Chipamp into xformer

[StanJ]

It is just an idea that came up the other day, and I am absolutely unsure weather it could work. Before trying it out, I would appreciate very much your experts opinions and guesses on that matter.

The idea is to let a couple, say 4, chipamps run into an interleaved audiotransformer. Such transformer would have on each side 4 separate sets of windings. Input/Output could be 1:1, or other. Each single amp would fire one set of windings. The described set-up would add up the power of all 4 amps (minus losses), at least that’s what I believe. Additionally, the amps should be able to drive loads of 2 Ohm or even less. If the transformer is properly designed it could also smoothen the sound of the individual amps.

I am successfully using hardwired amps based on LM3875TF, but the performed power is to low for some applications.

If you guys will tell me, that my idea is not completely weird and worth a try – I’ll wind an audiotransformer and check it. However, if you come to the conclusion that it is completely impossible due to any reason, I am happy to know before starting this project.

So, what do you think? Or: did anyone ever try it and has first hand experience?

[peranders]

How much power do you want? Supply voltage is an essential thing here.

[StanJ]

Hi Per,

the reqiured power should be between 200-250 Watt. I am using +/- 24 VAC.

And, what is more important, the amp should be able to drive speakers of as little as 2 Ohm.

[peranders]

I think it's a better idea to get a proper PS and choose a discrete powerful amp instead, especially if you want good sound quality.

[AndrewT]

one of the biggest design difficulties with valve power amplifiers is the output transformer.
You are potentially making your amp nearly undesignable.

[peranders]

Originally posted by StanJ
If you guys will tell me, that my idea is not completely weird and worth a try – I’ll wind an audiotransformer and check it.

I'll guess you have the answer but if you have the necessary skills for windning a good audio transformer you would probably not have to ask us.

Why don't you build 4 separate amps?

[SpittinLLama]

You're making it too hard. Set up all the chip amps to run in parallel as a single amp BEFORE the transformer. The PA type of design (Check AN-1192). Then add the transformer. As long as the impedance seen by the amps is within 4-8 ohms it will be just fine. You will need each amp to see 4 ohms for maximum power at +/-24V rails. The LM3876 is rated as a 56W amp so you'll only be able to get about 56W from each amp. The only trick is to design so that you get the maximum power form each amp. If you want to drive 2 ohms with 200W then go for supply rails that are +/-35V, tie all 4 amps in parallel and each amp will 'see' an 8 ohm load. This will give you the 200W you want. The transformer will not do anything but add power loss. If you need it for distributed power (70V systems, for example) then it can be used to step up the voltage or drive lower impedance loads by making the load look like a higher impedance but you will still never get more than about 200W from four LM3876. The chip amp can only do what it is designed to do no matter what you try.

Trust the Llama.
-SL

[analog_sa]

Originally posted by AndrewT
one of the biggest design difficulties with valve power amplifiers is the output transformer.
You are potentially making your amp nearly undesignable.

Hi Andrew

You are not entirely correct in this comparison. This output transformer is much easier to design than one for valves.

- driving impedance is almost zero, compared to 3-10k - high primary inductance is unnecessary which makes wide bandwidth much easier without interleaving

- very low DC in the primary, compared to a few volts even in a PP transformer. Toroidal core is possible.

[AndrewT]

Originally posted by analog_sa
This output transformer is much easier to design than one for valves.............. Toroidal core is possible.

are you going as far as actually recommending he, with your help, tries to design this transformer coupled parallel SS set up?

[BWRX]

All analog_sa said was that it would be easier to design than a transformer for a valve amp. I don't think anyone would recommend that someone do this unless they had time and money to burn!