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What's wrong with this Simmons e-drum amp?

Discussion in 'Amp Tech Center' started by control voltage, Sep 19, 2020.

  1. control voltage

    control voltage TDPRI Member

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    [image of the same model, from the internet:]
    [​IMG]


    I was given a Simmons DA200S amp, which is marketed to electronic drum players. It powers up, but only produces a static sound. Some of the static reminds me of sounds an effect pedal might make when its 9v battery is just about to run out completely. None of the inputs or controls on the front panel seem to affect the sound, with one exception: the subwoofer volume does change the quality of the sound, adding more low end to the static. It doesn't really get louder, just bassier.

    Looking at the signal flow diagram from the manual, I see that there are two 50-watt power amps (left and right mids and tweeters), and a 100-watt power amp for the subwoofer.

    I don't know much about electronics (yet), but it seems to me that, at the very least, the low-pass filter to the subwoofer power amp and speaker is working, and possibly that amp, too.

    The previous owner said it was working fine until he unplugged an instrument, leaving the cable plugged in to the amp, then heard a loud POP! when he touched the end of the cable. So, if he had it cranked up, a big transient peak would have gone through.

    Anybody have any guesses about what might have failed? I recorded some of the static, but don't seem to be able to upload a sound file here.

    Here's the signal flow diagram:

    simmons da200s_signal flow diagram.jpg
     
  2. glenlivet

    glenlivet Tele-Holic

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    FIrst, I have never owned (or even seen) one of these ... so I'm just making wild guesses from the block diagram.
    Plug in headphones...I'm guessing you get the static, and the volume controls will have no effect on it....and the sub volume will have no effect.
    Working back from there.....try sending something into the "line-in" input...see if you get anything from the headphones. This input signal will need to be a "line level" signal.
    If you get nothing there....then you probably want to start looking at low voltage power supplies (5v 24v etc). My guess is the you are getting no low voltage.
    According to the block diagram...it looks to me like the "line in" goes almost directly to the headphone out....with no volume controls or EQ circuits in the path. If that's not working then you probably don't have power to the headphone amps.
    If by chance the "line in" to headphones sigal does work.... the next likely suspect (IMO) would be the EQ section.
     
  3. control voltage

    control voltage TDPRI Member

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    Thanks very much for this! You're right about the headphone output. The static is there, but the subwoofer volume has no effect, nor do the other volume and EQ controls. I haven't tried sending anything to the "line in", but I'll do that tomorrow, and see if there's anything from the headphone output (or otherwise).

    I appreciate your taking the time to think about this. If I can get this amp working, it will be useful, and if I can learn about fixing electronics, all the better!
     
  4. Peegoo

    Peegoo Poster Extraordinaire

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    Are all of the input channels producing the same result? If so, it's a common (shared) buss issue.

    It's not a blown speaker because there are multiple drivers in that cab.

    I'm guessing a coupling cap between the pre and power stages has puked its guts, or perhaps the power stage itself let out some of the magic smoke.

    Pop open the cab and carefully examine both sides of the PC board(s), looking for tell-tale skid marks from a failed component. Don't zap yourself on any capacitors; even small ones can bite ya.
     
  5. Jon Snell

    Jon Snell Tele-Holic

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    Firstly as it is a drum monitor, I would check which speaker displays the fault and investigate from there.
    I think these are class D amplifiers and either work or they don't so I would guess a damaged speaker is the issue.
     
  6. control voltage

    control voltage TDPRI Member

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    OK, I plugged in a line-level signal to the line-in input, and got the same static sound through headphones as when nothing is going to the line-in. Also, none of the volume or EQ controls (including subwoofer volume) changed the sound through headphones. I'll try to check the low-voltage power supplies.

    Yes, all the input channels produced the same result.

    I have poked around a little on the PCBs with a chopstick, with no obvious results, but I haven't taken things apart to the point that I could see everything. I'll try that, and look for marks (carefully!) It would be great if the problem were a single capacitor, or something like that.

    I'll check the speakers, too. As I understand it, I can connect the leads to the terminals of a 9v battery, and a pop or thump indicates that things are working, or I can check resistance with a VOM, and if it's infinite, or something way off from the expected 8 ohms (4 for the midrange speakers), then the speakers are damaged.

    Thanks glenlivet, Peegoo, and Jon for the input! It may take me some time to investigate these various components, but I will report back with my results.
     
    Peegoo likes this.
  7. glenlivet

    glenlivet Tele-Holic

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    Maybe start by tracking down an IC or two.. (look up the mfg. spec sheet by the IC {chip} number) and see if they are getting the correct DC voltage on the power pins.

    I'm guessing they are not.

    That should at least verify that it's a Low voltage DC power supply issue.
     
  8. control voltage

    control voltage TDPRI Member

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    Thank you for explaining that process further! That will save me a lot of time I would have spent looking up how to go about testing low voltage power supplies.

    Whether I get it going again, or not, at least I'll learn some things.
     
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