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Old 4th November 2011, 07:24 PM   #11
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Hi Joachim,
thx for bringing that reg back to life. I had indeed never noticed that obviously wrong resistor value.
About the common mode choke: Sure this is a good idea on the DC side...?
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Old 4th November 2011, 08:28 PM   #12
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I forgot the smoothing caps. Sorry, here the devil is in the details and not god i am afraid.
Also a fuse should be used on the 230V AC side. My program can not draw a fuse, sorry.
I build this and it works. The common mode choke could also be put directly before the regulator after the 2200uF-10Ohm-2200uF filter bank. I have not tried this though. I would not put it after the regulator because the nice low 20mOhm output impedance would get lost. The choke has around 1.5Ohm.
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File Type: pdf Nobrainer Preregulator.TSC - TINA.pdf (8.2 KB, 204 views)
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Old 5th November 2011, 01:59 PM   #13
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Holger, do you think this is better ? The common mode choke is now moved into the AC part before the bridges.
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Old 6th November 2011, 12:41 PM   #14
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Hi Joachim,
I'll try both versions. Got to order parts anyway, and so I'll add some of those common mode chokes.
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Old 6th November 2011, 03:38 PM   #15
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Thanks when you try. That will safe me some time. I usually use the version after the diodes and it sounds really good but i maybe wrong.
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Old 9th November 2011, 01:31 AM   #16
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Here are my latest thoughts on the Nobrainer Discrete. This time the input stage is a diamond buffer. It can be also configured " the other way around " as a transimpedance input stage. The RIAA is active, driven by a class A output stage. The second stage is a Hawksford cascode also known as driven cascode. It returns the base current of the cascode into the amplification chain. Hawksford was not the one that invented it, i think Borbely was first ( but he never used it ), but it was baptized after Malcolm.
I like the circuit a lot. When the bias servo works it needs no adjustments. The RIAA caps are from small values, the circuit is economical with only 14 relatively cheep BJTs, no expensive low noise Fets are needed, its DC coupled. PSU rejection should be good.
The only disadvantage i see over the earlier Nobrainer is that now the input transistors are in series and there are 5 Ohm emitter resistors plus the 10 Ohm feedback resistor to ground so this is somewhat more noisy. The normal Nobrainer has around 20 Ohm noise impedance with the recommended transistors and this one would have 55 Ohm, on par with an AD797 that is considered " ultra low noise". Part of it can be canceled by using lower Rbe`transistors. With 2 Ohm transistors noise would be approximately 20 Ohms again. 6dB better then the AD796. I think this is no world record but decent.
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Old 9th November 2011, 02:34 AM   #17
jcarr is offline jcarr  United States
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Hi joachim: AFAIK, the "Hawksford" cascode was invented by Roy M. Hayes of Tektronix. The patent was filed in 1964, and was granted in 1969. The US patent number is 3423685, and the patent calls the circuit "bootstrapped cascode differential amplifier".

The circuit was being used by various US amplifier manufacturers such as Spectral in the mid-1980s, possibly earlier. Whenever I talked with Demian Martin or the other guys in or around Spectral, the circuit was called "bootstrapped cascode."

The circuit was also used by Japanese designers by the 1980s - some of the Japanese circuit-oriented books and magazines that I have from that period show this topology in use, although I would have to dig through the articles to recall what the circuit was called.

In fact, I first may have heard the term "Hawksford cascode" from you (grin).

hth, jonathan
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Old 9th November 2011, 03:28 AM   #18
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Thanks for that information. Malkolm introduced it to me in the early 90th but he never has claimed to have invented it. He made an AES paper that goes into much detail though.
That made that circuit somewhat popular with some.
I was not the first that used the name Hawksford Cascode. I think i got this name from this very forum but i am guilty to spread the name even more although it is not 100% correct. A japanese would never do that (: sorry, its not even artistic freedom, just lazyness.
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Old 9th November 2011, 03:30 AM   #19
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He calls it "Enhanced Cascode".
http://www.essex.ac.uk/csee/research...%20cascode.pdf
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Old 9th November 2011, 10:32 AM   #20
kamis is offline kamis  Serbia
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Quote:
Originally Posted by Joachim Gerhard View Post
Thanks when you try. That will safe me some time. I usually use the version after the diodes and it sounds really good but i maybe wrong.
Mr. John Curl uses CM chokes on DC side of PS in all current preamps he has designed, including Parasound JC-3 phono preamp.He got rave reviews for them, so he is on the right tracks.
I tried CM ckokes in the same way and got better dynamics and low level details. UI cores dual section CM chokes which I use are better than ring core types, and cheaper too.
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