D-104 Pre-amp Voltage question

[d1g1man]

I have a D-104 on it's way, it's not in my hands yet. I want to get ahold of the parts I need before it arrives.

My rig supplies 12V at the mic jack, I would like to feed power to the mic with it to eliminate the 9V battery.

I do not know how much current the pre-amp requires (anyone know?), so I need to know what is the best route to go to drop it down to 9V.

Should I use a resistor (what value?) or a zener diode (how many at 1W)?

Do I even need to drop it to 9V? Can I just feed it with the 12V?

Thanks, I am hoping someone has already done this and worked it out!

 

[HiDef]

You would be better off building another preamp. There are lots of good designs out there on the www. Most use an MPF-102. Only takes a handful of parts and is known to work OK with modern rigs that have very low current mic voltage available at the mic connector. The reason for changing the preamp is the MPF-102 acts like an old fashoned tube pre. High impedance in, meduim impedance out. The D-104 element gives very nice frequency response when it isn't loaded down by a lousy preamp. The original amplified Astatic mic stands used bipolar transistors. Those have too low of an input impedance. If you choose to keep the original amp look at the schematic. The mic gain pot adjusts the voltage. Be careful not to exceed the available current at your mic jack. It might be tiny.

Have fun!

 

[w8eeo]

When you have a few minutes it might be interesting if you would check a ham radio home page at: W2AEW's Web-Shack, www.dorkage.com
Alan W2AEW has one of the best solid state pre-amps that I've seen which includes controls for fine tuning to get balanced output over the frequency range of the d-104.
Also, on his page he has a link to some good information by another ham ND2M.

 

[HiDef]

I'm not quite sure that op amp chip has a high enough input impedance to take advantage of the entire frequency response of a crystal cartridge.

OP296GP pdf, OP296GP description, OP296GP datasheets, OP296GP view ::: ALLDATASHEET :::

The internal schematic shows bipolar transistors on the inverting/non-inverting inputs. Bipolar types are not high impedance input.

Normally a tone control is not needed with these mics. Maybe the tone circuit is trying to make up for tone lost due to an improper mic cartridge termination.

If I assume correctly here a different op amp could fix the problem.