Stupid resistor question...

A simple question for you folks...

In the schematics on the Jensen Transformer site (for instance, their DI schematic http://www.jensen-transformers.com/as/as007.pdf) , they use the following shorthand when referring to resistor values:

R1 8k06
R2 2k49

What does this mean? Is it as simple as 8k06 = 8.06 kOhms? 2.49 kOhms? Are they really expecting you to be that precise?

Thank you!

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I found my answer on the Jensen site... I was correct. I didn't know you could be that precise with resistors.

Learn something new everyday.

> R1 8k06 ... What does this mean? Is it as simple as 8k06 = 8.06 kOhms?

Yes. Decimal-points get lost on copies; the letter K stands for the point and won't get lost in the copier.

> Are they really expecting you to be that precise?

When you see resistors with 3-digit specs, it means they assume you use only 1% or better resistors.

You can build stuff with 10% resistors. Usually it comes out within a dB of the designed gain.

But if you build two channels, two gain-set resistors in each, with 5% resistors, and they fall at the worst end of the allowed 5% error, you can have a 2dB difference between the "identical" amps. If you try to use them as a stereo pair, you will get a very audible image shift.

And as Matt says, for common mode rejection you sometimes need matching better than 1%. A 1% mis-match gives 40dB CMRR even if the circuit would do 60+dB with "perfect matching".

Fussy audio makers like Jensen tend to use only 2% or better resistors, so worst-case error tolerances do not become audibly significant. And the 2% and 1% resistor nominal values are picked so they can't be confused with ordinary 10%/5% values like 8K2.

Also it used to be that 2% and better resistors were higher-quality than the carbon composition (charcoal and clay) used in 10% and 20% resistors. Not a whole lot of point in using Jensen parts with crummy resistors. However all current production resistors seem to be exceptionally high quality compared to the old stuff.

[quote author="StDomingo"]I can't see a 2k49 resistor on the schematic you've linked to. The 221k in the coupling circuit can be 220k.[/quote]

The 2k49 resistor is R2, directly below R1 (in the little dotted line box).

Thank you, everyone. It makes perfect sense, now. Jensen reccomends metal film resistors, which seems perfectly logical.

Just to check my math, the 10nf capacitor would be the same as a 10,000pf capacitor, right?

I love that I can ask stupid questions and not be blasted... at least, not publicly.

[quote author="b3groover"]

Just to check my math, the 10nf capacitor would be the same as a 10,000pf capacitor, right?

I love that I can ask stupid questions and not be blasted... at least, not publicly. [/quote]

.1uf --100nf --10,000pf

-Eric

[quote author="Eric H"].1uf --100nf --10,000pf[/quote]
No.
.1µF = 100nf = 100000pf
.01µF = 10nf = 10000pf

Best regards,

Mikkel C. Simonsen

[quote author="mcs"][quote author="Eric H"].1uf --100nf --10,000pf[/quote]
No.
.1µF = 100nf = 100000pf
.01µF = 10nf = 10000pf

Best regards,

Mikkel C. Simonsen[/quote]
Dang, I should know better than to involve myself with decimal points

Mikkel is correct,

-Eric

Not only have resistors become better, but also cheaper! There's not much to save on not using 1% resistors. 0,1% resistors are about 10-20 times as expensive though and I've only used those for the 6k8 phantomresistors...

Yes, that's a good point. The metal film resistors are not much more expensive than regular ones. I'll probably use them for all my audio circuits... why not?