Project Startup Help
Thought for 5 mins 28 sec
They’re still running. I’ll check final status once more and then give you the project links and current state so you’re not blocked waiting.
Worked for 21 sec
Created two separate PCB projects and started the split/place work in each:
- TX board: /timbochu/munkrofon-tx-pcb
- RX board: /timbochu/munkrofon-rx-pcb
Current status:
- TX clone: RX circuitry removed, board-mounted XLR replaced with compact XLR harness pads, 25 × 80 mm / 4-layer target set, placement still running.
- RX clone: TX circuitry removed, board-mounted XLR replaced with compact XLR harness pads, 25 mm width / 4-layer target set, placement still running.
- Master project remains unchanged as the system/reference design.
Open item:
- Both split-placement tasks are still running; they exceeded the wait window but are actively working on non-RF placement and verification.
Next step:
- Open each project link later to review the completed thread result, or ask me to check their status again.
Check split projects
Check TX status
Check RX status
Fix failed split tasks
Compare split BOMs
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Ask about this doc
TX Front-End Replacement Proof — AD8421 Single-Supply Strategy
Project: Munkrofon
Scope: Transmitter microphone front-end only
Question: Can the TX THAT1580 + ±5 V split-rail architecture be replaced with a simpler single-supply front end with negligible real-world compromise?
Conclusion: Yes, with AD8421 on a single +5 V analog rail. Direct 3.3 V micropower instrumentation amplifiers do not meet the noise target, but AD8421 provides a strong 90–95%-class real-world replacement while reducing TX rail complexity, power, and PCB area.
Scope: Transmitter microphone front-end only
Question: Can the TX THAT1580 + ±5 V split-rail architecture be replaced with a simpler single-supply front end with negligible real-world compromise?
Conclusion: Yes, with AD8421 on a single +5 V analog rail. Direct 3.3 V micropower instrumentation amplifiers do not meet the noise target, but AD8421 provides a strong 90–95%-class real-world replacement while reducing TX rail complexity, power, and PCB area.
1. Preferred Replacement
Selected front end
Analog Devices AD8421 instrumentation amplifier, single +5 V supply, gain set around 40 dB for Rev B prototype evaluation.
Why AD8421
AD8421 is the best compromise found between raw mic-preamp performance and product-level transmitter constraints:
- 5 V single-supply operation possible.
- 3 nV/√Hz input voltage noise, much better than low-power 3.3 V instrumentation amps.
- ~2 mA quiescent current.
- CMRR improves strongly with gain: about 134 dB typical at G = 100, DC–60 Hz.
- Gain set with one resistor:
G = 1 + 9.9 kΩ / RG. - Datasheet explicitly lists microphone preamplification and ADC driving as applications.
- Removes need for the TX negative rail.
Why not direct 3.3 V INA333 / AD8226-class
3.3 V-capable micropower instrumentation amplifiers save current, but their voltage noise is much higher:
- INA333: ~50 nV/√Hz → too noisy for a professional passive dynamic mic front end.
- AD8226: ~22 nV/√Hz → better, but still far behind THAT1580/AD8421.
- TLV320AIC3204 codec-only input: about 2 µVrms input-referred at high gain → usable for loud sources but not a robust pro mic-preamp replacement.
Why not INA849 / AD8429
INA849 and AD8429 have ~1 nV/√Hz input noise, close to THAT1580, but they require about 8 V minimum single supply or ±4 V dual rails and draw about 6–7 mA. They remove less power/rail complexity than AD8421 and are therefore not the best product compromise.
2. Revised TX Front-End Schematic Proposal
This is the proposed schematic topology before editing the live schematic:
Diagram
Proposed electrical details
Table
| Function | Proposed implementation | Notes |
|---|---|---|
| Preamp IC | AD8421 | Preferred single-supply replacement. |
| Supply | Single +5 V analog rail | A small boost is still required, but the TX negative rail and TPS65131 split rail can be removed. |
| Gain | Start at 40 dB, G ≈ 100 | RG ≈ 100 Ω using G = 1 + 9.9k / RG. |
| Input | Balanced XLR through protection/RFI network | Protection must be added before layout. |
| Biasing | Inputs biased around quiet reference / mid-supply | Required for single-supply operation and input bias-current return. |
| Reference pin | Low-impedance buffered reference | AD8421 datasheet recommends low REF impedance to preserve CMRR. |
| Output | AC-coupled into TLV320AIC3204 single-ended ADC input | Codec input handles 0.5 Vrms single-ended full-scale. |
| Codec drive target | 0.5 Vrms max into codec | Same target as TLV320AIC3204 datasheet typical full-scale input. |
3. Quantitative Comparison
Assumptions:
- 20 kHz audio bandwidth.
- 150 Ω dynamic microphone source impedance.
- 0 dBu = 0.775 Vrms.
- Representative gain target: 40 dB for close dynamic drum mic.
- Codec full-scale input target: 0.5 Vrms.
3.1 Input-Referred Noise
Table
| Front end | Input noise density | Integrated amplifier noise, 20 kHz | Including 150 Ω source thermal noise | Equivalent input noise |
|---|---|---|---|---|
| THAT1580 @ 40 dB | 1.4 nV/√Hz | 0.198 µVrms | 0.298 µVrms | −128.3 dBu |
| THAT1580 @ 60 dB | 1.0 nV/√Hz | 0.141 µVrms | 0.264 µVrms | −129.4 dBu |
| AD8421 @ high gain | 3.0 nV/√Hz | 0.424 µVrms | 0.479 µVrms | −124.2 dBu |
| TLV320 codec-only high gain | ~14.1 nV/√Hz equivalent | 2.000 µVrms | 2.012 µVrms | −111.7 dBu |
| INA333-class | 50 nV/√Hz | 7.071 µVrms | 7.075 µVrms | −100.8 dBu |
Result: AD8421 is about 4.1 dB noisier than THAT1580 at 40 dB gain with a 150 Ω source. That is measurable, but likely negligible in close-miked live drum use where stage/acoustic noise and wireless/audio codec behavior dominate. Codec-only and INA333-class options are not close enough.
3.2 Gain Range
Table
| Front end | Gain range | Practical Rev B target | Notes |
|---|---|---|---|
| THAT1580 | 0 to >60 dB | 30–40 dB fixed/provisional | Very flexible pro mic preamp. |
| AD8421 | 1 to 10,000 V/V | 40 dB / G≈100 | Enough range for dynamic mic. |
| TLV320 codec-only | PGA up to ~47.5 dB setting | May be enough for loud sources | Noise risk at high gain. |
Result: AD8421 gain capability is sufficient.
3.3 Headroom
Codec input target from TLV320AIC3204 datasheet:
- 0.5 Vrms single-ended full-scale input typical.
Required gain to reach 0.5 Vrms:
Table
| Mic signal | Required gain | dB |
|---|---|---|
| 1 mVrms | 500× | 54 dB |
| 5 mVrms | 100× | 40 dB |
| 20 mVrms | 25× | 28 dB |
| 100 mVrms | 5× | 14 dB |
For a close dynamic drum mic, 5–20 mVrms is a plausible operating region, so 28–40 dB gain is usually more relevant than 60 dB. AD8421 on +5 V has enough output swing to drive a 0.5 Vrms codec input when biased correctly and AC-coupled.
Result: AD8421 headroom is adequate for the expected use case, but weaker than THAT1580 for very hot or very quiet sources. Add pad/gain-option if flexibility is desired.
3.4 CMRR
Table
| Front end | CMRR evidence | Assessment |
|---|---|---|
| THAT1580 | Designed as professional differential mic preamp; excellent practical balanced performance; datasheet extraction primarily exposed PSRR/noise rather than full CMRR table. | Strong. |
| AD8421 | About 134 dB typical at G=100, DC–60 Hz; about 100 dB typical at 20 kHz and G=100. | Strong, sufficient for balanced mic input. |
| INA333 | ~100–115 dB typical depending gain; bandwidth limited at high gain. | CMRR okay, noise/bandwidth not enough. |
Result: AD8421 CMRR is adequate and likely not a limiting compromise.
3.5 THD+N / Distortion
Table
| Front end | Datasheet evidence | Assessment |
|---|---|---|
| THAT1580 | ~0.0005% THD+N at 40 dB, 5 Vrms output, 1 kHz. | Excellent. |
| AD8421 | Example ADC-drive spectrum showed THD around −100.9 dB; distortion curves support low distortion at audio frequencies. | Excellent enough for wireless mic TX; likely below codec/RF path limits. |
| TLV320 codec-only | ADC THD+N ~−85 dB typical at −3 dBFS. | Codec likely dominates over AD8421/THAT in final chain. |
Result: AD8421 distortion is not expected to be the limiting factor.
3.6 Current Consumption
Table
| Front end architecture | Approx TX front-end rail current | Notes |
|---|---|---|
| THAT1580 + TPS65131 ±5 V | THAT1580 ~7.9 mA plus split-rail converter losses; battery-equivalent often ~20–30 mA planning burden depending efficiency/load. | Highest power. |
| AD8421 + single +5 V boost/reference | AD8421 ~2 mA plus small +5 V boost/reference overhead; battery-equivalent likely ~4–8 mA depending boost/reference. | Major reduction. |
| INA333 / codec-only | Lowest current | But noise compromise too large. |
Result: AD8421 strategy likely saves ~15–25 mA from the TX operating current versus THAT1580 + split rail, which is meaningful for runtime.
3.7 Component Count / PCB Area
Current TX split-rail/preamp support includes roughly:
- THAT1580.
- TPS65131 split-rail IC.
- Two inductors.
- Two Schottky diodes.
- Four feedback resistors.
- Compensation caps.
- +5/−5 output caps.
- ± rail decoupling.
- Gain/coupling parts.
Proposed AD8421 strategy includes roughly:
- AD8421.
- One small +5 V boost or regulated +5 V source.
- One inductor and feedback network for +5 V if boost is used.
- Gain resistor.
- Reference buffer/divider/filter.
- Input bias/protection and output coupling.
Result: Component-count reduction is expected to be moderate, but layout complexity reduction is large because the negative rail and inverting switcher loop disappear.
4. Measurable Compromises
Table
| Metric | Compromise versus THAT1580 | Real-world significance |
|---|---|---|
| Input-referred noise | AD8421 is ~4.1 dB worse at 40 dB gain with 150 Ω source. | Usually acceptable for close dynamic drum mic; may matter for quiet sources. |
| Headroom | THAT1580 has much greater pro-preamp headroom on wide rails. | AD8421 is adequate for codec full-scale if gain/pad are chosen carefully. |
| Gain flexibility | THAT1580 is more purpose-built for mic gain optimization. | AD8421 range is still sufficient for fixed/moderate gain prototype. |
| Reference/bias complexity | AD8421 needs a quiet low-impedance REF and input bias returns. | Manageable; still simpler than split ± rails. |
| Future quiet-source use | THAT1580 is safer. | If future custom capsule or quiet sources are required, reconsider. |
5. Pass / Fail Against 90–95% Real-World Target
Raw lab-preamp performance
Fail to equal THAT1580 exactly. THAT1580 remains superior on purpose-built microphone-preamp noise/headroom.
Real-world Munkrofon transmitter performance
Pass. For a compact wireless transmitter using a close passive dynamic microphone, AD8421 is close enough to be considered within the requested 90–95% real-world performance band because:
- Noise is only ~4 dB worse at a realistic 40 dB gain point.
- CMRR remains excellent.
- Distortion is likely below the codec/RF path limits.
- Gain/headroom are adequate for close dynamic mic use.
- Power, layout, EMI, runtime, and PCB-area improvements are substantial.
6. Recommendation
Adopt the AD8421 + single +5 V TX front-end strategy for the next schematic revision, replacing the TX THAT1580 + TPS65131 ±5 V split-rail block.
Recommended next schematic change:
- Remove TX THAT1580 front end and TX TPS65131 split-rail generator.
- Add AD8421 as the TX balanced mic instrumentation amplifier.
- Add a small +5 V boost or other single +5 V analog source.
- Add low-impedance reference buffer/bias network for AD8421 REF and input bias returns.
- Keep/add XLR phantom/ESD/RFI protection before layout.
- AC-couple AD8421 output into one TLV320AIC3204 ADC input.
- Leave RX ± rails unchanged until RX output level/headroom is defined.
7. Decision
Replacement strategy proven for the stated application.
Implemented in the live schematic on 2026-07-27.
Implemented in the live schematic on 2026-07-27.
8. Implementation Record
The transmitter schematic was revised from the previous THAT1580 + TPS65131 ±5 V split-rail front end to the AD8421 single-supply strategy.
Removed from TX front end
- THAT1580 mic preamp U3.
- TX TPS65131 split-rail generator U13.
- TX split-rail support parts: L1/L2, D3/D4, R9–R12, C13–C19 from the previous ±5 V topology.
- Previous differential coupling arrangement into both codec inputs.
Added / replaced
- U3: AD8421ARMZ-R7 instrumentation amplifier.
- U13: TPS61023DRLR single +5 V boost converter.
- U15: OPA333AIDBVR low-power reference buffer.
- L1: 1 µH boost inductor.
- R6: 100 Ω AD8421 gain resistor, approximately 40 dB gain.
- R9/R10: TPS61023 5 V feedback divider.
- R11/R12/C17/U15: 2.5 V reference divider/filter/buffer.
- R13/R14: 1 MΩ input bias returns to buffered reference.
- C11: AD8421 output AC coupling to TLV320AIC3204 codec input.
- C12: unused codec input shunt capacitor.
- C13/C14/C15/C16/C18: local decoupling and boost input/output capacitors.
Verification after implementation
- Floating-pin errors: cleared in the checked set.
- Single-pin-net errors: cleared in the checked set.
- Remaining ERC warnings: Missing-power findings remain in the same known category as before, related to generated rails, charger/system rails, provisional RTX module power pins, and codec internal-LDO/filter rails.
Remaining schematic work before layout
- Add complete XLR phantom-power abuse, ESD, and RFI input protection.
- Confirm whether the +5 V boost is the final TX analog rail or should be replaced by a more integrated system power rework.
- Resolve or justify ERC missing-power findings.
- Lock passive packages/ratings and add test points.
1. Preferred Replacement
Selected front end
Why AD8421
Why not direct 3.3 V INA333 / AD8226-class
Why not INA849 / AD8429
2. Revised TX Front-End Schematic Proposal
Proposed electrical details
3. Quantitative Comparison
3.1 Input-Referred Noise
3.2 Gain Range
3.3 Headroom
3.4 CMRR
3.5 THD+N / Distortion
3.6 Current Consumption
3.7 Component Count / PCB Area
4. Measurable Compromises
5. Pass / Fail Against 90–95% Real-World Target
Raw lab-preamp performance
Real-world Munkrofon transmitter performance
6. Recommendation
7. Decision
8. Implementation Record
Removed from TX front end
Added / replaced
Verification after implementation
Remaining schematic work before layout
