Edit Aug 11, 2020: annotated BOM in MS Excel format here.
Announcements & Updates: I have been getting a lot of reports of builders experiencing sparks with connecting the power supply or melting the power switch at first turn on. Please make sure your MOSFETs have an insulator pad and insulator washer/bushing around the screw head. Check for no continuity between the tab(pin 2) of MOSFET and GND of board before startup. Also make sure polarity of your power supply input is correct. Positive goes to pin next to JST power switch jack.
This is a spin-off from the PCA (Pocket Class A) amp. It’s the same topology but I wanted a separate thread to discuss the technical aspects which are different. This amp is a joint effort between myself, BabyDontHertzMe (BDHM), and JPS64 whom both did a fantastic layout for the PCB. The DCA is designed for through hole components with lots of room for capacitor rolling options, a built in capacitance multiplier and CRCRC power supply section. There are 3 ground planes (PSU,Left, Right) that come together at a star topology. The board has almost identical high current traces on both sides that are joined with thousands of vias for a true low impedance path. Nominal design is for 20v Vcc, 125mA bias current and can be pushed as high as 25v Vcc for driving low impedance cans. Typical performance is 0.015%THD all H2 and a little H3 for 1vpp into 42ohm load. Can drive 42ohms as high as 544mW without clipping. Sound is powerful, and being zero global feedback, has an impressively wide and accurate soundstage. The signature is engaging and natural with no hint of fatigue. Tested with DT880-250, OB-1’s, and HE-400i. All sound fantastic and can get louder than you can handle comfortably without strain. In summary, it’s an easy to build amp and and designed for the DIYer who likes to tweak. The nice low noise PSU built in simplifies the power supply logistics.
Schematic of Production Board:
Actual PCB:
Stuffing Guide:
Please note that polarity of 4 jacks on front from left to right is +ve -ve / -ve +ve / +ve -ve / -ve +ve
Due to mirror symmetry.
Built up Amp:
Rear View
Measurements:
20.2v Vcc and 125mA bias
21.3v Vcc and 0.0066% THD
Power Measurement Test into 42ohm load:
Corresponding O-scope shot:
I was able to get 10.5vpp without clipping for 544mW into 42ohms.
Announcements & Updates: I have been getting a lot of reports of builders experiencing sparks with connecting the power supply or melting the power switch at first turn on. Please make sure your MOSFETs have an insulator pad and insulator washer/bushing around the screw head. Check for no continuity between the tab(pin 2) of MOSFET and GND of board before startup. Also make sure polarity of your power supply input is correct. Positive goes to pin next to JST power switch jack.
This is a spin-off from the PCA (Pocket Class A) amp. It’s the same topology but I wanted a separate thread to discuss the technical aspects which are different. This amp is a joint effort between myself, BabyDontHertzMe (BDHM), and JPS64 whom both did a fantastic layout for the PCB. The DCA is designed for through hole components with lots of room for capacitor rolling options, a built in capacitance multiplier and CRCRC power supply section. There are 3 ground planes (PSU,Left, Right) that come together at a star topology. The board has almost identical high current traces on both sides that are joined with thousands of vias for a true low impedance path. Nominal design is for 20v Vcc, 125mA bias current and can be pushed as high as 25v Vcc for driving low impedance cans. Typical performance is 0.015%THD all H2 and a little H3 for 1vpp into 42ohm load. Can drive 42ohms as high as 544mW without clipping. Sound is powerful, and being zero global feedback, has an impressively wide and accurate soundstage. The signature is engaging and natural with no hint of fatigue. Tested with DT880-250, OB-1’s, and HE-400i. All sound fantastic and can get louder than you can handle comfortably without strain. In summary, it’s an easy to build amp and and designed for the DIYer who likes to tweak. The nice low noise PSU built in simplifies the power supply logistics.
Schematic of Production Board:
Actual PCB:
Stuffing Guide:
Please note that polarity of 4 jacks on front from left to right is +ve -ve / -ve +ve / +ve -ve / -ve +ve
Due to mirror symmetry.
Built up Amp:
Rear View
Measurements:
20.2v Vcc and 125mA bias
21.3v Vcc and 0.0066% THD
Power Measurement Test into 42ohm load:
Corresponding O-scope shot:
I was able to get 10.5vpp without clipping for 544mW into 42ohms.
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Hi Pcgab,
Actually, anything above 4.7uF is enough for practical bass extension needed. The larger caps have a bit more EMI pickup but only noticed when my fingers touch the body. 12uF is fine as long as room on board permits. I have 6.8uF purple Clarity Cap on my Aksa Lender HPA and find that sounds great. That’s a good price too.
Truth be told, the $0.35 10uF 35v Silmic II sounds darn good.
X
Actually, anything above 4.7uF is enough for practical bass extension needed. The larger caps have a bit more EMI pickup but only noticed when my fingers touch the body. 12uF is fine as long as room on board permits. I have 6.8uF purple Clarity Cap on my Aksa Lender HPA and find that sounds great. That’s a good price too.
Truth be told, the $0.35 10uF 35v Silmic II sounds darn good.
X
Hi Pcgab,
Actually, anything above 4.7uF is enough for practical bass extension needed. The larger caps have a bit more EMI pickup but only noticed when my fingers touch the body. 12uF is fine as long as room on board permits. I have 6.8uF purple Clarity Cap on my Aksa Lender HPA and find that sounds great. That’s a good price too.
Truth be told, the $0.35 10uF 35v Silmic II sounds darn good.
X
Maybe I'll try an 8.2 instead, the 12's are likely a bit big for the board.
Thanks for the tips, X!
This might be useful for those who don’t have JST crimp tool:
JST XH 2.5mm 2-Pin Connector with LOCK Plug Wire Lengh 300mm x 10 Sets 726811952092 | eBay
10 sets is enough for 2 DCA’s
JST XH 2.5mm 2-Pin Connector with LOCK Plug Wire Lengh 300mm x 10 Sets 726811952092 | eBay
10 sets is enough for 2 DCA’s
Thanks, Idiosyncrasy. The “Swiss Cheese” traces and vias are a JPS64 signature layout technqieue. The extra vias connect two planes of essentially identical traces on both sides to increase metal and surface area for low impedance electrical paths. Side benefits are enhanced cooling and strength of the traces and pads from being pulled off due to rework. Board is 2mm thick and copper is double thick 2oz with ENIG finish. Board is very sturdy and substantially built. Fab houses do not charge any extra for extra vias.
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Yes, plus the cool blue color vs usual green. Note that parts are all easily sourced and low cost (BF862 JFET and IRF610PBF MOSFET). No matching needed (unless you really are picky about balanced left right then match the JFETs to within 5% Idss). Easy to do with low cost SMT JFETs. The performance to price ratio is extraordinary.
The Aksa Lender HPA has lower THD but similar sonic profile of SE Class A. The Aksa Lender also has more gain, if that’s what you like. But I would say that a no global feedback SE Class A like the DCA, will have better soundstage and imaging. The DCA can be driven to very high bias (tested to 150mA which means it can drive 300mA peak current) as it has provision for larger heatsink. So can drive lower impedance cans with more power. I think you will find that both sound similar in that they are very dynamic and natural sounding with smooth response and low low noise. They are cheap enough to enjoy many times. Don’t need to settle on one. DCG3 is a great amp but I have not listened to it side by side so can’t compare.
These look like nice heatsinks and will handle the thermal load just fine.
WAKEFIELD 627-15ABP Vertical Heatsink TO-220 34.9 x 12.7 x 38.1(mm) *NEW* Qty.10 | eBay
I currently use these:
To-220 Heat Sink 1 Hole 10 Pcs | eBay
WAKEFIELD 627-15ABP Vertical Heatsink TO-220 34.9 x 12.7 x 38.1(mm) *NEW* Qty.10 | eBay
I currently use these:
To-220 Heat Sink 1 Hole 10 Pcs | eBay
These Class 2 transformers have been found to be very low noise when used drive a DC step up.
GCi technoLogies AM-12800 12VDC 800mA Charger / Power Supply Amazon.com : GCi technoLogies AM-12800 12VDC 800mA Charger / Power Supply : Everything Else
Use something like this for the DC-DC step up or down.
That plus the built in cap Mx and CRCRC are all you need to have a PSU that’s as clean as a battery.
GCi technoLogies AM-12800 12VDC 800mA Charger / Power Supply Amazon.com : GCi technoLogies AM-12800 12VDC 800mA Charger / Power Supply : Everything Else
Use something like this for the DC-DC step up or down.
That plus the built in cap Mx and CRCRC are all you need to have a PSU that’s as clean as a battery.
Very interesting. I was under the impression that log pots were the goto pots for audio. Why do you prefer linear?
Most affordable logarithmic pots are actually a combination of two linear tracks that give a log approximation.
I've used the loading resistor method mentioned by Rod Elliott here ESP - A Better Volume Control with excellent results. High quality linear pots are easier to get and cost less. X is right about them tracking better, too.
I've used the loading resistor method mentioned by Rod Elliott here ESP - A Better Volume Control with excellent results. High quality linear pots are easier to get and cost less
. X is right about them tracking better, too.