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First Act MA104 Amplifier Modified

Posted by Mike Bingham on November 12, 2011 at 1:02pm
Views: 597
Tags: amplifier, Act, First, MA104
Here's a First Act MA104 guitar amp I found at the second-hand store. It is designed to work with a 14 VDC power supply but it does pretty well on a 9v battery. I added an external speaker jack to the back so I can plug into a speaker cabinet.The first part of the video shows the amp being played on its internal speaker, and the second part shows it through the Peavey monitor speaker. Next mod will be tweaking the clipping diodes to see what happens.

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Comments

  • Mike Bingham November 27, 2011 at 1:01pm

    Good info on the batteries, Hal. Thanks!  I'll have to rig up an AA battery pack.  The gain and distortion do have a lot of room for improvement.  I plan on lifting one end of the clipping diodes next to see if it will help clean up the signal.  If it does I'm going to try a pair of silicon diodes, a different kind of germaniums, and a "mismatched" set of germaniums to see if I can make the distortion a little more pleasant.  If any of the diode mods work I'll add a switch to bring them in or out and choose which diode pair I want to use.  I'll post a vid if it works.

  • Habanera Hal November 26, 2011 at 6:06pm

    I have re-cased several of these into CBs upgrading the speakers and hard wiring a switch to change from the 14v adaptor to a 9v battery (or 8 AAs - lasts much longer than a single 9v). Personally, I think they sound better at 12-14 volts than at 9, but what really irks me is that I find the gain to be virtually unusable in either mode.  I've tried to find some easy mods to fix that aspect and get a "cleaner" sound.  There was some discussion here: http://www.ssguitar.com/index.php?topic=1436.0 but as a neophyte at electrotronicalmethingies, I'm a bit daunted at trying to switch out capacitors, diodes and resistors.  Has anyone here tried this?

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  • Mike Bingham November 26, 2011 at 3:39pm

    Hey HOGS GRUNT - I'm glad the mods worked for you.   Enjoy the new freedom with your amp.  See Ya!

  • HOGS GRUNT November 26, 2011 at 11:52am

    Hi Mike, I have one of these little amps and have always like d the sound. Saw you mods and did the same and it is running on a 9v battery same as yours and sounds just as good as when it is plugged into the mains power supply. I often wondered if it would work but too lazy to try. Glad I have now as I have a fully portable-go anywhere- amp.

    Thanks man.

    Hogs.

  • Mike Bingham November 14, 2011 at 5:35pm

    Thanks for the comment Roadkill.  It's going to be used a bunch now.

     

    Thanks Wes.  It was amazing how much the bottom end improved. I don't know if you include that feature on the nice CBG amps you build but it might boost sales.  I can send you a diagram if you're interested and don't have one already.

  • Roadkill a.k.a. John Maw November 13, 2011 at 12:50pm

    A very useful little amp and great with the external speaker.

  • Mike Bingham November 12, 2011 at 10:00pm

    Hey Silent Jim - thanks for your comment. (I don't know about brilliant- some things just survive my tinkering somehow - LOL.)  I might try to post some details tomorrow on the external speaker mod. It brought the little amp alive.

  • Mike Bingham November 12, 2011 at 9:53pm

    Thank you for the kind words Uncle John.  I'm pretty stoked with the little feller. 

  • Uncle John November 12, 2011 at 5:38pm

    That lil dude has good sound and SURPRISING power.  The big dude plays well.

  • Mike Bingham November 12, 2011 at 4:34pm

    Thanks Jon!  That's been a fun little amp.  I'm going to see if I can add a bypass switch that will let me switch the clipping diodes in and out of the circuit and maybe get some more clean headroom out of it.  Gonna play with some different diode types too to see if I can shape the distortion. See you 'round

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