The Pure Tube Channel (PTC) is a single-channel Class A tube microphone preamplifier in a desktop/rackmount enclosure, built by IGS Audio around a minimalist signal path philosophy: Carnhill input transformer, two Class A military-grade tubes (6N2P-EW and 6N1P-EW), Edcor output transformer – and only two Mundorf capacitors in the entire audio path. Every passive component in a signal chain is a compromise; the PTC rejects that compromise by constructing the path with the absolute minimum of elements. Two XLR connectors on the rear panel (input and output) are joined by direct access to the tube sockets from the back of the enclosure without disassembly – facilitating tube rolling from the engineer's custom set that IGS Audio offers for the unit: 6N2P, 6N1P, 6B23P, 6BC8, 6BZ8. Maximum gain: 65 dB, SNR: –110 dB.
Signal path architecture – why every component choice matters
The PTC signal path follows a strict minimum-component philosophy: the Carnhill input transformer provides galvanic isolation and balanced input, the first 6N2P-EW double-triode (Class A) forms the voltage gain stage, the second 6N1P-EW double-triode (Class A) brings the signal to line level, and the Edcor output transformer delivers a balanced 600-ohm output to the next device in the chain. Two Mundorf capacitors are the only capacitive elements in the audio path – chosen for low ESR, thermal stability, and minimal phase influence. The absence of correction capacitors and surplus passive elements means every amplification stage operates with the full, uncorrected character of the tube, without tonal correction built into the circuit.
Hi-Z input and gain control
The Hi-Z input (1 MΩ) routes the guitar or bass signal directly to the first tube grid without an active buffer – in practice this means the electric instrument has a direct electrical relationship with the first triode and its saturation characteristics. The resulting character is not available in preamps with a buffered instrument input. Gain is controlled via a 6-step Gain switch and a 41-click Trim, providing the precision of 500-series module switching in a standalone desktop format. A –20 dB pad and +48V phantom power complete the feature set. Balanced microphone input impedance is 300/1200 Ω (selectable via the Carnhill transformer). Maximum input level +18 dBu, maximum output level +22 dBu.
KEY FEATURES
- Fully tube Mic/Hi-Z preamplifier, Class A, single channel
- Minimalist path: input transformer + 2 tubes + output transformer + 2 Mundorf capacitors
- Tubes: 6N2P-EW + 6N1P-EW (military-grade, Class A)
- Input transformer: Carnhill (balanced, 300/1200 Ω)
- Output transformer: Edcor (balanced, 600 Ω)
- Only 2 Mundorf capacitors in the signal path
- Gain control: 6-step Gain switch + 41-click Trim
- Hi-Z input: 1 MΩ, signal direct to tube grid
- Pad –20 dB, phantom power +48V
- Engineer's alternative tube set available: 6N2P, 6N1P, 6B23P, 6BC8, 6BZ8
- Direct rear-panel tube socket access without disassembly
TECHNICAL SPECIFICATIONS
- Type: tube mic/instrument preamplifier, Class A, mono
- Tubes: 6N2P-EW + 6N1P-EW (military-grade)
- Input transformer: Carnhill (300/1200 Ω)
- Output transformer: Edcor (600 Ω)
- Capacitors in signal path: 2× Mundorf
- Input impedance (balanced): 300/1200 Ω (Carnhill)
- Hi-Z impedance: 1 MΩ
- Output impedance: 600 Ω (Edcor)
- Maximum gain: +65 dB (6-step Gain + 41-click Trim)
- Pad: –20 dB
- Phantom power: +48V
- Operating level: +4 dBu
- Maximum input level: +18 dBu
- Maximum output level: +22 dBu
- SNR: –110 dB
- Connectors: 2× XLR (rear), Hi-Z jack (front)
