Suhr Reactive Load  [schematic]

Tube or solid-state, this section goes to eleven!
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acco
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Post by acco »

:D starting today this build: https://ibb.co/bQYVY9x

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evh0u812
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Post by evh0u812 »

Looks great. You might want to remove that bolt holding the inductor down and replace it with plastic cable ties. If it's not stainless the inductance won't be accurate.

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acco
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Post by acco »

@evh0u812 thanks a lot, I hadn't really thought about it I will follow your advice

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floris
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Post by floris »

Or use a nylon bolt.

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Post by floris »

acco wrote: 28 Jan 2021, 09:22 :D starting today this build: https://ibb.co/bQYVY9x
I see two problems in this build, if I see it correctly:
1) Why is there a connection between the 68 Ohm resistor and one side of the output transformer? The output transformer needs to be connected to earth there. The 68 Ohm resistor (parallel to the 0.6mH coil and the 22nF cap) should not be connected to earth.
2) Why is the other side of the output transformer connected to the 47k Ohm resistor? The 10k Ohm line out volume pot needs to be connected in between so it forms a voltage divider with the 47k Ohm resistor.

Where will you put the capacitor(s) (3x 80uF in parallel = 240uF) that go parallel to the big 6mH inductance?
Are the power resistors mounted off board on a heat sink?

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acco
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Post by acco »

thanks friend,the number 1 is an error I'll fix it as soon :worship: , the 47k is also wrong :cry: .
yes the power resistors are on the heatsink and the capacitors will go in their place when they arrive. THANKS for the corrections I will post photos during the next phase of the work.

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floris
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Post by floris »

Yes the 47k is in series with the 10k pot. But the WIPER of the 10k pot needs to be connected to the output transformer. The 47k resistor should not be directly connected to the output transformer. Please check again because it looks like it is not connected correctly.
edit: Oh it looks like you see this problem...

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floris
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Post by floris »

And don't forget to connect the "68 Ohm resistor // 0.6mH coil // 22nF cap" in series with the "3x80 uF capacitors // 6mH coil".

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m0rk
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Post by m0rk »

Guys, I wanna try and build a very simple reactive load box based on this Suhr design, I edited the schematic traced by soulsonic, omitted everything that I won't be needing and I just need someone with more experience than me to confirm that I did not go too far with it :D
Simple.jpg
Also I will be replacing the big 7 Ohm power resistors with 8 Ohm values, since I have them from a previous project (a simple dummy load box). Is this of any concern?
Please!

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floris
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Post by floris »

You need the Line Out! But you can leave out the balanced output if your have a DI box or some sort of transformer isolator, unless ground loops are not a problem for you.
The 8 Ohm resistors will be fine.

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m0rk
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Post by m0rk »

Thanks for your reply!
My amp has a built-in direct output socket, it's a Mesa Boogie Mark III, so I only want to replace the speaker with this reactive load, for silent recording.

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Optical
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Post by Optical »

The mark III output isnt isolated (just a divider on the output), so you might have ground loop issues.
But you can add the line transformer isolator easily to resolve

I also have a Mark II (green stripe), great amps

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m0rk
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Post by m0rk »

Mine is a purple stripe. Yep, great amp, totally love it!
And no, I don't get any ground loop issues on the direct output with my speaker plugged, so I hope I should be ok with this simple design.

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floris
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Post by floris »

Ah right your amp already has a Line Out from the speaker output, you'll be fine.

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m0rk
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Post by m0rk »

ok then, thank you guys, I'm like a total beginner and I really needed to run this by someone pro. :cheers

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Post by soulsonic »

Be sure to use a big heatsink so you don't need a fan!
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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m0rk
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Post by m0rk »

sure thing! by the way, thanks for sharing this, much appreciated!
never would have thought that a small box with a few electronic components could cost almost 500 euros here in Europe...

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Post by xbearxau »

Id really recomend fitting the line out. Its only a couple of parts and I promise you one day you will want to use this with another amp.

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m0rk
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Post by m0rk »

when that day comes I hope I will have enough knowledge to build something new and more complex, of my own design maybe :lol:

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