John Curl's Blowtorch preamplifier part II

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Wirewounds come very close to zero tempco!

Is that much of a concern in this particular application?

Also, are any of them non-inductively wound? Not sure how you'd pull that off in a potentiometer. And if they're not, how would that inductance effect cartridge loading? They'd certainly be good at picking up stray magnetic fields unless they were well shielded.

se
 
I use multigand trimmers in my circuits to trim for DC and minimum distortion.
Usually i use Spectrol ( now Vishey).
I use them in the signal chain with a resistor parallel. So when i have a resistor of say 470 Ohm i use a 5kOhm pot in parallel ( just an example).
That way i limit the pot range, so when it is a little bit of it is not a tragedy.
Performance wise i am happy with that configuration.
 
Steve, I would appreciate real information based on experience from other design engineers. If someone has actually used these hybrid pots, then I would value their input. I already know how to Google a data sheet, as you apparently have. I also have experience with multiturn wirewound pots as volume controls, so I know that they work well at line level, and I have various examples of multiturn wirewound pots at hand.
So my actual question is not directed at you, unless you have some actual experience with multiturn HYBRID wirewound pots, for better or worse.
Is there anyone else out there, who has some experience with these hybrid pots in audio circuitry?
 
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[snip] The digital readout might drift, and upset the customer. [snip].

John,

ONLY if you would actually 'measure' the resistance and feed that back to the read-out, which would be an awkward way to do it; it's never done that way AFAIK. So, using this as a termination for the cartridge, you probably wouldn't worry about it drifting a fraction of a percent.

jd
 
Jan, I am looking for suggestions, rather than general evaluations, as well as personal experience. Since the tempco of these pots is pretty good, and the enclosure will not change appreciably in temperature, as it will be on continuously, I am NOW not concerned about appreciable drift in this pots.
 
Wirewound pots and to a lesser extent hybrids sometimes have funky behavior at stop values. Assuming you want a non linear response to give you better matching at specific values, you will of course also be using a network of fixed resistors around the pot. Bourns showed some examples in their Ap book years ago. But without details about the range of values required it is hard to suggest a specific model or brand.

The material used for the base resistance wire changes depending on range.

Of course I suspect everyone is aware of the long term bad effects of any DC on the wiper.
 
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Jan, I am looking for suggestions, rather than general evaluations, as well as personal experience. Since the tempco of these pots is pretty good, and the enclosure will not change appreciably in temperature, as it will be on continuously, I am NOW not concerned about appreciable drift in this pots.

Yes but you must have SOME idea of the range of values you're looking for?
Termination of a cartridge, I'm no expert there but I guess low kohms to 10's of ohms?

jd
 
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