Democratic hybrid amplifier
The purpose of this amp to allow voiceless small triodes to express themselves as proud and brave as their big brother tenors can do ,and this with much more brio .
The triode domesticates the power inverting amplifier, imposing its character to be the dominant transfer function of the circuit ,eclipsing totaly the power amps voice.By this the tiny ECC82 for example behaves as a giant ECC82 output tube,with all its character exposed to the output.
LM3886 graph shows simulations of the transfer function of the power amp alone with 22k/C1/10k inT input 100k FB,Showing for C1 100p and 680p with a gain of 3, how the dominant pole is dependent of.
This architecture provides flexible adjustment of, open loop gain/dominant pole, allowing to adjust easily ,eliminating gray sound.(see gray sound or transient intermodulation distortion)http://www.diyaudio.com/forums/lounge/297145-transient-intermodulation-distortion.html.
The significant advantage over SE ,the triode is totally liberated from constraints of output loading and damping as these tasks are trusted to the "domestic", which allows the designer to adjust at will the operating current/voltage/loading, to tailor the required sound .And more, by adding the input voltage stage the two triodes complement each other .The input adjust more the vowels (adjectives) the output more the consonants (adverbs) ,adding a variable bootstrap provides the user still further fin adjustments.
The power amp
Of course a class A is best suited for this application.An example of a good class B is shown opa541 distortion curve showing 4% at 20kHz for 100mw, not suitable.But the LM3886 is an other pedigree.Two curves showing distortions at 20Hz and 20khz has no any difference, that is the timing of switching on/off of the outputs as well as the overlap is perfectly adjusted. After all it cannot be more round than a circle. Of course it is an IC ,but of different specie.This IC has unique kind of output transistors that can function up to 250°C instead of ordinary 150°C.By allowing it to function at vacuum tube temperatures it eliminates all thermal feedbacks ,behaving as if it is made of descreet components.By using appropriate PSU and heatsink of BASIC3886 presented at (LM3886 singing at HELL°) can deliver a very high dynamic sound with peak power of 85W.
The triode
I tried two triodes 12au7a (Shuguang) and ECC81 .Each type exhibits its own sound ,that can be tailored with great ease.The ECC81 ,a HF nonlinear triode, behaves like dynamic expander extracting from the sound unexpected detailes,like photoshop sharpness enhancer. Ugly but sharp . I invite guitar amp designers to give a trial with low plate voltage .
With 12au7a, a V/H oscilator tube, I designed a very specialized amp .A low definition amplifier. It is intended to hear the sound rather then listen to .That is an amp specialized for vowels (adjectives) and less in consonants (adverbs). Turner paintings style sounds, if you see what I mean. What best I can choose than an opera singer's voice , who must swallow the consonants to sing the vowels ,other than Andrea Bocelli's .As the amp is tailord for everlasting hearing of his voice ,bears his name. Unexpectedly, It resulted a luxurious sound ,wide, generous as 12au7 can sing ,projecting a breeze of auditive sensations ,without interrupting your thoughts .
This is not a Ferrari ,no, but certainly a limousine .
An ecc81 and 12au7a specialized amps are mounted on same chassis see the picture .the heatsink is heated by a 35W dissipating resistor.Now obsolete.
KOKORIANTZ
The purpose of this amp to allow voiceless small triodes to express themselves as proud and brave as their big brother tenors can do ,and this with much more brio .
The triode domesticates the power inverting amplifier, imposing its character to be the dominant transfer function of the circuit ,eclipsing totaly the power amps voice.By this the tiny ECC82 for example behaves as a giant ECC82 output tube,with all its character exposed to the output.
LM3886 graph shows simulations of the transfer function of the power amp alone with 22k/C1/10k inT input 100k FB,Showing for C1 100p and 680p with a gain of 3, how the dominant pole is dependent of.
This architecture provides flexible adjustment of, open loop gain/dominant pole, allowing to adjust easily ,eliminating gray sound.(see gray sound or transient intermodulation distortion)http://www.diyaudio.com/forums/lounge/297145-transient-intermodulation-distortion.html.
The significant advantage over SE ,the triode is totally liberated from constraints of output loading and damping as these tasks are trusted to the "domestic", which allows the designer to adjust at will the operating current/voltage/loading, to tailor the required sound .And more, by adding the input voltage stage the two triodes complement each other .The input adjust more the vowels (adjectives) the output more the consonants (adverbs) ,adding a variable bootstrap provides the user still further fin adjustments.
The power amp
Of course a class A is best suited for this application.An example of a good class B is shown opa541 distortion curve showing 4% at 20kHz for 100mw, not suitable.But the LM3886 is an other pedigree.Two curves showing distortions at 20Hz and 20khz has no any difference, that is the timing of switching on/off of the outputs as well as the overlap is perfectly adjusted. After all it cannot be more round than a circle. Of course it is an IC ,but of different specie.This IC has unique kind of output transistors that can function up to 250°C instead of ordinary 150°C.By allowing it to function at vacuum tube temperatures it eliminates all thermal feedbacks ,behaving as if it is made of descreet components.By using appropriate PSU and heatsink of BASIC3886 presented at (LM3886 singing at HELL°) can deliver a very high dynamic sound with peak power of 85W.
The triode
I tried two triodes 12au7a (Shuguang) and ECC81 .Each type exhibits its own sound ,that can be tailored with great ease.The ECC81 ,a HF nonlinear triode, behaves like dynamic expander extracting from the sound unexpected detailes,like photoshop sharpness enhancer. Ugly but sharp . I invite guitar amp designers to give a trial with low plate voltage .
With 12au7a, a V/H oscilator tube, I designed a very specialized amp .A low definition amplifier. It is intended to hear the sound rather then listen to .That is an amp specialized for vowels (adjectives) and less in consonants (adverbs). Turner paintings style sounds, if you see what I mean. What best I can choose than an opera singer's voice , who must swallow the consonants to sing the vowels ,other than Andrea Bocelli's .As the amp is tailord for everlasting hearing of his voice ,bears his name. Unexpectedly, It resulted a luxurious sound ,wide, generous as 12au7 can sing ,projecting a breeze of auditive sensations ,without interrupting your thoughts .
This is not a Ferrari ,no, but certainly a limousine .
An ecc81 and 12au7a specialized amps are mounted on same chassis see the picture .the heatsink is heated by a 35W dissipating resistor.Now obsolete.
KOKORIANTZ
Attachments
This post reminds me of an article I once read about efforts in the 1960’s to use an IBM mainframe to attempt translation of English to and from other languages. To test the effectiveness of the software, the text being tested was translated from English to another language, then immediately converted back into English.
It seems the results could be both unexpected and puzzling in certain situations.
When the computer started “spitting out” text about “Water Sheep”, it brought about some head scratching, until someone figured out that it was an erroneous two way translation of “hydraulic rams”!
It seems the results could be both unexpected and puzzling in certain situations.
When the computer started “spitting out” text about “Water Sheep”, it brought about some head scratching, until someone figured out that it was an erroneous two way translation of “hydraulic rams”!
I was intrigued why he chose to heat a heatsink with a big resistor; maybe to give the impression of greater power or even Class A? Then I realised that this was just a poetic way of saying that the heatsink was there to cool a big resistor; presumably the resistor was actually doing something useful in the circuit.
Just to be clear; I was not criticizing the design intention. Poster is looking for a particular sound (not straight-wire-with-gain). Taste is a matter of personal preference, and to each their own.
The use of hybrid tube / chip amp I like!
I do not like that the THD curves from the datasheet are used to describe the performance. I refuse to believe those performance levels can be acheived when the chip is heated to those levels.
How many watts can it deliver before the spike kicks in? And I mean measured....
I do not like that the THD curves from the datasheet are used to describe the performance. I refuse to believe those performance levels can be acheived when the chip is heated to those levels.
How many watts can it deliver before the spike kicks in? And I mean measured....
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Especially when the data sheet states the chip will shut down at 165C........
This basic circuit is usually called a "GainClone".
Quite a few variations around.
Here is a link to Joe's version
Gainclone amplifiers
Cheers,
Ian
Quite a few variations around.
Here is a link to Joe's version
Gainclone amplifiers
Cheers,
Ian
It seams I did not make myself understood about distortion requirement conditions.
The domesticated amp of class B can have crossover distortion ,it is of two nature.The overlap, that can provoke nonlinear transconductance ,can be greatly reduced by the second feedback loop of the triode.But switch timing error when the output transistors go boxing each other,instead of serving the output ,the second feedback loop degenerates further this type of distortion .(read McIntosh ,Audio Eng. mag.dec 1949)
There are two candidates for this application .The TDA7293 which requires a bazaar of components to operate and our beloved LM3886.This later is excellent as power HF tweeter amplifier, used even in high-end and professionel multiamplified loudspeakers .But as general use ,compared to another IC the LA4705 (1w to5w ),the Lm3886 sounds toy . Once domesticated by the triode ECC82,it recieves 60 times more negative feedback ratio than by stand alone 26db gain ,punishing 60 times more severely for the errors it commits .Now better discipined ,the tweeter amplifier sings with perfection down to tough male expressive voices ,such as Niel Diamond .What concerns below, is doubtful.Listening in the evening , the 8th unfinished symphony of Schubert,interpreted by the French National Orchestra,It sounded as if the artists are on strike ,delivering compulsory minimum service . Unexpressive ,boring ,even dull. I untightend the screw to release the thermal link IC/heatsink and the strike got lifted, the orchestra cheered up and the music was once more brava.
The same reason you need to heat the aquarium of tropical fishes ,this "domestic", all it askes is to work in warm.The heatsink was tailored for 70°C dissipating 35W ,so I offered a 35w dissipating resistor along with a termo switch of 70°C to the heatsink and I never heard the "domestic" complain of any thing else.
But the recent BASIC3886 heatsink and power supply replaces favorably .
KOKORIANTZ
The domesticated amp of class B can have crossover distortion ,it is of two nature.The overlap, that can provoke nonlinear transconductance ,can be greatly reduced by the second feedback loop of the triode.But switch timing error when the output transistors go boxing each other,instead of serving the output ,the second feedback loop degenerates further this type of distortion .(read McIntosh ,Audio Eng. mag.dec 1949)
There are two candidates for this application .The TDA7293 which requires a bazaar of components to operate and our beloved LM3886.This later is excellent as power HF tweeter amplifier, used even in high-end and professionel multiamplified loudspeakers .But as general use ,compared to another IC the LA4705 (1w to5w ),the Lm3886 sounds toy . Once domesticated by the triode ECC82,it recieves 60 times more negative feedback ratio than by stand alone 26db gain ,punishing 60 times more severely for the errors it commits .Now better discipined ,the tweeter amplifier sings with perfection down to tough male expressive voices ,such as Niel Diamond .What concerns below, is doubtful.Listening in the evening , the 8th unfinished symphony of Schubert,interpreted by the French National Orchestra,It sounded as if the artists are on strike ,delivering compulsory minimum service . Unexpressive ,boring ,even dull. I untightend the screw to release the thermal link IC/heatsink and the strike got lifted, the orchestra cheered up and the music was once more brava.
The same reason you need to heat the aquarium of tropical fishes ,this "domestic", all it askes is to work in warm.The heatsink was tailored for 70°C dissipating 35W ,so I offered a 35w dissipating resistor along with a termo switch of 70°C to the heatsink and I never heard the "domestic" complain of any thing else.
But the recent BASIC3886 heatsink and power supply replaces favorably .
KOKORIANTZ
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