hello,
do you know any commercial audio power amplifier prior 1969 architectured this way :
- full silicon
- first stage is a long tailed pair (differential pair arrangement)
- second stage is the voltage amplifier stage (VAS) with the collector being loaded by a constant current source (not the bootstrap capacitor arrangement)
- symetric power supply
- no coupling capacitor at the output (OCL arrangement)
In a nutshell, I would like to trace the very first "blameless" audio amplifier.
Such "blameless" audio amplifier must have been a (silent ?) milestone in a context where virtually all silicon audio amplifiers were variations on the theme initiated by H.C. Lin (RCA fellow) in 1956 : input transistor acting as VAS, feedback on the emitter, capacitive bootstrap in the collector.
At the moment I have the impression that the first "blameless" audio amplifier may have been the Sinclair Z30 and Sinclair Z50. If you dare removing R7. See attached picture. Quite regrettable is the rather imperfect class AB biaising arrangement. Actually, for this reason, it doesn't deserve the qualification of "blameless".
Or, maybe, the "blameless" concept showed long time before 1969 while designing audio integrated circuits ?
Any clues ?
do you know any commercial audio power amplifier prior 1969 architectured this way :
- full silicon
- first stage is a long tailed pair (differential pair arrangement)
- second stage is the voltage amplifier stage (VAS) with the collector being loaded by a constant current source (not the bootstrap capacitor arrangement)
- symetric power supply
- no coupling capacitor at the output (OCL arrangement)
In a nutshell, I would like to trace the very first "blameless" audio amplifier.
Such "blameless" audio amplifier must have been a (silent ?) milestone in a context where virtually all silicon audio amplifiers were variations on the theme initiated by H.C. Lin (RCA fellow) in 1956 : input transistor acting as VAS, feedback on the emitter, capacitive bootstrap in the collector.
At the moment I have the impression that the first "blameless" audio amplifier may have been the Sinclair Z30 and Sinclair Z50. If you dare removing R7. See attached picture. Quite regrettable is the rather imperfect class AB biaising arrangement. Actually, for this reason, it doesn't deserve the qualification of "blameless".
Or, maybe, the "blameless" concept showed long time before 1969 while designing audio integrated circuits ?
Any clues ?
Attachments
That is no so called blameless , it has no vas enhancement...
A 1969 model of this brand seems to satisfy the requirements though :
http://www.diyaudio.com/forums/solid-state/26046-sonab-amplifier-information.html
A 1969 model of this brand seems to satisfy the requirements though :
http://www.diyaudio.com/forums/solid-state/26046-sonab-amplifier-information.html
Worth checking is a possible "USA" origin of the "blameless" topology. Need to check authors like Daniel Meyer, Don Lancaster, Gary Kay. There may be articles from them in Popular Electronics. Will somebody check ?
I guess the "Leach amp" came much later, actually it can be viewed as a symetric version of the "blameless" : one NPN "blameless" loaded by one PNP "blameless". Right ? What year is the "Leach amp" ? Is it true it delivers a dull sound compared to "blameless" ? How possible ?
I guess the "Leach amp" came much later, actually it can be viewed as a symetric version of the "blameless" : one NPN "blameless" loaded by one PNP "blameless". Right ? What year is the "Leach amp" ? Is it true it delivers a dull sound compared to "blameless" ? How possible ?
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The best amplifier from 1968 was Bailey's "laboratory amplifier" which had many of the features of a modern circuit, but not all mentioned in the "blameless".
It had a differential input pair; medium impedance VAS load (moderate value resistor taken to a high voltage supply rather than bootstrap) and fully complementary output stage. Beats most of the circuits around at the time for audio, but was not presented as an audio circuit.
It had a differential input pair; medium impedance VAS load (moderate value resistor taken to a high voltage supply rather than bootstrap) and fully complementary output stage. Beats most of the circuits around at the time for audio, but was not presented as an audio circuit.
I took this schematic on the thread about the SONAB brand..
It s exactly the same schematic as the one popularized by D. Self
but with inverted polarity transistors ,i.e, a NPN differential..
The subsequent link display another version , with no vas buffer.
SONAB R4000 receiver annual service....
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Hi wahab, thanks for the schematics. Yes indeed the Sonab R4000/U700 is a "blameless" ancestor dating back from 1969. A nice milestone. Amazing to discover such quality in a box containing a tuner, a preamp and an amplifier. What do you think about the fuse in series with the output ? Is it there in both versions ?
And the Bailey's 30W amplifier dating back from 1968 ? Not a "blameless" ancestor ? Nothing on the radar from Heathkit, Hewlett Packard, Schlumberger or Tektronix ? Some oscilloscope vertical amplifier maybe ?
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I do not remember a Bailey amp having a diff input pair.
Nor pre 1970, neither commercial, but worth saying some words about it :
One of the most looking like a Blameless for its low power stages, but published fourteen years sooner, was the circuit due to B.J. Codd in Wireless World, October 1979, pages 81-85. I've never seen it mentionned anywhere since.
Its features :
- Diff input pair, 2 * 1 mA current source driven, 2 * 120 Ohm emitter degenerated, loaded by a Wilson 3 current mirror.
- Then a cascoded VAS loaded by a 3 mA current source, with 39 pF Miller compensation.
- Class A push-pull emitter followers buffering the output stage.
There was a clear search for very low distorsion.
Nor pre 1970, neither commercial, but worth saying some words about it :
One of the most looking like a Blameless for its low power stages, but published fourteen years sooner, was the circuit due to B.J. Codd in Wireless World, October 1979, pages 81-85. I've never seen it mentionned anywhere since.
Its features :
- Diff input pair, 2 * 1 mA current source driven, 2 * 120 Ohm emitter degenerated, loaded by a Wilson 3 current mirror.
- Then a cascoded VAS loaded by a 3 mA current source, with 39 pF Miller compensation.
- Class A push-pull emitter followers buffering the output stage.
There was a clear search for very low distorsion.
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Curiously , the second version has a simpler VAS but seems to use
a relay instead of fuses.
So 1979-14=1965 ! Are you are sure there was not a typo in the Wireless World dates ? Differential stage current source driven + loaded by a Wilson 3 current mirror + cascoded VAS : marvellous ! Were there germanium transistors in ? Were those amps commercially available or was it just a prototype ? Do you remember the exact article title in Wireless World ?
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hello forr, I noticed your posts #16 and #17 about B.J. Codd in Wireless World, October 1979, pp 81-85 in the "CFP For The VAS" subject.
http://www.diyaudio.com/forums/solid-state/88515-cfp-vas-2.html#post1811823
Actually, what makes you state that such B.J. Codd circuit is dating back from 1964 or so ?
I think it is very important to keep in mind that the topology being referred to ad nueseum as the "blameless" was in fact very, very, common for at least 2 decades before a certain D. Self came into the frey!
In fact it was probably the most common topology!!!
What Doug Self did (very well and hats off to him) was to re-analyse the topology and come up with various small tweaks to the design which, together,
vastly improved the topology. At a glance though the D.Self "blameless" looks pretty much the same as hundreds of other designs from the mid 70's onward...
Check out the Marantz Model 15 for an amp that was direct coupled to the speakers, had long-tailed pairs and current sources and was full complementary in the output stage circa 1966 or so.
In fact it was probably the most common topology!!!
What Doug Self did (very well and hats off to him) was to re-analyse the topology and come up with various small tweaks to the design which, together,
vastly improved the topology. At a glance though the D.Self "blameless" looks pretty much the same as hundreds of other designs from the mid 70's onward...
Check out the Marantz Model 15 for an amp that was direct coupled to the speakers, had long-tailed pairs and current sources and was full complementary in the output stage circa 1966 or so.
Indeed.
It was the thorough examination carried out and published by D.Self that became the "blameless standard".
Remove all the builder/assembler mistakes to improve the audio performance to a standard for which the builder/assembler cannot be blamed.
That paper was long overdue. Many of the single distortion mechanisms were already known of. Some had been discussed, some had been kept secret by "designers" who wanted to protect their IP.
D.Self opened up the can of worms and allowed us to remove them.
I do not believe that you must adopt an exact replica to create your own "blameless". It's more a case of adopting the methodology to ensure the builder/assembler does not incorporate a circuitry mistake that reduces the potentially good audio performance.
However if one wants to build a D.Self blameless amplifier then one must build an exact replica.
It was the thorough examination carried out and published by D.Self that became the "blameless standard".
Remove all the builder/assembler mistakes to improve the audio performance to a standard for which the builder/assembler cannot be blamed.
That paper was long overdue. Many of the single distortion mechanisms were already known of. Some had been discussed, some had been kept secret by "designers" who wanted to protect their IP.
D.Self opened up the can of worms and allowed us to remove them.
I do not believe that you must adopt an exact replica to create your own "blameless". It's more a case of adopting the methodology to ensure the builder/assembler does not incorporate a circuitry mistake that reduces the potentially good audio performance.
However if one wants to build a D.Self blameless amplifier then one must build an exact replica.
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Check out this thread..... http://www.diyaudio.com/forums/soli...d-across-emitter-resistors-4.html#post2675594
I think the first blameless was Bart Locanthi's amp from when he was working at JBL. It is also based on the Lin topology This would have been about 1968 (maybe JC can help out here). I took a look at his circuit and was amazed to find that all the things you need to do to create a TID free amp were in that design and, he also understood output stage distortion quite well too (inventor of the EF2 and EF3).
jez, thanks for having provided the Marantz Model 15 schematic. I'm taking the liberty to reproduce it here, from your post on DIYaudio http://www.diyaudio.com/forums/solid-state/194562-diodes-instead-across-emitter-resistors-2.html Very interesting post indeed. Will somebody organize a LTspiceIV simulation ?
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