Building McIntosh C28
Thought
nets {
net unnamed = C24:P2;
net unnamed = VR2:CW_2;
net unnamed = J1:3, J2:3, C4:P2;
net unnamed = C24:P1;
net unnamed = IC2:2OUT;
net unnamed = R10:P1, IC2:1OUT;
net unnamed = R6:P2;
net unnamed = C16:P1, IC3:VCC-, IC4:VCC-;
net unnamed = C27:P1;
net unnamed = C7:P2;
net unnamed = IC3:VCC+, IC4:VCC+;
net unnamed = IC2:1IN-;
net unnamed = VR1:CCW_1, GND:GND, VR3 CCW_2 - R16 P2:GND, VR2:CCW_1, R4 P2 - J2 1:GND, J2:1, C16:P2;
net unnamed = R10:P2;
net unnamed = VR1:CW_1;
net unnamed = IC2:VCC+;
net unnamed = R4:P2;
net unnamed = R4:P1;
net unnamed = C4:P1;
net unnamed = R14:P1;
net unnamed = J2:2;
net unnamed = VR2:WIPER_1;
net unnamed = IC2:1IN+;
net unnamed = VR1:CW_2;
net unnamed = C27:P2;
net IN_L = J1:2;
net unnamed = R11:P2;
net unnamed = VR1:WIPER_2;
net unnamed = C22:P2;
net unnamed = IC2:2IN+;
net unnamed = C11:P1;
net unnamed = IC2:VCC-;
net unnamed = R3:P1;
net unnamed = IC2:2IN-;
net unnamed = C17:P1;
net unnamed = IC3:2IN-;
net unnamed = VR2:WIPER_2;
net unnamed = C11:P2;
net IN_R = J1:1;
net unnamed = VR1:CCW_2;
net unnamed = VR2:CW_1;
net unnamed = C7:P1;
net unnamed = IC3:2OUT;
net unnamed = R11:P1;
net unnamed = R6:P1;
net unnamed = IC3:2IN+;
net unnamed = R3:P2, IC3:1IN-;
net unnamed = C22:P1;
net unnamed = IC3:1OUT;
net unnamed = R14:P2;
net unnamed = VR1:WIPER_1;
net unnamed = VR2:CCW_2;
net unnamed = R13:P1;
net unnamed = IC3:1IN+;
net unnamed = R13:P2;
net unnamed = C17:P2;
}
Thought
Thought for 7 sec
I hit an issue removing the old front end in one large batch, so I am decomposing the edit into smaller verified steps and continuing with the C28 rebuild.
Thought
Thought
Thought for 7 sec
- Added 1x BC550CBU as Q1 (Pins: C, B, E)
- Added 1x BC546BTA as Q3 (Pins: B, E, C)
- Added 1x BC639 as Q5 (Pins: B, E, C)
- Added 1x MJE340G as Q7 (Pins: E, B, C)
- Added 17x Generic Resistor as R19, R21, R23, R25, R27, R29, R31, R33, R35, R37, R39, R41, R43, R45, R47, R49, R85 (Pins: P2, P1)
- Added 7x Generic Capacitor as C7, C9, C11, C13, C15, C17, C18 (Pins: P1, P2)
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Project Specification
Scope
Build a McIntosh C28 style audio preamplifier in this project as a modernized analog line preamp inspired by the original architecture.
Architecture
Diagram
Design Intent
- Preserve the essential McIntosh C28 style signal path: input stage, gain control, tone shaping, and output buffering.
- Use modern low-noise dual audio op-amps for practicality and serviceability.
- Use dual analog supply rails for headroom and low distortion.
- Leave room for later additions such as phono equalization, filters, loudness contour, balance, and tape monitor functions.
Functional Blocks
- Input connectors and source selection entry points
- AC-coupled high impedance input buffer
- Gain and volume stage
- Active Baxandall bass and treble control section
- Low impedance output buffer
- Split-rail supply filtering and local decoupling
Initial Electrical Targets
- Line-level operation
- Dual supply rails based on +/-15V analog operation
- Film capacitors in the audio path where practical
- Star-ground friendly grounding strategy for later PCB work
Scope
Architecture
Design Intent
Functional Blocks
Initial Electrical Targets
