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Old 4th May 2011, 11:42 AM   #21
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>Do you know any types?

Not in particular, sorry. But good candidates are the ones that have a rail to rail output capability.

Een volk dat voor tirannen zwicht, zal meer dan lijf en
goed verliezen dan dooft het licht…(H.M. van Randwijk)
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Old 6th May 2011, 07:29 PM   #22
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This circuits also fascinates me.

But first - a short interruption. The author is Dutch. His first name is Wim and his surname is De Jager, not Jager. This translates into English as The Chaser, more or less.

Back to the circuit. Some of the devices, such as the matched pairs and output transistors used are now obsolete. Trying to simulate it is therefore a hassle as no models are to be found. I've tried...

However, I did manage to make a few substitutions and it works. The collector currents do indeed stay above zero, as advertised.

Here is my circuit with modern(!) devices and a plot of the collector currents in the output stage. It was done with LTspice IV. If there is any interest, I will post the LTspice file and the Spice models used.

The magic in this circuit lies in Q6, Q7, Q8 and Q9. Their base-emitter junctions form an uninterrupted loop, which makes it a translinear circuit. Through a bit of math, you come up with the equation

Ic6.Ic7 = Ic8.Ic9

With Ic8 related to Ic11 and Ic9 to Ic12, it becomes clear that they must all be non-zero for the above equation to hold. If anyone is interested, I can elaborate on the above math and on translinear circuits.

I would also like to know if this design has been used commercially. My guess is that it is not exactly cost efficient, as it uses a _lot_ of transistors for not a lot of watts. But then again, that should appeal to the flat earth brigade, hehehehe....
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Old 16th May 2011, 09:51 PM   #23
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I think I have found the reason that the design never caught on. A Fourier analysis on LTspice shows a THD of about 0.3% - not exactly ground breaking. It may well be that TIM is quite good but I have not investigated that. The 'high' THD may be caused by both transistors being on all the time. In his book Douglas Self goes on about the perils of class AB. Perhaps this design falls into that trap and in trying to solve one problem (switching distortion) it makes another one worse. Does anybody have any thoughts on the matter?
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Old 16th May 2011, 09:57 PM   #24
jcx is online now jcx  United States
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isn't that a little short in the current gain department? - beta enhanced VAS would have 2 more Q worth of gain - and still Cordell would recomend output triple
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Old 17th May 2011, 11:10 AM   #25
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Here's one (below) . They last 20 years and sound real good. D701 / 703 are geraniums. These simulated well sub'ed with schottky diode's . Just 4 transistors makes for the Vbe and the non-switching OPS. Circuit idles OP's at about 10ma (never shuts them off - "krill like").

PS- I have the real thing to reverse engineer (actually 2 of them).

Another way to get low Xover is to use either a "fancy Vbe" or thermaltraks.

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Old 17th May 2011, 11:21 AM   #26
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Linear Audio Vol 13 is out! Check out my Autoranger and SilentSwitcher
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Old 17th May 2011, 12:09 PM   #27
wahab is offline wahab  Algeria
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Originally Posted by janneman View Post
Are they from Germany ?...
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Old 17th May 2011, 07:30 PM   #28
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Old 19th May 2011, 08:08 PM   #29
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Germanium transistors? Are those dinosaurs still around?
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Old 19th May 2011, 08:23 PM   #30
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Here you go.
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The Devil is not so terrible as his math model is!
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