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Old 7th May 2012, 06:55 PM   #5211
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Quote:
Originally Posted by bcarso View Post
That is a nice article.

The circuit attributed to Birt on page 58 appears at least as early as 1987 in Steve Dove's Consoles article in Ballou's Handbook for Sound Engineers, ISBN 0672219832, and may be in the earlier series of magazine articles of Steve's that his chapter apparently recapitulates (I don't have the magazine series). I have forgotten the name of the person that Steve worked with in the UK who also claims he invented it [= ; there was an exchange sans Steve in the smaller breakaway-from-diyaudio forum some years ago about priority.

It's a nice idea and works of course, but my experience is it's a bit tricky to compensate.

BTY I have have been using That chips for quite some time. Their app's guy at one of the shows was quite helpful on a balky circuit. He was amused I was using their parts to build an optical power meter. I guess it is possible to not just steal from other fields for audio!


Brad
I am particularly amused by the Birt circuit. When CMU was doing work on speech recognition they had one of the faculty build an A/D converter using the then in sampling availability Sony A/D chip. The finished version was built in a copper case using all the techniques he knew. When it was done it only worked at 12 bits of resolution. I was asked to build one for them. The mic preamp circuit I used was the same! I also did a special power supply (But no where near as good as what I can do today.) I managed to get 14 1/2 bits of resolution, not the 16 the chip claimed. Still don't know if it was me or the chip. They didn't care as the software worked the same on 12 or 14 bits. So all that proved was 12 bits was enough.

I built three units for them. Then a grad went into business offering copies of it!

That was the late 70's as I recall.

I did not think anything in the unit was particularly new or ground breaking.

Last edited by simon7000; 7th May 2012 at 06:59 PM.
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Old 7th May 2012, 06:57 PM   #5212
dvv is offline dvv  Serbia
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Originally Posted by nigel pearson View Post
http://www.thatcorp.com/datashts/THA..._Datasheet.pdf

I know a similar chip SSM2019 which if memory serves me correctly was used in the Lehmann Black Cube phono stage ?

I have been told these are good also

THAT Corporation 300-series Low-Noise Matched Transistor Array ICs
Hot ding!

This really looks good - perhaps even a dream come true. ESPECIALLY the two+two matched NPN+PNP, that's practically the whole front end of a fully complementary power amp (with some additional work).

One can even use a four trannie chip for a cascoded front end.

To be honest, I had never even heard of this company until a few minutes ago, here.
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Old 7th May 2012, 07:24 PM   #5213
tvrgeek is offline tvrgeek  United States
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THAT makes some cool stuff. Notice the matching is not as close as you can do by hand. For production work though, what a way to go. Be careful of the voltage ratings.
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Old 7th May 2012, 07:24 PM   #5214
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I think that we should add a discrete output stage to the 1510, and it would be even 'better'.
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Old 7th May 2012, 08:10 PM   #5215
bcarso is offline bcarso  United States
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I like the THAT parts. By the way I was told that any of those arrays has the entire complement of transistors inside, and that it is just a package pin count limitation that prevents access to all of them.

I wish they could manage higher beta and lower rbb' though. I was also told that they experimented with higher beta, but the breakdown voltages became too difficult to control.
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Old 7th May 2012, 08:29 PM   #5216
SY is offline SY  United States
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Quote:
Originally Posted by john curl View Post
I think that we should add a discrete output stage to the 1510, and it would be even 'better'.
"Better" in what way? As it is, the distortion, noise, and CMR are superb. It has no trouble driving loads, and any crossover distortion is buried. They make another chip, the 1570, which will take the output from a 1510/1512 and drive balanced lines.
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Old 7th May 2012, 08:34 PM   #5217
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I always try for something 'better'. I am not comfortable with a Class B output stage, for my best efforts.
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Old 7th May 2012, 08:39 PM   #5218
SY is offline SY  United States
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What makes you say it's class B? More likely AB. Distortion residual is damn hard to see, but doesn't seem to be crossover.

And if it works, and works well (I can assure you it does, I'm VERY picky about my recording equipment), and is not limited by the output stage, I'm having trouble understanding the objection.
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Old 7th May 2012, 08:57 PM   #5219
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It is class B for all practical purposes.
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Old 7th May 2012, 08:58 PM   #5220
jcx is online now jcx  United States
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the less than generous conclusion is that someone can't design PS to keep Class B half-wave rectified currents from contaminating the signal path - Class A relaxes PSRR, common impedance, mutual inductance PS current coupling issues

but Class A bias with a few mA current sink on the 1510 output and a buffer for line driving would remove most potential objections

hard to do better with feedback R internal to chip

Last edited by jcx; 7th May 2012 at 09:16 PM.
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