Simulating a speaker load

Simulating a speaker load

Postby cmc64 » Mon Aug 20, 2012 7:44 pm

I searched around quite a bit and while I know I have read this before on this forum, I, of course, can not find the info now when it is needed.

I have a McIntosh MC2100 on the way. A JBL cab (or cabs) will soon follow.

But I need a pre-amp, And until I save up the cash to add to the upcoming sale of my Fender SuperChamp X2, I will be without one. Now, my SuperChamp (with upgraded tubes and a JBL K-110, actually not a bad little amp at all) has a 1/4" line-level output. I can use the SuperChamp as a pre-amp until I am able to purchase a dedicated one. It's not perfect, but the output is post-reverb, and it will work during the interim.

My question is this: I know there is some way to simulate a speaker load in a combo amp so when I use the line-out I won't hear the internal speaker (unless of course I want to) and I won't potentially damage the amp. IIRC, this can be done with a resistor of some sort but I really have no idea. If anyone can point me in the right direction I would be most appreciative.

Thanks guys1


Cheers,

cmc64
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Re: Simulating a speaker load

Postby Smolder » Mon Aug 20, 2012 8:09 pm

it's not terribly difficult. I built one with two big resistors inside a (mouser) box with a quarter inch jack. Mine is geared for 8 ohm and 50 watts. That would be plenty for the champ, but not near enough for your mac. I'll try to dig up the plans/source liturature for you tomorrow. Worst case, I can open mine up and shoot a photo. It's really simple.

edit: pretty sure i just googled 'dummy load' and found instructions... all parts came from mouser.

Image

http://www.soundonsound.com/sos/1994_ar ... yload.html
Last edited by Smolder on Tue Aug 21, 2012 7:44 am, edited 3 times in total.
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Re: Simulating a speaker load

Postby gpilcher2001 » Mon Aug 20, 2012 9:14 pm

Pull the power tubes. That will keep you transformer safe, that is if your line out comes before the PI? Also you can't use attenuators with solid state power amps. You'll ruin the amp! Can't seem to find a schematic on this amp. I would try pulling the power tubes and use the line out. If you don't get any signal then the line out comes from the power tubes ant you'll be stuck with your original thought. Greg....
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Re: Simulating a speaker load

Postby cmc64 » Tue Aug 21, 2012 8:34 pm

Thanks for the responses guys!

Smolder:
The 8Ohmn 50 Watt dummy load box will be perfect for the SuperChamp. I just need to shut down the speaker on the Champ and use the line out for the MC2100 so the box you built (and posted) should work just fine. I shouldn't have any worries about the MC2100 after the Champ, should I?


gpilcher2001:
I talked to Fender and they told me that the line out on the SuperChamp X2 is post everything. I would imagine that includes the power amp stage but I don't want to assume anything so I am going to call them tomorrow and confirm. You mentioned not using attenuators with solid state power amps. I wasn't planning on it - the Champ's manual said the line-out is designed to go direct to recording devices and sound reinforcement gear. Fender told me that using the line out to a power amp would work fine. So as far as the attenuators are concerned, am I missing something?

Thanks again guys!
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Re: Simulating a speaker load

Postby Smolder » Tue Aug 21, 2012 8:57 pm

cmc64... I would think so.I just followed the directions and it works for me, but I've mostly used it on 12-30 watt amps. I've never pushed it. I'm told they can get hot so be aware. The two 15 ohm are wired in parallel if that's not obvious from the image. My comment was aimed at you not using a small dummy load on a 100 watt stereo power amp.
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Re: Simulating a speaker load

Postby gpilcher2001 » Tue Aug 21, 2012 9:39 pm

My apologies I should have said dummy load. In reference to smolders first post saying " That would be plenty for the champ, but not near enough for your mac." You don't, iirc, need a dummy load for solid state equipment. The reason for the dummy load on a tube amp is to protect you output transformer. Webervst.com sells dummy load kits if you want something engineered. Greg...
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Re: Simulating a speaker load

Postby cmc64 » Tue Aug 21, 2012 11:59 pm

Smolder wrote:cmc64... I would think so.I just followed the directions and it works for me, but I've mostly used it on 12-30 watt amps. I've never pushed it. I'm told they can get hot so be aware. The two 15 ohm are wired in parallel if that's not obvious from the image. My comment was aimed at you not using a small dummy load on a 100 watt stereo power amp.


Gotcha, that's what I though you were getting at but I wanted to make sure. The dummy load would just be on the Champ. I did a bit of research and found a way to keep the heat down. I can't remember it now (using a higher ohm dummy load or a heatsink or something) as it is getting late but I bookmarked the page so I'll dig it up tomorrow.

The Champ is a 15 Watt amp so I don't have that much power to deal with.

Right-on. Thanks!!
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Re: Simulating a speaker load

Postby cmc64 » Wed Aug 22, 2012 12:02 am

gpilcher2001 wrote:My apologies I should have said dummy load. In reference to smolders first post saying " That would be plenty for the champ, but not near enough for your mac." You don't, iirc, need a dummy load for solid state equipment. The reason for the dummy load on a tube amp is to protect you output transformer. Webervst.com sells dummy load kits if you want something engineered. Greg...


I thought that was what you meant but wanted to be sure. I poked around and found a few pre-made kits and some DIY instructions. I did not come across the one at Webervst.com so thank you for that link. Gonna check it out when I get up. It's getting late......

Much obliged for your help!
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Re: Simulating a speaker load

Postby gpilcher2001 » Wed Aug 22, 2012 6:31 am

good to know you got shoes to wear when you find the floor.....
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Re: Simulating a speaker load

Postby cmc64 » Wed Aug 22, 2012 8:25 pm

gpilcher2001 wrote:Here you go. https://taweber.powweb.com/amptechtools/truload.htm Greg...


Now that looks NICE!

Thanks for the link.

You guys have been a great help!!!
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