Suppose for a moment that you were Nelson Pass, and you were about to order final PCBs for the Build Camp that takes place in 30 days. Each of the 25 builders needs 2 boards, plus you want some spares in case of loss or damage, so you decide you need to order at least 75 PCBs, and you need them in your hands in 25 days or less.
What would you do? How paranoid would you be? Remember that if you don't get 75 PCBs in time for Build Camp, the attendees' fun is ruined. Would you take any precautions against fab delays, shipping delays, lost parcels, damaged parcels, union strikes?
What would you do?
If I were Nelson Pass, I would decide to be somewhat paranoid. I would pay $202 for what amounts to an insurance policy. I'd order 75 PCBs from the fab called JLCPCB, choosing DHL express economy for shipping. Then I'd also order another 75 PCBs from another fab, the one called Smart Prototyping. To protect against a union strike or a warehouse fire at DHL, I'd select Federal Express IP shipping from the second fab. The extra cost of double-ordering is $202, and is completely unnecessary if everything proceeds normally. But, if something does go wrong, I have a second chance to get 75 boards in time for Build Camp, and that second chance costs me only $202. The extra boards don't go to waste, I can always put them in the diyAudio Store after Build Camp is over. However, I don't think I would take the bat-shite insane paranoia route of triple ordering, from yet a third fab (Elecrow) and yet a third freight company (UPS). But that's just me; what would you do?
price quotes from www.pcbshopper.com ; board size estimate obtained by rectal extraction
What would you do? How paranoid would you be? Remember that if you don't get 75 PCBs in time for Build Camp, the attendees' fun is ruined. Would you take any precautions against fab delays, shipping delays, lost parcels, damaged parcels, union strikes?
What would you do?
If I were Nelson Pass, I would decide to be somewhat paranoid. I would pay $202 for what amounts to an insurance policy. I'd order 75 PCBs from the fab called JLCPCB, choosing DHL express economy for shipping. Then I'd also order another 75 PCBs from another fab, the one called Smart Prototyping. To protect against a union strike or a warehouse fire at DHL, I'd select Federal Express IP shipping from the second fab. The extra cost of double-ordering is $202, and is completely unnecessary if everything proceeds normally. But, if something does go wrong, I have a second chance to get 75 boards in time for Build Camp, and that second chance costs me only $202. The extra boards don't go to waste, I can always put them in the diyAudio Store after Build Camp is over. However, I don't think I would take the bat-shite insane paranoia route of triple ordering, from yet a third fab (Elecrow) and yet a third freight company (UPS). But that's just me; what would you do?
price quotes from www.pcbshopper.com ; board size estimate obtained by rectal extraction
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Curious what voltage the PSU will be. 24V? 36V?
I have a spare VFET chassis (later Modushop build) that could be perfect for a stereo version of this amp. And a very nice dual-mono linear supply to go with that chassis. The only trick will be fitting MOT chokes or Hammond 195S4, either of which look to be suitable.
I bet this circuit would also do well with some of the higher transconductance Mosfets, especially if powered from a 36V rail. I found a stash of NOS Fairchild FQH44N10 parts and plan on sorting some of those for a second Aleph J. The spares would work wonders for this like they did for the ACA..
I have a spare VFET chassis (later Modushop build) that could be perfect for a stereo version of this amp. And a very nice dual-mono linear supply to go with that chassis. The only trick will be fitting MOT chokes or Hammond 195S4, either of which look to be suitable.
I bet this circuit would also do well with some of the higher transconductance Mosfets, especially if powered from a 36V rail. I found a stash of NOS Fairchild FQH44N10 parts and plan on sorting some of those for a second Aleph J. The spares would work wonders for this like they did for the ACA..
First estimate how low the MOSFET drain can swing before clipping or massively distorting the trough of a sinewave. Now you've got an equation for Vout_pk_pk as a function of Vtoprail. Use Vout_pk_pk to calculate the required minimum class A bias current, that can swing an 8 ohm load the full Vout_pk_pk.
Put it all in a spreadsheet and step Vtoprail from 10V to 44V. Make a plot of (RMS output power into 8 ohms) versus Vtoprail. Voila, there's your answer. The power supply voltage is whichever Vtoprail gives you XXX watts into 8 ohms. Use whatever value of XXX you think Mike Rothacher would design. I suspect (4W < XXX < 14W) but that's only a wild guess.
Since all the data is right there in the spreadsheet, you can also plot (required minimum class A bias current) versus Vtoprail, which will tell you how much current the power supply must deliver. Maybe this plot will show a transition point, where wall-warts can't do the job and you'll need to shift to laptop inline-brick power supplies.
Put it all in a spreadsheet and step Vtoprail from 10V to 44V. Make a plot of (RMS output power into 8 ohms) versus Vtoprail. Voila, there's your answer. The power supply voltage is whichever Vtoprail gives you XXX watts into 8 ohms. Use whatever value of XXX you think Mike Rothacher would design. I suspect (4W < XXX < 14W) but that's only a wild guess.
Since all the data is right there in the spreadsheet, you can also plot (required minimum class A bias current) versus Vtoprail, which will tell you how much current the power supply must deliver. Maybe this plot will show a transition point, where wall-warts can't do the job and you'll need to shift to laptop inline-brick power supplies.
Power supply is 12 volts. Would make an excellent amplifier for your car.
Busy building from breadcrumbs, Mike's photo from float-plane an attractive nuisance. Thanks Mike: Wayne sez I never met an airplane I didn't like.
He'd love the SeaRey. It's like a flying go-kart. 🙂 A little wind left over from the hurricane, red flags all the way down the beach, but it did just fine.
Driving these, 88db efficient, in a car?
https://www.alpine-usa.com/product/alpine-status-hdz-65-speakers
and hopefully a nice healthy 5A bias....minimum😈Power supply is 12 volts. Would make an excellent amplifier for your car.
If you own a fairly quiet car (like my Tesla), no problem.
The ACA mini drives my SR1's just fine - 3 ohm load, 87 dB, but then I don't
listen to a lot of disco....
My order of 100 boards for the first version arrived in about a week from PCBWAY. However I made some
improvements and I want perfection so I made some small changes and ordered a new batch.
I did not throw away the older boards, so I think we'll be OK....
My wife's ACA + REL Sub is running out of juice on 93 dB / W speakers (she likes EDM and Trip Hop). Perhaps a pair of bridged ACA's?
While bridged ACAs would be fun to build, EDM and Trip Hop would be better served by one of the larger amps, M2, F5, F6, etc.