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Old June 14th 21, 09:49 PM posted to uk.d-i-y
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Default An electronic question.

On 14/06/2021 17:55, Peter Able wrote:
On 14/06/2021 16:02, Fredxx wrote:
On 14/06/2021 14:10, Dave Plowman (News) wrote:
In article ,
*** Fredxx wrote:
On 14/06/2021 11:07, Dave Plowman (News) wrote:
An audio circuit I found online and have been playing with has an odd
design (to me).

It's op-amp based running off a (separate) +/-15v supply.

There are on board caps across the supply, which is common enough.
10 and
0.1uF in parallel. But instead of going to ground, they are wired
across
the +/-15v. Does that do the job as well? Or serves a different
purpose?

I would say it is normal for 0V to be treated as ground and all supply
decoupling off that.

I can perhaps understand an instance where you might not want to impose
power supply noise/switch/ripple current on the ground rail. It depends
on the nature of the power supply.


Thanks for conflicting replies chaps. ;-)


It always "depends" on the detail. :-)

The PS shown is a conventional transformer type with a regulator for
each
rail and conventional smoothing.


Are the 2 parallel caps associated with this 'conventional smoothing'?

The circuit suggests high quality op-amps and caps (on the audio
side) so
I doubt it's just to save component count.


The only explanation I can thing of is the op-amps have very high
power supply rejection ratio and the idea is to minimise ground current.

Personally I would have used OV / GND as a PS common and had two caps.
There are ways of minimise the injection of PS noise currents.



Shame you can't point us to the circuits.* Even with your extra notes,
above, there are still many questions arising - not least if your notes
are incorrect. (It does happen!)

Most Op Amps applications are inherently PSU-ripple insensitive.


I managed to find this article, which features different power supply
decoupling and some reasoning behind the choices.
https://sound-au.com/dwopa.htm

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Old June 15th 21, 01:17 AM posted to uk.d-i-y
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Default An electronic question.



Shame you can't point us to the circuits. Even with your extra notes,
above, there are still many questions arising - not least if your notes
are incorrect. (It does happen!)


Most Op Amps applications are inherently PSU-ripple insensitive.


They are a design from Elliot Sound Products. But the published schematic
doesn't show the supply rail side of the design. You have to buy the PCB
to see it.

--
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To e-mail, change noise into sound.
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Old June 15th 21, 01:23 AM posted to uk.d-i-y
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Default An electronic question.

In article ,
Fredxx wrote:
I managed to find this article, which features different power supply
decoupling and some reasoning behind the choices.
https://sound-au.com/dwopa.htm


Now there's a thing. It's a design from ESP I'm referring to. ;-)

--
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Dave Plowman London SW
To e-mail, change noise into sound.
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Old June 15th 21, 09:07 AM posted to uk.d-i-y
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Default An electronic question.

Depends is the answer as always. Those will do something but surely there
have to be capacitors across each supply half?
I'm assuming that the 0v is in fact earth for the circuit. The only time I
saw capacitors in the manner you suggest was when the full supply was used
as it is as a separate supply to another circuit. One then has to be very
careful with your earth!
Small caps across split rails are common to stop RF pick up though, that is
all I have seen. What exactly is this circuit doing? Normally if its audio
bespoke chips can be used that do not in themselves need split supplies.
Brian

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"Dave Plowman (News)" wrote in message
...
An audio circuit I found online and have been playing with has an odd
design (to me).

It's op-amp based running off a (separate) +/-15v supply.

There are on board caps across the supply, which is common enough. 10 and
0.1uF in parallel. But instead of going to ground, they are wired across
the +/-15v. Does that do the job as well? Or serves a different purpose?

--
*He who laughs last, thinks slowest.

Dave Plowman
London SW
To e-mail, change noise into sound.



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Old June 15th 21, 09:13 AM posted to uk.d-i-y
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Default An electronic question.

I had a lot of trouble with some of Uncle Clive Sinclairs monolithic power
amps that operated in a bridge config, so the speaker was not really
earthed at either end. Worked great until one of power op amps, for in
effect that was what they were, popped its clogs and cooked the speakers and
firied the other chip.



Those circuits used to pop up in car output stages as I recall.
Brian

--

This newsgroup posting comes to you directly from...
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Blind user, so no pictures please
Note this Signature is meaningless.!
"Theo" wrote in message
...
"Dave Plowman (News)" wrote:
I can see that. Just odd I've never seen it used before.


FWIW it's not wrong to use separate capacitors V+ to 0 and 0 to V-, but
effectively what you have there is half the capacitance from V+ to V- and
double the ESR, so you're adding components to make it worse. It might
make
sense where there are single-rail loads running between V+ and 0 - for
example digital logic, which are more the kind of thing decoupling
capacitance is intended for (high frequency switching loads rather than
general audio ripple).

Theo





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Old June 15th 21, 11:35 AM posted to uk.d-i-y
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Default An electronic question.

On 15/06/2021 00:17, Dave Plowman (News) wrote:
Shame you can't point us to the circuits. Even with your extra notes,
above, there are still many questions arising - not least if your notes
are incorrect. (It does happen!)


Most Op Amps applications are inherently PSU-ripple insensitive.


They are a design from Elliot Sound Products. But the published schematic
doesn't show the supply rail side of the design. You have to buy the PCB
to see it.


Assuming that Fredxx has the right link, I think that you should take it
with a little pinch of salt. An article originated 2000, referring to a
50+ year old Op Amp design (great advance though it was) is the first
hint. Concerns about supply impedance at audio frequencies is another.
If the guy was writing about designing with Dynamic Memory, then he'd be
closer to the mark. A bit OTT for audio.

Incidentally, you attack power supply noise at the power supply. I
wonder if the last components in your proposed PSU are - electrolytic
and / or other capacitors across the outputs.

At least he isn't trying to argue that no semiconductor device will beat
a 12AX7 ;-}

PA


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Old June 15th 21, 01:16 PM posted to uk.d-i-y
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Default An electronic question.

On 15/06/2021 00:23, Dave Plowman (News) wrote:
In article ,
Fredxx wrote:
I managed to find this article, which features different power supply
decoupling and some reasoning behind the choices.
https://sound-au.com/dwopa.htm


Now there's a thing. It's a design from ESP I'm referring to. ;-)


It's comforting to see not everything I say is drivel :-)

I do suggest it is more typical to decouple everything to ground rather
than +ve to -ve. And I was trying to think of a possible reason why this
configuration might be chosen and not simply to save a couple of components.

I suppose extra decoupling could always be added afterwards if there is
any PS noise or a perceived advantage. Without knowing more about the
power supply it is difficult to call.


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Old June 15th 21, 01:24 PM posted to uk.d-i-y
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Default An electronic question.

On 15/06/2021 08:07, Brian Gaff (Sofa) wrote:
Depends is the answer as always. Those will do something but surely there
have to be capacitors across each supply half?
I'm assuming that the 0v is in fact earth for the circuit. The only time I
saw capacitors in the manner you suggest was when the full supply was used
as it is as a separate supply to another circuit. One then has to be very
careful with your earth!
Small caps across split rails are common to stop RF pick up though, that is
all I have seen. What exactly is this circuit doing? Normally if its audio
bespoke chips can be used that do not in themselves need split supplies.
Brian



A centre tapped transformer with a full bridge can provide a +ve and -ve
outputs, with either a single capacitor or two, as per:

https://www.tubecad.com/2018/02/10/F...r%20Supply.png

Since Dave said there were regulators, and I assume of the linear
variety, there will already be decoupling before these regulators.

Another reason for having two caps, and decoupling from +ve and -ve to
0V is that many regulators are unstable (and sing or create lots of
noise) and specify a certain capacitance with a certain ESR on their
output.

Without more details this is all lots of speculation.
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Old June 15th 21, 02:36 PM posted to uk.d-i-y
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Default An electronic question.

On 15/06/2021 10:35, Peter Able wrote:
Assuming that Fredxx has the right link, I think that you should take it
with a little pinch of salt.* An article originated 2000, referring to a
50+ year old Op Amp design (great advance though it was) is the first
hint.


More than a hint, since transistorss weren't invented then let alone opanps

Concerns about supply impedance at audio frequencies is another.
If the guy was writing about designing with Dynamic Memory, then he'd be
closer to the mark.* A bit OTT for audio.

Incidentally, you attack power supply noise at the power supply.* I
wonder if the last components in your proposed PSU are - electrolytic
and / or other capacitors across the outputs.

But you attck nouse ON the power supply wherever its being generated

At least he isn't trying to argue that no semiconductor device will beat
a 12AX7 ;


In 1950, he would be correct

--
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returns of conjecture out of such a trifling investment of fact.

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Old June 15th 21, 02:45 PM posted to uk.d-i-y
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Default An electronic question.

In article ,
Peter Able wrote:
On 15/06/2021 00:17, Dave Plowman (News) wrote:
Shame you can't point us to the circuits. Even with your extra notes,
above, there are still many questions arising - not least if your notes
are incorrect. (It does happen!)


Most Op Amps applications are inherently PSU-ripple insensitive.


They are a design from Elliot Sound Products. But the published schematic
doesn't show the supply rail side of the design. You have to buy the PCB
to see it.


Assuming that Fredxx has the right link, I think that you should take it
with a little pinch of salt. An article originated 2000, referring to a
50+ year old Op Amp design (great advance though it was) is the first
hint. Concerns about supply impedance at audio frequencies is another.
If the guy was writing about designing with Dynamic Memory, then he'd be
closer to the mark. A bit OTT for audio.


I'd not read that article before.

Incidentally, you attack power supply noise at the power supply. I
wonder if the last components in your proposed PSU are - electrolytic
and / or other capacitors across the outputs.


The PS shown is fairly typical of a regulated analogue type designed for
use with audio circuits.

I generally fit 0.1uF ceramic close to each IC between each of the power
supply rails and ground.

At least he isn't trying to argue that no semiconductor device will beat
a 12AX7 ;-}


PA


--
*Oh, what a tangled website we weave when first we practice *

Dave Plowman London SW
To e-mail, change noise into sound.


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