Power Test under 51ohm load
Here is a 51ohm load connected to on board 270ohm load for total 42ohms, driving with 1khz sine wave, maxed out on the Cayin N3 as input source. Output still not clipped at about 9.12vpp (on o-scope) or 3.34vrms (on Fluke DMM). That's 265mW into 42ohms. The amp could probably be optimized for a little more.
Here is a 51ohm load connected to on board 270ohm load for total 42ohms, driving with 1khz sine wave, maxed out on the Cayin N3 as input source. Output still not clipped at about 9.12vpp (on o-scope) or 3.34vrms (on Fluke DMM). That's 265mW into 42ohms. The amp could probably be optimized for a little more.
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I forgot to max out the volume knob on the amp when I did the max power test, I was able to get quite a bit more: 4.78vrms into 42ohms or 544mW (with 180mA bias current and 25v Vcc). Listening now with HE-400i's - and they are too loud to listen at max volume. So this amp has the grunt to drive inefficient planars. Sound is very powerful.
I would get IRF610's from major suppliers. I have bought cheap ones from China and they look a bit off - thin copper tab for the heatsink. I have used them on cap Mx, but won't on an audio output. They are inexpensive but big enough to fake, so not worth the hassle of a fake.
Genuine Vishay IRF610PBF are $0.55ea for 10 or more.
Genuine Vishay IRF610PBF are $0.55ea for 10 or more.
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. I did the layout and JP did some fine tuning and via stitching.
Correct, but you could probably get away with 1/2W if you give them some clearance. CMF60 is officially rated for 1/2W.
In their description its given as constant current but voltage seems to be variable .. its little confusing..
One off topic question: can we use a single external power supply and use 2 of these boards and create a dual rail ( +/- ) power supply for an amp?
No, you need two external power supplies that are do not have their -ve output reference to earth ground. 2 prong Class 2 Wall transformers are ideal. As well as laptop smps without ground reference (2prong). Then connect outputs of DC step up in series for dual rail. There’s a lot more info on this in Alpha amp thread.
Pleas use 1W or 2W for 270ohm power resistors. I am using 2W and when Vcc is 24v it gets pretty hot. A good idea to over rate those. The 0.47R on CRC a 0.5w is fine. To estimate power dissipated, assume those four parallel dissipate 1/2Vcc at bias current. So Vcc of 20v is 10v drop across 67.5ohms and 125mA. Power is current time voltage or 312mW ea. Technically a 0.5w CMF55 should handle it but will be very hot. Give some breathing room above PCB for cooling on those.
How about virtual ground scheme as in pass b1r2 : B1 Rev. 2 , hereV+ V- r connected to positive and ground
Alright will do!
Are there any particular panel mount 3.5mm Jacks you'd suggest using? Otherwise I might try to tie down the ones specd for the pocket build.
Thought if we could use a pair of those dc-dc converter for a preamp with volume control ic which needs dual rails ..
The Switchcraft brand spec’d for PCA is very nice quality machined brass and nickel plated. Another good brand is Neutrik.
On desktop amps I prefer RCA input and 1/4in TRS output.
New thread to discuss technical aspects of the DCA here. I am just trying to keep the PCA discussions focused here in this current thread.
http://www.diyaudio.com/forums/head...ktop-class-dca-headphone-amp.html#post5433112
http://www.diyaudio.com/forums/head...ktop-class-dca-headphone-amp.html#post5433112
I have also used these (low profile), but personally, the positive click action on the Switchcraft are hard to beat.
Philmore 504KB 3 5mm Mini Stereo Panel Mount Jack | Full Compass
Philmore 504KB 3 5mm Mini Stereo Panel Mount Jack | Full Compass