[BudBurner]

On Jun 1, 7:55*am, BudBurner wrote:
On May 26, 10:46*am, BudBurner wrote:

* * *I have the service manual for aPhaseLinearP3800preamp and I
want to plagarize the moving coil preamp circuit for use in my own
design MC/MM preamp/RIAA *EQ circuit. However,Phase(Flame?)Linear
never specified a value for the inductor L100 in the input of the
moving coil head amp. Does anyone know the value of L100 or have a
unit open that an RCL bridge reading can be taken of L100? TIA!
* * *Bud

* * * * * Also, if someone could enlighten me on the purpose of the
inductor at that point in the circuit?
* * * * * Bud

Looks like I will have to answer my own question. After much
running about and emailing I got my hands on a physical unit. That
part is a type 73 ferrite bead on a piece of buss wire and its
purpose, along with the 330 pF capacitor in the negative feedback
loop, is for RFI protection. Since the preamp uses junction bipolar
transistors, there is a chance for radio signals to be detected,
rectified and amplified without these parts if you happen to live near
a strong radio transmitter or tv station.
Also, while I had the preamp in my hands, I upgraded their
selection of 4 npn and one pnp transistor in the moving coli head amp
with 2N4401 and 2N4403 transistors respectively for a readily apparent
decrease in the noise floor. The owner was more than pleased by the
result.
Bud