Very true. I guess they thought the "cool" safety glasses might impact their marketing video. Haha! They do show it with a shielded enclosure on the kickstarter page. Cubiio: The Most Compact Laser Engraver by Muherz —Kickstarter
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Verification build completed
I finally had a good day to work on this amp. The build went together well. It's a big project with all the little sub boards. There is an error on the volume pot board - one of the pads on the smaller right channel is not connected to anything - jumper it to the right input. The crossfeed filter has some errors - I managed to fix it partially so that it works but the defeat feature does not fully defeat it. Sounds great. Bias is 116mA with +/-17.5v under load. DC offset is -2mV and 6mV.
Completed amp before buttoning up:
Closeup:
Closeup of ebay voltage regulator (negative one):
Closeup of outputs and heatsink mounting:
Closeup of Xfeed:
Closeup of vol pot board and headphone jack board:
Amp with headphones and Cayin N3 playing:
Underside panel showing all the screw holes used to mount parts on the other side:
I finally had a good day to work on this amp. The build went together well. It's a big project with all the little sub boards. There is an error on the volume pot board - one of the pads on the smaller right channel is not connected to anything - jumper it to the right input. The crossfeed filter has some errors - I managed to fix it partially so that it works but the defeat feature does not fully defeat it. Sounds great. Bias is 116mA with +/-17.5v under load. DC offset is -2mV and 6mV.
Completed amp before buttoning up:
Closeup:
Closeup of ebay voltage regulator (negative one):
Closeup of outputs and heatsink mounting:
Closeup of Xfeed:
Closeup of vol pot board and headphone jack board:
Amp with headphones and Cayin N3 playing:
Underside panel showing all the screw holes used to mount parts on the other side:
Attachments
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Some Measurements
It's a pretty clean amp. I am using my Cayin N3 with 1kHz test tone. The N3 and Focusrite sort of limit the harmonic distortion measurements as the self THD of the DAC is about 0.003% at -1dB FS. I am keeping it in the -10dB to -20dB region.
Here are some FFT's driving a 51ohm 1W metal thin film dummy load resistor.
1.03Vpp into 51ohms:
2.76Vpp into 51ohms:
14.0Vpp into 51ohms:
One thing to note is how quiet the power supply is for being a wall plug supply. There is essentially no mains or its harmonics - quiet like a battery.
There is absolutely no audible noise/hiss/hum with the source turned off and the volume turned all the way up with my OB-1's which are 55ohms and 96dB. Normal listening voltage levels with OB-1's are about 100mVrms, so you can get an idea that the data in the plots are for ear blistering levels, or for very insensitive phones.
It's a pretty clean amp. I am using my Cayin N3 with 1kHz test tone. The N3 and Focusrite sort of limit the harmonic distortion measurements as the self THD of the DAC is about 0.003% at -1dB FS. I am keeping it in the -10dB to -20dB region.
Here are some FFT's driving a 51ohm 1W metal thin film dummy load resistor.
1.03Vpp into 51ohms:
2.76Vpp into 51ohms:
14.0Vpp into 51ohms:
One thing to note is how quiet the power supply is for being a wall plug supply. There is essentially no mains or its harmonics - quiet like a battery.
There is absolutely no audible noise/hiss/hum with the source turned off and the volume turned all the way up with my OB-1's which are 55ohms and 96dB. Normal listening voltage levels with OB-1's are about 100mVrms, so you can get an idea that the data in the plots are for ear blistering levels, or for very insensitive phones.
Attachments
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Thanks, Hugh. It sounds very neutral and very revealing with no caps in signal path. The amp has plenty of headroom for crescendos and will make my headphones recoil on bass kick drum. The casework was a royal pain as you can imagine. Took me better part of a day to assemble. I’m happy with the measured performance and how it sounds. The DC-DC PSU with low noise regulator works very well. It can drive power hungry planar magnetic cans quite admirably. I am using Fairchild TO220 FQP MOSFETs for first time - they sound great.