Here are some adorable photos of two young sisters, soldering a pair of Hedgehog amps as a gift for their grandfather: post #27 in another thread
Wow.
Wow.
Congratulations @micio_mao !! It's a very clean and tidy build. If you decide to buy banana jacks for the speaker terminals, the ones with M4 threads on eBay are very pretty. See Nelson Brock's post #48 in this thread: those are available on eBay, if you like them.
Here’s a listing for the smaller PSU’s. One thing that makes these amps popular is that they are relatively cheap, and saving money can make them accessible to more people such as university students. The PSUs are $30:
https://www.jameco.com/z/GST90A24-P...Power-Supply-2-5mm-Plug-Level-VI_2223494.html
The alternative is to splice a second cord and plug onto the bigger PSU. Cheaper still! Perhaps 3 meters of 2 conductor wire and a plug could be included in the kit….
A Nice little product kit could be a small metal box for marks filter with an input Jack for the PSU, and then wire and 2 plugs to run to the 2 amps. that way the amps are still the simple original circuit, but can be upgraded with a filter later if desired.
I love the small parts count of the original. Keeps things simple. So setting the pot manually is fine IMHO as building the amp without a meter to check the value of resistors is setting yourself up for failure, and since you should have a meter, setting the pot is just a fun step..
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Like many here I was instantly attracted to Nelson Brock's brilliant 'boxless' reimagining of Nelson Pass' ACA. More importantly, perhaps, so was The Lady.
I contacted Mark to take him up on his generous offer of PCBs and they are on the way to a friend in Florida. Thanks much, Mark. I don't live in the US and have found the easiest way to get parts is to 'warehouse' them at a friend and figure out getting them to me when all orders are complete.
I placed an order with Mouser for Mark's BOM. To be delivered to the Florida address. A few days went by with my Order Status showing 'Export Review'. I then got a rather terse email from Mouser requiring me to return a signed form to them indicating the intended use of the parts and details of my 'Forwarder/Broker'. The explanation given was that mine was a 'Routed Transaction'. I suspect that, because I am not resident in the US and paid with a credit card whose Billing Address was non-US, the order fell into this category. In nearly twenty years of buying parts from US providers I have never had to do this. I'd already - this year - placed and received several orders of parts from Digikey, Mouser themselves, Arrow and Newark using that same credit card without this requirement.
Anyway, I filled out the form, giving 'DIY personal amplifier' as the Intended Use and giving my friend's name and address but explaining briefly that he was not a broker or forwarder, merely someone who would hold on to the parts until I arranged to get them to where I live, and sent the form back to Mouser.
Some more days went by and I next got a response from Mouser indicating that my description of Intended Use was not good enough. I assumed the Broker/Forwarder was good enough as there was no mention of that. A little teed off as to why 'DIY personal amplifier' did not adequately describe the Intended Use for a bunch of mainly resistors and capacitors I sent a link to this thread and the ACA Redux thread along with a terse addition of my own promising to bear in mind the hoops I was jumping through next time I considered ordering from Mouser. A few more days went by and now the order appears to be ready to ship according to Mouser's Order Status.
During the delay I decided to see whether Digikey had the parts. They had the same parts availability as Mouser - everything in stock for immediate shipment except the TO-247s, the ZTX450/451s and the 0.68R 3W resistors. Those three items show - as of this writing - as being in stock at Newark. OIYF - Octopart Is Your Friend.
So, for what it's worth and mainly as an option for anyone in a similar 'overseas' position to me, I thought I'd attach the results of my Digikey parts search. I have Mark's blessing to do this and I have shamelessly used his BOM sheet as a basis. The usual caveats apply - buy at your own risk, I'm not responsible for any errors or inaccuracies etc etc.
If it manages to 'translate' across the new diyAudio platform the Part ID designations in the second column of the attached zipped spreadsheet are hyperlinks directly to the Digikey pages of the listed parts. Clicking on them saves a bit of copy and paste effort.
I contacted Mark to take him up on his generous offer of PCBs and they are on the way to a friend in Florida. Thanks much, Mark. I don't live in the US and have found the easiest way to get parts is to 'warehouse' them at a friend and figure out getting them to me when all orders are complete.
I placed an order with Mouser for Mark's BOM. To be delivered to the Florida address. A few days went by with my Order Status showing 'Export Review'. I then got a rather terse email from Mouser requiring me to return a signed form to them indicating the intended use of the parts and details of my 'Forwarder/Broker'. The explanation given was that mine was a 'Routed Transaction'. I suspect that, because I am not resident in the US and paid with a credit card whose Billing Address was non-US, the order fell into this category. In nearly twenty years of buying parts from US providers I have never had to do this. I'd already - this year - placed and received several orders of parts from Digikey, Mouser themselves, Arrow and Newark using that same credit card without this requirement.
Anyway, I filled out the form, giving 'DIY personal amplifier' as the Intended Use and giving my friend's name and address but explaining briefly that he was not a broker or forwarder, merely someone who would hold on to the parts until I arranged to get them to where I live, and sent the form back to Mouser.
Some more days went by and I next got a response from Mouser indicating that my description of Intended Use was not good enough. I assumed the Broker/Forwarder was good enough as there was no mention of that. A little teed off as to why 'DIY personal amplifier' did not adequately describe the Intended Use for a bunch of mainly resistors and capacitors I sent a link to this thread and the ACA Redux thread along with a terse addition of my own promising to bear in mind the hoops I was jumping through next time I considered ordering from Mouser. A few more days went by and now the order appears to be ready to ship according to Mouser's Order Status.
During the delay I decided to see whether Digikey had the parts. They had the same parts availability as Mouser - everything in stock for immediate shipment except the TO-247s, the ZTX450/451s and the 0.68R 3W resistors. Those three items show - as of this writing - as being in stock at Newark. OIYF - Octopart Is Your Friend.
So, for what it's worth and mainly as an option for anyone in a similar 'overseas' position to me, I thought I'd attach the results of my Digikey parts search. I have Mark's blessing to do this and I have shamelessly used his BOM sheet as a basis. The usual caveats apply - buy at your own risk, I'm not responsible for any errors or inaccuracies etc etc.
If it manages to 'translate' across the new diyAudio platform the Part ID designations in the second column of the attached zipped spreadsheet are hyperlinks directly to the Digikey pages of the listed parts. Clicking on them saves a bit of copy and paste effort.
I'm excited to say that we'll be building my ACA Redux as a part of Burning Amp 2022! 
For those unfamiliar, Burning Amp takes place in San Francisco on October 15th and 16th, the build is Saturday morning with workshops in the afternoon and the main event is all day Sunday. We have enough space for 30 participants, but I'll have spare kits from the first batch available the whole weekend.
Thread here
Website here
Tickets here
I realized I haven't shared photos of a completed Rev 1 yet, so here they are. My first batch of 100 kits will be Rev 2, and that's what we'll built at the event. They're mostly the same as Rev 1, but I changed some graphics, moved C4 next to Q4, and made some optimizations for ease of assembly.
For those unfamiliar, Burning Amp takes place in San Francisco on October 15th and 16th, the build is Saturday morning with workshops in the afternoon and the main event is all day Sunday. We have enough space for 30 participants, but I'll have spare kits from the first batch available the whole weekend.
Thread here
Website here
Tickets here
I realized I haven't shared photos of a completed Rev 1 yet, so here they are. My first batch of 100 kits will be Rev 2, and that's what we'll built at the event. They're mostly the same as Rev 1, but I changed some graphics, moved C4 next to Q4, and made some optimizations for ease of assembly.
Attachments
Great news about the updates to the ACA Redux and it being part of the upcoming Burning Amp event.
For those of us who aren’t able to get to San Francisco, I am wondering if there will be a group buy or similar opportunity for kits in the future. A while back i responded to a form where we could indicate interest in a potential group buy, and I am hopeful that that will eventually happen.
I am respectful of and greatly admire the level of skill required to develop devices such as this, and the level of effort to put together kits in today’s environment and run a build event at BA 2022. Your design has definitely piqued my nascent but growing interest in building an amp such as this, and makes me feel like I am quickly becoming one of the greedy boyz I read about here (hence this shameless post).
I wish you and BA 2022 build participants fun and success in October.
For those of us who aren’t able to get to San Francisco, I am wondering if there will be a group buy or similar opportunity for kits in the future. A while back i responded to a form where we could indicate interest in a potential group buy, and I am hopeful that that will eventually happen.
I am respectful of and greatly admire the level of skill required to develop devices such as this, and the level of effort to put together kits in today’s environment and run a build event at BA 2022. Your design has definitely piqued my nascent but growing interest in building an amp such as this, and makes me feel like I am quickly becoming one of the greedy boyz I read about here (hence this shameless post).
I wish you and BA 2022 build participants fun and success in October.
Here is a link to Not exactly a Group Buy: bare boards for RACAM (Round ACA Monoblock) where you can place an order for exactly ten PCBs, and the fab ships them straight to your door (including Customs and VAT) in less than two weeks. Then you source all electronic components yourself, including the "hedgehog" heatsink(s) and the Switch Mode Power Supply(s).
After building your amps, if you have any extra, left over boards you can give them away to other DIYers. Or put them into the Forum's Swap Meet and trade for interesting stuff from other hobbyists. Or sell them, either here or on eBay or Craigslist.
Clearly this option is not a perfect fit for the layzee boyz, since you'll need to exert yourself to find components and buy them, perhaps using more than one supplier. You may discover that XX is only in stock at Ersatzco while YY is only in stock at Phonus Balonus, etc. Some people truly enjoy this aspect of the hobby, others hate it so much they'd choose to skip the project entirely, rather than buy their own parts.
After building your amps, if you have any extra, left over boards you can give them away to other DIYers. Or put them into the Forum's Swap Meet and trade for interesting stuff from other hobbyists. Or sell them, either here or on eBay or Craigslist.
Clearly this option is not a perfect fit for the layzee boyz, since you'll need to exert yourself to find components and buy them, perhaps using more than one supplier. You may discover that XX is only in stock at Ersatzco while YY is only in stock at Phonus Balonus, etc. Some people truly enjoy this aspect of the hobby, others hate it so much they'd choose to skip the project entirely, rather than buy their own parts.
For the greedy (and layzee) boyz, I'm making a batch of 100 complete kits. 30 will go toward Burning Amp and the rest will be available for sale online some time in October.
@northpaw, I've got your interest recorded as well as anyone else who filled out the form. You'll get first dibs on that batch of kits
To those that have been waiting, thanks for your patience. I recognize it's been several months but things are happening behind the scenes.
This is my first time offering kits and there's definitely learning curve. Ultimately I decided not to structure this like a group buy. Instead, I'm only going to collect money once I have kits ready to ship. A lot of the upfront time has been spent finding a reliable source for the parts so when it's time for another batch the lead time will be much shorter. I'm hoping to always have kits "in stock" once I get the hang of things.
@northpaw, I've got your interest recorded as well as anyone else who filled out the form. You'll get first dibs on that batch of kits
To those that have been waiting, thanks for your patience. I recognize it's been several months but things are happening behind the scenes.
This is my first time offering kits and there's definitely learning curve. Ultimately I decided not to structure this like a group buy. Instead, I'm only going to collect money once I have kits ready to ship. A lot of the upfront time has been spent finding a reliable source for the parts so when it's time for another batch the lead time will be much shorter. I'm hoping to always have kits "in stock" once I get the hang of things.
A few of us got to hear these with Nelson’s SLOB speakers at the speaker builders camp earlier this year. They sound great, especially with efficient speakers. Gain is 10dB with a standard build, and can be boosted slightly with some tweaks to the input and feedback resistors.
A preamp is a good idea.
A preamp is a good idea.