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xrk971 Pocket Class A Headamp GB

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#2,221
Ok let’s make a list. I think I can do this for $62 ea fully assembled SMT and only TH parts need to be soldered on by user. I’ll need at least 8 people to indicate interest. Shipping will be circa $5 in USA and about $20 everywhere else (actual ship cost and taxes etc, TBD by Etsy interface when placing order). If you have ordered stuff from my shop before, you will have an idea.

You will get 1 board like this:
1699908425946.jpeg

1699908443231.jpeg


You need to supply RK09 (or equivalent) volume pot with switch, 3.5mm jacks (CUI or Switchcraft compatible), 2x 3.3uF film box caps or 10uF Silmic II caps, 4x 100uF 15v power rail caps, and JST 4 pin header

Pocket Diamond Buffer HPA PCBA GB
Name / Qnty / Country
————————————
Funch / 1 / USA
UncleMud / 1 / USA
 
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#2,222
QuantityReferencesValueManufacturerMPN
9C107, C108, C109, C201, C202, C203, C301, C302, C3031uFSamsungCL21B105KAFNNNE
4C112, C113, C114, C11547uFPanasonicEEU-FC1V470
2C101, C1023u3WIMAMKS2B043301H00KSSD
2C103, C10433pFSamsungCL10C330JB8NNNC
2C105, C106470pFSamsungCL10C471JB8NNNC
2C110, C11122uFSamsungCL31A226KAHNNNE
8R203, R208, R209, R210, R303, R308, R309, R31010RYAGEORC0603FR-0710RL
6R101, R102, R109, R110, R207, R30710KYAGEORC0603FR-0710KL
4R103, R104, R107, R1081K21YAGEORC0603FR-071K21L
4R201, R202, R301, R302100RYAGEORC0603FR-10100RL
4R204, R205, R304, R30522R1YAGEORC0603FR-0722R1L
4R206, R211, R306, R311221RYAGEORC0603FR-07221RL
4R212, R213, R312, R3132R21YAGEORC1206FR-072R21L
2R105, R1064K75YAGEORC0603FR-074K75L
2R111, R11247K5YAGEORC0603FR-0747K5L
2D201, D301greenLite_OnLTST-S270KGKT
1U101NE5532Texas InstrumentsNE5532DR
5Q102, Q201, Q204, Q301, Q304MMBT5401Diodes IncMMBT5401-7-F
2Q202, Q302MMBT5551Diodes IncMMBT5551-7-F
2Q203, Q303DMMT5401Diodes IncDMMT5401-7-F
2Q205, Q305DMMT5551Diodes IncDMMT5551-7-F
2Q206, Q306FZT853Diodes IncFZT853TA
2Q207, Q307FZT953Diodes IncFZT953TA
1Q101DMN3023Diodes IncDMN3023L-7
1RV10110KAlps AlpineRK0971221Z05
2J101, J102TRS_3.5mmCUI DevicesSJ1-3535
1J103XH_4pinJSTB4B-XH-A(LF)(SN)

You need to provide RV101, J101, J102, J103, C101, C102, C112, C113, C114, C115. Feel free to swap NE5532 with OPA1642 for the ultimate in sound quality.

Feel free to increase C112/C113/C114/C115 from 47uF up to 100uF or even 220uF. This will help improve stereo separation. Bend the legs 90 deg sideways and solder from same side as the holes are covered by SOT223 BJTs on other side. This gets the caps away from the PCB anyway to reduce exposure to heat.

Here is overall connections to power input, 3.5mm TRS jacks, and +/-9v power supply. Please note that the volume pot and TRS jacks do not have the same hole spacing as the Pocket Class A. So you will need to cut holes on a new tin. It is ever so slightly different by a few mm. Sorry about that. Also, the headphone out and audio input are now swapped from the PCA. There is no turn on issue (with batteries cutting out) as with PCA as the current inrush is manageable with 100uF power rail caps.

1699909370457.jpeg
 
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#2,234
Yes, after I get a chance to test it out and make sure everything is working well. The boards should be here in a week or so.

This is what the desktop board looks like:

1701020098562.jpeg


Lots of room for cap rolling on the input coupling caps. There’s a small helper board for connecting an off board volume pot with Micromatch IDC cable.

A big thanks to Jhofland for the design.
 
#2,236
The Pocket Diamond Buffer (PSB) is now on sale in my shop for $69. All SMT parts fully installed and all you need to do is to install through hole parts. Fully tested and verified to be working by me - hence 4 pin JST connector for power is pre installed.

https://xrkaudio.etsy.com/listing/1606375374

Only 7 units available in this first batch so get them while supplies last.
 
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#2,237
A couple of orders have come through for the PDB already. Thanks!

In case you haven’t seen the measurements. They look fantastic. Here is 50mW into 33ohms. About 0.0018% THD and perfect SE Class A harmonic profile.

1701213014442.jpeg

Ignore the 60/120Hz/and > 3kHz peaks (air pickup in noisy lab).

Max power of about 270mW into 33ohms. Clips at 373mW into 33ohms with lithium ion 9v rechargeable batteries. Noise floor is about -120dB.

More info on measurements here:
https://www.diyaudio.com/community/threads/pocket-diamond-buffer-pdb-headphone-amp.401404/
 
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#2,239
If you really want to make it great, add a DC output protection relay. I would use a solid state relay (SSR) scheme with a 2 second turn-on delay and instant-off at power off feature to prevent thump and protect from headphones from DC in case one rail collapses before the other. I ran out of room to implement the SSR on this small board though. You may want to tweak the bias current by increasing the 2.2R emitter resistors to 4.7R and this will let it run cooler without really affecting performance too much. But if you have good heatsinking, it’s fine as is. 🙂
Click to expand...
Thank you so much for responding to me. I have no choice, I will make a headphone amplifier like you have in the post. Because I don't have a delay circuit to turn on the headphones. I do not know how to design circuits. I can breed and solder)
But I'm still very grateful to you for responding to me.🙂
 
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