Hello all,
I've just put together my first attempt at an integrated amp design featuring 2x LM1875 chips for stereo output.
For the source I've included a phono preamp design based off the Muffsy PP-4 (https://www.muffsy.com/muffsy-pp4) and a relay input based on another Muffsy product (https://www.muffsy.com/muffsy-relay-input-selector-4) that connects to the phono, a general stereo RCA input, a 3.5mm aux jack, and a 3-pin JST connector to integrate with a separate project I'm working on.
Relay control will be handled remotely using an arduino or similiar via i2c.
For power I've put together a ±25V linear supply that will directly feed the amp sections and also connect to a pair of LM7815/7915 to feed the phono preamp.
I plan to use a 4 layer PCB to help in managing all the different voltage levels present in the design.
The total package fits into a 4in x 6in rectangle and has been designed to easily allow me to cut the board and separate the amp section from the input.
I am curious to get the community's thoughts on this design and any suggestions for improvements. Especially around grounding; I tried doing the star topology.
My current audio reference is an Anker Soundcore 2 12W Bluetooth speaker, so I'm hoping I can improve on that for audio quality 😀
The schematic and layout should both be attached.
I haven't made gerbers yet, put could share those in the future if anyone's interested.
Cheers!
I've just put together my first attempt at an integrated amp design featuring 2x LM1875 chips for stereo output.
For the source I've included a phono preamp design based off the Muffsy PP-4 (https://www.muffsy.com/muffsy-pp4) and a relay input based on another Muffsy product (https://www.muffsy.com/muffsy-relay-input-selector-4) that connects to the phono, a general stereo RCA input, a 3.5mm aux jack, and a 3-pin JST connector to integrate with a separate project I'm working on.
Relay control will be handled remotely using an arduino or similiar via i2c.
For power I've put together a ±25V linear supply that will directly feed the amp sections and also connect to a pair of LM7815/7915 to feed the phono preamp.
I plan to use a 4 layer PCB to help in managing all the different voltage levels present in the design.
The total package fits into a 4in x 6in rectangle and has been designed to easily allow me to cut the board and separate the amp section from the input.
I am curious to get the community's thoughts on this design and any suggestions for improvements. Especially around grounding; I tried doing the star topology.
My current audio reference is an Anker Soundcore 2 12W Bluetooth speaker, so I'm hoping I can improve on that for audio quality 😀
The schematic and layout should both be attached.
I haven't made gerbers yet, put could share those in the future if anyone's interested.
Cheers!
Interesting project. Your layout needs some work. I wonder about the use of star gnd when you have a high frequency digital component there. If any such devices are in the vicinity I'd design for better signal integrity and EMI immunity, which also reduces CM-noise energy on the board. This requires gnd-planes, at least one uninterrupted plane, no splits, covering the entire board. Usually on layer 2. This ensures proper return for the digital energy, so it does not have to go in larger loops and possibly create problems. I'd also use some isolation on the digital I/Os, opto or transformer (this requires the digital section also has isolated power not shared by the analog section). I have no idea of the I2C protocols or standards so not sure the best way to isolate (if even possible), but any digital near sensitive analog can benefit from isolation but most importantly proper layout with uninterrupted return on all signal and power traces.
Check out some Altium webinars on youtube, featuring Eric Bogatin or Rick Hartley. Many other great webinars about signal integrity and PCB layout on youtube worth watching.
Check out some Altium webinars on youtube, featuring Eric Bogatin or Rick Hartley. Many other great webinars about signal integrity and PCB layout on youtube worth watching.
I've made a host of revisions to my original design, mostly to improve grounding (per my understanding of best practices).
Layer 3 has been dedicated to grounding and consists of a power ground pour (upper portion) and a signal and digital ground pour (lower section).
Layer 2 has been dedicated to positive voltages. There are pours for amp V+ (25V), preamp V+ (15V), and VDD (3.3V).
layer 4 handles negative voltages and right channel signals.
The higher speed i2c signals are kept fairly constrained in the middle left portion of the board.
That digital portion will end up having its own dedicated power (likely coming from an arduino/raspberry pi/microcontroller).
The preamp circuit has been rearranged so that I could further reduce the board footprint from 4" x 6" to 4" x 5".
The traces from the relay outputs to the amp section inputs still feel a bit too long and susceptible to being noisy. Am I right in thinking that?
Would I be better to have a large copper pour on the top and bottom layers for the left and right relay outputs, respectively?
In theory, only one relay will be active at a time.
Attached are the updated layouts; a composite and a version with 1 layer per sheet.
Thanks!
Layer 3 has been dedicated to grounding and consists of a power ground pour (upper portion) and a signal and digital ground pour (lower section).
Layer 2 has been dedicated to positive voltages. There are pours for amp V+ (25V), preamp V+ (15V), and VDD (3.3V).
layer 4 handles negative voltages and right channel signals.
The higher speed i2c signals are kept fairly constrained in the middle left portion of the board.
That digital portion will end up having its own dedicated power (likely coming from an arduino/raspberry pi/microcontroller).
The preamp circuit has been rearranged so that I could further reduce the board footprint from 4" x 6" to 4" x 5".
The traces from the relay outputs to the amp section inputs still feel a bit too long and susceptible to being noisy. Am I right in thinking that?
Would I be better to have a large copper pour on the top and bottom layers for the left and right relay outputs, respectively?
In theory, only one relay will be active at a time.
Attached are the updated layouts; a composite and a version with 1 layer per sheet.
Thanks!