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-   -   I need comments about "100W power amp. elektor april 1982" (http://www.diyaudio.com/forums/elektor/47547-i-need-comments-about-100w-power-amp-elektor-april-1982-a.html)

jinkuchi 12th December 2004 02:05 PM

I need comments about "100W power amp. elektor april 1982"
 
I need comments about "100W power amp. elektor april 1982"
Someone built it for sell he change the power transistor to new one maybe for improvement.
I had listen to it. Its sound better than gainclone!
I need comments.

destroyer X 12th December 2004 02:10 PM

I am not entirelly sure, but Mr. John Mateus and Mr. Palesha made something alike
 
And they feel the amplifier as sounding very good.

They will appear to inform you details.

regards,

Carlos

jacco vermeulen 12th December 2004 02:41 PM

The 1982 Elektor amplifier must be the Crescendo.
I built it with left-over components, for comparing it with later Elektor amplifier models.
Though built by many people, it was said in the 80s to be a poor audio amplifier, nearly 10 years later i built it and had to agree.
The design is not very stable, and Mosfets IMO sound kind of nasty in AB mode. I still have a number of the mosfets used in that design. They have been off production for years, the shops that still sell those devices ask steep prices for replacement Hitachi's.

I thought the circuit needed a very high voltage powersupply for the rated output, 75 volts, so i used a small high voltage regulated supply for the front end, and a lower voltage powersupply for the output Hitachi Mosfets. It saved on dissipation, and i could use the toroidal transformers and electrolytes i had.
If it sounds better than the GC, it may comment more on the GC.

destroyer X 12th December 2004 04:30 PM

Jinkushi and Jacco, if you can, put some schematic to us
 
Will be very good to see it.

regards

Carlos

Rudy 12th December 2004 05:04 PM

2 Attachment(s)
"100W power amp. elektor april 1982"

this should be the one :)

AndrewT 12th December 2004 05:34 PM

Hi,
forget that '82 design using integrated darlingtons.
Use a modern but simple schematic. Try looking at Elliot Sound Products (ESP) for starters but there are lots of others.

destroyer X 12th December 2004 06:19 PM

Yes!...this one, ...John Mateus constructed this one and told me
 
That distorted the high frequencies.

I suggest him to:

- Reduce C7 and C8 to 10 picofarads
- Reduce C6 to 27 pf
- Remove 470pf from the input, unless you have one radio
amateur near you....less than 1000 feet,
- Include some capacitor (100N) in parallell with D1
- Remove the "distorters"; T5,T6,D2,D3,,R19,R17,R15 and R13
- Include a 1 uf non polarized capacitor from bias coletor to
emitter (t2)
- Increase C7 (input cap) to 2u2, use poliester, non polarized

Glue a cartoon (isolation) over a copper plate, the same amplifier size... and put it under the amplifier board, and connect this plate to ground...the amplifier likes to oscilate, that's the reason they put the "hinderburg", enormous "Aphocalipthic" capacitors from base to colector in the darlington units...they have big gain and like to oscilate....10 pf is enougth to block oscilation without destructing the wave shape.

I do not know if Mateus made those changes, he is a big friend o me...but the one is older than "mathusalém"....and may be forgot made the amplifier, and if that thing is an amplifier or an ashtray....ahahahaha...he will say terrible things to me.

Say terrible things...but talk with me..... if you forgot me friend, will be worst!!!

regards,

Carlos

Marc Vi 12th December 2004 08:44 PM

Jinkuchi,

I think I agree with the changes proposed by Carlos. Ik have some experience with the output transistors. If you use the original Philips ones, then they are stable, others will tend to oscillate.

Marc.

jacco vermeulen 12th December 2004 08:51 PM

Quote:

Originally posted by Rudy
"100W power amp. elektor april 1982"

this should be the one :)

Oops, forgot that one, it is not 100w in 8, but in 4 Ohm.
The one i mentioned must have been from the end of '82. A bit more power too, at least 130 watts in 8 Ohm.
I remember that Elektor did a couple more of those easy low cost designs later on.
I pity the GC.

guido 12th December 2004 11:29 PM

I've build that one back then for 'pa' use. With some friends we supplied music at small parties etc. I built it with 500VA transformer and some huge caps (2*20kuF iirc), well at least huge for me in those days ;) It's not suited well for PA use, shorten the output and you blow the darlingtons. I did include a dc protection circuit that saved the speakers when it happend.

As for hifi use, i guess there are better designs (as for pa).
But it served me well back then. It was the only amp that could drive the bass units. Some commercial stuff we had could not (even when they were rated more watts). And i used a small 'cool-tunnel' with a big pabst in front, it could go full throttle all evening.

We needed someone at the fusebox to switch it on. The stotzes kept going off:D

The only modification i made to the schematic were two diodes 1n4148 from base of T1 to T2 (both in a different direction) to keep the input voltage within some limits.

Still have it up on the attic, sometimes i use it to make some noise:) :)


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