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ACP+ Preamp/HPA for Yarra Preamp

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#83
I have good news folks: the production of the SMT prepopulated boards just got completed. Nicely soldered MELF resistors using solder paste stencil mask and hot air/hot plate. We have adjusted the resistors for a lower bias current that runs much cooler. Testing of the ACP+ as a preamp for the FH9HVX, this preamp sounds exceptional. I should be able to ship them out in a few days.
 
#86
Hey folks, just want to give an update. The prepop’d SMT boards were assembled and shipped to me from NY 13 days ago. USPS Priority Mail usually takes 2 days. I think holiday mail and Covid is definitely impacting the delivery. It still says in transit. It’s a 5-6hr drive by car. Please hang tight.

Merry Xmas everyone!
 
#89
Here is the BOM showing in bold the items that were prepopulated if you got that option. Note that X105 is a special MMA "fuseholder" style part that is not available from Mouser. We left R104 and R105 unpopulated and you should install a 200R to 500R multiturn trimpot across that and apply power to board with alligator clips and measure the bias current across a nominal 125ohm value and aim for 10mA current. Remove trimpot and solder permanent resistor. A regular axial leaded one can be bent to fit there or use an MMA or even 1206 chip resistor. I actually used 1206 and used two in parallel to trim the value. If you don't want to mess with it, imstall something like 68R to get started and get sound and tweak later.

BOM is attached below.

Edit: Actually R104 was also left unpopulated so that you can adjust the value as R104 and R105 are connected in parallel.
 

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#90
Happy New Year!

Status update on the prepop’d SMT board pre-orders. Sorry this is taking so long but the USPS Priority Mail package containing the assembled boards is stuck in limbo between NY and DC due to COVID-19. Apparently, the Dulles mail hub is the main one for the entire US Eastern Seaboard. It’s overflowing with US Mail trailers never unpacked. I heard that 8M packages are stuck over the holidays. We are told it’s not lost. Just going to be very delayed.
Thank you for your patience.
 
#95
For all the folks who ordered the ACP+ with SMT prepopulated parts, I have packed your boards and printed the labels and they ship out later today (Saturday).

There is still one set of boards with prepopulated SMT components available in case anyone wants one.

Also, plenty of bare PCBs left too.
 
#100
I put mine mostly together last weekend. I had too much difficulty fitting the heat sinks, and ordered some others to try. The ones I got from Amazon had too much bulk between the transistors and caps behind them. I did not want to bend the legs enough to squeeze them in. When some othe candidates arrive over the next week, or two, perhaps I’ll put up pictures of what fits.

After the heat sinks are mounted, and transistors are installed, I’ll do the biasing procedure.
 
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