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Accidentally connected 3.5mm line out to RCA preamp out - could this have affected my gear?

jaytrinitron

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Hey all,
very basic question incoming. So I was stupid: When attempting to connect my Topping NX4 dsd DAC's 3.5mm line out to my Magni 3's RCA line in using a 3.5mm to RCA cable, I accidentally connected the other end to the preamp RCA outs instead. (So basically, a 3.5mm line out on the Topping was connected to the preamp RCA outs on the Magni 3 directly and two outputs were connected to each other). Then, while wondering why no audio was playing when both devices were turned on, I proceeded to max out the volume to the magni 3 and turn it back down again. Finally, I realized my mistakes, turned both devices off, and moved the cable, and upon testing everything appears to work ok. But I am wondering, did I damage either of my devices, or the cable?

I'm not entirely sure but my thinking goes something like this: The Topping NX4 dsd has low output impedance (as measured by Amir), and was outputting a strong signal to the magni 3's output, which also has a low ouput impedance... so does that mean the signal may have, er, gone up the wrong way, so to speak? (I apologize for how dumb this is).
 

RayDunzl

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If it still works...
 
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jaytrinitron

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If it still works...
It does appear to work but I am afraid I may have destroyed something in my gear that isn't as easily audible. I am also just curious as to what goes on electrically when this sort of thing happens.
 

DonH56

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Most all audio outputs include series resistors and various protection circuits. If it still works you are fine. Line-level stuff is relatively low-voltage and low-power so hard to hurt (yes, it can be done, don't ask how I know this). The only time I have seen latent defects be a problem is when static electricity hit an output; it started OK but gradually got worse (noisey/distorted) over time (hours/days).
 

restorer-john

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Line outs will most likely be fine in that situation.

Don't do the same with amplifier outputs however, they go 'bang' fast in that situation.
 
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jaytrinitron

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Line outs will most likely be fine in that situation.

Don't do the same with amplifier outputs however, they go 'bang' fast in that situation.

So what about preamp outs, then? Preamp outs are what the Magni 3 has.
 

mansr

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Line outs will most likely be fine in that situation.

Don't do the same with amplifier outputs however, they go 'bang' fast in that situation.
I have also seen amps emit smoke due to insufficient load on the outputs. There's just no pleasing those things.
 

DonH56

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Thank you both. I am still wondering what happens electrically when this sort of connection is made though.

Preamp output == line-level output, they are the same

Electrically you shorted the outputs; internally you'd have to see the circuit and look up component specs. Many line (preamp) outputs include series resistors to bolster stability and offer some short-circuit protection, often around 100 ohms. Then there is typically short-circuit protection built into the output buffers, both line and headphone. Consider that it is common for headphone outputs to be briefly shorted by the plug on the headphones whenever you plug them into the jack. And if the preamp died every time someone accidentally grounded the RCA center pin whilst plugging in the other end there would be a lot of dead preamps (etc.) around. Some sort of short-circuit protection, or at least tolerance for a short, is built in to every (competent) design. Manufacturers know accidents happen and they do not want to deal with an unhappy customer and repair for any reason.

In your case chances are the headphone output was lower in impedance and would try to control the output, dumping current into the preamp, and that would probably trigger its protection or just shut off the outputs through reverse-biasing the preamp's output drivers. It is extremely unlikely there would be enough voltage to exceed the absolute max specs of the outputs at either end and current would be limited by the designs so you should be fine. Speaking as one who has managed to do similarly dumb things a myriad of times over a decade or three I would not fret about it.

Speaker (power) amplifier outputs also normally include protection but often less robust, e.g. a fuse on the power rail, and IME are more likely to sustain damage from a short. Power amplifiers provide orders of magnitude more power (voltage and current) and it is harder to build in short-circuit protection and keep the output impedance very low. As John said, power amplifiers tend to go "bang" where a preamp or headphone output will shrug it off.

FWIWFM - Don
 
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jaytrinitron

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Preamp output == line-level output, they are the same

Electrically you shorted the outputs; internally you'd have to see the circuit and look up component specs. Many line (preamp) outputs include series resistors to bolster stability and offer some short-circuit protection, often around 100 ohms. Then there is typically short-circuit protection built into the output buffers, both line and headphone. Consider that it is common for headphone outputs to be briefly shorted by the plug on the headphones whenever you plug them into the jack. And if the preamp died every time someone accidentally grounded the RCA center pin whilst plugging in the other end there would be a lot of dead preamps (etc.) around. Some sort of short-circuit protection, or at least tolerance for a short, is built in to every (competent) design. Manufacturers know accidents happen and they do not want to deal with an unhappy customer and repair for any reason.

In your case chances are the headphone output was lower in impedance and would try to control the output, dumping current into the preamp, and that would probably trigger its protection or just shut off the outputs through reverse-biasing the preamp's output drivers. It is extremely unlikely there would be enough voltage to exceed the absolute max specs of the outputs at either end and current would be limited by the designs so you should be fine. Speaking as one who has managed to do similarly dumb things a myriad of times over a decade or three I would not fret about it.

Speaker (power) amplifier outputs also normally include protection but often less robust, e.g. a fuse on the power rail, and IME are more likely to sustain damage from a short. Those provide orders of magnitude more power (voltage and current) and it is harder to build in short-circuit protection and keep the output impedance very low. As John said, power amplifiers tend to go "bang" where a preamp or headphone output will shrug it off.

FWIWFM - Don

Thanks, I appreciate this response, if only for my peace of mind. :p
 
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