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Old 8th October 2010, 08:07 AM   #21
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Fair point...

But for me, the objective is what I learn more than anything else. So given I understand how to generate a virtual ground via the voltage divider setup of the resistors, and I've never setup a virtual ground with a op-amp/active circuit, I'll probably give that a try.

And to be honest, I keep looking at that voltage divider arrangement, and intuitively I don't understand why that voltage divider is what defines the ground point between the rails, and not the varying resistance over both sides of the load (ie the amp)?

Perhaps I'll set it up in such a way that I can try it with and without the active virtual ground and see what happens....
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Old 8th October 2010, 08:53 AM   #22
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Default Quad 606 floating ground

...I found the schematic for the Quad 606 (I have no idea about the details of that amp...) floating ground setup. Can anyone give me a bit of insight as to the relative merits of the approach we've been discussing and this circuit?
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Old 8th October 2010, 10:05 AM   #23
AndrewT is offline AndrewT  Scotland
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the Quad 606 shows an active virtual ground.

Few components and little complexity.
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Old 8th October 2010, 10:10 AM   #24
AndrewT is offline AndrewT  Scotland
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Default Safety Earth & Virtual Ground

The chassis, if conductive, MUST be connected to Safety Earth (Protective Earth).

If the speaker ground in Quad's 606 schematic has an exposed conductive part then Speaker Ground MUST also be connected to chassis.

Similarly, if the input socket has an exposed conductive part, it too MUST be connected to Chassis.

This is why I asked in post13, "do you need to? "
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Old 8th October 2010, 03:53 PM   #25
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I apologize if i'm slow on the uptake...

By "do you need to" do you mean do you need to connect the virtual ground to the chassis ground (and hence to the earth on the mains plug)? or do I misunderstand?

To clarify by what I meant as safe grounding earlier, it pretty much just echo's what you just said. If you can touch it, and it conducts, then it should be connected to earth. Yes, absolutely. Is your point that you don't need to attach the virtual ground to the chassis ground (and hence earth), and that there's some sort of advantage to wiring the thing up this way?

Last edited by aspringv; 8th October 2010 at 04:00 PM. Reason: clarity and then an apparent bout of dyslexia
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Old 8th October 2010, 04:00 PM   #26
qusp is offline qusp  Australia
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Quote:
Originally Posted by godfrey View Post
Unfortunately the absolute maximum supply voltage for both LT1970 and LT1210 is 36V (+-18V), so neither can be used here.
agreed, I had misread the initial post as 24v, not +/-24v. they can be placed back to back for higher current, but voltage is a nogo. pity that its an excellent and quite novel chip that keeps part count to a minimum.

what you can do though is use it as a straight up opamp driving 0v from the center of a divider buffered by a mosfet or paralleled if higher current is needed

Last edited by qusp; 8th October 2010 at 04:03 PM.
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Old 8th October 2010, 04:02 PM   #27
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what do you think of the quad schematic? I'm curious to get feedback on efficacy as it'll be cheaper to do, vs the use of a LM3886?
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Old 8th October 2010, 04:11 PM   #28
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...just got your edit around the mosfet buffer. Does that result in a scalable solution - ie depending on cost I can set up a solution thats good for whatever current it has to deal with?
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Old 8th October 2010, 04:33 PM   #29
Salas is offline Salas  Greece
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Title changed into what asked by the thread starter.
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Old 8th October 2010, 06:53 PM   #30
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by aspringv View Post
By "do you need to" do you mean do you need to connect the virtual ground to the chassis ground (and hence to the earth on the mains plug)? or do I misunderstand?

To clarify by what I meant as safe grounding earlier, it pretty much just echo's what you just said. If you can touch it, and it conducts, then it should be connected to earth. Yes, absolutely. Is your point that you don't need to attach the virtual ground to the chassis ground (and hence earth), and that there's some sort of advantage to wiring the thing up this way?
if the audio terminals & connectors are not composed of exposed conductive parts then I believe the regulations allow the Virtual Ground to be isolated from the Chassis.

However,
what happens at the other end of the cables that are connected to this amplifier?

For the Safety of other users, visitors, children, I would always connect these insulated parts to the Chassis by way of a Disconnecting Network.
The advantage of the Virtual Ground is that all 3 poles of the dual polarity supply are isolated from the chassis. This leaves open the designer's choice of which to connect to Chassis, It does not have to be the Virtual Ground that gets the connection. You may obtain better performance by using one of the +/- voltage poles to the chassis.
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