Hello!
I'm still new to audio electronics and learning a lot as I go.
For context, I’m working on building my own USB microphone from scratch as a starting point for more complex personal projects. My current design is inspired by DIY Perks, but I’m designing my own preamp and power supply circuit. I’m working with a tight budget and limited access to specialized or hard-to-find components, so please keep that in mind.
Right now, I'm running into an issue with my power supply section of the circuit.
When the power supply is not connected to the rest of the circuit, it provides a stable +15V and -15V output. However, when I connect the preamp to the power supply, the voltage drops drastically to around 1.2-1.8V.
After testing, I discovered that when I directly supply the preamp with ±15V, it works perfectly. This suggests the issue might be related to the Darlington pair circuit.
Blue is micInput, Green is output (Power input connected to pre-amp) Red is output, Green is micInput (Direct ±15V connection)
Could you help me identify and resolve this problem? If there is anything else, don't be afrain to rag on me for that as well.
Thank you all in advance!
I'm still new to audio electronics and learning a lot as I go.
For context, I’m working on building my own USB microphone from scratch as a starting point for more complex personal projects. My current design is inspired by DIY Perks, but I’m designing my own preamp and power supply circuit. I’m working with a tight budget and limited access to specialized or hard-to-find components, so please keep that in mind.
Right now, I'm running into an issue with my power supply section of the circuit.
When the power supply is not connected to the rest of the circuit, it provides a stable +15V and -15V output. However, when I connect the preamp to the power supply, the voltage drops drastically to around 1.2-1.8V.
After testing, I discovered that when I directly supply the preamp with ±15V, it works perfectly. This suggests the issue might be related to the Darlington pair circuit.
Blue is micInput, Green is output (Power input connected to pre-amp) Red is output, Green is micInput (Direct ±15V connection)
Could you help me identify and resolve this problem? If there is anything else, don't be afrain to rag on me for that as well.
Thank you all in advance!
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Your schematic shows a couple of errors in the connection of the darlington pairs.
Q1 should have its collector in common with Q3 (not going to Q3's base) and its emitter should go to Q3 base.
The Q4 and Q5 darlington's arranged backwards - the emitter of Q4 should go the output (feeding your preamp) and the collectors are the inputs.
Q1 should have its collector in common with Q3 (not going to Q3's base) and its emitter should go to Q3 base.
The Q4 and Q5 darlington's arranged backwards - the emitter of Q4 should go the output (feeding your preamp) and the collectors are the inputs.
Thank you for the catch @abraxalito!
I can't believe I missed that. I have updated the circuit immediately.
This is the updated schematic
The signal is looking a lot better, but the amplification still isn't right yet.
Blue is micInput and Green is output
I can't believe I missed that. I have updated the circuit immediately.
This is the updated schematic
The signal is looking a lot better, but the amplification still isn't right yet.
Blue is micInput and Green is output
How strange - you had the inter-relation of Q4/Q5 correct on the earlier schematic but now its gone wrong in the same way as Q1 and Q3 were wrong on the first schematic. Only one emitter terminal goes to the output and two collectors go to the input.
After removing some of the capacitors, and editing the pnp transistors they way you specified, the circuit now officially works.
thank you so much for your help!