We had a very good turnout for the initial 50 PCB's on the Pocket Class A Headamp GB. All boards from GB1 now gone and i am starting GB2. In case anyone is interested please post your name and number of boards over in thread here:
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-19.html#post4993833
GB1 boards tested and verifed to work splendidly - amazing sound, for any headphone amp - size not a consideration:
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-19.html#post4993833
GB1 boards tested and verifed to work splendidly - amazing sound, for any headphone amp - size not a consideration:
Nice work!We had a very good turnout for the initial 50 PCB's on the Pocket Class A Headamp GB. All boards from GB1 now gone and i am starting GB2. In case anyone is interested please post your name and number of boards over in thread here:
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-19.html#post4993833
GB1 boards tested and verifed to work splendidly - amazing sound, for any headphone amp - size not a consideration:
Very Well done!!!
The layout was by BabyDontHertzMe - another very good layout artist. Prasi has done many others for me though.
Edit - saw that BDHM already responded - great layout that worked the first time.
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Fantastic design!
Smart use of both sides of the board, TH + SMD = top class build.
Congrats, guys!
Cheers,
Valery
Thanks, Valery. You should make one - GB2
the double sided design also keeps the hot Class A side away from the through hole parts. Kapton tape on the insides of the tin walls really improves radiative heat transfer out to keep things cool.Aksa helped me to adjust the circuit for a desktop high-bias version of the JFET-BJT using the venerable Toshiba 2SA1837 BJT driver. The bias current is set at 135mA with a 20.0v power supply provided by a 24v SMPS and a Juma cap Mx (IRFP240 based), followed by a low ESR 24mF cap array.
Here is the PCB layout as drawn using a Sharpie marker just before the acid etch:
Here is a closeup of the amp as built using SMT components where possible. I have 2.2uF 250v MKT input coupling caps, 390uF 20v Panasonic OSCON output coupling caps with 0.47uF 100v MKP bypass caps. The Niceness trimmer is set at 68R:
Here is the setup with the power supply consisting of 5amp 24v SMPS, cap Mx, and cap array:
With the above setup, I measured the following harmonic distortion profile for 1kHz excitation and 700mV output into 270R load. The stated THD was 0.0037% - a very nice low figure resulting from a superior output stage BJT and a nice hot running bias current. Some switch mode noise is still managing to leak through but it's down pretty low at -90dB to -100dB. However, the measured H2 component is -90dB (lower than predicted!) and the H3 is -12dB less than H2 and the rest is down in the weeds. This is an excellent result for such a simple amp and the profile is very nice:
Here is the measured (multi-tone) frequency response:
Listening to is so far with a couple of tracks has not disappointed me. Superb bass authority, very transparent and clear, great smoothness, nice highs. Super quiet when no music playing or during quiet passages. Those SMT resistors are probably not the best choice for this as they are running way over their rating at present (1.3w vs rated 625mW). As you can imagine, the PCB is hot to the touch from all that heat. I will thermally bond it to the aluminum case with some white RTV.
You make it look so easy to build the amp and the beyer dt880 looks really nice with the chrome.
I really want to build this amplifier but the 2sa1837 is obsolete part. I found sellers from china on ebay selling it. Not sure if they are fake (relabelled who knows what) or reproduction ones from china factory. Also saw bf862 on ebay from china sellers. They are half the price of what i would get from rscomponents. These shouldn't be fake right ?
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It really is easy. There are only two actives.
The BF862 is a low cost mass production JFET originally designed for automotive AM radios from what I recall. I have bought from AliExpress and eBay many times and the BF862 is good. Half price is about right.
The 2SA1837 is discontinued but large stocks are out there. I bought 100 from Mouser before they disappeared. But I have also bought some from AliExpress and they look genuine and work well as I have genuine ones of known origin to compare with. As long as the price is not too low. But you just won’t know until you buy them.
Interestingly, the 2SA1837 CFP amp above, beat many other amps in a blind audition here:
Blind Virtual Audition of Several Headamps
It’s one of my best sounding amplifiers, and to this day, remains a reference. I have managed to get the noise floor down flat like all my other amps as the above data is old.
But if you want something easy to make that sounds almost as good, try this one:
xrk971 Pocket Class A Headamp GB
The BF862 is almost guaranteed to be genuine.
Finally, if you want a really nice low distortion preamp/headphone amp, my latest project is here and has a GB going on. Here is this new preamp re-configured as a headphone amp:
Discussion here:
AKSA's Lender Preamp with 40Vpp Output
GB here:
AKSA's Lender Preamp with 40Vpp Ouput GB
The BF862 is a low cost mass production JFET originally designed for automotive AM radios from what I recall. I have bought from AliExpress and eBay many times and the BF862 is good. Half price is about right.
The 2SA1837 is discontinued but large stocks are out there. I bought 100 from Mouser before they disappeared. But I have also bought some from AliExpress and they look genuine and work well as I have genuine ones of known origin to compare with. As long as the price is not too low. But you just won’t know until you buy them.
Interestingly, the 2SA1837 CFP amp above, beat many other amps in a blind audition here:
Blind Virtual Audition of Several Headamps
It’s one of my best sounding amplifiers, and to this day, remains a reference. I have managed to get the noise floor down flat like all my other amps as the above data is old.
But if you want something easy to make that sounds almost as good, try this one:
xrk971 Pocket Class A Headamp GB
The BF862 is almost guaranteed to be genuine.
Finally, if you want a really nice low distortion preamp/headphone amp, my latest project is here and has a GB going on. Here is this new preamp re-configured as a headphone amp:
Discussion here:
AKSA's Lender Preamp with 40Vpp Output
GB here:
AKSA's Lender Preamp with 40Vpp Ouput GB
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If it is possible, will you be able to give links to aliexpress and ebay from where you have bought the BF862 and 2sa1837 before, through PM ?
The blind test thread is the reason I started looking into the BF862 CFP 2sa1837 amplifier. It was the first time I came across this headamp. Thanks for your time in uploading all the sound clips and doing the blind test thread. It was really interesting.
The blind test thread is the reason I started looking into the BF862 CFP 2sa1837 amplifier. It was the first time I came across this headamp. Thanks for your time in uploading all the sound clips and doing the blind test thread. It was really interesting.
BF862’s here:
Free shipping 100pcs/lot BF862,215 BF862 JFET N CHAN 20V SOT 23 Best quality-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
2SA1837 and 2SC4793 here:
10PCS 10PCS=(5PCS 2SC4793+5PCS 2SA1837) C4793 A1837 230V 1A TO220F new original-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
Note that the Toshiba’s above may not be real - but they work. For the amp, I used known genuine ones.
Free shipping 100pcs/lot BF862,215 BF862 JFET N CHAN 20V SOT 23 Best quality-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
2SA1837 and 2SC4793 here:
10PCS 10PCS=(5PCS 2SC4793+5PCS 2SA1837) C4793 A1837 230V 1A TO220F new original-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
Note that the Toshiba’s above may not be real - but they work. For the amp, I used known genuine ones.
Ok, I had some time and thought I would whip this up on a solderless breadboard first as the last time I did it on P2P veroboard it did not work. Well it works well and gets quite loud too so I obviously had something wrong the last time I did it. I am using 2SK170BL and all through hole components this time. I put a 100R trim pot in series with a 47R resistor to get a baseline 100R +/-50R adjustment range for the niceness knob. The solderless breadboard is kind of flakey - noisy with occasional crackles due to poor connections. So I will have to wait for a more permanent amp before measuring FFT and adjusting "niceness" knob. I know it works now so may just go ahead and hand-etch via Sharpie a small PCB for through hole/SMT as the SMT resistors are way easier to solder and require no drilling. I will probably make this as a "tea box" sized amp - a bit bigger than mint tin just because.
Hi Xrk971,
what is the final circuit diagram with niceness knob pot.
Any idea how does it sound when compare with Pass BA-3 preamp/frontend where also we have a pot to adjust the harmonic distortion content between 2nd and 3rd harmonic distortion.