Well I finally finished my ExtremA. (Link to Original Article on diyaudio.com.)
Parts.
Amp.
I believe with 1.3 ohm emitter resistors and plus/minus 19.6VDC, I'm getting about 79 WPC class A power.
Please correct me if I did the math wrong, I'm tired.
Here it is currently being tested it with a portable CD player into my differential buffer, then into ExtremA.
Power supplies are steady at 19.6 VDC, heat sink temperature settled down after an hour to 52 C on each.
I'm sitting in the garage listening to it, sounds ok with my little test speakers.
Will try on some real speakers soon. If someone comes over and helps me move it. It must be over 100 lbs.
It seems I always finish these things in the middle of the night, stay up late listening and post a few pics.
Parts.
An externally hosted image should be here but it was not working when we last tested it.
Amp.
An externally hosted image should be here but it was not working when we last tested it.
I believe with 1.3 ohm emitter resistors and plus/minus 19.6VDC, I'm getting about 79 WPC class A power.
Please correct me if I did the math wrong, I'm tired.
Here it is currently being tested it with a portable CD player into my differential buffer, then into ExtremA.
Power supplies are steady at 19.6 VDC, heat sink temperature settled down after an hour to 52 C on each.
I'm sitting in the garage listening to it, sounds ok with my little test speakers.
Will try on some real speakers soon. If someone comes over and helps me move it. It must be over 100 lbs.
It seems I always finish these things in the middle of the night, stay up late listening and post a few pics.
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More pics
Here are a few more pics.
Front without faceplate so you can see the front panel LEDs and the layout.
Side View.
Those Sanken's can make some heat.
You see a copper bar holding in a transistor. Why?
I snapped a tap inside the hole while threading it and could not get it out.
Sometimes you just have to build, not plan or make it perfect. Just build and get it done.
A lot of large parts like in a Pass amp.
2 transformers 16 VCT at 700 VA.
2 IXYS fast recovery bridge rectifiers- high power and high $ but I forget just how high.
Each channel has two 60,000 uF caps and four 22,000 uF caps.
Yet the current draw is so high I only get 19.6 VDC.
Adding caps will not increase the rails, you need to change transformers.
Got the huge case from somone here at diyaudio a few years back.
My soft start uses two CL-60 thermisters (10 ohms each if cold) in series with the primary for turn-on.
...Then after 4 seconds bypasses them using a 15A relay.
This is a fully balanced amp so it has XLR connectors.
A rear panel DPDT switch will ground the "negative" XLR input with RCA Ground so that
the amp can be used with unbalanced RCA sources. Simply flip switch and use RCA (but forgo benefits of balanced operation).
That is what the blue wires are for on the back panel.
The main filter caps have bleeding resistors across them as well as "snubberized" RC with film caps.
I forget the values I did this so long ago for another amp, an Aleph.
At the time people were saying to use brass screws to make connections on the
power caps because they conduct better. So I had some and used them then and still have them in there.
Here are a few more pics.
Front without faceplate so you can see the front panel LEDs and the layout.
An externally hosted image should be here but it was not working when we last tested it.
Side View.
An externally hosted image should be here but it was not working when we last tested it.
Those Sanken's can make some heat.
You see a copper bar holding in a transistor. Why?
I snapped a tap inside the hole while threading it and could not get it out.
Sometimes you just have to build, not plan or make it perfect. Just build and get it done.
A lot of large parts like in a Pass amp.
2 transformers 16 VCT at 700 VA.
2 IXYS fast recovery bridge rectifiers- high power and high $ but I forget just how high.
Each channel has two 60,000 uF caps and four 22,000 uF caps.
Yet the current draw is so high I only get 19.6 VDC.
Adding caps will not increase the rails, you need to change transformers.
Got the huge case from somone here at diyaudio a few years back.
My soft start uses two CL-60 thermisters (10 ohms each if cold) in series with the primary for turn-on.
...Then after 4 seconds bypasses them using a 15A relay.
This is a fully balanced amp so it has XLR connectors.
A rear panel DPDT switch will ground the "negative" XLR input with RCA Ground so that
the amp can be used with unbalanced RCA sources. Simply flip switch and use RCA (but forgo benefits of balanced operation).
That is what the blue wires are for on the back panel.
The main filter caps have bleeding resistors across them as well as "snubberized" RC with film caps.
I forget the values I did this so long ago for another amp, an Aleph.
At the time people were saying to use brass screws to make connections on the
power caps because they conduct better. So I had some and used them then and still have them in there.
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Not cool- hot!
After about 2 hours the heatsinks are holding at 54C. Very hot! I consider 60C too hot but I am ok with anything less.
I was worried that the heat sinking was insufficient but it just might work out after all.
The fins have little micro-serrations in them. Makes it tough on your fingers.
With a Class A amplifier I like to watch the temperature to make sure things are not getting crazy.
LEDs-
There is a green power LED in the center of the front panel that is always on.
The lower part of each side has a single green LED which illuminates when the nearby heat sink reach a preset temp.
At 45C on left and at 57C on right. Took about 15 minutes for the 45C LED to come on.
A Red LED on each side above the green one illuminates if either heat sink hits 68C, meaning - turn off!
So far only the 45 C on the left side has come on. Good news but not a symmetrical display!
After about 2 hours the heatsinks are holding at 54C. Very hot! I consider 60C too hot but I am ok with anything less.
I was worried that the heat sinking was insufficient but it just might work out after all.
The fins have little micro-serrations in them. Makes it tough on your fingers.
With a Class A amplifier I like to watch the temperature to make sure things are not getting crazy.
LEDs-
There is a green power LED in the center of the front panel that is always on.
The lower part of each side has a single green LED which illuminates when the nearby heat sink reach a preset temp.
At 45C on left and at 57C on right. Took about 15 minutes for the 45C LED to come on.
A Red LED on each side above the green one illuminates if either heat sink hits 68C, meaning - turn off!
So far only the 45 C on the left side has come on. Good news but not a symmetrical display!
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Massive job!
Is the hum problem solved?
Is the hum problem solved?
A good machine shop could have gotten it out. Ask how I know.
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Lgreen,
Okay, we need to go over a bunch of things, some stuff really needs to be changed. For starters.
1) You do have isolation between the BD139/140 on the heatsink do you?
2) Twist all primary and secondary transformer leads.
3) Twist all leads coming from the bridge rectifiers/PSU PCB/buffer caps.
4) Don't use crimp connectors, unless you first crimp and then solder them.
5) Clean up the wiring, twist all wires that carry AC current, route them clear of DC/signal wires.
I'd need more detail pics to give some more pointers, but these are recommended.
Cheers,
Sander.
Okay, we need to go over a bunch of things, some stuff really needs to be changed. For starters.
1) You do have isolation between the BD139/140 on the heatsink do you?
2) Twist all primary and secondary transformer leads.
3) Twist all leads coming from the bridge rectifiers/PSU PCB/buffer caps.
4) Don't use crimp connectors, unless you first crimp and then solder them.
5) Clean up the wiring, twist all wires that carry AC current, route them clear of DC/signal wires.
I'd need more detail pics to give some more pointers, but these are recommended.
Cheers,
Sander.
Here is what I used for parts (mostly, some things are just for full information).
The ExtremA Parts List (Nov. 2009). This is the most recent list.
I see in the original article the BD139/140 transistors are on thermal pads, I was wondering why, perhaps the packaging is different? Mine are not isolated from the heatsink (well they are-- just not necessary to use pads I don't think). They have a plastic encapsulation on both sides and in the through hole. The exact part is in my parts list.
While I tried to braid (twist) all the wires, keeping AC separate and apart from DC, this will be rechecked and things altered after I play with the amp. I always have messy wiring, I am just not that good at making stuff with a clean layout. Its an art. But I cannot hear any hum from the amp (speakers), there is some low mechanical hum from the big power transformers. I don't pretend to be a pro so lets not kid ourselves- I am lucky it works at all.
The original design uses about 16 crimp terminals per channel/ 32 per amp, I had to use a lot of crimp connectors. But I tried to solder the wire to the connector as well as physically crimp where I could.
The amplifier has a lot of wiring because of the thermal activacted LEDs, soft start, dual mono power supplies and separate PS/ Amp boards. Heck I put the on/off switch on the back panel to reduce wiring and its still messy.
Then again, this is the only known fully self contained ExtremA that I could find, so I am happy that it works. I'm always happy when they work!
The ExtremA Parts List (Nov. 2009). This is the most recent list.
I see in the original article the BD139/140 transistors are on thermal pads, I was wondering why, perhaps the packaging is different? Mine are not isolated from the heatsink (well they are-- just not necessary to use pads I don't think). They have a plastic encapsulation on both sides and in the through hole. The exact part is in my parts list.
While I tried to braid (twist) all the wires, keeping AC separate and apart from DC, this will be rechecked and things altered after I play with the amp. I always have messy wiring, I am just not that good at making stuff with a clean layout. Its an art. But I cannot hear any hum from the amp (speakers), there is some low mechanical hum from the big power transformers. I don't pretend to be a pro so lets not kid ourselves- I am lucky it works at all.
The original design uses about 16 crimp terminals per channel/ 32 per amp, I had to use a lot of crimp connectors. But I tried to solder the wire to the connector as well as physically crimp where I could.
The amplifier has a lot of wiring because of the thermal activacted LEDs, soft start, dual mono power supplies and separate PS/ Amp boards. Heck I put the on/off switch on the back panel to reduce wiring and its still messy.
Then again, this is the only known fully self contained ExtremA that I could find, so I am happy that it works. I'm always happy when they work!
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Banned
Joined 2002
Punishing Measurements.
I was looking at the amp on the scope with a 4 ohm load. Took a bunch of photos and here are a few. Probe at 1x and time div and v/div as indicated. I think I have the frequencies right but they can be computed using the time base.
I cannot see any bad behavior unless I really crank it up. At the "extremes". haha, bad joke. These are all into 4 ohms at the + output relative to ground (not relative to negative output). The best way to measure this is to take CH1 and add to an inverted CH2, but my scope CH2 was not up to par. I've got 2 scopes and each one has only one operative channel.
Clipping has some kind of osciallation. (Not sure if its in my source or in the amp as this went through my battery powered DRV134 box to make it differential.
Clipping behavior: 5V/div into 4 ohms.
Clipping is symmetrical- The Tek FG had some negative offset for this graph, had it been zeroed out you would see the same thing on the + half of the waveform too.
2KHz square wave. You see a little overshoot just visible in the graph.
5v/div into 4 ohms.
This one is pretty brutal.
20KHz square wave into 4 ohms at 2v/div.
I was looking at the amp on the scope with a 4 ohm load. Took a bunch of photos and here are a few. Probe at 1x and time div and v/div as indicated. I think I have the frequencies right but they can be computed using the time base.
I cannot see any bad behavior unless I really crank it up. At the "extremes". haha, bad joke. These are all into 4 ohms at the + output relative to ground (not relative to negative output). The best way to measure this is to take CH1 and add to an inverted CH2, but my scope CH2 was not up to par. I've got 2 scopes and each one has only one operative channel.
Clipping has some kind of osciallation. (Not sure if its in my source or in the amp as this went through my battery powered DRV134 box to make it differential.
Clipping behavior: 5V/div into 4 ohms.
An externally hosted image should be here but it was not working when we last tested it.
Clipping is symmetrical- The Tek FG had some negative offset for this graph, had it been zeroed out you would see the same thing on the + half of the waveform too.
2KHz square wave. You see a little overshoot just visible in the graph.
5v/div into 4 ohms.
An externally hosted image should be here but it was not working when we last tested it.
This one is pretty brutal.
20KHz square wave into 4 ohms at 2v/div.
An externally hosted image should be here but it was not working when we last tested it.
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Thanks.
Thanks Hugh. 6 years of DIY and you finally gave me a comment! Appreciate it. I have more than a few amps here, including one from your neighborhood, and will do a comparison. I am getting a little mechanical hum from the large transformers. Thinking that tightening or loosening the bolt may do something. Each tfo is on a rubber dampening pad. From the pics you may think that there is a risk of a shorted turn from the center bolt but I replaced the bolt with a shorter one so I don't have to face that horror (happened to me before with a GC).
Anyway, no electrical hum but have a little mechanical hum. Not bad at all.
I have a few Class A and AB amps here but swap in and out amps so often I think that I keep the electrical waste to a minimum relatively speaking. You can smell these things get hot, kind of scary.
You can ask me about the power bill but please don't ask me about the water bill- it does not pay to have a lawn in S. Cal.
Thanks Hugh. 6 years of DIY and you finally gave me a comment! Appreciate it. I have more than a few amps here, including one from your neighborhood, and will do a comparison. I am getting a little mechanical hum from the large transformers. Thinking that tightening or loosening the bolt may do something. Each tfo is on a rubber dampening pad. From the pics you may think that there is a risk of a shorted turn from the center bolt but I replaced the bolt with a shorter one so I don't have to face that horror (happened to me before with a GC).
Anyway, no electrical hum but have a little mechanical hum. Not bad at all.
I have a few Class A and AB amps here but swap in and out amps so often I think that I keep the electrical waste to a minimum relatively speaking. You can smell these things get hot, kind of scary.
You can ask me about the power bill but please don't ask me about the water bill- it does not pay to have a lawn in S. Cal.
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I was thinking about these measurements. I was not able to look at the differential behavior and so if the problems are offsetting and cancel out this would not be reflected. That is the value of having both scope channels working. It is also the value of a balanced/ bridged amp which is easy to forget about. I will try the other scope and see if I can get some differential measurements.
In the meantime, I have this hooked up to the main stereo over here. It does sound very very good. I am surprised by the deep powerful bass, I will compare this to the ultimate bass amp and DIY champ- the Krell Clone, later on. Noise? There is just the faintest HF hiss at the tweeter and no hum when the preamp is at mute. Highs are crystal clear and soundstage is excellent.
I did notice that for RCA and XLR you have to separately set the DC offset. If you set XLR offset to zero and try to drive with RCA you will get a little over double the offset.
While the input impedance of ExtremA is low, my preamps can drive this no problem. And I've got buffers and other things to take care of any issues.
In the meantime, I have this hooked up to the main stereo over here. It does sound very very good. I am surprised by the deep powerful bass, I will compare this to the ultimate bass amp and DIY champ- the Krell Clone, later on. Noise? There is just the faintest HF hiss at the tweeter and no hum when the preamp is at mute. Highs are crystal clear and soundstage is excellent.
I did notice that for RCA and XLR you have to separately set the DC offset. If you set XLR offset to zero and try to drive with RCA you will get a little over double the offset.
While the input impedance of ExtremA is low, my preamps can drive this no problem. And I've got buffers and other things to take care of any issues.
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Good project, a lot of work by the look of it.
That 20kHz square wave should be clean. This is not a super difficult task
for a well designed amp and in particular a class A amp.
Check the sig gen OP, each phase of unbal -> bal converter
unloaded, same loaded and then amp OP.
As they say GIGO.
Nice work,
cheers
Terry
Yeah, I was surprised by it too; could be the unbal-->bal converter which uses opamps. I'm looking into it further.
lgreen,
My pleasure, I try to always compliment people on good work.
I agree with Terry (who is a friend in fact), it should clip cleanly.
However, that is not to condemn it utterly, of more concern is the oscillation behaviour you noted.
Does it sound different/better than any other of your many amps, playing your usual test tracks? That is the question...... we build these things less for technical excellence than for listening pleasure, and in all the tech talk this is sometimes forgotten.
My recollection was that this is a very complex amp; it's very difficult in the face of a complex topology to maintain clean clip, complete stability, etc, these things are much underestimated. I favor NP's way of doing it; he works very, very hard to keep it simple, and that seeming simplicity belies a great deal of R&D for which he is famous.
It takes a long time to get really good at designing amps, and Sandor has probably done a very good job. But the complexity costs time, effort and money and should be discouraged.
Congrats again, BTW, I have the same scope as you!
Cheers,
Hugh
My pleasure, I try to always compliment people on good work.
I agree with Terry (who is a friend in fact), it should clip cleanly.
However, that is not to condemn it utterly, of more concern is the oscillation behaviour you noted.
Does it sound different/better than any other of your many amps, playing your usual test tracks? That is the question...... we build these things less for technical excellence than for listening pleasure, and in all the tech talk this is sometimes forgotten.
My recollection was that this is a very complex amp; it's very difficult in the face of a complex topology to maintain clean clip, complete stability, etc, these things are much underestimated. I favor NP's way of doing it; he works very, very hard to keep it simple, and that seeming simplicity belies a great deal of R&D for which he is famous.
It takes a long time to get really good at designing amps, and Sandor has probably done a very good job. But the complexity costs time, effort and money and should be discouraged.
Congrats again, BTW, I have the same scope as you!
Cheers,
Hugh
sound
The amplifier sounds great if you don't clip it. Its got to be pretty loud to audibly clip so I don't think this will be an issue most of the time. But you can hear a sizzle on the top end when you reach clipping.
After about 2 weeks of playing discs I know well (rock, acoustic guitar and vocals- no classical) I think it has more detail and almost as much weight as the Krell clone but will not play as loud and clean as the Krell will. I do know the Krell clips (and have measured this) but it just seems that you turn the volume up and everything keeps getting louder and louder till you can't handle any more volume.
The Krell (and all my diy amps except for DX) is noiser as well. It is time to disassemble the Krell and redo the grounding; the noise didn't bother me before but now with the ultra quiet DX and ExA, I want to achieve the same thing with the Krell. The ExA is far better than any of my gainclones which all sound thin in comparison. It seemed slightly better with less fatigue than the DX; its top end was better. But this was close, that DX is one very nice amp.
So far I really like it and will keep everyone posted.
The amplifier sounds great if you don't clip it. Its got to be pretty loud to audibly clip so I don't think this will be an issue most of the time. But you can hear a sizzle on the top end when you reach clipping.
After about 2 weeks of playing discs I know well (rock, acoustic guitar and vocals- no classical) I think it has more detail and almost as much weight as the Krell clone but will not play as loud and clean as the Krell will. I do know the Krell clips (and have measured this) but it just seems that you turn the volume up and everything keeps getting louder and louder till you can't handle any more volume.
The Krell (and all my diy amps except for DX) is noiser as well. It is time to disassemble the Krell and redo the grounding; the noise didn't bother me before but now with the ultra quiet DX and ExA, I want to achieve the same thing with the Krell. The ExA is far better than any of my gainclones which all sound thin in comparison. It seemed slightly better with less fatigue than the DX; its top end was better. But this was close, that DX is one very nice amp.
So far I really like it and will keep everyone posted.
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Hugh,
It does, I blame Lgreen's construction for it not behaving as many of the prototypes that were built (sorry!). As mentioned previously it will drive into class-B when it leaves the class-A setting, which is rather abrupt in terms of distortion.
This amplifier was designed and perfected using measuring equipment that far outclasses anything shown here. Particularly the AP System 2 was used to do all THD and stability testing as only that test system was capable of measuring THD that low. Ruthless testing and elimination was done to make sure this amplifier was unconditionally stable under all conditions. The fact that Lgreen's doesn't show this behaviour can in my opinion only be attributed to the 'shoe string' approach used in construction and him deviating from some of the design requirements.
I strongly disagree. The majority of this design is done by Bruno Putzeys, someone who has a long history of designing nothing but excellent performing amplifiers and other audio equipment. Bruno is someone that lives and breathes amplifier design like no one I've ever encountered, he is a prefectionist in every sense of the word. Stating that such a complex design should not be attempted is merely a sign of one's own incompetence and in no way a representation of Bruno's capabilities.
The ExtremA still is the best performing DIY class-A to date, but also one that is not for the novice builder. Lgreen has shown it can be built by the novice builder but I'd be surprised if it comes near the THD figures we measured on the prototypes as well as the final design presented in the published article.
Sorry if this reply rubs some folks the wrong way, but that's simply the way it is. Despite Lgreen's best efforts I wouldn't describe his ExtremA build as 'typical' for what the ExtremA is capable of.
Cheers,
Sander.
It does, I blame Lgreen's construction for it not behaving as many of the prototypes that were built (sorry!). As mentioned previously it will drive into class-B when it leaves the class-A setting, which is rather abrupt in terms of distortion.
This amplifier was designed and perfected using measuring equipment that far outclasses anything shown here. Particularly the AP System 2 was used to do all THD and stability testing as only that test system was capable of measuring THD that low. Ruthless testing and elimination was done to make sure this amplifier was unconditionally stable under all conditions. The fact that Lgreen's doesn't show this behaviour can in my opinion only be attributed to the 'shoe string' approach used in construction and him deviating from some of the design requirements.
I strongly disagree. The majority of this design is done by Bruno Putzeys, someone who has a long history of designing nothing but excellent performing amplifiers and other audio equipment. Bruno is someone that lives and breathes amplifier design like no one I've ever encountered, he is a prefectionist in every sense of the word. Stating that such a complex design should not be attempted is merely a sign of one's own incompetence and in no way a representation of Bruno's capabilities.
The ExtremA still is the best performing DIY class-A to date, but also one that is not for the novice builder. Lgreen has shown it can be built by the novice builder but I'd be surprised if it comes near the THD figures we measured on the prototypes as well as the final design presented in the published article.
Sorry if this reply rubs some folks the wrong way, but that's simply the way it is. Despite Lgreen's best efforts I wouldn't describe his ExtremA build as 'typical' for what the ExtremA is capable of.
Cheers,
Sander.
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