Just a quick bump to ask for any information on this question. I've been looking at the ads for the sbooster LPS and wondering how much improvement could be achieved. Thanks!
The ACA, like other Pass amplifiers, benefits a lot from a high quality linear power supply. The 24V power rail in the original implementation was a good solution for making an amp that was easy for beginning audio enthusiasts to build themselves.
Since then, there have been a number of us who have built the ACA with a variety of different power supplies. Some have chosen to build theirs in a separate chassis, with large amounts of total capacitance for each channel. I have been happy so far using a 300VA, 24V transformer, with fairly straightforward CRCRC supply filtration. What is common to most of these linear PSU efforts is higher voltage. The output stage of the ACA can make good use of 28V to 32V, especially with alternate Mosfets such as the IRFP140, IRFP150 or even the FQH44N10.
Since then, there have been a number of us who have built the ACA with a variety of different power supplies. Some have chosen to build theirs in a separate chassis, with large amounts of total capacitance for each channel. I have been happy so far using a 300VA, 24V transformer, with fairly straightforward CRCRC supply filtration. What is common to most of these linear PSU efforts is higher voltage. The output stage of the ACA can make good use of 28V to 32V, especially with alternate Mosfets such as the IRFP140, IRFP150 or even the FQH44N10.
Thanks, TungstenAudio, for the helpful response. Unfortunately I'm still at the beginning of developing my DIY skills, and still a bit reluctant to take on building a power supply from the ground up. I finished the ACA just this week, and am so impressed with it's abilities that the added expense of a more capable power supply seems justified, and was thinking in terms of something off the shelf. Thus the sbooster options. Or, if someone is aware of a similar, comparable LPS, that could be a good option, too.
Off-the-Shelf 24 Volt Linear Power Supply
Check out Astron:
28VDC Linear Power Supplies | Astron Corporation
These are used by hams (amateur radio operators) who value low-noise linear supplies for better weak signal work. These 28 Volt supplies can be adjusted down to 24 Volts for the ACA.
Check out Astron:
28VDC Linear Power Supplies | Astron Corporation
These are used by hams (amateur radio operators) who value low-noise linear supplies for better weak signal work. These 28 Volt supplies can be adjusted down to 24 Volts for the ACA.
I don't think this is such a great idea.
For the price of one of these you'll probably build 2 better ones, with better parts, better look and you'll be proud of it.
After all it will be sitting next to, or under your amp and you'll be looking at it all the time.
Linear PSU(single polarity) is as simple as a suitable transformer, a diode bridge, a few big caps, a few power resistors,maybe a DC choke if you have one at hand, an NTC, a case(that's where you spend the most, time and money if you want it to look the part).
Then you can add a CapMx to smooth the output even further, but that is optional.
No matter if you use a SMPS or a linear PSU it's always a good idea to fit a CRC or CLC bank in the amp case feeding directly the amps.
Some time ago in a different thread Mr. Pass said that a CRC with 47000uF - 0.5 ohm R - 47000uF will get you down to approx. 7 mV ripple.
So give it a try.
I agree. The poster was looking for an off-the-shelf linear power supplier. OTS, high current, low noise, linear power suppliers are rare, hard to find, big and expensive. They are now specialty items, replaced by switching supplies for most applications. Building your own linear supply is easy if you have the knowledge and resources to do so. Additionally, you can tailor it to your specific needs and application without any major compromise.
Universal power supply
Be warned that the next step on the slippery slope / yellow brick road following the ACA is likely the Pass F5 or Burning amp 3 from diyAudio. In both cases you also build the Diyaudio Universal power supply. This should also be suitable for the ACA but more experienced heads than me can confirm that. This can be built into a Galaxy 230 x 350 mm case to make a remote power supply, or built into the DeLuxe 4U case to use with a variety of Pass amp boards. The ACA is a gateway drug to other manifestations of Mr Pass design genius......
Be warned that the next step on the slippery slope / yellow brick road following the ACA is likely the Pass F5 or Burning amp 3 from diyAudio. In both cases you also build the Diyaudio Universal power supply. This should also be suitable for the ACA but more experienced heads than me can confirm that. This can be built into a Galaxy 230 x 350 mm case to make a remote power supply, or built into the DeLuxe 4U case to use with a variety of Pass amp boards. The ACA is a gateway drug to other manifestations of Mr Pass design genius......
The schematics for the diyAudio power supply may be used as a template for wiring your own, even if you choose not to use the PCBs that are available. Although the store boards are set up to provide both positive and negative rail voltages, they can be adapted to provide a pair of positive rails. The ACA will run best with a 300VA transformer, secondary voltage from 20V to 24V. That will yield two independent power rails from 24.5V to 29.5V or so, depending on your choices for rectifiers and the R in the CRC.
I have a question about the audio L/R and DC inputs on the ACA. I've noticed that there are no input filtering (chokes/bypass caps/etc...). I just built the NOIR preamp and now appreciate what all of that can do for the DC input if using an SMPS, and am now wondering why the ACA isn't specified with at least a bypass cap across the input, much less some of the other options.
I am building a linear external supply for a "premium" build of the ACA I just completed and it occurred to me that the build guide for the 1.6 has you connecting the inputs' negative to the DC negative/return without any bypassing either.
Is the assumption that this should happen back at the supply or just to keep things super simple?
I am building a linear external supply for a "premium" build of the ACA I just completed and it occurred to me that the build guide for the 1.6 has you connecting the inputs' negative to the DC negative/return without any bypassing either.
Is the assumption that this should happen back at the supply or just to keep things super simple?
After ACA...now what?
This discussion has been great to help clarify my thinking about my next DIY project(s). The ACA was my second build, the first being a Bottlehead Crack w/speedball - a point-to-point tube headphone amp with a small PCB addition. I enjoyed both projects immensely, and guess I'm now stricken with yet another deep hobby.
I'm also keenly appreciative of the Pass designs, having a X150 anchoring my main system. The ACA is for my shop, and I'm now awaiting the availability of the next batch of parts kits to build a 2nd one, to use in a monoblock setup.
OK, enough preamble. What I'd seriously appreciate is some advice on which of the First Watt amp clones would be a good next project, i.e within my limited skill set: no EE formal training, just some new soldering skills and a lot of motivation.
No doubt I'm not the first to ask this question, but interrogating the archives on the subject has yielded so many hits that its the proverbial drinking from a fire hose to get useful advice.
Thanks in advance!
This discussion has been great to help clarify my thinking about my next DIY project(s). The ACA was my second build, the first being a Bottlehead Crack w/speedball - a point-to-point tube headphone amp with a small PCB addition. I enjoyed both projects immensely, and guess I'm now stricken with yet another deep hobby.
I'm also keenly appreciative of the Pass designs, having a X150 anchoring my main system. The ACA is for my shop, and I'm now awaiting the availability of the next batch of parts kits to build a 2nd one, to use in a monoblock setup.
OK, enough preamble. What I'd seriously appreciate is some advice on which of the First Watt amp clones would be a good next project, i.e within my limited skill set: no EE formal training, just some new soldering skills and a lot of motivation.
No doubt I'm not the first to ask this question, but interrogating the archives on the subject has yielded so many hits that its the proverbial drinking from a fire hose to get useful advice.
Thanks in advance!
I‘d say take a look at the descriptions on Papa‘s firstwatt site to see which catches you most, and then look up if there‘s a build-guide or otherwise „followable“ thread. Find the balance between lust and ability (and parts availability).
As I see it, neither of them clones are impossibly difficult, or „solder and forget“, so it’s up to you... (I chose the f4 btw, and haven‘t started yet)
Thanks, folks, for the replies and information. I have been perusing the table on the First Watt site, and honestly would be thrilled to build anything from that list. I also have to confess there is no obvious need to fill, as I already have more than enough audio gear about. But that's hardly relevant!
What I was hoping to find was some practical advice on which of those amp options are simpler to build, and so I guess more within the scope of my limited skill set. Also, as mentioned, availability seems to be a big factor. In fact I've been waiting since about last November for the ACA parts kit/PCB so I can get on with the 2nd ACA. Any rumors around about how/when that will be available? I don't want to nag to guys who do the work to make this all happen, but it sure would be nice to have a general idea.
Again, thanks for the help.
What I was hoping to find was some practical advice on which of those amp options are simpler to build, and so I guess more within the scope of my limited skill set. Also, as mentioned, availability seems to be a big factor. In fact I've been waiting since about last November for the ACA parts kit/PCB so I can get on with the 2nd ACA. Any rumors around about how/when that will be available? I don't want to nag to guys who do the work to make this all happen, but it sure would be nice to have a general idea.
Again, thanks for the help.
I built an ACA version for a headphone with IRF830. Bias is around 120 mA.
I run both channels from their own 12 volt DC (disregarding post 1489) and it works. Fine. For this purpose of course only.
I increased the gate resistor to 270 ohm.
I have 470 uF as output - that simulated quite well,
It measured good with a 47 ohm load:
I have feedback 39k (in)/82k. So amplification is about 3x; 10 dB.
Sort of like the ACP+.
It stays very cool.
More voltage gives better power (and better harmonics probably because of headroom) but for headphone that is not needed. Goal: Fostex RP @ 32 ohms.
Enclose the circuit sims.
If the resonances do not go away I will try a lateral version on the bottom.
I run both channels from their own 12 volt DC (disregarding post 1489) and it works. Fine. For this purpose of course only.
I increased the gate resistor to 270 ohm.
I have 470 uF as output - that simulated quite well,
It measured good with a 47 ohm load:
- Goes down to 6 Hz
- upper limit is >500 kHz.
- But it has high freq resonances that then start to show; also as very high frequency ringing in the square wave. So. -> Placed 15 pF across the 82 Kohm feedback, now it is OK. So this reduces bandwith too, to 133 kHz.
I have feedback 39k (in)/82k. So amplification is about 3x; 10 dB.
Sort of like the ACP+.
It stays very cool.
More voltage gives better power (and better harmonics probably because of headroom) but for headphone that is not needed. Goal: Fostex RP @ 32 ohms.
Enclose the circuit sims.
- My 12V version on top.
If the resonances do not go away I will try a lateral version on the bottom.
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In a similar situation to yours I chose to build the M2X. The build thread is amazing and people are very helpful. Probably as much as the ACA thread. Summed to this, it is popular enough that a lot of problems and troubleshooting happened and are in the thread as well.
Sharing my bi-amp build
I decided to run each speaker driver with its own ACA to see what would happen. I’m so impressed. How fun! Sounds fantastic!
The build: The only piece I didn’t DIY was the turntable.
Rega turntable to boozehound labs phono amp to (blank no pre amp yet, waiting on the Korg nutube b1) to boozhound labs active crossover to the ACA with one side driving the woofer and the other driving the tweeter. I built the speakers too - scanspeak drivers, mahogany and walnut case. Sized and ported to spec.
I wonder what it will sound like once the korg is in the line. It sounds so great I hate to put it in. But, it will be nice to have volume control, and another input channel.
I decided to run each speaker driver with its own ACA to see what would happen. I’m so impressed. How fun! Sounds fantastic!
The build: The only piece I didn’t DIY was the turntable.
Rega turntable to boozehound labs phono amp to (blank no pre amp yet, waiting on the Korg nutube b1) to boozhound labs active crossover to the ACA with one side driving the woofer and the other driving the tweeter. I built the speakers too - scanspeak drivers, mahogany and walnut case. Sized and ported to spec.
I wonder what it will sound like once the korg is in the line. It sounds so great I hate to put it in. But, it will be nice to have volume control, and another input channel.
