ACA power supply ?
Hello to all and thanks for the vast information and support from all of you! I just completed assembly of my v1.6 boards and am awaiting delivery of the ACA chassis. I am planning on building a power supply for it, using the universal power supply board. Because of space limitations inside the case I was planning on powering the amp using one half of the PSU board for both channels. Would this be an acceptable approach? Thanks!
Hello to all and thanks for the vast information and support from all of you! I just completed assembly of my v1.6 boards and am awaiting delivery of the ACA chassis. I am planning on building a power supply for it, using the universal power supply board. Because of space limitations inside the case I was planning on powering the amp using one half of the PSU board for both channels. Would this be an acceptable approach? Thanks!
Thank you sir! A couple more questions, I've never used toroidal type transformers before and I'm not real clear on which to select, I know I need 24 volts to power the ACA and I think I need an 18 volt transformer for that application, does this sound about right? Also is a soft start board and speaker protection recommended. I will be using a pair of JBL-HLS-610 speakers which are listed as 88db.
The ACA will respond well to a good and carefully laid out linear power supply. I would like to recommend going to a quasi dual-mono arrangement if you can. A 300VA transformer with dual 22V secondaries has performed extremely well for me. I used a CRCRC arrangement for each channel consisting of 22mF > 1.82Ω > 10mF > 0.11Ω > 10mF. The 1.82Ω was a 25W chassis mount aluminum power resistor, and the 0.11 was a pair of 0.22Ω, 3W resistors in parallel. The chassis mount resistor may be mounted onto the heatsink or onto the baseplate, wherever there is room. The 10mF caps can be snap-in board mount 25mm diameter, and the 22mF can be screw terminal, chassis mount, 36mm diameter.
Use a GBPC type 35Amp bridge rectifier for each channel, bolted onto the baseplate to save space. Run the positive and negative supply wires next to each other; they don't need to be twisted, just right next to each other. The bridge rectifier will drop about 3 Volts, and the 1.82Ω power resistor will drop most of the remaining voltage to leave you with around 24.5 Volts on your ACA board. Try it
If you are committed to building a linear power supply inside the store ACA chassis (Mini Dissipante 2U, 200mm) then space will be at a premium. Even a 200VA transformer will be a tight squeeze, but can still work. You may need to be creative in your positioning of the ACA boards on each heatsink to avoid interference between the 3300 uF caps and the transformer. The power supply caps will be wedged into the corners of the chassis. The transformer will be best with 20V secondaries to get the full 24V on the boards, as the bridge rectifiers drop more voltage than is commonly acknowledged.
Since you haven't bought the transformer yet, you could try simply using the Mean Well 24V power brick which is also sold on the store. That will be the quickest and easiest way to some really find sound from your system. Then you could try using a Mini Dissipante 3U chassis to go all-out with a linear supply.
Thanks for the help TungstenAudio. I'm trying parallel mono mode: I jumped pins 2&3 of the XLR input, flipped the rear mono switch down, and jumped the black speaker terminals. The RCA plugs are both in the white inputs. Is this the right configuration?
Power seems cut (less volume). Bass seems stronger. Overall soundstage seems wider and everything is smoother, more liquid. But it's subtle and hard to A/B quickly.
One thing I don't understand: the black to black speaker jumper doesn't seem to matter. In or out, no obvious change in output.
Final question: if I bi-amped the KEF (four total ACAs), could I expect more loudness? It's the only thing I'm missing from these beauties.
Thanks again!
Power seems cut (less volume). Bass seems stronger. Overall soundstage seems wider and everything is smoother, more liquid. But it's subtle and hard to A/B quickly.
One thing I don't understand: the black to black speaker jumper doesn't seem to matter. In or out, no obvious change in output.
Final question: if I bi-amped the KEF (four total ACAs), could I expect more loudness? It's the only thing I'm missing from these beauties.
Thanks again!
This is correct. What it does is tie the inputs of the two boards together, and it also ties their outputs together.
It is possible that the lowered impedance seen by your preamp may be making it more difficult to drive the ACA monoblocks properly. When I converted mine to parallel mono, I had already performed the modifications which increased the input impedance of each amp and reduced the negative feedback slightly. Specifically, I increased R11 to 20kΩ and increased R12 to 90.0kΩ.
Another possibility is that the parallel monoblock configuration is less suitable for your system. You could try the self-inverting bridged configuration instead. There are instructions for this as part of the ACA 1.6 Illustrated Guide. Sounds like you may already have the switch for this in place.
The ACA will respond well to a good and carefully laid out linear power supply. I would like to recommend going to a quasi dual-mono arrangement if you can. A 300VA transformer with dual 22V secondaries has performed extremely well for me. I used a CRCRC arrangement for each channel consisting of 22mF > 1.82Ω > 10mF > 0.11Ω > 10mF. The 1.82Ω was a 25W chassis mount aluminum power resistor, and the 0.11 was a pair of 0.22Ω, 3W resistors in parallel. The chassis mount resistor may be mounted onto the heatsink or onto the baseplate, wherever there is room. The 10mF caps can be snap-in board mount 25mm diameter, and the 22mF can be screw terminal, chassis mount, 36mm diameter.
Use a GBPC type 35Amp bridge rectifier for each channel, bolted onto the baseplate to save space. Run the positive and negative supply wires next to each other; they don't need to be twisted, just right next to each other. The bridge rectifier will drop about 3 Volts, and the 1.82Ω power resistor will drop most of the remaining voltage to leave you with around 24.5 Volts on your ACA board. Try it
For newbies can you leave links to your prior posts showing photographs how are you perform the layout for these procedures . I myself and many others have been following your modifications and advancements and are interested. A photo is Worth 1000 words can’t wait to build one of your modified versions of the ACA ��
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Certainly, for the relative newbies out there, here is the link to the thread where I begin discussing the new ACA build with a linear power supply: ACA w/ premium parts.
The chassis used for this build is 3U high and about 305mm wide by 230mm deep in the interior. These heatsinks are currently dissipating 44 Watts per channel and are warm, but not hot to the touch. The closest chassis by Hifi2000 is the Mini Dissipante 3U, 330mm by 250mm. I've got a couple of these as well, to be used for more Mad Scientist type experiments.
The chassis used for this build is 3U high and about 305mm wide by 230mm deep in the interior. These heatsinks are currently dissipating 44 Watts per channel and are warm, but not hot to the touch. The closest chassis by Hifi2000 is the Mini Dissipante 3U, 330mm by 250mm. I've got a couple of these as well, to be used for more Mad Scientist type experiments.
Thanks. I actually don't have a preamp in the system. The ACAs are fed line level from the DAC. I attenuate volume digitally on my phone (Chromecast).
TungstenAudio;5678189 Another possibility is that the parallel monoblock configuration is less suitable for your system. You could try the self-inverting bridged configuration instead. There are instructions for this as part of the ACA 1.6 Illustrated Guide. Sounds like you may already have the switch for this in place.[/QUOTE said:
TungstenAudio, thanks for the response. It gives me a lot to chew on, don't think I'm going to try and cram all that into the regular ACA chassis. I will probably go with the switching supply instead. I have it in mind to build an Aleph, next and I may just use the PSU board for that one and put it in a bigger chassis. What are you using as a preamp on your ACA?
@odamone: It sounds like you have had a fun and productive time so far investigating some of the options for driving your speakers. It is really up to you now to decide what you like, and where to go from here. I have seen accounts here in the forum of multi-amping speakers using four or more ACA amps, but haven’t tried that myself, so I don’t have much to offer on that. If you choose to proceed in that direction, then you will be able to offer your advice from that experience. Another possibility to consider is building a single F4 to drive the current hungry section of your speakers. Having essentially unity gain, it can be driven from the output(s) of the amps driving another section, providing there isn’t any frequency band limiting.
@Centurion53: My main preamp is a Naim NAC 82 powered by my own DIY version of a dual HiCap DR supply. Primary source is a Naim CDX2, powered by another DIY version of an XPS DR. The takeaway from all this is that the ACA is capable of being part of the highest quality system.
I view the ACA as an amplifier similar to the Pass Zen V3 / V4. Originally intended for low cost, safety and ease of construction at modest power levels, it’s capable of much more with fairly simple modifications. I’ve been writing about this ongoing process in the thread that I linked above.
@Centurion53: My main preamp is a Naim NAC 82 powered by my own DIY version of a dual HiCap DR supply. Primary source is a Naim CDX2, powered by another DIY version of an XPS DR. The takeaway from all this is that the ACA is capable of being part of the highest quality system.
I view the ACA as an amplifier similar to the Pass Zen V3 / V4. Originally intended for low cost, safety and ease of construction at modest power levels, it’s capable of much more with fairly simple modifications. I’ve been writing about this ongoing process in the thread that I linked above.
Neat, huh?
The F4 manual is a great read. (Seriously, there's tons of stuff in there with how to use it, and since it's an unconventional amp, it can be used in unconventional ways.)
http://www.firstwatt.com/pdf/prod_f4_man.pdf
The F4 manual is a great read. (Seriously, there's tons of stuff in there with how to use it, and since it's an unconventional amp, it can be used in unconventional ways.)
http://www.firstwatt.com/pdf/prod_f4_man.pdf
I just read the f4 manual. Mind blown.
Use the ACA as, effectively, a preamp? So, the ACA isn’t too much power for the F4?
In this bi-amp configuration I could even put a passive preamp in front of the ACA and use that to attenuate the ACA and the F4.
I also have a bottlehead 2watt integrated s.e.x. that would work. But if the ACA can work, I’m sure it’ll sound better.
6L6, this would be my first venture into a non kit build. I really hope I don’t bite off more than I can chew. Thanks for the build guides.
Any tips for a beginner are most welcome. Especially any that help me avoid electrocution.
Use the ACA as, effectively, a preamp? So, the ACA isn’t too much power for the F4?
In this bi-amp configuration I could even put a passive preamp in front of the ACA and use that to attenuate the ACA and the F4.
I also have a bottlehead 2watt integrated s.e.x. that would work. But if the ACA can work, I’m sure it’ll sound better.
6L6, this would be my first venture into a non kit build. I really hope I don’t bite off more than I can chew. Thanks for the build guides.
Any tips for a beginner are most welcome. Especially any that help me avoid electrocution.
Another choice for a Preamp designed to drive a 25w Class A amps with 0dB gain is the Aksa Lender. It puts out 40Vpp in order to hit 25wrms into 8ohms. An ACA will not hit 40Vpp (as it has a 24v rail) and you would be basically left with 5-8wrms F4 if you used the ACA as a Preamp. That is, 8wrms is same as 8vrms or 22.6Vpp max from an ACA. Since F4 has no gain (0dB), the output can be no more than the input (or 22.6Vpp). If you want to fully use the 25w capability of the F4, the input drive needs to reach 40Vpp.
AKSA's Lender Preamp with 40Vpp Output
AKSA's Lender Preamp with 40Vpp Output
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