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  • Author Author: michaelkellett
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Fast Test Amplifier - Part 1

michaelkellett

A while ago (July 5th) in the discussion

 

https://www.element14.com/community/message/241748/l/programmable-frequency-generator#241748

 

I suggested an approach to building a low cost high frequency power amplifier.

The idea was to keep the design as simple as possible and base it on the classic 1970s bipolar transistor based HiFi power amplifier.

 

I've taken the idea a bit further and designed some boards, and finally got round to putting the parts on one and doing a bit of testing today.

 

The final schematic looks like this:

 

image

And the board looks like this:

 

image

 

I've been testing it cautiously using +/- 12V supplies (should be OK up to +/-18) and a 20 ohm load.

So far it looks quite good, small signal bandwidth is up to 10MHz but it can't do anything like full power at that frequency.

All the tests below were 12V pk-pk into 20 ohms:

 

Sine wave at 1MHz:

image

 

And the spectrum of the same:

 

image

 

Square wave at 500kHz:

 

image

 

And a close up to look at the slew rate:

 

image

 

So far it doesn't look too bad - quite a bit more testing to do and almost certainly some tweaking. I'm hopeful of meeting my target spec of 10W into 8 ohm load up to 2 MHz.

 

If anyone wants to build one I'll be posting the BOM and will put the Gerber files on Dropbox or similar.

 

MK

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  • Hi Michael,

     

    That's really neat, it could have science applications, or working with transducers. I'd be interested to replicate at some stage when you get the info posted.

    I've been busy on a DDS project recently - just a basic signal generator capability, using off-the-shelf boards. I'll hopefully get part of that documented today.

  • in reply to shabaz

    I had a few boards made -  I need to do a bit more work before I'm happy to inflict it on third parties but if you let me know when you are ready to play with one I'll put parts on another and send it to you.

     

    The board is designed to be bolted flat down onto a heatsink ( it needs serious thermal management) which is why I'm running it into 20 ohms and off lower than planned supplies.

     

    I'm off on hols for a week starting tomorrow so not much more will be done before the end of August.

     

    I won't get the control board done much before the end of September.

     

    MK

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  • in reply to shabaz

    I had a few boards made -  I need to do a bit more work before I'm happy to inflict it on third parties but if you let me know when you are ready to play with one I'll put parts on another and send it to you.

     

    The board is designed to be bolted flat down onto a heatsink ( it needs serious thermal management) which is why I'm running it into 20 ohms and off lower than planned supplies.

     

    I'm off on hols for a week starting tomorrow so not much more will be done before the end of August.

     

    I won't get the control board done much before the end of September.

     

    MK

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