Suggested affordable quiet amp for high efficiency speakers

Hi everyone,
I had a question about the possiblility of implementing a subwoofer output into this amp.
By doing so, I will open up more potential subwoofers to purchase that don't have speaker-level inputs and only have a single RCA input.

My goal is to have the audio come into the amp via the RCA the binding posts at the back, go through the volume pot and then the output of the volume pot goes to the inputs of both the left and right channel amps for the speakers but also has a downmixed mono RCA port that can be connected to a subwoofer. I want the volume control of my amp to also change the volume of the audio going to the subwoofer so they stay volume-matched.

Am I correct in the idea that I split off the output from the volume pot, through a series resistor on the non-ground lead, one for both left and right channel, then join the output of the resistors together before soldering that to the RCA post at the back of the amp to be connected to the subwoofer?

I've attached a terrible ms-paint dialog of what I mean. Scenario 1 is what would normally be set up, and scenario 2 is the one I am hoping to do.

Also, would the 220ohm 2w resistors I have purchased also work for this case?
Subwoofer Output.png




The kind of subwoofer I am talking about is something like this:
Subwoofer with only RCA Input.jpg



Thanks for your help!
 
Hi HAYK,
I almost have all the parts delivered, but I wanted to double check on the mods you mentioned are good to do with the amps.
I have attached a picture below. I know I need to remove the SMD output caps, and solder a leg of each of the blue caps to the output of the black things on the board, join the other leg and connect to two parallel 2w resistors, but where to I solder the output leg of the resistors to? I can't tell from the picture you uploaded in the other thread.

Thanks so much for your help!
IMG_20230605_140015.jpg
 
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Ah thanks Preamp, I'll double check the wiring of them. It was just a rough diagram, I'll make sure I get the correct cables in the right spots on the potentiomer.

HAYK, just to double check what you mean, I've completed the diagram as far as I understand you have explained it.
If you say it looks good, I'll be able to get the soldering iron out soon hehe!
I've attached the final guide below.

Thanks again for all your help and I'll post back with more progress as I have it!
Amp Mods Final.jpg
 
Hey bros, just a small update - all the parts have arrived! I will attempt to fit everything into the smallest case that I found that can just fit everything!

This is the case that I chose: https://www.aliexpress.com/item/100....order_list.order_list_main.11.5df81802hWWIyt

I have 3d modelled in FreeCad a base plate that will hold all of the PCBs that make up this amplifier and facilitate easy connection between the parts.
It is printing now, I'll see if the print worked overnight tomorrow and whether I need to make any changes to the tolerances and reprint.

I'm also toying with the idea of 3D printing the backplate as well, rather than bothering to drill through the aluminum. Might end up being easier, I'll see!

FreeCad Snippy.jpg
 
Hi fellas,
Just as an update, the 3D print of the base and back plate together as the same object fits nicely.
The print warped a little but thankfully not enough for me to need to do another print.

Now that the base plate is printed and the parts all fit I will try soldering as much of it together tonight as I can.

I am still waiting on a friend to drill the volume pot hole into the front plate so sadly I can't finish the amp tonight, but hopefully by next week it will be!

If anyone is interested in the part that I designed to be 3D printed to work for this amp and pieces please let me know and I will try to attach it.


4th.png


1st.jpg


2nd.jpg


3rd.jpg
 
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Hey fellas,
I've been going back and forward a few times on the design but have now settled on a separate power supply design.

For the few minutes I have had the amp working properly I can confirm that the noise floor is much better than any other amp I have.

I have however run into a few issues with it so far.

The main thing is, at the moment, the amp works very well for 1-2 mins, but then static noise seems to increase in one of the channels. When I remove power and wait a bit, and start again the noise isn't there, but after 1-2 mins it starts again.

I've blown a few of the mono amp PCBs. Once when I let the noise accumulate for too long one of the channels blew as well.

Does this point to something wrong with the large capacitors I am using with the build? Or is the problem likely somewhere else?
Does anyone have any suggestions? I have attached a picture of the capacitors I am using.

Thanks for any help in advance.
 

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