Does it matter if I use the IRFP 240 vs. the 140? My kit came with the 240 and it appears they are interchangeable. I plan on replacing the power brick with a higher voltage linear supply at a later date and going to a larger chassis as necessary. The DIY store does reflect the following difference but I am not sure that I understand how this difference impacts the build.
The 140 has a lower voltage (100v) vs the 240, but this is offset by the higher transconductance and higher current rating. As long as the supplies are less than +/-50V or 100V single-ended, I think it’s a slightly superior part.
The 140 has a lower voltage (100v) vs the 240, but this is offset by the higher transconductance and higher current rating. As long as the supplies are less than +/-50V or 100V single-ended, I think it’s a slightly superior part.
If you use your ACA in the "Bridged Mono" mode as it is called on the back panel of ACA 1.8, there is an error in the design that has been discovered. It is documented in posts 12084, 12085 and 12087 of the original ACA thread: https://www.diyaudio.com/community/threads/amp-camp-amp-aca.215392/
Fixing this flaw requires just changing one resistor on the back panel and will give you a couple more Watts output. It doesn't affect Stereo, Parallel or Balanced Modes.
If you dislike the Odd order distortion in the Bridged Mono mode, I have a mod that will make your ACA sound more like it does in the Stereo Mode, only louder.
Fixing this flaw requires just changing one resistor on the back panel and will give you a couple more Watts output. It doesn't affect Stereo, Parallel or Balanced Modes.
If you dislike the Odd order distortion in the Bridged Mono mode, I have a mod that will make your ACA sound more like it does in the Stereo Mode, only louder.
I found that with the mods that I liked the single stereo amp more than either of the bridged modes. There was more transparency than the parallel mode and I did like the tonal balance better than the bridged. So I am running a single amp from dual 36v supplies with FQH44n10's. Very interested to hear you mod for the bridged mode to see if some of what I like in the stereo amp can be preserved while increasing the headroom.
Just want to thank everyone here on this page as finally got my project all done and even with some test speakers sounding really good. Thanks for all your guys help can't wait for the next project.
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Which kit should I get if I plan on building with premium components and 36V SMPS? If I get the regular ACA kit, will the heat sink be too small?: 'Larger heatsinks of the Amp Camp Amp chassis allow for higher bias current'.
I see the ACA Redux kit is out of stock... Should I wait for that to come back in so I get the larger heat sink? It seems that is the only major part that will not be worth upgrading since it would be replaced right away.
Thanks,
I see the ACA Redux kit is out of stock... Should I wait for that to come back in so I get the larger heat sink? It seems that is the only major part that will not be worth upgrading since it would be replaced right away.
Thanks,
Hello @Robstr556
Very nice work 👍
Can I please ask you where you bought your enclosure, looks great. Maybe a link ?
Cheers
Eric
I would say yes, almost certainly. Make that definitely 😉
Remember that to take advantage of a higher supply (and presumably you want more voltage swing at the output) will mean also increasing the standing bias current. I'd bet you would be looking at around 70 to 80 watts dissipation per channel. Component values would need altering.
Also the required input voltage will need to be quite high given the low voltage gain of the ACA in order to get maximum output.
I think the input FET would be OK at that voltage as it would see around 32 volts across it.
Fwiw I don't think it a great idea all things considered. Also the higher output voltage will be subjectively very minimal at best in listening i.e. it won't sound much louder at all.
The ACA would only benefit from a higher supply voltage if different output Mosfets are used. Other builders and I have had success with FQH44N10. As these are now very difficult to find, there are other high transconductance Fets to try, such as the IXTQ75N10P or the IXTQ36N30P. These parts perform well with higher Vds. Of course the heatsinks need to be larger to dissipate higher power. I like the Mini Dissipante 3U chassis for higher voltage ACA.
As Mooly has indicated, the gain of one's preamp needs to be sufficient to provide a strong input signal to the ACA.
In all cases, the construction of a good linear power supply will give better sound than any kind of SMPS one can buy. This is from experience; I have tried various tricks to improve the performance with SMPS, and a good linear supply always sounds better. Fortunately a single 300VA (w/ 22V or 24V secondaries) makes it easy to build a good linear supply that reaches higher voltage for an enhanced ACA.
As Mooly has indicated, the gain of one's preamp needs to be sufficient to provide a strong input signal to the ACA.
In all cases, the construction of a good linear power supply will give better sound than any kind of SMPS one can buy. This is from experience; I have tried various tricks to improve the performance with SMPS, and a good linear supply always sounds better. Fortunately a single 300VA (w/ 22V or 24V secondaries) makes it easy to build a good linear supply that reaches higher voltage for an enhanced ACA.
I run mine with dual mono 36v supplies, the regular chassis is definitely too small.... That said, I still run mine that way. Instead of investing in a new chassis for it I got the Pass DIY 4U and am making an F5m .
Going with the 36 volt did give small improvements with the FQH44N10 transistors, but if you do all of the other mods you are most of the way there. Going with dual mono 24 volt supplies, gives you 95% of the benefits and you can keep it in the original chassis.
Thanks for the info. It sounds like going 36V will require a bit of re-engineering of the 'original' design and I don't know enough to make those changes. I'll stick to the original design/specs but upgrade parts like caps and resistors. I guess using 36V/FETS only squeezes a bit more power which is not that important since they will most likely be plenty loud for my living room. I like the idea of 'Nelson Pass' suggested upgrades if that list exists 🙂 I can imagine there are many 'spin off' designs which may or may not be fully vetted/tested and I don't know better to pick those over the original design. ( pros and cons of tweaking design ) I still have to go through the thread to get up to speed. Maybe I'll learn more about what upgrades/premium components are suggested and order those parts before I start soldering.
Hi
As tungsten said...better MOSFETs are a way to try.
first do the tungsten mods..
i use actually the IRFP044N Vishay
but i guess the FQA40N25 is a good one, its available at mouser and cost 3,52 exl. delivery each.
if you are quick the FQA27N25 is also available
chris
As tungsten said...better MOSFETs are a way to try.
first do the tungsten mods..
i use actually the IRFP044N Vishay
but i guess the FQA40N25 is a good one, its available at mouser and cost 3,52 exl. delivery each.
if you are quick the FQA27N25 is also available
chris
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I'm now thinking of getting the ACA MiniMax. Is the ACA Mini have the same capabilities as the ACA Kit? It comes with the Mini Dissipante 3U chassis tungsten suggested. Also, should I build the F5M instead? I don't know enough about which one to build, sorry for all the questions. ( slowing going down the rabbit hole )
By the way, are the FETS that come with the ACA MiniMax kit a top choice? They come from Nelson Pass's stock... would trying IXTQ75N10P or others still be needed if I get the ACA MiniMax?
By the way, are the FETS that come with the ACA MiniMax kit a top choice? They come from Nelson Pass's stock... would trying IXTQ75N10P or others still be needed if I get the ACA MiniMax?
I greatly prefer ACAmini to ACA. YMMV, of course, and both are a lot of fun.
Now the question of an ACA vs. F5 is 100% in favor of F5, all the Firstwatts are better amps than the ACA. (as you'd expect)
Now the question of an ACA vs. F5 is 100% in favor of F5, all the Firstwatts are better amps than the ACA. (as you'd expect)
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