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Old 14th June 2013, 03:24 PM   #1
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Default A resistor query

I'm modding my Bada PH32 hybrid amp and conveniently the PCBs have identified all parts except the last resistors before the signal out wiring.

Something I have never seen before - these resistors are enclosed by enamelled wire coils which are soldered seperately. They are 1 W carbons and are 5 band marked - brown/black/black/gold and strangely gold again when a 5 band resistor should have a last band of brown to denote 1%.

Using my m/meter on a max 2K setting I get 0.010 reading which I interpret as 10R is this right? I should add that I replaced the crappy little fan that came with the amp for a Noctua and this is contained with a damped, open backed slate box with the amp sitting on top, so heat is very effectively dissipated. So if the purpose of these coils is to aid cooling then can I safely discard them.

Assuming it is a 10R resistor will changing the value alter the gain a little, I'd like just a little more? If so what value should I be looking at?
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Old 14th June 2013, 03:40 PM   #2
DF96 is offline DF96  England
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Coils wound on a resistor are usually done this way to ensure low Q. The resistor value does not matter too much; a small change will make no difference. The coil is often there to prevent oscillation with a capacitive load.
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Old 14th June 2013, 09:43 PM   #3
Enzo is offline Enzo  United States
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Agree. And unless you unwound the wire from around it, your resistance reading is of the wire, not the resistor.

If you are not sure about your meter reading, get out an actual 10 ohm resistor and measure it on the same scale. Or even a 100 ohm resistor.

The resistance to the signal sees the very low resistance of the wire. Putting most any resistor in parallel with that piece of wire won't change that much.

Probably the reason those parts are not marked with a resistor number is that they are considered an inductor. Do you see anything like L1 or L101, or some L number near to them?
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Old 15th June 2013, 09:37 AM   #4
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Geat replies thank you,

DF96 - I shall refit the coils.

Enzo I removed both the coils and the resistors and that is when I measured the them, from the colours of the bands is 10R correct?

Also I thought that they might be some kind of inductor and no there are no markings at all.

I can easily re-use the resistors but is there any benefit to using quality resistors in their place, also I'm not a lover of carbon resistors. I intend to replace PSU power ones with Mills and their 5 W will easily fit the position.
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Old 15th June 2013, 09:44 AM   #5
balerit is offline balerit  South Africa
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It is a 10 ohm 5% resistor.
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Old 15th June 2013, 10:58 AM   #6
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balerit,
thanks for that.
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Old 15th June 2013, 11:43 AM   #7
DF96 is offline DF96  England
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There is absolutely no point in using 'quality' resistors for this job. At audio frequencies all that is seen is an inductor. At RF all that is seen is some resistance. The choice of 1W is to get the right size for the inductor winding; the resistor itself will not dissipate any power.
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Old 15th June 2013, 12:06 PM   #8
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Some times stray capacitence or the capacitence in pieze tweeters can cause the
impedience seen by the amp to look almost like a short at verry high frequencies
well above 20,000 hz. This small coil makes sure the amp is issolated from this effect.
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Old 15th June 2013, 01:07 PM   #9
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More excellent replies and saving me money as well, thanks to all.
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