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Old 23rd May 2003, 07:51 PM   #41
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I read the app note, built a gainclone, then talked with an engineer at National's Overture group.

I may well be fast in lining up with what he said, since I have yet to build a bridgeclone both with and without the servos.

I choose to rely on his advice until I do, which was that the servos result in a lower noise floor and reduce the extreanous current flowing between the amps, and that using the precision resistors alone was for those lacking the money or desire to use them.
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Old 25th May 2003, 11:13 PM   #42
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For what its worth, the engineer said the proformance with the servos is significantly better.
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Old 25th May 2003, 11:51 PM   #43
Cobra2 is offline Cobra2  Norway
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Default Bridge/paralell w. input-trafo

Please help with suggestions; my bridge/paralell (inveting input) "clone" have some slight distortion-issue.
Probably because of the trafo-input (LL 1540) http://www.lundahl.se/pdfs/datash/1540.pdf
that I use for signal-splitting.
Any good suggestions on this?

ArneK
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Old 26th May 2003, 06:46 AM   #44
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Thumbs up split

hi, you could also try a drv-134 for splitting......
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Old 26th May 2003, 07:10 AM   #45
Cobra2 is offline Cobra2  Norway
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Default Bridge/paralell w. input-trafo

Hi!
I first tried a "direct connection" from a balanced source, but this had too high signal level.
And then I used the LL1540 for splitting/balancing a single-ended signal.
But I think there must be a impedance-mis-match or something.
I'll hook up my scoope later.

Arne K
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File Type: jpg ll1540.jpg (17.0 KB, 1497 views)
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Old 26th May 2003, 07:32 AM   #46
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Hi Arnek,

what are you using to control the volume ?

mike
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Old 26th May 2003, 07:48 AM   #47
Cobra2 is offline Cobra2  Norway
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Default Re:Bridge/paralell ...

Hi!
I use a separate (active) pre-amp.

it's connected as on post 9, http://www.diyaudio.com/forums/showt...559#post161559
without the op-amps, but with the LL1540.
I use a 2 x 24V trafo, 600VA, dual bridges and 2 x 10 000uF PSU,
and every chip is bypassed with a 100uF Elna cap.
Trafo is connected as previous pic, with 33k as R/2 (x2).

Anyway, it seem to sound much better this morning, have left it on over night! (Maybe it is a "burn-in" issue).

Arne K
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Old 26th May 2003, 09:06 AM   #48
Cobra2 is offline Cobra2  Norway
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Default Tha "real" thing:

A picture...

Arne K
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Old 26th May 2003, 11:19 AM   #49
mikelm is offline mikelm  England
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Default Re: Re:Bridge/paralell ...

Quote:
Originally posted by Cobra2

Anyway, it seem to sound much better this morning, have left it on over night! (Maybe it is a "burn-in" issue).

Arne K

Well, if it sounds OK now great - otherwise perhaps you could check the DC offsets and work out how much current each pair of chips is sinking. If DC offset is more more than a few millivolts it might be worth zeroing each chip with a 50k multi turn pot on the non-inverting i/p

also have you thought to reduce the gain of the pre-amp and dispense with the transformer ? or if you keep it make sure there is no dc offset on the transformer i/p - they generally do not like DC atall ( not even a little bit )

cheers

mike
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Old 26th May 2003, 12:47 PM   #50
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Default Re: Re: ....Bridge/paralell ...

The good news, It sounds good now!
DC-offset out (without load) less than 20mV
DC-offset input ; less than 5mV.
I have added a pair of 100nF to the PSU, (without believing that it would do much difference), run it "hard/hot" for a period, let it cool down, and started to listen to it.
My impression now, is that it is very "correct", a bit dry, but with a slight forward soundstage. Imaging/3D is rock solid.

But it has nowhere the sheer guts and power of my N-channel-amp, not as liquid and musical...but for the price...and parts-count...I'll say I'm happy.

Arne K
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