I am talking about providing power to a pair of ACA boards, whether in a stereo amp, or used in tandem to drive a single channel in one of the bridged configurations. A 250VA transformer will be a good match for this, and the minimum I would recommend would be 160VA.
One of the big advantages of bridging the ACA is having a separate PSU for each channel, particularly when using the kit SMPS brick. If one is going to go to the extra effort and expense of building a linear power supply, then I believe it is worthwhile to use a separate secondary transformer winding for each board. Doing so can bring some of the benefits of a bridged configuration to a single stereo amplifier.
Recent experience has suggested that it is best to look for transformers with about 4.5 Amp capacity or greater it each secondary winding. The secondary voltage needed will depend on the scheme used to provide clean power to each board.
Just remember the ACA runs Class A. Each board needs 1.5A at 24 volts (36 watts) all the time. So a stereo ACA needs 72 watts. Better to over spec the transformer by at least 50% so 120VA minimum and 150VA better.
So the 250VA transformer should just power 2 monoblocks and give a little reserve.
What have you got against using 2 x 5 amp 'open' SMPS in the case and run them as 2 mono amps?
Same idea as Tungsten, just slower typing...
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Well, it depends… How big are your heatsinks? The standard ACA dissipates about 36 Watts per side, which is fine for the Mini Dissipante 2U chassis. I run a higher quiescent current in mine, so they are a bit warmer, but not hot.
When I started building ACA amps with linear power supplies, I switched to a larger chassis with bigger heatsinks. I have a pair of amps built in the old Hafler DH-220 chassis. One of these runs about 44 Watts per side, and the other is running at 48 Watts per side. I’ve written about the 44W per side build, which I call the ACA-220 v1. The hotter build is still somewhat a work in progress. Its rail voltage is 28.4V, and the quiescent current is 1.6 Amps for the time being. The voltage at the reservoir cap for each channel is 30.2V, which accounts for the remaining power dissipation.
There are also a couple circuit modifications that should be made. Besides increasing the current, it’s also a good idea to reduce the voltage across the input buffer JFET. I’ve done this with a simple RC filter of 499 Ohms and 100uF. I’ve also bumped R7 up to 12k. These are the values for the higher voltage build. BTW, the higher current allows the higher voltage to be used effectively, as well as placing the power MOSFETs into a different operating region.
Zener diode in the drain leg works pretty well in the M2x "Mountain View". Feel free to add current-increasing resistors and/or PSRR-improving capacitors if you see fit.
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I have the TotemMini paired to my ACA 1.5 with a 19v PSU. It is a perfect match! You will love the combo!
BUT!!!! As has been mentioned, this requires as an absolute MUST a PRE with gain. I have a WHAMMY (built with extra RCA outputs) that provides 14dB of gain which makes the combo sing!
Prior to that I used a Magni which required the HI setting to reach desired levels.
Without the PRE, the combo sounds weak and low. With the correct PRE, it's a perfect bedroom kit, in my opinion!
Since these are not conjectures but actual use case, I hope this helps clear out any remaining doubts that you would enjoy the setup!
Best regards,
Rafa.
There was a guy right here on this very thread, who downloaded a free PCB layout program "KiCad", taught himself how to use it, and laid out a single sided ACA so he could etch it at home. It was the first PCB he ever designed or etched.
I think it was about 9 months ago or so. Good luck!
I think it was about 9 months ago or so. Good luck!
Hi TungstenAudio, I am looking to buy heat sinks, the chassis I have has small ones.18x8x5 Have to see what I can fit in my chassis.
And aside from raising the quiescent current to 1.6A Where in the circuit do I put the RC filter of 499ohm and 100mf? (sorry, newbie question)
Got this :R7 up to 12kThank you.
Also thanks to RafaPolit and Mark Johnson and all others.
The closest equivalent to the old Hafler chassis I am using is the Mini Dissipante 3U / 250mm. You could also extend the capacity by getting the 300mm deep chassis instead. The Hafler heatsinks are quite impressive.
For the RC filter I mentioned, I placed the 499Ω resistor in between the power rail and the drain of the JFet. Then I placed a 100 uF cap between the drain and ground. See Mark Johnson's example for an alternate method using a diode instead of the RC filter. I might suggest a red LED instead of the 10V Zener, since we have less voltage to deal with than what the M2x uses.
Actually, I did not use KiCAD, but another program, forgot the name though....
But yes, It was the first print i designed with such a program.
The amp still functions great, the only difficult thing is soldering the powerFETS, since if you mount the PCB on the stand and know the how far the FETs pins are into the print,you cannot reach the pads to solder the pins...
ACA Bridged and Balanced Mono Blocks
I think this might be a dumb question. Can I have my ACA v1.6 Monoblocks hooked up with both an XLR cable to my balanced preamp and single ended bridged mode using the “rca-resistor thing” at the same time on two different inputs on my preamp?
Hope that makes sense to y’all.
Thanks.
Jim.
I think this might be a dumb question. Can I have my ACA v1.6 Monoblocks hooked up with both an XLR cable to my balanced preamp and single ended bridged mode using the “rca-resistor thing” at the same time on two different inputs on my preamp?
Hope that makes sense to y’all.
Thanks.
Jim.
Right. Thanks for the reply. I want to screw around a bit to see how the second order negative phase distortion with the single ended sounded. I thought I should be able to A/B between the two different connections just by pulling the pre amp out connection (single ended or balanced). I wasn’t sure if leaving both connections in place on the ACA would add any goofy sound or screw anything up, otherwise.
Thanks again.
Thanks again.
hamelka - Two things to consider in your comparison;
1) With phase changes you really need a short pause between listening. Just a few seconds, but it makes a huge difference. If you've ever had a component that had a phase switch you can flip it back and forth and never hear anything. Put just a small delay and you can. It's still a subtle effect regardless.
2) The difference in output levels between the two sources will be different. Make sure you turn it down and bring back up to the same perceived level, if you don't you'll almost always prefer the louder of the two.
1) With phase changes you really need a short pause between listening. Just a few seconds, but it makes a huge difference. If you've ever had a component that had a phase switch you can flip it back and forth and never hear anything. Put just a small delay and you can. It's still a subtle effect regardless.
2) The difference in output levels between the two sources will be different. Make sure you turn it down and bring back up to the same perceived level, if you don't you'll almost always prefer the louder of the two.
Very capable little amp!
I'm currently driving Quad ESL 57s with the ACA in a biamped setup. Not it's intended purpose at all. I built the ACA because I was intimidated by plunging directly into an M2 build. It really seems to outclass my beloved little el84 monoblocks. More detail, a lot more damping even thought it's just 8 watts, just as musical overall. Now I'm really ready to get going with the M2.
I'm currently driving Quad ESL 57s with the ACA in a biamped setup. Not it's intended purpose at all. I built the ACA because I was intimidated by plunging directly into an M2 build. It really seems to outclass my beloved little el84 monoblocks. More detail, a lot more damping even thought it's just 8 watts, just as musical overall. Now I'm really ready to get going with the M2.
Old man build
Hope this is the correct thread for this.
By way of introduction, as this is my 1st post, I’m kind of an older guy. Haven’t built an electronics kit in 60 years and have never touched a circuit board. Not sure why I decided to try the Amp Camp but I did. I’ve just spent the last few days learning to solder properly and I’ve built this thing. Worked perfectly first time.
To the people who have put so much time into this, congratulations on a job well done. You’ve made an old man very proud of himself and I thank you.
So now I’m ordering the second one.
Btw, if there are any people reading this wondering if you can do it, if I can anyone can.
Don
Hope this is the correct thread for this.
By way of introduction, as this is my 1st post, I’m kind of an older guy. Haven’t built an electronics kit in 60 years and have never touched a circuit board. Not sure why I decided to try the Amp Camp but I did. I’ve just spent the last few days learning to solder properly and I’ve built this thing. Worked perfectly first time.
To the people who have put so much time into this, congratulations on a job well done. You’ve made an old man very proud of himself and I thank you.
So now I’m ordering the second one.
Btw, if there are any people reading this wondering if you can do it, if I can anyone can.
Don