Yaesu FT-101 dynamic mic question
Now I have a dynamic hand mike and when I measure the resistance of the mike element it shows 500 Ohms.
Is it considered a low impedance capsule or high?
In any case, can I use it with this rig? I suspect there will be no real problem, but since there is a JFET input, I want to ask.
Thanks
500 ohms is regarded as low impedance in microphones. Dynamic mike has a coil of very thin wire.
Dynamic mics are around 600 ohms so it would be fine, the JFET amp is 47k input impedance.
But what is going on with J3 pin 2? An electret condenser mic would need power, a resistor to that so maybe Yaesu supports either dynamic or electret?
Hm... and this is shared with the PTT? Weird.
Since you say there will be no problem with the impedance of my dynamic mike, I think I will use this as I have seen some videos where they say the dynamic mikes do not catch up the background noise of the room, but just the voice of the operator.
The capsule seems to me a better quality one than the cheap electrets. I do not know I may be wrong.
But thanks that you mentioned it will work ok with this type of preamplifier.
Just about any dynamic mic will work. Pin 2 is paralleled to the patch input (for other audio sources), pin 3 is the PTT line.
Please remember this is a very nice bit of equipment but it is about 45 years old and in those days a dynamic mic was far more common than electrets, at least on communication equipment because they are immune to high RF field strengths.
Whether or not the background noise is picked up is nothing to do with impedance or microphone technology, it is determined by mic construction and pick-up pattern.
Brian.
My guess that that also, that any mike should work being low or high impedance. The Jfet will not load a high impedance source neither a low one. Now there may be loss due to the impedance mismatch, but does this really matter in this schematic?
Also not that I see the complete schematic, the pin 3 of the mike, seems it is connected directly to the 13.5v through RL-1 coil. Pin 3 seems to be shared with the PTT (J8). When PTT is enabled, this pin is grounded. So I think, why couldn't I use an electret mike and use pin 3 as the VCC for this mike?
Although I would prefer the dynamic capsule like you explained.
Conceptual problem....
If you power an electret microphone from the PTT line, and you ground the PTT line to transmit, you get no sound!
Brian.
Sure, foolish question!
Thanks
Brian I think my 500R capsule will work. See here https://www.ebay.com/itm/YAESU-HAND-...oAAOSwZ~ldlUaI at the third picture it says impedance 500R, which is exactly what my capsule is!
I'm not sure the picture is of an original FT-101 microphone, it looks more like a cheap CB microphone to me.
If you do a search for "PTT Microphone" it should turn up many alternatives, new and cheaper than that one. Consider that the switches in older PTT microphones tend to crackle and often the cables are fragile or broken. To repair an old one costs more than buying a new one.
Brian.
Yes I just repaired an old CB one with cracked plastics, basically soldered them with glue, now it works byt you should not drop this down...
The cost of the old hand mikes is not low, considering also the huge shipping. Further more after the changes in the USPS, they cannot send cheap anymore with a tracking number from USA, so the postage is really high in all items.
I think I will test mine and if it does not work ok, I will order a step up transformer to put inside the mike. But what short of transformer impedance for the primary and the secondary should I choose? I have a TL013 (8R-1K) but I think this won't be suitable at all.
I doubt you will need the transformer at all. 500R DC resistance (post #1) implies the impedance is higher than that so you should be OK. The matching isn't at all important anyway, you can adjust the mic level control to compensate for almost any input.
I might have the service manual for the FT-101 gathering dust somewhere. I have several Yaesu manuals but they have been stored away for many years and I can't remember which models they were for. If I have it you are welcome to it, I don't think I will be needing it in the future, my days of repairing transceivers are long gone.
Hint: add a resistor of 10R or so in series with the PTT switch, it shouldn't stop the relay working but it will help to protect the switch from directly discharging C54.
Brian.
Thanks Brian always helpful!
Is it this one https://servicerepairmanuals.net/rad...ervice-manual/ ? If yes, there is no need to pay the extra postage. But in any case I really appreciate you good will, thanks!
Thanks for the hint on the resistor and I totally agree about the gain compensation.
It is probably the same manual, it says it is scanned from the original Yaesu one. If I remember, its a folder with a large Yaesu logo on the front and maybe 50 pages inside.
Brian.