Home Stereo PCB Design for Desktop Speakers – Class A, AB, or D Amplifier Choice?

Hi there,

I'm a newbie. Just going to start with that. :)


I am a visual designer for products and have questions regarding PCB design and layout for a home stereo I am currently tackling.

It will be have a home desktop/bookshelf application for the average listener. NOT for hifi audiophilers.

Any help regarding PCB Design and Consulting services would be EXTREMELY helpful.

--> I'm sure I'm leaving out critical information necessary to answering my question so please inquire!

Thanks and Cheers!
Devin

P.s. check out my custom speaker build below.

My specialty is not audio design, but I'll throw in my 2¢ [hopefully someone with greater audio experience will chime in]:

At audio frequencies the board material and layout is not so critical. Just keep inputs away from outputs, and especially keep the final stage components away from the initial stage components. Also, keep the two [stereo] channels apart. Probably best to lay the board out like the layout of a typical schematic of this type -- [not sure if you are using ICs or discrete components, but the general flow should be, preamp at one end [lets say on the left side of the board, to make this discussion simpler], then interim stages from left to right, with the power stage on the right side of the board]. And the right channel on the top half of the board [again top or bottom is arbitrary, but chose top for ease of discussion], and left channel on the bottom half.

The only reason to deviate from that layout is if the board needs to be some other shape [or aspect] than what will accommodate that layout.

Also, make your power lines fat, especially the ones supplying the power stage. And if you can manage it, on the solder side of the board, do a copper pour for the "ground" trace, and run "buss lines" [on the component side] for the positive supply lines (typically there's a separate positive supply line for the preamp portion - which is "decoupled" from the main supply line(s)). If this design has a dual supply, then copper pour the ground line and "buss line" the positive and negative power line [on the component side of the board].

BTW: Absolutely love your speaker-lamp design!

I just noticed that the title of this "question" doesn't seem to correspond to the content. Are you asking what class of power amp to use for your design?

If you are totally new to electronics, to design a system from scratch is a little over-ambitious.
But if you google something like "DIY home hifi" or "DIY home music center", you would find a enormous range of detailed projects.
Instructables.com is a good site for a good range of projects.

Hi David. Very cool custom speaker you made. Regarding your question, are you asking which amplifier class is best suited for Home Stereos?

Thank you so much!

You really know your stuff! I really appreciate the thorough breakdown! I am probably going to have to get some help in this part of the design process and I will definitely get whoever ends up helping with this to read your advice!

Hi Jed,

Yes indeedy. I guess that's a good starting point - just knowing which is the most common amp for desktop / bookshelf speakers. A? B? AB? D? etc...

Thanks! I build one-off speakers from time to time to satisfy my creative bug - I use a class D amp for most of these, but am aware that they can be very pricey for what I'm trying to conquer - mass produce a speaker design.

I have taken apart various speakers to see what the guts look like and have re-used them in other one-offs like the one pictured, and they sounded fine (to the non-audiophile listener) and the circuitry also seemed relatively simple compared to the class D amps, so I assume they are more commonly used in mass production for their cost to quality ratio.

Re-read this and noticed i left a couple of things out:

* When running the power lines, try to either have a "central" (can also be on the edge or even somewhat threaded through the design) power line (or two if dual [positive/negative] supplies) that is fat -- like 100 to 300 mils (.1 to .3 inches) and then run lines off that to the individual components or run separate, also fat (but only around 30 to 50 mils) to each component from a common point at or near the supply source. And, in all cases, run separate supply lines to the three sections: pre-amp [if one is included], the mid stages, and the final, power stage. That is especially important for the power stage. The reason is: all traces have resistance. The fatter the trace the lower the resistance, BUT there is still resistance. When current is drawn through a trace, the resistance in that trace will produce a voltage. This voltage can introduce signal into the amplifying components which will be boosted along with the intended audio signal. This can cause crosstalk, distortion, and even oscillation. The higher the current through the supply line, the greater this voltage, thus the line to the power stage is the greatest culprit. Thus, it is most important for this line to go strait to the power supply, and for nothing else to be connected to this line.

* Make sure the power supply has sufficient capacity to handle the highest power in the final stage at the lowest frequency that will be reproduced there. This may mean, also, that the supply is sufficiently bypassed -- i.e. big enough capacitors to supply current at power peaks so that the voltage at the input of the regulator(s) never dips below the minimum for proper regulation. Also, capacitors on the output of the regulator(s) may help the "transient response" [i.e. immediately supply current at the beginning of each Bass Thump for instance], thus allowing the regulator to "catch up" [check the datasheet for the regulator of choice].

If Class-D is what you're looking for, there are numerous ICs that make this simple [except for the fact that they tend to have a package type that is difficult to deal with on a prototype/hobbyist level (such as the NCP2824)]. For that, there are both breakout boards, and inexpensive final products -- such as:

* https://www.sparkfun.com/products/11044
* https://www.adafruit.com/search?q=class+d

Most of these should supply enough power for the lamp speaker kind of thing you're talking about.

Or just Google: "class d mono amplifier circuit board"