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<!– Generated by hand for SushiDSP phase D6a. –>

jcm_v1b_cold

JCM800 2203 V1b cold clipper: the treble peaker into the grid and the unbypassed 10 kΩ cathode that produces the 2203’s asymmetric clipping and bias shift.

Status: simulated. Commit 2bdbf91 ran this block and committed its CSVs.

LTspice version: LTspice 24, the only detail 2bdbf91 records; the exact build is not recorded by that commit.

How the schematic is written

jcm_v1b_cold.asc carries the whole circuit as SPICE directive text on the sheet rather than as placed symbols with wires. Directive lines are netlisted verbatim by LTspice, so node names are explicit and the netlist cannot depend on symbol pin geometry that could not be checked without running the tool. Tube subcircuits are instantiated as X lines against ../models/12ax7_koren.sub, whose pin order is P G K.

Analyses

Both analysis lines live on the sheet as comments and tools/spice/export.py enables exactly one of them per run:

  • ;ac dec 40 10 20k
  • ;tran 0 40m 20m 1u (40 ms run, the last 20 ms saved as steady state)

.options plotwinsize=0 keeps the raw file uncompressed.

Probe and stimulus

  • Probed node: out (after the coupling cap, into the next stage’s 1 MΩ grid leak).
  • Input node: src
  • Source: V1 src 0 SINE(0 {AMP} 1k) AC 1
  • Input level(s): AMP is stepped over 10 mV, 100 mV and 1 V.

Stepped control

.step param AMP list 10m 100m 1

This block has no control, so per the D6a brief the input level is stepped instead. setting 0/1/2 in the CSVs corresponds to 10 mV / 100 mV / 1 V.

Components

Ref Value Nodes Spec reference
V1 SINE(0 {AMP} 1k) AC 1 src - 0 D6d block 2 stimulus
Rtp 470 kΩ src - g D6d block 2: 470 kΩ treble peaker
Ctp 470 pF src - g D6d block 2: 470 pF treble peaker
XV1b 12AX7_KOREN P=p G=g K=k D6b.3 Triode12AX7
Rp 100 kΩ B - p D6d block 2: 100 kΩ plate
Vplate 360 V B - 0 B+ per the D6a brief
Rk 10 kΩ k - 0 D6d block 2: 10 kΩ unbypassed cathode
Cc 0.022 uF p - out D6d block 2: 0.022 uF coupling
Rload 1 MΩ out - 0 next stage’s grid leak, added as the load

Judgment calls

  • The grid’s DC reference is the 470 kΩ peaker resistor back to V1, whose DC value is 0 V. That is the same reference the stage sees in the amp (through the preceding pot), so no separate grid leak is added.
  • Rload stands in for the following stage’s 1 MΩ grid leak. Without it the coupling cap has no DC return and the out node floats.

Note on the AC runs

AMP scales only the SINE(...) stimulus; the AC 1 magnitude is fixed. Stepping AMP therefore produces three identical AC sweeps (setting 0, 1 and 2) in <block>_ac.csv. Only the transient CSV carries three genuinely different runs. That is intentional: the acceptance criterion for this block is a transient null, and keeping one .step line for both analyses keeps the export path uniform.