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-   -   70V/100V line D class amplifier without a step-up transformer (http://www.diyaudio.com/forums/class-d/214273-70v-100v-line-d-class-amplifier-without-step-up-transformer.html)

Primate 11th June 2012 10:28 AM

70V/100V line D class amplifier without a step-up transformer
 
Hi,
Im planning to set up an system in my house with a speaker in almost every room using one amplifier (aprox. 150-200W). I will most probably use IRF IRAUDAMPs.

I have planned to make a D class amplifier but from what I have read on the forum there could be problems between the output stage in the D class amplifier and the transformer.

My question is does somebody have a schematic (or an idea) how to make an transformerless amplifier for high-voltage systems? Theoretically without the transformer and big heatsinks I could have a relatively small amplifier for the whole house.

Emerson Prado 11th June 2012 02:33 PM

Hi there,
First, the obvious part is to design with high voltages and low currents in mind. For 70V output, you'll need something above 100V per rail (assuming half bridge), specially if you plan some headroom - you'll need output devices which comfortably stand 300V or more. The output impedance will also be different, which changes numbers in the output filter.
But also keep in mind that, for a 70V line, you'll have transformers in the speakers anyway and, depending on the distances involved, the cabling can be another issue. It's good to have no transformer in the amplifier (less losses, less weight, better impedance curve), but do treat your load as a complex one. Consider a Zobel network in the amp side.
Best regards,
Emerson

Primate 12th June 2012 05:30 AM

I was intending to use half bridge although there could be more problems with it because of the power supply pumping since D class will be used. That is one of the reasons why I was asking for a idea/schematic which has a transformerless output.

I know I need to rise the voltage using at least a +-100V power supply but that means that I need a stronger power supply that can withold such power? My question is what is enough...if I usually need 250VA how much will I need for a 70V/100V line?

I was not aware that I could use a Zobel network but it makes perfect sense since we need to rise the voltage and adjust the impedance as well. Tnx and if you have any more suggestions keep me posted.

Ouroboros 12th June 2012 07:14 AM

I design this sort of amplifier as part of my job.
From my own experience with 100V output versions I strongly suggest you use a full-bridge architecture, with a supply voltage of +/-80V or slightly higher.
Don't forget that the load impedance on the amplifier for a 100V or 70V system is a function of the power tappings that are set on your speakers, so a post-filter NFB architecture helps to avoid the HF response changes you might get with a pre-filter NFB design, although if you place your output filter -3dB point high enough this may not be an issue for you.

As a full bridge design is using lower dc power rail voltages, then 200V MOSFETs can be used. For lower power (100W) amps the IRFR9N20 parts work well in the output stage.

darkfenriz 12th June 2012 07:20 AM

Current mode structure comes to my mind, with some voltage feedback from the output.
Cycle-by-cycle current limit is a minimum requirement.

ssanmor 12th June 2012 07:26 AM

At www.coldamp.com we have experience in that use of our modules, using two ampilfiers fed at +/-72V approx in bridge mode. Our users are reporting good results in this arena.

darkfenriz 12th June 2012 06:37 PM

Quote:

Originally Posted by Ouroboros (Post 3056533)
I design this sort of amplifier as part of my job.
From my own experience with 100V output versions I strongly suggest you use a full-bridge architecture, with a supply voltage of +/-80V or slightly higher.
Don't forget that the load impedance on the amplifier for a 100V or 70V system is a function of the power tappings that are set on your speakers, so a post-filter NFB architecture helps to avoid the HF response changes you might get with a pre-filter NFB design, although if you place your output filter -3dB point high enough this may not be an issue for you.

As a full bridge design is using lower dc power rail voltages, then 200V MOSFETs can be used. For lower power (100W) amps the IRFR9N20 parts work well in the output stage.

With a bridgable floating bridges you could even use 100V mosfets, like IRFB4212-like toys. Current mode friendly too ;)

Primate 15th June 2012 09:11 AM

Quote:

Originally Posted by Ouroboros (Post 3056533)
I design this sort of amplifier as part of my job.
From my own experience with 100V output versions I strongly suggest you use a full-bridge architecture, with a supply voltage of +/-80V or slightly higher.
Don't forget that the load impedance on the amplifier for a 100V or 70V system is a function of the power tappings that are set on your speakers, so a post-filter NFB architecture helps to avoid the HF response changes you might get with a pre-filter NFB design, although if you place your output filter -3dB point high enough this may not be an issue for you.

As a full bridge design is using lower dc power rail voltages, then 200V MOSFETs can be used. For lower power (100W) amps the IRFR9N20 parts work well in the output stage.

NFB architecture? No feedback maybe?

Since mono inputs ae used in 70V/100V systems I was thinking to use half bridge connection but with the normal CH1 and inverted CH2. At the output the CH1 speakers would be connected as is, but the CH2 speaker would be connected with inverted clamps. With that configuration the power supply pumping is (theoretically) minimised.

How do bridgable foloating bridges look like ? :)

I was not planning to use a current mode D class amplifier

authlxl 9th November 2013 01:55 PM

constant voltage amplifier without output transformers
 
Quote:

Originally Posted by Primate (Post 3055398)
Hi,
Im planning to set up an system in my house with a speaker in almost every room using one amplifier (aprox. 150-200W). I will most probably use IRF IRAUDAMPs.

I have planned to make a D class amplifier but from what I have read on the forum there could be problems between the output stage in the D class amplifier and the transformer.

My question is does somebody have a schematic (or an idea) how to make an transformerless amplifier for high-voltage systems? Theoretically without the transformer and big heatsinks I could have a relatively small amplifier for the whole house.


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