LM3886 chipamp project to start in a while

[shoq]

Hello everybody!

I've been reading on this forum for a couple of days since I used Google to find my way through all the articles on the web regarding LM3886 chipamps. Not without a reason, I want to build one myself! This obviously left only one option available, join this forum! Some very nice projects here and from what I've seen alot of dedicated and knowledgeable people gathered, respect!

My objective is: low cost, though not saving money on something which makes it sound or look better.

Therefore I would like to use the following:
- DIY LM3886 amplifier kit (2x) with PSU-pcb or assembled kit
- 300VA or 500VA Toroidal Encapsulated Transformer 2x25V or 30V (will it make any difference?)
- speaker protection?
- soft-power?

I also would like to make some kind of input selector/preamp. This should allow me to switch like four RCA-inputs and controlling the volume (no remote required). I found some input selector pcb-kits scattered on the web, but I don't which one might suit me. Pre-amp pcb/kits I haven't found much about, but I don't want to use tubes. Does anybody know what I should do regarding input selector/volume control/pre-amp?

Separately, both of these project will go in a case from Modushop.

[panson_hk]

Hi shoq,

You can also think about what performance do you expect from the project. For instance, how much output power for 8ohm/4 ohm do you need. It helps you finding a suitable power supply (transformer rating, reservoir capacitor size).

My opinion, Speaker protection circuit is a must.

[pacificblue]

Originally posted by shoq
- 300VA or 500VA Toroidal Encapsulated Transformer 2x25V or 30V (will it make any difference?)

Yes. Either of the voltage options limits the use of your amplifier to 8 Ohm speakers. 2x30 V brings you to the LM3886's limit and needs thorough heatsinking. If you want to be able to drive 4 Ohm speakers, use 2x18 V max with the isolated LM3886TF or 2x22 V max with the non-isolated LM3886T.
300 VA is enough for two channels.

Originally posted by shoq
- speaker protection?

Absolutely.

Originally posted by shoq
- soft-power?

Up to 500 VA usually not necessary, but it never hurts either.

Originally posted by shoq
I found some input selector pcb-kits scattered on the web, but I don't which one might suit me.

A simple point-to-point wired two pole selector will do. You can buy an expensive one like this, if money is not an issue.

Originally posted by shoq
Pre-amp pcb/kits I haven't found much about, but I don't want to use tubes.

With the LM3886 a preamp is not necessary most of the time. Try it without first. You can still add one later.

There are numerous preamp designs. Some come as kit others are designs you have to convert into a PCB yourself or join into a group buy of somebody elses layout. E. g. SOAP
or the Pedja Rogic buffer instead of a preamp.