xrk971 Pocket Class A Headamp GB

[agdr]

xrk971 - 2 boards
pcgab - 2 boards
zman01 - 2 boards
stellarelephant - 2 boards
samoloko - 1 pcb
lui04 - 2 boards
Morde - 2 board
cyteen - 2 boards
funch - 2 boards
syyma - 2 boards
av-trouvaille - 2 boards
Mituisho - 2 boards
bogde - 2 boards
faltinsen - 2 boards
vanofmonks - 1 board
M_Balou - 2 boards
dwpeterson - 1 board
agdr - 1 board

 

[xrk971]

Schematic

As requested, here is the full schematic for this amp. Not shown is the electrical connections for the two batteries in series for 18v.

Again, thanks to BDHM for the schematic and layout.

 

[walangalam]

xrk971 - 2 boards
pcgab - 2 boards
zman01 - 2 boards
stellarelephant - 2 boards
samoloko - 1 pcb
lui04 - 2 boards
Morde - 2 board
cyteen - 2 boards
funch - 2 boards
syyma - 2 boards
av-trouvaille - 2 boards
Mituisho - 2 boards
bogde - 2 boards
faltinsen - 2 boards
vanofmonks - 1 board
M_Balou - 2 boards
dwpeterson - 1 board
agdr - 1 board
walangalam - 2 boards

 

[Morde]

@xrk971: Thanks for the schematics! What is the meaning and value of R8/R16? I thought it was just a load value for the LTspice model to represent the headphone impedance. Do I need to connect it? Sorry for the noob questions?

Edit: I'm going to use this mainly with 70 ohm headphones. I suppose the 390uF output caps provided in the bom are sufficient for low frequency extension?

 

[AndrewT]

...................I'm going to use this mainly with 70 ohm headphones. I suppose the 390uF output caps provided in the bom are sufficient for low frequency extension?

It's a passive single pole filter. Calculate the F-3dB
It will have virtually no roll off @ 60Hz and probably no more than about -0.5dB @ 20Hz
F-3dB = 1 / 2PiRC = ~6Hz

 

[xrk971]

I use 270R as RL even when headphones not plugged in mainly to allow me to test the amp so it simulates my headphone. It could be a higher impedance like 600R or 1k even.

 

[gwrskien]

xrk971 - 2 boards
pcgab - 2 boards
zman01 - 2 boards
stellarelephant - 2 boards
samoloko - 1 pcb
lui04 - 2 boards
Morde - 2 board
cyteen - 2 boards
funch - 2 boards
syyma - 2 boards
av-trouvaille - 2 boards
Mituisho - 2 boards
bogde - 2 boards
faltinsen - 2 boards
vanofmonks - 1 board
M_Balou - 2 boards
dwpeterson - 1 board
agdr - 1 board
walangalam - 2 boards
gwrskien - 2 boards

 

[redarc12]

xrk971 - 2 boards
pcgab - 2 boards
zman01 - 2 boards
stellarelephant - 2 boards
samoloko - 1 pcb
lui04 - 2 boards
Morde - 2 board
cyteen - 2 boards
funch - 2 boards
syyma - 2 boards
av-trouvaille - 2 boards
Mituisho - 2 boards
bogde - 2 boards
faltinsen - 2 boards
vanofmonks - 1 board
M_Balou - 2 boards
dwpeterson - 1 board
agdr - 1 board
walangalam - 2 boards
gwrskien - 2 boards

redarc12- 2 boards

 

[xrk971]

Ok I have triple checked the layout vs the schematic. All looks good and I am almost ready to order boards. However, the fab houses in China will not open until Feb 3 after the Lunar New Year celebrations are over. So I will leave GB open for a few more days. In the meantime, please send me a PM with your PayPal email and where you are located (Country). I will send you an invoice.

Thanks,
X

We are currently at 38 boards:

xrk971 - 2 boards
pcgab - 2 boards
zman01 - 2 boards
stellarelephant - 2 boards
samoloko - 1 pcb
lui04 - 2 boards
Morde - 2 board
cyteen - 2 boards
funch - 2 boards
syyma - 2 boards
av-trouvaille - 2 boards
Mituisho - 2 boards
bogde - 2 boards
faltinsen - 2 boards
vanofmonks - 1 board
M_Balou - 2 boards
dwpeterson - 1 board
agdr - 1 board
walangalam - 2 boards
gwrskien - 2 boards
redarc12- 2 boards

To make ordering the BOM easy, here is a Mouser shopping cart for everything except the SMT resistors, SMT caps, and battery terminals.

http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=f8bb47c63f

 

[xrk971]

Update:

Thank to the folks who have provided me their email and payment!

xrk971 - 2 boards
pcgab - 2 boards - INVOICE SENT & PAYMENT RECEIVED
zman01 - 2 boards
stellarelephant - 2 boards
samoloko - 1 pcb
lui04 - 2 boards
Morde - 2 board - INVOICE SENT & PAYMENT RECEIVED
cyteen - 2 boards
funch - 2 boards
syyma - 2 boards - INVOICE SENT & PAYMENT RECEIVED
av-trouvaille - 2 boards
Mituisho - 2 boards - INVOICE SENT & PAYMENT RECEIVED
bogde - 2 boards
faltinsen - 2 boards - INVOICE SENT & PAYMENT RECEIVED
vanofmonks - 1 board
M_Balou - 2 boards
dwpeterson - 1 board
agdr - 1 board
walangalam - 2 boards
gwrskien - 2 boards
redarc12- 2 boards

 

[xrk971]

For C9 and C11, the 100uF 20v Panasonic power supply rail cap, I had specified part no. 20SEP100MX which I just found out is 10mm dia (but 8mm tall) may require a little off-center mounting (bend pins) to fit in the 8mm dia spot. There is an 8mm but taller (12mm) part that will fit on center but may be at the limit of height. You might want to look at it and see what works for you. I am going to stay with the previously selected part for now.

New 20SEP100M 8mm dia x 12mm tall radial can with 3.5mm lead spacing:

http://www.mouser.com/ProductDetail/Panasonic/20SEP100M/

 

[dw1narso]

Since getting the components is not easy in my country, I'm interested if someone could help arranging the groupbuy for the parts too... I don't mind of the profit is taken from that..

 

[xrk971]

Update on GB status

xrk971 - 2 boards
pcgab - 2 boards - INVOICE SENT & PAYMENT RECEIVED
zman01 - 2 boards - INVOICE SENT & PAYMENT RECEIVED
stellarelephant - 2 boards - INVOICE SENT
samoloko - 1 pcb
lui04 - 2 boards
Morde - 2 board - INVOICE SENT & PAYMENT RECEIVED
cyteen - 2 boards
funch - 2 boards
syyma - 2 boards - INVOICE SENT & PAYMENT RECEIVED
av-trouvaille - 2 boards - INVOICE SENT & PAYMENT RECEIVED
Mituisho - 2 boards - INVOICE SENT & PAYMENT RECEIVED
bogde - 2 boards
faltinsen - 2 boards - INVOICE SENT & PAYMENT RECEIVED
vanofmonks - 1 board
M_Balou - 2 boards - INVOICE SENT & PAYMENT RECEIVED
dwpeterson - 1 board - INVOICE SENT
agdr - 1 board
walangalam - 2 boards
gwrskien - 2 boards - INVOICE SENT & PAYMENT RECEIVED
redarc12- 2 boards
dw1narso - 2 boards - INVOICE SENT & PAYMENT RECEIVED

 

[Morde]

I'm a bit confused (again) about the schematic and the BOM. There's capacitors C6 and C11 marked as 47uF, yet those can't be found on the BOM. And I think that C9 and C4 are the 100uF rail caps you mention in post #31.

Will the amp work without the C6 and C11? I already ordered the components from Mouser and now I don't have the 47uF caps included in the order.

 

[xrk971]

Morde,
Sorry about that confusion. The amp schematic as drawn with 47uF caps works well for driving 250ohm headphones. I made the recommendation to use 100uF power rail caps (on the corners) for improved bass transient response, and 390uF caps for the C6 and C11 output caps to allow deep bass extension when using lower impedance headphones. If you have already ordered the BOM I recommended, you are good. Let me send out a BOM correlated with silkscreen name designations.

 

[Morde]

Ok, thanks a lot! I believe the BOM with part numbers correlated to the board markings will do the trick.

 

[stellarelephant]

Ok, thanks a lot! I believe the BOM with part numbers correlated to the board markings will do the trick.

This will help with assembly too.

 

[xrk971]

Can someone help me find something like this on Mouser? I don't know what they are called. JST-XH 4 pin PCB connector 2.54mm pitch male pins/female jack.

https://www.amazon.com/gp/aw/d/B00WO4SKF2/

 

[pcgab]

Can someone help me find something like this on Mouser? I don't know what they are called. JST-XH 4 pin PCB connector 2.54mm pitch male pins/female jack.

https://www.amazon.com/gp/aw/d/B00WO4SKF2/

This may be close:

http://www.mouser.com/ProductDetail...iMZZMs%2bGHln7q6pm%2bS0pk2Wo0XxnsSEzmf%2b6zo=

Im still poking at mouser, might find something closer.

 

[pcgab]

This looks like the mate to the connector I just posted:

http://www.mouser.com/Search/ProductDetail.aspx?qs=ph4zPCVRuvqoDX7hrEhxNA==


btw - I found these in

All Products > Molex > Connectors > Headers & Wire Housings

You can then filter on 4 position, 2.54mm pitch, etc.