Hi diyAudio!
I've been reading this forum since quite some time but now that I have a large project going on, I finally registered.
First of all, I'd like to introduce myself, so you know a bit of my background. I am a student of electrical engineering, 4th semester, in Germany. I have been building digital circuits with micro controllers since 2007. Digital is nice, because you can design a lot with the rule of thumb - especially when you work with "slow" processors of 20MHz.
Now I started something different:
I am currently building a nice preamp/amp combo which uses a new kind of controll concept to simultaniously use multiple amps. I will be sharing my details when its runing.
For the preamp, I could need your help. I'd like to use the CS3318 because it is said to deliver a solid performance and it offers everything I need. Please find attached my current schematics and board layout.
The whole thing is planned as two PCBs, one for the relay input switching, one for the actual preamp. The two PCBs can be stacked and interconnect with a fairly common pin header.
The digital part of the circuit (digital supply of the CS3318 and the input switching incl. relays) is powered from a 7805 and 7812 power supply. The 3,3V for the CS3318 is generated from the +12V supply via a LM317 circuit.
The analog supply consisty of a LM317/LM337 supply with +-15V (mounted off-board). This supplies other things like the phono stage (which is not shown here). The whole preamp however needs +-8V so those +-15V rails are converted down again with a LM317/LM337 circuit.
The CS3318 can not drive low impedance loads, and it should be driven from a low impedance source. That's why I added unity gain opamp buffers for both the inputs and the outputs.
I have only little experience when it comes to analog circuitry - so I'd like to hear your advice on my setup.
What do you think about the schematics?
I read that the CS3318s reset pin must be low whenever the digital supply is not present - otherwise the analog circuitry might be destroyed. So I added pulldown resistor for the reset pin - the level shifter should have high-impedance outputs when not powered. Is that alright or do I need a watchdog IC?
And probably more important: What about the layout?
Are the bypass caps allright?
What about the signal flow?
I read a lot, that its not a good idea to separate digital and analog ground. However, those two grounds come from different supplies with different transformers and are connected to the chassis in a star point. If I connect them again on the PCB i will have a ground loop. So I separated them on the pcb - is that alright?
Is it okay to have vias connecting the top and bottom analog ground plane all over the place?
Thanks in advance for your suggestions,
TheSlowGrowth
PS: I know there is another CS3318 Layout thread, but it uses a fairly different setup, so I thought I'd better open a new topic for this.
I've been reading this forum since quite some time but now that I have a large project going on, I finally registered.
First of all, I'd like to introduce myself, so you know a bit of my background. I am a student of electrical engineering, 4th semester, in Germany. I have been building digital circuits with micro controllers since 2007. Digital is nice, because you can design a lot with the rule of thumb - especially when you work with "slow" processors of 20MHz.
Now I started something different:
I am currently building a nice preamp/amp combo which uses a new kind of controll concept to simultaniously use multiple amps. I will be sharing my details when its runing.
For the preamp, I could need your help. I'd like to use the CS3318 because it is said to deliver a solid performance and it offers everything I need. Please find attached my current schematics and board layout.
The whole thing is planned as two PCBs, one for the relay input switching, one for the actual preamp. The two PCBs can be stacked and interconnect with a fairly common pin header.
The digital part of the circuit (digital supply of the CS3318 and the input switching incl. relays) is powered from a 7805 and 7812 power supply. The 3,3V for the CS3318 is generated from the +12V supply via a LM317 circuit.
The analog supply consisty of a LM317/LM337 supply with +-15V (mounted off-board). This supplies other things like the phono stage (which is not shown here). The whole preamp however needs +-8V so those +-15V rails are converted down again with a LM317/LM337 circuit.
The CS3318 can not drive low impedance loads, and it should be driven from a low impedance source. That's why I added unity gain opamp buffers for both the inputs and the outputs.
I have only little experience when it comes to analog circuitry - so I'd like to hear your advice on my setup.
What do you think about the schematics?
I read that the CS3318s reset pin must be low whenever the digital supply is not present - otherwise the analog circuitry might be destroyed. So I added pulldown resistor for the reset pin - the level shifter should have high-impedance outputs when not powered. Is that alright or do I need a watchdog IC?
And probably more important: What about the layout?
Are the bypass caps allright?
What about the signal flow?
I read a lot, that its not a good idea to separate digital and analog ground. However, those two grounds come from different supplies with different transformers and are connected to the chassis in a star point. If I connect them again on the PCB i will have a ground loop. So I separated them on the pcb - is that alright?
Is it okay to have vias connecting the top and bottom analog ground plane all over the place?
Thanks in advance for your suggestions,
TheSlowGrowth
PS: I know there is another CS3318 Layout thread, but it uses a fairly different setup, so I thought I'd better open a new topic for this.