Slaving a mark iv to jcm 800 with a loadbox (IR) captor x or suhr ir?

[omnio]

This is my first post in the forum although I have been reading forums since the beginning of internet...
I am going straight to the question for which I have not yet found a straight solution.
I have a mark iv bough new in 1991 and a moded marshal jcm 800 1981 vertical with (currently) a metropoulos fx loop. These two have been the only amps that I kept since 1990 and I am not going to sell....
I have never slaved the mark to jcm but I have been thinking to give it a try. I read a lot and concluded that I will use the fx send from the mark and not the slave out (as I want first to check only the preamp). I also read that I have to use a load box for the boogie. I also have a marshall powerbrake but lately due to other reasons, I have to start playing using headphones.
So, my questions are both related to amp slaving but also to choose the correct reactive load box. My goal is to be able to slave the amps by using one load box. Questions:
1. The volume will be controlled by the master volume knob on the jcm or the one on mark iv? I guess from jcm since this is going to be the power amp but what will happen if I use the volume on mark?
2. Regarding the above question, will the reply be different if I use the slave out?
3. I think I concluded either to two notes captor x or the suhr ir. I the manual of the suhr ir, it demonstrates how you can slave the amps for both using the headphones but also use it as load box. But I like a lot more the sound (and options) from captor x so, my question is, can captor x work both as IR (headphones) and as load box at the same time?
4. If not, my other idea is (if possible) to use captor x as IR and powerbrake as a load box which as I found only in one forum with no more details, that power brake can work as a load box if the knob is turned up to 2-3 clicks before full attenuation. Has anyone been using it like this?

I apologize for the long and confusing post, but my kids do not allow me any other typing...lol

thank you all in advance

 

[rarebitusa]

I've experimented a bit using different power amps with my other Mesa preamps. You can certainly obtain enjoyable combinations with that approach. With that I've typically run the Fx send of the preamp to the Fx return of the power amp. All of my amps had a master vol so the power amp volume was the main control, however the preamps chan masters also control the volume of the Fx Send, plus for many Mesa amps there is a level pot for the Fx Send. So they all kinda work together.

The Slave out is a tap off the output transformer. It's valid to use that as an input to the Fx return of the power amp, could be fun to experiment. Either way always have a speaker or reactive load on both of your amps output to prevent ever running the power section without a load.

I have a Captor but the Captor X is similar and fundamentally a load box with the download IR capability. I've looked at the Suhr IR and it operates in generally the same way as the X. No need to run the powerbrake with the X.

 

[omnio]

Thank you very much for your reply!
My goal is actually to use captor x (or suhr ir or…) for the ir and headphones so it should be connected to the speaker output of the power amp. This means that I have to use a load box just for the load on the mark iv. This is why I asked to the power brake acting not as attenuator but as load box.
Unless there is a way to use one load box for both.

 

[rarebitusa]

I don't think you can use a single load for both. The powerbrake, from what I could tell, is just a speaker attenuator so it needs to see some load on it's output. Typically a speaker. I have an old Scholz Power Soak which kinda works the same way, needs to have a speaker attached to it. But if the goal is completely silent playing you could use an 8 ohm resistor of some decent wattage and run max attenuation on the powerbrake.

Not sure how the MarkIV fx loop works. If it's a series loop then running a jack in the FX send would disconnect the power section and if there is no FX return signal it would have no output. I'd still have a speaker on it's output either way.

 

[omnio]

Good idea with the resistor on the output of the powerbrake! I will get into it. It should be difficult to diy one.
Regarding the use of one load ir box for both amps, in the manual of suhr, page 9:
https://media.suhr.com/wp-content/uploads/2020/10/13163126/Reactive-Load-IR-100220.pdfshow that it can be used for amp slaving but not so sure that this setup can be used for silent playing with headphones. Maybe I should send also an email to suhr support. lol

Mark iv has a series fx loop so indeed you are right, power section will be out of the equation, and this, for my first attempt, to have. For sure I would connect a load box even I read that if you run the amp low and turn master volume to 0, the chances to damage it are minimal.

 

[rarebitusa]

Ahh yes the Suhr "slaving" is taking the R-Loads DI (non-IR) out of amp #1 to the FX Effects return of the 2nd amp. Which you can run at a much lower volume. with a cab Of course you can run the PowerBrake on the 2nd amp with a speaker and get it at a whisper volume level if desired. FWIW if amp #1 is the Mark IV using the Slave Out to drive the FX return of amp #2 is in essence the same approach.

Probably stating the obvious here...

WRT the headphones, that is the "IR" signal you'd be hearing with the amp it's the load for, in that case it's amp #1. So in the "slaving" example the headphones would always just be monitoring amp #1 with an IR cab model. To get headphones out on amp #2 you'd have to physically swap the amps position ie: #2->#1

 

[omnio]

You are absolutely right. I am trying so hard to find a way to do it with one box and I missed the obvious...
The ir box should be connected to the amp that suppose to have the cab connected - replacing the cab itself. The dummy load box will be connected to the slaved amp.
So:
boogie speaker out > load box
boogie slave out or fx send > marshall fx return
marshall speaker out > ir load box
Suhr does not support the above setup which I am trying to achieve so the only way to do it is as rarebitusa mentioned above with a resistor or a dummy load box on the boogie.

 

[Jay Omega]

You are absolutely right. I am trying so hard to find a way to do it with one box and I missed the obvious...
The ir box should be connected to the amp that suppose to have the cab connected - replacing the cab itself. The dummy load box will be connected to the slaved amp.
So:
boogie speaker out > load box
boogie slave out or fx send > marshall fx return
marshall speaker out > ir load box
Suhr does not support the above setup which I am trying to achieve so the only way to do it is as rarebitusa mentioned above with a resistor or a dummy load box on the boogie.

If you want the color and sound of the Mark IV power section and graphic EQ, you need to load the Mark IV. Taking the signal from the slave out port will work fine. In this scenario, the channel volumes, master volume, and the slave level will all be useful to control volume. The presence controls will also be active.

Another idea would be to remove the power tubes from the Mark IV and use the effects send from the Mark IV into the effects return of the Marshall. This way, the Mark IV does not need a load, but the graphic EQ, presence controls, master volume and slave volume will not be active. You can control the level of the Mark IV output using the channel volume controls.

 

[omnio]

Thank you all for your replies!!!!
Yesterday a friend gave me to test torpedo captor x. Also, I had couple of metal power resistors 200w 8 ohm and some 4 ohms so I did some soldering to a neutrik ts 1/4 and used it as dummy load on the mark iv.
I did both tests (slave out and fx send) and I really liked the slave out option, as as you mentioned apart from the power section (6l6) other things were also available such as eq and presence. Blending 6l6 and el34 from the jcm was quite impressive and huge!!!
Captor was connected to marshall speaker out and used my headphones and everything worked perfectly. Of course it needed some tweaking, as initially there was too much clipping, from my "default" settings with cab.

Much appreciate your help guys!