Combo Amp Build

Posted by Paul Craig on February 20, 2016 at 1:56pm

I'm building a Combo Amp for someone.

The cabinet is Pine 13" wide x 15" tall and 11" deep. All glued together and used a 1/2" roundover bit in my router for the edges.

The speaker is a vintage 10" Utah 15W 8ohm. The amp is my dual Im386 chip bridged amp design. Can run on 9volt battery or walwart and output is 1 to 2 watts.

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Replies

  • Paul Craig May 27, 2016 at 1:54am

    The tone circuit helped tame the brightness a tad. I had 2 choices, put a tone pot in before the signal got to the chips or put 2 tone pots on the output lines that would probably mess with the volume too much. So I chose to put it in before the signal gets to the chips.

    Drew out the new schematic.306552217?profile=RESIZE_1024x1024

  • Paul Craig May 25, 2016 at 3:11am

    The speaker has a break in time period and might get a little darker later, but a tone pot would still be a good idea if it works okay.

  • Paul Craig May 25, 2016 at 3:10am

    Almost every guitar and CBG played with this amp comes out sounding very bright. Guessing it's the speaker that is doing that because the original/first amp that I made was used with a different speaker and was less bright sounding.

    Thinking of adding a tone pot to take away some of the brightness if that is wanted. I'll give it a try out this week.

  • Paul Craig May 18, 2016 at 6:33pm

    More pics.306551868?profile=original306551878?profile=original306552716?profile=original

  • Paul Craig May 18, 2016 at 6:32pm

    And it's done.

    New schematic drawing coming up soon.306556540?profile=original306556654?profile=original306557689?profile=original

    A few last pics.

  • Paul Craig May 17, 2016 at 4:25pm

    Got it working.

    Ended up using 10uf caps in the output wires to the speaker.

    All I have left to do is cover the speaker baffle, affix it to the cabinet and wire the speaker. Then it's done.

  • Paul Craig May 16, 2016 at 12:38am

    Got my chips Saturday from Jameco. Will try to get back to this tomorrow.

  • Paul Craig May 1, 2016 at 3:02pm

    So I rewired the board and made a new control plate.

    It seems that the IM386N1 chips are bad. I've used the N1 on Ruby amps without issue and they were available locally at Radioshack, My original dual chip amp that I built suffered damage from power polarity reversal, but this build should still be working since there wasn't an issue with reversed power polarity. I'm beginning to believe that the N1 chip isn't well suited to this dual chip amp. 

    In a couple of weeks I'm going to order some N3 chips and give them a try. Hopefully they will be better than the N1's.

    • Scott aka Farmer Ted > Paul Craig May 1, 2016 at 5:59pm

      So true, I have had a few of a batch of IC chips test bad/not work properly.

      Might be the right choice to get the N3's, simply for the higher output (700mW per IC for the N3 versus 325mW for the N1).

      Hope it works for you.

    • Paul Craig > Scott aka Farmer Ted May 2, 2016 at 3:13am

      Thanks, I hope it works out too. Should be better than the N1.

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