One was to change the outside case from STEEL to ALUMINUM. I personally could hear the difference. Different input IC's were tried, and interestingly enough, each had its own 'personality' so to speak.
Then the unit went to selected dealers, and others in the audio business. They always give feedback as to features, etc. They always want MORE. And so it goes.
In building the JC-3, it was a little more involved. I had to design it and send it to my long time associate, Carl Thompson, for layout, then get a test board from him to stuff (usually with the available components in my lab, but sometimes like with some the IC's I had to special order), test it, and give back to Carl any mistakes either he or I made. Then a 'final' board is made, instructions are sent to Taiwan as to how to make the board and what parts to use. It is ALWAYS difficult to get people to use the 'right' parts, they really want to save a few pennies, wherever they can, and this can destroy the sound quality of the product, so I have to be watchful. In the JC-3 case, it was not so difficult, because they already made the JC-2 preamp, so they had good resistors, connectors and capacitors on hand, in stock.
Still, several revisions had to be made: One was to change the outside case from STEEL to ALUMINUM. I personally could hear the difference. Different input IC's were tried, and interestingly enough, each had its own 'personality' so to speak.
Then the unit went to selected dealers, and others in the audio business. They always give feedback as to features, etc. They always want MORE. And so it goes.
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LSK170 SERIES DELIVERS DIRECT PIN FOR PIN REPLACEMENT OF TOSHIBA'S 2SK170:
Linear Integrated Systems - Press Release
Linear Integrated Systems - Press Release
I have found the choice of phono cartridge a real challenge. There seems to be dozens of companies and maybe 100 or more different models. The actual difference between different models from the same manufacturer is of concern, because I cannot determine what the REAL differences are.
With my many decades experience with moving coil cartridges, I have found significant listening differences with every one, even when the frequency response, etc was pretty much the same between models, especially within the normal 30-15KHz range. Why this is so, has always intrigued me.
When it comes to a modest design like the JC-3, it is impossible to optimize the S/N for EVERY phono cartridge ever made, that someone might find in a closet, or bought 30 years ago. The reason for this is because of two main reasons: Rated output at operating level and intrinsic inductance, and sometimes, resistance.
Back in the good old days of the '50's and '60's, tubes ruled, and HIGH input levels were necessary to overcome the intrinsic noise that THESE tube stages generated. As an example, just look at a Dynakit PAS-3 phono stage, and analyze it.
This required much more output turns on the phono cartridge, and this had a secondary 'advantage' that I will go into later, but inductances typically as much or more than 1 Henry were put into popular phono cartridges in the past. So, if you got your turntable from your late great-uncle, for example, you might find this type of phono cartridge with it. More later.
With my many decades experience with moving coil cartridges, I have found significant listening differences with every one, even when the frequency response, etc was pretty much the same between models, especially within the normal 30-15KHz range. Why this is so, has always intrigued me.
When it comes to a modest design like the JC-3, it is impossible to optimize the S/N for EVERY phono cartridge ever made, that someone might find in a closet, or bought 30 years ago. The reason for this is because of two main reasons: Rated output at operating level and intrinsic inductance, and sometimes, resistance.
Back in the good old days of the '50's and '60's, tubes ruled, and HIGH input levels were necessary to overcome the intrinsic noise that THESE tube stages generated. As an example, just look at a Dynakit PAS-3 phono stage, and analyze it.
This required much more output turns on the phono cartridge, and this had a secondary 'advantage' that I will go into later, but inductances typically as much or more than 1 Henry were put into popular phono cartridges in the past. So, if you got your turntable from your late great-uncle, for example, you might find this type of phono cartridge with it. More later.
Now, there are at least 2 reasons why OLDER moving magnet cartridges had so much inductance. First, absolute output needed to be high. For example, the JC-3 'might' be as much as 20 dB quieter than a Dyna PAS-3, with a low Z drive, therefore the cartridges had to give lots of output. Second, the inductance combined with the load capacitance and the 47K (specified) load, to create a ROLL-OFF within the audio band, in order to flatten out the high frequency response that would have been tipped up by the relatively undamped high frequency tip-mass resonance, that happened within the audio band, decades ago. Together, this created a 24 dB/oct low pass filter. This REALLY helped to prevent potential slew rate problems later made by Moving Coil cartridges. These phono cartridges could not slew themselves out of a 'paper bag'. '-)
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With the introduction of Moving Coil cartridges from Japan, as well as Denmark and Germany, the picture changed a bit. While MOST of these cartridges still needed a step-up device, either a transformer or a special, low noise electronic gain box, some phono cartridges such as the Denon (sp) had enough output to run direct, IF the shorted input noise was low enough. This gave birth to the Levinson JC-2 phono stage and many others.
As the years went by, Shure and others worked to LOWER the dynamic tip mass and change the diamond cut, in order to INCREASE the self resonance at high frequencies. THEN, a very high inductance became a liability, and had to be reduced. So, inductance was cut to 1/2 H or less, in order to flatten the cartridge with a new contour, and extend the effective bandwidth of the cartridge. The different models, over the years, of the Shure V15 cartridge, show this the best. This also makes it easier to use a quality IC with bipolar input and get reasonable noise performance. The DCR of the cartridge lowers too, so a good shorted input noise has more advantage than in the past, where the relatively high DCR of the cartridge would swamp any really low noise input, either bipolar or jfet.
As the years went by, Shure and others worked to LOWER the dynamic tip mass and change the diamond cut, in order to INCREASE the self resonance at high frequencies. THEN, a very high inductance became a liability, and had to be reduced. So, inductance was cut to 1/2 H or less, in order to flatten the cartridge with a new contour, and extend the effective bandwidth of the cartridge. The different models, over the years, of the Shure V15 cartridge, show this the best. This also makes it easier to use a quality IC with bipolar input and get reasonable noise performance. The DCR of the cartridge lowers too, so a good shorted input noise has more advantage than in the past, where the relatively high DCR of the cartridge would swamp any really low noise input, either bipolar or jfet.
Hi John,
Thanks for this overview.
In your experience with moving coil cartridges that put out in the range of 0.4mV, what inductance have you seen in them?
Cheers,
Bob
Hi John,
I thought I had seen somewhere that it was between 500uH and 5 mH. If it was only 500uH, inductive reactance at 20 kHz would be about 63 ohms, beginning to get into the range of the typical 100 ohm load and possibly having some influence on HF attenuation (it would create a pole at about 32 kHz. This is not so bad, although it inflicts a 1 dB loss at 16 kHz (assuming first order and no interaction with tip resonance).
However, if the inductance were higher, as possibly might be the case for a higher-output MC, then the 100 ohm load against the cartridge inductance would likely be problematic.
On the other hand, if it was only, say, 100uH for a 400-uV MC, then this is way not an issue.
Anyway, that's why I wondered what the actual number was for a 400-uV MC; I just wanted to see what ballpark it is in.
Cheers,
Bob
Bob, somewhere there might be an MC cartridge with more inductance than nominal. Sometimes for MORE output, they use a ferric ring to the coil to raise the output. This might give you the 'aberration' you seek. However, since the early days, more than 35 years ago, we could not find any significant change with variation in resistor loading, as far as frequency response is concerned, in most MC cartridges.
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