Steve Eddy,
I agree it won't be easy and I will have to distinguish my product from the rest. I am planning to make a high end speaker that won't cost mega bucks to purchase. My biggest holdup has been that I want the product to be self powered and I am not an electrical designer so I have been on this website now for awhile learning what I can.
I agree it won't be easy and I will have to distinguish my product from the rest. I am planning to make a high end speaker that won't cost mega bucks to purchase. My biggest holdup has been that I want the product to be self powered and I am not an electrical designer so I have been on this website now for awhile learning what I can.
The application uses a motor driven pot. LDR's don't get down to 5 Ohms very easily (even though the company has and is using the computer calibrated part of the process). My first suggestion would be relays but they bring a lot of issues at this level- 1, more contacts (this is philosophical) 2, inductive pulses from switching them, since the relays are in close proximity to very low level signals this is an issue, 3, the number of resistors to make 4 decades of audiophile acceptable resistors gets expensive as well.
Its quite possible to get multigang precision pots for a price. An encoder on a single pot may make sense, especially if the pot is nonlinear so the low end is spread out.That plus the computer calibration would be a clean solution. It may not need a wirewound pot to implement either. (I wish I subscribed to loading cartridges).
Its quite possible to get multigang precision pots for a price. An encoder on a single pot may make sense, especially if the pot is nonlinear so the low end is spread out.That plus the computer calibration would be a clean solution. It may not need a wirewound pot to implement either. (I wish I subscribed to loading cartridges).
It isn't that difficult with an encoder and micro.
With an incremental encoder a homing function needs to take place at each power up. Read the encoder and pot together in a calibration mode as suggested, if you want to go that far.
For more accuracy I'd look at 2 pots and 2 encoders. One for each channel. Cal each; position against pot reading. Save the files and control the pot based on the files.
We do this same kind thing hundreds of times a day.*
* I designed a test fixture to measure roller screws using this method. I used a 5K count rotary encoder and a linear encoder in 1 version and a linear pot in another. I used a servo drive to collect the data so I didn't have to rewrite the code. Accuracy is .0002 inch.
With an incremental encoder a homing function needs to take place at each power up. Read the encoder and pot together in a calibration mode as suggested, if you want to go that far.
For more accuracy I'd look at 2 pots and 2 encoders. One for each channel. Cal each; position against pot reading. Save the files and control the pot based on the files.
We do this same kind thing hundreds of times a day.*
* I designed a test fixture to measure roller screws using this method. I used a 5K count rotary encoder and a linear encoder in 1 version and a linear pot in another. I used a servo drive to collect the data so I didn't have to rewrite the code. Accuracy is .0002 inch.
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Ah, but if it doesn't cost mega bucks, the high end won't take it seriously, and regular folks wouldn't appreciate it enough to justify even the non-mega buck price. Catch 22. 😀
se
Now what happens when the pot wears out in 10 yrs , replacing it could be pain in the **** ...
Very , very difficult , worse if self amplified , from experience audio folks like to pick and choose their electronics....
How much use would a cart loading pot see? OTOH there are those that tune VTA for each LP.
Live in the dark, Scott. It does make a difference for a SPECIFIC setting on everything else.
Use a Bourns 3680 digital read out resistor driven by dash pots. A nice rube Goldberg solution with good resolution. MC loading is kind of funny people either want one resistor of virgin Gold fleece soldered in or lots of choices on a remote control.
John,
How would the average audiophile know how to adjust that capacitance loading on a MC cartridge? Just by ear or would there be a more specific way to do that? I have an older Harman Kardan integrated amplifier that does in fact have a four position switch for this function but since I never had a turntable hooked up to it I have never experienced how it changes the sound.
How would the average audiophile know how to adjust that capacitance loading on a MC cartridge? Just by ear or would there be a more specific way to do that? I have an older Harman Kardan integrated amplifier that does in fact have a four position switch for this function but since I never had a turntable hooked up to it I have never experienced how it changes the sound.
Personally, I would do it with paralleled resistors and CMOS switches - the on resistance flatness of these gets down to 0.05R, which should keep the distortion under control. I can't imagine that pots would do a better job ...
With that low an on-resistance the problem might be the parasitic capacitances - they're probably into 3 figures pF. 0.05ohm flatness would suck rather at under 1mV across them (MC cart remember). Still with a very low noise power supply to the CMOS switches that'd probably fly. Epoxy potting with bright logo stick-on label on top the module can take care of the fashion issues - though Charles Hansen gets away with openly talking about CMOS switches in his products. For the top end stuff though I understand he uses motorized attenuators?
John,
1. What is "VERY expensive" in your case?
2. Have you considered miniature toothed belt + largish pulleys to join the dual and single pot shafts? Something like this:
Miniature Timing Belts From SDP/SI
Those VTA/SRA adjusment freaks just try to match the distorsion characteristic of their Pickups with their hearing preferences of their bat ears. 😀
Spheric tips are not very sensible when set up properly once.
Resistive Cartridge loading makes difference, almost its needed to control the top resonance around 20 Khz. Cartridge tolerances are usually much more effective. 🙁
When frequency response is almost linear and the Cart/Arm resonance set around 11 Hz, the load is not extrem critical, but audible.
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