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Post subject: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 12:02 am
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[cross-posted on other forums]

Hi All,

I have some nasty white noise and pops/bangs happening on my Prosonic when running with the solid state rectifier, and I'm hoping someone here will be able to help me figure out what to replace.

It's hard to describe so I put a video up on youtube: http://youtu.be/S1oYRBgbh98?t=1m

Skip to 1:00 and enjoy!

Sometimes it's a slower buildup than this - the noise might come in low and build over the course of a minute or so before a big pop comes and it goes quiet again. Output power doesn't seem to be affected.

The power tubes are all relatively new, and it doesn't happen when the amp is running in class A mode on the valve rectifier.

Any suggestions for what's going wrong here?

Thanks in advance for looking.

Cheers,
Mark


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 12:41 am
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Did you do a new bias with your new output tubes ?

Also bias check is needed with solid state rectifier .

IMO the bias is too hot . I can not listen your video for now .


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 1:02 am
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Sounds like that solid-state replacement rectifier has a bad solder point(s). Which becomes more audible as the amp warms up. Many times, it's poor solder job on the wires within the pins.

If the amp never did this with a tube rectifier --- I'd go back to a good tube rectifier. Whether you buy new issued or NOS, buy it from someone who tests the tubes and ferrets out bad ones.

Such as TAD:

http://www.tubeampdoctor.com/product_in ... anguage=en


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 1:12 am
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+1 BMW

Now I hear it on You Tube


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 2:43 am
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BMW2002Ti wrote:
Sounds like that solid-state replacement rectifier has a bad solder point(s). Which becomes more audible as the amp warms up. Many times, it's poor solder job on the wires within the pins.

If the amp never did this with a tube rectifier --- I'd go back to a good tube rectifier. Whether you buy new issued or NOS, buy it from someone who tests the tubes and ferrets out bad ones.


This amp does not have a "solid-state replacement rectifier" -- it was engineered from the outset to operate with either a tube or a built-in diode stack......

http://ampwares.com/schematics/prosonic.pdf

Thus, several different modes of rectification are provided. This was one of Zinky's final designs before leaving FMIC and he gave it several unique-to-Fender bells and whistles. I would look first to the bias-select switch on the rear panel and examine it closely for pitted, corroded, or dirty contacts.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 3:28 am
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Arjay,

Ok, complicated. Maybe it is the "recto" switch. Good contact cleaner worked in well, may solve the issue.


Thanks!


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 3:43 am
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Indeed......complicated is an understatement.

Bruce wanted a "jack of all trades" amp that could deliver Fender cleans, AC30 crunch, and full-stack grunge and for the most part he succeeded. The traditional blackface tones are close and the OD mode delivers "Boogie-esque" distortion and compression but the pseudo-Vox voicing was somewhat less than realistic (regardless of recto mode, it just isn't possible to make a pair of 6L6's sound like EL84's). Still, it was a good design with a pleasing drive channel that hissed far less than amps in FMIC's current lineup. And it was assembled with real solder.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 8:29 am
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Hi Everyone,

Thanks for the input, I'll look at reflowing the solder joints and examine the selector switch on the back. I'll do my best to remember to report back with the results!

Just to add my personal thoughts to Arjay's comments on the amp - I think it's an amazing beast! When I bought it I compared it with a whole music store's worth of amps, but nothing sounded and felt as alive and organic as the Prosonic. If you ever get a chance to try one make sure you do. The downsides are it's not a quiet amp in terms of the baseline noise level, and even with the recommended mod I still get a pop on channel switching if the reverb's on. I wouldn't trade it though, it's an awesome amp.

Cheers,
Mark


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 9:16 am
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Having just gone through a 2 week "ordeal" with a Prosonic...I have to agree with Mark. The Prosonic is certainly a remarkable beast. I was prepared to trade a Lonestar Special for a "low mile" Prosonic (& $$ from the owner).

I arranged to have the Prosonic re-tubed & serviced by a local tech, insuring that all the Fender Tech notes were applied. My only complaints to the tech were that the amp hummed way too much as the reverb was turned up...and as the volumes were increased. I do enjoy quite practice time at home and the reverb hum was over the top annoying.

Long story short....the hum never went away.

Glorious breakup at volume...manageable size & weight....3 recto settings....

I'll keep my Lonestar for now, but there will be a Prosonic in my future!


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Wed May 28, 2014 10:54 am
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markbt wrote:
Hi Everyone,

Thanks for the input, I'll look at reflowing the solder joints and examine the selector switch on the back. I'll do my best to remember to report back with the results!

Just to add my personal thoughts to Arjay's comments on the amp - I think it's an amazing beast! When I bought it I compared it with a whole music store's worth of amps, but nothing sounded and felt as alive and organic as the Prosonic. If you ever get a chance to try one make sure you do. The downsides are it's not a quiet amp in terms of the baseline noise level, and even with the recommended mod I still get a pop on channel switching if the reverb's on. I wouldn't trade it though, it's an awesome amp.

Cheers,
Mark


I use to own a Prosonic back in 2002 and really like the concept of it. I didn't keep it long and traded it in on some other gear.
As time went on I thought about that amp from time to time and when the Super Sonic 112 came out, I felt I have a second chance. long story short, finally got a Super Sonic 112 and I got to say, I'm just as happy with it.


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Fri May 30, 2014 11:01 am
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stratele52 wrote:
Did you do a new bias with your new output tubes ?

Also bias check is needed with solid state rectifier .

IMO the bias is too hot . I can not listen your video for now .


Just reporting back with an update, stratele52 nailed it!

I opened the amp up and re flowed joints on the power board, and while doing that noticed that someone had been there before and lingered a little too long with their soldering iron. Some of the pads have been lifted, but it all works just about. Whilst I had it open I checked the bias and discovered it was way too hot, I guess the last tech who looked at it didn't check the bias. I dialed the bias back and replaced the power tubes with some better able to cope with being in a Prosonic, and now all seems well.

Cheers,
Mark


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Fri May 30, 2014 11:07 am
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Another happy outcome......sounds good, Mark.

Rawk on!

8)

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Horrible Noises from my Prosonic
Posted: Fri May 30, 2014 11:07 am
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Very good! Hopes that the fix stands the test of time.

As a side note... You are not the first owner to discover that an amp which had its bias adjusted by a "tech" --- was way off nominal value. Needing a big time re-adjustment, right afterwards. Some techs adjust the bias, with the amp not at steady operating conditions.

Proper method goes something like this: Crank the adjusting pot full CCW (or coldest setting). Let amp warm up for a good 10-15 minutes, checking the output tubes for any red plating. Then, adjust the bias. Play the amp, listening to amp's tone and overall response -- through volume range. Re-check the idle bias.


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