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Does GL1500 AM radio sound slightly distorted?

  • Yes I hear some distortion on audio peaks.

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  • I can't really tell but AM sounds OK to me.

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  • I can tell and my AM reception is really clean.

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  • I don't listen to AM.

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2006 Wing, 1989 Wing, Past: Honda Elite, Suzuki 450, Honda VT500, 84Wing
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Hi,

Has anyone with a golden ear noticed distortion on the AM radio in the gl1500? It adds a garble to the audio peaks which is most noticeable on speech. I like AM for the sports and talk up here. FM in this territory sucks noodles.

I have traced this on mine to what Panasonic calls the noise "branker" circuit. It is really "noise blanker".

I notice it gives a crackling sound to the audio which is pretty annoying. I am probably going to put a bypass switch on it so it sounds better when parked and I am listening to the ball game. However, I tested the radio with the noise blanker bypassed and while the audio is much cleaner there is static from the sparkers with the engine running. So it works for what it is designed for but at the expense of the fidelity of the AM audio.

Now has anyone else noticed the same thing now that I've pointed it out?? I want to figure out if the radio is misbehaving or that's the best it can do.

BTW the chip, Hitachi HA 12429, that is used for a noise blanker is not available and I cannot find a data sheet on it to even know what's in it. However the circuit it's in is fairly sophisticated so Panasonic spent some time on this.

Other than that the radio performs very well as far as reception goes. I'm in VT and listen to WFAN 669 out of NY after the sun goes down clearly.

The sound quality is not by any means superb, merely or barely adequate, IMHO. Being 22 years old I'm sure the radio will benefit from new capacitors in the audio path but I'm putting that off until the winter which should clean that up quite a bit. I want to extend the high end.

I did patch in a jack for the Ipod or sat radio and that seem to go well. May add an outboard amp system further down the road. Just want it to sound clean.
 

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Similar to your statement about the old radio in need of caps... I would imagine that RF sections have drifted out of peak some time ago (111k miles is a lot of vibration). Likely too, the coupling (through T8) of the IF into the HA12429 could be out as well...

Dimes to doughnuts, I'd recommend a good tune/tweak before working at a bypass solution... at least give the radio a chance to perform as designed. There's gotta be a half dozen x-formers in the AMrx path that would be in a questionable state of alignment after 22yrs and 111k miles of rattling about.
 

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2006 Wing, 1989 Wing, Past: Honda Elite, Suzuki 450, Honda VT500, 84Wing
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Discussion Starter #3
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You have a great point. However without a generator I'm not going to attempt an alignment. The sensitivity of the AM radio is very good so I don't think it is too far out.

I did tweak T8 for max output which is all I'm sure you can do with it. But I have no info on how that chip or circuit works. But what I'm hearing sounds like crossover distortion or clipping or assymetric demodulation but the scope says otherwise. However, bypassing the circuit cleans it up very nicely. So there is some sort of non linearity that is a byproduct of what ever is done to clip the impulse noise from the sparkers.

I hear a similar distortion on my S38 Hallicrafters with the noise limiter in which is a couple of 1/2 wave rectifiers (6H6 double diode octal tube) biased to chop the tops off the wave form at a certain level.

I just want to know if this is a design fault and is widespread or should I keep trying to fix it.

Have you noticed the same on yours? You can hear it plainly on accessory.
 

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I get no clipping on the AM Section of either of the radios here. However, DX reception from south of the boarder here does have a few stations that seem to over-compress and/or clip at the source (doesn't seem to be your issue if you can kill the NB and remove the clip).

I'd suspectsomething od like a low IF feed to the HA12429 that allows the AF to peak/swamp circuit since the device is a differential amp. There should be a Ham or local Tv/Radio shop that could help you assure that the radio is dead-on to see if you're chasing ghosts. Perhaps a quick call to the folks at SierraMC could yeild good results as well.
 

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2006 Wing, 1989 Wing, Past: Honda Elite, Suzuki 450, Honda VT500, 84Wing
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Discussion Starter #5
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What you are describing from the sotb stations is how I could describe the sound I get. Do they sound that way on non Honda radios?

Do you have a clear print of the schematic of the section around the HA12429? My scanned copy is not clear as to the pin functions of the chip. Do you have a data sheet for it? I can't find a data sheet. I think it was specially made for this radio and the data sheet never published.
 
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