Seriously, I NEED very high resolution and NO COMPROMISE in the resistive portion. It is pointless to go ahead with it, IF I cannot achieve what I need.
As before, thanks to everybody for their input.
As before, thanks to everybody for their input.
He is not old! I was middle-aged before his JC stuff first hit the market!
[I suspect that we are about the same age! 1942 job in my case.🙂
[I suspect that we are about the same age! 1942 job in my case.🙂
We are approximately the same age, brianco.
For everyone else: I want CONTINUOUS change in resistance, not switched resistors.
For everyone else: I want CONTINUOUS change in resistance, not switched resistors.
No switched resistors, thank you. Think! What kind of switches are next to perfect? Relays? Let's keep it to a minimum.
Both switched and continuous ( use one dual gang pot per channel - one side for load other for servo) have compromises . . .
Nevertheless, interesting design challenge.
Nevertheless, interesting design challenge.
Personally, I would always go for silicon switches - I haven't heard the 'best of the best' in physical connect mechanisms, but every one of the latter type I have come across I can always 'hear' - the better the 'transparency' the more obvious the impact in terms of affecting quality.
Hello John, do you have a particular MC loading pot in mind ?.
I have seen a couple of motor assemblies that could connect to a standard 1/4" shaft.
Dan.
We already have initially selected a 10 turn pot and put a motor on it. It is problematic, physically, and EXPENSIVE. BUT with a few adjustments (compromises) we can probably use it.
I did ask for outside opinions here, because many of you are competent engineers and you might give me some new insight that I missed.
Ed Simon came closest, as he recommended splitting the channels and using a stepping motor of normal resolution. He gave me the 1.8 degree step, which is standard, and this allowed me to more precisely predict whether I could achieve the performance necessary. It appears to me that a 2000 ohm pot would probably work, and I might try it.
Now, WHY do I need such a complex solution for something that is usually ignored or given nominal adjustments? (more later)
I did ask for outside opinions here, because many of you are competent engineers and you might give me some new insight that I missed.
Ed Simon came closest, as he recommended splitting the channels and using a stepping motor of normal resolution. He gave me the 1.8 degree step, which is standard, and this allowed me to more precisely predict whether I could achieve the performance necessary. It appears to me that a 2000 ohm pot would probably work, and I might try it.
Now, WHY do I need such a complex solution for something that is usually ignored or given nominal adjustments? (more later)
The eastern answer would be that as the system becomes more transparent the more important each part becomes . Since this is at the front of the stages it will have a large effect. That's my take.
It is best to use a linear progression because it it more 'transient proof'. The input levels here can be typically 100uV, and even less. The gain of the phono stage alone is typically 80dB at 10Hz, and the output voltage can be 10V or more (single ended). If there is a problem, then you could destroy your loudspeakers, and guess WHO gets sued?
I formally tried to give a history of cartridge loading, but when I got it finalized, my computer crashed! What a drag.
Instead, I will give you an abbreviated version of what I wrote:
Originally, transformer loading set the actual loading of the cartridge. The transformer gain was set for what was necessary to get the output of the cartridge to standard levels.
The more transformer gain, the lower the load impedance of the cartridge.
When the Levinson JC-1 became available 40 years ago, the input loading depended on the source impedance, dynamically. So, with a 2 ohm source, it might be 100 ohms or so. But with a 10 ohm cartridge, it would be lower, and with a 40 ohm cartridge, it would be much like a summation mode input, as is often discussed here. This worked at the time, but for no specific reason. (more later)
Instead, I will give you an abbreviated version of what I wrote:
Originally, transformer loading set the actual loading of the cartridge. The transformer gain was set for what was necessary to get the output of the cartridge to standard levels.
The more transformer gain, the lower the load impedance of the cartridge.
When the Levinson JC-1 became available 40 years ago, the input loading depended on the source impedance, dynamically. So, with a 2 ohm source, it might be 100 ohms or so. But with a 10 ohm cartridge, it would be lower, and with a 40 ohm cartridge, it would be much like a summation mode input, as is often discussed here. This worked at the time, but for no specific reason. (more later)
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