[Yaesu] RE: FT-1000 60 Hz Hum Problem

[Marty Rosenzweig <marty@cmn.net>]

Greetings,
Well Marinos gets the grand prize today! I tried a pair of Koss phones 
and no hum. The Koss measured about 240 ohms...I know that's DC 
resistance, not impedance, but it does indicate a much higher impedance 
than the Yaesu phones which measure about 34 ohms DC. A couple of 220 
ohm resistors in series with each "channel" and the hum is gone with a 
somewhat higher AF gain control position than without the resistors. 
Interesting that Yaesu doesn't design phones appropriate for (at least) 
this radio (or maybe not designing radios for common low impedance 
phones!), and it also explains why some FT-1000 users don't experience 
the hum at all.
I expect it's all an exercise in technology and the radio really doesn't 
perform any better now, with the modification, but the knowledge is 
worth the effort!
That brings me to the question of what people like in headphones, 
particularly for the 1000, I guess? I bought the Yaesu phones to 
optimize voice and, primarily, CW response  as opposed to the wide 
bandwidth of high quality audiophile phones. They're also much lighter 
than the Koss I used to use.

Any ideas?

Thanks to everyone who responded and ain't the Internet (and this list) 
a great resource?

73,

Marty
WO0Q


Marinos Markomanolakis, M.D. wrote:

> Dear Marty,
>
> My 1000D has the same low hum noticeable only when using the 
> headphones and having the AF pot all the way CCW. I have seen this in 
> other rigs too TR7, Tube radios etc and it is related to the use of 
> low impedance headphones.
> If you try using headphones with low (16 Ohm) impedance that either 
> have volume control or you can add a variable resistance in series 
> with them before going to the radio, you will see the problem 
> disappearing when you increase the resistance and returning when going 
> back towards the 16 Ohm.
> Then you can check the added resistance value with a multimeter and 
> add a small (or 2 one in each channel) resistor within a Radio Shack 
> large stereo plug and then connect your headphones through it to the 
> 1000D.
> Of course in doing so you will have some attenuation in your audio but 
> the hum will be gone.
>
> Hope this helps,
>
> 73,
> Marinos, sv9dru/w4 or KI4GIN
>
>
> > Greetings,
> > I have a 1992 FT-1000 which, with the RF and AF gain CCW (off) and
> > everything disconnected from the radio except a pair of Yaesu
> > headphones, has a very noticeable 60 Hz hum (about 5 mv on the scope,
> > both channels (ie., main and sub in "stereo").


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