# 8E2?

Discussion in 'General Electronics Chat' started by Jaguarjoe, Feb 6, 2013.

1. ### Jaguarjoe Thread Starter Active Member

Apr 7, 2010
770
91
I'm still a body end dot guy so this one is new to me:

What is the value of an 8E2 resistor? It can't be 8^2, and if it was 8.2Ω, it should be 8R2. Or, as usual, am I missing something obvious again?

I'm like that Farside kid trying to enter the Engineering Bldg. He was pushing on the door with all his might while the sign on the door said pull.

It is an isolation resistor at the output of a 5532 opamp driving a 32Ω headphone from a 4.5v supply.

Is this explained somewhere?

Thank you,

Joe

2. ### tracecom AAC Fanatic!

Apr 16, 2010
3,939
1,430
I never heard of it either, but when I google 8e2 resistor, I get a lot of hits for 8.2 Ω resistors.

3. ### #12 Expert

Nov 30, 2010
18,091
9,664
Maybe it's like a personalized license plate, "eight-e-two"

But seriously, you have it in your hand, don't you? Measure it with an ohm meter.

My guess is 8.2 ohms because that would protect the amplifier and not waste most of the power for the headphones like an 82 or an 800 ohm resistor.

Last edited: Feb 6, 2013
4. ### Audioguru Expert

Dec 20, 2007
10,605
1,182
The minimum allowed supply voltage for an NE5532 is 6V but yours is 4.5V that might drop to 3V. Not good.

The datasheet for an NE5532 opamp shows the minimum load is 600 ohms and the minimum output into 600 ohms is 12V. Then the maximum current is 12/600= 20mA.

Your load is 32 + 8.2= 40.2 ohms. Then a peak of 20mA produces a peak output of 40.2 x 0.02= 0.8V. Then the maximum output is 0.57V RMS. The maximum power in each earphone is 6.4mW RMS. Not very loud.

5. ### Jaguarjoe Thread Starter Active Member

Apr 7, 2010
770
91
By no means is this "my amplifier". I've been Googling to see how other people make headphone amps. Lots of options, some much better and some much worse than others, obviously the 5532 solution as is done by Vellman in their \$10 kit is not acceptable.
I've been gyrating around 1/2 of a TL074 in parallel. or 1/4 of a TLC074. The TLCx looks like a nice part. If there's something better than it, please let me know.

#12-

I don't have that 8E2 in my hand, its only on paper. I wanted to figure out the simple circuit but didn't want to assume what an "8E2" was. I'm confident it's a typo, E and R are next to each other on the keyboard.

6. ### WBahn Moderator

Mar 31, 2012
23,162
6,976
I second your suspicion that it is just a typo. I wouldn't be too surprised to discover that there is some convention for using a different letter to indicate different types of resistors, but I've never heard of it and it would have to apply even when a units prefix was available to use as the radix mark.

7. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
727
8E2 is odd. 8.2 is often 8R2 or 8.2Ω, though devices are so small, the decimal point isn't visible.

8. ### KrisBlueNZ Member

Oct 17, 2012
111
14
I've seen E used as R in that way. It was a long time ago, in some European designs. Philips, I think. I never knew the reason behind it.

9. ### DerStrom8 Well-Known Member

Feb 20, 2011
2,424
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I agree with Kris. Both E and R have been used to symbolize "ohms", and it varies from country to country. I'm willing to bet that it's 8.2 ohms.