Suhr Reactive Load  [schematic]

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

Floris thanks for posting with me you pose some interesting scenarios. However I can't tell the difference from the reactive load using line out vs the resistive load line out. The Line out is taken from the 8 ohm tap of the OT and then a voltage divider network. The reactive load is just basically taking the place of a speaker or motor if you will. The line out doesn't react to the reactive load any differently than a resistive load because all the OT sees is a load. Now if you would put a line out after the attenuator it would sound different as a speaker does and you would hear the resonance freaquency differences. I've used both reactive and resistive in the line out situation and can't tell them apart but using the Thru is very different. Maybe my Fletcher Munson curves are off at my older age lol. Anyway
Thanks for posting and I will be back after more research.

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Post by Ampkat »

Ampkat wrote: 07 Jan 2021, 23:12 Floris thanks for posting with me you pose some interesting scenarios. However I can't tell the difference from the reactive load using line out vs the resistive load line out. The Line out is taken from the 8 ohm tap of the OT and then a voltage divider network. The reactive load is just basically taking the place of a speaker or motor if you will. The line out doesn't react to the reactive load any differently than a resistive load because all the OT sees is a load. Now if you would put a line out after the attenuator it would sound different as a speaker does and you would hear the resonance freaquency differences. I've used both reactive and resistive and a speaker in the line out situation and can't tell them apart but using the Thru is very different. Maybe my Fletcher Munson curves are off at my older age lol. Anyway
Thanks for posting and I will be back after more research.

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floris
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Post by floris »

>"The reactive load is just basically taking the place of a speaker or motor if you will."
Yes, exactly. The reactive load has two purposes:
1) Convert the power of the amp into heat so that the amp does not die.
2) Let the amp behave as it would with a speaker connected.
This results into a different signal at the amp speaker output than with a resistive load, but does not sound like a speaker.

>"The line out doesn't react to the reactive load any differently than a resistive load because all the OT sees is a load."
The tube amp output stage will/should behave differently if it's a reactive v.s. a resistive load.

>"Now if you would put a line out after the attenuator ..."
Where in this reactive load would you put the line-out? It's not an attenuator and had no speaker output.

>"... it would sound different as a speaker does ..."
The reactive load-box will not make it sound like a speaker does. The IR after the line-out will make it sound like a speaker does.

Regards, Floris

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Post by m0rk »

good job! but I guess we are still waiting on that list for the first design of yours :)
any chance??

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Post by karhya »

I think people that are not into audio electronic may not know which kind of capacitor is needed. Electrolytic or film capacitor ?
Also on your last build, you have a funny looking resistor (the 9W 62Ohm). What kind of resistor is it ?
Your output transformer, where did you buy it ? The price goes from very affordable to so expensive. Where is the sweet spot ? Why this one ?
Finally, which brand for the components ? They are so many ^^

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Post by m0rk »

karhya wrote: 12 Jan 2021, 20:27 I think people that are not into audio electronic may not know which kind of capacitor is needed. Electrolytic or film capacitor ?
Also on your last build, you have a funny looking resistor (the 9W 62Ohm). What kind of resistor is it ?
Your output transformer, where did you buy it ? The price goes from very affordable to so expensive. Where is the sweet spot ? Why this one ?
Finally, which brand for the components ? They are so many ^^
So true that...

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Post by evh0u812 »

Anyone know how to reduce the treble content of the suhr load? I've been studying this thread and the gear page reactive load thread. Looks like reducing the 62r resistor will do it? Would like to have a switchable presence control of sorts.
Any ideas?

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Post by floris »

evh0u812 wrote: 23 Jan 2021, 06:56 Anyone know how to reduce the treble content of the suhr load? I've been studying this thread and the gear page reactive load thread. Looks like reducing the 62r resistor will do it?
Yes reduce the 62 Ohm resistor to reduce the treble peak in the reactive load.
Or tweak the frequencies at/after the line out with a tone control or equalizer.

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Post by soulsonic »

floris wrote: 23 Jan 2021, 17:08
evh0u812 wrote: 23 Jan 2021, 06:56 Anyone know how to reduce the treble content of the suhr load? I've been studying this thread and the gear page reactive load thread. Looks like reducing the 62r resistor will do it?
Yes reduce the 62 Ohm resistor to reduce the treble peak in the reactive load.
Or tweak the frequencies at/after the line out with a tone control or equalizer.
I would do this using the eq on whatever you've got it plugged into.
I've been using my Suhr for several months now and overall I'm satisfied with it, apart from still being suspicious of it adding distortion with the fan & signal LED. I've used it with two very different amps and haven't really noticed any excessive treble content. It has always been plugged straight into my computer's audio interface (either an M-Audio Delta 1010 or Behringer UMC404HD) and then I would do cab sim with either Amplitube or Trve Cab. I can't say I've ever really felt the need to cut the treble response using either, though if I did, it would just be a matter of loading an eq into the DAW and cutting the highs a bit. Usually I am able to find a frequency response I like by just fiddling with different cab responses. Now that I've thought about it, that's what I would really recommend; to play with whatever your cab sim is to get the treble response you want. Could just be a matter of loading a different IR.
Haven't tried it with an analog cab sim filter yet, though I plan to soon. I have a tweaked version of ROG's Condor that I built a few years back with a headphone amp that I really like the sound of. Need to mod it to remove the little amp sim circuit and have a proper balanced line in from the load box.

Seeing that the load box project info that was posted has been deleted, I'll make an effort to build one and make a project to share. Can't give a timetable on that, though.
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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Post by evh0u812 »

[/quote]
Yes reduce the 62 Ohm resistor to reduce the treble peak in the reactive load.
Or tweak the frequencies at/after the line out with a tone control or equalizer.
[/quote]

Planning on building the attenuator design that was here fed by the suhr load so eqing it after the load isn't an option. I've breadboarded it and its a phenomenal attenuator, but I'd like to be able to cut some highs at really low attenuator volumes to fill out the sound. Once you really lower the volume the top end feels more prominent. (The complete opposite of every attenuator I've ever used ). Need to calculate the total amount of current flowing through the 62r resistor to figure out if a 3w wire wound pot could be used to dial in a series resistance as a faux tone control. Say maybe a 22k resistor and a 39k pot.

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Post by soulsonic »

Since that attenuator is active, there's nothing stopping you from adding an active tone control circuit between the load and attenuator thing.
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Post by evh0u812 »

Doesn't work that way unfortunately. The input to the active component of the attenuator isn't line level. It's connected to the output of the amp through a pot. With that pot almost all the way up you're asking whatever EQ you install to handle the full voltage of the speaker output. I'm sure you can imagine the voltage that 100 watt plexi would be putting out.

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Post by soulsonic »

evh0u812 wrote: 25 Jan 2021, 22:30 Doesn't work that way unfortunately. The input to the active component of the attenuator isn't line level. It's connected to the output of the amp through a pot. With that pot almost all the way up you're asking whatever EQ you install to handle the full voltage of the speaker output. I'm sure you can imagine the voltage that 100 watt plexi would be putting out.
You could easily make a simple "James" style tone control using transistors running off the same 37 volt rails and it would have plenty of headroom.
Also, the output isolation transformer is a 1:1, so it's not lowering the voltage at all, and I routinely run the volume pot on my original Suhr all the way up or almost all the way up guess what, it doesn't blow up the line level inputs on my sound card. In fact, with a lower powered amp in the 15 watt range, it's actually a bit anemic. You're forgetting there's a 47.5K resistor (R9 in my schematic) in series with the pot. 47.5K with 10K divider means, even all the way up, you're only going to be getting about 5 volts coming out with a 100w amp blasting into it.
Hell, you could even just have a passive low pass filter with a pot and capacitor (just copy a Rat's tone control!) and that might do all you need without any additional active circuitry.
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Post by evh0u812 »

Was overthinking it. 5k log pot and a 100n cap from the attenuator volume pot wiper to ground is perfect. Well that was easy. Lol

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Post by acco »

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

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