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In Reply to: RE: to be clear... posted by Tre' on January 16, 2017 at 08:10:11
To make this work, we must also question the level of distortion, below which, we have "fidelity". NO amplifier, even instrument amp, is perfect, so where is it "good enough"? And again, I'd say at the output levels I use, I'm guessing distortion is actually very low. In this amp I've also eliminated two prior pre-amp stages and thus, eliminated the distortion from them. Introducing feedback isn't something I'd see doing to help distortion at the end of the day. I might do it to improve damping factor, however.
Follow Ups:
If you are at or below 0.3% THD, when full power is produced, you definitely are good to go. Only folks with the very best hearing can(?) detect that, when the driving signal is a pure sine wave. Under 1% is probably OK, when a complex music waveform is present.
IM distortion is another matter, as it is much more irritating than harmonic distortion.
Eli D.
I attempted to measure output power and distortion (distortion on my old Leader LDM 171). I got 7.6w out just prior to clipping. And IF I used the distortion meter correctly, it was about 2.3% distortion. Of course that made me suspicious that I was doing something wrong. Power was too low, distortion was too low. I figured 7 to 8 watts was what I'd get with triode wired EL84's so I took a peak under her skirt and sure enough, sometime long ago I converted to triode. As for the distortion reading, I'm not at all sure I did that correctly, seems like you should put a test signal in both the amp and analyzer but the instructions don't say anything about that. I also don't know if the amp should be on a dummy load, but I assume so. Anyway, distortion is suspect to say the least.
"seems like you should put a test signal in both the amp and analyzer"
No, you just match the frequency with the distortion analyzer. You did it right.
You have to deduct the distortion of your generator to get an accurate number. It's complicated but the manual should walk you through it.
IMO 2.3% is high considering that it's a PP circuit and all the even ordered distortions should be canceling.
IMO 2.3%, made up of 3rd and 5th and (God forbid) 7th, will sound much worse than 2.3% of 2nd.
BTW My objection to kitch29's post was his redefinition of the term "distortion". To me he said that "as long as it sounds good to the listener then it can't be described as distorted".
That's just not true. What if the listener has no idea what the recording should sound like? Personal preference for a particular type of sound is not the same as low distortion.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Thanks. My signal generator is an old and cheap one, and I don't have a manual, but I'll take a look on line and see what I come up with.
The manual for the distortion analyzer should describe the mathematical process for accounting for the generator distortion.
Run the generator straight into the distortion analyzer to get your base line distortion and then work from there.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
nt
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