Nothing is completely non-inductive! SMT resistors are low-inductance.
Cylindrical film resistors can have a spiral track and be more inductive, but not to a level that ever matters for audio. Only WW resistors get to the dozens of turns to hundreds of turns where inductance becomes significant at audio.
Just the leads on a through-hole resistor have more inductance than an SMT device in total (other than an SMT inductor!). The extra inductance of a spiral (well helical to be pedantic) track on a film resistor will not be that much more.
It takes 8µH to develop 1 ohm of reactance at 20kHz, whereas stray inductances are measured in nH.
These green WW are tough little things but not really resistive above a few 10s of kHz. Allready at 10kHz the phase is 6 degrees. At 100kHz the phase is close to 45degrees. The 'resistor' is trying damn hard to act like an inductor now.
Not sure I'd use this series of WWs anywhere in the audio path, at least when more resistive options exist.
Not sure I'd use this series of WWs anywhere in the audio path, at least when more resistive options exist.
Attachments
Very interesting indeed. Do you have measurement of other power resistor like the Panasonic ERG? Or Vishay MRA? Thanks.
I have some Welwyn 100r wire wound resistors.
I made up a simple circuit with 100R metal film and 100R Welwyn wire wound as a potential divider. My sig gen goes up to 2MHz and at that frequency there is no phase shift.
I can only conclude the Welwyn WW resistors are wound back on themselves to cancel out inductance.
I made up a simple circuit with 100R metal film and 100R Welwyn wire wound as a potential divider. My sig gen goes up to 2MHz and at that frequency there is no phase shift.
I can only conclude the Welwyn WW resistors are wound back on themselves to cancel out inductance.
Did a quick scan of some more, the ones I found in my drawer. Dont have time to detail them, just look at the pic's name for info.
Generally the lower the resistance the more inductive it becomes (if same construction). Most 100ohm resistors are pretty much 100ohm up till way high, less than 100ohm they tend to become more inductive, above 100ohms they become more capacitive. The parasitics are relative to the resistance, a 1inch long resistor is about X much inductive and as the resistance gets lower the inductive part starts to show more and more, capacitive its the same, starting to dominate as resistance becomes higher.
So some of the 100mohm and 50mohm resistors measured here are pretty good.
Generally the lower the resistance the more inductive it becomes (if same construction). Most 100ohm resistors are pretty much 100ohm up till way high, less than 100ohm they tend to become more inductive, above 100ohms they become more capacitive. The parasitics are relative to the resistance, a 1inch long resistor is about X much inductive and as the resistance gets lower the inductive part starts to show more and more, capacitive its the same, starting to dominate as resistance becomes higher.
So some of the 100mohm and 50mohm resistors measured here are pretty good.
Attachments
Vishay do no inductive and non magnetic wire wound resistors.
https://www.vishay.com/docs/31801/mra.pdf
https://www.vishay.com/docs/31801/mra.pdf
Where do we get those? It seems to me they are made to order and must be very expencive.
Too bad carbon composition resistors are so poor in tempco and noise b/c they are nonmagnetic, noninductive, and pulse tolerant.
The caddock mp850 series is noninductive and precise but poor pulse tolerant.
Great reasistors for emiters or source position in the amplifiers after my experience
MRA-05R4700FE12 Vishay / Mills | Mouser
Futaba MPC74 metal plate cost less and are fantastic indeed.
Best regards
MRA-05R4700FE12 Vishay / Mills | Mouser
Futaba MPC74 metal plate cost less and are fantastic indeed.
Best regards
Hi Nigel,
How can we detect phase shift with simple scope and siggen? Perhaps you care to explain. Thanks.
Very easily. I just made a potential divider with 100r metal film resistor and 100r wire wound resistor.
I put one scope lead on input and another at the connection of the two resistors and compared relative phases on the scope at 2MHz.
No shift in phase at all.
An externally hosted image should be here but it was not working when we last tested it.
