Headset/intercom compatibility

Ken Ibold

Ken Ibold

Final Approach
Joined
Feb 21, 2005
Messages
5,888
Location
Jacksonville, Florida
Display Name
Display name:
Ken Ibold
My Pitts has some trouble with the intercom, which I have been told is due to an incompatibility between the headset(s) and the intercom. The intercom is a Sigtronics SPA-400, which apparently has been modified with what the paperwork calls an ISC load modification. The paperwork for this mod says it is used when the radio connected to it has a low-impedance headphone output (less than 100 ohms). It involves adding a resistor to the headphone audio output circuit. However, I haven't yet traced the wiring and the resistor may have been removed. The radio was changed from a Narco to an Icom A200 at some point.

The symptoms are these: With a passive DC plugged into one station and a Lightspeed 25XL in the other (makes no difference front or back), the intercom volume is marginal (or less) and is lost in the noise at any power setting above about 50 percent. The individual headset volume controls are on max and the radio volume is nearly on max, with marginal volume there, too. I understand this is a noisy airplane, but I've been in noisy airplanes before that had useful communications.

Any suggestions/ideas?
 
Ken Ibold said:
My Pitts has some trouble with the intercom, which I have been told is due to an incompatibility between the headset(s) and the intercom. The intercom is a Sigtronics SPA-400, which apparently has been modified with what the paperwork calls an ISC load modification. The paperwork for this mod says it is used when the radio connected to it has a low-impedance headphone output (less than 100 ohms). It involves adding a resistor to the headphone audio output circuit. However, I haven't yet traced the wiring and the resistor may have been removed. The radio was changed from a Narco to an Icom A200 at some point.

The symptoms are these: With a passive DC plugged into one station and a Lightspeed 25XL in the other (makes no difference front or back), the intercom volume is marginal (or less) and is lost in the noise at any power setting above about 50 percent. The individual headset volume controls are on max and the radio volume is nearly on max, with marginal volume there, too. I understand this is a noisy airplane, but I've been in noisy airplanes before that had useful communications.

Any suggestions/ideas?
Click to expand...

The impedance of the Lightspeed headsets is only 150 ohms when switched to mono mode which is lower than most and I've had trouble mixing them with some other headsets on simple intercom systems like the SPA-400 which drive all the headphones in parallel (and in your case inparallel with the radio output). The intercom you have is really only capable of driving 600 ohm headsets well so IMO your best bet is to get a different intercom. It just so happens that I have a spare PM-1000 II that would solve your problem and you can have it if you promise to take me flying in your Pitts.
 
Sounds (reads?) like a fair bargain to me!
 
SCCutler said:
Sounds (reads?) like a fair bargain to me!
Click to expand...

Maybe not if it involves flying his Pitts to Minneapolis for the ride! (just kidding Ken).
 
lancefisher said:
Maybe not if it involves flying his Pitts to Minneapolis for the ride! (just kidding Ken).
Click to expand...
Well I'm planning OSH in it this year, anyway. Minneapolis isn't THAT much farther, and I can drop in on my sister and ask her for money.
 
Ken Ibold said:
Well I'm planning OSH in it this year, anyway. Minneapolis isn't THAT much farther, and I can drop in on my sister and ask her for money.
Click to expand...
Mandatory night-before stop in Peoria. :):goofy:
 
Ken Ibold said:
Well I'm planning OSH in it this year, anyway. Minneapolis isn't THAT much farther, and I can drop in on my sister and ask her for money.
Click to expand...

Dibs on the ride from OSH to FCM! :D
 
You must log in or register to reply here.
Back
Top