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FDP Forum / Amp Mods, Repairs, and Projects / Yet another line out question

K9 Big Dog
Contributing Member


Molon Labe!
Jul 15th, 2017 05:58 AM   Edit   Profile  

OK, I picked up a used H&K Red Box Pro, and a cable that has dual spade connectors on one end and a 1/4" plug on the other. The RB Pro is passive. The plan is to put the spade connectors on the extra lugs on one of my Bassman RI's speakers and then use the XLR out on the Red Box (and it's cabinet simulator) to go to the PA, thereby just tapping the signal off one of the speakers.
The Red Box has a input select switch for line level or speaker out. My guess is speaker out but I just want to be sure so I don't wreck my amp. Am I right?

Most applications would call for putting the Red Box in between the power amp and the speaker but I'm think that just tapping off one of the speakers should be ok because the Red Box wouldn't be seen as a load.

Contributing Member

The rain sounds like

a round of applause
Jul 15th, 2017 07:54 AM   Edit   Profile  

Hey brother, there are several ways to do it.

Click the link below. The stuff on the left side is in simple English.

I think the stuff on the right side is technical engineering gobbledygook because I can't understand any of it.


K9 Big Dog
Contributing Member


Molon Labe!
Jul 15th, 2017 08:39 AM   Edit   Profile  

I have that sheet, I just want to be sure that the way I want to connect is kosher because I'm connecting in a slightly unorthodox manner. By tapping off of the spare speaker lugs to the input only of the Redbox, the output from the speaker tap won't be passing from the Redbox input to its own Thru port and back to the speaker. The Box will be getting what amounts to a parallel signal to what the speaker is getting (I think). Because the amp will still have its original load on it I'm hoping that this won't affect it at all. I'm reasonably sure that is ok but I figured I'd ask the experts here. As long as this is a safe move I should be ok.



Jul 15th, 2017 08:55 AM   Edit   Profile  

There may be a better, or easier to understand, way.

I believe that the Bassman RI uses a non-standard way of hooking up the speakers. It doesn't connect to the amp chassis using a regular old 1/4" plug with speaker wire. It uses spade lugs (somebody at Fender must have been working overtime the day they came up with that).

Weber makes an adapter cable set that allows you to easily connect a power attenuator to the Bassman. It has two cables.
- Spade to 1/4" male to connect to the input of the attenuator.
- 1/4" male to spades to connect from the output of the attenuator to the speakers.

Replace the attenuator with the Red Box and you should be off and running.

The cable looks easy enough to build your own if you have the parts. But the price from Weber is so stupid cheap that it may not be worth the trouble to do your own.

And in case it isn't obvious: Don't operate your tube amp without a speaker/load connected.

Weber Bassman speaker to attenuator adapter

(This message was last edited by ejm at 06:54 PM, Jul 15th, 2017)

Steve Dallman
Contributing Member

Merrill, Wisconsin

Age is just a number...mine is big
Jul 20th, 2017 05:51 AM   Edit   Profile  

The in and through on the RedBox are connected in parallel, so the way you want to hook the box up is just fine.

K9 Big Dog
Contributing Member


Molon Labe!
Jul 23rd, 2017 05:54 AM   Edit   Profile  


FDP Forum / Amp Mods, Repairs, and Projects / Yet another line out question

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