Building McIntosh C28
2:51
Looking into schematic components.
Analyzing the schematic.
Looking for "Left channel low level stage BOM only: list Q1 Q3 Q5 Q7, R19 through R49, R85 R86, and capacitors associated with the left low level stage with exact values, types, and any substitute part notes." in C28_BOM_DIY-%D7%A8%D7%A9%D7%99%D7%9E%D7%AA-%D7%A8%D7%9B%D7%99%D7%91%D7%99%D7%9D-%D7%9E%D7%9C%D7%90%D7%94-%D7%A7%D7%9C%D7%95%D7%93-98ffbe6a-0b85-41a0-b472-e4da1fb9a5fd.xlsx
Looking for "Left channel low level stage only: extract transistor designators, resistor designators and values, capacitor designators and values, and exact connectivity or signal flow for the left channel." in low-level-stage-48f8121a-6ea7-4e91-8ff5-f365059467f1.pdf
Searching for components.
Finished searching for components.
Looking for "For the LEFT channel only, list exact connections to Q1: what connects to base, collector, and emitter, including resistor and capacitor designators and numbered nodes." in low-level-stage-48f8121a-6ea7-4e91-8ff5-f365059467f1.pdf
Looking for "For the LEFT channel only, list exact connections to Q3: what connects to base, collector, and emitter, including resistor and capacitor designators and numbered nodes." in low-level-stage-48f8121a-6ea7-4e91-8ff5-f365059467f1.pdf
Looking for "For the LEFT channel only, list exact connections to Q5 and Q7: what connects to each base, collector, and emitter, including resistor and capacitor designators and numbered nodes." in low-level-stage-48f8121a-6ea7-4e91-8ff5-f365059467f1.pdf
Looking for "For the LEFT channel only, list every numbered interface node 24 25 28 29 30 31 32 and 1 2 3 4 5 6 7 8 with the components directly attached to each node." in low-level-stage-48f8121a-6ea7-4e91-8ff5-f365059467f1.pdf
Thinking deeply about your request.
Planning preamplifier rebuild.
Clarifying project documents.
Creating a high-level plan.
Working on your request.
Analyzing the schematic.
Evaluating circuit inspections.
Working on your request.
Searching the project.
Searching for assets and documents.
Searching 2 domains.
Looking for project assets.
Searching 2 domains.
Search complete — 50 results across 2 domains.
Preparing implementation details.
Outlining the requirements process.
- Rebuild the left-channel low-level stage of the McIntosh C28 preamplifier by removing the modern NE5532-based front end and replacing it with the discrete, transistor-based topology derived from the uploaded low-level-stage PDF and BOM spreadsheet.
- Analyze the Current Schematic
- Locate the existing left-channel NE5532 op-amp based circuitry in the current project.
- Identify and mark the components that conflict with the desired C28 discrete stage.
- Remove or Isolate Conflicting Circuitry
- Remove or isolate the modern left-channel structure to prevent interference with the new design.
- Integrate C28-Derived Left-Channel Stage
- Refer to the uploaded low-level-stage PDF and BOM spreadsheet to identify all specific components, specifically the discrete transistors (e.g., Q1, Q3, Q5, Q7) and their supporting resistors and capacitors.
- Add the identified discrete components into the project schematics for the left-channel low-level stage.
- Wire the added components according to the connectivity and topology shown in the reference documents.
- Verification and Documentation
- Review the updated left-channel schematic for correctness against the C28 reference, ensuring that all connections and part values match the BOM.
- Document the changes made, explaining the transition from the modern NE5532 circuitry to the discrete C28-based left-channel stage.
- All conflicting modern op-amp components in the left-channel are removed or isolated.
- The discrete transistor-based left-channel low-level stage is accurately built according to the provided PDF and BOM, with correct parts and wiring.
- The schematic reflects a faithful C28-derived left low-level discrete stage ready for production.
Started implementing a plan
#Goal
- Rebuild the left-channel low-level stage of the McIntosh C28 preamplifier by removing the modern NE5532-based front end and replacing it with the discrete, transistor-based topology derived from the uploaded low-level-stage PDF and BOM spreadsheet.
#Implementation plan
1. Analyze the Current Schematic
1. Locate the existing left-channel NE5532 op-amp based circuitry in the current project.
2. Identify and mark the components that conflict with the desired C28 discrete stage.
2. Remove or Isolate Conflicting Circuitry
1. Remove or isolate the modern left-channel structure to prevent interference with the new design.
3. Integrate C28-Derived Left-Channel Stage
1. Refer to the uploaded low-level-stage PDF and BOM spreadsheet to identify all specific components, specifically the discrete transistors (e.g., Q1, Q3, Q5, Q7) and their supporting resistors and capacitors.
2. Add the identified discrete components into the project schematics for the left-channel low-level stage.
3. Wire the added components according to the connectivity and topology shown in the reference documents.
4. Verification and Documentation
1. Review the updated left-channel schematic for correctness against the C28 reference, ensuring that all connections and part values match the BOM.
2. Document the changes made, explaining the transition from the modern NE5532 circuitry to the discrete C28-based left-channel stage.
#Success criteria
- All conflicting modern op-amp components in the left-channel are removed or isolated.
- The discrete transistor-based left-channel low-level stage is accurately built according to the provided PDF and BOM, with correct parts and wiring.
- The schematic reflects a faithful C28-derived left low-level discrete stage ready for production.
Task completed.
0:19
Execution stopped due to insufficient credits.
6:52
Accessing knowledge base.
Looking for "left channel low level stage Q1 Q3 Q5 Q7 R19 R21 R23 R25 R27 R29 R31 R33 R35 R37 R39 R41 R43 R45 R47 R49 C7 C9 C11 C13 C15 C17 C18 values and substitutions" in C28_BOM_DIY-%D7%A8%D7%A9%D7%99%D7%9E%D7%AA-%D7%A8%D7%9B%D7%99%D7%91%D7%99%D7%9D-%D7%9E%D7%9C%D7%90%D7%94-%D7%A7%D7%9C%D7%95%D7%93-98ffbe6a-0b85-41a0-b472-e4da1fb9a5fd.xlsx
Started: analyzing schematic and extracting left-stage parts
Searching for components.
Finished searching for components.
Looking for "left channel exact wire connections for R19 R21 R23 R25 R27 R29 R31 R33 R35 R37 R39 R41 R43 R45 R47 R49 C7 C9 C11 C13 C15 C17 C18" in low-level-stage-48f8121a-6ea7-4e91-8ff5-f365059467f1.pdf
Analyzing the schematic.
Execution stopped due to insufficient credits.
5:31
Analyzing the schematic.
No changes applied.
0:04
Applied changes.
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;
}
Applied changes.
0:07
Applied changes.
Applied changes.
Added 28 components
0:07
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)
Diagram
- 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.
- 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
- 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
Welcome 👋
Flux helps you build PCBs faster with an AI teammate!
Create your account to collaborate, stay updated, fork your own version, and get instant answers from our AI agent.