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Old 6th June 2008, 09:18 AM   #11
togo is offline togo  Austria
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Thx for your reply.

I have certainly testet this snubber a long time before, but it makes no different.
I have postet the schematic of the power supply.
The caps in there aren't very big.
So i have put in additional 100/100V on each side, and surprise it makes no different.
It is also very strange to me that i have this fall from 90 to 70.
I don't understand this amp :-)

PS: the hole housing and hetsinks are conected with the ground from the psu :-)
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Old 6th June 2008, 09:28 AM   #12
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The +/- 90 are in series with the +/-12. What apparently happens is that the +/-12V discharge very quickly to zero, that automatically makes the +/-90 jump 12V downwards. If you increase the cap of the +/-90 that only makes it worse. You should increase the cap after the +/-12 bridge.

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Old 6th June 2008, 03:00 PM   #13
ntropy is offline ntropy  Switzerland
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Post all schematics you have. I can't see for what the +/-12V is actually used. I would like to see as well how the 70...75V for the power stage is generated.
I would first measure if you can see this "jump" at the potentimeter P1 just to rule out that that it's not caused by the power amp stage.
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Old 7th June 2008, 12:29 AM   #14
Bonsai is offline Bonsai  Taiwan
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I have the complete set of articles on CD.

In the articles they warn about layout and in particular about how the drivers are heatsinked - I believe its something about capacitive coupling.

This is a CFA - so its very fast and without good layout you could have oscillation problems.

Read through the article carefully and take note of the construction guidelines
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Old 7th June 2008, 12:33 AM   #15
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Quote:
Originally posted by Bonsai
I have the complete set of articles on CD.

In the articles they warn about layout and in particular about how the drivers are heatsinked - I believe its something about capacitive coupling.

This is a CFA - so its very fast and without good layout you could have oscillation problems.

Read through the article carefully and take note of the construction guidelines

I always ground my chassis and heatsinks.

The amps I have built have always been none critical about layout as they have been built on veroboard.
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Old 7th June 2008, 03:48 AM   #16
Bonsai is offline Bonsai  Taiwan
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I am not surprised you do not have oscillation problems

1. Your designs are VFA
2. You have very high DC/LF gain (no degeneration resistors remember) and massive HF loop gain killing miller caps

Thse designs are a bit more amenable to veroboard construction. That said, you can still build good stuff on veroboard if care with grounding is taken.

CFA is an entirely different matter.

Please read the Elektor article - they are quite specific about not grounding the pre-driver and drive r heatsinks because of oscillation.
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Old 7th June 2008, 03:52 AM   #17
Bonsai is offline Bonsai  Taiwan
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I jus t took a look at th e circuit above - it is not the Gigant I know.

I think Elektor published the 'Gigant' in Europe and one called the Titan in the UK. The Titan is CFA - the circuit above is VFA.
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Old 7th June 2008, 10:13 AM   #18
Horexx is offline Horexx  Germany
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Togo showed the plan of the GIGANT (500W at 4 Ohm).
It was published Mai 1986 in ELEKTOR (Germany).
I have the magazin here.
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Old 7th June 2008, 10:32 AM   #19
Bonsai is offline Bonsai  Taiwan
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I just checked - the one I have is Titan 2000 by T Geisberts. Also 500W into 4 Ohms but totally different circuit to the one above (many more components, CFA etc). Someone on the site about 2 or 3 years ago mentioned that this Titan 2000 was publisjed by Elektor in Germany and the Netherlands but under the name Gigant 2000 - I think thats why I got confused.

Here are the Specs of the Titan 2000

300W into 8 Ohms
500W into 4 Ohms
800W into 2 Ohms

Distortion .005% (no frequency or power level quoted)

SR 85V/uS

OL Bandwidth 55Khz

Power Bandwidth 1.5Hz to 220Khz (it uses a servo - hence the bottom end only going to 1.5 Hz)
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Old 9th June 2008, 09:15 AM   #20
togo is offline togo  Austria
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Thx for your replies.
here are some more schmeatics.

Instead of 3x 10.000F/100V i have take 2x 22.000F/100V
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