K3 Harmonic Distortion

[Paul Fletcher]

Joe Subich, W4TV-3 wrote

The solution is simply not pushing the output gain and keeping
the output under 1V peak and use high impedance devices.  With
the speaker amplifier 800 mW into a 16 Ohm speaker shows less
than .01% THD+N - if more audio is necessary 1V peak will easily
drive a good quality 100 watt per channel stereo system.  With
Line Out, 1V peak is plenty for good s/n soundcard operation.

73,

   ... Joe, W4TV
   

The problem I have with all of this is that my K2 doesn't exhibit this issue at all. On my K3 I can clearly hear distortion/harmonics on SSB at moderate volumes through the cans in my Heil headset. In spec or not in spec, it simply shouldn't happen. Elecraft sell the Heil headset marketed for their radios and if headphone impedance mismatch is an issue then surely they wouldn't sell it?

A local fellow K3 owner does not hear the effects I hear with the same set up so it's down to hearing response. The issue is real, not everyone hears it.

The debate about THD etc. is all valid but regardless of this I still hear it and it drives me nuts. The only solution I've found is to run with the AF gain down when listening on cans which might be OK unless I'm in a noisy environment which is why I'm wearing cans and need to run more gain. The irony of this is that I can avoid the problem when it isn't a problem.

Sorry if this has appeared to be a rant but I feel that this is very much a real issue that does not affect everyone. That doesn't mean it shouldn't be addressed.

Also, solving the problem by getting closer to my maker is not amusing  I waited long enough for the radio in the first place.

Cheers,
Paul M1PAF

[Julian, G4ILO]

The measurements that have been made seem to suggest that the problem is not regular distortion or clipping. I am wondering if it is some kind of quantisation effect due to the fact that the signal processing is digital or analog? I am thinking of the fact that there are people who claim that vinyl (analog) LPs sound better than CDs, and FM radio sounds better than DAB.

Personally I find it hard to understand what the complaints are about. SSB signals usually have quite a lot of distortion in any case, due to compression and ALC and the fact that they are transmitted through an amplifier whose response would certainly not be described as "linear" by any hi-fi buff, not to mention any multipath distortion effects introduced by the ionosphere. It's hard to imagine what the K3 could be doing to the signal to make it sound worse. I just don't expect hi-fi audio when listening to the ham bands.

Perhaps the K3 is allowing you to hear the original signal "warts and all", much as a top-end hi-fi would make recordings that were acceptable on average equipment sound unpleasant? I do find the K3 audio to have rather too good a frequency response, and so on mine I have used the RX equalization to cut the topmost frequency by -16dB and the next one down by -8dB, which to my ears gives a much more restful sound.

[NZ0T]

This may be a glass half full response but being an old hearing impaired guy has it's positives:

1.  Ignoring XYL when needed and excusing it by pointing to hearing aids.
2.  Sleeping like a baby every night with said hearing aids removed.
3.  Not hearing any distortion in my K3.

Life is good

73,  Bill NZ0T

Julian, G4ILO wrote

The measurements that have been made seem to suggest that the problem is not regular distortion or clipping. I am wondering if it is some kind of quantisation effect due to the fact that the signal processing is digital or analog? I am thinking of the fact that there are people who claim that vinyl (analog) LPs sound better than CDs, and FM radio sounds better than DAB.

Personally I find it hard to understand what the complaints are about. SSB signals usually have quite a lot of distortion in any case, due to compression and ALC and the fact that they are transmitted through an amplifier whose response would certainly not be described as "linear" by any hi-fi buff, not to mention any multipath distortion effects introduced by the ionosphere. It's hard to imagine what the K3 could be doing to the signal to make it sound worse. I just don't expect hi-fi audio when listening to the ham bands.

Perhaps the K3 is allowing you to hear the original signal "warts and all", much as a top-end hi-fi would make recordings that were acceptable on average equipment sound unpleasant? I do find the K3 audio to have rather too good a frequency response, and so on mine I have used the RX equalization to cut the topmost frequency by -16dB and the next one down by -8dB, which to my ears gives a much more restful sound.

[David Cutter]

I haven't done the sort of testing that you must do for your applications,
but I've used the OEP8000 transformers in several applications with good
results for speech only.  I've no idea of its high frequency response.  They
are tiny in comparison.
http://www.oep.co.uk/admin/UploadDocuments/OEP8000.pdf

David
G3UNA

>
> I've ordered a couple of TTC-108 transformers today and will run some
> experiments with them over  the next week or so. I've looked at similar
> transformers developed for modem and telephone line coupling, but not the
> TTC-108 specifically, when trying to find a cheaper output transformer to
> use with the Softrock Lite receivers. There, the emphasis was more on high
> frequency response, up to 100 KHz, but distortion was also a major issue.
> The solution of choice in my opinion for the Softrock receivers turns out
> to be a MILSPEC Triad transformer, SP-70, with excellent frequency
> response and quite low distortion. In single lot prices, an SD-70 costs
> about four times as much as a TTC-108.
>
> Jack
>
>

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[Jack Smith-6]

David:

Even a rather poor transformer improves significantly when driven by a
"zero ohm" source such as an op amp. The typical modem line transformers
that are spec'd at 0.5% THD, for example, come in one to two orders of
magnitude better when driven by a low impedance source. In fact, it's at
the point where my lowest distortion audio generator (HP 200CD) isn't  
good enough to measure a $4 transformer when driven by an op amp. I'm
generator limited at -63 dB at the moment.  I hope to improve that
measurement floor in the next week or so.

Driving the same transformer with a 600 ohm source Z brings you back to
the 0.5% THD range.

It's all quite interesting and reminds me again that "it's not what you
don't know that's the problem; rather it's what you think you know that
bites you in the backside."

Jack


David Cutter wrote:

> I haven't done the sort of testing that you must do for your
> applications, but I've used the OEP8000 transformers in several
> applications with good results for speech only.  I've no idea of its
> high frequency response.  They are tiny in comparison.
> http://www.oep.co.uk/admin/UploadDocuments/OEP8000.pdf
>
> David
> G3UNA
>
>>
>> I've ordered a couple of TTC-108 transformers today and will run some
>> experiments with them over  the next week or so. I've looked at
>> similar transformers developed for modem and telephone line coupling,
>> but not the TTC-108 specifically, when trying to find a cheaper
>> output transformer to use with the Softrock Lite receivers. There,
>> the emphasis was more on high frequency response, up to 100 KHz, but
>> distortion was also a major issue. The solution of choice in my
>> opinion for the Softrock receivers turns out to be a MILSPEC Triad
>> transformer, SP-70, with excellent frequency response and quite low
>> distortion. In single lot prices, an SD-70 costs about four times as
>> much as a TTC-108.
>>
>> Jack
>>
>>
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[Joe Subich, W4TV-3]

Julian,

> The measurements that have been made seem to suggest that the
> problem is not regular distortion or clipping.

I disagree.  Every set of measurements I have made shows the
speaker and headphone amplifiers in the K3 are very clean
right up to the point that they begin to clip.   Those who
can not get sufficient "clean" audio should be looking for
more efficient headphones or higher power external amplifiers.

73,

   ... Joe, W4TV
 

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Julian, G4ILO
> Sent: Thursday, September 04, 2008 5:20 AM
> To: [hidden email]
> Subject: RE: [Elecraft] K3 Harmonic Distortion
>
>
>
> The measurements that have been made seem to suggest that the
> problem is not regular distortion or clipping. I am wondering
> if it is some kind of quantisation effect due to the fact
> that the signal processing is digital or analog? I am
> thinking of the fact that there are people who claim that vinyl
> (analog) LPs sound better than CDs, and FM radio sounds
> better than DAB.
>
> Personally I find it hard to understand what the complaints
> are about. SSB signals usually have quite a lot of distortion
> in any case, due to compression and ALC and the fact that
> they are transmitted through an amplifier whose response
> would certainly not be described as "linear" by any hi-fi
> buff, not to mention any multipath distortion effects
> introduced by the ionosphere. It's hard to imagine what the
> K3 could be doing to the signal to make it sound worse. I
> just don't expect hi-fi audio when listening to the ham bands.
>
> Perhaps the K3 is allowing you to hear the original signal
> "warts and all", much as a top-end hi-fi would make
> recordings that were acceptable on average equipment sound
> unpleasant? I do find the K3 audio to have rather too good a
> frequency response, and so on mine I have used the RX
> equalization to cut the topmost frequency by -16dB and the
> next one down by -8dB, which to my ears gives a much more
> restful sound.
>
> -----
> Julian, G4ILO. K2 #392  K3 #222.
> http://www.g4ilo.com/ G4ILO's Shack  
> http://www.ham-directory.com/ Ham
> Directory    http://www.g4ilo.com/kcomm.html KComm for
> Elecraft K2 and K3

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[P.B. Christensen]

>  "As near as I can see from tracing from one sheet to another, U29, a
TLV320ACC23 DAC with integrated headphone amplifier drives the TTC-108
LIN OUT transformers directly. Headphone and speaker audio, in contrast,
are derived from a second TLV320 DAC driving a LM4950 amplifier for
speaker output and an LM4811 for headphone output..."

Jack,

I am coming into this discussion a bit late, so my apologies to all for any redundancy.  I believe the device listed as U29 on the K3 schematic may be a mis-print and my best guess is that's it's the Texas Instruments TLV320AIC23 -- as is the case with U7.

The device's H/P output (presumably used for the LINE OUT function) is rated to function down to nearly a zero-ohm load.  

http://focus.ti.com/lit/ds/slws106d/slws106d.pdf

By contrast, the device's line-level output (unused on U29) is specified to function into a Z of no less than 10K-ohm.  So, absent any large variation in noise level between the two outputs, Elecraft's choice of using the H/P output was a wise one since the transformers can be driven by a very low-Z.  However, currently the TI device is coupled to the transformers with 600-ohm built-out resistors.  

Once you receive your TTC-108 transformers for testing, it would be an interesting exercise to incrementally change the value of the build-out resistors from a low-Z source -- all the way down to zero, and note the effect of THD/IMD sensitivity as a function of driving source Z.

It would be an even more interesting exercise to run the identical test using the Triad transformer you mentioned as well as the Holy Grail of all audio line transformers, a Jensen type.

Paul, W9AC

[KK7P]

> ...I believe the device listed as U29 on the K3 schematic may be a
> mis-print and my best guess is that's it's the Texas Instruments TLV320AIC23
> -- as is the case with U7.

The schematic is correct, U29 is a TLV320DAC23.

73,

Lyle KK7P

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[P.B. Christensen]

Hmmm....my schematic shows TLV320ACC23 for U29.

Paul, W9AC

----- Original Message -----
From: "Lyle Johnson" <[hidden email]>
To: "P.B. Christensen" <[hidden email]>
Cc: <[hidden email]>
Sent: Friday, September 05, 2008 1:22 PM
Subject: Re: [Elecraft] K3 Harmonic Distortion

>> ...I believe the device listed as U29 on the K3 schematic may be a
>> mis-print and my best guess is that's it's the Texas Instruments
>> TLV320AIC23
>> -- as is the case with U7.
>
> The schematic is correct, U29 is a TLV320DAC23.
>
> 73,
>
> Lyle KK7P
>
>

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[KK7P]

Paul Christensen wrote:
> Hmmm....my schematic shows TLV320ACC23 for U29.

I see that, too.  The "D" is missing.

Lyle
>

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[Rich]

I am not an audiologist (?) but isn't a harmonic that is 45db below the fundamental tone essentially non-detectable to normal hearing?  Kind of why the harmonics of a RF carrier are to be 40dbs down.

Rich

[Jim Brown-10]

On Fri, 5 Sep 2008 17:51:42 -0700 (PDT), Rich wrote:

>I am not an audiologist (?) but isn't a harmonic that is 45db below the
>fundamental tone essentially non-detectable to normal hearing?

It depends on the order of the harmonic. There are studio processors that
INTENTIONALLY generate 2nd harmonic and add it to the signal. The control
that adjusts the level is called "warmth." :)  3rd order distortion is more
audible and more objectionable. Higher orders become increasingly more
audible and ojectionable, primarily because they are less musical!

BTW -- the science of this is called physhochoacoustics -- the study of how
we hear and perceive what we hear, and much is known about it. It is one of
many disciplines that are part of the Acoustical Society of America, of
which I am a member.

73,

Jim K9YC


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[David Woolley (E.L)]

Rich wrote:
> I am not an audiologist (?) but isn't a harmonic that is 45db below the
> fundamental tone essentially non-detectable to normal hearing?  Kind of why
> the harmonics of a RF carrier are to be 40dbs down.

The transmitter limits are legislative/engineering compromises.  They
reflect what is achievable at an acceptable price.  For most amateur
radio operators, at the receiving end, one would want a limit
independent of output power and maybe 10dB below sky noise, in 10 Hz, at
the boundary of the transmitting site.

Even unintentional transmitters are allowed a lot more than that by the
legislation.

As transmitters, amateurs would not want such limits, as they would make
stations prohibitively expensive, or limited to QRPP.

Note that amateurs experiment with ultra-low bandwidth transmissions, so
in some case, one might want 10dB below sky noise in 10mHz, or even 1mHz
(m used correctly).

--
David Woolley
Emails are not formal business letters, whatever businesses may want.
RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.
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