McIntosh MCP1
Little is documented about the McIntosh MCP1, and what survives comes from a single enthusiast account rather than factory literature or period reviews. The record shows it was an all-transistor power amplifier — a departure from McIntosh’s tube heritage — and one that is “relatively rare today as a collectible.” Notably, the units encountered in the field were actually MCP1A variants, so the exact distinction between the two designations remains unclear.
What makes the MCP1 technically interesting is its power supply: a transformer-less, capacitive-drop design delivering ±28V DC rails, with two large resistors and significant capacitance. The final amplifier operates with a floating ground — no ground or common terminal ties to the chassis — which means the speaker load must be fully isolated from the chassis. The output stage is complementary-symmetry, using two pairs of complementary power transistors per channel mounted on shared anodized heatsinks whose fins protrude above the top cover. Output coupling is handled by non-polarized electrolytic capacitors, and the input stage uses a differential pair with transistor biasing. A protective delay relay guards against DC at startup.
The chassis itself is idiosyncratic. A single-screw “spanner” holds the top cover in place, and the included manual offers no schematic for the final amplifier circuit — only a pictorial wiring diagram. The rear panel uses a 4-terminal connector system attaching to a European-style barrier block, with a pre-attached three-wire IEC cord. The unit provides for connecting two pairs of loudspeakers, which is unusual for a monoblock. The AC line hook-up diagram on the top cover illustrates multiple speaker wiring configurations.
Reliability is a genuine concern. The power supply resistors run very hot, compromising long-term dependability, and output transistor failures have been observed due to internal design and heat. One unit was found with a poorly mounted capacitor whose positive lead was not well isolated from the chassis — a failure there could put DC on the output. The speaker line fuse is underrated. After prolonged service, the output stage — though more robust than most — suffers from fatigue due to improper biasing. The internal wiring is described as a “mass of wiring,” with unsleeved leads from the driver board running in close proximity to the main board.
No original price, production years, frequency response, THD, or weight figures have been located. The mention of International Rectifier parts suggests a late-1960s or early-1970s origin, but that is inference, not documentation. Period advertisements from Audio Classics, Ltd. indicate that the company bought, sold, and traded precision stereo components such as the MCP1 Audio (March 1990, p.121).
Known Specs
- Type: Solid-state monoblock power amplifier
- Power output: 2 x 70 VA at 4 or 8 ohms
- Damping factor: at least 21 (24)
- Power requirements: 120V, 50/60Hz, 2 VA
- Dimensions: 19"W x 5-1/4"H x 13-7/8"D
- Output terminals: Accepts No. 10 to No. 18 gauge wire
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.