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SS amp hum/crackling troubleshooting question.

gfen

gfen

Aug 21, 2014
1,381
1,975
lehigh valley
Disclosures
stayed at a holiday inn, once...
#1
I need some assistance in maybe diagnosing a problem with a solid state amp.

I received a SWR Workingman 2004 as a bonus with a cab I picked up from CL today. It was advertised as "good working condition," and the seller seemed friendly and honest, told me to let him know if there was any problems or I wasn't satisfied, so I'm planning to follow up with him tomorrow. The price I paid was really more than enough for the cab alone, the head was mostly free money and I planned to flip it anyways, but I'm a little disappointed if it's busted.

It's got a low volume hum, and when you play anything through it there's varying levels of distortion. An open G string produces much less of the crackling than an open E.

The hum/crackling is ever present in all variations of the below:

These are the steps I have taken to try and isolate issues:
Tried both inputs, the Passive/Active and the Passive.
Tried the Effects Return input.

Tried both Speaker 1 and Speaker 2 output.
Tried Effects Send output.
Tried the Stereo Headphones output, with the Speaker On switch both in on and off positions.
Looped the Effects Send/Return with a patch cord.

Tried different speaker cables.
Tried the various pots in all different points (maxed, minimized, middle "off" detent).

The clipping light does not come on in during any of these problems.
Both fuses appear good.
All the pots turn smoothly with no noise with the exception of gain and the effects blend, which have a slight amount of noise when turned.


I haven't had it open, yet, to look inside. I'm no technician, and if it's not going to be visibly easy to spot, I'm just wasting my time but am willing to check it anyways.

Any advise, or should I just give up?

postscript: the fender 115 cab works like a champ and was worth the total price paid, $80, so there's that upside. :)
 
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#3
B-string said:
Is the crackling present in the headphones? You haven't said if you tried a different cab or the same cab with all tests (could be the cab that is damaged).
Click to expand...

You're right, I didn't. I just edited my OP to include that.

Yes, the hum is ALWAYS there, regardless of input or output. I have only tried one cab thus far, plus the phones.
 
#5
Forgot to note, the cab is good. I tried it with an alternate head and it's perfect. I have not tried an alternate cab (although I could tomorrow, I don't think that's the problem).

The hum is always present, even with only the cab or phones connected and no inputs.
The crackling noise is ever present when sound is played through.
The crackling noise, as noted, gets more warbly and "electronic" sounding as notes get deeper. Not really sure how to explain that better.

All volumes we're dealing with here are low, btw, so it's not me running the amp at the limit. I didn't get home til late. We're talking below 11 o'clock on master and gain.
 
#6
Okay, good info. It could be as simple as power supply caps being bad or some bad solder joints. It is of course, hard to say from here. Either flip it as a "repair or parts" head if you are happy with the deal and cab or contact the seller and see if they want to return some cash for the head. Needs more experienced help on your end with full test equipment. You have done a good job checking so far.
 
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#7
Any idea of what the approximate cost of having a real shop run a diagnosis is? IE, $20 or $50 or more? I've never dealt with any repairs, yet.

Should I even bother opening it up and eyeballing it, or am I basically going to be looking at a circuit board, stroking my chin, and making inspired, "hmm..." noises?

Could a guy who was handy with small electronics and a multi meter help isolate this if he has no amp technician experience? Or are we moving into oscilloscopes and schematics level diagnostics to actually figure it out?

And thank you for your assistance.
 
#8
gfen said:
Any idea of what the approximate cost of having a real shop run a diagnosis is? IE, $20 or $50 or more? I've never dealt with any repairs, yet.

1) Should I even bother opening it up and eyeballing it, or am I basically going to be looking at a circuit board, stroking my chin, and making inspired, "hmm..." noises?

2) Could a guy who was handy with small electronics and a multi meter help isolate this if he has no amp technician experience? Or are we moving into oscilloscopes and schematics level diagnostics to actually figure it out?

And thank you for your assistance.
Click to expand...

1) Most likely, although you could check for interconnecting cables that could be re-seated (don't break any connectors). Burnt parts maybe?

2) Just a multimeter will be of little use.

Bench fees are all over the map, $40 to $100. Ask some shops for the basic bench diagnostic fee, be sure to tell them the unit model so they will know if the service info is on hand.
 
#9
Update:
Finally got around to opening this up, looks like there's a loose cap. Wobbles on its base. Is this probably the sole issue? Or, likely going to be deeper than that?

As stated, I'm not a technician. Is this user fixable? If it is, is it a matter of jsut replacing it or will I still have to pay a diag fee?

Also willing to estimate what sort of prices I'd pay to fix it, but at that point it's me being lazy and not calling a local shop. :)
 
#11
Believe it or not, I do understand exactly what you're talking about. With careful work, this could be a thing I could learn to do... but.. I also decided about 10 minutes after I posted the above that I didn't care. Someone made an offer on CL, I've explained to him the exact problem and he sounds like he knows what he's getting into/experienced in microelectronics.

I'd rather have the money in pocket than spend on an amp repair that I don't really care about other than it's a toy I could further own. I've got enough toys.

You've been helpful, I've been needly. I'm also thankful for the help, even when I wasted it. :)
 
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#12
gfen said:
Believe it or not, I do understand exactly what you're talking about. With careful work, this could be a thing I could learn to do... but.. I also decided about 10 minutes after I posted the above that I didn't care. Someone made an offer on CL, I've explained to him the exact problem and he sounds like he knows what he's getting into/experienced in microelectronics.

I'd rather have the money in pocket than spend on an amp repair that I don't really care about other than it's a toy I could further own. I've got enough toys.

You've been helpful, I've been needly. I'm also thankful for the help, even when I wasted it. :)
Click to expand...

The process is never wasted if learning anything is the outcome. Includes knowing when to let go in this case, congrats on the deal. :)
 

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