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Here is the response of the ACA with 100, 130 and 1k. The scales are similar to highlight differences and the trace starts at 20kHz. 1k is getting to the point where the response starts to fall away past 20khz
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I would like to make a proclamation.
This amp has ZERO noise at idle, I mean NOTHING. Because of this, anyone thinking about this for computer speakers (where you are close, where you do hear noise that would normally be lost at 10 feet) - DO IT!!! As long as you know it is running at 60-70 watts 100% of the time, this is PERFECT for computer speakers.
This amp has ZERO noise at idle, I mean NOTHING. Because of this, anyone thinking about this for computer speakers (where you are close, where you do hear noise that would normally be lost at 10 feet) - DO IT!!! As long as you know it is running at 60-70 watts 100% of the time, this is PERFECT for computer speakers.
yes, this is the whole point of the exercise, the higher the grid stopper resistance the lower is the turn over frequency, and as long as it is outside the 20khz band limit, then fine...
6L6: I decided to go with SMPS, as you suggested, for my new stereo single chassis ACA build. If I use two seperate SMPS laptop blocks, one for each channel, should I be concerned if both the DC inlet jacks share a common chassis ground?
The DC jacks I have are chassis mount and are made of metal, so both of them are attached to the chassis and therefore chassis ground is common. If they were linear supplies, I wouldn't be concerned, but I am not familiar with the way a SMPS works. No other part of the amp is electrically connected to the chassis.
The chassis I am using was originally intended to be used with an IEC power inlet, so I made a metal plate to cover the hole and to place the two DC power inlets on. If they can't share ground through the chassis, I can fabricate a plate out of plexi or wood instead of steel so that the inlets are insulated from the chassis and each other.
Please let me know what works.
Tony Tecson: I am at the point where I was about to install the DC inlets, and I thought that it might be an issue. I haven’t drilled the plate out yet.
TungstenAudio: I own a pair of the earlier monoblock ACAs and was hoping to use a spare pair of 24 Volt, 2.5 Amp SMPS supplies that I have. I suppose that I need to buy a single SMPS with a higher current rating, although I much prefer using what I already own.
If you think about it logically (no offense intended), two isolated amps, each with its own SMPS in the same chassis is basically the same as monoblocks - provided there is no physical connection through a connecting back plate or otherwise.
@tizman In which case using plexi or wood would solve the problem. That's what I would do anyway...
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A few things spring to mind here.
First is that the original ACAs were monoblocks with an SMPS each.
I do not know if the SMPSs had their mains earth / ground connection connected to their negative output. If they did then the 2 chassis were effectively joined electrically.
Second, depending on what pre-amp you use, chances are the 2 input RCAs are joined at their screen ( ground ) outer connections. Just plugging them in will therefore join the 2 chassis together electrically...
So is using 2 identical SMPSs a real problem?
If you believe it is then you have to think about the following.
Is there a connection from mains ground to the negative output on your 24 volt SMPSs? Measure it. If there is that will join the negatives together anyway.
Have you isolated the ACA board from the chassis, i.e. used plastic not metal mounting hardware? If not the 2 grounds are connected via the metal of the chassis through the 0 volt tracks on the boards.
Have you wired the red speaker terminals together as in the build guide? If you have then the 2 ground negatives are joined together.
And again if your RCA screens are connected together at the pre-amp, then the 2 grounds still get connected together.
I guess after all that the answer is suck it and see. Nothing bad will happen... Alan
I've been DIYing and dabbling in electronics for years. I still want to dabble but as I'm older now, I really don't want to get that deeply involved in a build. That's why I didn't want to start something like a First Watt build.
I use 88db speakers and listen to classical music at 50-55db MAX at a sitting distance of 8-10 feet away.
Would one ACA be useable in this setup?
What "upgrade" parts should I order from Mouser to stuff the board before mounting?
I always wanted a Pass design as well as a pure Class A SET. So this little amp "could" fill both wants. What I would like out of an amp is mostly "quality" sound. An example is my Sherwood S-5000 that uses EL84 tubes, has a musical quality that I love. Detail is nice, but mainly it's quality sound I'm after. I use stereo subs so the bottom end will be supplemented.
If I like how the first ACA turns out, then I'll order the second.
I use 88db speakers and listen to classical music at 50-55db MAX at a sitting distance of 8-10 feet away.
Would one ACA be useable in this setup?
What "upgrade" parts should I order from Mouser to stuff the board before mounting?
I always wanted a Pass design as well as a pure Class A SET. So this little amp "could" fill both wants. What I would like out of an amp is mostly "quality" sound. An example is my Sherwood S-5000 that uses EL84 tubes, has a musical quality that I love. Detail is nice, but mainly it's quality sound I'm after. I use stereo subs so the bottom end will be supplemented.
If I like how the first ACA turns out, then I'll order the second.
Hi Sunscreen,
Simple answer is yes, quite usable. You do not tell us the impedance of your speakers, but 6 to 8 ohms is the sweet spot for a stereo ACA. If you feel you do need more power then build another.
Upgrade parts? Personally I would spend my money elsewhere, but there is a whole other thread devoted to using Premium parts, thanks to TungstenAudio, have a read through that. ACA amp with premium parts and a couple of spin offs too.
At the end of the day it is diy and your choice, just don't expect one answer...
Any way you will not be disappointed that is for sure.
Simple answer is yes, quite usable. You do not tell us the impedance of your speakers, but 6 to 8 ohms is the sweet spot for a stereo ACA. If you feel you do need more power then build another.
Upgrade parts? Personally I would spend my money elsewhere, but there is a whole other thread devoted to using Premium parts, thanks to TungstenAudio, have a read through that. ACA amp with premium parts and a couple of spin offs too.
At the end of the day it is diy and your choice, just don't expect one answer...
Any way you will not be disappointed that is for sure.
I have a stereo ACA too, and use it in a similar matter: smallisch 88dB speakers, and a wide band of music from classic to jazz to rough pop/electronic music.
It works very nicely, but I have to say that only after I was able to hook a good preamp (wayne‘s ba2018 line-stage) the combo seemed complete. It is a joy to listen to them!
(I don‘t know, but maybe this—a good preamp making ACA swing and sing—could apply to your situation too?)
It works very nicely, but I have to say that only after I was able to hook a good preamp (wayne‘s ba2018 line-stage) the combo seemed complete. It is a joy to listen to them!
(I don‘t know, but maybe this—a good preamp making ACA swing and sing—could apply to your situation too?)
What does the impedance look like?
I am currently driving FF125wk Frugel-Horn Mk3 downstairs with a single ACA. It plays pretty loud (24x24’ room with 8 & 12’ ceilings, it does start choking a bit when we open the garage door and use it for outdoor sound.
The impedance response of this loudspeaker is quite flat.
dave