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Old 4th July 2004, 11:17 PM   #11
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Default hehehe. maybe not so perfect designer

Maybe something wrong, or missed.
Honored your visit Mr Pass, nothing can scape from your skilled eyes.

Mikek is another one that has deep atention in circuits too.

regards all

Carlos
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Old 5th July 2004, 02:19 AM   #12
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Which schematic is in discussion, the green sch or the white sch?

AKSA, what do you think of Darlington or Triple darlington emitor output at the output stage? They can reduce bias needed in the VAS stage, but are they adding more complex phase shift so they are more vunerable to oscilation, compared with direct output transistor from the VAS/Vbe multiplier?

If darlington is good, is it better to use mosfet as the buffer, like you said in post #2 ?
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Old 5th July 2004, 02:51 AM   #13
thanh is offline thanh  Viet Nam
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I can't access www.gieocites.com.Please post the schematic
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Old 5th July 2004, 02:52 AM   #14
AKSA is offline AKSA  Australia
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Hi Lumanauw,

I try to avoid triple darlington EFs in output stages.

As you say, they shift phase more than the usual double EFs, and while in a powerful amplifier you might need to run a high stage current through the VAS, with proper transistor choice you can still make them sound good. There is also the question of local stability; EFs are prone to self-oscillation because of negative resistance characteristics on the base, so three in a row is probably more susceptible than two.

I have not yet done work on use of mosfet drivers, but hope to look at it soon. This idea shows great merit, I feel, because it makes the amplifier more load tolerant. The final frontier is driving an electrostatic with a PP Class AB SS amplifier.

Cheers,

Hugh
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Old 5th July 2004, 06:46 AM   #15
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Quote:
EFs are prone to self-oscillation because of negative resistance characteristics on the base
Is this why some designs have base resistors (like 20-100ohm) for every stage of triple darlingtons?

How about the sound. The amp with darlington or triple darlington EF stages, and an amp who drives output stages directly from VAS, are they sound different?

Also, I see mosfet output stages, or Lateral ones, usually dont have driver. The gates attached directly to VAS. Are mosfet output stages dont need big VAS current?
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Old 5th July 2004, 07:47 AM   #16
sajti is offline sajti  Hungary
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There are lot of amplifiesrs with triple EF, and they sounds good (Mark Levinson large amplifiers).
I made some amplifiers with MOSFET ouput, even with 4-5pairs of IRFP240/9240. For this amplifiers I used high current VAS stage. The highest current was 100mA, with MJE15032/15033. I applied some emitter followers between the input and VAS.

sajti
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Old 6th July 2004, 01:06 AM   #17
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Default I will put a lot of Brazilian circuits, the first will be Quasar, Mr Snerewsky brand

Mr. Snerewsky, old Tcheco-Eslovakian family living a century in my country, borned here, made a Amplifier Industrie, together his father and 2 brothers.

From 1962 to 1982 the made wonderfull amplifiers, and schematic, always the same.....long tail, differential input, CCS, complementary drivers and complementary output, protection is the old one, using some voltage developed over emitter resistors.

Schematic has no values, this way i am preparing it, cannot put the factory one to not broke rules.

The factory close its doors because of Government decisions.... the amplifiers where expensive, only to rich people, not cheap ones, all the enclosure where heatsink.

Some models used big needles to measure power, consider the design related to 1962!!!, this design is already beeing discussed in our forum.... so, take a look as Mr. Snerewsky was a Pioneer!

Factory closed in 1982, thousands units already working, and as new, because anodized metal works.

One of the Snerewsky brothers are living in USA, he is connect with appartment and houses sales...my god!.... what we loose!

The problem here was the decision to evolute Amazon State, the capital Manaus, inside Amazon Jungle, and near Amazon RIver needed some help, had big development early 18 hundred, passed century, because or Englishman exploration of natural Latex to make rubber.... and now a days, not doing that anymore because some better Asiatic Markets.

This way, my Government decided to open the Market, with no taxes to free import and export from Manaus, a free place to business... and all rich factories moves to Manaus, and from them received boards completed from China...mounting and putting brazilian names on their panels.... this way, Brazilian QUASAR died!

I will put "THE MAN" picture, the factory old picture and one image of their amplifier.... schematic will delay some time.

regards,

Carlos
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Old 6th July 2004, 01:29 AM   #18
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Quote:
Originally posted by lumanauw
AKSA, what do you think of Darlington or Triple darlington emitor output at the output stage? They can reduce bias needed in the VAS stage, but are they adding more complex phase shift so they are more vunerable to oscilation, compared with direct output transistor from the VAS/Vbe multiplier?

If darlington is good, is it better to use mosfet as the buffer, like you said in post #2 ?
Triple Darlington can be made to measure better, but my ear
leads me back to Darlingtons. I've tried Mosfets as buffers for
BJT outputs, and some reason I've never figured out, I never
liked the results.
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Old 6th July 2004, 01:36 AM   #19
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Default Sorry Nelson, small interruptions to put pictures

And them, please, go ahead.

Carlos
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Old 6th July 2004, 01:37 AM   #20
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Default One more picture, the factory

They are five, just a minute Pass.

Carlos
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