What is the safe are for impedance values?

[keantoken]

Hello.

I'm wondering what the safe-area values are for commercial impedance values so that I can connect a circuit up to my stereo without exploding anything. I've heard it varies, but I've never gotten anything disputably solid.

Thank you for your time,

- keantoken

[Iain McNeill]

Can you expand on what you're trying to do a bit?

I'll assume you're talking about amplifiers and speakers where 8ohm speakers are safe on just about any amplifier but as impedance drops 4ohms, 2ohms, some amplifiers could output too much current and exceed their thermal dissipation limits.

It depends on many, many factors. That's why you've never seen a definitive answer - there just isn't one.

Having said that, class A amplifiers are probably the "safest" - they'll blow your speakers before they self destruct. Class D amps will blow their fuse before they self-destruct. Class B depends on what is the weak link out of the amp design, its power rating, its heatsinking, the speaker design, driver choice and the signal you're playing.

[keantoken]

Well, first of all, I'm not talking about speaker outputs, I want to test one of my circuits by plugging it into the input of my stereo or soundcard so that I can record and listen to how it sounds.

I want information on most of the different impedances in the commercial world like phono, video, microphone input, headphones, etc.

I'm asking this so that I can expand my database of knowledge and hopefully know this beforehand when I'm trying to do another project.

Thanks for you input,

- keantoken

[dave_gerecke]

Hello Keantoken, you would have to post some sort of information as to what circuit you are trying to plug in, and what circuit you are connecting it too. As Iain indicated there is no definitive answer. The influence here is Ohm's law. Whether something can be connected depends upon whether you will have too much voltage or current from the sending circuit for the receiving circuit to handle. I would suggest posting schematics or specifications of equipment for people to be able to help you.

Peace,

Dave

[gain]

imo, if your circuit can drive 10k loads without significant attenuation (aka ~1k output impedance), you shouldn't have any problems plugging it into a stereo or soundcard. line level input impedance on most audio equipment usually ranges from ~10k to almost infinity.

[gain]

Originally posted by keantoken
so that I can connect a circuit up to my stereo without exploding anything.

to help make sure nothing explodes, wire a 100k pot between the circuit and the stereo. connect the wiper to the stereo's (+) input terminal (middle RCA pin), connect one end of the pad to ground, and the other end of the pad to the output from the circuit.

turn on the stereo with the 100k pot turned all the way down (wiper touching grounded side), then VERY SLOWLY turn the pot up until you start to hear sound. this will protect the stereo from your circuit applying too much drive to it.

[AndrewT]

Hi Keantoken,
is your native language english?
Try asking a simple question and not jumbling a series of questions into one sentence.

[keantoken]

My circuit has no problem driving a 10k load. So I am assuming you mean that it really rests on how much voltage you're pumping in?

I'm not expecting to be delivering any more than 100mV, and the output voltage isn't dependent on the output impedance. So I guess the question I really need to be asking here is how much voltage can commercial equipment take before going boom?

Sorry for having to put up with me, I have a tendency to write and speak in a more indirect manner because I assume people can understand me well.

- keantoken

[AndrewT]

Power amps can easily take 100mVac without risk of damage.
Similarly line level pre-amps can take 100mVac and no damage.
If either of these are fitted with Input DC blocking capacitors then they can survive 100mVdc as well.
Specialised preamps, like microphone and MC +MM cart amps will need to be checked to ensure they can cope with 100mVac. They will almost certainly overload but whether they would be damaged is a difficult question.

[keantoken]

Hmm. Well I guess that clears most of it up, thanks for you help, everyone.

- keantoken