Hi everyone
I recently read about the old QUADs and the interesting technique adopted by these amplifiers. It is a strategy, other people would use the word trick. It is a low power class A circuit which is used to correct errors in the second power circuit in class A/B.
there is a lot of talk about the class to which the amplifiers belong and the type of sound they produce but too little about the design of the electronic scheme chosen by the designer. I can understand that this topic is not very interesting for many people but it is not essential to go very in depth, it is a brief description of the properties that derive from it is sufficient. Having said this, it would be nice if someone would like to mention other ingenious circuit strategies whose existence I probably don't know.
I recently read about the old QUADs and the interesting technique adopted by these amplifiers. It is a strategy, other people would use the word trick. It is a low power class A circuit which is used to correct errors in the second power circuit in class A/B.
there is a lot of talk about the class to which the amplifiers belong and the type of sound they produce but too little about the design of the electronic scheme chosen by the designer. I can understand that this topic is not very interesting for many people but it is not essential to go very in depth, it is a brief description of the properties that derive from it is sufficient. Having said this, it would be nice if someone would like to mention other ingenious circuit strategies whose existence I probably don't know.
The experience first:
The ear perceives differences, which it reconstructs into frequencies, into music. Since components audibly modulate the signal considerably,
I would look for circuits that
a) have few components,
b) do not use half-wave separated amplification,
c) use as few power supplies as possible,
d) use power supplies with the simplest possible design.
Amplifier also refers to voltage amplification. However, I would also consider pure followers.
Balanced concepts have the advantage of eliminating power supply fluctuations and impurities, for example, but have the disadvantage of audibly increasing their modulations by doubling the components. Here I would pay attention to symmetrical balancing: through transformers.
Compared to tubes, transistors sound baked, doughy: Material and potted.
Analog amplification:
1: If you want maximum resolution and homogeneity, start with single-ended.
2: Then look for push-pull amplifiers consisting of identical and half-wave balanced components, tube PP, or tranny PP like Susan's "Zero Feedback Impedance Amplifiers": https://www.diyaudio.com/community/threads/zero-feedback-impedance-amplifiers.42259/
3: A complementary transistor push-pull amplifier does not belong in the audio sector. But even here there are some quite good-sounding, well-tuned examples that are a lot of fun, but have nothing to do with "high end": e.g. Hiraga's Class A, Le Monstre, Pawel Macura's PP, or HORCH and some others;-)
4: Concepts that work half-wave asymmetrically, for example by running a half-wave via a bias transistor or a bias control network, are still unsuitable: The majority among the analog complementary transistor push-pull amplifiers, such as NAIM.
This is my basic show;-)
The ear perceives differences, which it reconstructs into frequencies, into music. Since components audibly modulate the signal considerably,
I would look for circuits that
a) have few components,
b) do not use half-wave separated amplification,
c) use as few power supplies as possible,
d) use power supplies with the simplest possible design.
Amplifier also refers to voltage amplification. However, I would also consider pure followers.
Balanced concepts have the advantage of eliminating power supply fluctuations and impurities, for example, but have the disadvantage of audibly increasing their modulations by doubling the components. Here I would pay attention to symmetrical balancing: through transformers.
Compared to tubes, transistors sound baked, doughy: Material and potted.
Analog amplification:
1: If you want maximum resolution and homogeneity, start with single-ended.
2: Then look for push-pull amplifiers consisting of identical and half-wave balanced components, tube PP, or tranny PP like Susan's "Zero Feedback Impedance Amplifiers": https://www.diyaudio.com/community/threads/zero-feedback-impedance-amplifiers.42259/
3: A complementary transistor push-pull amplifier does not belong in the audio sector. But even here there are some quite good-sounding, well-tuned examples that are a lot of fun, but have nothing to do with "high end": e.g. Hiraga's Class A, Le Monstre, Pawel Macura's PP, or HORCH and some others;-)
4: Concepts that work half-wave asymmetrically, for example by running a half-wave via a bias transistor or a bias control network, are still unsuitable: The majority among the analog complementary transistor push-pull amplifiers, such as NAIM.
This is my basic show;-)
Nah, 3-stage class B every time, performant, reasonably simple and efficient (go class G or H for more efficiency at the expense of complexity) 0.001% or less distortion commonly achieved. Class A heats the room, wastes energy, cooks itself to an early grave, generally good for low power only IMO, headphones, line-level etc.
Opinions definitely vary, you'll discover...
Opinions definitely vary, you'll discover...
Devialet supposedly made small classA amp nested inside big classD amp with great success. I liked the sound at audio show.
That is not the circuit of the Quad 405. An op amp is used, but it serves only as the input stage.
the topic is not to comment on the design of the quad. that is just an example. the theme is to make a list of all those designs that make use of magic tricks.
If you are interested in unusual but well-designed amplifiers, read all threads involving @IanHegglun He designed and built many unusual amplifiers.
I made only two DIY class-AB amplifiers, one that had its emitter resistors go up in flames and one that still works well after 30 years. The latter uses a variant of the class-AB bias loops that to the best of my knowledge were invented by Han Huijsing and Frans Tol around 1976. You can read all about it here:
"Audio power with a new loop", Electronics World February 1996, pages 140...143, https://worldradiohistory.com/UK/Wireless-World/90s/Electronics-World-1996-02-S-OCR.pdf
I made only two DIY class-AB amplifiers, one that had its emitter resistors go up in flames and one that still works well after 30 years. The latter uses a variant of the class-AB bias loops that to the best of my knowledge were invented by Han Huijsing and Frans Tol around 1976. You can read all about it here:
"Audio power with a new loop", Electronics World February 1996, pages 140...143, https://worldradiohistory.com/UK/Wireless-World/90s/Electronics-World-1996-02-S-OCR.pdf
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Here's something to have fun with.
https://sites.google.com/site/francisaudio69/6-lamplificateur/6-9-schémas
https://sites.google.com/site/francisaudio69/6-lamplificateur/6-9-schémas
DEF amplifiers are example of unusual design. They combine depletion type and enhancement type semiconductors that work in output stage against each other, providing reduced distortion:
https://www.diyaudio.com/community/threads/def-amp.300136/
Examples that made wide DIY adoption possible are SissySIT and LuDEF:
https://www.diyaudio.com/community/threads/sissysit.326536/
https://www.diyaudio.com/community/threads/ludef.369990/
This is just a biased personal opinion with no actual knowledge behind. Ask him to explain with arguments, why is an amplifier without opamp “better” or why designers that use them “suck”.
BTW, I “suck”.
I say that all good amplifiers sound the same regardless of how they were designed.
Ed
Pavel Macura, 20 years ago:
https://web.archive.org/web/20040701052058/http://www.pha.inecnet.cz/macura/index_en.html