Studio .22 cap job: can I do it myself?

[Whoopysnorp]

I suspect that my Studio .22 may benefit from having the caps redone, as it is sounding a little duller than I believe it should be (even with new tubes). I've never had a cap job done on any of my amps but I am curious about whether it's something I could handle. I wouldn't say I have a strong knowledge of circuits, but I understand the basics, and I can solder just fine. I'm well aware that caps can potentially hold lethal voltages inside them, and I actually followed some instructions to build a cap discharging device out of a voltmeter probe and a resistor and I think something else a while ago. Is there anything to it other than getting the proper cap values, putting them in with the proper polarity, making sure you don't overheat the board with the soldering gun, and making sure you don't kill yourself?

 

[camsna]

That's pretty much it! Just remember that caps are polar so you've gotta put them in the right way, like a battery. If you don't - it could be an unhappy time.

And - if you could get the caps from Mesa so that they say 'Mesa' on them - that would be a good choice, too.

 

[MJ Slaughter]

Whoopysnorp,

I just completed a cap job on my DC-10 and found it to be well worth the effort. There was a little hum to begin with which is why I went down that road but once completed the feel and tone of the amp was much improved. Whether you do it yourself or not is another matter but if you’re careful it’s not a big deal. My biggest issue was getting the old caps off the PCB without destroying traces. There are some traces under some of the caps so don't go digging in with a razor blade. After gathering techniques from different people I took the advice of a local tech. Clip the leads then slice the old plastic covering and pull the old cap out. Then it's much easier to carefully cut the old silicone and left over covering off the PCB.

Monsta-tone warned me about not burning/melting wires with my soldering iron but I did it anyway. Repaired it and moved on.

 

[stomper]

Your amp would definitely benefit from a cap job. I've owned my studio .22 for twenty years and it is on its third set of caps. I use it almost every day, and gig with it on occasion.

Unfortunately, the studio.22 is perhaps the most difficult amp to work on. The circuit board was installed upside down at the factory. When you look in the amp, you are seeing the bottom of the board. The first time I did a cap job on the amp, it took 45 minutes to make a diagram of wires and get the board out enough to reach the parts. The whole job took several hours.

You have a very cool amp. Try and find someone to do the job for you if you are not completely confident in your skills. I would highly recommend the cap job either way.

 

[Whoopysnorp]

Yeah, I noticed that about the board. I'm mentally prepared to do what's necessary to get the board out of there.

So, only the electrolytic caps need replacing, right? Are there any metal film caps in there? I assume they don't need touching...,

 

[stomper]

Just change the electrolytic caps. Look for any resistors that may be burned or melted. Change them if necessary. Randall Smith changed a resistor in the footswitch supply from 1watt to 2watts as production went on. I had to upgrade mine after that resistor burned up causing the circuit to fail. Take your time and good luck!

 

[Whoopysnorp]

One more mystery here: the schematic specifies a 320 uf cap in the negative supplies, but the cap actually on the board in that position is a 220 uf. Should I replace it with the higher value?

 

[stomper]

220uf is the correct value. The schematic says 220 it is just blurry.

If you can obtain the schematic for the 22+ it is easier to read.

 

[Whoopysnorp]

I have the 22+ schematic as well but it also looked like it said 320. I don't have the amp at the moment to check that cap but since it seems to work fine as is, I'll stick with 220.

 

[Whoopysnorp]

I am DEFINITELY glad I did this job! The overall tone is much much better now, and I can actually get a clean sound that I like. It was a good experience educationally as well. Fortunately, I didn't need to take any additional steps to discharge the filter caps, as they only measured about two volts when I began work. I replaced them with Sprague Atoms. Now I'm thinking I might want to do this on my other amps as well!

 

[myqqy]

Oh God, something else for me to worry about when it comes to my amps and tone... so... since I'm just starting to read about circuit boards and amp parts, can someone provide some tips on knowing if you amp might benefit from a cap change? :shock:

 

[Whoopysnorp]

From what I understand, electrolytic caps are in most cases basically at the end of their service life after about 20 years. If your caps are that old, you may want to consider it. In my case, my amp kind of had "there's a blanket over it" syndrome, and it was breaking up way too early for my taste. That particular attribute, though, could also have been caused by a bad LDR causing the channels to interact (I replaced those too).

 

[myqqy]

Thanks for the info! But, what is "LDR"?

 

[camsna]

Light Dependent Resistor

 

[Whoopysnorp]

Right...it's a sealed package containing an LED and an optical sensor. The sensor reads the LED and controls signal flow based on whether the LED is on or off. It's how the channel switching works in these amps.