Having nothing better to do and a lot of stuff laying around I put something together in an IBM data tape case. This is something mostly done with "junk" and I have not bothered to respect many design and layout guides but excluding some noise issues, it sounds stupidly good, sounds better than many dac's that ended up on my bench.
I will draw the full schematic once I have some time .
USB AQ dragonfly red DAC with blown headphone amp chip. The balanced signal goes in a single triode, grid and cathode ( interesting design found online on a ess dac , i believe something called buffalo dac). The tubes are GE 5654 pentodes, connected as in the cheap 6j1 preamp circuit.
The power supply is based on two dual 9.5v trafos with 3 secondaries in series and a voltage doubler ( running at about 60+v on plate) . The fourth 9.5v secondary is fully rectified to drive the heaters in series, getting about 11.6v DC.
The dac 5V is powered from a 5v700mA wall usb charger board ( Blackberry charger I believe).
I dimmed the blue led on the logo as it was too bright as the picture shows ( the dragonly case and blue led is design only) .
Daily use, love the sound, now i need to replace the 5V with a linear and test some 300ohm res on heaters to ground, having a bit of hum at high volume and no signal. Also a bit of whining ( hoping to improve with a good linear on 5V for dac) , but with music impossible to hear.
Any advice to improve this crazy thing ?
I will draw the full schematic once I have some time .
USB AQ dragonfly red DAC with blown headphone amp chip. The balanced signal goes in a single triode, grid and cathode ( interesting design found online on a ess dac , i believe something called buffalo dac). The tubes are GE 5654 pentodes, connected as in the cheap 6j1 preamp circuit.
The power supply is based on two dual 9.5v trafos with 3 secondaries in series and a voltage doubler ( running at about 60+v on plate) . The fourth 9.5v secondary is fully rectified to drive the heaters in series, getting about 11.6v DC.
The dac 5V is powered from a 5v700mA wall usb charger board ( Blackberry charger I believe).
I dimmed the blue led on the logo as it was too bright as the picture shows ( the dragonly case and blue led is design only) .
Daily use, love the sound, now i need to replace the 5V with a linear and test some 300ohm res on heaters to ground, having a bit of hum at high volume and no signal. Also a bit of whining ( hoping to improve with a good linear on 5V for dac) , but with music impossible to hear.
Any advice to improve this crazy thing ?
A universal box will only be a basic output buffer after the internal preamplification /headphone driver. Can't really make this work without directly to the DAC's output. My circuit feeds the dac outpus straigh into the tubes and gets amplified.
The Lampizator guy has a lot of designs , this is a variant of his designs , much simplified.
Try Salas' Reflektor-d for the 5v.
Whats the freq. of the hum?
Cheers and good work!
Greg
thanks but waaaay to much perfection for this project.
I am staring to point the hum at my PC as after I stop the music after 10 sec the whine changes and lowers in intensity. it is a digital noise. on youtube misic I also have a whine after I hit stop , then a really small thump and it quites down . hitting play starts it again.
I also noticed something interesting. It seems to have some leakage on output as i put a direct input amp ( max volume) with a test speaker and the membrane "breathes" in a strange pattern . I need to pop the scope on the output to see what is going on as it seems it leaks DC that moves the coils , from a ss dac I have no issues.
I am staring to point the hum at my PC as after I stop the music after 10 sec the whine changes and lowers in intensity. it is a digital noise. on youtube misic I also have a whine after I hit stop , then a really small thump and it quites down . hitting play starts it again.
I also noticed something interesting. It seems to have some leakage on output as i put a direct input amp ( max volume) with a test speaker and the membrane "breathes" in a strange pattern . I need to pop the scope on the output to see what is going on as it seems it leaks DC that moves the coils , from a ss dac I have no issues.
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