22+22 transformer

[thetube0a3]

Hey,
Lookin for a 22+22 toroid that is 200-250va or larger,

I see Avel has one but its only 160VA

I'm lookin to throw together an LM3886 amp to drive 4 ohm speakers but theres a chance i'll want to drive 8 ohm occasionally as well and a 18+18 just seems to be a bit on the limp side IMO.
I figure 22+22 will get me as close to the 28-30v ballpark the chip calls at 4 ohm for maximum output without cooking it.


Any recommendations?

[danielwritesbac]

Antek - AN-3222
It has the amperage capacity for your 4 ohm speakers.

P.S. If you're accustomed to tube sound, check out the inverting amp designs at decibel dungeon. Those are more stable than average.

[thetube0a3]

WOW thats PERFECT. Cheaper then the Avel ones as well.

Even located near me. Tho the rubber washer for mounting looks kinda funky?

Thanks a lot, I spent all weekend looking for transformers and its difficult searching in google as you rarely find ones an end user can buy.

[cjkpkg]

I have purchased many toroids from Antek and they have performed flawlessly. Good Luck!

[thetube0a3]

Whats the typical power output the LM3886 will do into a 4ohm load with a 28+28v supply? According to the data sheet it looks like 70-80W RMS. If so thats crazy.

How difficult is it to keep cool?

[cjkpkg]

I run 8 ohm speakers and I am using a 25+25 200VA unit. I use the HSIFES50295 from here and they barely get warm.

here is my amp in progress

[danielwritesbac]

Originally Posted by cjkpkg

I run 8 ohm speakers and I am using a 25+25 200VA unit. I use the HSIFES50295 from here and they barely get warm.

here is my amp in progress

That's right, the LM3886 varies heat output mostly with load. Stability and clean power count too! Voltage doesn't vary heat output as much as the other factors.

If your LM3886's run cool on minimal heatsinks, then your design is clean and stable, and then you could say that it can run 4 ohm speakers (if you double the heatsink) while also using a 25+25 transformer on a dual rectifier supply.

Other notes:
*Load is less likely to kill a chipamp than voltage, but voltage sure will kill a chip--voltage spikes during operation wear out the tiny output transformers inside. This is why you don't want to run the chip amp at maximum rated voltage.
*Dual rectifier power supplies can sometimes make cleaner power at lower voltage than single rectifier supplies, although the difference can be minor.
*With the chipamp, its so sensitive that current capacity of the transformer is important to the tonality of the amplifier. The transformer is going to ring a sound into the power supply. Make that a low pitch. Just like a bell, the larger transformer makes lower pitch sounds which are not as obvious to the ear (some of this sound always gets into the amplifier via the power circuit). This is why I posted earlier with a 300va transformer. You can use smaller transformers if also using capmulti or SMPS or Regulated power supply.

[thetube0a3]

the tiny output transformers inside????

A larger transformer makes lower pitch sounds!?!?


come on now,


I don't even have a response to either of those. I'm completely speachless. I can only hope you meant to say output transistors.......

[danielwritesbac]

Originally Posted by thetube0a3

the tiny output transformers inside????

I meant to say transistors. sorry!!

Originally Posted by thetube0a3

A larger transformer makes lower pitch sounds!?!?

come on now,

I don't even have a response to either of those. I'm completely speachless. I can only hope you meant to say output transistors.......

I'm going to have to play it safe and say it like this:
.

It applies to the extent of the sensitivity of the given chip amplifier: Every pin is potentially an input.

Power + Input = Amplifier.

There are many reports of "shouty" with LM3886 and LM3875

The larger current capacity transformer provides greater support for the amplifier to create lower pitches of music.

You can see why the 300va will be more helpful than a 160va.

[thetube0a3]

Daniel : you had me worried there

This luckily is not my first lm3886 project

Here are some pictures of my last one.

Its a basic BPA-200 with dc servo's and a single lm3886. They are used as a woofer\tweeter amp setup with a swappable linkwitz-riley crossover. been in use since mid 2008. Did just under 220W / 59W at clipping both amps driven into two 8 ohm resistive loads.









They bolt into the backs of a pair of 1977 Powered Advent's.