I had a long think about this and it seems to me publishing the circuit as shown in the book couldn't do much harm. Neither Rowan nor Allen are with us any longer. The caveat is that the heirs of either one could claim copyright, so a notice is included.
It should also be noted that the basic circuit was first published in EW+WW 1971 and the author of that article had a patent application in progress, so there's that as well. Voltage rails for these output parts should probably be lower than the 45V shown, maybe 35-40V would be more appropriate.
It should also be noted that the basic circuit was first published in EW+WW 1971 and the author of that article had a patent application in progress, so there's that as well. Voltage rails for these output parts should probably be lower than the 45V shown, maybe 35-40V would be more appropriate.
Attachments
Last edited:
Thank you for posting this. I agree, no harm done of copyright notice is applied and this from 1970’s.
The trick is Q7 being driven only from one of the “long neck pair” (LNP). Sort of like the Aksa Lender front end used in the ALPHA amp above which also achieves dominant 2nd harmonic output. This asymmetry is key to removing the typical behavior of a LTP front end which is usually dominant third harmonic.
The front end from the Alpha does not need to drive a 1.3A idle bias current output stage. Could also be usual Class AB with say, 80mA quiescent bias current. It just won’t have the same Class A smoothness but the harmonic profile would be similar.
The trick is Q7 being driven only from one of the “long neck pair” (LNP). Sort of like the Aksa Lender front end used in the ALPHA amp above which also achieves dominant 2nd harmonic output. This asymmetry is key to removing the typical behavior of a LTP front end which is usually dominant third harmonic.
The front end from the Alpha does not need to drive a 1.3A idle bias current output stage. Could also be usual Class AB with say, 80mA quiescent bias current. It just won’t have the same Class A smoothness but the harmonic profile would be similar.
Last edited:
There are a number of errors in the circuit as drawn by Rowan. R12 has no value associated with it, and the zener and associated cap will go bang if they are added as shown. The transistor types Q1 to Q7 are selected from what was available in LTSpice, and are not the originals which were in the BC series. The output transistors are from the original EW+WW article and are clearly not what was used in the reference brick.
Last edited:
Just picked up a Behringer UCA222 USB interface off Fleabay for AU$39.00 brand new. It's only 48kHz and hasn't got the balanced inputs yours has, but as they say ... never mind the quality, feel the price!
Rob
Interesting.
I have noticed same behavior with amplifiers using a basic bootstrap Vas.
But strong Monotonic harmonic can also be encouraged if the Vas transistor is
not the greatest or heavily loaded.
Having Modeled the Classic JLH69 Class A Amplifier.
The Harmonics show a typical Strong 2nd Harmonic.
But with Aggressive Idle currents the 3rd Harmonic can also be rather
high.
Going back to class AB
The so called " forbidden topology" which is a CFA output
with feedback.
Will actually also produce Harmonics similar to the JLH Class A
Very strong Second and 3rd
Even more Hilarious Fact if anyone is familiar to the Velleman K8060
Very basic Complementary Class AB Darlington Amp
Again with a basic Bootstrap Vas
The overall Harmonics are the same if not better than the JLH class A
I used to use UCA222 but found the noise floor limiting as many of my amps have very low noise floor.
I also have the UM2 and it has balanced inputs. I have not tried it with REW yet but it might not be too bad. $49.
https://www.amazon.com/dp/B00EK1OTZ...abc_N2KZG31E144V7360Z476?_encoding=UTF8&psc=1
The plot thickens. The owner of the only Magic Amp in Australia, previously identified as Peter M, sent me some old photos showing the power transistors. He thought this might help in my design efforts but in fact it has not. The photos show two pairs of transistors made by a company called Hiral Semiconductor, a company of which there seems to be no remaining trace. The name Hiral is of Indian origin and there is a Hiral Jain working at NXP but that's a long shot.
The part numbers themselves are likewise untracecable. My 40 year old transistor equivalents book shows no such parts as EB203 and ED203. Pics attached.
The part numbers themselves are likewise untracecable. My 40 year old transistor equivalents book shows no such parts as EB203 and ED203. Pics attached.
Attachments
According to some reading on Australian hifi sites, the Hirel ED203/4 was the NPN device and the EB203/4 was the PNP device. The specs are roughly 20A, 200W and 200 MHz. They were used by Peter Stein in his ME-100 amplifier in 1976 and by several companies building PA systems around Sydney, notably Jands. The company was a boutique manufacturer based in Tokyo and are no longer in business.
Nice part, but unobtainium.
Nice part, but unobtainium.
The interesting part of this design is that the crossover distortion and output device balance parameters can be tweaked to suit the listener. I believe the alignment process was a bit of a bear, since these guys were both consumate perfectionists.
not really a new concept as it was discussed somewhere else already:
https://www.diyaudio.com/forums/pass-labs/262821-class-ap-amplification.html#post4077413
https://www.diyaudio.com/forums/att...103312011-crossover-distortion-hartsuiker-jpg
https://www.diyaudio.com/forums/att...over-distortion-blomley-amplifier-vcc-60v-jpg
I don't believe I was claiming it as a new concept, since the amplifier in question was designed in 1975 and I've already stated it was loosely based on EW+WW 1971 (Blomley's circuit).
What is different is the implementation, which I believe will prove to be exemplary since I knew the designer and he was an obsessive for details. I've heard once again from the owner of the original amp that's still in Australia and he has finally prodded his son into action. It will be shipped up to me as soon as he (the son) can visit the Post Office. Right now that's not possible due to Covid lockdown.
I've been waiting since 2018 for this to happen, so it's a good day for me.
@Dreamth My apologies if my reply sounded dismissive, I didn't mean it that way. I thank you for pointing out this ongoing and very interesting thread, it has strong convergence with the directions I was intending to take and has saved me a considerable amount of future work. One Duvel for you!
Last edited:
Well yeah, nothing special at all except the 200 MHz bandwidth.
I selected very similar BJTs to those you suggested, because 30 MHz seems to be about the best available and the plastic packages are very convenient.
A typical "engineer" would choose 4 MHz Motorola parts and screw up the design completely. And then claim, "See? It makes no difference!"
Last edited: