Changing ground reference of general electronic devices.

This entire thread isn't going well at all. I don't think anyone established what part of the world the TS/OP is in.
There's a CHANCE that -220 is Neutral of some European system rather than the L1 or L2 side of a split phase system of the US.

Some people call the terminals of a battery +12 and -12 which it isn't.

All of you have to sort that out before continuing.

Where is 0 V?
 

WBahn

Joined Mar 31, 2012
25,255
I'm pretty sure the TS indicated that they were in New England (Connecticut?). Maybe that was in another thread. Anywho, many of the responses have been very explicit about only being applicable to the U.S. (or similar) systems and the TS hasn't batted an eye (or finger, as the case may be).
 
the TS said:
I have a dac.
It uses opamps to null the DC at its output, therefore allowing direct coupling to amplifiers without the use of a capacitor.
The amp I want to couple it to has -220v (below earth ground) bias voltage on the input.
Assume audio AMP
Assume DAC.
Assume 120 VAC Power
Assume this offset is 220 Volts DC

Question: How to you connect ANY conventional audio source to this amp without letting out any smoke?

Question2: Has this voltage been measured? Question is measured to what?

So, a receiver comes in for repair (2 prong cord) and what was found is the primary transformer had a short to ground, so now we have a messed up reference. it might play AM/FM fine, but you can't connect say a DVD player or you get shocked.

I also have a hard time figuring out why this particular amp would have a -220 DC power supply in it at all? SMPS generally puts it at 336V DC at least somewhere. I hope you won't tell me this is a 50 W amplifier?

Is there a possibility that the amp is defective? Is the meter defective?

In AC, there's possibilities of what's called a phantom voltage, As a simple example, you can have a power strip with symmetrical capcitors as a line filter, but somehow the earth ground connection to the wall is broken. This means that the stuff plugged into the strip may see 60 VAC UNTIL you draw say a milliamp from it. Then it drops to zero.

What you think are Isolated supplies can give rise to phantom voltages due to leakage paths. A 120 V mains transformer may not be "isolated" to 3000 V.

So, it's like attach a DAC to an output and the DAC has no connnection to ground everyone seems to be happy. But the USB conenction, if it has one, is connected to ground. It would still be relatively happy.

But the 220 VDC is generally way to high. I've seen some electronic instruments that would let you raise the negative input 30 v above grund, but that's it.

-220 VDC offset just doesn't make any sense. Especially a DC offset. The reason that it makes no sense is that any source with a grounded input should/could blow something up or at the very least be shock hazard.

taking a look at my stereo it's all 2 prong plugs. The connections to earth are in two places. The turntable (thats for hum), so it isn;t really ground and the FM coax, which isn't quite ground either. It should be potential free. The antenna gets grounded and it should be earth.

So, in a sense if something was "defective", there would be an offset that you might not know about because all of the metal pieces are elevated.
The coax would help here, so it could not happen.

How about then:
What model DAC?
What model Amp? And we'll hope it's not a "flame or plasma speaker". http://excelphysics.com/products/arc-plasma-speaker-kit
 

grahamed

Joined Jul 23, 2012
100
Hi

I don't think this thread will ever go anywhere - it started as ill-defined nonsense and hasn't really moved on.

"Although technically the output is 3 pin XLR so one of the pins is "ground". Would leaving this pin disconnected from the amp cause any issue?"

Spectacular! The designer probably "assumed" the pin/connection was required.

"The input is usb from the computer, digital is basically PWM right? So a capacitor should work here?"

Digital is basically PWM? Use a capacitor? bah, no way, or maybe use a couple to lose the -220V DC instead?

Where does this -220V DC come from? What's it for? If it were a valve/tube amp I might expect +220V though I have seen large negative biases. Maybe it is some bizarre golden-eared audiophile attempt at a constant current source using only a high-voltage and a large resistor.

Did the designer of the amplifier ever expect anyone to connect to this -220V point? If so did s/he include capacitors? Why?
 

Thread Starter

coinmaster

Joined Dec 24, 2015
502
I don't think this thread will ever go anywhere - it started as ill-defined nonsense and hasn't really moved on.
I don't think we are reading the same thread. It's run its course and has pretty much been concluded. I'm always up to talk about more solutions though.

Spectacular! The designer probably "assumed" the pin/connection was required.
Or because 3 pin XLR is a standard interconnect pinout.
The pin is connected to amplifier ground therefore joining the grounds of DAC and amp. I'm going to assume, this might possibly be because the dac could be chassis grounded? This is a general assumption of course, my DAC has a 3 prong power pin so I'm pretty sure it's earth grounded but I'm wondering if there's some obscure reason why not using XLR ground pin might cause an issue.

Digital is basically PWM? Use a capacitor? bah, no way
Why?
 
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Thread Starter

coinmaster

Joined Dec 24, 2015
502
Hello again, I've circled back around to this topic in my project. At this point I need to decide whether or not I am going to continue with this floating DAC.

My plan of attack is to buy an isolation transformer and then use a leak resistor to set the new ground reference
Screenshot_53.png
I'd isolate the entire DAC inside an enclosure.

Then I could use the optical input to interface between dac and computer.
The problem with the optical interface is the sample rate with optic cable is pretty low.
The way I understand it, the more sample rate you have, the more headroom you have for software volume control without sample reduction within hearing range. So I would prefer to use a USB cable but I would have to isolate the voltages from the computer.
I was thinking of using a capacitor or something but I'm not sure if it's that simple. I'm not sure what kind of connections are involved with the usb interface and what kind of duty cycle the signals have. Is there some way I can find out?

This is the DAC http://www.audio-gd.com/Pro/dac/NFB12015/NFB12015EN.htm
 
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Thread Starter

coinmaster

Joined Dec 24, 2015
502
Direct coupling between stages. The B+ of the input stage is at the bias voltage of the output stage which means the bias of the input stage is way below 0.
 
Direct coupling between stages. The B+ of the input stage is at the bias voltage of the output stage which means the bias of the input stage is way below 0.
What's good for 'DC' amplification is both unnecessary and cumbersome (to say the least) applied to AF amplification -- IOW, unless 'flat' response to the low milliHertz and 'beyond' is required - please consider use of an appropriately designed amplifier... If, on the other hand, such response is indeed required, please consider proper instrumentation amp design (meaning, among other features, implementation of a 'balanced' input buffer)...

Best regards and good luck
HP
 
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Thread Starter

coinmaster

Joined Dec 24, 2015
502
Yeah well my personal experience says different. I've learned that is it useless to listen to other peoples opinion on the whole "cap vs no cap" argument.
 
Yeah well my personal experience says different. I've learned that is it useless to listen to other peoples opinion on the whole "cap vs no cap" argument.
By the same token I've learned it's useless to attempt intellectual discussion with confirmed empiricists -- That said, there are other ways...;)

Best regards - and, sincerely, good luck!
HP:)
 
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Aleph(0)

Joined Mar 14, 2015
597
By the same token I've learned it's useless to attempt intellectual discussion with confirmed empiricists -- That said, there are other ways...;)

Best regards - and, sincerely, good luck!
HP:)
By the blood of John Locke I say TS is audiophile:rolleyes:!

HP I say it's cool to tell him he's on sinking ship but I wouldn't stay around and drown to prove point:D!
 

Thread Starter

coinmaster

Joined Dec 24, 2015
502
I love how easily things get off topic when I mention direct coupling. My entire interest in electronics spawned from the massive improvements I heard by removing caps from the signal path. Most people that claim there is no difference don't even try it for themselves or base their opinions on limited testing. I trust my own experience and my own ears over the word of people on the internet, sorry.
I guess I should have learned by now that mentioning this subject in a thread that is trying to get something done is a thread killer. I'll go ask somewhere else for advice.
 
I love how easily things get off topic when I mention direct coupling. My entire interest in electronics spawned from the massive improvements I heard by removing caps from the signal path. Most people that claim there is no difference don't even try it for themselves or base their opinions on limited testing. I trust my own experience and my own ears over the word of people on the internet, sorry.
I guess I should have learned by now that mentioning this subject in a thread that is trying to get something done is a thread killer. I'll go ask somewhere else for advice.
At considerable risk of whipping a dead horse...
Were you to take a theoretic (as opposed to empirical) approach you would discover your goals to be readily achievable via practical means, in addition, I daresay, to the fact that your present design errs further from 'ideal' than you seem to believe...

I think I will never understand why some people prefer 'trial and error' to comprehension and, hence, design? --- If you're happy with it, then sincerely, more power to you!:) --- Speaking for myself, I cannot offer advice and/or assistance in bad conscience...

Best regards
HP
 

Thread Starter

coinmaster

Joined Dec 24, 2015
502
If it was a sound science then people wouldn't be constantly arguing about it for decades. I don't put any trust into the science since it seems more likely at this point that its just convenient to cite the 'known' textbook science then for people to experiment and hear the results for themselves. I am not a believer in snake oil but as someone that has actually done the work of experimentation the results speak for themselves.

Which is why I am doing further testing by seeing what happens if I completely remove every capacitor from the direct signal path but I guess I'll ask elsewhere since sadly people can't keep their heads focused when this subject is mentioned.
 
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cmartinez

Joined Jan 17, 2007
6,785
Which is why I am doing further testing by seeing what happens if I completely remove every capacitor from the direct signal path
I, for once, am very interested in learning about your results. And would appreciate it if you could post comparative data on both caps vs no caps versions of the audio circuit.
 
I, for once, am very interested in learning about your results. And would appreciate it if you could post comparative data on both caps vs no caps versions of the audio circuit.
Ditto!:)

But @coinmaster please! Be true to your cause - to wit; let's see some quantitative data (obtained, for instance, via a SA -- as opposed to your 'ears') -- Anecdotal 'evidence' is as no evidence whatever...

it seems more likely at this point that its just convenient to cite the 'known' textbook science then for people to experiment and hear the results for themselves.
I, for one, am not advocating blind acquiescence or deference to convention - but, rather, reasoned support of your assertions!

If it was a sound science then people wouldn't be constantly arguing about it for decades
The 'argument' (such that it is) for direct coupled AF amplification circuitry has, to my observation, very little to do with science and everything to do with that 'species' of empiricism which, IMNSHO thinly guises something akin to iconoclasm for its own sake:rolleyes: --- Again - let's see some quantitative data!:)

To another point -- your assertion that our insistence upon consideration of your application/direction constitutes a 'change of topic' is curious and, frankly, in my opinion, 'comes off as' preemptively defensive:confused:...

For all that -- should you indeed be right - it is a trivially simple matter to demonstrate as much! -- Ya see - truth is a bit like rain - it doesn't care who gets 'wet'!:cool::cool::cool:

Best regards
HP:)
 
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