xrk971 Pocket Class A Headamp GB

[slk23]

Nice work! Cool that you were able to fit that filter inside the tin. How does it sound?

Sounds awesome! But I need a better DAC than my laptop's to take full advantage of the PCA.

 

[twocents]

Very nice build!
Yes, the better the DAC, the better the PCA sounds. Enjoy.

 

[xrk971]

Sounds awesome! But I need a better DAC than my laptop's to take full advantage of the PCA.

Khadas Tone Board 1 is very good about $100.

 

[slk23]

Khadas Tone Board 1 is very good about $100.

Interesting.... I'm also considering the Topping D10s.

 

[xrk971]

If you can afford it, the SMSL SU-9n is one of the top 2 DACs tested by ASR. $400 is actually a deal for what this DAC can do. I have both and the SMSL is certainly superb sounding. It has balanced outputs as well.

 

[vdupham]

Khadas Tone Board 1 is very good about $100.

Hi this DAC board is standalone board or I need raspberry pi ?

 

[xrk971]

It needs a computer so a Pc or maybe a Rpi works? USB connection.

You can also use Khadas VIM3 SBC.

 

[vdupham]

It needs a computer so a Pc or maybe a Rpi works? USB connection.

You can also use Khadas VIM3 SBC.

Hi I am using Apple Dongle with Android UAPP app. I plan to use Khadass with UAPP, is it okie ?

 

[xrk971]

Khadas is USB DAC, you need to check their website to see compatibility.

Works fine on my windows PC. I am not sure about Android but since VIM 3 SBC is Linux based, I would imagine that it will work.

 

[vdupham]

Hi can I use 1uf Capacitor for input cap ?

 

[xrk971]

Yes, the input impedance is controlled by the 47k resistor so corner frequency for -3dB is fc=1/(2pi R C). R=47k and C=1uF

I get 3.4Hz for fc so you can expect flat response 2 octaves above this or 13.5Hz

 

[vdupham]

Yes, the input impedance is controlled by the 47k resistor so corner frequency for -3dB is fc=1/(2pi R C). R=47k and C=1uF

I get 3.4Hz for fc so you can expect flat response 2 octaves above this or 13.5Hz

I planned to use 1uf Mundorf Silver Gold Oil capacitor for input cap ? Do you it is better than normal capacitor ?

 

[xrk971]

Capacitors are very subjective. Good ones won’t hurt but my ears have a hard time telling if I have a good $1 polycarbonate cap or a $50 paper in oil foil Mundorf.

These sound incredible and incredible value. Look for them on eBay.

“Polycarbonate Capacitor 5uf 50v 5% MC1-13714J”

 

[vdupham]

Can you post lastest Schematic vs BOM ? I find out schematic and BOM not work together at all.

 

[xrk971]

I haven’t changed schematic since original was released. Through the years, parts upgraded for caps, and MOSFETs changed. If you can’t find BF862, then need to use 2SK209. In which case resistors changed. I know it’s a lot to follow.

The major changes:

1. MOSFETs use ZXMN10GTA (2 needed)

2. Pot now use AliExpress since Alps discontinued:

https://a.aliexpress.com/_mLF5Cyk

3. Output caps use a pair of Panasonic SEPF 1000uF 16v per channel (4 needed) where C2A1/2 and C2B1/2 go. Alternatively, a pair of SEPF 390uF are also great. Larger values needed for lower impedance headphones.

4. Input caps still 2.2uF 50v Wima MKS or Elna Silmic 10uF 35v electrolytics, C1A and C1B

5. JFETs use Toshiba 2SK209BLif you can’t find BF862.

Use resistors shown here (R1=1.3k, R3=39R, R4=330R):

6. Changed resistors to accommodate 2SK209 per recommendation in thread. See schematic above.

7. Rail caps use Nichicon 2200uF 16v where C5A/B are.

But this is DIY, feel free to cap roll and see what you like. Some people like Panasonic FC as outputs. Some people like an MKP filmcap for bypass. Etc.

 

[vdupham]

I haven’t changed schematic since original was released. Through the years, parts upgraded for caps, and MOSFETs changed. If you can’t find BF862, then need to use 2SK209. In which case resistors changed. I know it’s a lot to follow.
View attachment 1108491

The major changes:

1. MOSFETs use ZXMN10GTA (2 needed)

2. Pot now use AliExpress since Alps discontinued:

https://a.aliexpress.com/_mLF5Cyk

3. Output caps use a pair of Panasonic SEPF 1000uF 16v per channel (4 needed) where C2A1/2 and C2B1/2 go. Alternatively, a pair of SEPF 390uF are also great. Larger values needed for lower impedance headphones.

4. Input caps still 2.2uF 50v Wima MKS or Elna Silmic 10uF 35v electrolytics, C1A and C1B

5. JFETs use Toshiba 2SK209BLif you can’t find BF862.

Use resistors shown here (R1=1.3k, R3=39R, R4=330R):
View attachment 1108493

6. Changed resistors to accommodate 2SK209 per recommendation in thread. See schematic above.

7. Rail caps use Nichicon 2200uF 16v where C5A/B are.

But this is DIY, feel free to cap roll and see what you like. Some people like Panasonic FC as outputs. Some people like an MKP filmcap for bypass. Etc.

I can find BF862. Because last time I can not follow Output Cap, I saw 47uf and other Capacitor without value in the schematic so I can not find value.

 

[vdupham]

So can I follow this schematic, just only one output capacitor ?

 

[xrk971]

Use as large a value of output cap as you can fit. Dual 1000uF SEPF 16v is one of my favorite. Alternatively, a single 2200uF laid on its side works too. You can use a small 1uF film bypass cap on the other side if you want.

 

[vdupham]

Use as large a value of output cap as you can fit. Dual 1000uF SEPF 16v is one of my favorite. Alternatively, a single 2200uF laid on its side works too. You can use a small 1uF film bypass cap on the other side if you want.

Hi Can I use one more bypass capacitor 0.01 uf with input 2.2uf capacitor ?

 

[xrk971]

Doesn’t need it if input is already film cap.