I don't think it matters very much. As it only has a small signal voltage across it distortion will not be an issue. For HF stability it ought to have fairly low inductance, so maybe not a wirewound.
Metal film and metal oxide film are both spiral (as in helix) cut. This is equivalent to wound.
Carbon film may also be spiral cut.
Carbon composition don't have "windings" as such, but they still have length and the inductance that goes with it.
Carbon film may also be spiral cut.
Carbon composition don't have "windings" as such, but they still have length and the inductance that goes with it.
Not quite equivalent. Film resistors have a few wide turns. Wirewounds have many narrow turns, so much greater inductance. Film resistors can be substantially non-inductive up to VHF frequencies, although this does depend on resistor value too.
We are talking emitter resistors here.
My 0r1 & 0r22 have about two turns on them. That is very similar to a spiral cut film resistor.
My 0r1 & 0r22 have about two turns on them. That is very similar to a spiral cut film resistor.
I guess the answer is to measure one. Two turns will not give much inductance, and it will be a lossy inductor anyway so not much risk of a high Q resonance.
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I believe that for most audio applications, standard 5W, ceramic boxed WW resistors < OR5 can be considered non-inductive. This is what you see on most DIY amplifiers posted here and in commercial amplifiers too. I've also encountered many tubular 2, 3 and 5W WW types that are significantly inductive (~1 uH) so there are differences in construction - perhaps by using lower resistivity wires and more turns in these open types.
I guess there will always be some brands that are exceptions but it's good to know that most of these cheap, durable and widely available parts can be fine.
I guess there will always be some brands that are exceptions but it's good to know that most of these cheap, durable and widely available parts can be fine.
Question
What kind of advantages or disadvantages brings the change of the emitter resistors
Let say we change every 0,22 Ohm WW or Ceramic 3W 5% resistor with 5 parallel x 1R Metal Film 0,6W 1% resistors ?
Of course I'm talking about the change in PCB layout prototype
What kind of advantages or disadvantages brings the change of the emitter resistors
Let say we change every 0,22 Ohm WW or Ceramic 3W 5% resistor with 5 parallel x 1R Metal Film 0,6W 1% resistors ?
Of course I'm talking about the change in PCB layout prototype
None.
If you use the correct resistor value and ensure it never runs hot/warm then you should not be able to measure any difference in performance.
There's no accounting for the bat eared fraternity, that will claim anything to get attention and sales.
If you use the correct resistor value and ensure it never runs hot/warm then you should not be able to measure any difference in performance.
There's no accounting for the bat eared fraternity, that will claim anything to get attention and sales.
the inductance of the single huge resistor ( dimesions) would be more then 50nH
In case 5 parallel small 0,6W resistors total inductance is the common inductance value ( around 10nH) divided by the number of inductors being connected in parallel.
So the total inductace should be ( even considering additionall PCB traces) much lower then the single one
Isyn't the inductace of the emiter resostors ( in power transistor) important factor ?
Hi ...
In Linear Audio Volume 1 there's an article on distortion in resistors. The author measures various known and less known resistors and there's actually quite some difference between resistor types.
A relatively cheap resistor is the Xicon 1% metal film resistor (e.g. available from Mouser). One - to me - interesting observation in the article is that higher wattage resistors typically have a lower distortion value (about 6 dB from 1/4 watt to ½ watt).
Best regards,
Jesper
In Linear Audio Volume 1 there's an article on distortion in resistors. The author measures various known and less known resistors and there's actually quite some difference between resistor types.
A relatively cheap resistor is the Xicon 1% metal film resistor (e.g. available from Mouser). One - to me - interesting observation in the article is that higher wattage resistors typically have a lower distortion value (about 6 dB from 1/4 watt to ½ watt).
Best regards,
Jesper
If you look into the data sheet of the Caddock MP915 non-inductive power resistors you will see Inductance 10nH
then you can read that :
http://www.diyaudio.com/forums/multi-way/113209-resistor-inductance-4.html
so my assumption about 50nH and 10nH wasn't that far from reality
There is some merit to low inductance resistors in emitter circuits but this would actually be more important in MOSFETs AND assuming you have done a lot of work on PCB routing, AND you insist on designing an extremely wideband amplifier. Normally just bending the legs of a through-hole component will give you more inductance than the actual component, unless it's an inductor 🙂 and in most cases the wire and trace routing will contribute FAR more.
Another reason why the resistor should be taken with a grain of salt is that for most high-performance power BJTs, that's only the 'external' resistor, adding to internal resistive structures. Case in point would be the average LAPT BJT.
A change in the value of the resistor does indeed have influence as it changes a few things like output stage gm, output resistance, and of course the required idle current for minimum distortion, however this would be far beyond the scope of a simple answer.
Changing a wirewound or packed-foil resistor with a metal film or similar resistor will change behavior in the case of overload. Wirewound resistors can withstand very high peak currents and dissipation, compared to the rated value. More than metal film etc resistors, which in the case of drastic and potentially catastrophic overload, may result in the resistor going open rather than the BJT giving up the magic smoke.
Another reason why the resistor should be taken with a grain of salt is that for most high-performance power BJTs, that's only the 'external' resistor, adding to internal resistive structures. Case in point would be the average LAPT BJT.
A change in the value of the resistor does indeed have influence as it changes a few things like output stage gm, output resistance, and of course the required idle current for minimum distortion, however this would be far beyond the scope of a simple answer.
Changing a wirewound or packed-foil resistor with a metal film or similar resistor will change behavior in the case of overload. Wirewound resistors can withstand very high peak currents and dissipation, compared to the rated value. More than metal film etc resistors, which in the case of drastic and potentially catastrophic overload, may result in the resistor going open rather than the BJT giving up the magic smoke.
The distortion in a resistor will always be entirely negligible whan compared with the distortion in the active devices in a typical SS PP output stage. Resistor distortion may (just) be worth thinking about for a feedback resistor, but not for the emitter resistors.
Choosing the right value or equivalently choosing the right quiescent current is far more important than worrying about what type of resistor. Gnats and camels?
Choosing the right value or equivalently choosing the right quiescent current is far more important than worrying about what type of resistor. Gnats and camels?
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+1
I read more than once it is recommended to use good quality 1/2W resistors in traditional feedback locations.
Right now I have a couple of burned emitter resistor I can't identify their values. Even with DMM.
Usually the values are from 0.22 to 0.33 to 0.47 ohms 5 watts.
Can the 0.33 ones be used in a replacement if we don't know the right value?
0.33 is in the middle of the usual range so is a reasonable choice if you don't know the right value. You might need to adjust the quiescent current to minimise crossover distortion.
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The real question is how do these Technical Brain guys manage to eliminate the emitter resistors altogether ?
Technical Brain TBP-Zero EX Amp & TBC-Zero EX Preamp (TAS 213) | The Absolute Sound
Technical Brain TBP-Zero EX Amp & TBC-Zero EX Preamp (TAS 213) | The Absolute Sound
Technical Brain Amp
@ Bigun
Only $69,995/pair 😱
The only JP Patent with that # i found is this
Not TB ? If anyone can locate the patent, please post the link 🙂
Technical Brain TBC Zero Review and Test | Hi-Fi
**********
Emitter resistors can & have been be eliminated in amps before now. But "usually" with just one output pair !
@ Bigun
Only $69,995/pair 😱
The only JP Patent with that # i found is this
Not TB ? If anyone can locate the patent, please post the link 🙂
Technical Brain TBC Zero Review and Test | Hi-Fi
**********
Emitter resistors can & have been be eliminated in amps before now. But "usually" with just one output pair !
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