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Red Box seaker cab simulator

8/23/1999 7:37 PM
Dave James
Red Box seaker cab simulator
Hi All,  
Can anybody give me information concerning a speaker cab simulator called "Red Box"? Info like:  
I've seen/heard one of these things in use and was, frankly, AMAZED at how good it sounded. But I can't seem to find them in any store around the San Jose, CA. area.  
Dave James  
8/24/1999 3:11 AM
Jim S.

They're made by a German company, Hughes & Kettner (sometimes known as just "H&K". I own one and, when I gigged regularly, it seems to work very well. I think I paid around $100 for it. Mine uses a 9-volt battery or phantom power (the output is an XLR connector). I believe the latest version (different versions are referred to as "Mark II", Mark "III", etc.) has a totally passive circuit that doesn't require any DC power source. I don't know if this new one sounds any different from mine.
8/24/1999 12:16 PM

You can find the schematics for some of H&K preamps at "the unofficial H&K site". I believe the speaker simulator in these units is the same as the Red Box. The simulator uses 3 opamps from a TL084. First there's a ~100Hz peak to simulate the resonance of the cabinet. Then there's mid/high shelving boost for presence and two Sallen Key low pass filters that give a 24dB/octave treble rolloff. Maybe in the Red Box the fourth opamp is used to get a ballanced output.  
The newer "Red Box Pro" doesn't use batteries and also simulates the output stage distortion according to H&K so there must be some differences.
8/24/1999 12:48 PM
Mike Burgundy

H6K unofificial site;  
I reckon the new one is a transformer and some filtering, right? The VTwin uses a coil in itīs speaker sim, also looks interesting.
8/25/1999 1:42 PM

To get the same response with a passive circuit you would need 3 coils, 4 capacitors and a few resistors. One RLC to give the peak at 100 Hz, a simple RC circuit for the "presence" and a fourth order passive filter (C-L-C-L) to give the treble rolloff. It's much more close to what a speaker sounds like than the VTwin thing. Plus a transformer for impedance matching/ballanced outputs/ground loop breaking.
8/24/1999 7:11 PM
Dave James

Thanks for the timely info - I checked in at the H&K website and found all that I needed...even local suppliers!  
Thanks again,  
8/25/1999 3:03 AM
CJ Landry

I would like to build one. Does anybody have one they could trace out or have the schematic for it. It can't be that difficult.  
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