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 Post subject: Love my F30 but...
PostPosted: Mon Sep 26, 2011 12:42 pm 
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Bottle Rocket

Joined: Sat Sep 24, 2011 9:27 pm
Posts: 20
First, this is my maiden voyage into any forum of any kind; my apologies up front if I break any rules. I REALLY enjoy my F30 combo (stock except for new JJ tubes). The issue, however, is the white/hiss noise at higher gain/master volume levels. I'm predominantly a stay at home player and this amp excels at bedroom levels but when I have the occasional opportunity to turn it up, I can't get past the above mentioned noise. It's especially apparent on the clean channel, (which is one of the best I've heard). The gain channel noise is there but not really that bad. Would running a noise reduction pedal thru the FX loop help quiet down the noise? (I run the mix at 50% for time based effects and EQ). I really want to keep the amp but I'm having a really hard time getting past the clean channel noise. Maybe proper counseling would help. Also, I'm a tube amp simpleton, so if someone out there has some advice (mods?) I'll do my best to understand. Thanks!


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 Post subject: Re: Love my F30 but...
PostPosted: Mon Sep 26, 2011 4:30 pm 
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Welcome!

First, it will help if you can explain what exactly is in the signal chain, including what guitar/pickups, all the way to the speaker. What's in the loop? What are the knobs all set at?

High noise is not uncommon in the gain channel, though I have had 2 F50s and not had any issues with that. On the other hand, it's not normal for the clean channel to have that. UNLESS you have the gain and treble cranked.

You may well have a microphonic or noisy tube, or you may have a bad switch/relay/opto in the amp.

The gain channel and clean channel share ALL tubes, and almost all circuitry. There is a bit of a difference in the tone circuits, and there is one more gain stage that gets switched in for the gain channel. SO if the clean channel is noisy, I would expect the gain channel to be noisy. One exception is if it is a gain stage that comes late in the chain (after FX return, or phase inverter). The high front-end gain of the gain channel may overcome noise at the back-end.

Typical troubleshooting tips apply:
tap the tubes one at a time with a pencil eraser to see if one is especially microphonic.
Swap the preamp tubes around. If the symptom changes, you can narrow down a bad tube
New (or even old) power tubes. The fact that you have new tubes does not rule out a bad tube. In fact, new tubes these days seem to be horrible for reliability and quality. JJ is getting a reputation for poor quality as well.

In my opinion, you absolutely should not need noise reduction on the clean channel. I would assume something is wrong. May be your guitar, cables, stomp boxes, or may be something in your amp. Start by removing as much as you can (guitar straight into amp, nothing in loop).

Good luck

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 Post subject: Re: Love my F30 but...
PostPosted: Mon Sep 26, 2011 5:19 pm 
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Mark I

Joined: Fri May 05, 2006 12:04 pm
Posts: 35
I had a similar problem in my 22+. I was told to swap preamp tubes one at a time - sho' 'nuff, one of them was bad. That amp also ran JJs for power, BTW.

My F30 (also running JJs) is surprisingly quiet, so I don't think it's the amp itself, though high-gain usually does translate into high noise that would be annoying in a small space.


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 Post subject: Re: Love my F30 but...
PostPosted: Tue Oct 04, 2011 5:33 pm 
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Bottle Rocket

Joined: Sat Sep 24, 2011 9:27 pm
Posts: 20
Thanks for the advice, fellas. It is appreciated. As far as I can tell, short of removing the guts (which I'm not qualified to do), I've done the guitar/cord/FX chain/swap tubes a number of times/ trouble shooting. It's got to be a circuit issue because it's really hissy with nothing plugged in. Man, I really wish I my ears could get over it, but that's not going to happen. Thanks again for the advice.


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 Post subject: Re: Love my F30 but...
PostPosted: Wed Oct 05, 2011 4:32 pm 
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It's possible that there is a bad (or no) solder joint on a ground connection. That seems to be common with Mesa. I have a Studio Pre that had a missed solder joint on the FX send jack. The ground wire was run through the eye in the tab, so it made contact intermittently. A dab of solder and all good.

The PC board is wave soldered, so it should be fine. But you could easily check the wires running to all the switches and jacks to see if there's a healthy solder joint. Pulling the chassis out of the shell does not require a PhD. Just be careful not to touch anything. Letting it sit for a couple days to discharge first is also a good idea.

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 Post subject: Re: Love my F30 but...
PostPosted: Wed Oct 05, 2011 6:58 pm 
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Bottle Rocket

Joined: Sat Sep 24, 2011 9:27 pm
Posts: 20
Yet again, HOPE! Thanks very much. I'll pull the board and let it sit so as not to zap myself. I'll let you know. I REALLY want to keep this amp.
Curious, where is the stored energy that could harm you?


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 Post subject: Re: Love my F30 but...
PostPosted: Wed Oct 05, 2011 7:23 pm 
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Dual Recto

Joined: Mon Jul 16, 2007 1:01 am
Posts: 2828
Location: SoCal
If you don't know what you're doing, you can kill your self, even if the amp is "off" and unplugged from the wall.
Seriously, there's hundreds of deadly volts stored in the amp, even with the amp "off".


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 Post subject: Re: Love my F30 but...
PostPosted: Wed Oct 05, 2011 8:22 pm 
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Bottle Rocket

Joined: Sat Sep 24, 2011 9:27 pm
Posts: 20
Thanks for the warning! When can I expect it to be safe? I have removed the chassis but was very careful not to touch anything.


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 Post subject: Re: Love my F30 but...
PostPosted: Wed Oct 05, 2011 8:23 pm 
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Bottle Rocket

Joined: Sat Sep 24, 2011 9:27 pm
Posts: 20
....or put it back in and forget the whole thing?


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 Post subject: Re: Love my F30 but...
PostPosted: Wed Oct 05, 2011 8:40 pm 
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The big power supply capacitors store almost 500V. They are very dangerous. And, you don't know where that voltage goes on the PC Board. However, they also bleed off slowly over hours or days, so they should be OK after letting your amp sit unplugged for a couple days. BUT always assume they are charged, and don't touch anything.

You should also use the one hand rule - one hand touches the amp, one hand stays away. This keeps your heart out of the current path if the worst happens. Best NOT to touch anything inside the chassis.

As long as you have the chassis out, just inspect all the wires running to pots, switches, etc. The high volts will not be on the wires, just on the PC board, especially near the tubes. Try to look but don't touch.

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 Post subject: Re: Love my F30 but...
PostPosted: Wed Oct 05, 2011 8:55 pm 
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Bottle Rocket

Joined: Sat Sep 24, 2011 9:27 pm
Posts: 20
I did inspect the guts without touching anything. Besides some strange, randomly placed glue goop, everything looks ok. I'm not quite ready to go see Jesus resulting from messing with a silly amp so it's going back together tomorrow. How in the world do amp techs feel comfortable working on these things? Voltage meters?


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 Post subject: Re: Love my F30 but...
PostPosted: Wed Oct 05, 2011 11:56 pm 
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I started working on tube amps at 16. I never cared much if I got shocked or burned - it just gave me some good stories to tell my friends. I was lucky enough not to die. Some basic care should assure that you won't be critically injured, but in this day and age a lot of people are not OK with getting hurt when they make a mistake. Amp techs do get shocked. :shock:

Also, the smart techs discharge the caps with a resistor first. It takes some experience and a schematic to get them all, but it's a super easy way to make things safer. For sure you have to do that before you replace the high Voltage caps :D

I'm edu-ma-cated (I have a Master's in Electrical Engineering), but I still take stupid chances, like wiring wall sockets hot. Some of us are just not too bright :idea:

I will admit that the power stage of my 2:90 and my Electradyne both make me a little nervous...
Voltmeters are helpful, but you need one that can hold off 1000V. Some don't, and will arc right in your hand. Avoid the $4.99 meters. Fluke makes some great ones.

Anyhoo, if you didn't see anything obvious, then somebody who know what they're looking for will have to go through it. Good luck!

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 Post subject: Re: Love my F30 but...
PostPosted: Thu Oct 06, 2011 6:44 am 
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Bottle Rocket

Joined: Sat Sep 24, 2011 9:27 pm
Posts: 20
Your help has been greatly appreciated and sorry if I sounded juvenile but the whole "hiss" thing has been frustrating. I worked with a number of electrical engineers during my time on the Space Shuttle program here on the Space Coast of Fl. (I'm no engineer by any stretch). Anyway, I have no business messing around with the guts so it's going back together and up for sale. I would love to get my hands on the Electradyne but way too much for my needs. You have been a great help and thanks!


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 Post subject: Re: Love my F30 but...
PostPosted: Thu Oct 06, 2011 11:33 am 
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Joined: Thu Oct 15, 2009 1:30 pm
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Location: San Francisco Bay Area, CA
My pleasure. I didn't mean to imply that you sounded juvenile at all. Tube amps are tricky, even for people who know what they're doing. It takes a lot of experience to be comfortable with them. I'm kind of stuck in between wanting to help people get their feet wet and not wanting to be liable for what happens next...

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 Post subject: Re: Love my F30 but...
PostPosted: Thu Oct 06, 2011 11:47 am 
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Forgot - Mesa has been quite reasonable in my opinion for bench charges. If you really like the amp, get it fixed. But if you were looking for an excuse to try something else, then this is a good one :D

On that note, you might try the TA series. The Electradyne is way more than I need as well in terms of power, but the tone and simplicity are exactly what I like. It's worth a look. They're more reasonably priced used for sure, as a lot of people are finding they're just not for them.

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