# Group Project: Let's build an L-Pad. Anyone?



## traynor_garnet (Feb 22, 2006)

I've been wanting to try my hand at soldering. I've also been shocked at the ever escalating price of attenuators. So, I thought it would be fun to build an L-pad attenuator as a group online project and see how it goes.

If a few of us try it we could help each other out, source parts, and share a few laughs (I am NOT the world's most handy guy; the may end up in a complete disaster! lol). I don't expect miracles from a simple L-Pad, but I used one years ago and was amazed at how good it sounded when it was only attenuating a bit of volume. My goal is too build something that can slightly tame my 20 watt combo and have fun/learn something in the process.

Anyone else interested?

TG


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## keto (May 23, 2006)

Find a schematic or layout and I might be interested.


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## J S Moore (Feb 18, 2006)

How about this one?

http://www.hearditontheweb.com/images/pdf/attenuator.pdf


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## keto (May 23, 2006)

That's not difficult at all, and in fact I have everything on hand except the high voltage resistors and the heatsink compound. Nice clear layout on that one.


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## Lincoln (Jun 2, 2008)

Looks pretty simple. I could use one of them, count me in.


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## greco (Jul 15, 2007)

If one was to make an L-Pad configured to 8 ohms (my amp has 8 ohms output) and have the L-Pad connecting to 2 speakers with with a total impedance of 16 ohms, could the L-Pad act as a way of getting around impedance mismatch (to "protect" the amp)? 

I'm not concerned about the attenuation function...I just want to run 2 x 10" speakers (2 x 8 ohms) and not be worried about my amp.

I'm sure I read about this in the past...but I can't seem to find that application when searching the internet today. Maybe my old brain is fooling me...yet again...LOL

I did build a simple dummy load with a Vishay power resistor (as seen below)










These are very good resistors with about 1% tolerance, IIRC. 
Mine was about $10.00 for 75 watts @ 4 ohms. I only used one.
But they do get VERY HOT and therefore need a good heatsink!! Just a warning !!

Cheers

Dave


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## J S Moore (Feb 18, 2006)

I don't think you need to worry about a 2 to 1 mismatch if it's a tube amp. Might not sound good but it won't hurt it.


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## blam (Feb 18, 2011)

That looks simple enough. I might be interested in building one of these as well


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## greco (Jul 15, 2007)

J S Moore said:


> I don't think you need to worry about a 2 to 1 mismatch if it's a tube amp. Might not sound good but it won't hurt it.


Thanks Jon....Why am I so anal about impedance mismatch?

Going back to my original question...Can the L-Pad be used to "fool" the amp into thinking that there is impedance matching? 
Anyone have any references? 
Is my brain deteriorating?

Cheers

Dave


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## dcole (Oct 8, 2008)

Try putting an 8 ohm resistor in series with your speakers. If the speaker load is 8 ohms the amp would see 16 ohms, but you might get to much bass out of your speakers. You can definetly fake you load how ever you want.

I have heard that the Bridged T attenuator is a good alternative to the standard L-Pad.

The following link has some info on building them: Adam's Amplifiers: Attenuation


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