Ok folks, for the Pocket Class A Headamp GB, if you are interested, please quote this post and add your name. When I get at least 5 people with 2 units ea or 10 people with 1 unit ea, etc. (minimum 10 boards), I will place the order for the boards.
My pricing is the usual to cover shipping and nominal costs of fab and hassle of conducting a GB. Put it this way, I am not getting rich off of it
$17 for 1 board outside of continental US (CONUS). $12 for one board within CONUS.
If you want two boards, add $5 so $23 or $17 for two boards outside CONUS, and inside CONUS, respectively.
In case you are wondering what the BOM will cost, between $20 and $30 depending on your choice of components. Not including batteries or Altoids tin.
Would anyone be interested in a fully-built and tested unit, with same SE Class A topology and fits in an Altoids tin, but has added feature of turn-on delay protection relay, and uses top of the line components (WIMA, Panasonic OSCON, Alps, etc.)? Pricing is TBD based on interest.
Board will look like this:
It's SMT on one side and through hole on the other side. The SMT's are 0805 - easy to hand solder - don't worry about it.
Many thanks to BDHM fot the layout and Agdr for the baseline Altoids tin footprint and pot/jacks/LED Eagle files. Could not have gotten this far without you guys.
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Pocket Class A GB Order List:
xrk971 - 2 boards
funch - 2 boards
(add your name and number of boards here. Please use quote feature to grow list.)
The MKS caps in the BOM from Wima are PET - polyethylene terephthalate
http://www.mouser.com/ds/2/440/WIMA_MKS_2-11660.pdf
http://www.mouser.com/ds/2/440/WIMA_MKS_2-11660.pdf
Lastest BOM is here
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-2.html#post4967657
The main error is qnty 12 x 270R needs to be
qnty 4 x 270R and qnty 8 x 470R.
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-2.html#post4967657
The main error is qnty 12 x 270R needs to be
qnty 4 x 270R and qnty 8 x 470R.
Another two transistor amp - this one has a FET input and a BJT output with a niceness knob that lets you dial in the harmonic profile. Thanks to Aksa for design.
http://www.diyaudio.com/forums/solid-state/301164-mosfet-source-follower-headamp-32.html
This implementation has a DC-to-DC converter and a cap multiplier to "linearize" the SMPS.
http://www.diyaudio.com/forums/solid-state/301164-mosfet-source-follower-headamp-32.html
This implementation has a DC-to-DC converter and a cap multiplier to "linearize" the SMPS.
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The 2SA1837 Reigns Once Again
My new JFET-BJT amp is now tweaked for high bias hot running (135mA) desktop use. With a BF862 on input stage and Toshiba 2SA1837 driver on the output stage and 20v power supply - the sound is incredible. Amp matches simulation for harmonic distortion measuring in at -84dB for H2 and at -96dB for H3 and nothing else, with a measured THD of 0.0037% (37ppm) while driving 700mV into 270R load. All on 2 transistors and made possible by the superlative 2SA1837. These are at EOL but still available for $0.70 on Mouser.
http://www.diyaudio.com/forums/solid-state/301164-mosfet-source-follower-headamp-34.html
I am using a 24v SMPS and mosfet cap multiplier followed by a low ESR cap bank.
This is my new reference headamp. The 2SA1837 is the new King - giving the LU1014D nothing to claim but higher current - not needed here in a headamp.
Sound clips available here:
http://www.diyaudio.com/forums/solid-state/301164-mosfet-source-follower-headamp-34.html#post4974324
My new JFET-BJT amp is now tweaked for high bias hot running (135mA) desktop use. With a BF862 on input stage and Toshiba 2SA1837 driver on the output stage and 20v power supply - the sound is incredible. Amp matches simulation for harmonic distortion measuring in at -84dB for H2 and at -96dB for H3 and nothing else, with a measured THD of 0.0037% (37ppm) while driving 700mV into 270R load. All on 2 transistors and made possible by the superlative 2SA1837. These are at EOL but still available for $0.70 on Mouser.
http://www.diyaudio.com/forums/solid-state/301164-mosfet-source-follower-headamp-34.html
I am using a 24v SMPS and mosfet cap multiplier followed by a low ESR cap bank.
This is my new reference headamp. The 2SA1837 is the new King - giving the LU1014D nothing to claim but higher current - not needed here in a headamp.
Sound clips available here:
http://www.diyaudio.com/forums/solid-state/301164-mosfet-source-follower-headamp-34.html#post4974324
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Update on the thermal issue with the resistors. It's no problem now - in fact I think I found a good way to make very low inductance precision power resistors. Just use a PCB with two wide copper pads (bar shaped) and solder the needed 1% SMT resistors across them in parallel to achieve desired value and thermal rating. And as I found out, bond the bottom of the PCB to a heatsink with a thin layer of silicone RTV and the whole things stays fairly cool to the touch. What was too hot to touch is now just warm.
In my case, I made a precision 1% 1.5w capable ultra low inductance power resistor for cost of 5 x SMT resistors ($0.04).
In my case, I made a precision 1% 1.5w capable ultra low inductance power resistor for cost of 5 x SMT resistors ($0.04).
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Some listening impressions:
- Tracks recorded from playback through the amp are very similar sounding to the reference material - so sounds like the HA is mostly transparent
To nitpick:
- Reference tracks sound just a tiny bit more dynamic
- To my ears sounds like the HA is adding a slight bit of top end shimmer; and on the acoustic rock track I got an impression of just a bit more "space" vs the reference
Excellent work X!
- Tracks recorded from playback through the amp are very similar sounding to the reference material - so sounds like the HA is mostly transparent
To nitpick:
- Reference tracks sound just a tiny bit more dynamic
- To my ears sounds like the HA is adding a slight bit of top end shimmer; and on the acoustic rock track I got an impression of just a bit more "space" vs the reference
Excellent work X!
Thanks!
As soon as I measure and match the 50 bf862's I have here already I'll have it up and running.
I was waiting for the test socket I ordered to get delivered, but there's no telling when that will be. So I may just go through and measure all these suckers and try to get a group with close idss.