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xrk971 Pocket Class A Headamp GB
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Old 2nd June 2019, 05:12 AM   #1901
rbalu72 is offline rbalu72  India
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Quote:
Originally Posted by xrk971 View Post
I just implemented the above diagram and it works well. I added a CRCRC after the cap Mx and before the amp. It can still play music even when charging via USB as shown in photo below. My charger module has just one connection for the battery and the output. The battery itself has the smart protection circuit built in. I am running at a full 18v Vcc to see how well this can play low impedance phones. I have also retrofitted the new resistor values for low impedance. It turns out adding a parallel 4k7 chip resistor to 1k makes it an 820R so you don't need to uninstall. I did swap out the 270R R5 for 220R though.

Here is closeup of the trace cut and the new solder pads added to go to battery and cap Mx input:
Click the image to open in full size.

Here is testing the flat-pack for functionality before putting it in the case:
Click the image to open in full size.

Here is the finished amp undergoing a charge and playing music at same time:
Click the image to open in full size.

I don't mind opening the lid to charge. Having the power switch function to turn on/off the cap Mx is a nice touch.

Here is FFT for 1Vpp itno 270ohms (0.05% THD all H2 and H3):
Click the image to open in full size.

Here is FFT for driving 50ohm load (0.24% THD, and about same harmonic profile)
Click the image to open in full size.

The DC step up and CRCRC combo is doing a great job with keeping noise to a minimum level, flat at -130dB.
Can someone point to a link to find a lipo battery pack thats used here? Many thanks
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Old 2nd June 2019, 07:29 AM   #1902
xrk971 is online now xrk971  United States
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xrk971 Pocket Class A Headamp GB
I think it was a 52mm x 51mm x 7.8mm thick 2600mAhr battery.

3.7V 2600mAh Li-Polymer lipo Battery For Power Bank mobile phone PDA GPS 785251 | eBay
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Old 21st June 2019, 03:44 PM   #1903
xrk971 is online now xrk971  United States
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This amp topology is now also available as an add-on daughterboard to the Aksa Lender preamp/headphone amp. But gives you choice of BF862, 2SK209, or 2SK170 for the input JFET.

AKSA's Lender Preamp with 40Vpp Ouput GB

Click the image to open in full size.
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Old 16th July 2019, 05:10 AM   #1904
xrk971 is online now xrk971  United States
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Latest NHB BOM for PCA to drive both low and high impedance headphones.

Code:
PCA BOM for low (32ohms) and (600ohm) high impedance cans	
July 16, 2019			
				
Check	Label on Board	Qnty	Value	Notes
	R1	2	100k	0805 1/8W Metal Oxide Film 1%
	R2	2	47k	0805 1/8W Metal Oxide Film 1%
	R3	2	1k	0805 1/8W Metal Oxide Film 1%
	R4	2	47R	0805 1/8W Metal Oxide Film 1% (nominal is 47R, increase for higher bias)
	R5	2	270R	0805 1/8W Metal Oxide Film 1%
	R6	2	47R	0805 1/8W Metal Oxide Film 1%
	R7(1-4)	8	470R	0805 1/8W Metal Oxide Film 1%
	RLED	1	12k	0805 1/8W Metal Thin Film 5%
	RL	2	270R	0805 1/8W Metal Oxide Film 1%
	C1_A/B	2	10uF 35V	Elna Silmic II (silk insulator),  -ve terminal faces front edge
	C2_A1/B1	2	1000uF 16V	Panasonic OSCON SEPF
	C2_A2/B2	2	1000uF 16V	Panasonic OSCON SEPF
	C3	2	2200uF 16V	Nichicon, use shrinktube on legs
	C4A/B	4	100nF X7R 	0805 X7R 100v
	Q1	2	BF862	N-junction JFET (NXP)
	M1	2	ZVN4306	N-ch MOSFET (ZETEX/Diodes Inc) or ZXMN10A08GTA
	Input	1	3.5mm stereo jack	Switchcraft
	Output	1	3.5mm stereo jack	Switchcraft
	Pot	1	10k linear w/ power	Alps Rk09 with 6mm shaft with flat
	LED	2	3mm	blue and white included, use shrinktube on +ve leg
	BATT	1	JST 4-pin 0.1in pitch	
	Vol Knob	1	6mm shaft with flat	Machined Aluminum with plastic core
	PCB	1	v1.0	1,6mm 2-layer PCB
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Old 17th July 2019, 03:12 AM   #1905
yourownbuzz is offline yourownbuzz  Australia
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What happened to the revised low bias values from your earlier post a few months ago?
Looks like these recent ones reverted close to the original BOM values?

Quote:
Originally Posted by xrk971 View Post
Latest NHB BOM for PCA to drive both low and high impedance headphones.

Code:
PCA BOM for low (32ohms) and (600ohm) high impedance cans	
July 16, 2019			
				
Check	Label on Board	Qnty	Value	Notes
	R1	2	100k	0805 1/8W Metal Oxide Film 1%
	R2	2	47k	0805 1/8W Metal Oxide Film 1%
	R3	2	1k	0805 1/8W Metal Oxide Film 1%
	R4	2	47R	0805 1/8W Metal Oxide Film 1% (nominal is 47R, increase for higher bias)
	R5	2	270R	0805 1/8W Metal Oxide Film 1%
	R6	2	47R	0805 1/8W Metal Oxide Film 1%
	R7(1-4)	8	470R	0805 1/8W Metal Oxide Film 1%
	RLED	1	12k	0805 1/8W Metal Thin Film 5%
	RL	2	270R	0805 1/8W Metal Oxide Film 1%
	C1_A/B	2	10uF 35V	Elna Silmic II (silk insulator),  -ve terminal faces front edge
	C2_A1/B1	2	1000uF 16V	Panasonic OSCON SEPF
	C2_A2/B2	2	1000uF 16V	Panasonic OSCON SEPF
	C3	2	2200uF 16V	Nichicon, use shrinktube on legs
	C4A/B	4	100nF X7R 	0805 X7R 100v
	Q1	2	BF862	N-junction JFET (NXP)
	M1	2	ZVN4306	N-ch MOSFET (ZETEX/Diodes Inc) or ZXMN10A08GTA
	Input	1	3.5mm stereo jack	Switchcraft
	Output	1	3.5mm stereo jack	Switchcraft
	Pot	1	10k linear w/ power	Alps Rk09 with 6mm shaft with flat
	LED	2	3mm	blue and white included, use shrinktube on +ve leg
	BATT	1	JST 4-pin 0.1in pitch	
	Vol Knob	1	6mm shaft with flat	Machined Aluminum with plastic core
	PCB	1	v1.0	1,6mm 2-layer PCB
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Old 17th July 2019, 04:01 AM   #1906
xrk971 is online now xrk971  United States
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These are for the baseline amp with usual 7mA bias current through JFET and for lower impedance headphones. The ultra low 120uA JFET bias was an experiment and although sounds great, but I am not ready to say it’s the “new baseline”.
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Old 18th July 2019, 12:24 PM   #1907
ItsAllInMyHead is offline ItsAllInMyHead
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Thanks for putting up the new BoM. Are C4 and C5 pads ideally sized for 0805 or 1206 parts? I've seen both in the thread. I had 1206 in my BoM, but I was not sure if I missed a board revision or it's just that either work.
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Old 18th July 2019, 05:04 PM   #1908
xrk971 is online now xrk971  United States
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Actually sized 1206 but I use 0805 because I have them and it fits.
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Old 30th July 2019, 12:39 AM   #1909
xrk971 is online now xrk971  United States
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Folks,
I just ran out of PCA PCBs and will need to order resupply. So if you are looking for them in my shop or for kits, you will notice that they are not there. Please come back on a few weeks and I should have them in.
Thanks,
X
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Old 12th August 2019, 06:33 PM   #1910
potatopie17 is offline potatopie17  United States
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Hello xrk971 I just ordered your last kit and it works fine but runs on the hot side.
checked across R7 resistors and one channel shows 5.8v and other shows 6.9v so how do I adjust the current? R4?

thanks
Benjamin
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