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xrk971 Desktop Class A (DCA) Headphone Amp

Founder of XSA-Labs
Joined 2012
Paid Member
A simple 1N400X diode on the input supply upstream of everything would have prevented this. Maybe will be in next amp - adds 0.6v drop but not an issue with an adjustable DC-DC step up as input.

You have a perfect setup with 10v output and 20v Vcc, and 5mA bias current through the JFET. 10v over 68R is 150mA - a super powerful drive for almost any hedphone. Very nice.
 
The chain goes as follows..
1) USB signal reclocker Uptone Regen to an AudioQuest Jitterbug (latter isn't necessary.)
2) DIY AK4490 based DAC Powered by an ifi ipower 12V
3) the DCA

VERY VERY clean.. Just a tinge of warmth. The correct amount. ASMR details really come out amazingly.. Vocalist breaths really come out with more depth than ever before! I love this chain!

Now for chassis :D thinking of getting it sheet metal fabricated.
 
I just had an idea - no reason why the DCA has to be used in only one area! Since I screwed everything onto that tablet stand, I could bolt on say a 3x 18650 battery holder and use that as an input into the step up.... Just have to try it later to see if the batteries can hold up to ~2.5A load. That would make it semi portable around the place!

(just for reference - it draws 0.5A @ 19V from that laptop adapter)
 
Founder of XSA-Labs
Joined 2012
Paid Member
That converter requires minimum 9vdc to work properly I think. Try a higher voltage battery or you need a step up from 5v to 12v first.

Here’s the description.

Module name :250W boost constant current module

Module properties: non-isolated step-up module (BOOST)

Input voltage: DC8.5V-48V

Input current: 10A (MAX) exceeds 8A please enhance heat dissipation

Quiescent current: 10mA (12V liter 20V, the output voltage, the higher
the current will increase too quiet)

Output voltage: 10-50V continuously adjustable

Constant] range: 0.2-8A

You can try the MT3608 DC step up they are designed for lower voltage and max out at 24v out. They are finicky though and often blow up if you adjust the pot too quickly. Get several as $1.

Look what I found on AliExpress
MT3608 2A Max DC DC Step Up Power Module Booster Power Module for arduino Diy Kit-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
 
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2A seems to be the max output so I guess it can draw however much it wants from the input? Not sure...it did heat up and then I pulled the plug on it. The step up wasn't damaged though.
Yep will leave it running straight off the 3608!
Also took the opportunity to swap in the 10k uF caps , even with the fat chisel it still takes some effort to solder suck the ground pins due to the larger sinking capacity of the board I guess.
 
Hi XRK,

My board arrived at my office today, no thanks to the SA Post Office and C&E eedjits. They've been on a go-slow/strike for a while now.

Many thanks, and will slowly be about building this up, though I have the greater part of the components. Just a few other concurrent projects happening.

Regards,
Kevin
 
The efforts of about an hour matching jfets. Aliexpress ones seem to have higher current than the ones I got from rs components (6.xx ones)
 

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