Helios 1R Stereo Type 69 Mic Pre/3-Band EQ #PTR245 (Used)

The Helios 1r Stereo Type 69 is a modern interpretation of the classic Helios Type 69 mic preamp and equalizer circuit, originally found in the consoles at Olympic Sound Studios during the late 1960s and early '70s. Reimagined in a 19-inch rack-mount chassis with an internal power supply, the 1r departs from the original module format while retaining the core circuit topology that defined the Type 69 sound. Growing increasingly rare, these units were produced in the UK by Tony Arnold's Helios Electronics Limited from the early 2000s until the mid 2010s.

ALL DISCRETE COMPONENTS

Built using all discrete components, the mic preamp is centered around a Sowter Type 8666X input transformer, chosen to replicate the character of the original Lustraphone transformers that defined the Olympic Studios sound. Input impedance is 1200 ohms, and a switchable secondary winding provides -20 dB of mic attenuation. The unit runs on a 32-volt rail from an internal switching power supply.

PANEL CONTROLS

Front panel controls are straightforward and well-organized. A toggle switch selects between mic, attenuated mic (-20 dB), and 10 kOhm line input. A seven-position Elma rotary switch serves as the gain control for both mic and line inputs, offering -5 dB and 0 dB line gain positions and five mic gain steps ranging from 20 dB to 70 dB in 10 dB increments. Additional toggles handle phase (polarity) flip, EQ in/out, phantom power, and a trim pot for fine input level adjustment.

3-BAND PASSIVE EQ

The 3-band passive equalizer combines RC and LC tone circuits. The high-frequency shelf operates at 10 kHz with a 6 dB-per-octave slope and up to ±10 dB of range. The LC-based midrange section offers nine frequency choices — 0.7, 1, 1.4, 2, 2.8, 3.5, 4.5, 6, and 16 kHz — with Peak and Trough (boost/cut) switching and up to 15 dB of gain. The Q starts wide at three octaves around 700 Hz and narrows to two octaves by 6 kHz, tightening further as boost or cut increases.

The LC-based bass section provides up to 15 dB of boost or cut across five peaking frequencies — 30, 80, 120, 240, and 400 Hz — or a fixed 70 Hz shelving mode with 3 to 15 dB of roll-off in 3 dB steps. An additional 12 dB-per-octave high-pass filter can be engaged at 40 or 80 Hz, useful when combining bass boost with low-end cleanup. Rotating the bass control fully counterclockwise bypasses the section entirely, keeping the signal path clean.

OUTPUT STAGE

The output stage uses an unbalanced emitter follower circuit with a Philips/BEC electrolytic coupling capacitor — a deliberate design choice mirroring the original Helios topology. Dick Swettenham found that the engineers at Olympic preferred this circuit's character over transformer-coupled outputs, and it remains a defining part of the Type 69 sound.

FEATURES:

• Two classic Helios Type 69-style mic preamp and equalizer circuits housed in a single 19-inch rack-mount chassis with internal power supply
• Sowter Type 8666X input transformer
• Toggle switch selects mic, attenuated mic (-20 dB), and 10 kOhm line input
• Seven-position Elma rotary gain control
• Phase (polarity) flip, EQ in/out, phantom power, and a trim pot controls
• 3-band passive equalizer combines RC and LC tone circuits
• Output stage with unbalanced emitter follower circuit with a Philips/BEC electrolytic coupling capacitor