I used to read audio magazine reviews about legendary amplifiers. Then I collected their circuit diagrams, in order to find out what is their secret. So I came across a British 2x40W integrated amplifier in a nice wooden box. That was said having similar soft sound as a tube amplifier, "smooth fatigue free listening experience". Studying the circuit diagram I noticed there is a transistor in the signal path, with its emitter directly grounded 😵 I found similar solutions in other well respected amplifiers.
I don't think emitter resistors are the only mechanism in play in a Creek 4040, for example, which may fit your terse description in that it has no emitter resistors to the negative rail of the output stage (they are Darlington type output transistors) but a critical feature is that the power transformer is quite small and the rail voltage will drop under load, somewhat like the protection afforded by emitter resistors. Not everything you see on a schematic will be clear in its effect until you do the math on all circuit voltages as they change under load with the program signal and dynamic load. You need to build and test an amplifier circuit fully, both channels or perform a simulation of them in LTspice or TI TINA programs for example, to observe and understand all the dynamic changes, not just those we imagine by following the one audio path line on the schematic and likely ignoring what else is going on.
The point of saying this is that omitting the resistors may have little to do with generating nice sounding harmonics. There could also be reasons like other faults in a design where several cost-cutting measures are in effect at the same time and these could also be having a pleasant sound effect - a good reason to build it and see just how good or perhaps tedious, the effects become over time
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The point of saying this is that omitting the resistors may have little to do with generating nice sounding harmonics. There could also be reasons like other faults in a design where several cost-cutting measures are in effect at the same time and these could also be having a pleasant sound effect - a good reason to build it and see just how good or perhaps tedious, the effects become over time
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I'd consider building a clone of a JBL SA-600.
This classic spec'd near 100dB distortion performance. It introduced the triple output stage. Would you believe it was introduced in 1966 -- so far ahead of its time it's difficult to comprehend. Plenty of amps 30, 40, even 50 years on don't approach this level of accuracy.
This classic spec'd near 100dB distortion performance. It introduced the triple output stage. Would you believe it was introduced in 1966 -- so far ahead of its time it's difficult to comprehend. Plenty of amps 30, 40, even 50 years on don't approach this level of accuracy.
You can argue that amplification is a solved problem, or you can argue that it's an area of exciting and active development.
If it's a solved problem, then why doesn't McIntosh publish schematics for their more recent amps? Why be secretive if an amplifier is a commodity, no more mysterious in its design than a pair of shoes or bottle of ketchup?
On the other hand, the SA-600 solved it about as well as anything that has come out in the 56 years since. JBL designer Bart Locanthi had it figured out. It even has two-pole loopgain roll-off like the Honey Badger and other popular modern super-accurate amps. It's incredible that this was available to buy off the shelf when it was -- when the median solid state amp made closer to 1% distortion with sizzly treble, when thermal instability was a common issue, when half of amps were still using germanium outputs for Pete's sake.
I've never heard one. I'd like to.
Ah, maybe I shouldn't have put the SA-600 on a pedestal. In my memory it was a 100dB amp, but it isn't. Distortion is more like 80dB in stock form into 4 ohms. Still very good for its time.
If you had one, it'd be a good mod to feed both the IPS and VAS with a current regulator diode -- that cuts several dB of distortion. Then you could change one connection that Locanthi missed: instead of grounding the collector of VAS transistor Q9, connect it to the output rail. Now the two VAS transistors just about cancel each other's nonlinear Cob so that the IPS doesn't see it at all. That takes a few more dB of distortion off. That's getting to be about a 95dB amplifier, albeit not 1966 anymore.
If you had one, it'd be a good mod to feed both the IPS and VAS with a current regulator diode -- that cuts several dB of distortion. Then you could change one connection that Locanthi missed: instead of grounding the collector of VAS transistor Q9, connect it to the output rail. Now the two VAS transistors just about cancel each other's nonlinear Cob so that the IPS doesn't see it at all. That takes a few more dB of distortion off. That's getting to be about a 95dB amplifier, albeit not 1966 anymore.
Manufacturers will "keep service manuals a secret" at times for one good reason...
To elevate and continue their profits, of course.
They get you with their high-end costs initially, and then when it needs service, get you again, by being only able to send it back to the manufacturer, or a certified service center.
Bose is one of these greedy crooks.
I've had customers bring in those "wave radios" and had to turn them down at the counter, informing the customer that I cannot gain access to service material.
"You gotta send it back to Bose, and they'll get you good for repairs!"
Well, I tend to disagree. I have a Hiraga Classe A amp still lying around. I have build that amp almost 30 years ago and the design was already quite some time older than that. It uses all the original parts from the original design, with some transistors going back to the 70s. In direct comparison with a Purifi amp (by many considered to be one the very best class D design at the moment), all I can tell is that they sound a little different but I certainly can't point out a clear winner. It totally depends on the loudspeakers it has to drive. On one set the Hiraga had a wider soundstage and was more easygoing with more air and ultrafine resolution. On another pair of speakers, the Purifi stood out with more grip and authority. But again, totally depending on the speakers there really was no clear winner. And that is with somewhere around 35 to 40 years in between designs !
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I think you are reinforcing my opinion that the modern amps are now good enough to replace thise vintage pieces. Class D is energy efficient. The original Hiraga parts are v hard to find, archeology it is.
Well actually you stated this
While I stated that there was still no clear winner between a 40-year-old design and a modern (by many considered the very best example) class D design.
Yes off coarse Class D is quite a lot better in efficiency, that's exactly the reason why I don't use the Hirag anymore, it was replaced with better-sounding class AB amps that have even better efficiency than the Purifi amp if played under 10 watts of output which means in 99,99% of the time it is playing music. The full-power efficiency is more interesting for PA use, in normal home conditions the real-life efficiency of Class D is not any better than any other topology besides Class-A. For instance, I have an ICEpower 1200AS2 running my woofers which has an idle consumption of 35 watts, the 250W Class AB amp it replaced had an idle consumption of 20 watts. Looking at the efficiency curves of both amps you would need to run the ICEpower amp at a continuous level above 25 watts to become more efficient. At full power it is a totally different story, the ICEpower becomes a lot more efficient there. Now, what the percentage of time do you play your music that loud?
You made a point. It is interesting to consider the relationship between standby consumption to max output power, specially with battery operated equipment.
Aside:
A Hiraga Classe A has NOTHING to do with "High End"! It is a four-stage-complementary-transistors-push-pull-design! But it does sound better than the very most pp-designs and, as read above, the most D-Class-amps.
To get on the track of good sound, good designs: Should you hear concepts with dual-mono power supplies, connect those power supplies together. If the sound should change, then start scratching your heads;-)
... and scratch again, and again, and again...-)
A Hiraga Classe A has NOTHING to do with "High End"! It is a four-stage-complementary-transistors-push-pull-design! But it does sound better than the very most pp-designs and, as read above, the most D-Class-amps.
To get on the track of good sound, good designs: Should you hear concepts with dual-mono power supplies, connect those power supplies together. If the sound should change, then start scratching your heads;-)
... and scratch again, and again, and again...-)