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Old 26th Jun 2020, 1:04 pm   #16
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: Ceramic cartridge preamps revisited

With the solid bootstrapping in that circuit, a bipolar would work a treat, but need a couple more resistors to set the input bias. In return, operation would be much more consistent.

JFETs used to turn up in more places than they really suited because some people were more comfortable with them than with bipolar devices. There was a 'Gee, they're just like little valves!' factor which gave some people warm and fuzzy feelings -Pat Hawker was a bit of a sucker for them

With the bipolar operating as a series-feedback arrangement and with the input bias chain bootstrapped, the input impedance can easily be made high enough that you can add a shunt resistor to set any other value of Zin to make the cartridge happy.

As an alternative approach, it's also feasible to run a piezo-electric cartridge into a low-Z amplifier, treating it as a current source and to equalise the resulting slope. The Wireless World Bailey-Burrows preamp does this properly. It's quite a rare technique.

David
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