Hi everyone!
I would like to humbly ask that everyone please be kind to me as I am new to the forum. Your patience is tremendously appreciated!
I am thinking about building (or modifying) my Project Amp to class A Standards.
I think Class A is for me as I am wanting to absolutely minimize distortion and I am willing to pay for the Electrical Power to do it (I am a BSEET working in the electrical power industry).
We talked about class A amplifiers in college but focused and built primarily class AB and Class D in lab (wether we like it or not the industry revolves around these designs right now). As with any project I begin, I wish to start with research and approach class A Amplifiers as a Novice while learning the particular aspects of this class.
Any class A design that I will commit to build will be solid-state (nothing against our fellow tube fans). I really prefer the more predictable and stable operating characteristics of IC's.
My early research has revealed that there is a tremendous amount of material on the web (more "this is my design" and "what I did's" than theory and application).
So what I sincerely hope is that someone here can help me get to "The Real Good Stuff" so I can develop/select/modify a design and deplete my checking account in the not too distant future and start the building and testing process (I always love how very few people mention the testing part...).
As far as construction I am pretty confident I can handle most designs, but I am looking to start a little higher up the ladder since I have built many electronic circuits in and out of college (PCBs, enclosures, the whole ball of wax!).
I am very much looking forward to this groups suggestions since you are much more versed on this subject than I. Thanks Everyone. Hope to hear some suggestions!
__________________
I would like to humbly ask that everyone please be kind to me as I am new to the forum. Your patience is tremendously appreciated!
I am thinking about building (or modifying) my Project Amp to class A Standards.
I think Class A is for me as I am wanting to absolutely minimize distortion and I am willing to pay for the Electrical Power to do it (I am a BSEET working in the electrical power industry).
We talked about class A amplifiers in college but focused and built primarily class AB and Class D in lab (wether we like it or not the industry revolves around these designs right now). As with any project I begin, I wish to start with research and approach class A Amplifiers as a Novice while learning the particular aspects of this class.
Any class A design that I will commit to build will be solid-state (nothing against our fellow tube fans). I really prefer the more predictable and stable operating characteristics of IC's.
My early research has revealed that there is a tremendous amount of material on the web (more "this is my design" and "what I did's" than theory and application).
So what I sincerely hope is that someone here can help me get to "The Real Good Stuff" so I can develop/select/modify a design and deplete my checking account in the not too distant future and start the building and testing process (I always love how very few people mention the testing part...).
As far as construction I am pretty confident I can handle most designs, but I am looking to start a little higher up the ladder since I have built many electronic circuits in and out of college (PCBs, enclosures, the whole ball of wax!).
I am very much looking forward to this groups suggestions since you are much more versed on this subject than I. Thanks Everyone. Hope to hear some suggestions!
__________________
johnzimm said:
Here's some places you might want to start:
1 - The 'JLH' amp, a John Linsley Hood design dating back to the mid-60's. There's a topic here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=3075
and a popular web page at:
http://www.gmweb.btinternet.co.uk
(this wasn't working for me at the time of writing, for some reason)
you can get kits at:
http://users.breathe.com/williamshart/classa.htm
2 - Rod Elliott's 'Death of Zen', which is a very similar architecture to JLH's:
http://sound.westhost.com/project36.htm
the 'Zen' bit is a reference to...
3 - Nelson Pass' Zen series of amps. These are described at:
http://www.passdiy.com/amps.htm
plus of course there's a whole Pass Labs topic on DiyAudio.
4 - The Aleph series of amps, also from Mr. Pass. There's not so much info on these on passdiy, but the Pass Labs topic here is a good place to ask.
5 - The 'Monster' amp by Jean Hiraga. There's a schematic here:
http://www.bonavolta.ch/hobby/fr/audio/monster.htm
6 - You could make yourself a Musical Fidelity A1 clone. There's a useful web page here:
http://www.mhennessy.f9.co.uk/mf_a1/
Personally, I don't have any experience of any of these, but I thought you deserved an answer by now!
If you want my (uninformed) opinion -
(1) and (2) are good, solid designs, and you shouldn't have any problems getting an easy-to-assemble kit.
(3) is more intended as a learning experience, not a genuine attempt at a hi-fi amp. I wouldn't, for instance, want one as my reference amplifier.
(4) is sold commercially as an amp with a good reputation; I'd imagine it's a bit ambitious if this is your first project
(5) is just a bit mad. Car batteries plus every variety of large PSU capacitor thrown in for luck, yet a tiny power output. You might, of course, want something totally mad.
(6) also found fame as a commercial amp; it's unlikely you'll find any kits or PCBs, but it might be simpler than (4).
Relatively low output power goes with the territory, of course.
Cheers
IH
(3) is more intended as a learning experience, not a genuine
attempt at a hi-fi amp. I wouldn't, for instance, want one as my
reference amplifier.
IH,
for someone who hasn't built a ZEN amp you seem pretty sure
that it isn't HI-FI quality.... hmmmmmm. ok.
I'd say my SOZ is HI-FI, and i actually built one
Zen's are educational though! a nice bonus to go with the nice sound!
moe29
attempt at a hi-fi amp. I wouldn't, for instance, want one as my
reference amplifier.
IH,
for someone who hasn't built a ZEN amp you seem pretty sure
that it isn't HI-FI quality.... hmmmmmm. ok.
I'd say my SOZ is HI-FI, and i actually built one
Zen's are educational though! a nice bonus to go with the nice sound!
moe29
johnzimm said:
I think Class A is for me as I am wanting to absolutely minimize distortion and I am willing to pay for the Electrical Power to do it (I am a BSEET working in the electrical power industry).
If "absolutely minimal distortion" is your goal, I'm not sure that class A is the answer. Many class A designs call for little (or even no) negative feedback, resulting in higher THD numbers. But then, THD isn't everything... I'm no expert, but the consensus seems to be that high amounts of negative feedback are more detrimental to the sound than higher (but still within reason) distortion levels.
I've heard a lot of amps in time and must say that the best sounding amp was definitely the AlephX. Sure there will be amps out there with better characteristics.
Take a look at the birth of this nice amp here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=3748
Here you will find a very good reference to a 'special version':
http://www.diyaudio.com/forums/showthread.php?s=&threadid=5980
And here is my implementation of this beauty:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=14979
BTW, a warm welcome to the forum.
Keep us informed.
/Hugo
Take a look at the birth of this nice amp here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=3748
Here you will find a very good reference to a 'special version':
http://www.diyaudio.com/forums/showthread.php?s=&threadid=5980
And here is my implementation of this beauty:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=14979
BTW, a warm welcome to the forum.
Keep us informed.
/Hugo
If absolute distortion numbers are the goal, check the class A design in D. Delf's book (or even his trimodal for which pcbs are available via his website). Randy Slone has one in his amplifier book as well. Both look a lot like their class B designs but biased into Class A. The distortion numbers are ultra low -- few hobiests will have the equipment to verify them.
No - I haven't built them - I live in rather warm climat and don't have AC. I'm not being funny by saying this - I've an aquaintance who uses class A's and I don't know how he stand to use them in the summer months. Self's Trimodal is cute in this regard - you can swith it between class A and B - he labels it Winter and Summer - but he lives on a cold wet island!
No - I haven't built them - I live in rather warm climat and don't have AC. I'm not being funny by saying this - I've an aquaintance who uses class A's and I don't know how he stand to use them in the summer months. Self's Trimodal is cute in this regard - you can swith it between class A and B - he labels it Winter and Summer - but he lives on a cold wet island!
I have been told THD under 1% is inaudible
and even Mr. Pass has amplifiers rated for 1% THD.
D. Self's book focuses alot on lower distortion perhaps
for technical reasons, because as an engineer it's
the cool thing to do.....not necessarily for audible reasons.
And tube amplifiers are even worse for THD and people love it
What is more noticable is power levels and low powered
amplifiers are typically overdriven by the end user
which causes audible nasties..... if you need 50w, design
for 2x more min. - hehe
and even Mr. Pass has amplifiers rated for 1% THD.
D. Self's book focuses alot on lower distortion perhaps
for technical reasons, because as an engineer it's
the cool thing to do.....not necessarily for audible reasons.
And tube amplifiers are even worse for THD and people love it
What is more noticable is power levels and low powered
amplifiers are typically overdriven by the end user
which causes audible nasties..... if you need 50w, design
for 2x more min. - hehe
moe29 said:
As I said, this as my uninformed opinion. I'm paraphrasing threads such as this one:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=12508
in which NP himself warns that it's "not for everybody".
I wouldn't want somebody to build one with the wrong expectations, and then accuse Nelson of peddling poor designs. Personally, I've got nothing but admiration for someone who's prepared to risk his company's and personal reputation in an open, online forum like this one.
Cheers
IH
A further observation: 1% at 20kHz into 4-ohms at rated poer is one thing (which along the lines of the NP figure, I suspect). 1% at 1k into 8 ohms at 1W is something very much lessthan that.
Moral: to talk about distortion and what it means, a single data point is of little value, you really need to the the plot against frequency and against power.
Moral: to talk about distortion and what it means, a single data point is of little value, you really need to the the plot against frequency and against power.
further thoughts...
Hello again Everyone,
Thanks so much for the replies, I will look into Nelson's designs. I believe he is capable of producing excellect work and I find it frustrating that I could not listen to any of his creations through some local facility here in the Michigan/Indiana border, USA.
After reading everyones' posts I have some thoughts to throw into the pool for feedback:
It was my understanding that in a class AB Push-Pull (FET, BJT etc.) that the weak point of the design was the "zero crossing" (the point at which the signal was switching between the transistors.
Even if the Push-Pull was completely enclosed within the feedback loop of, say, a proper Op Amp driver then it will generate a fair amount of distortion from zero-crossing, especially at Higher Volumes (say 50-60% of a given design's rated output). The class AB we constructed in lab in college, was analyzed and while relatively small compared to the output waveform the zero crossing transients were viewable on the oscilloscope. Because Transistors in general do have differing amounts of Td-on, and Td-off (PNP's as I recall are significantly slower than NPNs) there will always be this transient distortion on the outputs).
Class A, as I understand it, typically does not suffer from this problem because of the biasing of the Output Stage (Single, Push-Pull, etc. ). By biasing the Transistors from slightly to "half-on" (again depending on the type of stage employed), Td-on, Td-off fall out of the picture in terms of contributing noise transients. Of course keeping the DC currents within the stage and Isolated from Speaker is much more critical (something Class AB saved us from). So eliminating Td from a design is something I would like to experience before I pass my personal Judgement as to whether class A has nothing to offer when compared to Class AB.
What does somewhat perplex me is the talk regarding "feedback" (negative or other). When I think of feedback, I am thinking in terms of a differential operational amplifier and its critical feedback loop. This is critical in an operational amplfier driving Push-Pulls in Class AB.
But in certain aspects of Class A, I don't understand the importance of feedback (or its exclusion) in output stage amplifier design (I am an electrical power engineer by trade and thus not versed in Production Amplifier Design). Unless "feedback", is merely the term applied to the return path of the NPN(PNP) base-emitter current of a given output stage transistor. At this point I am not sure how critical this is beyond a "suitable" return path... So I would welcome some enlightenment.
I do fully understand the comments regarding driving strong speakers with a weak amp. Obviously, Overbuilding is a consideration (I have had to educate fellow employees about basic audio, electronics, and the wonderfully creative power ratings the audio industry seems to keep inventing).
Speaking of that, could someone educate me as to this new amplifier power rating at 1kHZ that is showing up in manufacturers specs all over the place and why it is necessary beyond Peak or RMS Power?
Happy Monday!
John Zimmerman
Hello again Everyone,
Thanks so much for the replies, I will look into Nelson's designs. I believe he is capable of producing excellect work and I find it frustrating that I could not listen to any of his creations through some local facility here in the Michigan/Indiana border, USA.
After reading everyones' posts I have some thoughts to throw into the pool for feedback:
It was my understanding that in a class AB Push-Pull (FET, BJT etc.) that the weak point of the design was the "zero crossing" (the point at which the signal was switching between the transistors.
Even if the Push-Pull was completely enclosed within the feedback loop of, say, a proper Op Amp driver then it will generate a fair amount of distortion from zero-crossing, especially at Higher Volumes (say 50-60% of a given design's rated output). The class AB we constructed in lab in college, was analyzed and while relatively small compared to the output waveform the zero crossing transients were viewable on the oscilloscope. Because Transistors in general do have differing amounts of Td-on, and Td-off (PNP's as I recall are significantly slower than NPNs) there will always be this transient distortion on the outputs).
Class A, as I understand it, typically does not suffer from this problem because of the biasing of the Output Stage (Single, Push-Pull, etc. ). By biasing the Transistors from slightly to "half-on" (again depending on the type of stage employed), Td-on, Td-off fall out of the picture in terms of contributing noise transients. Of course keeping the DC currents within the stage and Isolated from Speaker is much more critical (something Class AB saved us from). So eliminating Td from a design is something I would like to experience before I pass my personal Judgement as to whether class A has nothing to offer when compared to Class AB.
What does somewhat perplex me is the talk regarding "feedback" (negative or other). When I think of feedback, I am thinking in terms of a differential operational amplifier and its critical feedback loop. This is critical in an operational amplfier driving Push-Pulls in Class AB.
But in certain aspects of Class A, I don't understand the importance of feedback (or its exclusion) in output stage amplifier design (I am an electrical power engineer by trade and thus not versed in Production Amplifier Design). Unless "feedback", is merely the term applied to the return path of the NPN(PNP) base-emitter current of a given output stage transistor. At this point I am not sure how critical this is beyond a "suitable" return path... So I would welcome some enlightenment.
I do fully understand the comments regarding driving strong speakers with a weak amp. Obviously, Overbuilding is a consideration (I have had to educate fellow employees about basic audio, electronics, and the wonderfully creative power ratings the audio industry seems to keep inventing).
Speaking of that, could someone educate me as to this new amplifier power rating at 1kHZ that is showing up in manufacturers specs all over the place and why it is necessary beyond Peak or RMS Power?
Happy Monday!
John Zimmerman
John Z, It is my recommendation that you build one of Nelson's class A designs. You don't know enough to be able to change much at first.
Class A is best, on all accounts, but it is not practical with very large power outputs. Mostly because it heats the room too much when operating big amps. The actual power spec that we normally relate to is AVERAGE POWER, that is derived from the RMS Voltage. Don't think too hard about it, it is a technicality that is discussed by professors. Good luck, and I'm sure that it will sound OK.
Class A is best, on all accounts, but it is not practical with very large power outputs. Mostly because it heats the room too much when operating big amps. The actual power spec that we normally relate to is AVERAGE POWER, that is derived from the RMS Voltage. Don't think too hard about it, it is a technicality that is discussed by professors. Good luck, and I'm sure that it will sound OK.
From my own experience as a not elektronic - experienced diyer i recommend you to build a Zen V4
http://www.passdiy.com/projects/zenv4-1.htm
and in case you think about further improvements on the sound - take a close look towards your speakers. They are more imortant if we want to talk more about THD numbers and so on.
http://www.passdiy.com/projects/zenv4-1.htm
and in case you think about further improvements on the sound - take a close look towards your speakers. They are more imortant if we want to talk more about THD numbers and so on.
johnzimm;
You may be able to expedite your quest by reading this
thread.
http://www.diyaudio.com/forums/showthread.php?threadid=7200&highlight=amp+challenge
Every engineer strives for technically perfect designs, but
in the end, is it audible based on real world testing of
humans ? You be the judge....
Amplifier designers /=/ You can measure things you can't hear and
you can hear things you can't measure[tm]
You may be able to expedite your quest by reading this
thread.
http://www.diyaudio.com/forums/showthread.php?threadid=7200&highlight=amp+challenge
Every engineer strives for technically perfect designs, but
in the end, is it audible based on real world testing of
humans ? You be the judge....
Amplifier designers /=/ You can measure things you can't hear and
you can hear things you can't measure[tm]
So many Johns, so much confusion. Mike, I don't know if you could easily build one of my amps. The only schematic that I have ever published on a power amp was in 'The Audio Amateur' in 1981. That was already a 5-10 year old design at the time, so it doesn't have servos, etc that I would use today. It would be better to get an old Parasound 2200 and mod it up.
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