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Author Topic: ICOM IC-738 External speaker help...  (Read 2575 times)

Posts: 9

« on: August 18, 2013, 03:06:30 PM »

I recently purchased a pair of 2 way bookshelf speakers for an Icom 738. I cant seem to find the correct connector/soldering configuration to make them work properly. Any help appreciated... Thank you.

Posts: 100


« Reply #1 on: August 19, 2013, 01:11:04 PM »

I recently purchased a pair of 2 way bookshelf speakers for an Icom 738. I cant seem to find the correct connector/soldering configuration to make them work properly. Any help appreciated... Thank you.

Solder the ground wire to the ground on the jack for the radio and the other two wires on the center. Should be good to go. IF, the radio audio output can drive the speakers. Likely better off with one speaker than two.

Posts: 9

« Reply #2 on: August 22, 2013, 03:07:51 AM »

I hadn't considered the audio output being inadequate...that's likely the problem. Thank You.

Posts: 5688

« Reply #3 on: August 22, 2013, 08:37:49 AM »

HiFi/Stereo grade speakers are not typically going to be very efficient.  They are all about using power, supplied by the Audio Power Amplifier, to create faithful reproduction of the full 20Hz to 20KiloHertz audio spectrum. 

These kind of speakers are not of much use for Amateur Radio IMHO, as they will overemphasize both bass and treble frequencies that are not even a part of the intelligence signal found in the communications radios we use on the ham bands. 

That means that the tweeters will be dutifully reproducing frequencies within their range, but those frequencies on the HF bands are going to be the undersired parts of the communication, static, noise, etc. and this can serve to obliterate the part you desire to hear, the spoken voice or the CW note. 

The bass woofer is also overkill and will overemphasize lightning crashes and other lower frequency noised that again are not what we are trying to hear on the HF bands. 

Investigate a "Communications Speaker" that is designed for the purpose of what we do, these are going to take into effect the rather narrow frequency range of the SSB mode, as well as the AM and CW, will tout the needed higher Efficiency spec so as not to overtax the small Audio Output amplifier inside your rig, and the frequency response will be centered on the frequencies of interest for human spoken voice, CW, etc. 


Posts: 4

« Reply #4 on: August 25, 2013, 05:28:36 PM »

I've heard Bob Heil, K9EID, recommend powered studio monitor speakers a number of times (not cheap computer gaming grade stuff).  I believe he uses a small in-line mixer to tailor the audio to his liking.  I've used them for years without a mixer.  If you can turn down your RF gain, turn up your AF gain, and hear hiss or hum, your receiver's AF stages are already lacking.  The quality of RF and IF stages in receivers also varies widely.  If what your receiver is putting out isn't clean, it shouldn't be up to your passive speaker to clean it up.  I've taken a number of commercial external speakers apart (Kenwood, etc.), and seen what they sell as a "good" communications speaker - typically small paper cones with hardly any magnet, in a fancy painted cabinet.  Some had built-in passive LC networks, which do give some bandwidth control, but often only adds more distortion. 

If you do go the route of a studio monitor, check the specs to make sure it is magnetically shielded and RF bypassed to save some headaches, and has a fairly flat frequency response.  Most modern (and many not so modern) radios have a low level AF output which works well with these speakers.  My current receiver has plenty of IF filtering along with DSP processing when I need it, and sounds great on my monitor speakers (dual receivers, so I use the optional setting to split the audio to two channels).  I like my audio clear, so as to hear the subtle effects of propagation, or even QRM.  It has also made it easier for me to understand the accents of some DX stations.
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