inductor in series or not

[AllenB]

I'd guess so, since the existing inductor doesn't itself look like it would easily dissipate 5W.

The usual caution when doing this. During your early discovery listening sessions, go over and feel it a few times when it seems appropriate.

 

[mboxler]

Just to clarify. The 6 ohm descriptor next to the inductors is the impedance of the inductor at the given frequency. A 1mh inductor has an impedance of 6 ohms @ 950hz. A 2mh inductor has an impedance of 6 ohms @ 475hz. This has nothing to do with DCR, as I see it.

 

[ianbo]

Good point. Not sure why that's on the circuit diagram, however.

 

[Tubenstein]

You haven't said where you want to use the copper foil inductor. In the tweeter circuit? Or on the mid/bass?

For the tweeter, you want to keep the resistance of the trap the same as the original, so if you use the 2.24R coil, you need to add a resistor in series of around 2.2 or 2.3 ohms. If you use the foil coil, you need a resistor around 3.7 ohms.

If you use the foil coil on the midrange, you will have increased the series resistance by 0.2R. That will cause a small change in the response, notably a small reduction in level - I'd guess around 0.2dB.

Can I parallel 3 x 6.8R 5w carbon resistor for 2.27R and then wired in series with the 2.24R coil?

 

[ianbo]

Yes, that would work. But a single 2.2R would also be absolutely fine.

 

[egellings]

So long as the single resistor can handle the wattage, if that's an issue, of the 3 paralleled resistors, then that will be fine.

 

[ianbo]

Well, it doesn't need to handle the same wattage as three paralleled resistors could. It just needs to handle the power it's going to be presented with in the circuit. In the original crossover, there's a very light gauge air core coil there - something like 29 AWG, I'd guess. I reckon that a single 5 watt resistor, sharing the load with the new coil, will be fine.

 

[Tubenstein]

If I put Mills MRA-12 2.2R, then it would be safe.

 

[egellings]

Well, it doesn't need to handle the same wattage as three paralleled resistors could. It just needs to handle the power it's going to be presented with in the circuit. In the original crossover, there's a very light gauge air core coil there - something like 29 AWG, I'd guess. I reckon that a single 5 watt resistor, sharing the load with the new coil, will be fine.

Presumably, the resistors were sized to possibly handle that much wattage. If it's known that they will never see that kind of power, then a lower wattage rating, such as 5W, would be just fine.

 

[Tubenstein]

Well, it doesn't need to handle the same wattage as three paralleled resistors could. It just needs to handle the power it's going to be presented with in the circuit. In the original crossover, there's a very light gauge air core coil there - something like 29 AWG, I'd guess. I reckon that a single 5 watt resistor, sharing the load with the new coil, will be fine.

The Jantzen 1mH Air Core Wire Coil is AWG26, not 29AWG

 

[ianbo]

Yes, I know. If you read what I wrote in post #47 again, I said that the original tweeter inductor, the one with 4.5 ohms DCR, must be something like 29 AWG.

(Why did I estimate 29AWG? Because there is a Jantzen 29AWG coil available which is 1mH, 0.44R.)

 

[ianbo]

Sorry, that should have said 4.4R

 

[Tubenstein]

I just found a 1mH copper foil indictor 20AWG that has DCR 0.8R. Should I put a Mills MRA-12 3.7R in series with this particular inductor for 4.5R as well?

 

[mboxler]

Yes that will work, although I find it hard to believe the original inductor had 4.4 ohm DCR. That's a lot of resistance for a wire. You did measure that out of circuit, right?

 

[Tubenstein]

Yes that will work, although I find it hard to believe the original inductor had 4.4 ohm DCR. That's a lot of resistance for a wire. You did measure that out of circuit, right?

I measure each inductor from the stock crossover.

BTW, any drawback by putting a 2.2R resistor in series with the 1mH DCR 2.24R?

 

[mboxler]

The 1mh inductor and 4.7uf capacitor create a deep notch at around 2320hz. Any added series resistance (including the DCR of the inductor itself) simply makes the notch less deep. You may be okay without the added resistor, but there's no drawback to adding a series resistor.

 

[Tubenstein]

The 1mh inductor and 4.7uf capacitor create a deep notch at around 2320hz. Any added series resistance (including the DCR of the inductor itself) simply makes the notch less deep. You may be okay without the added resistor, but there's no drawback to adding a series resistor.

The stock 1mH inductor has DCR of 4.5R. So the added 2.2R resistor along with the 1mH inductor (2.24R DCR) just set the DCR back to 4.5R, right?

 

[mboxler]

Right

 

[Tubenstein]

BTW, I want to buy a copper foil 1mH 18AWG inductor that has 0.54R DCR. Is that suitable to replace the stock 1mH iron inductor that has 0.6R DCR without putting a 0.06R resistor in series?

 

[mboxler]

That inductor by itself is fine. All your connecting wires could add up to the difference anyway 😎