I used these ones from amazon cheap £15.99
https://www.amazon.co.uk/gp/product/B01DDX7J9U/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
KeerSen DC 24V 10A 240W each channel as it was a few quid more I thought ill have more amps. cant say how they compare with other more expensive supplies, only that i prefer sound now compared with 18v old power supplies
edit I am using a slow running 200mm silent fan with the original kit heat sinks after re bias they run very hot otherwise
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24V is perfect for the ACA. Mine have been running so for a long time.
Even more is possible, as stated here in this thread by mighty ZM. Only you have to take care of your JFets, which means cascoding it. Scheme can be found within this thread.
Cheers Ernst
Just finished ACA with transformer power supply (CRC filter). But get only 4.5W output power (light clipping, approx 3.5% THD ). Power supply gives 18.8V, ACA has R15 mod, Iq=1,33A. I got only 6V RMS @ 8Ohm load. Gain is approx 13.5 dB. Slightly addjusted trimpot to get symmetry in output signal. I am confused by such low output power. Should it be below 5W or not in my conditions?
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Can ACA drive 4ohm speakers?
Does the ACA’s match well with 4 ohm, 91dB full range speakers?
I saw a post that made me doubt if I should continue with building this amp - it was from the thread “ACA amp questions” where mstomaso asked if the ACA’s would drive his Martin-Logan Motion 12 (4 ohm, 92dB) speakers, and if he should consider changing the output resistors and upping the PSU. The reply from Nelson Pass:
“You can start scaling and playing with the ACA, but then you will have another
amplifier, at which point you might look around at other contenders.
Not very likely that the stock ACA will satisfy you into the ML's.”
I searched this thread for posts on driving 4ohm speakers but could not find clear answers.
Thanks.
Does the ACA’s match well with 4 ohm, 91dB full range speakers?
I saw a post that made me doubt if I should continue with building this amp - it was from the thread “ACA amp questions” where mstomaso asked if the ACA’s would drive his Martin-Logan Motion 12 (4 ohm, 92dB) speakers, and if he should consider changing the output resistors and upping the PSU. The reply from Nelson Pass:
“You can start scaling and playing with the ACA, but then you will have another
amplifier, at which point you might look around at other contenders.
Not very likely that the stock ACA will satisfy you into the ML's.”
I searched this thread for posts on driving 4ohm speakers but could not find clear answers.
Thanks.
Hi,
I've build ACA just for fun some time ago and played them with my Troels Gravesen Vifa C17 d'appolitos.
They are probably some 3-4dB more efficient than 91dB, but certainly low ohm regions (two 8ohm woofers in parallel). I liked it.
Still considering putting ACA in a better box and maybe start using it more often. I usually listen in the evening so low heat ACA would fit the bill.
I've build ACA just for fun some time ago and played them with my Troels Gravesen Vifa C17 d'appolitos.
They are probably some 3-4dB more efficient than 91dB, but certainly low ohm regions (two 8ohm woofers in parallel). I liked it.
Still considering putting ACA in a better box and maybe start using it more often. I usually listen in the evening so low heat ACA would fit the bill.
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Just be realistic with your expectations. The ACA has a damping factor 3. That translates into an output impedance of 2.67 ohms. And it has just 1 output device per channel. So if you get a little mushy bass don't be surprised with a 4 ohm load (which might dip to 3 around 100-200 Hz).
I definitely would bump up the PS rail to 24V. Eek out as much power as you can.
After some thrills, build an F5, F4, F6, Aleph J and finally VFET. Then live with your VFET happily ever after...
Best,
Anand.
I definitely would bump up the PS rail to 24V. Eek out as much power as you can.
After some thrills, build an F5, F4, F6, Aleph J and finally VFET. Then live with your VFET happily ever after...
Best,
Anand.
I just finished one channel of my ACA, and it seems to work fine, but certainly isn't very loud - even with a 95dB 8 ohm speaker.
'Wide open' on a volume control pot between the CD player and the ACA is just 'a bit too loud' in a 12' x 14' room; for 'normal' listening to jazz, the volume control needs to be about 90%.
It's very difficult to believe that this is a 6-8 watt amp (I'm running it at 24volts with the R15 mod, bias set at 10 volts); I have some pretty low powered tube amps, but they are all louder than this.
Is the ACA designed to require a preamp with gain (not just a buffer) for normal use with a CD player?
Can the input sensitivity be changed by reducing the value of R11 (input resistor)?
Before I go to the trouble of wiring up the other channel and making a case, etc. I want to make sure this amp will be useful in my small living room.
Thanks for any suggestions!
My ACA was indeed running on 24V.
I tried first two 19V 4/5A Dell bricks, but Meanwell 24V turned up to be way superior.
Before the thrills with ACA I've built Mini Aleph which was and is my main amp.
And yes the bass with Mini A is better. Actually everything is better. This is not to say that ACA was bad.
I'm actually interested in M2 or F6 now.
VictoriaGuy,
The overall gain of the ACA is 14dB. You may be used to substantially higher gain, perhaps 26 dB gain. There is no way to modify the input sensitivity of the amp without affecting feedback, distortion, linearity, etc...see the ACA article for details.
Still, I would be careful about making any conclusions listening in mono...
Use a preamp, etc...
Gain and power output are 2 different things.
My pre is passive as such in MY system with 96 dB efficient speakers, a 4V source, that having an amp with an overall gain of 20dB works best, irrespective of the power output. So either using a an active preamp (6-10dB) or building a transparent gain stage into the ACA would be a viable option. Like the AMB Alpha 24.
One must understand that the ACA is an introductory platform. It is to teach the basics of amplifier design using principles heralded by Pass during the Zen amp development a long time ago. With the advent of switching supplies and subsequently laptop bricks, one of the most expensive parts of an amplifier, that is the power supply, became inexpensive and suddenly, the Zen design was made more accessible to new diy'ers of the millennia. This comes from a man who lives very simply to provide us fodder to conjure and personalize our own diy amplifier creations. I'm pretty sure it tickles his heart.
Thank you Nelson. Bless you.
Best,
Anand.
The overall gain of the ACA is 14dB. You may be used to substantially higher gain, perhaps 26 dB gain. There is no way to modify the input sensitivity of the amp without affecting feedback, distortion, linearity, etc...see the ACA article for details.
Still, I would be careful about making any conclusions listening in mono...
Use a preamp, etc...
Gain and power output are 2 different things.
My pre is passive as such in MY system with 96 dB efficient speakers, a 4V source, that having an amp with an overall gain of 20dB works best, irrespective of the power output. So either using a an active preamp (6-10dB) or building a transparent gain stage into the ACA would be a viable option. Like the AMB Alpha 24.
One must understand that the ACA is an introductory platform. It is to teach the basics of amplifier design using principles heralded by Pass during the Zen amp development a long time ago. With the advent of switching supplies and subsequently laptop bricks, one of the most expensive parts of an amplifier, that is the power supply, became inexpensive and suddenly, the Zen design was made more accessible to new diy'ers of the millennia. This comes from a man who lives very simply to provide us fodder to conjure and personalize our own diy amplifier creations. I'm pretty sure it tickles his heart.
Thank you Nelson. Bless you.
Best,
Anand.
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Something is wrong. I'm using an ACA with a vol pot (no preamp) driving 86db speakers and can't use full volume in a similar room with out 24v or the r15 mod
Yes, it's designred to requre buffer with volume pot at the input or preamp if your CD output level below 1.4V RMS. Trimpot of ACA must be set for symmetry clipping, not to 10V
Trimpot of ACA must be set for symmetry clipping, not to 10V
Can you explain a bit more? I think I understand.
I have test equipment - oscillator and scope , etc. , so I'm sure I can do this. Increasing the input voltage from oscillator at 1kHz eventually causes the 'bottom' of the output sine waves to flatten - clipping. Are you saying that adjusting the P1 (bias) trim pot can make this clipping symmetrical?
And, does this affect the gain?
Yes, you are quite right- I thought of this after posting the message last evening. It won't take long to wire up the 2nd amp and see.
I'm going to undo the R15 mod as the temperature right at the output MOSFET is high - 58 deg. If that doesn't work I'll go to a larger heatsink - I have a few in the scrap box here- though the heat is not distributed very effectively across the sink - the outer edges are fairly cool.
Thanks for all the (quick) replies - it's nice to have 'thinking material' with the morning coffee here!
Yes (on top an bottom). And this is not affect to the gain. But this is affect on volume/distortion (i.e. higher volume - less distortion).
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I have 50 deg C, 58 deg - is not so much, I think it's OK.I'm going to undo the R15 mod as the temperature right at the output MOSFET is high - 58 deg
I know that the B1 and similar buffers are popular - I may build one in the future.
For now, using a volume control pot (no buffer amp) between the CD player and the input to the ACA - what value pot should I use?
I have a 10k log pot in there now.
I've never seen a very clear explanation of the 'input impedance' issue beyond 'not loading down the source device', which would normally imply (to me) using a higher value pot...but most SS projects seem to use lower value pots at the input.
For now, using a volume control pot (no buffer amp) between the CD player and the input to the ACA - what value pot should I use?
I have a 10k log pot in there now.
I've never seen a very clear explanation of the 'input impedance' issue beyond 'not loading down the source device', which would normally imply (to me) using a higher value pot...but most SS projects seem to use lower value pots at the input.
1 KOhm IMHO. Because negative FB connects directly to the input of ACA, and NFB gain is - R12/R11. If you add the source output resistance (5Kohm in your case in 50% volume and 10K volumepot, for example), the gain will be decrease.
PS
sorry my english