cm08rb01 inductor

[Danlampton]

I need one of these. Digikey has them but I have to buy 500.

I'd be glad to buy 100 if others want the rest. In lieu of that, does anyone know where I can get a small quantity?

It is 40uH with an 8mm core and 4 leads/posts.

[doctor]

I need one of these. Digikey has them but I have to buy 500.

I'd be glad to buy 100 if others want the rest. In lieu of that, does anyone know where I can get a small quantity?

It is 40uH with an 8mm core and 4 leads/posts.

Hi Danlampton,

If, as I suspect, this common mode filter is used in the DC input keyboard circuitry,
you can simply solder two jumpers instead. Nothing bad will happen.

In this circuitry common mode filter is used against external EMI.
Now each device must satisfy the requirements of specific EMI standards.
A device is tested under worst case conditions. But if your customer uses
this device at home, probability of strong external interferences is very
small. You can try.

But if, in any case, you need or want to find suitable replacement, you should
perform a work similar to the work of a component engineer.

As a rule, I do not write “how to repair” because lack of time, but this question
(how to find suitable replacement) may be a common interest issue.

And if I will have a time, I will write corresponding procedure.

Good luck,

[Enzo]

Actually, the Digikey web site says they do not have them, but they would get them for you if you wanted to order 500 or more. Zero on hand.

I agree with what Doctor said mostly, but I think the filter action is more about preventing the unit from radiating EMI OUT rather than not letting it in. Either way, bypassing it with a wire will probably not cause any problems.

[km6xz]

If you are needing that exact planform it must be due to pc boards already laid out. What is it used for in your circuit, is it being used in its traditional role of common mode filter where all 4 pins are used?
If you really need that exact part, a 500 lot purchase is not too bad for per item price, put the remainder on eBay. You can also try a small lot run from one of the many Chinese producers of custom assembles and components. I needed a ceramic filter for 3,000 little receivers we use as a tour guide audio systems. The original was not of the correct bandpass so I put out a request for bit on a Chinese materials site and got 2 good bids at a price that was hard to turn down. They made them to my spec and all worked as claimed.

[doctor]

Actually, the Digikey web site says they do not have them, but they would get them for you if you wanted to order 500 or more. Zero on hand.

I agree with what Doctor said mostly, but I think the filter action is more about preventing the unit from radiating EMI OUT rather than not letting it in. Either way, bypassing it with a wire will probably not cause any problems.

On this occasion, I would like to illustrate some types of interferences and related filters.

External EM fields cause mainly two types of interferences pickuped by electronic circuitries.

1. The first type is called differential mode interferences.

One of such interferences is produced by parasitic diodes that appear in points of bad contact.
The diodes rectify regular (differential mode) currents, which are induced by the external EM field.
The interference may be reduced by regular RC/LC filters – for example, the filters at the guitar
and microphone amp's input.
Removing these filters is undesirable.

2. The second type is called common mode interferences.

External EM field may induce into two neighboring wires currents propagating in the same direction.
These (common mode) currents close to ground through parasitic capacitances.

Common mode filters are used to suppress this type of interference (see attached picture presented
by Murata Co.)

In low power electronic musical equipment, these types of filters are mostly installed on DC power supply input.
They can be removed (and replaced with jumpers) when the device is used in an EM "quiet" venue, with a power supply of good quality.
If the device is used on a stage where projectors, dimmers and high power amps are present (all of them are sources of high currents and thus produce strong EM fields), then an absence of common-mode filters is very likely to cause noise.

3. Filters for preventing outside conducted radiation are used in devices working with high frequencies and relatively high currents (such as switchable power supplies).
These filters can't be removed and replaced with jumpers under any circumstance.

Best of luck to anyone who finds this information useful.

[Danlampton]

Thanks so much for the help. You guys have been a great help for me on this new adventure.