On Sun, 2006-10-15 at 11:57 -0400, Mark DeBord wrote:
> I am amazed at all the different answers to this question. Some are hearing
> the distortion, others are not; some in their headphones (in only one side),
> some on the internal speaker.
>
> To add to the list of differences, I hear the distortion with the headphones
> (in both sides) and with an external speaker (Icom SP-20 and the Ten Tec
> speaker), but when using the internal speaker, I can not tell it is there. I
> also can use a communications speaker like the famous Motorola 4 inch
> speakers we all see at the hamfest and the distortion is not as bad. I know
> it is because the narrow bandwidth of the speaker masks the distortion. But
> of course everyone's audio is average.
The Motorola speaker also has quite high efficiency and gets a good
listening level with less audio power. Could be that the different
speakers and different headphones require quite different power levels,
some approaching the voltage or current swing limits of the analogue
audio output stages. Could be that some loads lead those sometimes
quirky ICs to have ultrasonic parasitic oscillations. I'd try an 8 ohm
resistor in series with a 220 pf capacitor across the speaker and
headphone terminals to load any parasitics about 10 KHz. Might be a
magic bullet, won't hurt anything else.
>
> I went to the Ten Tec hamfest and took the Orion with me to get them replace
> the RIT control and discussed with them about the distortion of which they
> will look at that too. I am still waiting to find out what is found (if
> anything).
>
> The distortion is in v2.059 and also the v2.057 (the other version that was
> included with the latest release). However, previous V2 versions and also
> all the V1 versions do not have the distortion.
Which tends to point at the gain distribution and some AGC not quite
protecting the digital parts from over range counts.
>
> It also is curious to me that the AGC was supposedly not touched on v2.057
> according to the release notes, but the distortion is there).
Isn't there at last two AGCs in the radio? One to keep the broad band IF
signal from driving the input ADC into clipping, another in the digital
circuits to level the desired output? Testing with external attenuation
on the antenna should show up problems in the first AGC.
>
>
> My friend has an Orion I also and he can hear the distortion as well on his.
> I had heard others were hearing it on the Orion II as well, but at the
> hamfest, I listened on an O II in the tent and did not hear the distortion
> (they had the external Ten Tec speaker).
>
> So, what is going on that some hear it and others do not? Some say they get
> rid of it by adding hang time. This helps, but does not get rid of the
> distortion.
>
> It is going on 3 weeks now so maybe I will hear from Ten Tec soon on my
> repair of the RIT and will let everyone know if there is any difference with
> the distortion once I get it back. I am wondering with it is possible there
> is slight manufacturing/component differences that is causing the distortion
> in some and not in others.
Try my parasitic suppressor at the speaker connector.
>
> Thanks,
> Mark KA4ICK
>
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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