Audio amplifier design, basic questions.


Joined Feb 17, 2009


Joined Nov 9, 2007
Non inductive resistors can be made by biflar winding on a former.

That is you double over the length of wire and wind the doubled piece round the former.

Another alternative is to set the wire out zig zag.

In each case the inductances cancel for the two halves going in opposite directions.


Joined Nov 30, 2010
+1 on the OMG. Do not let an accessory like a Zobel circuit stop you. Millions of amplifiers don't even have one!

Thread Starter


Joined Dec 18, 2014
ah ok, will ditch the zobel network. The article in post #147 made me think i would need one if i want to be able to connect an inductive load such as a speaker. will have a read in the morning. thanks again guys.


Joined Nov 9, 2007
For high power resistors this is what I have done.
Two 5 watt resistors can handle perhaps 200 watts if immersed in water.
For a few minutes anyway. Enough time to take measurements and adjust bias.
Actually I used it to test a power supply for 30 minutes. Applied 32v ~3a.
The water got rather warm. Some bubbles were produced. That's all.
Interesting, but why a thermally insulating plastic box?
Have you considered circulating the water to a cooler?

Here is a pair of 10 ohm non inductive resistors I made as a poor student in 1970 and have used ever since.
It was made from a length of electric fire wire and can glow red/white at high current.
This makes it non linear have you checked how linear your resistor is?


Joined Nov 13, 2008
Interesting solution, studiot. Your's has many resistance possibilities.
Wood & nails was my first breadboard.
I wanted something close to 8 ohms to make offset & bias adjustments to audio amps.
Truthfully, I used a glass jar with a metal lid as the first version.
It worked fine for over 10 years but got rusty.
So I put this one together using the same resistors. Have not used water in it yet.
A metal box has never been needed. This container holds more water than the jar did.
I don't expect I'll ever need something more elaborate.
The 10 ohms is stable enough. 8 ohms would be better. 2 of these would be better still. (4 ohms or stereo)
I could try cooking oil instead of water but have not.
Is there a dye that changes color with temperature? That might be fun.


Joined Nov 9, 2007
Yes it's now going rusty (the nails) in the garage, but winding it zig zag makes it non inductive.
I measured the length for 1 ohm and banged the nails in. That makes tappings at 1 ohm intervals as you see.
ETI copied me a few years later by drilling holes in a paxolin frame and stringing resistance wire.

So long as I measure the current and voltage I don't need accurate resistances, however the resistance is pretty stable up to 3 amps current and I have used the pair of resistors to test transformers, power supplies and amplifiers.