I need comments about "100W power amp. elektor april 1982"

[mjagpereira]

I buil the so called mini-crescendo with the 2sk135/2sj50. I enjoyed it for a while but....not any more. I also build the accessories that where destined to the "big" crescendo and now
i'd like to use this protection circuits in another amp but lost the article. Can anyone email me a copy.

jpereira@afn.min-agricultura.pt

Thanks.

[lineup]

Protection Circuit
hmmm...
I have most of the magazines Elektor .... swedish version
Will take a lot of time and effort to find the actual Issue for that protection.
What year it was? Do you know?

[blueskynis]

I do not understand the purpose of C12 and C13 in B. Crescendo (140W) schematic, posted here. How do they affect PSRR?

Also, according to D.Self, R12 and R14 looks like are not needed. I am wondering why do people still put those resistors, even in some modern commercial designs.

[lineup]

C12, C13 I am not 100% sure why they are needed
but they are in parallell with R17,18 and so makes a filter.
Which makes those 10k more transparant at high freq.

About R13,14 you and Douglas Self are correct.
They improve nothing.
Even they tiny, tiny reduces the gain in input,
which is not what we want.

But this is for homebuilders, so they are often added initially
when we measure to balance the current in input pair.
When we have trimmed perfect 50%-50% in differential pair,
we can remove them and replace with a jumper.
Or let them be, they wont effect performance in a feedback amp anything we can notice.
With that high Vce across transistors.

So R13,14 just to give an easy way to measure current across.

In amplifiers for example with very low voltage across transistors, we could need to use a resistance or diode 1N4148, 0.6V
to make both transistors work in same low Vce (Vsat) area. And work under same consitions.

[sivan_and]

There was an amplifier circuit in "Elektor" using Buz series of mosfets..will post full details when i can get hold of the article and magazine.

[blueskynis]

Thanks lineup

[mjf]

[QUOTE]Originally posted by mjagpereira
i'd like to use this protection circuits in another amp but lost the article. Can anyone email me a copy.

hello.
i have found this one.it shows a dc protection circuit for the crescendo.
greetings....................

[mjagpereira]

Thanks, mjf.
This is going to help.

[DuncanV]

About the 100 Watt Elektor design, using BDX66/67: Actually, this is not an original Elektor design. It was first sold as a Philips kit and published by Elektor once Philips decided to stop selling their DIY kits in the early 80's. Even the pcb layout is exactly the same

This amp was my first audio amp project!