[Elecraft] K3 Hissy and Noisy Audio

[Jay Bromley]

Hi Joe,

You wrote:
>> > Please NO!  I already run RX Audio bands 1 and 2 at -16 dB to
>> > eliminate excessive bass - no more bass, please!

You also wrote:
> You won't see much on the headphone output because of the 10 uF
> coupling capacitors. The effect is quite obvious on both the
> speaker output and the line output (if you have made the line
> out modification [R19/20] in K3AF Mod Rev 3).
>
> If you replace the 10 uF headphone coupling capacitors with
> 330 uF caps as recommended by W9AC the headphone output will
> more like a good external speaker.

On Paul's mods, I've been there and done that on both a stock K3 and a 
modified one.  I still don't hear the excessive bass you were mentioning and 
more important I can't measure it!  I went back this morning and measured 
the speaker out and for that matter all other outputs for fun.  When I go to 
RX EQ bands 1 and 2 and put them at -16 dB I see a gentle roll off starting 
at 200 hz.  However I see the same gentle roll off at zero dB on RX EQ bands 
1 and 2.  On the line output I see a little less bass than the other outputs 
and I would expect this since it has a transformer in line that the speaker 
and phone output doesn't.  In fact I don't see a change if I go crazy 
boosting RX RQ bands 1 and 2.

Joe, I am not complaining mind you, I am just not seeing this excessive bass 
you posted in your message at zero or a huge reduction in bass response 
at -16 on bands 1 and 2.  LO cut is still at 0, I am still on LSB at 2.8 BW.

So I am still must be missing something here.  BTW this K3 has all the AF, 
speaker mods, per the K3 Enhancement and Application Notes page.  Also I do 
run from time to time a nice bookshelve and external amp speaker system. 
The walls are very safe here from excessive bass response.

73 de jay/w5jay..




>
>> Looking at Spectra right out of the Phones output, I don't
>> see where bands 1or 2 do all that much in lowering K3's bass.
>
> You won't see much on the headphone output because of the 10 uF
> coupling capacitors. The effect is quite obvious on both the
> speaker output and the line output (if you have made the line
> out modification [R19/20] in K3AF Mod Rev 3).
>
> If you replace the 10 uF headphone coupling capacitors with
> 330 uF caps as recommended by W9AC the headphone output will
> more like a good external speaker.
>
> 73,
>
>   ... Joe, W4TV
>

>>
>>
>> Hi Joe,
>> Looking at Spectra right out of the Phones output, I don't
>> see where bands
>> 1or 2 do all that much in lowering K3's bass.
>>
>> Having the rig on SSB using the 2.7 Khz filter, the "Lo" on
>> 0, I see no
>> change on bands 1 and 2 when I set them to -16.  What I am
>> missing here?  I
>> have never seen or heard too much bass in the K3.
>>
>> I did a plot at 0 dB, one at -16 on band 1 and another one on
>> -16 on band 2
>> if anyone would like to see them.
>>
>> 73 de w5jay/jay..
>>
>>
>>
>> >
>> >> Perhaps NR could also be improved with more low
>> >> frequencies in the passband.
>> >
>> > Please NO!  I already run RX Audio bands 1 and 2 at -16 dB to
>> > eliminate excessive bass - no more bass, please!
>> >
>> > The hiss many seem to be complaining about is broadband
>> noise in the
>> > audio (speaker) and/or headphone amplifier.  It is more noticeable
>> > when driving low impedance loads (8/16 Ohm) due to the
>> relatively high
>> > gain (14 dB) of the speaker amplifier and the high
>> frequency boosting
>> > effect of the 33 pF capacitors in  parallel with the gain setting
>> > (feedback resistors).
>> >
>> > 73,
>> >
>> >   ... Joe, W4TV
>> >
>> >
>> >
>> >>
>> >>
>> >> I concur with what has been said regarding the "hissy" audio.  The
>> >> receiver audio seems to be on the mid-range to high frequency side
>> >> without enough low frequencies in the passband.
>> Experiments with RX
>> >> EQ apparently have not done anything to eliminate this hiss, but
>> >> maybe the firmware can be adjusted to increase the low-end
>> response
>> >> of the receiver passband.  If this doesn't work, maybe a component
>> >> change is in order.
>> >>
>> >> I also think the noise reduction is too sharp in both SSB and CW.
>> >> Perhaps NR could also be improved with more low frequencies in the
>> >> passband.
>> >>
>> >> Roy Morris  W4WFB
>> >> K2 #2225
>> >> K3 #323