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Old 24th November 2012, 07:51 AM   #221
dadod is offline dadod  Croatia
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Thanks Kevin, I appreciate your contribution in this forum.
What is your opinion about MJE15034/15035 from ONSEMI as a drivers?
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Old 25th November 2012, 02:53 AM   #222
Struth is offline Struth  Canada
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Hi Guys

MJE15034/35 look a lot like MJE15030/31 except for having a much higher voltage rating. Gain is fairly flat and consistent over normal driver-stage current requirements. GBW curves for the 34/35 look a little scary for low currents, but the same curves for 30/31 do not go below 100mA, so may look similar.

The lower-voltage MJE15030/31 is ubiquitous and has proven itself to be a favoured choice in many high-end designs. Bryston has used them since they became available. The 30/31 are seen in amps up to +/-75V rails, even though their rating is only 150V. If you are doing a class-G amp or something with +/-100V rails, the 34/35 should give similar performance.

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Kevin O'Connor
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Old 29th November 2012, 04:56 AM   #223
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Default Still playing around

Ditched the CCSs to try bootstrapped resistive loading and it isn't too shabby. It definately isn't as touchy with getting offset in check. I think I'd like to play with the BIGBT some more, maybe just go stupid and try the BJTs in a CFP driven by a smaller MOSFET. Simmed distortion doesnt change much until just shy of clipping, about 3V off the rails.
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Old 29th November 2012, 09:06 AM   #224
AndrewT is offline AndrewT  Scotland
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The NJLs each have a thermally coupled diode, are you using those somewhere in the circuit?
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Old 29th November 2012, 12:43 PM   #225
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Quote:
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The NJLs each have a thermally coupled diode, are you using those somewhere in the circuit?
No, I just used the models that best fit what I currently have on hand, which is some 2SC3281 and 2SA1302 I bought in the early nineties and never used. It wasn't my intention to confuse the issue showing specific devices.
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Old 29th November 2012, 05:14 PM   #226
Struth is offline Struth  Canada
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Hi Guys

Jkuetemann, see my earlier posts regarding non-CS versions of this buffer:

114 - Rs for CSs

116 - schemo showing Rs for CSs and class-A bias servo

136 - paragraph-5, discusses offset advantges of Rs

186 - performance of bootstrapped-R version with triple-EF, doubled outputs, local filters, plus layout and schemo - THD <0.002% measured across the band (limit of Radford test system)

All my circuits have proper input and output referencing, as detailed earlier.

In the past I tended to add CSs and current mirrors to assure performance and to eliminate critical R values in certain circuits. After building a lot of different things and many of each, I'm finding certain simplifications to be worth the added effort of matching devices. The overall distortion profile becomes balanced, benign and low-order.

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Old 30th November 2012, 07:55 AM   #227
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Quote:
Originally Posted by jkuetemann View Post
I think I'd like to play with the BIGBT some more, ...
Way to go

I can not tell you how pleased I'm with them and how good these are in real world practice. Only that I prefer to use verticals (IRF610/9610) for drivers as they're faster and likes to drive more current. VAS stage, no matter which topology, driving BIGBTs breathes with full lungs at all times.
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Old 30th November 2012, 12:10 PM   #228
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I remember the old philips BD to have <100mhz ft, am i correct? If not, apologizes.
Not correct, Typical ft at 30ma is 150Mhz. The most important factor is the 30ma, which is where a typical driver is biased at. At this current toshibas manage around 70Mhz and onsemi a dismall 20 to 30 Mhz.
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Old 30th November 2012, 12:17 PM   #229
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Hi Guys

The Philips data books provide Ft info for the BDs where Motorola's does not.

You are free to use my share of BDs in all your amps for "superior" performance. I've never had to bias the 2SA/2SCs any hotter than any other device to have amazing performance, but maybe things work differently in this time zone?

Frankly, I think my hearing must be going because I can't hear anything over 1MHz.

Have fun
Kevin O'Connor
No thanks, I dont want what will probably be fakes or junk second source. The bds have long been discontinued and only the fairchild second source seems to be capable of similar performance. Clearly you dont understand the distortion mechanisms with push pull emitter followers so I wont waste further time with you on the subject in this time zone.
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Old 1st December 2012, 03:46 AM   #230
Struth is offline Struth  Canada
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Hi Guys

Clearly I do not understand things the same way as you, homemodder. Rather, what I understand is that there is more to BJT performance than mere Ft. Gain flatness over the current range actually used is more important and does not require that this be coincident with the maximum Ft point of the device. In this view, I am joined by name designers whom I respect.

Lazycat, I finally took a closer look at your discrete IGBT circuit and understand why you like it. If you took out the diode between the BJT collectors, you have a formof Bryston Quad-complimentary output stage in effect, with a mosfet driver instead of BJTs, and without voltage gain. The combination of an emitter and a collector working the load for each signal half has a profound effect on the distortion spectrum, generally making it more balanced and benign.

Have fun
Kevin O'Connor
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Last edited by Struth; 1st December 2012 at 03:55 AM.
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