Designing the pcb

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
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Re: Designing the pcb

Post by JR. » Sun Feb 22, 2015 9:24 am

Signal ground is more signal than ground in some situations.

Power supply grounds should be looked at like plumbing. Current flows in and out of power supply pipes while single ended loads will dump current into ground drains to return to the power supply.

Grounds also serve as shields to absorb noise to keep that noise out of the signal output.

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Re: Designing the pcb

Post by mediatechnology » Sun Feb 22, 2015 10:40 am

The supply bypass on every chip would go to the supply ground.
Is this still a single-supply design?
If so, the supply bypass for op amps should be from Vcc to Vee. (e.g. pins 8 and 4 of a dual op amp)
Although Vee connects to DC supply ground it is better practice to have the bypass capacitors - at least the smaller ones - connect directly to the device pins.
Taking a capacitor from Vcc to a dirty ground bus might then place a lot of series inductance between the bypass cap and Vee.
Better to have the C across the device pins and then extend Vcc and Vee to their respective supply and DC return.

If you have a limiter in this (or an overload indicator) be mindful of the peak current in the detector's capacitor.

Also +1 to what JR said.
In a single-supply design some signal currents may return to the rail-splitter and some to the Vee/DC/signal ground.

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Re: Designing the pcb

Post by carlmart » Thu Feb 26, 2015 10:16 am

No, even if I am not too sure of the decision, we jumped to a split supply design.

Sorry I didn't inform that when I opened the thread, but I'm glad you remember it.

The split supply is more "conservative", IMHO, and I'm not sure it will serve well my original purposes for this box project.

But it will allow using it as an audio preamp alone, and perhaps I can get to power a DSLR camera using the +12v from the supply.

As the original power would come from an external 14.4v battery, we simply feed it in through the XLR-4 connector and send it to the separate DC outputs.

I'm not too sure what voltage to go to in order to maximize battery life: +/-9v, +/-12v or +/-15v. Also what DC-DC to pick is not a closed matter yet.

Some suggest using a pump inverter, others to go directly to a +/-V supply, with an LT chip. For the prototype we will be using the LT demo card, that outputs +/-12v.

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