St. Rock React:IR - frequency response on XLR ports & graphs with Suhr RL & Mesa 4x12 OS cab)

[2dor]

I got my hands on this loadbox about 3 months ago and I think it's pretty much the best value reactive loadbox out there.

Given I also own the Suhr Reactive load (plain one, no IR) and 3 cabs, I set off to plot the frequency response of my amps through each load and I saw something that I need some help with.

With the Amp connected directly to the React:IR, when I take the measured signal from the React:IR's DI.Bal.Out or Bal.Out. interfaces I see a high frequency cut-off from about 4K and up.

If I connect the Amp to the Suhr Reactive load and bypass the Suhr's internal load by connecting the React:IR to the Suhr's THRU port, the frequency response doesn't exhibit that high-end roll-off.

I used a MOTU M4 interface for these measurements and nothing else in between the loadbox (Suhr or React:IR) and the audio interface inputs.

I've ran this test multiple times since I first noticed it, routed the React:IR to my XLR mic inputs (with the unit powered off and phantom power and the unit powered on with its own supply), had the PAD on the Bal.Out. on and off, went to my Line Inputs as well.

Green = Suhr's internal load bypassed with React:IR connected to the THRU port. DI signal captured for measurement from the Suhr's XLR out to one of my MOTU Line Inputs (TRS jack)

Orange = React:IR connected directly to the amp. DI signal captured from the Bal.Out XLR out of the React:IR (with no IR applied) and out to one of my MOTU Line Inputs (TRS jack)

Blue = React:IR connected directly to the amp. DI signal captured from the Di.Bal.Out XLR out (with the unit powered from its own PSU) of the React:IR and out to one of my MOTU XLR Mic Inputs

If anybody has these 2 and could do a similar test, I'd love to see what you get.

 

[2dor]

Added the Suhr RL frequency response to the graph as well (Pink).

 

[eggpl@nt]

I've wanted to buy one for what feels like years now, but they've been out of stock (completely understandably so). When St Rock mentioned a new version is on the way, I started checking the website again because I will buy one.

 

[2dor]

I connected the React:IR into the Suhr (into its THRU port) and re-ran a sweep into the amp's FX return.

I recorded the output of both the Suhr RL and the React:IR and I see the same stuff.

At this stage, I'm not sure what to make of it anymore.

 

[2dor]

So I got a Behringer GI100 Ultra-G that can stand between the Amp and Cab and puts out a supposedly clean DI of the raw amp signal.

I hooked up the gear as follows:

Amp-> Behringer GI100 -> ReactIR

the DI signal coming from the XLR of the Behringer GI100 compared to my other measurements looks pretty damn different than if you were to tap the signal coming out of the React:IR XLR balanced outputs.

Not sure what the deal is with that spike at 50Hz but there is none of that high frequency roll-off present and the curve looks very similar to that of the React:IR when I had it hooked up to the Suhr's THRU port.

@st.Rock I know you folks are working on the next iteration of the unit. Would there be anything that could be done to the current Rev3 unit to get rid of that roll-off on the XLR ports?

 

[st.Rock]

yes
some old version's of React:IR have "problem" on DI XLR out.
You can take signal from Main Out without IR - in this case no cut on high freqs.
Or need to remove one smd part in deep of react:ir to fix DI out.
Loadbox and attenuator have not cut on high freqs. It's only on DI out.

 

[2dor]

yes
some old version's of React:IR have "problem" on DI XLR out.
You can take signal from Main Out without IR - in this case no cut on high freqs.
Or need to remove one smd part in deep of react:ir to fix DI out.
Loadbox and attenuator have not cut on high freqs. It's only on DI out.

Oh nice!! Can you point out which one has to go out?
I'd love to do it on my unit

 

[2dor]

yes
some old version's of React:IR have "problem" on DI XLR out.
You can take signal from Main Out without IR - in this case no cut on high freqs.
Or need to remove one smd part in deep of react:ir to fix DI out.
Loadbox and attenuator have not cut on high freqs. It's only on DI out.

It seems that both my Di.Bal.Out and Bal.Out ports have this roll-off

 

[st.Rock]

it's depends from input knob -( on max it will be minimal roll-off.
Other details in PM

 

[MirrorProfiles]

it's depends from input knob -( on max it will be minimal roll-off.
Other details in PM

Oh thats interesting. This is comparing the curve against the line out on my Ampete. Green is with the input knob maxed, red is when its lower.

 

[2dor]

I took out my Ceriatone King Kong for some additional measurements just on the Rect:IR's load but hooked up to the amp using the Behringer GI100 ultra-G di box.

I hooked up my Mesa 4x12 OS straight cab exactly the same and the measurements show they're like in between 1-2 dB apart from each other. DI was running on an internal 9V battery here.

If I use phantom power (48V) to power the DI, the graph is slightly different but still between 2 dB of each other but then again, this behavior is caused by the Behringer DI box not the load.

My conclusion is that the React:IR's load is great but the units like the one I have (Rev3) suffer a bit from the behavior @st.Rock confirmed on the XLR ports and input volume.

BUT there are ways around it (using a DI like the Behringer GI100 or something like a Kemper DI probably) for folks that want to juice out that extra delta and get as close to what the React:IR's frequency response / impedance curve was intended to deliver.

 

[2dor]

And just so people can gauge how it stacks up to the competition, here's the React:IR and the Suhr Reactive Load on the same graph together, both measured through the same setup (going into the Behringer GI100 and then into the Amp).

1.5 ~ 2 dB delta in the lower resonant frequency; the rest is probably down to component tolerances.

 

[2dor]

Figured out I was shooting way too quiet sweep signals into the FX return of the amps.

Reshot the React:IR (chained to the amp using the Behringer GI100) and the Suhr; both loads connected to the amp in parallel
(amp output flipped to 4 ohm for two parallel 8 ohm loadboxes).

They are very close with the React having a slightly thicker low-end.

 

[Rotors]

I also have one of these units.
Could someone please explain to me in simple step by step terms how I can test my unit to see if it has this fault.

Not sure what program to use or how to do the sweep test etc.

Thanks in advance.

 

[2dor]

I also have one of these units.
Could someone please explain to me in simple step by step terms how I can test my unit to see if it has this fault.

Not sure what program to use or how to do the sweep test etc.

Thanks in advance.

You'll need to figure a couple of things out but here's what you need to do:

1. Connect the amp to the reactive load; set the "Input" level at noon
2. Connect the output of the reactive load to the audio interface input
3. Connect one of your audio interface's Line Out ports into a reamp box (Palmer Daccapo/Trave, Radial X-aMp, Signal Art, Walrus etc.)
4. From the reamp box output, go into your tube amp's FX Return
5. In the DAW, load up a new track with a sine sweep WAV file
6. Route that track out of your audio interface's Line Out (the exact same Line Out you've connected to the reamp box)
7. Make sure you run that sweep at a lower volume / level; ideally you won't want the poweramp to go into distorting
8. Capture the signal coming from the Reactive Load into the audio interface within the DAW
9. Use the "Tone Match" feature to match the "original sine sweep" you loaded in the DAW to the signal you got from the reactive load
Normalize to 0 dB maybe for consistency
10. The resulting "Match" WAV file is an IR; it represents the frequency response of your amp connected to the reactive load at the "Input" level set at step 1

11. Without touching any dials on your amp, set the "Input" level on the St.Rock unit at max
12. Repeat steps 2 - 10

You'll have the frequency response of the reactive load now with the "Input" at noon and Max.

Download REW (room eq wizard) - it's free - and just drag&drop those 2 IRs inside the window that pops up. Look at the graphs and identify if the highend response looks different between the two of them.

Hope this helps.

 

[Rotors]

Wow, thank you so much 2dor for your time and efforts explaining all of this.
It is very much appreciated.

Kind regards

 

[2dor]

For folks wondering how the first React:IR and the React:IR II reactive load frequency responses look like, here's what I have.

Because of a known condition with some of the early units, the first React has a high-end frequency roll-off unless the "Input" knob is cranked up (problem with this workaround is you can easily clip the input of the load if the amp's cranked up).

Knowing this, I used the Behringer GI-100 for the XLR output and simply hooked the first React:IR loadbox to it as a dummy cab.