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Old 30th September 2012, 04:02 AM   #1371
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by scott wurcer View Post
Not a chance that the JE990 fit in a DIP space.

Erik's paper using a current feedback pair (adding a darlington) for high current output.

http://www-f9.ijs.si/~margan/Articles/Class_B_Dist.pdf
I see what you mean -- Class B switching --- or, crossover distortion. Ok. Got it. Probably just throw another bias diode at it. But, the topology is pretty nice in this article. Thermally stable. I'll look at error signal with a scope and see. The level should be pretty low -- the circuit I applied it to had modest gnfb and the THD + N is extreamly low. I wont be able to measure improvements until the test gear gets better. Which I am working on. BUT, because you say its an issue, I'll look at it further.
Which is better IYO - Erick's or the Diamond buffer for an output stage? Thx - RNM

Last edited by RNMarsh; 30th September 2012 at 04:10 AM.
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Old 30th September 2012, 04:23 AM   #1372
RNMarsh is offline RNMarsh  United States
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Doesn't Liberty Instruments offer multitones software for audio tests??

Even HP (I mean Agilent) has put the software as a seperate offering - rather than in firmware .....
See ''Signal Studio for Enhanced Multi Tone''

-RNM

Last edited by RNMarsh; 30th September 2012 at 04:30 AM.
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Old 30th September 2012, 07:20 AM   #1373
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Quote:
Originally Posted by scott wurcer View Post
Not a chance that the JE990 fit in a DIP space.

Erik's paper using a current feedback pair (adding a darlington) for high current output.

http://www-f9.ijs.si/~margan/Articles/Class_B_Dist.pdf
Thanks for the link Scott - a very interesting article.
I instantly recognised the graphs from time way back when I fist read it but then forgot about it.
The mind shudders to think how much more I have forgotten..

I'll ask Erik if I can post it online.

jan
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Old 30th September 2012, 09:08 AM   #1374
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Has anything concrete come out of the 135 pages? I think there was something by Scott Wurcer but I couldn't see it. But maybe I fell asleep along the way.

Anyone point me to a link to the schematic?
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Old 30th September 2012, 11:27 AM   #1375
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Originally Posted by kgrlee View Post
Has anything concrete come out of the 135 pages?
Lol - patience, gourmet chefs are at work. Too many, in fact...
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Old 30th September 2012, 01:12 PM   #1376
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I agree with Scott that one circuit doesn't fit all apps. In one of Walt Jung's articles he expounds the virtues of virtually noisless mosfet constant current sources. John Curl has posted some all fet/mosfet topologies. I certainly think that this effort should be, in it's final form, something that can't be accomplished with a chip op amp. I believe the output stage should operate Class A with no chance of ever getting out of Class A. I think the bandwidth should extend to 100Khz. I think the completed circuit should be able to produce a 40 volt peak to peak square wave at 100Khz with no ringing or overshoot and sit there and cook for an hour even if you have to use heat sinks. The 2n5551/2n5401 transistors have been used successfully in several other modern attempts. It should be made with readily avalable parts not obsolete or scarce or so new it is unobtainium. Ray
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Old 30th September 2012, 01:18 PM   #1377
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Pete Basel had a thread 5 years ago on the JE990 with some interesting research. Maybe one good idea would be to do a simple FET version since it seems the FET version is a trade secret.

In the thread there is a discussion about output devices and bias. If you look at the schematic the MJE devices are selected. In Pete's sim he uses stock 1N914 and Motorola models for the outputs. There is little hope the values for Is in the models will give exactly the right bias current. I would always provide for trim of the output stage bias, or just to get a sim to work, adjust the 1N914 Is until the output devices have the right current.

Simulation of the JE-990 OP Amp By Deane Jensen
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Old 30th September 2012, 02:00 PM   #1378
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Wangine in Taiwan did a jfet input version of the 990 more than 20 years ago for a Parasound preamp Called the P-Fet 900, I think.
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Old 30th September 2012, 02:39 PM   #1379
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1378 posts and umteen circuits later, there ain't much real hardware.
So we did some soldering today.
Not yet tested. Will take some time to trim DC, etc. first.


Patrick
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File Type: jpg Kaneda Opamp V5 top.jpg (104.8 KB, 344 views)
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Old 30th September 2012, 03:36 PM   #1380
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Here is the first output buffer that was simple enough without compromising performance. I'm still looking at G = 10 and up performance because there is a some fine scale work needed to insure stability at low gains. Also as bcarso points out there might be an opportunity for power on latch-up so there might be a simple clamp needed somewhere. I don't think this is a big problem.

The output stage is biased all the way back from the input (via Q15 and Q16). If you follow the signal path this gives a feed forward slew boost directly to the output, unfortunately this only works in both directions if one of the fully differential input stages is used.This idea appears in many current feedback amps and this single gain stage approach provides the same opportunity. I will eventually repost all three ideas for input stages including this output stage. The other two versions were the Rush cascode and the complimentary version with hard to get FETs.

All versions rely on the input biased at 5mA per side. R8 provides trim of output bias which should be at 8mA. This gives a total supply current of 25mA. R19 should be chosen to give ~1mA for the supply voltage used. The values of R7 and C1are open to experimentation to vary GBW product and slew rate.

Nothing is chiseled in stone I'm sure there are numerous choices of devices that will work. At this waystation things look pretty good for G = 10 and up, 600 Ohm and 1000pF drive. Considering all the diode connected transistors could just be diodes there are only 16 or 18 active devices needed.

Attached are 20k 20V p-p THD and 100k square wave response (600 Ohm load)
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File Type: jpg cir1.jpg (96.1 KB, 359 views)
File Type: jpg cir2.JPG (59.5 KB, 318 views)
File Type: jpg cir3.JPG (45.3 KB, 280 views)
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