LM3886 opinions sought

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I have two 25v 225va transformers and two psu boards kicking around from a previous project that I want to do something with.

I intend to use LM3886 chips on a fairly low budget, so most likely a point to point jobbie. As I see it I have three options, a stereo build using one transformer and psu, dual mono using both or a monoblock sat by each speaker.

I know it is overkill to use 225va for a single chip, but since I've got them and I have never heard monoblocks I am leaning that way a bit. I have a Pass diy B1 here so the longer interconnects should be no problem.

Chassis costs aside what do you think? I know I'm not going to get data sheet performance with p2p, it's more about getting some use from what is currently an expensive paper weight (and using up some bits from the biscuit tins).



John
 
They are 25 volts AC so around +-35 volts DC. It won't ever be anywhere near flat out and will be well cooled so I was thinking I might be ok. How close to the limit do you reckon is too close? The absolute limit with signal is given as 84 volts.

I have done a point to point LM1875 and a 3875 before, liking the results. I think the 1875 is a lovely sounding chip if you don't need a lot of power and is a tiny thing when done.

Thanks for the input
 
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I currently run 2 inexpensive LM3886 from eBay with a 28VAC toroidal, with an iPhone as the only input. They will take full power from the iPhone with only a very rare clip (2-3 times in the last 2 months) but have to run the iPhone at 100% to get it to clip. I typically listen at 40-50% on the iPhone though and they do just fine.
I have both chips on a 7-1/2 x 2-1/4 x 2 inch finned heatsink, running in my basement (60 degrees F right now)
I am running a Mauro Penasa LM3886 with 22VAC torroidal (same size heatsink) - and it certainly sounds better, it will be up to you if $150 compared to $20 is worth the difference, just more refined in most every way.

Edit - this is running on 4-ohm DIY speakers (4-ohm woofer, 4-ohm tweeter), but the industry would probably say they are 6-ohm nominal.
 
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If the budget was available I would love to hear a Myref or Modulus implementation of the 3886 but I can't justify the costs as things are.

The amps I have are at the minimalist end of things. My first was a chipamp.com LM3875 which is still playing daily some 11 years later and taught me all about the invisible lacquer on transformer secondaries. That was followed by a couple of point to point builds with more of the "optional" stability components included, so I have yet to hear the best sound you can get from them.

Interesting to hear you are running on even higher voltages than I was proposing too.
 
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There are way smarter people on this forum than I, so I can only say that it works...not that it is the best long-term solution.
For me - $20 is not enough to warrant not using the toiroidal I already had, even if they get destroyed. I did make sure to have speaker protection, just in case.
After being a mosfet guy in all my previous amps - I was surprised and have been very happy with the LM3886 amps. Much better and stronger bass than I expected and easy to listen to. My previous Class D cheap amps always seemed to be shrill and my ears got tired of listening to them after 30-45 minutes.
Good Luck on whatever you build - sure it will sound great and give you years of entertainment.
 
2x25VAC is a bit much for a single LM3886 as you'll get about ±35-36 V DC out of it. I explain my reasoning here: LM3886 Output Power. You could choose to drop the supply voltage a bit using a 5.6 V, 5 W zener in series with each supply lead.
You could also implement a simple zener regulator with a transistor (requires four components). You'll probably want a darlington transistor as shown here - or a MOSFET. You'd want the transistor on a heat sink ... which it could share with the LM3886.
zr2.gif

Then you get the bragging rights to having a regulated supply... Read the full circuit description here: Transistor-Zener Diode Regulator Circuits

Should you later decide to drop in a MOD286 in mono configuration for 100 W into 4 Ω, you'd have the supply and heat sink ready to go. Just remove the zener diode or regulator and drop in the MOD286.

Tom
 
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A bit of an update.

Further biscuit tin rummaging turned up four LM338s that I bought years ago to try a regulated chipamp using CarlosFMs design. I didn't get round to it at the time so I think I will try those at 28 volts to start with, and maybe try discrete regulators eventually.

What are your collective thoughts on the best way and place to create a signal ground when point to pointing? I can't do it on the RCAs due to the distance.

I have used a one ohm resistor from the power ground as a signal ground point on a previous build which seemed to work nicely, so that is probably the plan unless I've missed something.

John
 
I currently run 2 inexpensive LM3886 from eBay

Do you have a picture of what they looked like? I was going through the options one day and ordered one mono board for about 5€, so not a big loss if it's no good.

LM3886TF AC 20~28V 60W Sound Audio Amplifier Mono Digital Power AMP DIY Kit | eBay

I know that there are better designs out there, but I just need a mono amp that does the job decently. Need to upgrade one LM1876 from my 2.1 amp to this, so it can better drive a 4 ohm subwoofer.
 
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