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What is the Cyrus 1
The Cyrus 1 is a British integrated amplifier (pre-amp + power amp) from Cyrus / Mission made in the mid-1980s. It has separate MM & MC phono stages built in, along with line-level inputs. It is known for being a clean, good-value component even many years later.
What’s inside originally
The Cyrus 1 (1988) phono stage is an op-amp based RIAA equalizer with different gain paths for MM and MC.
• Period schematics show that it used general-purpose bipolar op-amps common in the 1980s — typically NE5532 or similar (sometimes TL072 in certain units).
• These were respectable at the time: low noise for MM, decent bandwidth, but by modern standards they can be improved upon.
If you want a safe, noticeable upgrade:
• Replace the original NE5532 with LM4562 / LME49720 → same pinout, much lower noise, very stable in audio circuits.
Hypothetical Modifications / Where to Insert
Assuming you have a single op-amp stage (or two) for MC/MM & RIAA, here’s how a replacement might work:
• Drop-in op-amp chip: Replace the original with a modern audio op amp (e.g. LM4562, OPA1612 etc.).
• Compensation: If modern op-amp has higher slew rate or bandwidth, add small compensation capacitors or adjust layout to avoid oscillations. Possibly include small series resistor at input or in the feedback loop.
• Check supply decoupling: New op-amps often need clean supply decoupling; add or replace bypass caps (e.g. 0.1 μF + 10–47 μF) close to the IC.
• Match input impedance & loading: The load the cartridge sees (both impedance & capacitance) should remain close to original, unless you’re prepared to re-engineer the input network. Changing loading drastically can alter frequency response (especially high frequencies) of MM cartridges.
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