A good way to approximate the impedance of a set of headphones is to measure
the DC resistance
and multiply the result by 1.5.
I suspect the hum you we are hearing is not from poor power supply filtering.
It's more likely because of
the giant power transformer that's right behind the headphone jack. Yaesu had
to include separate headphone
amplifiers because of the second receiver and they look like an afterthought.
I have always found the best
results when using headphones with around 70ohms impedance.
Dave
WA0ZZG
Message: 2
Date: Mon, 26 Jul 2004 15:24:35 -0600
From: Marty Rosenzweig <marty@cmn.net>
Subject: [Yaesu] RE: FT-1000 60 Hz Hum Problem
To: yaesu@contesting.com
Message-ID: <41057693.5070703@cmn.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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
_______________________________________________
Yaesu mailing list
Yaesu@contesting.com
http://lists.contesting.com/mailman/listinfo/yaesu
|