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Re: [Amps] IM distortion and such

To: "" <>
Subject: Re: [Amps] IM distortion and such
From: "Jim Brown" <>
Date: Mon, 26 Jun 2006 12:18:55 -0700
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On Mon, 26 Jun 2006 13:15:59 -0400, Tom W8JI wrote:

>A good engineer can sort that all out and make good 
>decisions, a bad design would include things that never pay 
>back. One of the best engineered amps on the market was the 
>SB220. It was amazingly cheap for the results, and they had 
>a very good service life when operated according to 
>manufacturing specs. That amp is a prime example of good 
>engineering for the market place. 

EXACTLY!  While I don't know enough about the SB220 to know 
whether you're right about that particular amp, I strongly agree 
that one of the most important components of good engineering is 
spending money where it is needed, and not where it isn't, based 
on the intended use. I live and work in the pro audio world, 
where, for the most part, this sort of philosophy rules.  "No 
compromise" designs result in those $800 hammers for which we 
decry the excesses of government contracts (and $8,000 amps). 
Indeed, there's a whole cottage industry of audio tweak vendors 
selling serpent lubricant to those who think they're buying the 
ultimate -- magic cables to connect loudspeakers, $10,000 power 
amps that might put out 100 watts, etc. 

Likewise, a wise buyer chooses a product based on his/her own 
needs, not some wild ideal. If that amp is going to sit on my 
operating shelf and see the light duty you describe, I can buy an 
amp based on that sort of design tradeoffs. On the other hand, if 
I'm going to truck it around on DXpeditions, or expect it to see 
heavy duty during contests, and want very low distortion so that I 
don't wipe out other operating positions in a multi-op station, I 
ought to belly up to the bar for a more conservative design. 

In an earlier post, you described several nice engineering moves 
that resulted in better performance at a good price. Another 
example are Bill Whitlock's excellent small signal audio 
transformers, sold under the Jensen name. Inherently, a good audio 
transformer will act like a 2-pole low pass filter, but Bill has 
tweaked his design to optimize the strays so that it becomes a 3-
pole filter with a -3 dB point at about 300 kHz. 


Jim Brown K9YC

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