Weird resistor values in USA circuit!

[mole42uk]

I am building an American designed audio sweep generator which claims lots of good things and has several discrete active components (in the absence of heater pins, I assume they must be 'transistors').

However, it does call for several peculiar 1% resistor values, for example: 4.02kΩ; 5.01kΩ; 22.6kΩ. These are not values I've seen before and I wondered if there was some special resistor mine in the USA which produced them? Or maybe I'll have to spend some time selecting components to make them up?

Most of them are doing divider duty, not switched range selection, and if I hadn't read a test report on a completed instrument I'd have thought they were the result of someone number-crunching without reference to the standard resistor value tables. But, there must have been at least one built!

Any thoughts (apart from "build another design.."...!)

[Alan Stepney]

You can find 1% resistors fairly easily these days.

Or, just carefull chock through a pile of the nearest standard value and will probably find what you want.

Of course, if you want to get technical, you can select 2 (or more-probably more ) standard values to make up what you want.

[kellys_eye]

The 4k02 and 22k6 are available in the E48 series though the 5k01 doesn't show on even the E192 series! That particular one could be a typo?? (5k10 or 5k11).

I strong doubt you'd even be able to measure the error(s) introduced by using the nearest preferred value.

[KeithsTV]

They're in the E96 series for resistor values. Google E96 resistors and there are charts showing the values available in the various series. e.g. the E6 series has 6 values with each value having a 20% tolerance, E12 has 12 values with a10% tolerance etc.

As Alan said 1% resistors are easy to obtain these days, it's probably harder to get hold of 10% resistors.

Keith

[mole42uk]

I haven't any problems with 1% resistors (many of the ones in my stock are 1% at small power ratings), but I don't often need to buy from the E96 series!

The 5.01kΩ resistor appears several times in the circuit and parts lists, so I don't think it's a typo. I'm beginning to think someone had a nicely stocked E192 cupboard.....It's odd about the 5.01kΩ though because although the gap in the E192 series is filled by tolerance spread, a 5.01kΩ would have to be SUT from 5.05 or 4.99 and there are three in the circuit.

A mystery!

[Radio Wrangler]

E96 is the natural series for 1% resistors. It produces bins of +/-1% width, so any resistor you make can be shipped as one preferred value or another. The centroid values are often irrational numbers, so the convention is to round to 3 significant digits.

For E24 etc the convention was to round to 2 significant digits. Confusingly, there are now lots of 1% resistors sold on the 2-digit E12 and E24 values.

[pbengtech]

I have inherited a box of large ( I thought they were Hunts capacitors until I looked closely) black precision resistors.
Most are E192 range ie 118.92K and 124.99k but some are 423.93 and 474.07 k ohms and other unusual values.
They must have been made for something special!
has anyone encountered them in circuits?
Phil

[KeithsTV]

I've come across that sort of resistor used in precision oscillator circuits and DC amplifier applications where precise gains are required. They are typically 0.5% to 0.1%.

I once had to build a thermometer using linearised thermistors (two thermistors in a single package) which required a network of precision resistors to obtain a linear resistance vs temperature characteristic over a limited temperature range. The resistors were supplied with the thermistors.

Keith

[orbanp1]

Hi Richard,

Any chance you could post the schematics?
Then we could comment on the validity of the 1% tolerance requirement as well.

Regards, Peter

[mole42uk]

I have nearly finished drawing it up in Eagle. When it's done I'll post it here.

I think the odd-value resistors are largely to control the top and battom limits on the various controls - the 10k frequency range pot has a 5.01k at the top end and a 1.1k at the bottom. I got some 4.99k resistors which will be replacing thwe 5.01k!

[cmjones01]

I've noticed a trend towards using E96 and E192 resistor values in recent years in industry. As modern surface-mount components they're no more difficult to get hold of than E12 or E24 values, but they are a whisker more expensive. They're often seen in applications like voltage regulators, where the finer resolution of the resistor values means that the nominal value of, say, the output voltage can be very close to its desired value, and can be relied upon in production runs of thousands of units. That's not such a concern in home construction!

In cases like the one we're discussing here, sometimes I wonder if values like 5.01k get chosen because a naive calculation shows that 5k would be the right value, and 5.01k is the nearest that's in the catalogue. There's probably no need for it to be that precise, and a more experienced designer might have gone through the normal process of figuring out how to get the same result with E12 values. I guess we'll understand when we see the circuit diagram.

Chris

[Radio Wrangler]

Sometimes you will see precision resistors, like 1% or 0.1% ones used not for their precision, but also for tighter temperature coefficient bounds which usually come along as part of the package.

Another reason is that although resistors HAVE to make noise (unless cooled to absolute zero temperature), some make a lot more noise than the absolute minimum.

Carbon composition are at the worst end of the scale, and the common surface mount thick-film 'chip' resistors are pretty bad for noise. The good guys are metal-film thin-film resistors which come close to the theoretical minimum.

This isn't just an esoteric parameter needed only at CERN, it makes measurable differences in small signal stages. Radio front-ends, mike preamps, record player input stages. Less obviously it can be a limiting factor in voltage-controlled oscillators, limiting their phase noise performance.

Between a good resistor type and a bad one, there can be as much as 20dB difference in noise output. That's 10:1 in volts.

In a lot of places, resistor noise isn't significant, but it's good to spot the places where it does matter, and to know what can be done.

David

[Diabolical Artificer]

Unless they're current sense resistors, surely the value doesn't matter that much. Consider the application and use common sense.

A.

[GMB]

I have seen 1% resistors like this that are basically cheating.

So rather than make the right value, they do the usual and then measure what they get - and mark the resistor with the exact measured value to 3 digits.

I think this happens when the 1% aspect is not the actual value as such but the stability being offered. So whatever it was, it won't change much, and the paint tells you what you started with.

[emeritus]

Back in the 1970's when we were designing PLL oscillators at Plessey, we had problems with stability that turned out was due to noise injected by a resistor in the loop filter at a point in the loop where the signal level was very low. Changing to a low noise type completely eliminated the problem.

[FrankB]

The "oddball" value resistors are pretty common here many pieces of test equipment.
Signal generators, multimeters, scopes, etc. Even in TV sets I have found them in the discriminator circuits, and in some of the monitoring lines for the microprocessors.

In the past I have just ordered them from the local wholesaler/jobber or gone to the mail order catalogs. Now, since I have bought up the leftover stock from so many failed TV shops, I have a good supply of most of the values I need.

[AC/HL]

What we're observing is probably no more than evolution, as Darwin might have said. In the early days resistors would be hand selected, manufacturing techniques struggled to get even 20%, and early valve circuits were happy with that.
Fast forward, they can make resistors to any value required, and automatic test equipment probably makes sub 1% cheap and easy, like everything else these days.
What was professional precision only a few years ago is now commonplace, and the complexity of even mundane domestic equipment takes advantage. Why make something that needs expensive adjustments when it can be made accurate by design.

[Andy Green]

The Orban range of Optimod analogue broadcast audio processors used a lot of E96 values as they contain a lot of precision analogue audio phase matched filters. These were designed in the 70s and 80s and uses military grade components, many are still working with original components thirty off years later