API 2500 vs PuigChild 670: Modern VCA Speed vs Vintage Tube Soul
Tansel Günay (aka Punkat) — Punkat Music Sàrls | Steinsel/LUXEMBOURG
Two classics, two philosophies: API 2500 is a modern VCA with ultra-fast response and deep control, while PuigChild 670 (Fairchild-style vari-mu) delivers musical, tube-saturated leveling with program-dependent releases. Below is a mastering-focused comparison plus my own real-world recipes.
VCA vs Vari-Mu
Thrust
Program-Dependent
M/S (Lat/Ver)
Feed-Forward/Feedback
Mix/Parallel
Quick Summary
- API 2500: VCA, very fast (attack to ~0.03 ms), precise, punchy. “New” (feed-forward) vs “Old” (feedback), Thrust detector EQ (Norm/Med/Loud), knee control, partial linking & link filters, parallel Mix.
- PuigChild 670: Vari-mu tubes/transformers; fixed Time Constants 1–6 (~0.2–0.4 ms attacks, releases 0.3 s → program-dependent up to ~25 s); Lateral/Vertical (M/S) matrix, simple controls.
- Rule of thumb: API = punch/control (EDM/rock/pop). PuigChild = glue/bloom (acoustic/jazz/orchestral/vocals).
Topology & Controls
API 2500
- Engine: VCA; Old/New detector (feedback/feed-forward).
- Thrust: detector EQ (Norm/Med/Loud) — stable lows, energized mids/highs.
- Shaping: Knee (Hard/Med/Soft), stepped Attack (.03–30 ms), Release (0.05–2 s or Variable), Mix for parallel.
- Stereo: Link % and HP/LP/BP link-shape filters — prevent channel “dragging”.
PuigChild 670
- Engine: Vari-Mu in the audio path; musical saturation from tubes/transformers.
- Time Constants: 1–2 fast, 3–4 classic glue, 5–6 program-dependent levelling.
- Linking: Linked, independent L/R, or Lateral/Vertical (M/S) for center vs sides shaping.
- Character: smooth edges, stereo cohesion at modest GR.
Tone & Use Cases
- EDM drums / energetic bus → API 2500: fast transients; Thrust “Loud” keeps subs tidy and punch bright.
- Modern pop/rock mix bus → API 2500: Feed-Forward + Med/Soft knee = tight control with clarity.
- Acoustic / jazz mix → PuigChild: program-dependent release breathes; tube warmth & cohesion.
- Vocal bus → PuigChild: TC 5–6 classy levelling, tasteful saturation.
- Mastering (clean & punchy) → API 2500: sub-safe GR with partial link & HP link-shape.
- Mastering (vintage glow) → PuigChild: low-mid body, gentle HF smoothing.
My Usage in Mastering
1) EDM / Modern Pop — API 2500 Bus Shaper
- Type: New • Knee: Medium • Thrust: Medium
- Attack: 0.3–3 ms • Release: 0.2–0.6 s or Variable ≈ 0.4 s
- Link: 60–80% • Link Shape: HP (80–120 Hz)
- GR: ~1–2 dB avg • Mix: 75–90%
2) Acoustic / Jazz — PuigChild Leveller
- TC: 4–5 on mix bus; 6 for vocal-centric programs
- Mode: Lateral/Vertical → tame Mid lightly, let Sides breathe
- Target GR: 1–3 dB peaks
3) Sequence — Glue then Sweeten
- Step 1: API 2500 pre-limiter for shape/punch
- Step 2: PuigChild post-EQ for cohesion (TC 4–5)
- Tip: honest A/B level matching before the limiter
4) Vocal-Forward Pop/Jazz
- PuigChild: TC 6 on vocal stem, ~1 dB avg GR
- API 2500: on music bus, 0.5–1.5 dB GR, Thrust Med
Mastering Playbooks (Fast Presets)
API 2500 — Modern Bus Glue
- Mode: New • Knee: Med • Thrust: Med
- Attack: 0.3–3 ms • Release: 0.2–0.6 s / Var
- Link: 60–80% • Link Shape: HP
- GR: 1–2 dB avg • Mix: 70–90%
PuigChild — Musical Levelling
- TC: 4–5 bus glue; 6 vocal-led
- Lat/Ver: Mid-tame, Side-bloom
- Hum: Off unless desired