SPOTFIRE TUBE AUDIO® - PR5
PR5 Valve RIAA Phono Preamplifier Kit
The SpotFire PR5 is a vacuum-tube RIAA phono preamplifier designed for accurate vinyl playback with moving-magnet (MM) cartridges, and moving-coil (MC) cartridges via optional step-up transformers.
It is intended for builders who want a quiet, stable, all-valve phono stage engineered for real systems, not a cosmetic accessory.
What a Phono Stage Does
A phono preamplifier boosts the very small signal from a turntable cartridge to standard line level and applies RIAA equalisation to reverse the frequency shaping applied during record cutting.
Accurate equalisation, low noise, and stable gain are essential if vinyl playback is to sound natural and uncoloured.
Design Philosophy
The PR5 is an all-valve design that preserves the harmonic structure of analogue playback while remaining faithful to the source material.
It is designed as a natural companion to the SE5 power amplifier, but integrates equally well with any high-quality line-level amplifier when upgrading a vinyl front end.
Circuit Configuration
The PR5 uses 12AX7 / ECC83 / 7025 valves arranged as two Constant Current Draw Amplifier (CCDA) stages.
Cathode followers drive the RIAA equalisation network, maintaining RIAA accuracy as valves age and providing a low-impedance output capable of driving long or high-capacitance interconnects without loss of performance.
Dual MM Inputs
The standard PR5 kit is fitted with two switchable moving-magnet (MM) inputs, making it suitable for:
two turntables, or
a single turntable with multiple tonearms
Input selection is handled from the front panel.
Moving-Coil Capability
For users with moving-coil (MC) cartridges, one input can be configured for MC operation by adding optional Lundahl LL9226 cobalt-based amorphous-core step-up transformers directly to the PCB, or by using external step-up transformers.
This allows convenient switching between:
a high-performance MC cartridge for critical listening, and
a more robust MM cartridge for everyday use
Step-up transformers provide extremely low-noise gain for MC cartridges without introducing solid-state devices into the audio path.
Compact, System-Matched Design
The PR5 has a compact footprint and is designed to visually and mechanically match other SpotFire components.
Its size makes it well suited to integrated systems without occupying excessive shelf space.
Controls & Interface
The front panel features a solid metal balance control and toggle switches for power and input selection.
Rear-panel connections include:
phono inputs
line-level outputs
turntable earth connection
Blue LED valve illumination is fitted as standard and can be customised to other colours if desired.
Build Options
The PR5 is designed for straightforward assembly by a competent hobbyist.
Two build options are available:
Solderless kit, supplied with pre-assembled and tested PCBs
Full DIY kit, allowing all components to be soldered by the builder
The solderless option significantly reduces build time and removes the need for specialised soldering skills.
Power Supply & Noise Control
The power supply is designed so that mains power does not enter the chassis.
DC heaters and an earth-loop breaker are used to minimise hum and buzz, particularly in high-gain phono applications where noise control is critical.
Safety Notice
The PR5 contains potentially hazardous internal voltages of up to 280 V DC.
Builders must follow all assembly instructions carefully and apply standard electrical safety practices during construction and servicing.
Dimensions:
154 mm (W) × 240 mm (D) × 115 mm (H)
Pricing
The PR5 kit (excluding valves) is AUD $999.
Refer to the shop page for additional options and pricing.
Why Choose the SpotFire PR5?
- You want genuine tube sound with modern low-noise performance
- You want to listen to your vinyl as the artists intended - using tubes
- You prefer a phono stage that’s expandable, tweakable, and serviceable
- You run multiple turntables or plan to try MC cartridges in the future
- You value made-in-Australia engineering and support
SpotFire PR5 vs Other Phono Preamps
| Feature / Design Point | SpotFire PR5 | Typical Tube Kit | Solid-State MM/MC |
|---|---|---|---|
| Gain Structure | 12AX7 CCDA, high gain + cathode follower | 12AX7 high gain only | Op-amps or discrete transistors |
| RIAA Equalization | Accurate passive network | Often varies as tubes age | Digital or op-amp EQ |
| MM/MC Support | 2xMM standard, MC via Lundahl option | 1xMM only | MM/MC selectable (sometimes internal) |
| Tube Rolling / Customization | ✅ Easy (4x 12AX7) | ✅ Possible, often noisy or unusual tubes | ❌ Not supported |
| Output Drive Capability | ✅ Low-Z buffered output | ⚠️ Moderate output Z | ✅ Very Low-Z |
| Noise Floor | ✅ Very low (DC heaters) | ⚠️ Moderate hum and noise likely | ✅ Very low |
| DIY Friendliness | ✅ Solderless or full DIY | ⚠️ Full solder, poor instructions | ❌ Usually no DIY |
| Component Quality | ✅ High Quality, polypropylene film caps, gold tube sockets, | ⚠️ Basic component quality | ✅ Depends on brand |
| Power Supply | ✅ External 12V adapter (safe) | ❌ Internal AC transformer | ✅ Internal regulated or external adaptor (safe) |
| Price vs Sound | ⭐⭐⭐⭐½ – High value tube sound | ⭐⭐ – Looks good, mixed Quality | ⭐⭐⭐⭐ – Clean sound, less character |