My 100W 8 Ohm Dummy Load Project

got questions or ideas on audio bench setups or test equipment?
Post Reply
User avatar
4thtry
Posts: 23
Joined: Tue Mar 30, 2021 7:48 pm

My 100W 8 Ohm Dummy Load Project

Post by 4thtry »

Greetings everyone,

I salvaged the chassis and heatsinks from an old, burned-out auto-sound amplifier to make a new stereo 8 ohm dummy load. The old amp was a Sanyo PA6100 with two large aluminum finned heatsinks on each side.

_DS75966.jpg
_DS75966.jpg (130.79 KiB) Viewed 126 times

I started out by drilling and tapping the big heatsinks and then bolting the resistors to them with #10-32 machine screws. These are the 100W 8 ohm dummy load resistors sold by Parts Express (#019-020).

_DS75971.jpg
_DS75971.jpg (134.73 KiB) Viewed 126 times

I used four banana jacks for amp inputs, four banana jacks for scope inputs, and two heavy duty DPDT toggles switches to switch between dummy load and external speakers. You will notice in the photo that I removed about 1/4" of the plastic insulator from the lower set of banana jacks and then drilled 4 small holes near the ends of the jacks to accommodate clip-on style test connectors. This allows me to use my fully compensated 10X oscilloscope test probes to make all measurements.

_DS75998.jpg
_DS75998.jpg (143.09 KiB) Viewed 126 times
User avatar
4thtry
Posts: 23
Joined: Tue Mar 30, 2021 7:48 pm

Re: My 100W 8 Ohm Dummy Load Project

Post by 4thtry »

I cut holes in the other end for a pair of external speaker banana jacks:

_DS76004.jpg
_DS76004.jpg (140.42 KiB) Viewed 124 times

Then I wired it all up with #18 NTE hookup wire:

_DS76013.jpg
_DS76013.jpg (128.43 KiB) Viewed 124 times
User avatar
4thtry
Posts: 23
Joined: Tue Mar 30, 2021 7:48 pm

Re: My 100W 8 Ohm Dummy Load Project

Post by 4thtry »

I bolted the heatsinks back onto the sides and soldered the 8 ohm 100W resistors to the switches.

_DS76043.jpg
_DS76043.jpg (133.13 KiB) Viewed 124 times

I silicone glued a small wooden block between the two switches to keep them from twisting loose:

_DS76056.jpg
_DS76056.jpg (132.94 KiB) Viewed 124 times

The finished unit:

_DS76071.jpg
_DS76071.jpg (120.25 KiB) Viewed 124 times
User avatar
4thtry
Posts: 23
Joined: Tue Mar 30, 2021 7:48 pm

Re: My 100W 8 Ohm Dummy Load Project

Post by 4thtry »

-
Finally, I mounted the dummy load to the side of one of my test bench partitions. My calibrated 10X scope test leads clip onto the bottom set of banana jacks. The amp under test then connects to the center set of banana jacks. And the two switches along the top flip between dummy load and a pair of external monitor speakers. It will handle over 100 watts per channel into 8 ohms and can be wired externally in series or parallel to handle single channel 4 or 16 ohm tests as well.

_DS76103.jpg
_DS76103.jpg (136.2 KiB) Viewed 123 times
Hugo
Posts: 146
Joined: Sun Feb 28, 2021 10:20 am

Re: My 100W 8 Ohm Dummy Load Project

Post by Hugo »

Very nice.
BTW, you don't need audiophile cables for a dummy load 🤓
User avatar
Tom_S
Posts: 84
Joined: Thu Feb 25, 2021 2:29 am

Re: My 100W 8 Ohm Dummy Load Project

Post by Tom_S »

Looks great Bill! I like what you did with the modified bananas. You also get bonus points for repurposing that old Sanyo amp.
User avatar
4thtry
Posts: 23
Joined: Tue Mar 30, 2021 7:48 pm

Re: My 100W 8 Ohm Dummy Load Project

Post by 4thtry »

Thanks, Hugo and Tom. Much appreciated. I should have built this contraption a long time ago. Really cleans up all the cable clutter on my work bench. :D I do plan to replace the thick audiophile cables with much more flexible, low resistance type banana plugs. I have to be careful, though, because some of the cheap banana cables that I have measure fairly high in terms of series resistance (using DATS V2).

Bill
Hugo
Posts: 146
Joined: Sun Feb 28, 2021 10:20 am

Re: My 100W 8 Ohm Dummy Load Project

Post by Hugo »

4thtry wrote: Sat Jul 17, 2021 3:17 pm I have to be careful, though, because some of the cheap banana cables that I have measure fairly high in terms of series resistance (using DATS V2).
Oh yes, I have had banana plugs go up in flames, though not with an amplifier.
Post Reply