Topic: ohm...

[yug du nord]

don't know where to ask this, so here it is. 

does anyone have an understanding of ohms?  my pre has dual-1/4" balanced outputs @ 600ohms, and an 1/8" unbalanced output @ 50ohms.  what's the difference?

thanks.

this same question is asked in the "Pre's, AD's, Processors" forum as well.  didn't know where to ask, so i asked in both forums.  sorry for the double space.

[KLowe]

same thing here...
I have two sets of cans.
the Beyer DT 990 pro is 250 ohm
the Sennheiser 280 pro is 64 ohm

....now I can tell you the price difference so I assume more ohms is a good thing...but I have no clue as to why.

[yug du nord]

same thing here...
I have two sets of cans.
the Beyer DT 990 pro is 250 ohm
the Sennheiser 280 pro is 64 ohm

....now I can tell you the price difference so I assume more ohms is a good thing...but I have no clue as to why.

The Busman BSC1's have an impedance rating of < 200ohms.  I know that "low impedance mics" are rated at < 600ohms.  Which I think most mics we use in the field are considered?

[aegert]

Ohms in this case is a term of impedance = Z it is an aggregate number representing the combination of Capacitence, Inductance and Resistance of a given system..

You typically want to match the impedance of the devices at either end of a transmission line...

Now thats what I learned in transmission line theory in EE school ROFL... 'Bout all I remember LOL


A

[KLowe]

so..... it would be "ideal" for my headphone amp to have 280 ohm to match my earphones?

[yug du nord]

Ohms in this case is a term of impedance = Z it is an aggregate number representing the combination of Capacitence, Inductance and Resistance of a given system..

You typically want to match the impedance of the devices at either end of a transmission line...

Now thats what I learned in transmission line theory in EE school ROFL... 'Bout all I remember LOL


A

so is 600ohms better than 50ohms?  or does it only a matter of matching devices?

[aegert]

In the headphone world you really are going to have a tough time matching the impeadence of the headphones to the amp... You really just need to make sure the  amp can drive the headphones.. If you have a lowers impedance in your head phone it will be easier to drive.. so My senn 595's @ 50ohms or ultrasone pro750's at 40ohms are louder from my headphone amp than  the senn 650's @ 300ohms...

A

[KLowe]

In the headphone world you really are going to have a tough time matching the impeadence of the headphones to the amp... You really just need to make sure the  amp can drive the headphones.. If you have a lowers impedance in your head phone it will be easier to drive.. so My senn 595's @ 50ohms or ultrasone pro750's at 40ohms are louder from my headphone amp than  the senn 650's @ 300ohms...

A

aaaaaaaaaaahhhhh   i see...............

+t

[DSatz]

ouch ouch ouch ouch aegert, watch out--transmission line theory is for radio frequency circuits, or audio frequencies in very long lines such as transcontinental phone lines. Apart from that, though, we don't use matched impedances in audio any more--not since Western Electric stopped being the dominant manufacturer of studio equipment.

In short, we use "voltage transfer" rather than "power transfer," and that requires that the source impedance be low and the load impedance be at least an order of magnitude higher than the source impedance.

Unfortunately this gets gummed up in spec sheets a lot. Some manufacturers tell you what load impedance their equipment can work into--i.e. the minimum recommended load impedance of the other equipment that you're going to use--and they call it the "impedance" of their own equipment. That is very confusing and not straight talk at all, but unfortunately it's quite common especially with gear from the Far East; this problem goes back decades.

If in fact the output impedance of a mike preamp is really 600 Ohms I'd be a bit surprised. That's a little high. I think it's more likely that they're giving 600 Ohms as the lowest impedance that the input of the next item in the signal chain can have, but I could be wrong--what preamp are we talking about?

--best regards

[KLowe]

DSatz....what does OHM mean as far as headphones go?

....does a Beyer dynamic with an ohm of 280.....need more than 280 to function properly...

Please expand on OHM and headphone/speakers if you can.

Thanks.

K

[DSatz]

mshilarious, your reply is spot on; thank you. I actually think it's good to specify what an appropriate load impedance for a piece of equipment might be. I'm only complaining when manufacturers give that as the "impedance" of their own equipment, since that confuses the heck out of a lot of people. For example, some manufacturers might say that the impedance of their microphone is "600 Ohms" when they really mean that the microphone should always be looking into a load of at least 600 Ohms (at the input of any preamp, mixer or recorder that you connect it to).

If a microphone really had a 600 Ohm output impedance, then it should only be connected to an input that's at the very least 3 kOhms, and preferably 6 kOhms or greater. But studio microphones are supposed to have an output impedance of 200 Ohms or less, by European standards anyway.

The concept of "impedance matching" is simply out of place in any discussion of baseband analog audio in the post-World War II era. And yes, among other things that implies that many ads for high-priced cables in Stereophile, etc., are based on technical nonsense whether the writers of those ads realize it or not. It's just Ohm's Law in action. If audiophiles in general understood Ohm's Law, which is really not hard to learn, it would simple things up a whooooooole lot in this business ...

--best regards

[yug du nord]

If in fact the output impedance of a mike preamp is really 600 Ohms I'd be a bit surprised. That's a little high. I think it's more likely that they're giving 600 Ohms as the lowest impedance that the input of the next item in the signal chain can have, but I could be wrong--what preamp are we talking about?

Thanks all for the fantastic input...  lots of good knowledge here! 

I am specifically talking about an Applied Research and Technology (A R T) USB Dual Pre.  It's specs state that the:

:Input Impedance   > 300K Ohms (1/4" input)
                           > 4K Ohms (XLR input)

:Output Impedance 600 Ohms (balanced 1/4")
                           50 Ohms (unbalanced 1/8")

[DSatz]

OK, with ART anything is possible; they make (in my opinion) some rather strange design decisions at times. It's quite possible that the specs mean what they say, and that the output impedance of their balanced line outputs really is 600 Ohms. If so, that's not necessarily a problem as long as you don't try to connect those outputs to equipment with too low an input impedance (less than 3 to 6 kOhms).

You're probably using the 50-Ohm headphone output for connection to unbalanced playback equipment anyway, no? If so, then this whole bit of strangeness needn't concern you.

--best regards

[yug du nord]

OK, with ART anything is possible; they make (in my opinion) some rather strange design decisions at times. It's quite possible that the specs mean what they say, and that the output impedance of their balanced line outputs really is 600 Ohms. If so, that's not necessarily a problem as long as you don't try to connect those outputs to equipment with too low an input impedance (less than 3 to 6 kOhms).

You're probably using the 50-Ohm headphone output for connection to unbalanced playback equipment anyway, no? If so, then this whole bit of strangeness needn't concern you.

--best regards

I'll have to try and figure out what the input impedance is on an SBM-1(RCA's) and Hi-MD(1/8")...  I've been running the balanced 1/4" outputs > RCA's on Sony SBM-1.  And also balanced 1/4" outputs > 1/8" input on Hi-MD.  When I've ran 1/4" output > 1/8" input on Hi-MD, I've been getting "phantom track marks"...  many of them.  Could that be a result of this issue?  Would I be better off using the 1/8" output from preamp > either RCA's (SBM-1) or 1/8" (Hi-MD)? 

Thanks again...

[yug du nord]

Well the SBM-1's line-in (phono jack) has an impedance of 47kilohm.  Not sure about the Hi-MD's line-in (1/8") yet...  it might be 5k ohm (not sure if that's for the line-in or mic input...  or if it's even correct?). 

Still tryin' to figure out if I should be using the 600ohm output or the 50ohm output?  It'll probably take me a bit to grasp what y'all are saying...  thanks again for all the heady input!

...mshilarious...  is there an issue with the ART being a USB pre?

[morst]

Uncleyug asked about which preamp output to use over in the "Upper Midwest" thread, and I made a fairly detailed reply, which I will post here.
One thing I will add before I paste in my comments from the other thread, is to reiterate the comment that headphones with very low impedence will be thirsty for current (and hence, power) so a dedicated headphone amp will help them sound their best.

anyone have an understanding of ohms?  my pre has dual-1/4" balanced outputs @ 600ohms, and an 1/8" unbalanced output @ 50ohms.  what the difference?

I know enough to be dangerous. Ready for the long version??!

Ohms is a measurement of resistance to direct current (DC) flow, or in the case of alternating current (AC) signal like an audio signal, the function is called Impedance, and it's measured in Ohms. The two most important tidbits I remember from high school electronics class are Ohm's Law and the power formula (voltage in Volts * current in Amperes = power in Watts)
Ohms's Law: where I is the current in amperes, V is the potential difference between two points of interest in volts, and R is a circuit parameter, measured in ohms (which is equivalent to volts per ampere), and is called the resistance.

Essentially, what it means is that a "high impedance" circuit will have less current flow than a "low impedance" one at the same voltage level- in other words, a low impedance input is thirsty for more juice than a high impedance one.

Now with regard to outputs - the important thing about audio is the "balanced" vs "unbalanced" - To balance a circuit, there has to be three conductors. One is the ground, or zero reference. The other two are called plus and minus. Plus is your audio signal, compared to ground. Minus is a phase-inverted version of plus, and it's basically used as a safety copy at the receiving input in order to cancel any noise induced along the cable. This is how microphone cables with 3 conductors can be used to carry signals extremely long distances (1/4 mile is not impractical!)



Now when you say you have an unbalanced output at 50 Ohms, I bet you are skipping something. Unbalanced outputs are usually in the 50K Ohm range. This means that the output only sends a little bit of current for each voltage change (think of Voltage as water pressure, and Current as rate of water flow)

Normal home (consumer) audio connections are all unbalanced. Your 1/8" mini output is most likely going to be a normal unbalanced, two-conductor "Tip-Sleeve" audio output. Your 1/4" balanced output is going to be a three-conductor "Tip-Ring-Sleeve" output. If your recorder or A>D converter has unbalanced inputs, it will be easiest to use the 1/8" output on the preamp. If your recorder or A>D has XLR connections you will probably want to use an adaptor to take advantage of the balanced circuit.