1987 Marshall Keyboard 20 amp..... experience

Discussion in 'The Squawk Box' started by 5F6-A, May 18, 2017.

  1. 5F6-A

    5F6-A Senior Member

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    [​IMG]

    Got this 80s beauty for a reasonable price... will I be able to use it for guitar? We'll see....
     
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  2. Guitar Rod

    Guitar Rod Senior Member

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    Cool! I was watching your original thread to see if it makes a good guitar amp or not. Now we get to find out. Before Johan Segeborn figured it out too! :D
     
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  3. 5F6-A

    5F6-A Senior Member

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    I had a blast with it last night. I have to say that I bought it mainly for its speaker (i.e. Celestion G10L-35) but I’ll explain more about this later. First impressions:

    It still has the original label from the Marshall factory with model, serial number, a list of who tested it, did the packaging, etc. Nice touch....

    The slightly oversized cabinet is fairly well made. It looks better than -for example- my Lead 12 combo which is a bit uglier (tall and narrow). The wood they used in the Milton Keynes factory feel rock-solid, probably decent quality plywood; it all seems 1987 original.

    All the jacks work fine and thankfully, none of the pots were noisy or crackly. It was a bit dusty but nothing to worry too much about. The only odd thing is that I have to keep a plug in the headphone socket for the amp to work. Strange…. To be fair, it doesn’t bother me too much and I didn’t pay that much for it so I’m not that bothered but I wonder what is causing this peculiar behaviour.

    Tone wise, as expected, there’s a impedance mismatch problem. I plugged the guitar directly into the amp and the sound was okay: very clean, somehow weak and dull. these characteristics are typical of impedance issues and somehow anticipated: the input of a dedicated keyboard amp is not designed for the high impedance output of the guitar. Anyway, I could almost get away with it by cracking the treble knob, lowering the mid knob and leaving the bass knob at 12 o’clock. What was apparent was what cool beasts those Celestions were! Even with the mismatch the Celestion coped great. My goodness, it was hard to believe that that amount of musical low end came from a single 10 incher!

    With pedals the tone came alive significantly but I’m going to try to plug into a preamp to really make this amp link correctly with the guitar. I have a Joyo ACTone that should work. I’ll try it soon and I'll keep you posted, guys!
     
    Last edited: May 18, 2017
  4. 5F6-A

    5F6-A Senior Member

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    Plugged in the ACTone preamp this morning for a quick test; all the issues that I had previously were gone. Hurray!!
    As soon as I engaged the pedal I was left with a great late 70s Marshall sounding amp. To be honest, I was expecting more of a VOX vibe (due to the nature of the preamp pedal) but the Marshall DNA was so prevalent that the tone was certainly more Marshallesque than Voxy. Not to worry, the amp sounds great. Also, the mid knob of the ACTone is set at 500Hz so I could knock it down a notch to compensate the lack of 500-700 Hz dip that most amp builders implement in guitar amps to avoid that hard and nasty midrange. Pseudo-Fender scooped tone? No problem, just tame the mid knob and lower the gain.

    Anyway, what impressed me the most was the quality of low end available. Those 10" Celestions are great at producing a healthy dose of robust low-end that complements the speakers' natural tendency to roll-off excessive highs (similar its bigger brother, the G12-65). The cabinet is very resonant and reinforces those low frequencies without being too boomy. Also, the Joyo EQ section is very effective in case you need it.

    One of the morals of this story is that I can see why the amp was not that successful as a keyboard amp. No tweeter and a dark-ish speaker probably makes this amp a little lacking in the sparkle department if used exclusively for keyboards. But for guitar, it's just the ticket provided you have a preamp to counteract the impedance mismatch problem. Any of the Tech21 character serie pedals (or clones) would serve you well although the Marshall character is never lost. I can imagine loads of these amps completely forgotten, gathering dust in many homes, garages, churches, community centres, etc. If you can find one at a decent price, you might want to do what I did.

    Bless you guys. Keep on rocking!
     
    Last edited: May 20, 2017
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  5. 5F6-A

    5F6-A Senior Member

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  6. Guitar Rod

    Guitar Rod Senior Member

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    Sounds like a good pedal platform. Good find!
     

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