EMRFD Message Archive 1929

Message Date From Subject
1929 2008-08-12 14:54:52 WA0ITP IC Audio Amps. Was EMRFD Fig 1.17 Audio amp
It does look good, as does National's LM4951 and 4861. Nice family of audio
I love this radio stuff !
72, 73 Terry, WAƘITP

----- Original Message -----
1930 2008-08-12 15:31:08 Craig Johnson, AA... Re: IC Audio Amps. Was EMRFD Fig 1.17 Audio amp
Thanks for the interesting discussion.

I agree that an IC would provide the easiest solution for a headphone
driver. For my particular application, however, I am limiting myself
to discrete components, even if the performance is less than I could
get with an IC.

-Craig, AA0ZZ
1932 2008-08-12 22:25:28 Rick Re: IC Audio Amps. Was EMRFD Fig 1.17 Audio amp
Hi Craig and group. This is indeed an interesting discussion. One bit I would like to
interject in the spirit of "Experimental Methods in RF Design" is to keep in mind what is the
experiment. When all you need is a some low distortion audio gain and you don't want to
design the amplifier, there are many good IC choices.

But it is often possible to improve performance over available ICs with an all discrete
design. Several reasons for this are that you can choose which specs to improve and which
to relax, and you are not limited to the on-chip components available to the analog IC
designer. My discrete designs use large capacitors and transformers wherever they offer
an advantage. That permits independent bias circuits with AC coupling between stages,
exceptionally clean bias and power supplies, and just enough current to do the job, as
illustrated in the other gentleman's transformer output class A audio amplifier example.

Also, a cascade of AC coupled single-transistor class A stages may be designed
1935 2008-08-13 20:02:42 Ashhar Farhan Re: IC Audio Amps. Was EMRFD Fig 1.17 Audio amp
in a recent transceiver, i went overboard and plugged in a 'HiFi'
audio module from toshiba. It has a lot of head room with a capability
to deliver 20 watts RMS (TDA 2002). I nearly lost my hearing, when by
mistake, I touched the hot lead of the volume control with my screw

there is a lesson here. better stick to QRP even on the audio side.
You will have to put up with a bit of THD and clipping once in a
while, but it will save you some hearing impairment.

- farhan

1936 2008-08-14 05:05:12 Allison Parent Re: IC Audio Amps. Was EMRFD Fig 1.17 Audio amp
Rick makes some good points. Here are a few other reasons
for building discrete.

Can be made with part on hand at 2AM.

Its is easier to tweak the values for more power, more gain,
and bandwidth can be contoured with feedback.

The latter in receivers is important as there is no sense reproducing
all the hiss above 4khz to overload the ears.


1937 2008-08-14 07:39:56 Tom Hall Re: IC Audio Amps. Was EMRFD Fig 1.17 Audio amp
When making a decision for an audio amp between discrete and IC, sometimes
the decision is easy when the component is free. I was following a recent
discussion on audio distortion in the K3 on the Elecraft reflector and
decided to take a look at the schematic to see just what they were using for
audio. The chip is an LM4950. So I went to
http://www.national.com/pf/LM/LM4950.html to view the specs and found it was
a 3.1W stereo or 7.5W mono IC. Scanning further down the page I saw that you
can order free samples and ordered 3. Within 2 days I had them in my hands.
I figure they will make pretty good amplifiers where current draw is not an
issue. There are two case styles to choose from when ordering samples. I
chose the TS version in a TO-263 case. I cut off the edge connector on a
defunct memory card and mounted the IC by slightly spreading the leads on
the IC. That's about as far as I've gotten but plan to finish it and try it
out this weekend if time permits.

Tom, AK2B

[Non-text portions of this message have been removed]
1938 2008-08-14 07:44:56 Jim Miller Re: IC Audio Amps. Was EMRFD Fig 1.17 Audio amp
take a look at the ti tpa6101a2 or tpa6102a2 depending on your gain needs.


jim ab3cv
1941 2008-08-14 11:43:09 Kenneth Stringham Re: IC Audio Amps. Was EMRFD Fig 1.17 Audio amp

I have never seen more than about a Watt needed for transceiver audio output levels and many times much less is needed.

I agree that we should tailor the audio channel response, but this should be done ahead of the amplifier where we can control all aspects of the passband and BTW, many of the chip amplifiers can be easily adjusted even at 2am with standard parts.

Ken - AE1X
1945 2008-08-14 16:03:53 Jim Miller Re: IC Audio Amps. Was EMRFD Fig 1.17 Audio amp


Pout = 50mW into 16ohms

Iq = 320uA

Isd = 50nA

Vss = 1.6 - 3.6V

8pin soic

i bought some for a project i'm planning but haven't tried them yet.


jim ab3cv
1950 2008-08-15 09:08:53 John Levreault Re: IC Audio Amps. Was EMRFD Fig 1.17 Audio amp
The problem that I see with many of the latest parts is that they're
designed for very low supply voltages. This is not compatible with the
many QRP designs which are designed to run off a 12 or 14V supply. To
further complicate matters, an audio power amp, whether it's driving
headphones or a loudspeaker, draws current, possibly many 10's or 100's
of milliamperes, if not more, on audio peaks. This will cause a lot of
dissipation in any circuitry used to drop the 12V down to 3.6 or 5V. Of
course, switchmode DC-DC converters can help, but their noise is a real

Whether this tradition of 12V radios will continue is anyone's guess.
There's no reason why you can't build a receiver with very high
performance that's powered with a couple of batteries. But once your
transmitter gets above a watt or so, you really do need to consider 12V,
if not more.

Decisions, decisions.

de John NB1I

Jim Miller wrote:

>Pout = 50mW into 16ohms
>Iq = 320uA
>Isd = 50nA
>Vss = 1.6 - 3.6V
>8pin soic
>i bought some for a project i'm planning but haven't tried them yet.
>jim ab3cv
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