Bright cap mod

Help!I'maRock!

Help!I'maRock!

Mediocringly Derivative
I've had this Fender Musicmaster Bass amp for a while now, and it sounds great. However, it's super bright and hates the Pickle Drive. My experience with other SF amps tells me there's probably a bright cap. But I don't know crap about amps, so I turn to you, Weiners.

Here is the schematic:

Fender%20Musicmaster%20Bass.jpg


1. Is there a bright cap?
2. If so, which one is it?
3. How can I clip it without electrocuting myself?

Thanks!
 
There really is no bright cap in this circuit but you can make some changes.

1) Replace the .0047 cap for a .01uF cap. Change the 470K to 1M and you should be good.

2)

upload_2016-10-24_9-59-59.png


3) As for not electrocuting yourself
  • Unplug unit from wall.
  • Use a bleed resistor, I use 10K and connect to a couple of alligator wires on each end. Connect one end to chassis ground, connect other end to + side of the 20uF cap. Use your right hand only.
upload_2016-10-24_10-4-28.png


  • Use DMM to verify voltage is now at 0
  • Proceed to mods.
 
If you can, build one of these "Light Bulb Limiters" prior to turning on.

It will protect the amp and you should something not work right.

Lightbulb_Limiter1.png


LightBulbLimiter.jpg
 
Modern Saint said:
There really is no bright cap in this circuit but you can make some changes.

1) Replace the .0047 cap for a .01uF cap. Change the 470K to 1M and you should be good.

2)

View attachment 30233

3) As for not electrocuting yourself
  • Unplug unit from wall.
  • Use a bleed resistor, I use 10K and connect to a couple of alligator wires on each end. Connect one end to chassis ground, connect other end to + side of the 20uF cap. Use your right hand only.
View attachment 30234

  • Use DMM to verify voltage is now at 0
  • Proceed to mods.
Click to expand...

So the answer is no, I can't do it by myself. Thanks!
 
I agree w/Saint on the mods. You might also, or instead, look at that .01uf coupling cap between v1a and the tone/vol control. that could increased to a .047uf or even a .1uf to increase the bass frequencies passed.

A more subtle change might be increasing the cathode bypass cap on v1a to a 25uf.

Something to consider though; adding bass frequencies at the front-end of a pre-amp can have some unintended consequences. It *may* be just what you want, but it can also result in woofiness and loss of definition.

My recommendation would be find someone who can mod your amp and let you try it before committing. They are simple mods to do and undo, especially on a point-to-point amp - if you know what you're doing.

The use of an audio transformer instead of a PI tube is pretty interesting.

Also, something to consider: has it had the filter caps replaced? If not, old/dried up filter caps can most definitely result in a thin sounding amp.
 
Since you’re already on the path to mods, why not just have an effects loop installed so you can put an EQ pedal in the loop?
 
jp_nyc said:
Since you’re already on the path to mods, why not just have an effects loop installed so you can put an EQ pedal in the loop?
Click to expand...
Mark Wein said:
And then he can hot glue a Boss Micro Cube amp in there too! Or better yet, a Line 6 Spider.
Click to expand...

Yeah, an effects loop isn't going to happen. I wouldn't use it anyway.

The only need this amp has is to take it down from Bright to Normal. That starts with the Hasserl mods, and maybe a new speaker (the old one sounds good and is sufficiently loud enough).
 
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