Dummy Loads For Audio Amplifiers.wmv
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- čas přidán 29. 11. 2012
- A comparison of the commercial non-inductive resistors to wire-wound resistors and the effect the inductance has on overall impedance. In the discussion I get powers of 10 off a couple of times while talking but I hope you can see the real message. It is difficult to say everything perfectly but the accurate analysis is in the instruments and data sheet. I might also add that the four (4) large resistors have the inductance of only one resistor since two are in parallel (which halves the inductance) and then in series with another pair just like it which would give an inductance value of only one resistor. Inductance introduced by the connecting wires to the loads (depending on the length) could be a significant part of the circuit inductance that would affect frequencies at 20 KHz and above but very little effect on lower frequencies.
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Nice job. Thanks for the info! Nice lab you have there to! I was wondering about this in relation to cathode bias resistors and you answered it for me. Non-inductive is best but not necessary for audio work.
Thank you for making this video, I am assembling a Crossover for a High cost speaker and was hoping to find inductance info. This was absolutely perfect! Thanks for your work and sharing your findings. Excellent diversity of resistors too. Perfect! thank you for spreadsheet with different Hz ratings.
Very timely info for me. Just what I was looking for .
Thanks ! Really enjoy your videos !
David: I know this is an older video but the subject is still relevant. I did some measurements on some 200W "non-inductive" resistors for audio work; they are similar in appearance to the "non-inductive" ones you tested. On an HP 4263A LCR meter (10kHz) I am getting 8.10 ohms at 8.9 deg which works out to about 20uH. At 20 kHz we have 8.4 ohms of impedance. This will be fine for an audio dummy load. I also checked the resistance at 21C (8.06 ohms) and 81C (8.09 ohms). I was more concerned about the tempco, but the numbers say they will be fine. Thanks for the video and information.
Great video. Hope you're still reading comments. Curious to know if inductance would change signficantly with increased current since your measurements were done essentially at 0 amps but under load that would not be the case. Thanks!
I would be looking at instabilities in the ultrasonic range with the inductive resistors. Some solid state amps go unstable with a few uH of inductance.
Connecting wires are probably 48 inches - which adds several uH. I have had to connect a ground wire from the casing of the heatsink (I have a ground connector mounted on it) to the amplifier under test with the low inductance 1% precision resistors to quell high frequency (ultrasonic range) instabilities in rare cases but this has never happened with the larger wirewound ones (single channel) . Possibly an interaction between L&R channels on a common heatsink?
Am glad you did this video. I didn't want to spend 300 bucks on non-inductive resistors when 30buck wire wound did the trick. I actually want to compare the two my self to see the actual difference in the numbers...if the output is less than 5% different between the two, then can you really complain?
Thanks for your comments - I completely agree with you - you may want to watch the video I made on high power 8 ohm loads from hot water heater elements - probably the most economical and certainly the highest power dissipation you will get for your money.
ElPaso TubeAmps Well I got lucky and found a 1ohm 1kwatt resistor on ebay for 35 bucks shipped. I also scored 9 40ohm 300watt resistors WITH MOUNTING HARDWARE for 35 bucks shipped...the hardware alone is over 50.00.
How long are the wires going to the precision resistors? More than a couple of inches of wire adds up to a substantial amount of inductance. I would not expect a few micro henries of inductance to have any effect on the audio range.