The UNSET testing is proceeding slowly. There are too many things diverting my attention right now. There have been too many days where I don't even get to listen to my working UNSET.
I have never seen a 7370 tube before, so I had to look it up. It looks like a 5687 with a 40/20 volt heater. These odd heater voltages were often found in telephone systems. Good NOS tubes are hard to find for them.
Yes, it is but is not a traditional cylindrical mount. It has two holes that screws into a flat milled onto the bottom half of the blue aluminum tip that appears to be bonded to the carbon fiber tone arm shaft.
My initial measurements of the FFT of the noise floor shows that the preamp is very quiet at -120dB noise floor at 1kHz for 47kohm and 40dB gain setting with no hash anywhere on the tilted 1/f noise floor. There is a small blip at 60Hz which I think is EMI picked up by the 4 skinny wires from the cartridge through the tone arm.
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Thanks for checking! I think I am going to redesign the amp using an ECC99 which is similar but uses standard 6.3v heaters. The 7370 has been getting harder and harder to find.
A new speaker design was on the bench last night July 11, 2021: this is a 6.5in 2-way design that I am developing for LSA. The predicted (blue) and measured response (orange) looks excellent. Another passive “Harsch-like” crossover with asymmetric slopes and positive phase on both drivers. XO frequency is at 3.8kHz.
Predicted impedance:
Listening in mono - driven by TD7293 amp, it is sounding excellent. Very nice tonal balance and clarity. The distortion on this OEM woofer is very low and it has a wide bandwidth allowing such a big crossover frequency.
Predicted impedance:
Listening in mono - driven by TD7293 amp, it is sounding excellent. Very nice tonal balance and clarity. The distortion on this OEM woofer is very low and it has a wide bandwidth allowing such a big crossover frequency.
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On the bench tonight, July 14, 2021 is the LuFo Lite - a very simple amp that drive a few watts into either speakers or headphones. I am testing it with a 12v SMPS so only 8v after the cap multiplier. It is running at 2.6A bias current and I am not sure why it is so much higher than the simulation that was predicted (1.7A). However, 8v seems perfect for the heatsinks that I have as they run 43C and the music is plenty loud.
Here is a video of its first sound playing on a 3FE22 test speaker.
LuFo Lite First Sound - YouTube
Schematic and predicted distortion:
Here is a video of its first sound playing on a 3FE22 test speaker.
LuFo Lite First Sound - YouTube
Schematic and predicted distortion:
WOBT (in the wee hours) July 16, 2021: I finalized the crossover design for my new speaker - it measure and sounds great.
https://www.diyaudio.com/forums/attachment.php?attachmentid=967853&stc=1&d=1626553795 is a commercial product so no part number available for the drivers.
Predicted impedance:
Frequency response of channel A and B:
Polar response:
https://www.diyaudio.com/forums/attachment.php?attachmentid=967853&stc=1&d=1626553795 is a commercial product so no part number available for the drivers.
Predicted impedance:
Frequency response of channel A and B:
Polar response:
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and best wishes with this design.
Thank you, Francois G!
On the bench tonight, July 18, 2021: I just finished up my LuFo Lite headphone amp (that can play 3w into 8ohms). It sound superb. Perhaps one of the best headphone amps I have heard.
On the bench tonight, July 18, 2021: I just finished up my LuFo Lite headphone amp (that can play 3w into 8ohms). It sound superb. Perhaps one of the best headphone amps I have heard.
On the bench last night July 27 was a set of custom bifilar wound balanced chokes. Spec was 60mH and 0.5ohm DCR at 10kHz. These are 600w Class EI cores with a 0.1mm airgap. They measured well - identical reactance curves that lie on top of one another. Also checks out at 60mH at 10kHz and gives 160mH at 20Hz. They got a little banged up in shipment but seem to measure and work well. These are for the balanced LuFo 100w single ended Class A amp.
Listening to it in SE mode (non balanced output):
It sounds very good. The reactance varies smoothly and linearly over the audio range. Whereas the MOT has dips and peaks around 5kHz.
These are heavy suckers:
Listening to it in SE mode (non balanced output):
It sounds very good. The reactance varies smoothly and linearly over the audio range. Whereas the MOT has dips and peaks around 5kHz.
These are heavy suckers:
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Looking forward for hearing it in stereo!