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Proof of concept: An $8.01 passive preamp... in a cigar box!

a pre-amp typically feeds an attenuated (and sometimes equalized, filtered, or otherwise processed) signal to a power amplifier. This one, being passive, can only attenuate (e.g., the very high level line output of a CD player, to control its volume).

This little gizmo can also be used as a "pad" or "trimmer" for a single component (given its low cost) - to attenuate the output of a "loud" component in one's system and thus "match" it with other components in one's system - so that the volume level is relatively consistent from input to input (e.g. CD, phono, tuner, etc.)
 
Thinking about making one of these myself. Are Alps Blue Velvet decent pots to start with? Is 100k still the ideal value?
 
Sorry to crap on this thread, but how is a pot in a box with a couple of resistors a "design"? I built one of these back when I was in secondary school (high school for Americans) to use an early Philips CD player with a 150w Maplin MOSFET amp kit.

Lee.
 
leesonic said:
Sorry to crap on this thread, but how is a pot in a box with a couple of resistors a "design"? I built one of these back when I was in secondary school (high school for Americans) to use an early Philips CD player with a 150w Maplin MOSFET amp kit.

Lee.
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Why the hangup on terminology, Lee? Is it because it's simple? Good design is simple, man! :-)

But you may be right: design is probably too strong a word for it. I didn't spend a lot of time designing it, and neither did Lorne or ashok before me or even Harry Haller, probably, for that matter...

It's really more of a "formula" and the reference to it as "Haller's design" is about giving credit where credit is due. Haller introduced the formula to much of the online DIY community a few years back in a very good thread. Up to that point, I'm not sure anyone had taken the time to really dissect this little de-err... formula and explain it in detail.
 
Redboy said:
Why the hangup on terminology, Lee? Is it because it's simple? Good design is simple, man! :-)

But you may be right: design is probably too strong a word for it. I didn't spend a lot of time designing it, and neither did Lorne or ashok before me or even Harry Haller, probably, for that matter...

It's really more of a "formula" and the reference to it as "Haller's design" is about giving credit where credit is due. Haller introduced the formula to much of the online DIY community a few years back in a very good thread. Up to that point, I'm not sure anyone had taken the time to really dissect this little de-err... formula and explain it in detail.
Click to expand...

I wasn't criticizing the use of a cigar box for a preamp, that's WAAAY too cool. I just wondered about the parts inside, and how a pot and a couple of resistors counts as a "design".

I seem to be turning into the collector of old and defective NAD 3020 amps, and bringing them back to life. I would like to "design" a power amp based on the 3020, but who want's a 20wpc power amp? Aha! My "design" would use paralleled output transistors and higher supply rails to produce more watts per channel. But does this count as a design? All I'm doing it reworking the original design. I'd like to be able to design new circuit boards for it, but I can't seem to find any software that's easy to use, or boards that are cheap to produce.

Lee.
 
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