Circa 5v over R106/R109 (960R) and 10V over the resistor bank on both channels and 20V from CM so looks like I got away with my blunder.
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.
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.
An externally hosted image should be here but it was not working when we last tested it.
It sings!!!! Wow what a clean amp! Pairs amazingly with my relatively bright headphones.. (Audiotechnica AD2000x)
Nice work! I see a Firefly DAC, and a box next to DCA. What source are you using?
Not too many amps can sound cleaner - low and flat noise floor (-130dB) if built as recommended.
Not too many amps can sound cleaner - low and flat noise floor (-130dB) if built as recommended.
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 😀 thinking of getting it sheet metal fabricated.
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 😀 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)
(just for reference - it draws 0.5A @ 19V from that laptop adapter)
That idea seems to have failed. The step up output isn't constant with a varying input voltage...so it would require a dedicated step up for each input voltage...
X did the blue board step up you also recommended keep a constant output voltage with varying input?
X did the blue board step up you also recommended keep a constant output voltage with varying input?
I recall the DC step ups I used were regulating the output to be constant. Which one do you have?
This one: DC DC boost converter Constant Current Mobile Power supply 10A 250W LED Driver-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
set for a 25V output with 19V input, when I apply 5V it gives ~12V out under load, 28V no load. Only drawing about 180-200mA (fluctuates) from the 5V power supply..
set for a 25V output with 19V input, when I apply 5V it gives ~12V out under load, 28V no load. Only drawing about 180-200mA (fluctuates) from the 5V power supply..
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
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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Oops. Without reading the description I just assumed it would work the same as the little 3608 ones. Still have a bunch of those from the pca - will give those a go! Not sure how such a tiny thing would hold up to the power dissipation
Alright got it hooked up to a 3608 at 23.5v it's drawing 1.5A from a USB port. Seems to be holding up fine. However when I used it to step up to 12V to feed the other step up, it draws in excess of 3A @ 5V. Just have to wait for the 18650 battery holders to arrive to try with batteries 😉
That’s strange that current goes that high. I would not run it at 3A it will blow up. Just use it to make 24v and its good for that as 1.2MHz switching grew is way above audio band.
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.
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
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
Good to hear that you got the amp despite the flakey SA postal service. It’s an easy build so don’t put it off too long. Great bang for the buck performance - will beat many other amps far more complex and expensive.
Cheers,
X
Cheers,
X
Nice work. That’s why you have better chances of matching from same batch (tape strip) of JFETs. You have some great choices in there.
Hi X
I've measured a load of BF862s on the DCA with R106 at 910R and R107 as 56R by taking voltage over R106.
How would this convert to Idss?
Would higher Idss be better for the DCA or Simple HPA, or does it make no difference?
Thanks
I've measured a load of BF862s on the DCA with R106 at 910R and R107 as 56R by taking voltage over R106.
How would this convert to Idss?
Would higher Idss be better for the DCA or Simple HPA, or does it make no difference?
Thanks