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Old 14th September 2014, 06:07 PM   #3281
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SAE "hypersonic class A" used em
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Old 19th December 2014, 03:49 AM   #3282
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Hey all. I compiled the noise measurements from this thread so far. I may have missed some, and not all the measurements were made on all transistors.

Code:
BJT noise measured by Richard Marsh

Q		Hfe	Ic	Vce	10Hz	100Hz	1KHz	10KHz	100KHz	Rb

BC337		700@5mA	3mA	15V		3.5nV	0.6nV	0.65nV	0.53nV	17.4
BC327		407@5mA	3mA	15V	5nV	0.7nV	0.5nV	0.55nV	0.55nV	10.8

BC550C										167
BC560C			3mA	15V	3nV	2.5nV	1.6nV	1.6nV	1.6nV?	170

2N4401		170@5mA	1mA	15V	1.5nV	0.9nV	0.65nV	0.65nV	0.8nV	38
			3mA	15V	4.5nV	1.3nV	0.6nV	0.6nV	1.3nV	38
2N4403										40

2N5087		460@5mA	100uA	15V	2.5nV	3.2nV	1.4nV	1.5nV	1.3nV
		460@5mA	3mA	15V	2.2nV	4nV	0.8nV	0.7nV	0.75nV

2N2907A		280@5mA	3mA	15V	6nV	2.4nV	0.95nV	0.75nV	0.75nV
2N2219A

2SA970			3mA	15V		4.5nV	1.1nV	0.9nV	1nV	25
2SC2240GR	330@5mA	3mA	15V?	2nV	2.8nV	0.7nV	0.65nV	0.6nV	39

2SB737			3mA	15V		4.2nV	0.35nV	0.5nV	0.3nV

2N2222

MPSA18										900?

NOS:	
2N2484A			3mA	15V	40nV	12nV	4nV	2.6nV	2.4nV
2N2222A		133@5mA	1mA	15V	3nV	1.2nV	0.9nV	0.85nV	1nV
			3mA	15V	4.5nV	3.3nV	0.9nV	1nV	0.9nV
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Old 17th January 2015, 02:59 PM   #3283
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Has anyone built the Wurer or KPeter (linuxguru) with real parts and bench tested it? Thanks , G.R.
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Old 17th January 2015, 03:15 PM   #3284
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Quote:
Originally Posted by grhughes View Post
Has anyone built the Wurer or KPeter (linuxguru) with real parts and bench tested it? Thanks , G.R.
Ken Peter Schottky-switched Class-AB buffer: not yet built, still in simulation (on again, off again - no pun intended). It looks good, but requires careful matching of a BJT Vbe to 2x Vf of the schottkys, and quiescent current may be a bit twitchy (depends on ambient temps).

My attention was diverted by some full-range speaker builds, so I'll get back to this in a month or so.
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Old 18th January 2015, 07:11 PM   #3285
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Thanks! Why can't it be biased full Class A? 1 volt peak to peak output will drive most power amps to clipping. It certainly should do that in Class A. You used 2n4416 as current sink. Is the 2n4416A OK? I have them on hand. Thanks G.R.
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Old 19th January 2015, 05:04 AM   #3286
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Quote:
Originally Posted by grhughes View Post
Thanks! Why can't it be biased full Class A? 1 volt peak to peak output will drive most power amps to clipping. It certainly should do that in Class A. You used 2n4416 as current sink. Is the 2n4416A OK? I have them on hand. Thanks G.R.
Ken Peter's output stage will also work in Class-A, for sure, but it wouldn't really be required because crossover distortion is not an issue there. In fact, fior normal line-level loads of (say) 10k and above, it will effectively be running in Class-A anyway.

You can use almost any JFET with Idss > ~2.5 mA as the LTP current source, as long as you adjust the source resistance to make the LTP tail current about 2 mA (1 mA though each leg). Even that's not critical - if you lower the tail current, it will still work, but with lower GBW and higher THD.
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Old 20th January 2015, 03:06 PM   #3287
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Quote:
Originally Posted by grhughes View Post
Thanks! Why can't it be biased full Class A? 1 volt peak to peak output will drive most power amps to clipping...
BTW, there's another Class-A buffer with very low distortion that's been on my back-burner for a few years - the Cantilevered Cascode Buffer. The latest variant is just a random find of mine about a month ago:

Cantilevered-Cascode Buffer (CCB) aka LinuxBuffer

Its claim to fame is that it produces predominantly 2nd/even-harmonic distortion.
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Old 20th January 2015, 09:50 PM   #3288
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Suppressing the odd, 3rd and 5th is a very good idea. I believe that most of the unpleasant distortions reside there. Thanks, G.R.
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Old 24th January 2015, 03:44 AM   #3289
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This is my implementation of Blameless topology with output class A single ended. In simulation harmonic profile is good
THD at 2.74Vp/600 Ohm, 20kHz -> 0.000078% (sim result)
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