What is that static sound when playing notes under high gain? (Randall solid state)

[Dave Locher]

Dear electronics experts and amp gurus,

When I play single notes with high gain (green channel, gain 8-10, volume 2-5) on my 1978 Randall RG100ES into a 2x12 cabinet I am getting a sort of static noise that is loud enough to be noticeable. It might do it with chords as well, but I can't hear it.
This noise is louder when I boost the signal going into the amp with an eq pedal or a clean boost.

Today I tried two different guitars, three different cables, with and without pedals, and plugging the cabinet into each of the two speaker out Jacks. Still there.

It does not make this noise when running clean, no matter how loud I play. And it is definitely louder and more noticeable when boosted. That is the part that confuses me most. It seems to do it more with higher notes, but it could be that the lower notes just cover it up more?

Any idea what could be causing this? It is driving me nuts! I've owned this amp for 25 years and I don't think it did this before, or maybe I just didn't notice it.

 

[Gearjoneser]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Solid state amps get their gain from transistors instead of tubes, and the technology is much better today than it was in 1978. That's the simple answer, although there's no way for us to know whether it's that or if your amp is just old and the components are nearing the end.

The last time I played one of those amps was the mid 80's and I didn't particularly care for their buzzy gain then either. Sell it, and upgrade while it still works.

 

[Dave Locher]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Thank you, but I really like this amp. IF it is dying it has to be just one inexpensive component.

 

[misterwhizzy]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Thank you, but I really like this amp. IF it is dying it has to be just one inexpensive component.

Good luck finding it.

 

[zzmoore]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

It could be a multitude of things.
That amp is so old and has "no" value......pull the chassis, check all the normal in and outputs...throw a meter on some of the main diodes and resistors, see if anything reads funny, and just do a visual for any parts that look like they have gotten Hot/Warm over the years and might need replacing.....especially in your Lead/Gain channel if i read your post correctly.
If you are not too experienced with Electronics, this would be a Great Amp to learn with.
good luck

 

[GoldenVulture]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Solid State amps have a power supply section and it may not be running as high voltages as a valve amp but it will have large capacitors\filter caps there. You say you've had the amp 25 years. Those caps could well be dying . Not working well enough to deliver enough power when you make it work hard, hence static/distortion.
If your handy with a multimeter hook it to the main power supply cap/s and observe its voltage over a period of about 25 mins. It should appear steady. If it changes much over the next 25 mins or so or If it wavers or changes radically , they're probably shot [ caps ].

 

[zzmoore]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Yeah, but he is not getting 120Hz hum.......through he could still have tired PS Caps.
He is getting fizz, for the first time, on the just lead channel. :dunno:

 

[Dave Locher]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Thank you GoldenVulture, that is useful advice.
One question, though: do you mean check the cap voltage while the amp is just on, or while actually playing?

 

[Dave Locher]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Yeah, but he is not getting 120Hz hum.......through he could still have tired PS Caps.
He is getting fizz, for the first time, on the just lead channel. :dunno:

It's a sort of a crackling sound that is kind of under/behind the note. It might be there all the time but I only hear it when sustaining a single note on the G string (which I do on a couple songs).

 

[GoldenVulture]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Thank you GoldenVulture, that is useful advice.
One question, though: do you mean check the cap voltage while the amp is just on, or while actually playing?

Either/both: Playing and watching what the multimeter reads : Just on and observe over time.

 

[GoldenVulture]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Yeah, but he is not getting 120Hz hum.......through he could still have tired PS Caps.
He is getting fizz, for the first time, on the just lead channel. :dunno:

I don't think that's as noticeable as the voltages are not as high as valve amps.
His description reminded me of what transistors do when they're starved of voltage; Static like distortion .
Coming at it from a trouble shooting angle; Always start at the power supply.
:friday:

 

[Dave Locher]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Okay, so these are really naive questions because I've never worked inside an amplifier before but I am familiar with wiring in general (automotive, guitar, and house) so I will be careful not to kill myself.
I've attached images of the wiring schematic, a shot of a chassis identical to mine, and a gut shot of the same model but 10 years newer.

If I understand you correctly, GoldenVulture, we are talking about the two large black capacitors next to the transformer right? And I'll have to turn the chassis upside down to get to the leads. (I don't know if this is common, but this chassis is open on the bottom; the cabinet has a thin sheet of aluminum that it sits on when installed. The only way to access any of the components is through the bottom of the chassis.)

 

[Kamanda~SD]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Do you have any clips? We are making alot of assumptions over something we haven't even heard

 

[GoldenVulture]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

Okay, so these are really naive questions because I've never worked inside an amplifier before but I am familiar with wiring in general (automotive, guitar, and house) so I will be careful not to kill myself.
I've attached images of the wiring schematic, a shot of a chassis identical to mine, and a gut shot of the same model but 10 years newer.

If I understand you correctly, GoldenVulture, we are talking about the two large black capacitors next to the transformer right? And I'll have to turn the chassis upside down to get to the leads. (I don't know if this is common, but this chassis is open on the bottom; the cabinet has a thin sheet of aluminum that it sits on when installed. The only way to access any of the components is through the bottom of the chassis.)

I can't read that circuit, it's too compressed.[ It's a Randall, Model ? ]
Most likely those caps, yes. If the top cover is buckling or bulging or the outer wrap is shrinking , they're most likely heat damaged.

PS: can't see a gut shot.

 

[zzmoore]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

I don't think that's as noticeable as the voltages are not as high as valve amps.
His description reminded me of what transistors do when they're starved of voltage; Static like distortion .
Coming at it from a trouble shooting angle; Always start at the power supply.
:friday:

That makes sense.....something turning On an Off, or not all the way On and Off as the voltage degrades enough to get below their supply needs.
Good Call

 

[Dave Locher]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

I will physically inspect the caps tonight when I get home from work if I have time (small kids = no time!), since that is quick and easy. Next step will be to check them out with my multimeter.

If I don't find problems either way with those I will try to record a clip sometime in the next few days. I think even my iPhone will pick up the noise I'm referring to.

Thank you all so far!

 

[GoldenVulture]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

I had a quick look at the circuit.[ found a copy ] C38 and 39 . C 38 should read 40V. and C39 -40V.

 

[moshpit817]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

It's a sort of a crackling sound that is kind of under/behind the note. It might be there all the time but I only hear it when sustaining a single note on the G string (which I do on a couple songs).

If you have little to no experience digging around in amplifiers BE CAREFUL!! YOU CAN GET COOKED !!

 

[Dave Locher]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

I had a quick look at the circuit.[ found a copy ] C38 and 39 . C 38 should read 40V. and C39 -40V.

Thank you! You have been more than helpful and I appreciate it.

Don't worry, mosh pit, I will be careful. I don't want to charbroil myself or the amp.

 

[Dave Locher]

Re: What is that static sound when playing notes under high gain? (Randall solid stat

I believe I might have found the problem: scratchy pots! I pulled off the back panel and the capacitors look and feel as new, no apparent bulges or shrinkage. But I noticed that the master volume on the lead channel is noisy toward the low end (where I play at home). I rotated every pot back and forth several times and that seemed to dramatically reduce the crackling noise. I suspect one of the pots was sitting right at a crackey spot?
This makes sense because I used the heck out of the amp from the time I bought it until around 2001, but then it sat unused for a couple years before I started playing again.
I'm going to get some cleaner for the pots and see if that totally eliminates it. Keeping my fingers crossed that it is that simple!