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AWESOME! It's an afternoon that will last a lifetime! As I type this, I can hear my daughter's stereo playing from upstairs...
Technically yes, but could you tell in a double blind test
Maybe
I think I'll install banana jacks on my ACA for easy reversal.
Hello there.
Yesterday I built the ACA with a friend, but there was a mistake as the amp won't sound in the right side and the left sounds really bad.
Right now, reviewing it, I've seen that we placed the small transistors in pairs in each side. This means there are 2 ZTX450 on one side and 2 of the others in the other side.
Before placing them in their right position, as I know nothing about this kind of electronics, I'd like to know if the transistors may have been damaged. Is this possible? Is there a way to measure them? I must say that nothing smelt to burned when powering up.
Many thanks, this thread is very helpfull.
Yesterday I built the ACA with a friend, but there was a mistake as the amp won't sound in the right side and the left sounds really bad.
Right now, reviewing it, I've seen that we placed the small transistors in pairs in each side. This means there are 2 ZTX450 on one side and 2 of the others in the other side.
Before placing them in their right position, as I know nothing about this kind of electronics, I'd like to know if the transistors may have been damaged. Is this possible? Is there a way to measure them? I must say that nothing smelt to burned when powering up.
Many thanks, this thread is very helpfull.
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I wouldn't think anything would be damaged... that is probably the simple answer, and probably true. The impedances are high and so available currents are low.
Fitting the FET in place of the Bjt sees a 10k limiting current. I'm sure the FET's are fine.
Fitting the Bjt in place of the FET could see up to around 24 milliamps flow if you happened to connect it a certain way. You could also reverse bias the Bjt which could impair the noise figure of the device (in theory) but given its intended use as a 'brute force' current limiter bypassed by a 1000uF cap that's hardly an issue.
Fitting the FET in place of the Bjt sees a 10k limiting current. I'm sure the FET's are fine.
Fitting the Bjt in place of the FET could see up to around 24 milliamps flow if you happened to connect it a certain way. You could also reverse bias the Bjt which could impair the noise figure of the device (in theory) but given its intended use as a 'brute force' current limiter bypassed by a 1000uF cap that's hardly an issue.
Hi, Rafa! Thanks for your very informative insights.
I guess I have to check my source. For now, I use NAD and Pioneer cd players and a Rega DAC.
Rafa, I checked the output level of my CD player and DAC, and both give 2.1 V.
You are right. I think I need an active preamp for the ACA. Is there a DIY active preamp you can recommend?
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I'm one chassis away of testing the WHAMMY headphone amplifier modified to have a line out to be a PRE for my ACA.
Other than that, I know very little of DIY, I'm very new to this.
I did purchase a Schiit Magni and it does a decent job at high gain. In low gain I found I was almost requiring to keep it a full volume. Its $99 so I thought it won't hurt to give it a try.
I'll report further on the WHAMMY as a PRE, hopefully by the end of this week, or sooner if I get a bit irresponsible with work
.Rafa.
Hello,
I am new here, be nice =).
I have experience soldering and assembly electronics and looking for affordable high quality audio. I have a goal of creating a raspberry PI powered DAC, and the pre-outs into the ACA. I would like to power SVS Prime Towers SVS Prime Tower Speaker | Floorstanding Speakers for Home Theater & Stereo. Would the ACA be suited to power them? I will drive a subwoofer separately from pre-out on my raspberry PI DAC.
Configuration will be so, notice all DIY audio path except for speakers:
Raspberry PI, Kali Locker, Piano 2.1 DAC (digital crossover enabled) -> Hopefully a ACA -> SVS Prime Towers
Any help would be appreciated.
I am new here, be nice =).
I have experience soldering and assembly electronics and looking for affordable high quality audio. I have a goal of creating a raspberry PI powered DAC, and the pre-outs into the ACA. I would like to power SVS Prime Towers SVS Prime Tower Speaker | Floorstanding Speakers for Home Theater & Stereo. Would the ACA be suited to power them? I will drive a subwoofer separately from pre-out on my raspberry PI DAC.
Configuration will be so, notice all DIY audio path except for speakers:
Raspberry PI, Kali Locker, Piano 2.1 DAC (digital crossover enabled) -> Hopefully a ACA -> SVS Prime Towers
Any help would be appreciated.
Can someone help me to explain the basic operation of the amp, particularly in the CCS part?
I've read Nelson Pass' "Amp Camp Amp #1" but sadly I'm too stupid to understand it.
Looking at the SIMPLE VERSION 1 schematic, if there is a CCS that drives the MOSFET and the speaker, won't the current flowing thru the speaker coil be constant? So when the input signal to the gate of Q1 varies due the the input signal, the voltage across the MOSFET drain and source varies (is amplified), but the CCS keeps the current constant, right?
So, if there is constant current flowing thru Q1 why doesn't that cancel the input sound waveform current variation and the output waveform dead silent because the current thru the speaker is constant and not varying wrt the music signal?
Obviously that's not the case...I am obviously missing something very basic...
I've read Nelson Pass' "Amp Camp Amp #1" but sadly I'm too stupid to understand it.
Looking at the SIMPLE VERSION 1 schematic, if there is a CCS that drives the MOSFET and the speaker, won't the current flowing thru the speaker coil be constant? So when the input signal to the gate of Q1 varies due the the input signal, the voltage across the MOSFET drain and source varies (is amplified), but the CCS keeps the current constant, right?
So, if there is constant current flowing thru Q1 why doesn't that cancel the input sound waveform current variation and the output waveform dead silent because the current thru the speaker is constant and not varying wrt the music signal?
Obviously that's not the case...I am obviously missing something very basic...
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I'm one chassis away of testing the WHAMMY headphone amplifier modified to have a line out to be a PRE for my ACA.
Other than that, I know very little of DIY, I'm very new to this.
I did purchase a Schiit Magni and it does a decent job at high gain. In low gain I found I was almost requiring to keep it a full volume. Its $99 so I thought it won't hurt to give it a try.
I'll report further on the WHAMMY as a PRE, hopefully by the end of this week, or sooner if I get a bit irresponsible with work
Rafa.
May I suggest a 2nd ACA for a monoblock setup.
I'm running ACA's in bridged monoblock mode, driven by a unity gain Schiit Saga preamp. This combination sounds very good, and will drive my 94db, 8ohm speakers to much higher SPL than I want.
$-wise, the cost of a second ACA is a very reasonably priced upgrade.
I hear a lot of good things about the Whammy, though.
Probably can't go wrong either way.
Can't speak to your front end, but sonically, the ACA is not likely to be the weak link in your (or most) proposed setup.
Speakers - Compare the output power spec of an ACA to the minimum recommended power spec of your speakers.
I tried an ACA as a stereo amp, and 2 as monoblocks to my 8ohm, 94db efficiency speakers and prefer the latter for all music at all volume levels in my smallish, decently acoustic treated room.
Although sound was very good at lower volumes with stereo amp configuration.
So much depends on your room and what you want your stereo to accomplish.
Easy thing about making this decision is that if you build an ACA successfully, and it doesn't work out for you, they seem to go very quickly when they do come up for sale; usually offered by audioholics smitten by the SS Class A sound and want to go up the ladder.
I should be at the bench working on my Aleph J now.....
Rafa, your low gain is 2 volts (6db), your high gain is 7 volts (17db). The low gain is supposed to be more detailed and precise, the high gain less so. I provide the voltage and db gains (from the Schiit specs for the magni) as a reference for the levels required to get the ACA working well. The voltage gain can be increased until the ACA starts clipping. If your preamp is producing too much gain for the ACA you will need a volume attenuator to eliminate the clipping.
I think the key is here:
"These elements are chosen to control Q2 in such a way that it acts as a DC constant current source which also varies AC-wise so as to favorably help the amplification provided by Q1."
So does this mean that the DC current is constant with no signal, but the AC audio signal still varies on top of it?
Also wondering what the "favorably help the amplification" means...
Mazeppa, your Schiit Saga preamp is a passive buffer preamp with a gain of 0 db as per the Schiit specs. However the signal you are feeding your ACA is refined and buffered by the preamp to sound just right. I have no idea what DAC you are using. Your speakers are pretty efficient and with the monoblock configuration you have plenty of power to drive them. The Saga, by the way is a beautiful piece of work, great choice! The Aleph J would also be my choice as a follow up to the ACA.
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