[R-390] Headphone recommendation

[Roger Ruszkowski]

Ed,

Awesome solution to this problem.

Roger AI4NI




-----Original Message-----
From: djed1 <djed1 at aol.com>
To: flowertime01 <flowertime01 at wmconnect.com>; r-390 <r-390 at mailman.qth.net>
Sent: Fri, Nov 29, 2013 1:05 pm
Subject: Re: [R-390] Headphone recommendation


As Roger noted, the R-390A was designed for 600 ohm headphones.  If you want to use 8 ohm phones, you need a transformer- or do a simpler trick which I discovered.
The phones are fed off the local audio line using a resistive divider (6.8K and 820 ohms).  When you use low-Z phones in parallel with the 820 ohm resistor, you load the divider down and reduce the voltage by about a factor of 10.  What I did was to add a resistor in parallel with the 6.8K to increase the voltage by about a factor of 10.  Fortunately, both ends of the 6.8K resistor are brought out to the terminal strip.  So I put about a 1K resistor across terminals 6 and 8.  This resulted in good audio to my low-Z phones.  This reduces the local audio a bit, but is not a problem (assuming you have a transformer on the speaker)
Ed  W2EMN

 

 

 

-----Original Message-----
From: Roger Ruszkowski <flowertime01 at wmconnect.com>
To: r-390 <r-390 at mailman.qth.net>
Sent: Fri, Nov 29, 2013 5:47 am
Subject: Re: [R-390] Headphone recommendation



Jeff,

Pick your self up a small (5watt) line voltage transformer for
speakers. Radio Shack use to stock them.

These will transform the 600 ohm local from the 
receiver to 8 ohms in todays head phones. The line out of the
receiver is a 1/2 watt. Some what less at the front panel head phone jack.

You can put the transformer on the back of the receiver or make up a small
patch box on a cord with another jack in the patch box that matched the modern
head sets of today.

You can run what ever you like in 8 ohm  head sets that way.
Many more options than good hi impedance head sets and better
frequency response if you are going to listen to music of short wave AM.

A real op would never hang a phone over his ear.
And never imagine sticking a bud in his ear.
When the day is done you would still like to have your hearing intact.

I can not imagine wearing the muff style phones. while spinning the knobs on an 
R390
Just my choice.

I like my 50's vintage high impedance head phones.
My two sets are tight on my big head but I wear them on my temples and do OK.

Roger AI4NI


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