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TOPIC: U5 and U1 OpAmp

U5 and U1 OpAmp 2 months 1 week ago #1744

  • Coelhomatias
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Hi, I have a question,
Why do you have the MCP6002 in the BOM instead of the TL072 like you have in the schematic? I was reading both datasheets and found some weird stuff. For example, the max Vdd-Vss is 7V and you power all the OpAmps with 9V, also the GBW is bigger in the TL072 and has less noise voltage density. I don't know if I'm missing something but I would appreciate if you would explain this to me please. Thank you in advance and great looking pedal btw!!
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U5 and U1 OpAmp 2 months 1 week ago #1751

  • synesthesia
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Hi there.
Well, Of course there's some similarities which you have found between those chips but be sure there's a significant designing trick and nothing to concerns you. For more information visit This topic.
Desperate electronics enginner | Passionate audio hobbyist.
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U5 and U1 OpAmp 2 months 1 week ago #1753

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Hi, for U1 you can use a TL072 op-amp, no problem with that.

For U5 (The op-amp that makes the current sink for the PT2399) you NEED a rail to rail op-amp, the MCP6002 is perfect (the TL972 does not sound good). The thing with this op-amp is that its output needs to go very low, almost to 0V, that's why you need a rail to tail (and U5 is powered at 5V).

I end up using 2xMCP6002 instead of TL072 + MCP6002 because for the end user it's easier to source one op-amp that 2 different models. I know that you are abusing the supply on U1, but we have been doing it for a long time in other projects without problems.
Why do you have the MCP6002 in the BOM instead of the TL072 like you have in the schematic?
Sorry for the confusion, I am updating all the schematics now with the same parts as the BOM.
also the GBW is bigger in the TL072 and has less noise voltage density.
You are totally right, the TL072 is Vn = 18 nV/√Hz (Typical) which is great. I am thinking that for now on I am going to use a TL072 + MCP6002 in the kits and update the assembly manual.
Thanks for the heads up. ;)

EDIT: I have been doing some listening tests and rewrite this post.
Last Edit: 2 months 1 week ago by Ray.
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U5 and U1 OpAmp 2 months 6 days ago #1759

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Thank you Ray for the explanation, I was a bit confused with it but you made things clear now. I will be trying a TL072 + MCP6002 combo and will post the build in this forum once i'm finished. I like you guys very much and appreciate your work, keep doing what you do! Thank you again for the reply and good luck for all your future projects!
PS: you should update the analysis also, it has a few mistakes and typos if I'm not mistaken.
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U5 and U1 OpAmp 2 months 5 days ago #1762

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Thanks for the feedback, I am updating now the schematic, BOM, manual, etc to include the TL072 option. I will have a look at the Analysis too. Thanks.
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