However, the quasi output stage (half CFP anyway) and a booststrap VAS are actually the essential sources of a desirable sound effect common to such retro designs, so you see it's really not a good idea to scrap them.
I totally agree, sound effects.
I wonder if those that do prefer these amps with sound effects ever think that one could also modify the source to the amp like cd player to do these sound effects instead and then just use a wire with gain amp.
Maybe Im wrong here and all sources no matter what are perfect and the problem is always the amp.
Sure, if you want to emulate the sound of a simple 1970's amplifier, then thats the way to go, but this design needs to flip the LTP and VAS round to get a NPN driver for the VAS if you really want to be authentic, however, by deliberately using an inferior design to achieve a desired effect by causing distortion, you are building an effects unit, not a hifi amplifier.
Many, many DIYs follow this old school of amp design. It has little to do with recreating the original amplifiers, rather it's just incorporating the bits that have proven to do something more satisfyingly than basic amplification, as an entertainment device. There is nothing within reason, other than tradition and purist notions which say that an amplifier for personal entertainment should have ultra low distortion, flat response or any linearity perfection that may be deemed essential in other applications like PA, recording, broadcast production etc.
Such amplifiers are not necessarily awful in specs; most will be better than typical commercial amplifiers anyway. What designers seek to do with any residual distortion is to manipulate the design so that the relative levels of the harmonics diminish somewhat like natural sound sources. This can work astonishingly well, if all the design details are patiently checked out in real time and some listening expertise is brought to bear on the project. No, its not textbook SOTA or standard EE practice but then those guys have clients with minuscule budgets and schedules rather than themselves to satisfy.
Whether you wish to categorise them as effects units or not, they function principally as amplifiers and have been sold alongside plain vanilla "hi-fi" amplifiers for decades. If you include the current flood of hybrid designs (why else would you throw a tube in a solid-state design?) they represent a large and respectable slice of hi-end electronics.
I don't think it is easy to dismiss this "high-end" market and this thread shows one inexpensive way of getting involved and possibly closer to one's ideal of great sounding audio.
Keep up the good work, Gaetan.
Such amplifiers are not necessarily awful in specs; most will be better than typical commercial amplifiers anyway. What designers seek to do with any residual distortion is to manipulate the design so that the relative levels of the harmonics diminish somewhat like natural sound sources. This can work astonishingly well, if all the design details are patiently checked out in real time and some listening expertise is brought to bear on the project. No, its not textbook SOTA or standard EE practice but then those guys have clients with minuscule budgets and schedules rather than themselves to satisfy.
Whether you wish to categorise them as effects units or not, they function principally as amplifiers and have been sold alongside plain vanilla "hi-fi" amplifiers for decades. If you include the current flood of hybrid designs (why else would you throw a tube in a solid-state design?) they represent a large and respectable slice of hi-end electronics.
I don't think it is easy to dismiss this "high-end" market and this thread shows one inexpensive way of getting involved and possibly closer to one's ideal of great sounding audio.
Keep up the good work, Gaetan.
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One to ask the designer perhaps. They appear to serve no useful purpose.
(The 1N4148 in the negative rail could see transients at switch on that exceed its limits... supply rise time dependent)
You see that in old Grundig amps, too. Presumably this is intended to keep VAS loading in check at AF while ensuring a driving impedance as low as possible at higher freqs, i.e. making the output stage as fast as possible, which then in turn allows going easier on the compensation. How it works out in practice, no idea. Effectively not having a base stopper is a bit risky WRT local oscillation, but then again if VAS output impedance keeps dropping long enough it may still work out...
BTW, I wouldn't trust bias stability in this circuit much.
BTW, I wouldn't trust bias stability in this circuit much.
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