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Discrete vs monolithic op amps for audio

unclejed613

Well-Known Member
Most Helpful Member
i think liquid nitrogen might actually strip the aluminum layer and the top coating off the disk, from the dissimilar contraction of the materials. or it could fracture the plastic into very small pieces.

i've heard of cryogenically de-stressing rifle barrels to improve accuracy, and that does work, but that's a large piece of steel that often does have uneven stresses in it that make it flex unevenly with changing temperature, changing the point of aim. in that application cryogenic treatment makes sense, but treating cables to change their conductivity characteristics does not. there's a myth that metals in wire and connectors is "crystalline", and therefore wires act like "billions of tiny crystal rectifiers". not so... metals that are in crystalline form are usually very brittle, which when it exists in wire is a symptom of metal fatigue. copper and other metals in wire are ductile and flexible, both desirable qualities in wire. brittle metals like tungsten are not used in wire (except in incandescent bulbs), but even so, do not exhibit anomalies in their conductivity or act like semiconductors. conductors exhibiting such properties would generate large amounts of shot noise.
 

Ubergeek63

Well-Known Member
had you read the spec, it is 125W into 8 ohms unclipped. I got 100W at 0.03% looking at the graph.
But the graph showing BTL distortion clearly shows clipping beginning at 90W when the supply is 50V. At 142W the distortion is 2% to 5%. The graph of "Unclipped Output power Vs Supply Voltage" shows 142W with a 50V supply.


The datasheet for the LM3886 says that its output into 8 ohms is typically 50W at 0.1% max distortion with a 70V supply. But the graphs of THD vs Output Power show 60W at 1kHz with only 0.002% distortion and show 60W at 20kHz with only 0.01% distortion.

The LM3886 has only 11 pins in two rows and has a metal tab that is bolted to a heatsink. The web is full of optional circuits and pcb designs.
at 35W dissipation at 1KHz you need a VERY good heatsink... unless you do not expect extended low frequencies.... having done an amp at lows the current demand, and hence that thing's dissipation skyrocket.

frankly down there in the mud THD wise it all becomes specmanship ... and salesmanship... you are getting down in the range that the instruments are better than the ear.
 

audioguru

Well-Known Member
Most Helpful Member
People don't play music at full blast continuously. If the peaks are clipping then the average power is 1/10th or less.
At work I was told to play an Electrovoice PRO amplifier at full power continuously. It smoked then stopped after less than one minute. Our PRO amplifiers were guaranteed to play continuously at any power and did. I saw many of our amplifiers sold but never saw a failed one.
 

Ubergeek63

Well-Known Member
People don't play music at full blast continuously. If the peaks are clipping then the average power is 1/10th or less.
At work I was told to play an Electrovoice PRO amplifier at full power continuously. It smoked then stopped after less than one minute. Our PRO amplifiers were guaranteed to play continuously at any power and did. I saw many of our amplifiers sold but never saw a failed one.
good for you... I had to do the same thing... but with no power (12V @ 3A, that also had to supply our display and a CD changer) and no heat sink... a class d and, LF limit, power limit, and some big caps kept the thing running... and even at 0.5% THD rating (TPA032D04) is sounded good (car speakers in the treadmill structure vented at the floor)

we had a lot of failures due to power plugged into the speaker terminals and over voltage of the amp's absolute max of 13V - i think this was 8 yrs ago, best solution on the market at the time.
 
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unclejed613

Well-Known Member
Most Helpful Member
People don't play music at full blast continuously. If the peaks are clipping then the average power is 1/10th or less.
At work I was told to play an Electrovoice PRO amplifier at full power continuously. It smoked then stopped after less than one minute. Our PRO amplifiers were guaranteed to play continuously at any power and did. I saw many of our amplifiers sold but never saw a failed one.
continuous full power is also VERY bad for speaker voice coils. unless it's a type of speaker that has ferrofluid to help with the heat dissipation and an aluminum coil form, most voice coils will smoke if kept at their rated power for very long. unfortunately a lot of people have got used to a lot of compression in music, and the over-use of compression raises the average power level a lot closer to full continuous power than has been the norm in the past. this is a lot harder on amps and speakers. i used to work at a music store that rented out sound equipment, and every monday was spent replacing blown tweeters and crossover parts. inexperienced sound system operators, first of all didn't use hearing protection. so when they began suffering from short-term high frequency loss, would turn up the highs until they could hear the "sizzle" again. then the tweeter protection would kick in, reducing the highs about 10db (poly-switches, incandescent lamps, or MOSFET bypasses are usually used for this), so they would crank up the highs even more. in the case of poly switches, the poly switch would overheat and short, dumping a lot of high frequency energy into marginally overheated tweeters, and frying them. the poly switch would then burn open. crossover caps would then smoke. in the case of lamps or MOSFETs, the lamp would burn out, the MOSFET would short along with burnt caps, etc..

a class AB amp also has a difficult time with material averaging between 70 and 80% of full power, because it's in this range where an amp dissipates the most heat. a lot of manufacturers burn-in their amps 24-48 hours at this power level to weed out marginal components.
 

galed

New Member
a really good amp shouldn't have a sound of it's own... which is really the point here.
right. but then it comes down to recording quality and DAC performance. I'd imagine an amplifier could either amplify or cancel distortions that come from other parts of the system

High endAudio is, unfortunately, full of con artists. There is also a lot of extraordinary individuals who are always pushing the envelope. The key is to figure out who belongs to which category.
Just to stir up debate, which companies out there making amps are in which category? Who's really innovating?

The class-D amplifier has the distortion of a cheap PA amp or guitar amp.
with all due respect, there's some serious research going on here at the university of colorado with class D amps.


Do you guys have any good resources for designing circuitry with an eye towards audio?
 

unclejed613

Well-Known Member
Most Helpful Member
actually some of Pioneer's high end receivers use an ICE amp using chips from Bang&Olufsen which incorporate class D operation with negative feedback, and actually are good amplifiers.

tomorrow evening i will post some of the best audio design resources in my blog, so i don't have to keep posting the same info every time somebody asks about it, and i will put a link to the article here...

companies that are really innovative are usually the small shops that experiment with amp designs and when they find something really good, they either build it for retail, sell kits over the internet, or publish their ideas on the web and let you build it. i will look for some of these and put them in my listing on my blog
 

audioguru

Well-Known Member
Most Helpful Member
I'd imagine an amplifier could either amplify or cancel distortions that come from other parts of the system.
Distortions are errors in frequency response caused by the output transformers of vacuum tube amps (reduced bass and treble), speaker resonances due to the very low damping factor of vacuum tube amps or even harmonics added by vacuum tubes.
Some recording engineers equalize the recording so that it sounds good to them or sounds good only when played on their speakers in their environment.

It is difficult to "cancel" distortion. Chop off all the high frequencies to remove the harmonics but then the sound is muffled like a telephone.

How can you "fix" the poor damping factor of an amplifier?
When a solid state amplifier with an output impedance of 0.02 ohms tells a speaker to stop, it stops almost immediately. Like live classical music.
But when a vacuum tube amplifier with an output impedance of 8 ohms tells a speaker to stop, the speaker keeps on resonating for a fairly long time. Then bass is boomy and treble shrieks. The sound is smeared. Like good old Rock and Roll.

Do you guys have any good resources for designing circuitry with an eye towards audio?
Douglas Self had many detailed articles about excellent audio amps on the web but he removed them recently because he is now selling his book. Maybe an internet archive service can find them.
 

bychon

New Member
Actually, the tubes amplified. My point in that exercise was to see if an excellent ear could detect the transistors. The ears failed. They failed because I used good design principles for the transistor applications. This is the kind of guy that claims that if I put a cathode bypass cap in the circuit, then cut it loose at the tube socket leaving only the ground connection, it still affects the sound. Technically, yes. There are a couple of puffs between the cut wire and the tube socket, but can you perceive it? I say, If a house fly lands on an aircraft carrier, will it change the way the engine noise radiates through the deck plates? Technically, yes, but can you perceive it? I just had to know if the almighty ear could detect active transistors in the signal path if they were properly designed. So, hooray for buzzwords, but testing in a real world will reveal the truth. I don't argue with the musician. He's as bull headed as anybody I know. I just slip in the transistors and don't tell him.
 

audioguru

Well-Known Member
Most Helpful Member
Very expensive amplifiers are sold with vacuum tubes glowing on top. The vacuum tubes are not part of the amplifier's circuit and the owners love the "tube sound".
 

Ubergeek63

Well-Known Member
Actually, the tubes amplified. My point in that exercise was to see if an excellent ear could detect the transistors. The ears failed. They failed because I used good design principles for the transistor applications. This is the kind of guy that claims that if I put a cathode bypass cap in the circuit, then cut it loose at the tube socket leaving only the ground connection, it still affects the sound. Technically, yes. There are a couple of puffs between the cut wire and the tube socket, but can you perceive it? I say, If a house fly lands on an aircraft carrier, will it change the way the engine noise radiates through the deck plates? Technically, yes, but can you perceive it? I just had to know if the almighty ear could detect active transistors in the signal path if they were properly designed. So, hooray for buzzwords, but testing in a real world will reveal the truth. I don't argue with the musician. He's as bull headed as anybody I know. I just slip in the transistors and don't tell him.
Thank you ... that is what I have been saying

dan
 

unclejed613

Well-Known Member
Most Helpful Member
audio design resources.... this ought to keep you busy for a while... :p
http://www.electro-tech-online.com/blogs/unclejed613/129-audio-design-resources-web.html

you would think that audio, being in the sub-basement of the electromagnetic spectrum, would be super easy to design equipment for. but audio straddles the domain between (almost ) DC, ELF frequencies, and the beginning of the RF spectrum (3khz and above), and device characteristics can change rapidly in this region. audio power amplifier instabilities and distortions can extend from less than 20khz to tens and hundreds of Mhz (MOSFET output transistors have been known to oscillate at well over 100Mhz).

also, the ear is generally difficult to fool, and can be surprisingly sensitive to certain types of distortion. test equipment is more sensitive, but can't tell the difference between "nice sounding" distortion and "nasty" distortion.
 
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