Hello,
I want to make a portable DAC+headphone amp. Powered by mains, but not huge and heavy like my normal DAC with tube output and OTL headphone amp.
On the other hand, I want to get the best out of it what I can.
I stick to the AD1865 in NOS config, and TPA6120 at the end. What is in between is new to me again. Last time I've used opamps was lots of years ago.
I would appreciate if you would look at it and tell me if you have concerns if it works, or, how would you improve it.
Thanks a lot,
JG
View attachment sch.pdf
I want to make a portable DAC+headphone amp. Powered by mains, but not huge and heavy like my normal DAC with tube output and OTL headphone amp.
On the other hand, I want to get the best out of it what I can.
I stick to the AD1865 in NOS config, and TPA6120 at the end. What is in between is new to me again. Last time I've used opamps was lots of years ago.
I would appreciate if you would look at it and tell me if you have concerns if it works, or, how would you improve it.
Thanks a lot,
JG
View attachment sch.pdf
Aren't you going to want some LPF action?
C23 and C28 might be better on the other side of the volume control. As they are their attenuation will vary with volume setting.
Might also want to include an additional 27k to 100k fixed resistor to provide a DC path to ground independent of the volume control wiper.
Cheers
C23 and C28 might be better on the other side of the volume control. As they are their attenuation will vary with volume setting.
Might also want to include an additional 27k to 100k fixed resistor to provide a DC path to ground independent of the volume control wiper.
Cheers
Yes! 
The need for R10 and R16 depend on the I-V op-amp chosen. Some wouldn't like a 47pF load without the isolating series resistor.
You're right -- including them for external connections is considered good practice.
I'm also a little concerned about C30 and C31. Usually one of the layout goals is to reduce capacitance at such a node.
Still not seeing a typical LPF or *Reconstruction Filter*.
Regards
The need for R10 and R16 depend on the I-V op-amp chosen. Some wouldn't like a 47pF load without the isolating series resistor.
You're right -- including them for external connections is considered good practice.
I'm also a little concerned about C30 and C31. Usually one of the layout goals is to reduce capacitance at such a node.
Still not seeing a typical LPF or *Reconstruction Filter*.
Regards
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The basic LPF suggested is a simple 10nF foil cap paralell to the I/V resistor. In this config, with no I/V resistor, I know I need something else, but, I want to make the most simple possible. With the interstage transformer like the LL1527XL, the trafo itself acts as an LPF.
I have a built PCBA with no opamp circuit followed by, but I'm thinking to hack it in air wired mode as proto and measure how much the sampling freq and harmonics coming through. But yes, the LPF is still a question. On the other hand, I saw examples not using an LPF at all, or only an RC.
Thanks,
JG
I have a built PCBA with no opamp circuit followed by, but I'm thinking to hack it in air wired mode as proto and measure how much the sampling freq and harmonics coming through. But yes, the LPF is still a question. On the other hand, I saw examples not using an LPF at all, or only an RC.
Thanks,
JG
No LPF -- or simple RC -- has been used when the sample rate is much higher than 44k1 -- but IIRC, you were planning to run the AD1865 at NOS rates.
Also, if you have an I/V resistor, the signal is a voltage. The inverting input of an I/V op-amp is a Virtual Ground, not a variable/signal voltage.
You're welcome,
Cheers
edit: By the way, *The basic LPF suggested* is by itself *Not Applicable* without the rest of the circuit/implementation details ..
Also, if you have an I/V resistor, the signal is a voltage. The inverting input of an I/V op-amp is a Virtual Ground, not a variable/signal voltage.
You're welcome,
Cheers
edit: By the way, *The basic LPF suggested* is by itself *Not Applicable* without the rest of the circuit/implementation details ..
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