They may have (or may not, depend upon circumstances) too high inductance.
BTW, some 5W wirewound resistors have 250V rating only, so check manufacturer's specification before ordering.
WWounds are more expensive, but virtually noiseless. I've never had an issue with them. Values above 50K are expensive. TIP: In tube preamps design for low impedance triode working with negative foldback feedback between stages. This reduces internal impedance and makes wirewounds an ideal application.
Ref Morgan Jones valve amps 3rd ed p.499. Some excellent preamps Brimar eg.VP10 were designed around this technique.
richy
While the Carbon Film resistors are quieter than carbon comp, they are noiser than metal film and wire wound. This probably only matters in the first gain stage of a power amp, but will matter more in line amps and phono amps.
It would be interesting to measure system noise with different resistor types in say a LTP driver stage to see if it made a measureable difference that mattered.
Wire wound is going to have inductance, but how much? I've only measured a 10 Ohm 100W Ohmite. I'll see if I can find some other WW resistors in the lab and measure them to see wht order of magnitude we are talking about with respect to inductance.
It would be interesting to measure system noise with different resistor types in say a LTP driver stage to see if it made a measureable difference that mattered.
Wire wound is going to have inductance, but how much? I've only measured a 10 Ohm 100W Ohmite. I'll see if I can find some other WW resistors in the lab and measure them to see wht order of magnitude we are talking about with respect to inductance.
Ah-.. not as much as you think.The average circuit layout has alot of inductance. Mouser does stock non inductive versions.
However, sometime ago I was curious about any differences in sound quality and I couldn't detect any. Modifying a driver and o/p stage have nil effect,other than better resistance to transients, however the there's alot of personal issue. SE designers with global nfb or any nfb seem quite particular on component choice, whereas with p-p designs, I've tried various places in the circuit where I thought wirewound would have an influence, and to no avail. The global nfb loop (if enough of it) does an excellent job of cleaning up overshoots and ringing, which in all cases arise from the o/p transformer and wiring.
Perfomance wise, your choice, I say there's nothing in it, other than cost.
I have them simply because of reliability issues.
richy
5K1 5W 5% Dale CP-5-56, made in Mexico 5251 Ohms 3.89mH@1KHz - at 20KHz this should be 489 ohms for an impedance increase of 9.8% increase
5K1 6.9%5W 10% TRW, 4959 OHms 2.8mH - @20KHz 352 Ohms, 7% increase
5K 5% 12W Clairstat 4968 Ohms 3.75mH - @20KHz 471 Ohms, 9.4% increase
I didn't find any wire wound resistors in the 1-5K range below 5W so one would have to make an educated extrapolation. Physically smaller resistors will have to use smaller wire for more resistance. Since the circumferance dereases linear rate with size more turns will be needed. Smaller wire has a larger resistance per unit length which helps compensate for the smller circumference. I would expect the inductance to increase, but not at a linear rate. 10-20% increase in impedance at 20KHz is a reasonable effect caused by the inductance.
So, in an LTP anode ckt it probably won't matter if you use wire wound resistors since the two resistors will track, and the LTP shows minimal gain change with such a small increase in load impedance.
Bypassed cathode resistor, no problem other than slight resonance caused by the LC network.
On the other hand, the resistors in a circuit like a RIAA equalization network will be very sensitive to such changes.
Bottom line is WW is nice, but be careful where you put them.
5K1 6.9%5W 10% TRW, 4959 OHms 2.8mH - @20KHz 352 Ohms, 7% increase
5K 5% 12W Clairstat 4968 Ohms 3.75mH - @20KHz 471 Ohms, 9.4% increase
I didn't find any wire wound resistors in the 1-5K range below 5W so one would have to make an educated extrapolation. Physically smaller resistors will have to use smaller wire for more resistance. Since the circumferance dereases linear rate with size more turns will be needed. Smaller wire has a larger resistance per unit length which helps compensate for the smller circumference. I would expect the inductance to increase, but not at a linear rate. 10-20% increase in impedance at 20KHz is a reasonable effect caused by the inductance.
So, in an LTP anode ckt it probably won't matter if you use wire wound resistors since the two resistors will track, and the LTP shows minimal gain change with such a small increase in load impedance.
Bypassed cathode resistor, no problem other than slight resonance caused by the LC network.
On the other hand, the resistors in a circuit like a RIAA equalization network will be very sensitive to such changes.
Bottom line is WW is nice, but be careful where you put them.
Ah yes: may be calibrated but test equipment has problems differentiating results on the skinny inductance setting. Philips PM6301 is typ and has two settings. see pic. You have to consult user manual as resistance swamps readings.
Another way is to use an RF generator with Cp and find resonance.
richy
Another way is to use an RF generator with Cp and find resonance.
richy
Attachments
Lp gives a reading of several hundred H. I tried a couple differnt settings with no reasonable effect.
I'll have to try a tank circuit and frequency generator to see if I can find a resonance. Parallel or series?
Parallel with a series resistor driving it and look for a peak on the parallel tank.
I'll have to try a tank circuit and frequency generator to see if I can find a resonance. Parallel or series?
Parallel with a series resistor driving it and look for a peak on the parallel tank.
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