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-   -   Salas DCG3 preamp (line & headphone) (https://www.diyaudio.com/forums/analog-line-level/296406-salas-dcg3-preamp-line-headphone.html)

lykkedk 6th October 2016 04:53 AM

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Salas.

Looking very pleasant, your'e freinds gear :)

Well... I will be done with my preamp software-layout in a couble of day's (I think :D), so next project will be the psu.

I have at moment no headphones, but i would like to make the preamp capable of driving fancy ones, if i ever got some.

Do i need 1 or 2 psu's then ?

The picture i have attached, shows 2 psu's right?

Jesper.

Salas 6th October 2016 10:53 AM

Drive in a heavy load is a matter of the output stage's current swing ability before clipping and not about mono psu or double mono psu. When you bias at 100mA with 17V rails it can give 156mW on 32 Ohm but when at 150mA it will be 360mW for instance. As you move to higher impedance cans it becomes more of a voltage swing thing than current. Both bias examples will do 400mW on 300 Ohm and 200mW on 600 Ohm when running on the same 17V rails.

Assuming that any supply arrangement chosen will be correctly covering the current demands that is. Two supplies is a quality choice to minimize the interaction of channels across a common supply. Especially when they are pulling high current peaks.

Our yesterday auditions were purely in line preamp's role where the output stage current swings are silly low anyway. For some reason this arrangement I prepared gives a subjective result that my friend maintains is easily better than with his beta build when he compared them on his own. There he has a tight matrix board layout, a single 500mA CCS shunt supply, two single op-amps, and a remote controlled pot. Both preamps run at same 100mA bias. Is it the different pots or the double DCSTB or the layouts or something else he is not sure at the moment but he will investigate his version better by building and comparing solutions as he said. Anyway one thing is certain, that the specific pre+psus pcbs system as developed arranged and proposed to be done in this thread are doing the business very well.

Yes the picture shows a two psus board (four polarities). The DCSTB board will be made as pictured plus two bleeder resistors I added across the front. One board but breakable in the middle. To can be arranged in a box to anyone's wish. I prefer them unbroken facing the DCG3 using short rail wires between them.

lykkedk 6th October 2016 01:39 PM

Quote:

The DCSTB board will be made as pictured plus two bleeder resistors I added across the front. One board but breakable in the middle. To can be arranged in a box to anyone's wish. I prefer them unbroken facing the DCG3 using short rail wires between them.
Salas... fantastic answer :)

Whatever i deside, i would like to have the two bleederresistors, on my DCSTB-board, if you would kindly care to show me, how they are attached!

And another thing. What about the DCG3 schematic, are there any changes to that, as for now?

... More quistions to come (for sure ;))

Jesper.

Salas 6th October 2016 06:33 PM

Schematics changes no. Bleeders go one across each output psu cap. After I will have also examined the rack ready preamp further as a system and my notes will be richer I will post a PDF that will have the schematics the boms and the practical points concentrated in one doc. As I promised from the start.

lykkedk 8th October 2016 09:47 AM

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Hi here.

I did a clone of the PCB, it's layout is with "hand draw" in mind, so a little more space around traces/part is needed :)

About GND-plane (which isent drawn yet), i am in doubt, if it should be connected to GND ?
Also, is it something one do, for avoiding "hum"?

RED traces = TopLayer
BLUE traces = BottomLayer

all here have a good saturday ;)

Jesper.

lykkedk 8th October 2016 09:57 AM

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Bad picture... Sry...

Here is corrected one :

Jesper.

AndrewT 8th October 2016 09:59 AM

"isent" should read isn't.
Short for: is not.

AndrewT 8th October 2016 10:02 AM

The audio does not need to be connected to Protective Earth. Is that what you meant with GND?
Quote:

i am in doubt, if it should be connected to GND ?
The enclosure of mains powered equipment needs to be connected to PE for safety.
All exposed conductive parts need to be connected to that protected enclosure for safety.
Neither of these have anything to do with audio.

Get your audio circuits to work properly without any enclosure and without any connection to mains earth.

Then assemble your package so that it is safe to use.

lykkedk 8th October 2016 10:15 AM

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I got it confussed up i think :confused:

What i meant is, that schould i connect the GNDPLANE to GND on PCB ?

Nothing about safety GND or like.

AndrewT 8th October 2016 12:55 PM

The ground plane is just a very wide trace that happens to cover the whole PCB.
If you have a separate ground trace on another layer then you need to connect these somewhere.
That chosen location must not force a trace to carry two different AC currents that could cause an undesired interaction between the voltage drops.


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