Bench Amp test rig

[Techknowman]

Over the past few weeks I have been designing up a test rig for hooking up amps.
This last weekend I started building up the pieces.
Its setup so that I can select inputs A or B which are isolated stereo inputs via Binding posts.
These allow me to hook up a set of speakon connectors to Set A and 1/4" standard jacks for Set B. and depending on which I need I flick a switch. I can also hook banana jacks and other combinations. These have taps for my oscope to connect easily to.

Then there is a switch that ether sends the Audio signal(s) to the speakers or a dummy load. another Switch allows me to select an internal 8 Ohm 100W stereo load or an external 4 Ohm 1KW stereo load.

An additional switch allows me to select to monitor the dummy load through a high resistance to the speakers or headphones with separate "volume" knobs.

This allows high volumes for testing without having to blow my eardrums.

http://techknowman.com/Electronics/Power/Power-Cnt.jpg
http://techknowman.com/Electronics/P...ower-Cnt-1.jpg
http://techknowman.com/Electronics/P...ower-Cnt-2.jpg
http://techknowman.com/Electronics/P...ower-Cnt-3.jpg
http://techknowman.com/Electronics/Power/Heatsink.jpg
http://techknowman.com/Electronics/Power/Dummy-Load.jpg

[jrfrond]

We have similar switch boxes here that I built. On your speaker/load selector, you'll want a center-off switch to test SS amps under no-load conditions. You'll need a hefty toggle switch here.

I use 4 ohm 250W Arcol resistors bolted to a thin metal plate and attached to the back of the bench. They are connected to a rotary selector switch (the heaviest-duty I could find) to configure them for 2/4/8 ohms. This is in the box also. When we need to burn-in high-power amps, I go direct to the 1kW 4 ohm loads with #10 cable. These are fan-cooled for obvious reasons.

[Techknowman]

The small unit mounted to the salvaged copper heatsink is fan cooled and good to 100W a channel at 8 ohms
The unit I have tagged as Dummy load is 4 ohm resisters that I have no real idea how many watts they are. they are 1.5" diameter and 12-14" long each.
I couldn't find any part number on them. I have put 360W at 24VDC into them and they barley got warm! So they must be hefty!

I have included my schematic. As I'm thinking about it at the moment.

http://techknowman.com/Electronics/P...%20control.pdf

[J M Fahey]

24V into 4 ohms gives me 144W. Please check. Thanks.

[Enzo]

Maybe he did it in metric...

[Techknowman]

Maybe he did it in metric...

Yea it was metric watts! LOL.
I screwed my math up plus i looked at the wrong figure I wrote on my scratch pad.
It was 36VDC into 4 ohms @ 9 amps = 324W
I'm guessing these resisters are 2KW or more.

[J M Fahey]

Probably, because in PMPO they would have been around 3800W

[Techknowman]

I did find a number on the big 4 ohm resisters
R250 4(Ohm)K (Ohm symbol)
LD IWAKI

12" long 1.5" dia hollow ceramic with wavy fins all around it, the fins are the windings and are .25W by .010 thick

I found a PDF from the manufacturer. it looks like R250 means its a 400W unit if I read japanies correct?
The 4Ohms is Ohms the K denotes +/-10% tolarance

[J M Fahey]

Please post a link to the datasheet.
My son can read it for me.
Thanks.

[Techknowman]

This is one of the resisters from the unit

http://www.iwakimusen.co.jp/buhin/20-CR-1.pdf

[jrfrond]

The 1kW Milwaukee loads we use look similar, with metal brackets that we just sit them on the concrete floor with. We could barbecue on them when cooking some large power amps. Seriously!!!

We got lucky with these. When Crest moved their facility out of NJ to MS, they donated some of these to us. They had hundreds mounted on custom racks in the "Kitchen" (the amp-cooking room).