radix
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EDIT: The LF/HF Filter button was engaged, which caused the bass and treble rolloff. I'm making new measurements of the multitone and gain/THD vs frequency.
I just picked up a 1-owner McIntosh C30 (1985-87). I believe this was their first preamp to use transistor switching instead of relays. I got it from the son of a guy who collected (or should I say hoarded) hifi gear. He said his dad had 6 pairs of L100's. He has the Mc MCD7000, their first cd player, some Cerwin Vega speakers, several tube amps and really a whole garage full of stuff.
For being about 40 years old, it looks in great shape and isn't awful performance. the only physical issue is a loose fuse holder. I think I'll get a rebuild kit and recap it, then we where I am again (anyone have suggestions where to get a rebuild kit, or are the ones on ebay ok?).
Here's some measurements with my QA403 going into the CD input and out from the Main output. Loudness is set to "flat" and the 5-band EQ is disabled. The unit is rated at 0.007% THD 20-20k. The frequency response is supposed to be within 1/2 dB 20-20k.
Here's 1kHz at 0dBV. The volume control is at 50%, which looks to be about unit gain (1 click above 50 is actually a little closer to unity). This actually looks pretty good!
Here's the same thing at 6dBV (2V). Again, pretty nice.
This is with the volume control at 75% (eyeballing it).
And if I go to 75% (1 more click on the volume control), the distortion jumps up. I'm not sure what causes this yet. EDIT: This is likely clipping because the input level (6 dBV / 2V) was too high for more gain.
Here's a multitone. You can see that < 50Hz and > 10 kHz there is a significant rolloff. This is done with the volume control at 50% (about unity gain). EDIT: This is with HF/LF rolloff button engaged.
And here's the gain vs frequency and THD vs frequency charts. Both done at 50% volume. EDIT: This is with HF/LF rolloff button engaged.
I just picked up a 1-owner McIntosh C30 (1985-87). I believe this was their first preamp to use transistor switching instead of relays. I got it from the son of a guy who collected (or should I say hoarded) hifi gear. He said his dad had 6 pairs of L100's. He has the Mc MCD7000, their first cd player, some Cerwin Vega speakers, several tube amps and really a whole garage full of stuff.
For being about 40 years old, it looks in great shape and isn't awful performance. the only physical issue is a loose fuse holder. I think I'll get a rebuild kit and recap it, then we where I am again (anyone have suggestions where to get a rebuild kit, or are the ones on ebay ok?).
Here's some measurements with my QA403 going into the CD input and out from the Main output. Loudness is set to "flat" and the 5-band EQ is disabled. The unit is rated at 0.007% THD 20-20k. The frequency response is supposed to be within 1/2 dB 20-20k.
Here's 1kHz at 0dBV. The volume control is at 50%, which looks to be about unit gain (1 click above 50 is actually a little closer to unity). This actually looks pretty good!
Here's the same thing at 6dBV (2V). Again, pretty nice.
This is with the volume control at 75% (eyeballing it).
And if I go to 75% (1 more click on the volume control), the distortion jumps up. I'm not sure what causes this yet. EDIT: This is likely clipping because the input level (6 dBV / 2V) was too high for more gain.
Here's a multitone. You can see that < 50Hz and > 10 kHz there is a significant rolloff. This is done with the volume control at 50% (about unity gain). EDIT: This is with HF/LF rolloff button engaged.
And here's the gain vs frequency and THD vs frequency charts. Both done at 50% volume. EDIT: This is with HF/LF rolloff button engaged.
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