Lm3875 vs lm3886

[geraldfryjr]

Yes ,it comes to 49.35v exactly which would be fine for a bridged amp.
But for parallel amp, it requires a bipolar supply and it would be to much voltage.
It would have to be regulated down by 8 volts.
I have been working with and recording rock and roll bands for a number of years and I do like it very loud occasionaly.
But as far as the high power goes, my esl's present a load as low as 1 to 2 ohms and some musical transients can be as high as +20db (100 times) over the average music power.
By monitoring the signal with a scope I have found this to be very true.
So it is not just a matter of rms power and how loud it goes (somewhat).
I have 10 of these 200 watt transformers and I got them for $20 a piece and it is what I have as I don't have the funds to by any larger ones at the moment (+$400).
I already have every thing I need minus a few more chips to finnish the project. jer

[a.wayne]

Antek trannies are very reasonable 600-800 VA is under a 100.00

[geraldfryjr]

Yes ,I see that they have very good prices and would rather get a couple,but that is impossibile until my economy gets better.
However I am thinking of feeding them with a SMPS circuit to boost the power handling.
Adding another secocdary winding or two or three to handle the current demand would be very easy to do for a VA rating of 400watts to 600 watts or so as 800watts may be pushing the primary current to far for these transformers .
Just another idea and that is some thing I will try at a much later time.
But could be done very simply since there is two seperate 120v windings.
Right now I just need to get some thing going, because my current amp is just not cutting the mustard at all by any means.
I know could go with a discrete amp design but I already have the chips and I am very curious to see how well it would work.
Sorry didn't mean to hijack this thread. jer

[pacificblue]

Originally Posted by geraldfryjr

But for parallel amp, it requires a bipolar supply and it would be to much voltage.

You can use single supply with any configuration.

Originally Posted by geraldfryjr

But as far as the high power goes, my esl's present a load as low as 1 to 2 ohms

If the load is 1 Ohm a BPA should ideally have 8 parallel channels. For a 2 Ohm load 4 channels would be sufficient.

Originally Posted by geraldfryjr

Yes ,I see that they have very good prices and would rather get a couple,but that is impossibile until my economy gets better.
However I am thinking of feeding them with a SMPS circuit to boost the power handling.

You have no money for a transformer, but you do have for a 500+ VA audio grade SMPS?

[geraldfryjr]

yes,I know how to setup an opamp for single supply operation.
However this would require rather large output capacitors therefore quite costly and would take up alot of space.


yes,I have had plans try a BPA with a total of 16 devices.
It maybe overkill and a disceret design might be a better choice for over 600watts.
Although I am very curious to find out if and how well something like that would work.


No,but I do have lots of dead computer supplies laying around and a switcher to drive one of my transformers cores could be made very easly.
jer

[pacificblue]

Originally Posted by geraldfryjr

No,but I do have lots of dead computer supplies laying around and a switcher to drive one of my transformers cores could be made very easly.

Some stomach feeling tells me that normal power transformers are not the optimal choice for a switching supply. To transform a square wave at a switching frequency in the tens to hundreds of kHz range requires at least a ferrite core. Many people even use powder cores, though others say that ferrite cores are the best choice.

[geraldfryjr]

The torriodal power transformers that I have ,have shown some results with square waves .
The best I have ever seen before compared to an E-I type.
With just my whimpy amp driving a 16v winding with a 60v peak to peak 10khz square wave I get a good 400v peak to peak square wave on a 120v winding.
After 10khz then slewing distortion from the amplifier sets in.
But what goes in ,comes out as far as waveshape.
I have measured the response of this transformer to be good to 1mhz with two peaks at around 310khz and 620khz or so using just the signal generator.
1mhz is the limit of my generator using using a sine or square wave.
The square wave test was good to at least 300khz but I remember that 50khz to 100khz was almost perfect,this was what sparked the idea.
I can easly retest and post some pictures if you like. jer

[geraldfryjr]

The preliminary tests and study I did can be found on the "material for esl" and "step-up transfomer design" threads.
Lots of good stuff there. jer