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Old 12th December 2004, 01:05 PM   #1
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Question 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.
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Old 12th December 2004, 01:10 PM   #2
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Default 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
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 12th December 2004, 01:41 PM   #3
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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.
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Old 12th December 2004, 03:30 PM   #4
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Default Jinkushi and Jacco, if you can, put some schematic to us

Will be very good to see it.

regards

Carlos
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Power supply; ripple, filter, noise, stability and the use of capacitance multiplier... Portuguese and English; https://www.youtube.com/watch?v=sSm0ku1eIgg
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Old 12th December 2004, 04:04 PM   #5
Rudy is offline Rudy  Belgium
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"100W power amp. elektor april 1982"

this should be the one
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Old 12th December 2004, 04:34 PM   #6
AndrewT is offline AndrewT  Scotland
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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.
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Old 12th December 2004, 05:19 PM   #7
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Default 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
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Old 12th December 2004, 07:44 PM   #8
Marc Vi is offline Marc Vi  Netherlands
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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.
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Old 12th December 2004, 07:51 PM   #9
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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.
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Old 12th December 2004, 10:29 PM   #10
guido is offline guido  Netherlands
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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

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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