Oops! I populated the board a couple of years ago and installed it recently after a couple of years of fretting about tapping the untapped heat sinks of the chassis I bought. (The tapping went well) When I populated the board, I already had an operating ACA monoblocks made from a kit from the DIY Audio store, and had read a post about reduced feedback written by TungstenAudio. I changed the input resistor R11 to 20k and the feedback resistor to 90.9k as he did in his premium parts build. I figured that I already had a “normal” ACA, so why not try something different for the second one? Does this explain the higher noise with this new build using the same SMPS blocks? I tried the earlier ACA and the new ACA in my system, and the new one has substantially more noise when using the same SMPS units.
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I tried the 19 Volt SMPS units I used on the older monoblock ACAs before switching to 24 Volt operation, and there is no noise through the speakers using them. All I can hear is the slightest hiss with my ear at the mouth off the mid and tweeter horns.
Sorry foe all the questions! Here is another one. I don’t really need the extra watts provided by the 24 Volt supply and the increase in bias to 12 volts. With respect to just sound quality, is the ACA better at 24 Volts B+ and 12 Volts of bias compared to the older original setup, or is it just a question of watts? My speakers are 104 DB/W/M, so SQ is far more important than a couple of extra watts of output to me.
I’m hoping it was done because most people need more power than the original ACA could provide, and not for sound quality reasons. I build SET amps, so the original ACA had more watts than any other DIY tube amp in my stable at the time. The new version competes with a 300B amp in terms of output. 5-6 Watts is plenty for me.
With 24 bolts, it has a little more power, but if 5W is all you need and you have better sound with the 19v, the schematic is identical! All you would need to do is set the DC balance to 10v instead of 12v. The Build guide contemplate both options for v1.6:
Amp Camp Amp V1.6 Build Guide - diyAudio Guides
Also, since it's a matter of moving the pot just a bit, you can actually try both and see if you detect a different sound?
Hi
my system need a bit more power because of my 4R 84dB speakers. so i like 24V because of single supply schematic of this amp the supply and the setup of DC about 12,3-...12,4 Volt. (i end up with 2,05A amps each channel with proper heat checks... and the first listening test is very nice)
in the premium ACA thread many people try some modifications and additionally THD measurements are existing by them.
Class A work very good if you set up more bias current (watch the heat of the power MOSEFET´snd the amp housing).
chris
my system need a bit more power because of my 4R 84dB speakers. so i like 24V because of single supply schematic of this amp the supply and the setup of DC about 12,3-...12,4 Volt. (i end up with 2,05A amps each channel with proper heat checks... and the first listening test is very nice)
in the premium ACA thread many people try some modifications and additionally THD measurements are existing by them.
Class A work very good if you set up more bias current (watch the heat of the power MOSEFET´snd the amp housing).
chris
It's not just the extra Watt or two that you get from the 24VDC, but also the extra headroom, slightly reduced distortion. I know it's not much but with some systems can be a huge improvement.
Try it to find out for yourself, all other opinions are really redundant because no-one else has exactly your setup.
I have returned the ACA mono locks to the older 19 Volt version, and on the new 24 Volt stereo single chassis ACA, I have changed R11 back to 10K Ohm from 20K Ohm and the feedback resistor to 68K Ohm from 90K Ohm. I will do some listening and report back.
Amazing, no? I find Pass amps almost always have two characteristics. Dead quiet and it seems the the music just effortlessly pours out, yet the details still seem to all be there! Other stuff too of course depending on the model. For example, how effortlessly, tonal differences, and ability to handle more complex music. IMHO
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Noisy ACA
I still have noise coming through the speakers with the 24 Volt laptop supplies on the one chassis stereo ACA I have that is set up for 24 Volt operation. When I plug in the 19 Volt supplies into the same ACA, there is no noise. Does this indicate a problem with the supplies? Also, one 24 Volt supply on one channel, and one 19 volt supply on the other channel results in noise in both channels. Only two 19 volt supplies results in no noise.
I still have noise coming through the speakers with the 24 Volt laptop supplies on the one chassis stereo ACA I have that is set up for 24 Volt operation. When I plug in the 19 Volt supplies into the same ACA, there is no noise. Does this indicate a problem with the supplies? Also, one 24 Volt supply on one channel, and one 19 volt supply on the other channel results in noise in both channels. Only two 19 volt supplies results in no noise.
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there was no need to alter anything in settings of amp, for temporary test with 19V supply
simple - you did change PSU - no noise
back to old PSU - there is noise
conclusion - find permanent replacement for noisy PSU
btw. can you somehow explain arrangement of these two channels, each of them having separate PSU?
from situation of one 19 plus one 24 , there is noise , I'm curious where is common link, through which noise from one PSU/channel can creep in second channel ......
simple - you did change PSU - no noise
back to old PSU - there is noise
conclusion - find permanent replacement for noisy PSU
btw. can you somehow explain arrangement of these two channels, each of them having separate PSU?
from situation of one 19 plus one 24 , there is noise , I'm curious where is common link, through which noise from one PSU/channel can creep in second channel ......
Zen Mod: Thanks for your quick reply. The amplifier is a single stereo chassis with two DC power inlets on a plate on the back panel that was originally made for an IEC inlet. I am using two laptop bricks because I had two identical ones handy rated for 24 Volts and 2.5 Amps each. Because of the separate DC inlets for each channel, I can use a 19 Volt on one channel and a 24 Volt on the other channel for testing purposes. Using two of the 19 volt supplies result in near silence at the speaker. I posted in this thread a few days about my concerns with having a shared ground for the two supplies. Attached is a photo of the back panel of the amp that shows how it is configured.
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Hi Tizman
Well done this ACA.
About noise i guess that Zen Mod wrote is a good idea:
I'm curious where is common link, through which noise from one PSU/channel can creep in second channel.
it seams that the 2x SMPS with 19V have the same "GND" if you connect both into your amp.its fine.
But with 19V and 24V supply you get noise -my idea is that the 24V give not the same "GND" at the inlet as needed.
check with DMM - multimeter. you should not have a voltage between these two SMPS.
i think you do not check the way the power AC plug in your wall outlet..
chris
Well done this ACA.
About noise i guess that Zen Mod wrote is a good idea:
I'm curious where is common link, through which noise from one PSU/channel can creep in second channel.
it seams that the 2x SMPS with 19V have the same "GND" if you connect both into your amp.its fine.
But with 19V and 24V supply you get noise -my idea is that the 24V give not the same "GND" at the inlet as needed.
check with DMM - multimeter. you should not have a voltage between these two SMPS.
i think you do not check the way the power AC plug in your wall outlet..
chris
Zen Mod: I went through my stash, and found a TDK FAW24-4R2 supply. It is a 100 Watt supply with 24 Volt DC at 4.2 Amps. Are these kinds of supplies usually better than generic laptop blocks? Also, is 4.2 Amps enough for an ACA?
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My recent ACA build is so quiet I can push my ear to the cone of the connected full-range driver speakers and hear nothing (that is with it connected to a preamp, sitting 2' from my wireless router). It is astonishingly quiet. If there is noise, either I got lucky or there is something you should be able to improve.