Questions about building my first chipamp

[JDawg]

I'm thinking of getting a LM3857 amp kit from audiosector and I have a few newbie questions.

I read the manual and i it says it comes with 2 amplifier and 2 rectifier boards. The instructions only uses one rectifier board for both amps so what is the second board for?

I was also doing some reading on Decibel Dungeon about adding a discrete buffer which supposedly improves sound quality. The circuit looks simple enough to build but it needs plus/minus 15-20 volts to operate. What would I need to do to get the power needed for the buffer circuits?

[AndrewT]

Just build the simplest power amp with the fewest nice to have add-ons as can make the amplifier reliable.

Once you have got this mono amplifier working you will see what has to be fitted inside a chassis. Listen to it. Keep it for reference.

Now you are ready to try another build with enhancements. You have something to compare them with.

[asbjbo]

The second rectifier board is for dual mono application (two trafos). If you only use one trafo, use one rectifier board to feed both amplifier boards.

[ChrisA]

Originally Posted by JDawg

I'm thinking of getting a LM3857 amp kit from audiosector and I have a few newbie questions.

I read the manual and i it says it comes with 2 amplifier and 2 rectifier boards. The instructions only uses one rectifier board for both amps so what is the second board for?

I was also doing some reading on Decibel Dungeon about adding a discrete buffer which supposedly improves sound quality. The circuit looks simple enough to build but it needs plus/minus 15-20 volts to operate. What would I need to do to get the power needed for the buffer circuits?

The second power supply board is in case you want to build two mono amplifiers. But if you are doing stereo just use one board to feed both channels.

Some people like to build mono amps either because they are after better stereo channel seporations or because they are building the amp into a speaker cabinet to make a powered speaker.

How to get the power for the other preamp/buffer? Well don't yui have two power supply boards? Build a second power supply using the smallest size transformaer you can find and a couple regulators. But as said above. Build you first amp as simple as possable. Eliminate every part you don't need. Later build another amp. with buffers and volume controls and so on.

[JDawg]

Ok I guess maybe I'll start with just building the amp and then adding more to it later.

I would like to put a volume control but I'm not sure which pot to get. I found an ALPS stereo log pot but it comes in 10K, 50K, 100K and 250K. How do I know which one I should get? Would the 10K one work?

[AndrewT]

build an AC coupled amplifier. Add all the stability controlling components that the manufacturer states are or might be needed.
Keep the chip cool. It does not perform as well when it's hot.

Add the lowest value potentiometer that all your sources can drive properly. The safe value is to go straight to 100k, but this compromises performance, particularly treble and interference.

The better values are at the low end to avoid those two problems.

[lanchile]

Originally Posted by JDawg

Ok I guess maybe I'll start with just building the amp and then adding more to it later.

I would like to put a volume control but I'm not sure which pot to get. I found an ALPS stereo log pot but it comes in 10K, 50K, 100K and 250K. How do I know which one I should get? Would the 10K one work?

Just add a 25k/50k potentiometer and you will be ok. I build two of Audiosector amplifier kits, they sound good and are easy to build.Make sure you use hefty power supply at least 10,000uf per channel. I know it comes with 10uf caps, but if you want to getter better bass just add more capacitance to power supply.

[JDawg]

Originally Posted by lanchile

Just add a 25k/50k potentiometer and you will be ok. I build two of Audiosector amplifier kits, they sound good and are easy to build.Make sure you use hefty power supply at least 10,000uf per channel. I know it comes with 10uf caps, but if you want to getter better bass just add more capacitance to power supply.

Those 10,000uf capacitors are those big ones right? I think I'll stick with the ones supplied in the kit to start and then add larger ones later.

I already purchased all the parts to build the amp and I'm just waiting for them to arrive. I decided I'm going to build and add the buffer circuit I read about on the decibel dungeon website. I figured out how to make a separate power supply for it and the buffer circuit looks easy to build. I do have a question about one of the components though. Here's the link to the circuit:

Building a pre amp for a Gainclone chip amp.

It says that a polypropylene film cap is probably the best option for the output dc blocking capacitor. My local electronics stores don't have any polypropylene film capacitors but they do have electrolytic capacitors. So what would happen if I used an electrolytic capacitor instead? If I had to use polypropylene film ones then I need to order online and they're a lot more expensive too.

[pacificblue]

Originally Posted by JDawg

So what would happen if I used an electrolytic capacitor instead?

Film caps have better electrical characteristics, just like a 100.000 € car has better specs than a 20.000 € car.
Some people notice a difference, others don't. Most who do, prefer the film caps. Also most people don't even try, but buy the film caps just in case.
You will only find out by trying whether they are worth the higher price. For the pure function you don't need them. On the other hand for the pure function you don't need a preamp for a chipamp either. And film caps are not that expensive either, at least in reasonable sizes and as long as you don't buy exotic types.

[JDawg]

Originally Posted by pacificblue

Film caps have better electrical characteristics, just like a 100.000 € car has better specs than a 20.000 € car.
Some people notice a difference, others don't. Most who do, prefer the film caps. Also most people don't even try, but buy the film caps just in case.
You will only find out by trying whether they are worth the higher price. For the pure function you don't need them. On the other hand for the pure function you don't need a preamp for a chipamp either. And film caps are not that expensive either, at least in reasonable sizes and as long as you don't buy exotic types.

Thanks for the explanation. I probably don't need this buffer circuit but I was curious to see if it really did improve sound or not. Its a simple enough circuit to build and add to the chipamp so I might as well try it. As for the capacitors I'll probably try both and see if it makes any difference.