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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Doug Self Preamp from Linear Audio #5
Doug Self Preamp from Linear Audio #5
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Old 30th November 2017, 03:18 PM   #891
rmaudio is offline rmaudio  United Kingdom
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Quote:
Originally Posted by Mooly View Post
I take the view that an opamp requires to see a low impedance supply.

As most (but not all) opamps have no notion of what or where ground is, then to my way of thinking the main supply decoupling should be between the opamp supply pins themselves.

Adding a cap to ground from each supply pin effectively places the caps in series as seen by the supply pins. The available 'ground' point close to the opamp is invariably some physical distance from a reference 'star' point and so the caps now have the possibility of actually coupling rail induced noise into the audio ground relative to other points on that ground trace.
Pushing theory aside just for a moment - single capacitor rail to rail decoupling appears to work reliably.
But I'd say that although the 'not star ground' point is valid - it's less relevant if using a 'ground plane' approach.
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Old 6th December 2017, 07:29 AM   #892
cowboy99 is offline cowboy99  United States
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Doug Self Preamp from Linear Audio #5
Got parts ordered, I've read everything at least twice and believe I understand everything.
Time to BUILD very soon.
One thing I unsure of: Is the most recent supplied power supply board and associated KAD_ADJ_PWR_SUPPLY.pdf define the 17V setup or 15V ? Seeing how the tranfo is 18V leads me to question whether it'll be sufficient for 'adjusted' 17V rail match.
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I'm kinda curious about that myself........
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Old 6th December 2017, 12:44 PM   #893
Rick G is offline Rick G  United States
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Doug Self Preamp from Linear Audio #5
cowboy99,
Mine works just Fine at +-15V. I see no advantage to push it to 17V, IMHO.
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Old 6th December 2017, 01:13 PM   #894
DouglasSelf is offline DouglasSelf  United Kingdom
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Quote:
Originally Posted by Mooly View Post
I take the view that an opamp requires to see a low impedance supply.

As most (but not all) opamps have no notion of what or where ground is, then to my way of thinking the main supply decoupling should be between the opamp supply pins themselves.

Adding a cap to ground from each supply pin effectively places the caps in series as seen by the supply pins. The available 'ground' point close to the opamp is invariably some physical distance from a reference 'star' point and so the caps now have the possibility of actually coupling rail induced noise into the audio ground relative to other points on that ground trace.
I completely agree.
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Last edited by DouglasSelf; 6th December 2017 at 01:16 PM.
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Old 6th December 2017, 01:16 PM   #895
DouglasSelf is offline DouglasSelf  United Kingdom
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Quote:
Originally Posted by Rick G View Post
cowboy99,
Mine works just Fine at +-15V. I see no advantage to push it to 17V, IMHO.
Well, the advantage is that you get 1.1 dB more headroom.

Not a lot, its true, but you get it at zero cost. I have been running 5532s off +/-17V ever since they became affordable.
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Old 11th December 2017, 02:12 AM   #896
reedcat is offline reedcat  United States
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The pair of LM317TG/LM337TG in my power supply gets pretty hot even at idle. Is this normal?

I am using the KAD Adjustable variety, which is based off of +/- 17V schematic in Small Signal Audio Design book (Fig 25.5 page 714 of 2nd edition) by Doug Self
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Old 11th December 2017, 06:18 AM   #897
diyralf is offline diyralf
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You can even operate the 5532 with + -20V.
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Old 11th December 2017, 06:20 AM   #898
diyralf is offline diyralf
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Quote:
Originally Posted by reedcat View Post
The pair of LM317TG/LM337TG in my power supply gets pretty hot even at idle. Is this normal?

I am using the KAD Adjustable variety, which is based off of +/- 17V schematic in Small Signal Audio Design book (Fig 25.5 page 714 of 2nd edition) by Doug Self
What is the voltage between in and out and what is the current?
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Old 13th December 2017, 07:29 PM   #899
heijnsva is offline heijnsva  Netherlands
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Default Power supply in a separate chassis/ grounding

Hi, I'm planning my build and i have the PCB's and some of the parts. I've read the thread and that has been very helpful so i think there will be no major problems. One question i have right now is that i think i will put the power supply in a seperate box and i'm not sure what to do with the safety ground. Is it OK to use safety ground on the power supply only or does the preamp chassis need safety ground as well? IE through the power supply line? If that the case, how does one keep audio ground separate?

TIA Vincent
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Old 13th December 2017, 07:37 PM   #900
scottjoplin is offline scottjoplin  Wales
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I've not connected safety earth (PE) under those circumstances. If you want to be certain there is no way for mains to get to the chassis, fuse the low voltage supply. The only other way it could would be via the interconnects and that would depend on the precautions taken in the connected equipment
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