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Old 16th November 2012, 08:06 AM   #31
bcmbob is offline bcmbob  United States
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Thanks Nigel, That's probably a rather complex area for a thread like this, but it did prompt me to try to refresh my understanding of the classifications. Found a good page on Wikipedia (power amplifier classifications section down the page) that has layman level explanations for those who are interested.

I'll be interested in hearing more about the class A / chipamp relationship from others.
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Old 16th November 2012, 11:11 AM   #32
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Douglas Self describes a blameless amplifier . He includes a class A amplifier to be certain he offers all possibilities . He does this by converting his blameless class B to pure class A . In doing this he finds a small advantage as we should expect . One thing he does look at is maintaining negative feedback to the highest possible frequency to get blameless class B .

The Yamaha A + AB is one of my favourite amplifiers . I am not a great fan of others they have made . I have always said to myself one day I will make one . The Douglas Self example seems best . His designs are available as kits .

Daniel I 101 % agree with you . In my job I crave the 67% efficiency of a class B amps ( G , H also ) . If I get it I don't need complex solutions . I suspect a blameless amp can sound better than the class A version as it doesn't saturate the power supply . A controversial point of view and I am being deliberately that . Many know I knock Mr Self , I suspect he is >95% correct . The book is a bargain . However like appreciating art it should be your guide and not dictate your taste .
Distortion In Power Amplifiers

One can attempt class A from chip amps with a pull up or more usually down resistor to the voltage rail ( up to +ve ) . It has to pull a lot of power to do anything . If we can get to 4 W in A then maybe it is doing something ? As long as the amp is beefy enough and the resistor also it is a simple switch job to test it . Doubtless the power supply will be an issue if so . I have tried it and it is possible . Things will get very hot . Valves( tubes ) offer simple class A , my advice is learn the transistor versions first if at all . Valves require much study . Most valve kits need personalizing . Most transistor kits less so .

Returning to the nub of my argument . 18 - 0 - 18 V AC 160 VA is my universal transformer choice ( 2 for 2 x 100 W amp ) . Use as few or as many as required . 35 A bridge rectifier ( cheap , easy to fit ) . As many > 22 000 uF 35 V capacitors as required . 15 - 0 - 15 AC an alternative if looking more to the +/- 20 or 40 V DC range . If a beginner can learn this one thing the success of the amplifier is almost guaranteed . By that I mean better than commercial designs . Being ultra simplistic one can over engineer 100 % more than I suggest and perhaps still be spending wisely . 160 VA for class B 100 W is almost as small as one should dare go .

I will say something again to be deliberately controversial . I suspect most people who think about these things think of an amplifier as it's transistors and how they are arranged . I suspect most commercial amplifier designers think it is the quality of the power supply that determines the outcome ? The active circuit is the icing of the cake . Most high quality circuits I suspect on a blind listening test will be hard to identity between very good and best we can do . A low grade power supply should be obvious and will degrade the best amplifier in the world into something below an off the shelf Rotel budget amp .

Many Japaneses amplifiers in the past had circuits so absolutely blameless they must be as near perfect as we can get ? Many sounded very mediocre . They were penny pinched in the power supply department . One day I must buy one and give it what it should have had . The Yamaha I so love perhaps was forced by it's class A side to be properly equipped ? It sounded wonderful . Possible the best amplifier reference in the World ?
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Old 16th November 2012, 07:18 PM   #33
redjr is offline redjr  United States
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Originally Posted by bcmbob View Post
RaHza

I'm going back to basics on a new chip flavor with this kit. You can purchase a mono setup at the same site.The vendor is very good with customer support if you get stuck. You can of course go all the way back to making your own board or breadboard assembly (per Andrew & Daniel) for even more learning and adventure
I'm putting together the same little amp. Fired it up the other night and got some pretty clean audio on the bench. With a speaker up to my ear I could not hear any hum. Quiet as could be. Haven't finished the enclosure yet, but will upload some pics soon.

Rick
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Old 16th November 2012, 07:48 PM   #34
bcmbob is offline bcmbob  United States
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Hey, sounds like great fun. I haven't placed my order yet as I am waiting a response from the vendor. Since I'm testing other approaches I've requested some information on a Pass F5 based kit that I might purchase at the same time.

Very interested in your build pics and your impressions once everything has settled in.

Thanks, Amp Addicted in Michigan.
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Old 16th November 2012, 09:05 PM   #35
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Originally Posted by nigel pearson View Post
. . . In my job I crave the 67% efficiency of a class B amps. . .
For example, not all Class 5 Efficient supplies are switchmode--some are linear. Likewise Class B amplifiers aren't limited to any prefabricated efficiency figure. I've done several in the range of 70% to 80%, and notice that Class D also does ~80% while driving 4 ohm speakers or half the output power brag while driving 8 ohm speakers (and I'm not impressed with 92% efficiency at the cost of half power). This little fact often comes as a surprise to people who assume Class D won't need a heatsink (kerblooie). When it comes to durable current Linear has switchmode beat--My linear efforts will haul out their maximum current, endlessly, without breaking, much unlike switchmode technologies that are only good for half of their brags. Ever tried a 300w computer power supply in a PC that actually needs 300w? Won't even start.

In my view Linear still has some life left in it, but we need interesting challenges, such as: "Contest: Class B power amp in a mint tin." sort of thing where the parameters force paying attention to efficiency of linear electronics. Without the crutch of giant heatsinks and endless space, the linear designer would then have to pay attention, since the crutch of swamping clumsy with bias would not be available.

I'm not suggesting power amp in a mint tin except as a design exercise for assuring efficiency. However, I've never used a heatsink that large for a Philips Class B car chip (11w to 8R *2 channels). Even though a mint tin is an ostentatiously large heatsink for efficient Class B, a problematic factor is heat at the capacitors.
I would love to see some creativity and design instead of cranking up bias dials.
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Originally Posted by nigel pearson View Post
. . .Returning to the nub of my argument . 18 - 0 - 18 V AC 160 VA is my universal transformer choice ( 2 for 2 x 100 W amp ).. . .
OH! Quad Rail! Now it makes sense. That looks handy for some applications. Instead of the 2 transformers, we could substitute use 4 of double-insulated 25v SMPS (implying that earth ground is later assigned to speaker ground via ground loop breaker) But, sir, the title of this thread is Basic, and I don't think that the quad rail is basic.
This thread needs either 1 transformer or 1 SMPS.
SO, either 1 of 18,0,18vac transformer, a power board and LM1875 or
an SMPS and a car chip for less chance of a shock.
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Last edited by danielwritesbac; 16th November 2012 at 09:07 PM.
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Old 16th November 2012, 09:30 PM   #36
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Originally Posted by danielwritesbac View Post
Likewise Class B amplifiers aren't limited to any prefabricated efficiency figure.
I recently posted the figure (78.5%), for a capacitively-coupled class-B amp at least. I looked for a while but couldn't find a derivation for direct-coupled and transformer-coupled class-A or class-B efficiencies.
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Old 17th November 2012, 09:37 AM   #37
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I recently posted the figure (78.5%), for a capacitively-coupled class-B amp at least. I looked for a while but couldn't find a derivation for direct-coupled and transformer-coupled class-A or class-B efficiencies.
Would love a link . And Daniel .

Sorry guys for deliberately making it complicated . The simple message was 160 VA 18- 0 - 18 AC would have been the ideal place for me to start many years ago when buying parts .


I sincerely believe a good amplifier is 80 % PSU . If crossover distortion is minimal and distortion below 0.1 % THD with sensible bandwidth then it should outperform most signal sources . In the ideal world it can drive Quad ESL 63 speakers . That requires 15 Watt class A as an ideal starting point . Surprisingly the low sensitivity of that speaker seems not to be a problem . I suspect it's genuine 60 dB + dynamic range shows detail which makes it loud enough when maybe running at only 90 dB typical ? Any of the amplifiers discussed here should be able to drive them . From memory they have 42 Hz - 3 dB if the room is large enough . That is the lowest note on a bass guitar at realistic volume ( have done that ) . Not many speakers better that . Reputation says they have no bass , not so . The 8R 2 uF power tests seen from the 1950's onwards was to represent them as an approximate load .

Efficiency is important . It allows minimal heat sinking and optimizes the use of the power supply . I would be the first to believe excellent class B can beat good class A .

Some will not know that the retail price of an amplifier might be 1000 % the price of it's parts . Buying in small quantities we should say 300 % . We have a very good chance to beat a commercial design even at 300 % . It implies we might do it for less than half the price if our time is not accounted for . It might also interest people to know that the manufacturer is lucky to retain 10% over the price of parts . All the costs are promotion ,distribution , new products and tax .
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Old 17th November 2012, 10:48 AM   #38
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Would love a link .
I have no link. I was doing some nose-in-a-book homework. It wasn't immediately obvious to me that the formulae changed for other coupling methods, so it's been bouncing around in my head ever since. I wasn't sure how interesting it would be to others here, so I've been keeping it on the down low. It isn't difficult math to follow:
Since VOUT(RMS) = 0.707*VCEQ
and IOUT(RMS) = 0.707*Ic(sat)
then Pout = 0.5*VCEQ*Ic(sat)
Substituting VCC/2 for VCEQ, we get Pout = 0.25*VCC*Ic(sat)
ηmax = Pout/Pdc = 0.25*VCC*Ic(sat)/(VCC*Ic(sat)/pi) = 0.25*pi
ηmax = 0.785 = 78.5%

The mint tin linear amp isn't so hard to imagine with today's ultra-miniature parts, but getting to the 5-10 wpc realm still seems a stretch. I assume that doesn't include the psu.
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Last edited by sofaspud; 17th November 2012 at 10:53 AM. Reason: readability
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Old 17th November 2012, 11:15 AM   #39
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My best attempts just before clipping seldom are as good as they should be . I doubt if I ever did better than 65% and that seems to slip if the phase angle is other than resistive . I never studied it in great detail . Intended to do it soon , especially class H . I have no real interest in the absolute efficiency . I am interested in how small the heat sink can be . If the amp is only 20 % efficient at 1 W that will not be a problem . Yamaha make the efficiency of class AB seem very poor in the paper below . If I remember correctly TDA 2030 is claimed at 65% typical .

This is close to my experiences .
Amplifier Efficiency

Yamaha see it differently .

http://download.yamaha.com/api/asset...asset_id=53052
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Old 17th November 2012, 11:49 AM   #40
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Wading through all the *&"p, the guy is a total newbie.

1. What does he want to learn ?

Chip amps are fine but don't realy teach you very much.

With a chip amp he will probably learn how to layout an amplifier, learn how to build a PSU and achieve acceptable results.

The next step up is using discrete components. The Vellerman kit is simple, it's not very good and is over priced but it does teach you a bit more about amplifier basics.

The ILP HY** route is "Black Box" building. Again, you learn about layout and PSU design.

My question is, is this going to be the start of a long hobby - it was in my case.

Obtain a nice big box - a second hand amplifier is a good place to start.

Try a fairly basic kit and see how it goes. If that works then you can try to better it, learning along the way.

Once you have achieved the results that you are looking for, then think about finishing the project with a nice chassis.

Personally the JLH or HIRAGA Class A 10W designs are a very good starting point.

http://www.ebay.co.uk/itm/SC-HOOD-JL...item23200d4717

Last edited by KatieandDad; 17th November 2012 at 11:56 AM.
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