AstroSim

DeadAstronautFX Astro-Sim Cabinet Simulator. Background information - cultural elements.

Thermionic Studios is building two(2) AstroSim cabinet simulators. They will be available for rental once completed.

Controls

Image from Reference Image

• Switch 1 - "Gain": Switches between three different gain settings, left to right: Bright, Dark, and Middle.
• Switch 2 - "Vintage/Modern": Switches the the sound of the output between a vintage or a modern speaker cabinet.
• Knob 1 - "XLR Vol": Adjusts the volume going to the XLR-out jack with fully clockwise being full volume.
• Knob 2 - "Hi": Adjusts the high or treble frequencies.
• Knob 3 - "Air": Never really had a control like this. It sounds like it focuses (clockwise) or muddies the output sound.
• Footswitch 1 - "On/Off": This footswitch toggles the pedal between engaged/active ("On"), and bypassed ("Off")

Bypass: True

The DeadAstronaut AstroSim is a true bypass effect.

General Information

This has been built into a pedal, but this may well have been the overlooking of the function of a cab sim since DeadAstronaut has been building pedals prior to building this "effect". The true benefit of such an effect is to be able to plug an instrument signal chain directly into a mixing console instead of pulling out an amp and mic'ing it up. A cabinet simulator can make all of that set up irrelevant if you know that the cab sim is the kind of tone you're looking for. But, if this "effect" is the last piece of equipment before plugging directly into a soundboard, then the question still stands if this effect shouldn't be on a pedalboard but sitting instead on a console or computer recording interface.

The other thing that you'll notice, especially with DeadAstronaut's current build manual: the PCB was designed to be housed in a smaller 1590B-sized enclosure. However, in order to accommodate the XLR output jack, DeadAstronaut's manual shows the PCB sitting inside a larger 1590BB-style enclosure. If you can forego the XLR out, building this in a 1590 is perfectly acceptable. We're currently working on seeing if a 125b / 1590N1 enclosure will be able to house both the PCB and the XLR output jack despite the all-around smaller size.

PCB Issue

After running and checking the circuit on the PCB for building, we noticed that the output traces on the board have been printed in reverse: output 1 is actually output 2 per the schematic, and vice-versa. Something you may want to keep in mind if you've bought an AstroSim from DeadAstronaut yourself. Probably would have pulled my hair out spending hours trying to figure out why the jack didn't have any sound.

This will probably be a new practice moving forward on all PCBs before assembly.

Phase Inversion: Yes

Didn't actually expect this to invert phase when we received this but an inspection of the schematic shows that the very first gain stage inverts the signal, and then doesn't get corrected ("What about IC2_B??", you say? Read on...).

DeadAstronaut actually designed this specifically for the XLR output. An XLR output is called a "balanced output" as opposed to an instrument cable, which is an "unbalanced output". The reason being is in order to reject line noise. The way a balanced line works is actually pretty smart. What will happen is that the two signals, each inverted from the other, will tend to pick up the same sorts of errant signals and noise as these signals travel simultaneously, and side-by-side in the balanced cable.

The XLR Magic Out

Here's where the magic of the balanced cable now gets put into play. The receiving side: the console, or mic preamp, or whatever will take one of those signals and invert it again. What this then subsequently causes is for any errant signals or line noise to get its phase reversed while the original signals are put back into the same phase. When the two in-phase signals (desired) are mixed back together again, the errant signals or other line noise (not desired) have now had their phases reversed and therefore get mixed together out-of-phase. The two out-of-phase signals then cancel each other out, thereby providing a clean signal.

This is why much longer cable lengths for XLR (typically microphone) are so easily tolerated. They've been engineered to use the property of phase cancellation to "disappear" unwanted line noise and other possible signals that the line may be otherwise picking up.

Note that the other half of the first Opamp which goes to the headphone output doesn't invert the signal again in order to put it back into it's original phase.

Schematic ID	Electronic Part	Action	Phase State
IC1_A	NE5532	Inverts	Inverted
IC1_B	NE5532	Non-Inverting	Inverted
IC2_A	NE5532	Non-Inverting	Inverted
IC2_B	NE5532	Inverts	Original

Schematic

© Copyright 2019, Thermionic Studios

Artists

We are currently unaware of any artists actively using the pedal now, or who have in the past.

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Additional Sources