Hi all..
My electronics schooling and day-to-day practice of it was all left behind a few careers and many years ago. Getting back into home audio repairs as a hobby again and am building up some of my test equipment. I recall having a handy amp loadbox back when I worked in a shop as a kid.. 4 and 8 ohm switchable input impedance with a volume controlled set of outputs on the back that we could hook a speaker into monitor the output while soak-testing an amp.
Component-wise Im figuring the load resistors will be 8ohm, 100w-ish, 100k 1w or similar and a 10k audio taper pot.
Am I out to lunch or any suggested changes?
thanks for any help you can offer.. Im waaayyy stale, haha.
My electronics schooling and day-to-day practice of it was all left behind a few careers and many years ago. Getting back into home audio repairs as a hobby again and am building up some of my test equipment. I recall having a handy amp loadbox back when I worked in a shop as a kid.. 4 and 8 ohm switchable input impedance with a volume controlled set of outputs on the back that we could hook a speaker into monitor the output while soak-testing an amp.
Component-wise Im figuring the load resistors will be 8ohm, 100w-ish, 100k 1w or similar and a 10k audio taper pot.
Am I out to lunch or any suggested changes?
thanks for any help you can offer.. Im waaayyy stale, haha.
Looks ok, but the 100k may be too high.
To catch soft noises etc. at least add a switchable lower value in parallel with the 100k.
The 8R resistors should be noninductive types.
To catch soft noises etc. at least add a switchable lower value in parallel with the 100k.
The 8R resistors should be noninductive types.
Thanks, Im ok with lowering the 100k, I absolutely just pulled that value out of thin air as I wanted it to have minimal effect on the rest of the circuit..
Thanks for the non-inductive note, will pay attention to that.
The 0-10k in shunt to a 8r speaker will do almost nothing until the last 0.1% of rotation.
You want a 10 to 50 Ohm trim. Loudspeaker attenuator, L-pad, for tweet level or distributed sound.
https://www.parts-express.com/L-Pad-50W-Mono-3-8-Shaft-8-Ohm-260-252
Feed it through say 100 Ohms 10 Watts so it has little loading on your main load and can't be turned up much too loud.
You want a 10 to 50 Ohm trim. Loudspeaker attenuator, L-pad, for tweet level or distributed sound.
https://www.parts-express.com/L-Pad-50W-Mono-3-8-Shaft-8-Ohm-260-252
Feed it through say 100 Ohms 10 Watts so it has little loading on your main load and can't be turned up much too loud.
Switchable 8-4 ohm 100-200W load is fine, but yur attenuator can not drive a speaker, but a power amp.
Options:
1) buy a cheap power amp board (and matching supply) to drive any external speaker at variable volume
2) make a fixed attenuator, say 100 ohm 10-20W plus a 5 or 10 ohm 5W as the lower branch speaker volume will be quite bearable inside your shop butb still give you a realistic idea about amplifier capabilities.
For night use you might add a switchable 1 ohm resistor in parallel with speaker to attenuate it even further to whisper level.
3) a 100 ohm load in parallel with a 4/8 ohm amp load under test does "nothing" if fed from any normal power amp, so don´t worry about that, 99% of amplifiers are voltage sources.
FWIW this is my "3 AM attenuator" for Guitar players, go figure:
here the main resistor R1 is the load to make it even simpler.
Simple as is, it sports (switchable) variable attenuation and even selectable damping factor (which is important in Guitar speaker situation).