The Swamp Witch Pedals Silver Birch is a dual gain stage overdrive voiced after a Sunn Model T amp. Delicious Audio describes it as "a very flexible dual gain stage overdrive voiced after a Sunn Model T amp", and as an overdrive with distortion capabilities, so it sits between a straightforward overdrive pedal and a fuller distortion pedal in what it can do1.
Controls and modes
The pedal carries two gain channels, Channel I and Gain Stage II, with Gain Stage II the brighter of the two. The bottom row holds a bass and treble shelving EQ. The controls, as described by Delicious Audio1:
| Control | What it does |
|---|---|
| Channel I Gain | Adjust the gain for the low/midrange channel1 |
| Gain Stage II | The brighter gain stage1 |
| Lows | Post-gain, cut or boost lows1 |
| Treble | Bass and treble shelving EQ on the bottom row1 |
| Volume | Make it softer or louder1 |
| Bypass Switch | Turn it off and on again1 |
The footswitch on the right switches the relationship of the two gain stages between Parallel and Series. In series mode there is more gain overall and the brighter Channel II is last, tightening up the sound, while in parallel you can get lower gain tube-like drive tones1. That makes the mode switch the main character control on the pedal: series for a tighter, higher-gain voice, parallel for softer, more open drive.
Sound and circuit
Delicious Audio sums up the pedal's character as "Warm and round. Boomy and haunting. Rich and cutting."1. Under the hood it works through a circuit employing CMOS hex inverters, a chip-based gain approach, with the overall voicing taken from the Sunn Model T amp1.
Power and switching
The Silver Birch runs on 9V and draws 50mA1. Switching is relay true-bypass soft-click switching, so the pedal is out of the signal path when off and the footswitch action is quiet1.
With a 50mA current draw1, the Silver Birch needs a 9V supply with enough current headroom; a low-current daisy-chain output may not be sufficient.
Videos
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Questions
Is the Swamp Witch Silver Birch true bypass?
Yes. The Silver Birch uses relay true-bypass soft-click switching, so when the pedal is off your guitar signal passes through untouched. The soft-click relay also keeps the footswitch quiet compared with a mechanical click switch. The bypass switch itself does exactly what it says: turn it off and on again.
What power does the Silver Birch need?
The Silver Birch runs on 9V and draws 50mA, so a standard 9V DC pedal supply with enough current headroom will run it. Because it draws 50mA, check that any daisy-chain output or battery-style supply you use can supply that current alongside your other pedals.
What is the difference between parallel and series mode on the Silver Birch?
The right footswitch changes how the two gain stages relate. In series mode there is more gain overall and the brighter Channel II sits last in the chain, tightening up the sound. In parallel mode you can get lower gain, tube-like drive tones from the two stages working side by side.
Does the Silver Birch use CMOS hex inverters?
Yes. Delicious Audio describes the Silver Birch as working through a circuit employing CMOS hex inverters, the same kind of chip-based gain approach found in a number of boutique overdrive and distortion designs. That circuit is voiced after a Sunn Model T amp.
What does the Lows knob do on the Silver Birch?
The Lows knob sits after the gain stages and cuts or boosts lows. It works alongside the Treble control as a bass and treble shelving EQ on the bottom row of the pedal, letting you shape the low end after the drive character is set.
Sources (1)
- Swamp Witch Pedals Silver Birch Overdrive, Delicious Audio, 2021-11-29