weak constitution, bought a cheap SS amp.

[drgonzonm]

Hi My name is Dr Gonzo NM,
I am  bass-oholic and an amp-oholic. 

I fell off the wagon (stage), and bought a used FirstAct MA104 for $3.99 sin power supply .  I thought it would match up well to my red Mini-Squier. 

I am so -oholic, bought it knowing It would not play any of my basses. 

Does any know the 12 steps to begin the recovery process for amp-olicism?   

I headed the nearest 2nd Handshop to find a power supply.  Found one

Apparently, this $25 amp (new price,without wall-wart) was being bought and then modified.  Caps and resistors being changed, But the big problem is the less than adequate speaker needs to replaced.

Looking for a schematic, there suppose to be several out there.  several variants.  If I find one, I'll post it. I might evern post some gut shots. 
(amp-olicism is a terrible affliction ).

[drgonzonm]

I found one schematic, It appears incomplete, as I can not find were Q1 is attached. 

My thoughts, heavily shared with most of the world.  The amp is a toy, it is sold as a toy.

but remember the difference between men and boys is the price of their toys. 

[shooter]

this $25 amp

that's not an amp, it's a cheap pedal

I can't make Q1 work on either IC without an R or 2 on the base, otherwise I think I'd use it in the front-end

[PRR]

> found one schematic

That plan is clearly flawed. The "power" chip is not shown. There "must" be a ground at the C14 R6 C16 C20 R13 junction.

Assuming that- first stage gain is up-to 4,000(!!), tone loss small, 2nd stage gain about 5, and power stage gain is 50? Gain of a guitar amp needn't be a lot over 1,000, here we seem to have 1,000,000.

Or, figuring the first gain pot will be set so 20mV from guitar just-clips the diodes, 1st stage gain is about 20. Set 2nd gain pot to half. Gain is 2,500. So there may be a "playable" condition with 1st pot way-down (under "1)", 2nd pot near "3" or "2".

Hiss level at useful gain will be higher than necessary, but probably not obnoxious compared to the tiny racket this will make with knobs turned up.

You know the drill. Replace the crap speaker. A *good* car speaker will be better. Ideally a guitar-market Six, Eight, or why not Two Twelve? Will need new cabinet. Now you can annoy further than your property line, and with solid bottom. But still sounds like crap. So replace the chippery with honest tubes. Maybe one 12AX7 and one 6V6.

[PRR]

It must be a toy. Sold at Toys"R"Us:

http://www.toysrus.com/buy/guitar-amplifiers/first-act-guitar-practice-amplifier-black-2419339

$10 cable for it (great picture!):

http://www.toysrus.com/product/index.jsp?productId=2383268

There is also a portable electric guitar. I am so tired of permanently built-in guitars.

http://www.toysrus.com/product/index.jsp?productId=34442936
(Ah-- they mean the amplifier is built IN to it. You are not tied-down by a 4-pound amplifier.)

[drgonzonm]

Apparently the toy amp is being "hotrodded",
Recommendations to improve Gain control include replacing R2 with 1k ohm (is 270) and changing C4 from 10 to 1 uf.

Other suggestions also include removing D2 and D3.  Others replace d2 and d3 with LEDs, (never provided the color). 

The picture shown on Toys R us website shows an amp that will not accept 5" speakers.  The chassis as installed claims too much baffle real estate.

My copy has the chassis installed 90 degrees, so 5 inch and possibly 6 inch speakers will fit. 

The power chip on this amp is a UTC 2003 op-amp, other versions apparently contain a 2030 chip. 

A few users replace the 14v dc wall wart with 24v dc wall warts for a little more output. 

If the amp is a pedal, it won't take too many stomps from my size 12's    I believe it had pedals in its ancestry. 

Need to find my tripod, so I can take the gutshots.  (the pcb trace will be easy. but the component side a lot tougher because pcb is mounted perpendicular to metal chassis, held in place by the pots, (got to save money, by minimizing screws.   

I will also post side by sides with the mini squier and acoustic bass, adds more credence to the toy aspect of the amp.
I apologize up front for taking advantage of the 12 step program.  It works, but a parody follows 
step 1, we are powerless;  yep I bought an amp without a power supply.
step 2, greater power; I used an 18v adapter not the 14v suggested. 
step 3, turning over our will;  Hey guys, I asked for input
step 4, Make a search; I made a search for a schematic and found an incomplete one. 
step 5, Admit our faults; I laid it out, and told you, that I bought a cheap amp,
step 6, defects in character; As pointed out, the amp has many defects.
step 7, humbly ask to correct defects;  This is tough one, I probably won't change R2 and C4. 
step 8, make amends;  I guess that means removing this thread
step 9, make direct amends; I really should remove this thread
step 10, take an inventory;  ok I have several other amps that need TLC before I mess with this one
step 11, seek out the higher power.  I spotted a lower voltage wall-wart with a higher milli watt output
step 12, Spiritual awakening;  No!!, I won't take it to church. 

appreciate your time and your patience on my musings. 

[shooter]

I won't take it to church. 

that's good, cuz God invented the analog world and man corrupted it with SS