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Old 15th July 2011, 03:56 PM   #201
SimontY is offline SimontY  United Kingdom
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Any gains from the extra cap, Andrew?

Could we use a small film cap, say 470nF or 2.2uF? Is low impedance a key factor?
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Old 15th July 2011, 04:05 PM   #202
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A film cap could work well, but remember you are tying the output of two active regulators together with it - so really high Q /low-ESR isn't good and will promote ringing on either or both supplies (hence my note on damping). Small film cap with a series reisstor could be worth a try, say 1ohm. But a small oscon seems to work OK generally, esp if you have largish caps on the 1541 pins already (eg 47uF).

Definitely something to play with that works better if you can drive a 'scope!
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Old 15th July 2011, 06:58 PM   #203
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Actually I think there is - seems more lively but my mind is on this .....g D flip flop thing I've got myself embroiled in - sorry.
I'll be firing it ( DEM ) up again soon then I'll report back on both things with something a bit more coherent

btw...It's on the alpha 5 - tonight it'll be on the alpha because.... it works and is stable.

Have you got any 10 uf oscons spare ?

You can have one if not

Andrew
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Old 15th July 2011, 10:59 PM   #204
SimontY is offline SimontY  United Kingdom
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I've not and thanks but I'll just find something else like a film + damping resistor.

So it works on one player, good luck implementing it on the main one

Simon
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Old 15th July 2011, 11:52 PM   #205
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Yes - it may be exquisitely temperamental to impementation if you dont have a scope, but if it works, you can look at better answers [ eg floating a 10.0v reg between these pins - that's a gross hint, which definitely needs a 'scope ]
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Old 16th July 2011, 12:06 AM   #206
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Yes Simon - it's a winner - go ahead
It's another step - not huge but there's more to the edges of percussion and it feels like the attack speed is just more lively - as I reported on the ' 5 '.
I wish I could describe this stuff better - apologies.

I also wish I understood better why these little tweaks work.
Yes I can read the explanations by you and Martin and others too but it's just grasping it that ' does me in '

DEM method is aborted and I'm implementing this instead ( attachment )
Flip flop's are now officially for holidays not CD Players.

Anyway, once I get this running I'll post pics

Martin - thank you - it's a nice one

Andrew
Attached Images
File Type: gif dem-from ws.gif (29.5 KB, 130 views)
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Old 16th July 2011, 12:10 AM   #207
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Walter - you too - give this a go - it's good un..

Andrew
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Old 16th July 2011, 03:21 PM   #208
wlowes is offline wlowes  Canada
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Quote:
Originally Posted by AndrewGM View Post
Walter - you too - give this a go - it's good un..

Andrew
Ok - now for a head scratcher... does C227 not already do this?
-5 @ pin 26 goes to digital ground via c221,c222
-15 @pin 15 goes to analogue ground via c224,c225
digi and ana ground are tied together via c227. Basically we are adding caps to c227
I think I actually killed that one some time ago thinking it would be good to have digital ground not send very high frequency over to analogue ground. I thought at the time it was good. I have a couple of options in my used cap drawer. There is a BGN 47U at one extreme. At the other end are my newly aquired 1500pf silver mica russian military looking for a use. perhaps its time to experiment. Thoughts?
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Old 16th July 2011, 03:53 PM   #209
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Had a look at the schematic now - no, this extra cap i suggest is doing something quite different.

C227 is odd to me - most other implementations (and the quietest way of doing things) would be to have just one ground plane and the analogue and digital grounds going into it. The only reason these have different pins on dacs is to keep the current loops inside the chip separate - sharing one tiny internal bond wire for all digital and analogue 0v return current would badly degrade performance by crosstalk.
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Old 16th July 2011, 04:43 PM   #210
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Martin - are you saying get rid of the cap 227 altogether and put a wire link across connecting both D & A grounds together ?
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