3*lm3886 power amp

[Maxhax]

I've decided to build a two channel power amp based on 3*lm3886 for each channel.

I've previously built a simple lm3886 two channel (the kit from BriantGT) with just a normal Alphs pot and just one input. This thing sounds amazing, but it lacks the power to drive my Pioneer HPM-110. Bass dont seems as controlled as it is with my Pioneer A-676 amp, especially on higher listening levels.

My plan is therefore to buy a HLLY DMK-IV to use it as a pre-amp, DAC and headphone amp. This will be combined with the above mentioned power amp.

The PA150 looks like something I could use for this project. I just cant find anywhere to buy them. There's a few on ebay that looks similiar, but I'm not sure its the proper ones (I've a hard time to trust chinese companys).

Do you know if there's any legit PA150 pcbs on ebay, or do you know where I could get two? I do not want to put an order on just two pcbs cause it'll get to expensive. Maybe one of you got two spare ones from a previous group buy? Or do you have other suggestions instead of the PA150?

I'm also not sure what recrifier to use. Will the recrifier from my previous amp work to drive 2x3*lm3668 with the simple modification of adding more/bigger caps? Schematic can be found here:http://chipamp.com/images/ps.gif or do you suggest something else?

Thanks / Maxhax

 

[jackand08]

It depends on which configuration you want to use the LM3886. If you want to double its power output to around 120W, then you will need only 2 of them wired in bridge operation. You would only be able to use this amp into 8 ohms otherwise dissipation in the chips will destroy them.

another alternative (which could use 3 chips) is to parallel the 3886's. This still only gives you an output power of one chip (~68W) but gives you increased current capability and easier operation into lower impedance loads. This type of amp can be more difficult to build though as components in the gain stages must be precisely matched to ensure that each device shares the current equally.

As for the rectifier, I would probably go with a higher specification device as having 3 LM3886's in parallel will definitely be stressing them, not to mention the current drawn by the capacitors at startup (because they are basically empty). When adding more channels, having more capacitance will help but too much can just be a waste of money and not be beneficial.

 

[AndrewT]

Parallel chipamps are more difficult to get right compared to your first single chipamp amplifier.

Have a good read of the National application notes and read through the woes experienced by builders in this Forum, if you want a first time successful build.

A voltage amp chip (LME49810, 811, 830) and a discrete output stage is a simpler build and has a lot more potential compared to paralleled chipamps. Again lots of info on this Forum.

However, I am wondering why your existing set up has a lack of bass.
Can you post details of the speaker and your "as-built" schematic?

 

[Maxhax]

Thanks for the information.

Lack of bass might not be the best way to describe my problem. It just doesnt seems to be that good controlled. It doesnt deliver that punchy feeling that I get from my Pioneer amp. Its hard to explain, atleast in a language that I dont master.

Speakers are old but this is the best I can find: HPM-110

The amp consists of the LM3886 stereo kit from chipamp.com, found here. Amp is built as the schematic suggests, without any modifications. Its powered by a 2*24v 225VA toroidal transformer. Star grounding is used.

Setup looks like this Digital source (TV or computer)-->DPA Enlightenment DX32 DAC-->Amp (Pioneer A-676 or the gainclone)-->Pioneer HPM-110

The solution with using a voltage chip and a descrete output stage seems to be what I'm looking for. I've dig into this for sure.

Thanks

 

[AndrewT]

I wonder if the Pioneer amp has a deliberate hump in the bass frequency response to give the impression that it is producing strong bass, when in reality it is exaggerating the 2nd harmonic of the missing bass which is designed to fool our ears?

3886.
Did you fit the 47uF for the optional Ci?

The RC time constant of that 47uF is ~32ms. This will cripple the bass of the chipamp. 330uF or 220uF should be much better.

 

[Maxhax]

The Pioneer amp is used in direct mode, bypassing all the sound adjustments. This does not mean that It'll keep the sound untouched, but it should. I dont have anything else to compare with right now.

I've read from a forum thread somewhere else that the speakers might get as low as 3.7ohm during some frequencys.

The optional cap is not installed.

Maxhax

 

[bcmbob]

BrianGT

I wonder if the Pioneer amp has a deliberate hump in the bass frequency response to give the impression that it is producing strong bass, when in reality it is exaggerating the 2nd harmonic of the missing bass which is designed to fool our ears?

3886.
Did you fit the 47uF for the optional Ci?

The RC time constant of that 47uF is ~32ms. This will cripple the bass of the chipamp. 330uF or 220uF should be much better.

Andrew, I didn't put anything in Ci in my BrianGt amps. I have two 220uF caps on hand and would like to know if your recommendation matches or enhances the BrianGT design.