I re-analyzed my amps. My setup is a bit different, but I doubt the differences are due to our setups. I'd trust either way of doing it. I have two of these amps, so I started with the first one, and played with the knobs until the response curve was within +/- 0.5 dB of flat, shown by the blue curve.
Next, I measured the second amp with the same knob settings, and got the orange curve. Also, the two amps have different amounts of overall gain -- one is louder than the other when they're both dialed to the same volume level, something I've always compensated for by ear.
Then I re-adjusted the second amp to make it flat too, the green curve.
Picture shows the two amps and their flat settings, which I will mark with a Sharpie. I'm not particularly worried about a 2 dB difference, since "flat" is not a holy grail for me. What I've found is that "flat" is just a useful starting point. Also, I'm just curious about this stuff.
My setup is a PC audio adapter with software that I wrote. My goal was to create textbook-quality curves, so I can see subtle variations.
Now, why are these amps different? They were made at different times, in different countries, since GK moved their production to China and then back to the US. Also, minor design changes throughout a long production run are not terribly uncommon. There are some other differences. The older amp uses a Vactrol in its limiter circuit, and the newer one, a JFET gain control circuit. Both have the "vintage IcePower sound," and Bob's layouts are always works of art.
Next, I measured the second amp with the same knob settings, and got the orange curve. Also, the two amps have different amounts of overall gain -- one is louder than the other when they're both dialed to the same volume level, something I've always compensated for by ear.
Then I re-adjusted the second amp to make it flat too, the green curve.
Picture shows the two amps and their flat settings, which I will mark with a Sharpie. I'm not particularly worried about a 2 dB difference, since "flat" is not a holy grail for me. What I've found is that "flat" is just a useful starting point. Also, I'm just curious about this stuff.
My setup is a PC audio adapter with software that I wrote. My goal was to create textbook-quality curves, so I can see subtle variations.
Now, why are these amps different? They were made at different times, in different countries, since GK moved their production to China and then back to the US. Also, minor design changes throughout a long production run are not terribly uncommon. There are some other differences. The older amp uses a Vactrol in its limiter circuit, and the newer one, a JFET gain control circuit. Both have the "vintage IcePower sound," and Bob's layouts are always works of art.
