Sourced and fabricated simple open baffles with Altec Biflex 420a originally in a console. With that console’s original come tweeters. 1st order crossover.
The ACA parallel mono powers these well. One of my smaller single ended tube amps could not. Another EL84 single ended amp sounds amazing through the Altecs, with large ElectraPrint OTs. The ACA impresses and I suspect in the next hour will improve as it heats up.
The ACA parallel mono powers these well. One of my smaller single ended tube amps could not. Another EL84 single ended amp sounds amazing through the Altecs, with large ElectraPrint OTs. The ACA impresses and I suspect in the next hour will improve as it heats up.
I've finished the amp using Tungsten Audio values of 20K for R11 and 91K for R12.
It sounds good driving GRS planars from 500Hz up, will wait for it to burn in.
One question is that on turn on, there is a sound from the speakers I can only describe as an upward chirp for 2 or 3 seconds. Has anyone else experienced this, or have any suggestions about what might be causing it? Not an issue causing any problems as far as I can tell.
It sounds good driving GRS planars from 500Hz up, will wait for it to burn in.
One question is that on turn on, there is a sound from the speakers I can only describe as an upward chirp for 2 or 3 seconds. Has anyone else experienced this, or have any suggestions about what might be causing it? Not an issue causing any problems as far as I can tell.
The big output cap charging up.
To eliminate it one way is to feed the output of the Meanwell in a CapMx with a MosFet, which in turn powers the ACA. It works as a LPF slowly ramping up the output voltage.
To do that though you need your Meanwell to output 4 more Volts, 28VDC at least due to the loss in the series Fet.
You can also try an RC filter after the Meanwell consisting of let say 0.22R - 10000uF to slow down the start up but it want be that effective.
Thanks for your replies.
Stanislav, I'll save the info you've given for future reference, but as it is an artefact of the SMPS, and not a problem with the amp, I can easily live with it... and not have to dive straight away into more soldering, but just listen to the music.
Stanislav, I'll save the info you've given for future reference, but as it is an artefact of the SMPS, and not a problem with the amp, I can easily live with it... and not have to dive straight away into more soldering, but just listen to the music.
Hello ACA lovers..😀
I’ve build the original a few years back (except it’s powered at 24Vdc) and will soon be needing a project to feed my amplifier building addiction 😈
I’d like to try the modified ACA with Tungsten Audio mods. Did someone managed to create a PCB for that ?
I’ve seen many people using a cap multiplier with the ACA, is it really required?
Thanks for your help.
Eric
I’ve build the original a few years back (except it’s powered at 24Vdc) and will soon be needing a project to feed my amplifier building addiction 😈
I’d like to try the modified ACA with Tungsten Audio mods. Did someone managed to create a PCB for that ?
I’ve seen many people using a cap multiplier with the ACA, is it really required?
Thanks for your help.
Eric
Thanks for reaching out.
I also have these boards but they are kind of big since they include the rectifier bridge, filtering capacitor, a capacitor multiplier and then the actual ACA with Tungsten mods.
If nobody has a PCB with only the ACA (with mods) I can try to use a portion of the pcb...I’ll wait a bit..I’m never in a rush.
Thanks
I also have these boards but they are kind of big since they include the rectifier bridge, filtering capacitor, a capacitor multiplier and then the actual ACA with Tungsten mods.
If nobody has a PCB with only the ACA (with mods) I can try to use a portion of the pcb...I’ll wait a bit..I’m never in a rush.
Thanks
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@Eric
The attached aca16 mods file is correct. Almost all of the parts are simple substitutions. C101 is an extra part that may be soldered on top of R12. Adding R16 requires a careful trace cut. There are several examples of how this was done by other builders. These days I would probably leave R5 and R6 at 100 Ohms.
As I worked more with the ACA, I found that substituting IRFP140 Mosfets for Q1 and Q2 sounded better as well. The other big improvement is building a linear power supply to provide 28V to 30V power rail. This can be done with a single 300VA transformer with two 24V or 25V secondary windings. I used 26MB40A block rectifiers and a CRCRC filter for each channel and found that a single amp built this way sounded better than either of the two bridged amp configurations.
Regarding alternate Mosfets: While the FQH44N10 parts were still in production, several of us found them to be superior to even the IRFP140, especially when using higher voltage power rails. Surplus parts occasionally show up online, but caution is advised to avoid Chinese fakes. The next best bet would be the IRFP048 Mosfets that are sold in the store as part of the F6 transistor kit.
The attached aca16 mods file is correct. Almost all of the parts are simple substitutions. C101 is an extra part that may be soldered on top of R12. Adding R16 requires a careful trace cut. There are several examples of how this was done by other builders. These days I would probably leave R5 and R6 at 100 Ohms.
As I worked more with the ACA, I found that substituting IRFP140 Mosfets for Q1 and Q2 sounded better as well. The other big improvement is building a linear power supply to provide 28V to 30V power rail. This can be done with a single 300VA transformer with two 24V or 25V secondary windings. I used 26MB40A block rectifiers and a CRCRC filter for each channel and found that a single amp built this way sounded better than either of the two bridged amp configurations.
Regarding alternate Mosfets: While the FQH44N10 parts were still in production, several of us found them to be superior to even the IRFP140, especially when using higher voltage power rails. Surplus parts occasionally show up online, but caution is advised to avoid Chinese fakes. The next best bet would be the IRFP048 Mosfets that are sold in the store as part of the F6 transistor kit.
@TungstenAudio
Thank you very much for such a detailed answer and all the additional info. Much appreciated!
BR
Eric
Thank you very much for such a detailed answer and all the additional info. Much appreciated!
BR
Eric
Thanks for your recommendation. Your smps filter is amazing, I use it everywhere; Pass clone F3, TDV amp, my original ACA.
I have my ACAs on order; I'll be building them for XLR mono use. I started reading this thread from the beginning, then it started jumping around, and then I decided to at least read the posts from this year. And then one of those more recent posts said to go back to post #15 and follow those mods. I do want to go ahead and do some drop-in mods while I'm assembling them, and then plan on doing an external linear power supply at some point in the future. As a reminder, this is the list of mods in post #15:
On board, drop-in replacements
C1: 4700 uF, 35V; Nichicon KG series "Gold Tune"
C2: 1000 uF, 16V; Nichicon RNL series Aluminum Organic Polymer
C4: 100 uF, 35V; Nichicon RL8 series Aluminum Organic Polymer
R11: 20 kOhm, 1/4W, 1% metal film
R12: 90.9 kOhm, 1/4W, 1% metal film
On board add-on components
R4b: 2.0 Ohm, 2W, 2% metal oxide; added in parallel w/ R4
C101: 10 pF, 500V, 5% Silver Mica; added in parallel w/ R12
Off board substitution
Bridging Resistor: 68.1 kOhm, 1/4W, 1% metal film
I only want to do drop in replacements as I'm just getting my feet wet. My question is this: Does it make sense to do all of the above drop ins, and none of the others? Or is there a more narrow selection of drop in mods due to NOT doing the others. I don't completely understand the interplay one mod has on another and am really working on actively learning by reading and watching videos. Thank you in advance for any guidance you can give this neophyte.
On board, drop-in replacements
C1: 4700 uF, 35V; Nichicon KG series "Gold Tune"
C2: 1000 uF, 16V; Nichicon RNL series Aluminum Organic Polymer
C4: 100 uF, 35V; Nichicon RL8 series Aluminum Organic Polymer
R11: 20 kOhm, 1/4W, 1% metal film
R12: 90.9 kOhm, 1/4W, 1% metal film
On board add-on components
R4b: 2.0 Ohm, 2W, 2% metal oxide; added in parallel w/ R4
C101: 10 pF, 500V, 5% Silver Mica; added in parallel w/ R12
Off board substitution
Bridging Resistor: 68.1 kOhm, 1/4W, 1% metal film
I only want to do drop in replacements as I'm just getting my feet wet. My question is this: Does it make sense to do all of the above drop ins, and none of the others? Or is there a more narrow selection of drop in mods due to NOT doing the others. I don't completely understand the interplay one mod has on another and am really working on actively learning by reading and watching videos. Thank you in advance for any guidance you can give this neophyte.
The list of drop-in replacements accomplishes the goal of driving less efficient speakers a bit more smoothly as the amp is being driven closer to its maximum output from a 24V supply. I developed this set of modifications while using a pair of ACAs to drive my older Vandersteen 2C.
A good replacement for R4 is a single 0.5 Ohm,3W resistor. This helps increase the bias current through the output transistors. Consider using a set of alternate Mosfets as well, listed a couple posts prior.
A good replacement for R4 is a single 0.5 Ohm,3W resistor. This helps increase the bias current through the output transistors. Consider using a set of alternate Mosfets as well, listed a couple posts prior.
Thank you for the reply; and quick!
Let me ask you this, do these mods make less sense if I am going to run efficient speakers and should spend the time/money/effort on the power supply?
Or do you feel they are worth doing regardless and I might as well while I’m assembling parts and supplies anyway?
Let me ask you this, do these mods make less sense if I am going to run efficient speakers and should spend the time/money/effort on the power supply?
Or do you feel they are worth doing regardless and I might as well while I’m assembling parts and supplies anyway?
The mods still work with efficient speakers. And they aren’t expensive vs other good quality components.
If you are willing to build a linear power supply and use higher transconductance Mosfets, the benefits of those efforts will be very worthwhile. Bridging a pair of amps probably wont be necessary, but you could experiment with bi-amping.
If you are willing to build a linear power supply and use higher transconductance Mosfets, the benefits of those efforts will be very worthwhile. Bridging a pair of amps probably wont be necessary, but you could experiment with bi-amping.