An in-line preamp such as the Alctron or FETHEAD is certainly NOT
suitable, if only because they need 48V phantom power.
Why do you think you need a preamp? Have you tried connecting
directly the SM58 to the input? It should work. Now, maybe if it
works but has not enough "juice", you may have to add a preamp,
but you would not need much gain. The SM58 delivers about 2mV at
normal speech level at a distance of about 2ft, so with close
talk, it should be OK for the required 7mV for full excitation.
Le 24/02/2025 à 06:38, Dan KE6PO via
groups.io a écrit?:
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On Thu, Feb 13, 2025 at 02:37 AM, Goran Finnberg wrote:
Is this really the original schematic or a fake
copy.
Unknown. This is one I found from multiple net sources, but the
origin was not stated.?
However, the circuit seemed suspicious, which led to my
question. The FET info makes better sense now, yet the design
purpose is only inferred. I am trying to solve a practical
problem here...
For example:?
?
- Given a dynamic (moving coil) microphone like the Shure
SM58,
- To be used with a Ham Radio like the Yaesu 900,
- The radio includes some signal processing/compression for
the mic input,
- 48V Phantom power in not supplied per se,
but 5VDC is available on the mic connector,
- The radio assumes a balanced mic input and has a 600ohms
Zin,
- The SM58 has a Zout of 300ohms,
- According to the SM58 wiring diagram, the mic cartridge uses
a transformer interface to the XLR connector.
- So, is a preamp needed in such an application and, if so,
what kind of preamp?
Any help here is appreciated.
TIA,
Dan?
