Guitar Amp Modification

[Ty34er]

Off topic from a tech page (sort of) but I didn't want to make a membership on another random forum yet.

 

I bought a guitar amplifier from a flea market for cheap. I plugged it in to test it and it "worked". It technically does make a sound but it's famously bad.

 

Apparently I bought a First Act MA104 Guitar Amplifier, which, as mentioned is famously bad. I already have it taken apart (already sucks and has no warranty, might as well get experience) so does anyone have any suggestions? I would post a picture of a schematic or something, but First Act really hates giving away that information.

 

(Notes: some things I was able to research and find were to replace the speaker with a lower ohm and wattage one and to replace its power brick because 14V DC is apparently too much for it and 9V is usually better.)

[schwarzerrogen]

First Act is the cheapest of the cheap. Add into the fact that it's a surface-mounted PCB solution, and that leaves you with very little actual modification room to get it to sound better, unless you have a very powerful knowledge of both circuits and guitar amp design. As well even a speaker modification may be out of the question as no one quite knows what impediance or power rating the amp can handle. I would guess it's 8', 8ohm, 15 watt, but we don't know.

 

One thing to keep in mind, especially with guitar amps, is that if the output stage doesn't get the correct impedance on the speaker you'll kill the amp outright. If this was a tube amp, like an SLO-100, an older pre 2006 Mesa (when their internals took a massive design change), or a Marshall, I could have been of actual help... but First Act is very unwilling to release their 'design' because in most likelihood it's a stolen design.

[Ty34er]

It probably is a stolen design but what are you going to do. I might just buy a new cheap amp since I'm more a casual player than anything else. Thank you.

[straight_stewie]

One of the things they are useful for is to plug your phone into and use as a loudspeaker. Cheap amps actually work quite a bit better than you'd imagine for that purpose, but not as good as similarly sized equipment meant for that purpose.

[Ty34er]

At this point, I broke the volume knob and when trying to find a new one online (I wish Radioshack was still around), I couldn't find a smaller body 100k Ohm pot (original was linear though log would be nice). I might jerry-rig something just so I have an extra amp just in case.

[mr moose]

Ebay for the knob.  As for the rest of the amp,  if you can find an old electric organ, salvage the speaker out of one of those and replace the shit sounding one.    Set all the tone controls to zero and use a decent preamp/pedal board.    That should hold out at least until you can afford something half decent.

[kilgore_T]

just remember the grand heritage of f*cking your shit up and putting it back together all ugly like

 

 

[mr moose]

17 minutes ago, kilgore_T said:

just remember the grand heritage of f*cking your shit up and putting it back together all ugly like

 

 

Not too forget that Brian May made his own guitar too.

[Tcrumpen]

On 12/10/2017 at 9:12 AM, Ty34er said:

Off topic from a tech page (sort of) but I didn't want to make a membership on another random forum yet.

 

I bought a guitar amplifier from a flea market for cheap. I plugged it in to test it and it "worked". It technically does make a sound but it's famously bad.

 

Apparently I bought a First Act MA104 Guitar Amplifier, which, as mentioned is famously bad. I already have it taken apart (already sucks and has no warranty, might as well get experience) so does anyone have any suggestions? I would post a picture of a schematic or something, but First Act really hates giving away that information.

 

(Notes: some things I was able to research and find were to replace the speaker with a lower ohm and wattage one and to replace its power brick because 14V DC is apparently too much for it and 9V is usually better.)

Is it valve or solid state?, also the speaker might still be of use

[Mutoh]

On 10/12/2017 at 4:23 AM, schwarzerrogen said:

First Act is the cheapest of the cheap. Add into the fact that it's a surface-mounted PCB solution, and that leaves you with very little actual modification room to get it to sound better, unless you have a very powerful knowledge of both circuits and guitar amp design. As well even a speaker modification may be out of the question as no one quite knows what impediance or power rating the amp can handle. I would guess it's 8', 8ohm, 15 watt, but we don't know.

 

One thing to keep in mind, especially with guitar amps, is that if the output stage doesn't get the correct impedance on the speaker you'll kill the amp outright. If this was a tube amp, like an SLO-100, an older pre 2006 Mesa (when their internals took a massive design change), or a Marshall, I could have been of actual help... but First Act is very unwilling to release their 'design' because in most likelihood it's a stolen design.

Impedence mismatching is more an issue with tube amps. SS amps generally can take more abuse with mismatched impedences.

 

5 hours ago, Tcrumpen said:

Is it valve or solid state?, also the speaker might still be of use

Its a cheapo SS First Act practice amp with a generic 4 inch speaker that wont ever sound good driving a guitar signal. You can buy these on ebay for less than 20 bucks so I doubt anything is really useful.

 

Personally OP, if you want to play around with it for fun, go for it but I wouldnt throw money into it. Upgrading a speaker on that thing wouldnt be the best thing. If you want to try to fix it up for giggles, go for it but I would rather spend my money towards a better amp as there really isnt much you can do with your First Act.

[Tcrumpen]

1 hour ago, valdyrgramr said:

I think my fave guitar/amp mod would be the hotrodding of a jcm 800. 

If you have a spare £1500 yeah ....

[HarmInTrying]

Check out Uncle Doug on Youtube. He reworks vintage tube amps, scratch builds amps, and he's a highschool science teacher of some sort, so his explanations of electro-magnitism and circuitry are pretty tangible for the layman. 

 

https://www.youtube.com/user/Stratosaurus1

 

I'd say just slap a 10" Celestron blue in there and call it a day.

Don't even tighten the screws; it'll be like natural distortion!

[Mutoh]

1 hour ago, HarmInTrying said:

Check out Uncle Doug on Youtube. He reworks vintage tube amps, scratch builds amps, and he's a highschool science teacher of some sort, so his explanations of electro-magnitism and circuitry are pretty tangible for the layman. 

 

https://www.youtube.com/user/Stratosaurus1

 

I'd say just slap a 10" Celestron blue in there and call it a day.

Don't even tighten the screws; it'll be like natural distortion!

The blue wont fit in there and will cost like 15 times the amps value haha!

 

1 hour ago, valdyrgramr said:

Or, you can just buy a Johnson JM-150 which perfectly emulates it.  I'm not usually a fan of emulation, but this thing is great.  It also has the history as the first modeling amp.  The only difference is that the actual tube amp has slightly brighter tone.  But, if you have a good enough guitar you won't notice it too much.

As a person who has owned a few vertical input JCM 800s I dont really find that too true. YMMV though. Id rather an Atomic Amplifier personally. That to me is closer in tone and response and you have the ability to load your own IRs, has midi, has DI, can choose what outputs do what etc... really powerful tool that can be used standalone or with a poweramp and cabinet if you want a more traditional sound.

 

 

[bowrilla]

There's nothing worth doing with or salvaging form that amp. Seriously … nothing.

[Mutoh]

2 hours ago, valdyrgramr said:

I didn't say it was dead on lol.  But, it's better emulation and closer than most to the JCM 800.  It actually has 2 built-in JCM 800 settings in it from factory.  Standard and hot-rodded.  Have you actually played with both a JCM 800 that was hot-rodded and the JM-150?

You can read up more on the amp here.  The biggest issue with the amp is that the pre-sets outside of the amp emulation are crap until you mod them, but the amp modeling is very good.  Presets being like the SRV settings and the Hendrix one.

https://reverb.com/item/263223-johnson-millenium-jm-150-2x12-stereo-combo-guitar-amplifier-with-amp-modelers-and-effects
 

Ive played a Friedman modded 800 and a few Splawns so Im familiar with the "Hot Rod" Marshall sound and feel. Im also familiar with Johnson amps as they are quite frequently sold in our used markets. Scott Grove/GroovyDJS also infamously liked to peddle these amps and say they were the best amp ever much to the chagrin of a lot of people haha.

 

Stock presets are usually bad on a lot of modellers, sure. I dont disagree with that!