redesign of leach amp pcb for integrated TO-247 output devices - Page 28 - diyAudio
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Old 24th May 2005, 11:52 AM   #271
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AndrewT:
>Hi Boraomega,
>re Thiel network on output.
>I have seen a few designs with a pi network rather than the >two L pad versions proposed by Thiel.
>Would the pi version with RC to ground from both ends of the >inductor help with the rf rejection senario?
.What values should be used? How about doubling R and halving >C for each CR?

Frankly, I don't have any "firm" and final opinion about that addition (another Zobel after the coil), mostly due to the fact that I have never devoted any significant time to test it "from all angles". Some first impressions were that it could (eventually) be useful if you assume that the capacitance of speaker cable will be of the order of several tens of nano-farads, which would really be a grotty affaire. Most of the currently available speaker cables will have somewhere between a few hundreds pF up to the maximum of, say, 1,5nF for reasonable room length wiring, hence, I don't see the point. I've tried it only once in practice, and I haven't noticed any influence in either direction (positive or negative). It could be that some further investigations will reveal much more, but as I said, first impressions haven't justified any significant time and effort investment from me. It is possible that I am equally wrong about that........
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Old 24th May 2005, 07:24 PM   #272
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pooge wrote:

This feature was not in his original amp from 1976. It was added in a later revision. It was published in an article in May of 1988, in IEEE Transactions on Consumer Electronics. This feedback technique bypasses the pole in the output stage caused by the load capacitance for improved stability. It has been said the output inductor may not even be needed.

--- Thank you for info! I never followed this design chronologically (I haven't follow it at all by all means!) apart from seeing it in "Audio" in our University Library way back in '76 and again more than 20 years later when customer brought schematic with request to build that amp for him. Without having original schematic to compare, I presumed that this feature was there from the very beginning which is obviously not the case ( If you don't have a photographic memory, don't rely on it!).
Anyway, I don't think that exact moment or revision in which that mod appeared for the first time, is of a crucial relevance for our current theme.

macgyver wrote:

What are 100ohm resistors in near of Q18-21 devices (TO-247 layout)? Where will the another head "leads"? I don't find them in the leach schematics or part list.

---No, you won't find them for they are my additions for connection of my design of universal protection system. They are actually sampling points, and you can freely neglect them unless you are interested to make that protection system too. That protection system is not designed specifically for Leach amp, but is pretty much universal and applicable to just about all modern amps with complementary pairs in output stage and split supply. Some of incorporated additional features are: protection against DC on speaker terminals, delay for speaker switching, thermal protection and protection against incorrect (too low) load impedance.
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Old 24th May 2005, 07:54 PM   #273
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"No, you won't find them for they are my additions for connection of my design of universal protection system. They are actually sampling points, and you can freely neglect them unless you are interested to make that protection system too. That protection system is not designed specifically for Leach amp, but is pretty much universal and applicable to just about all modern amps with complementary pairs in output stage and split supply. Some of incorporated additional features are: protection against DC on speaker terminals, delay for speaker switching, thermal protection and protection against incorrect (too low) load impedance."


Could you send me schematic to the protection circuit?

b8_beat@hotmail.com
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Old 24th May 2005, 09:34 PM   #274
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"macgyver" Check your mail!
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Old 24th May 2005, 09:38 PM   #275
pinco is offline pinco  Croatia
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Hy

You can faind that schematic and PCB, on Dr. Borivoje web page, and other useful staff related to DIY audio........ I made his Studio amplifier and I am very satisfied with that project....,
http://www.bas.abshost.net/mojiprojekti1.html

Pomoćni uređaji / OMNI protektor

Vinko

(Radili ste i leach pojačalo!, imam isprintan cili projekt za njega, koji su vaši dojmovi o njemu kao originalu te posli vaše prepravke, mislim na signalne te izlazne tranzistore koji su ipak nešto moderniji, )
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Old 25th May 2005, 07:00 AM   #276
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boraomega ,

I would like to have your protection ckt too , or why not post it on the site for everyone ,
Rajeev
systems_rajeev@rediffmail.com


pinco

How can I read on that website , its not english , also it needs virtual jawa machine in the pc which I do not have in mine .
__________________
RL
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Old 25th May 2005, 08:10 AM   #277
pinco is offline pinco  Croatia
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You must have java v.m. , then you have menu, click "pomoćni uređaji" and "OMNI protector"

http://www.bas.abshost.net/mojiprojekti1.html


Vinko
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Old 25th May 2005, 12:31 PM   #278
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I will try ASAP to post here everything related to that protection system.
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Old 25th May 2005, 03:18 PM   #279
mik is offline mik
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Dobro dosao Boro!
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Old 25th May 2005, 09:02 PM   #280
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Lep pozdrav za MIK-a i Vinka!

As I promised, here are files of my protection system. It would have to be divided into several posts because of pixel and KB limits (max. 100KB & 1000x1000pixels) for uploads on this forum. First one is the schematic.
Attached Files
File Type: pdf omnischem.pdf (58.8 KB, 1385 views)
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