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Recording equipment by Magic Death Eye LLC.

June 2023

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New design Magic Death Eye Stereo Compressor

With the cost of 6386 tubes skyrocketing because of only one company (JJ) making them, and other difficult manufacturing hurdles, I spent 3 years redesigning my compressors.
The new models use the very abundant and still manufactured 12AU7 dual triode. This is not a remote cutoff (vari-mu) tube. It does have the widest bias range of all the common 12A(X)7 type tubes.
The 12AU7 can still deliver 5mA of current at -20 volts bias at 350v plate. A 12AX7 shuts off at -3 Volts.
All this means is that the 12AU7 can be slowly turns off over a wider control voltage range, closer to how a vari-mu tube like the 6386 or 6BC8 works.

So I set out to match the performance of my old design with a new design. I rewound transformers, introduced discrete op amps, amassed piles of prototypes and after 3 years, finished a design I’m proud of.
Both the stereo and mono use four 12AU7’s per channel flanked by an input and output transformer.
The stereo has a new EQ loosely  based off the Sontec, using a discrete op amp (Jensen 918 circuit) with the filter circuit in the feedback loop.
There is 6dB of cut and boost for both high and low bands. Each band has 2 frequencies. There is also a 20Hz 24db/octave low cut filter.
I made sure the unit is very serviceable and robust in design.

The Op Amps in the EQ section are my version of the Jensen 918 discrete Op Amp. This was the predecessor to the famous Jensen 990.
I designed them 2 amps to a module and they are socketed and can be switched with another version of the op amp I have designed.

I have been using vintage GE 12AU7’s but any brand 12AU7 works just fine. Some go deeper into compression than others.
Matching isn’t that crucial with the new design. There is no more balance pot as its not needed. Better matching means deeper compression but even an unmatched pair
will easily give you -10db of compression. A good matched pair will go to -20db of compression with very reasonable distortion specs.
The new “DANGER” lights show when the compression is bottoming out. This is more useful than the previous “balance” lights.

 

 

 

Experimental 7 segment display model:

Using this new design, I wanted to experiment with relay based attenuators. Instead of the Elma switches on the standard model, I built modules containing a microchip
that controlled a set of relays and resistors for perfect stepped stereo matching. The audio sees exactly what it would see with regular stepped switches. Resistors and mechanical (relay) switches.
There is no digital processing of the audio.
The micro controller is controlled with a rugged wirewound pot. So the turn is continuous but the steps are shown in 7 segment LED displays.
I really like the 80’s look (hence the Jordache horse) of this system and the clicking sound of the relays when turning the dials. Its more work and complexity so I’m just testing the waters for now.

The new mono¬† compressor uses the same four 12AU7 transformer “block” as the stereo but the path is much simpler with no EQ.
I decided to use an all discrete signal path with the 918 Op Amps.

The compression sound and feel is just like the old units. This is the ultimate vocal or single instrument compressor. Its smooth tube compression is a real treat.
Any setting sounds good and doesn’t fall apart. You can slam things or just put a gentle touch on a vocal. I’m very excited about this new design.

 

 

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STEREO compressor plugin

 

Available for $149 at the DDMF web site.

Demo it before you buy it!

 

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