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Constructing a new load box/line out : Amps

Constructing a new load box/line out

For amp builders.

Constructing a new load box/line out

Postby IAmTheWalrus » Thu Dec 15, 2016 2:07 am

Never tried to run my amp into my DIY load box wide open before.

About 15 minutes of playing on "10" with the amp going straight into load, I shut everything down to check for issues.

Heat sink on load box was thermonuclear hot. :shock:

Was running one 16 ohm 150W power resistor bolted to a heat sink. After some research I started redesigning this thing.

Here's what I'm building:
Image

This will give me a 16 ohm load rated at 300W.
A step-down audio transformer to line out.
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Re: Constructing a new load box/line out

Postby RitchiesPartyHat » Thu Dec 15, 2016 3:55 am

That's cool - slap a reverb or delay after it, then to a power amp+speaker.

Still think you need to try the "Triple Variac Mod" (as seen on Metrodope) :lol:
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Re: Constructing a new load box/line out

Postby IAmTheWalrus » Thu Dec 15, 2016 1:49 pm

Farmin' ain't easy...
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Re: Constructing a new load box/line out

Postby RitchiesPartyHat » Fri Dec 16, 2016 2:08 am

I'm on the fence re: reactive loads. Primarily because I haven't tried one yet.
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Re: Constructing a new load box/line out

Postby IAmTheWalrus » Fri Dec 16, 2016 2:44 am

Here's the thing most people don't understand about reactive/resistive loads for tube amps...

If you're recording direct, you want a reactive load.

If you're tapping a signal off a tube amp that's running louder than is feasible for your venue, then sending that signal to another, clean, preferably solid-state amp - you want a resistive load with a good quality audio transformer for the line out. A reactive load used like this is going to sound awful.

The whole reason to use a reactive load is because the better reactive loads mimic what a speaker does with the signal. Speaker emulation.
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Re: Constructing a new load box/line out

Postby IAmTheWalrus » Sat Dec 24, 2016 9:19 pm

Pretty much finished at this point.

Image

Drilled and tapped all screw-holes for the power resistors directly into the aluminum heat sink. Bolted them down with thermal paste.

Twisted transformer leads to input, and line out volume pot.

Device is VERY transparent, very quiet after resolving ground loop issue. Runs warm, but not hot.

Running 100W tube amp (plexi) into this with vol on 8. Line out into solid state power amp running effects (delay, reverb, etc.)

schematic:
Image
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Re: Constructing a new load box/line out

Postby RitchiesPartyHat » Sun Jan 01, 2017 11:21 pm

Very nice - and clean work!
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Re: Constructing a new load box/line out

Postby IAmTheWalrus » Thu Jan 05, 2017 5:37 pm

Made one change since this schematic & images was posted.

Changed the white wire that runs from the volume pot to the line-out jack to a shielded cable.
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Re: Constructing a new load box/line out

Postby RitchiesPartyHat » Mon Aug 07, 2017 4:22 am

We should put that schematic in the vault for safekeeping and reference.
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Re: Constructing a new load box/line out

Postby IAmTheWalrus » Mon Sep 11, 2017 6:28 pm

Farmin' ain't easy...
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