"Greg Mayman" bravely wrote to "Roy J. Tellason" (04
Feb 04  08:54:00)
 --- on the heady topic of "BAG OF CHIPS"

 -=> Roy J. Tellason said to Greg Mayman
 -=> about "BAG OF CHIPS" on 01-29-04  04:05.....
 RJT> It's a ceramic pickup,  basically the same idea.  The only thing I
 RJT> need to put in there is something to give me the proper equalization...

 GM> Usually no equalization was used. I don't know whether the
 GM> pickups contained some inbuilt correction for the "wiggle" in the
 GM> RIAA curve, but I rather suspect it was ignored.

 GM> If you want, you can use the following network either between the
 GM> pickup and the preamp or between the preamp and the following
 GM> stage.

 GM> in ------+---- C1 ------+------- out
 GM> .        |              |
 GM> .         ---- R1 ------+----- R2 ---- gnd

 GM> Typical values:

 GM> (a) between p/u and preamp: R1 = 510k, R2 = 2.2M, C1 = 150 pF
 GM> R2 is chosen to give a suitable load to the pickup.

 GM> (b) following preamp: R1 = 2200, R2 = 10k, C1 = .033uF
 GM> R2 may be a 10k volume control.

I think your above network would tend to make a ceramic cartidge sound
a little extra "strident" but I could be wrong. Well, they all sound a
little strident already... ;-)

But I don't think that fixing the riaa wiggle is a real priority in a
type of transducer which has so many sonic anomalies. An article I
read about this explained that the way ceramic cartridges behave tends
to roughly follow the riaa curve and as such the correction is
basically automatic.

The only problem seems to be due to loading the capacitive impedance
nature of the pickup that tends to lose bass response and as such a
bit of bass boost is usually added. (+12dB starting at 250Hz?) The
load resistance is often in the megohm range but I've seen Philips
using a 100K load but with added correction.

Also, since the output sensitivity level is in the 100's of millivolts
and more, often only a unity gain buffer is used between ceramic
pickup and the amplifier.

 Mike
 ****

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