Hello everyone,
I've been working on a schematic for a preamp designed specifically for my piezo contact mics, based on the Altoids piezo preamp by Stompville. My goal is to create a compact preamp powered by phantom power, utilizing basic SMD components to minimize soldering and keep costs down. I’ve settled on the TL072 as the op-amp for both buffering and amplification.
I would appreciate any feedback you might have on my design. Here are some specific questions I have:
1) Does the TL072 work well with the used supply and bias voltage?
2) Are the voltage ratings of the capacitors sufficient, particularly for C15 and C18?
3) Are the 100µF capacitors in the power supply section necessary, or can they be omitted? I couldn't find SMD 50V 100µF capacitors in the basic parts category. Or are there other viable replacements?
4) I want to replace the Zener diode D3 with an SMD part. What characteristics should I look for in a replacement?
5) What is the needed wattage rating for the resistors R4 and R5? Is 1/8 W enough or should it be 1/4 W?
Thank you for your help! I’m looking forward to your insights and suggestions.
Best regards,
Benni
I've been working on a schematic for a preamp designed specifically for my piezo contact mics, based on the Altoids piezo preamp by Stompville. My goal is to create a compact preamp powered by phantom power, utilizing basic SMD components to minimize soldering and keep costs down. I’ve settled on the TL072 as the op-amp for both buffering and amplification.
I would appreciate any feedback you might have on my design. Here are some specific questions I have:
1) Does the TL072 work well with the used supply and bias voltage?
2) Are the voltage ratings of the capacitors sufficient, particularly for C15 and C18?
3) Are the 100µF capacitors in the power supply section necessary, or can they be omitted? I couldn't find SMD 50V 100µF capacitors in the basic parts category. Or are there other viable replacements?
4) I want to replace the Zener diode D3 with an SMD part. What characteristics should I look for in a replacement?
5) What is the needed wattage rating for the resistors R4 and R5? Is 1/8 W enough or should it be 1/4 W?
Thank you for your help! I’m looking forward to your insights and suggestions.
Best regards,
Benni
Not a definitive answer, just things that stand out to me......
The TL072 should be fine.
Cap voltage... looks much to low to me. I really would not use lower than 63 volt for those to cover all connection possibilities it could see.
The 100uF's are OK but equally with a Zener regulated supply you could go much much lower to something like 22uF.
The Zener will conduct (destructively) as soon as your 'VCC' voltage exceeds the Zener voltage. The supply feeding 'VCC' must be current limited to avoid damage. Any low power (say 0.6 or 1.3 watt) 33 volt Zener is fine. Current must be limited to around 15 milliamps for a 0.6 watt Zener.
Edit... or is that where your 1k's come in, deriving Vcc from the phantom power?
1/8 watt is fine for those 180 and 120k resistors. Normally both would be the same value for a virtual earth.
You may have other errors in the diagram 🙂
C5 at 22pF for example. That will only pass ultrasonics.
R12 and R13 at 1k (they load the opamp output and seem unnecessarily low)
Why two TL072 when you have one half unused and one set as a unity gain. One TL072 would be enough.
The TL072 should be fine.
Cap voltage... looks much to low to me. I really would not use lower than 63 volt for those to cover all connection possibilities it could see.
The 100uF's are OK but equally with a Zener regulated supply you could go much much lower to something like 22uF.
The Zener will conduct (destructively) as soon as your 'VCC' voltage exceeds the Zener voltage. The supply feeding 'VCC' must be current limited to avoid damage. Any low power (say 0.6 or 1.3 watt) 33 volt Zener is fine. Current must be limited to around 15 milliamps for a 0.6 watt Zener.
Edit... or is that where your 1k's come in, deriving Vcc from the phantom power?
1/8 watt is fine for those 180 and 120k resistors. Normally both would be the same value for a virtual earth.
You may have other errors in the diagram 🙂
C5 at 22pF for example. That will only pass ultrasonics.
R12 and R13 at 1k (they load the opamp output and seem unnecessarily low)
Why two TL072 when you have one half unused and one set as a unity gain. One TL072 would be enough.
The op-amp's negative supply pins are only decoupled, not connected to anything else. As you have a single supply, they should be grounded.
As your input and output are ground-referenced perhaps loose C7/9/11 so that Vbias is also ground-referenced. With it being coupled to the +ve rail it will see rail noise and that will go through the output.