Power supply for amps

[frankwas]

How did you fix the noise problem?

I got a pcb from a site and had it made for very cheap. I actually had two made for R180, which is about $25.

You would believe it, I finished the velleman kit, and it sounds pathetic in comparison and it is twice as expensive!!!

 

[audioguru2]

I finished the velleman kit, and it sounds pathetic in comparison and it is twice as expensive!!!

The cicuit for the Velleman kit amp is simple and basic. The National amp IC is the best they can make. No wonder Velleman don't say what is its distortion at anywhere near its full output.

 

[frankwas]

Yeah. I am actually disappointed in velleman for that.

I have another question: What is the purpose of the 2R7 resistor and the 100nF cap on the output?

Also, what would you recommend I use for a low-pass crossover for a sub? An inductor or a electronic crossover. If an inductor, how do I make one?

Thanks in advance!

 

[audioguru2]

Hi Francois,
Speakers are inductive which causes them to have a high impedance at high frequencies. The RC networks at the amplifier outputs are "zobel networks" that are a low impedance at high frequencies to prevent the amplifiers from oscillating.

An inductor and capacitors to make a passive crossover network for a sub would be huge and have a high resistance which would ruin damping of the sub.
Use an active crossover circuit instead. There is a second-order sub crossover project in our projects section, but I think a crossover should be 3rd-order instead. Rod Elliot has a 3rd-order crossover project but it isn't for a sub, it is for 3-way speakers. You could re-calculate its parts for your sub. You should also have a highpass for the main speakers as part of the crossover network.

 

[frankwas]

Ok. Because I forgot to put that in but it still sounds ok. But I'lll have to put it in.

Do you think it's wise to buy a active car audio amp, since all my speakers are car speakers anyway?

 

[audioguru2]

Do you think it's wise to buy a active car audio amp, since all my speakers are car speakers anyway?

What is "an active car audio amp"?

 

[frankwas]

Sorry. I meant to say active car crossover. 

 

[audioguru2]

An active crossover circuit for a car might use a single 12V supply and an output coupling capacitor. When power is turned on or off then the coupling capacitor will charge or discharge and make a loud "BANG" in the sound system.
A home active crossover circuit will probably use a positive and negative supply, so its coupling capacitor won't charge and discharge and won't make a noise.

 

[frankwas]

Oh ok.

I just blew my velleman amp!! Just couldnt keep up. Now I need to find an amp that preferably uses two 3886's in parallel and that has a single sided pcb design to go with it. 

Do you perhaps know of any? I looked at diyAudio, but have not found anything yet.

 

[audioguru2]

A guy called Gevv joined our forum a few months ago and posted many projects with the RAR file type, and having a password I think is gevv. I saved some of his projects and many are amplifiers using the LM3886, some paralleled.

EDIT: This file is without a password and has a 100W into 4 ohms amplifier project using two LM3886 ICs. Its pcb is double-sided.

PA100_2x_LM3886_in_parallel.rar

 

[frankwas]

Thanks.

I was really considering that design, but I can't get double sided PCB's made as of yet. Do you perhaps know of any other amp, even if it is not a 3886 design that will have rms 100W output or more?

Thanks a lot for all your input!!!

 

[frankwas]

I just hooked up my sub to one of my 3886 amps and it played it perfectly!!!

But now, I have two transformers that I would really like to use so that I can connect two more amos to it. The one is a 20-0-20 3.2 A per secondary winding. Will I be able to use this one to power the amps just like the origianl 160VA I used? Because I remember that you said earlier that the voltage would be too high for the amp to handle, but what if I get some way to lower the voltage? The other transformer is a 30-0-30 5A per secondary transformer. What would you suggest I do?

Thanks!!!

 

[audioguru2]

I just hooked up my sub to one of my 3886 amps and it played it perfectly!!!

Maybe you didn't drive it higher than 68W into 4 ohms. You don't have a circuit to limit its output power, so it might exceed 68W then its SPiKe protection circuit will become active. They say that the protection circuit really messes up the sound and it sounds horrible.

I have two transformers ... one is a 20-0-20 3.2 A per secondary winding

It will be fine with a single LM3886 IC, a 4 ohm speaker will receive about 64W and the transformer will not be overloaded.

The other transformer is a 30-0-30 5A per secondary

The voltage is too high for the LM3886. A different amp that uses it will provide about 170W to a 4 ohm speaker.

Have a look at the amp circuits at www.ampslab.com/projects.htm .

 

[frankwas]

The c200 is a great design!!! Could you please recommend a way that I can design a pcb for it?

 

[audioguru2]

The c200 is a great design!!! Could you please recommend a way that I can design a pcb for it?

Ampslab tempts you with their circuit and its good spec's, because they want you to buy their kit. It is probably a good deal.

 

[frankwas]

Hehe! Yeah, I'll probably order it someday.

I have a question about my amps. On my tweeter and midrange speakers I get a lot of noise, even when there is no signal. I have not put in the Zobel network. Can this be the problem? What else can I do to insure the cleanest sound possible?

Thanks!

 

[audioguru2]

Without the zobel network, the amplifier might oscillate and blow your tweeter. It will be noisy if it is oscillating, and maybe is getting hot.

If the noise is a high frequency hiss, and it reduces when the volume control is turned down, then the noise comes from the source that feeds the amp.

I don't think you posted the schematic you are using. The datasheet for the LM3886 has 3 different schematics.

 

[frankwas]

Hi guys! Sorry for the silence. Had a lot to do! I finally finished my amps and speakers. Just need to finish off my speakers. As soon as I'm done i'll post photos. The sound quality is phenomenal!!!! I would really recommend if anyone wants to build a cheap, good quality amp the lm3886TF is the best!

Thanks for all your inputs! I really appreciated it! Now, onto the next project