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6CY7 dual triode valve amplifier

I’ve always wanted to know what the “tube magic” was all about. There is much opinion in the science of music production, probably because music and its perception is highly personal and subjective. Ive always imagined that since transistor amplifiers were “perfect” with their large amounts of negative feedback, great linearity, and low THD that tube amplifiers must add something to sound that generates their appeal. From the reading I’ve done it has to do with harmonics.

After getting back into headphones because of my kids, I decided to try building a tube amplifier that would drive my nighthawks. More specifically I wanted to build an amp that would be sort of an old school / new school hybrid, one that used circuit boards and SMT components for good EMC considerations, but had no semiconductors at all and no negative feedback.

I owe much credit to Matt at cascadetubes.com, whose design of the 6CY7 amp is what I used with some modifications. This amp appealed to me not only because of the SET topology featuring no negative feedback (second stage does have degeneration), but also because the first and second amp stages for each channel were in their own tube. › Continue reading

Tags: Electronics

Air quality sensor (TVOC and eqCO2)

I’ve been curious about the inexpensive gas sensors available now and whether they are useful at all. They are being built into new equipment to estimate air quality. I decided to pick one up and attach it to my K64 dev board for some hands on evaluation.

Its very responsive, but I haven’t achieved what I want to call a steady baseline. There’s an odd requirement in the datasheet to perform a measurement every second, and you can preload a baseline reference but it’s not clear exactly what you gain from that. There is also compensation for humidity but I don’t currently have that sensor. Here in Colorado its always pretty dry anyway.
At home it is usually in the 100-200ppb range for TVOC, sometimes climbing to almost 1000. I live in an older home so I guess that isn’t a surprise, however when I reset it and it turns back on sometimes the readings will be lower. At work its rarely above about 30ppb.
Sensirion has provided a nice document that describes TVOC in more detail and gives ranges for acceptable levels. It also hints that you can calibrate the sensor with ethanol but doesn’t explain how.
If anyone has used one of these and has more information on improving accuracy please leave a comment.

Tags: Electronics