JSX Hiss, unwanted noise and tube life issues...

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby CastleJoe » Sat Oct 31, 2009 6:32 pm

Thought you guys might be interested in the email I sent Customer Service...

Hi Guys,

My Names *****, I live in Adelaide South Australia... I own a JSX head played and signed by Satch.. I love this thing... However I have been experiencing many issues with it... Power Tube life is very short. 3- 4 months in fact.. Considering the Head never sits on the Quad to help prolong tube life and I only play through the unit for a max. Of 1.5 hours in one sitting per week.. The tubes should be lasting closer to 1 -1.5 years... The amp has been back to Peavey Australia twice and has been sent to a number of Peavey approved amp techs.. Resulting in the same thing...

I get told the valves have had it, the valves get replaced and I get charged (Peavey Aust didn’t charge me the last time.).. I know the valves have had it, what I want to know is why aren’t my tubes lasting..

In addition to this the amp is starting to Hiss pretty bad. Ive purchased a noise reduction unit (in the amps loop), a Furman Power Conditioner to power the amp and a Voodoo Labs Pedal Power Plus 2 to power the pedals, to prevent any ground loops... None of this helps to control the Hiss from the amp.

The Hiss is even apparent through the clean channel, but on the Crunch and Ultra its Hissing like a snake.. So when the Noise Gate opens you get this mix of Hiss/Noise with the amps tone.. Resulting in a fizzy sound coming through on the High mids and above. I have also recently noticed that the amp makes some random crackling and pops from time to time (loud to). At first I thought it was a faulty lead. But then realized it was coming from the amp.

I have been experiencing the tube life and increasing Hiss issues for nearly 2 years now and Ive had enough.. Ive been doing some reading and its possible that the Plate resistor may be faulty, adding Hiss and crackling/pops to the amps signal.. I can also see the solder joints for a number of of pins on Power tube sockets are getting hot. I would imagine that this would also shorten Power Tube Life?

There is only one Amp Tech I trust in Adelaide, and thats Frank from FMAudio. Can I request a copy of the amps schematics so we can work out whats going on here... In addition to this if the amp is not able to be fixed can I please have a replacement. If I contact Peavey Australia they seem to want me to tell them exactly whats wrong with the amp for them to consider replacing the chassis. Im not an amp tech and obviously cant do this.. Not to mention that it seems to be a difficult task for any amp tech to resolve. I know at the time when Frank had my amp he spent a fair bit of time trying to work out whats going on, the other guys.. well, I struggled to a discussion about my experiences.

I seem to treated with scepticism when I explain the issues and experiences.. Peavey Aust said they had a guy with 20 years guitar playing experience play it and he couldn’t fault it??? Put new tubes in the thing and it sounds awesome for about 2 weeks. Having said that Ive been playing Guitar for 30 odd years, owned a number of different tube amps, and have never gone through such a fiasco before...

Im currently recovering from Cancer and all I currently have is my music. I dont need this grief any longer. I need a result one way or another. I am asking for your assistance in this matter. I am looking at dropping my amp of to Frank in the next week or so. Work I want is to fault find, plus a complete re-valve, again... I am going to ask him to replace the Plate resistor regardless.

Also other work to consider, I have been told that the JSX board is rated at 63vdc but the Filter Caps are only rated at 60vdc.. If this is true as the tubes age (in a short time) the tubes draw more current. And in no time at all the Hiss is going to get worse. Its been recommended that 100vdc caps be put in place as this silences the amp at all gain stages and levels. Can you please advise if you feel this may be a contributing factor, or if the Caps might be faulty and contributing to the Hiss...

If the issue cant be resolved can you please give authorization to swap my chassie out for a new item, and have Frank set it up with my tubes of choice. I want to keep the Heads case as its signed by Joe Satriani. My contact at Peavey Australia has been Bosco... This has been a long ordeal and I need it to end ASAP.

Id like to thank you for you assistance in advance. Look forward to your timely response.

Kind Regards,

(My Name)

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby Enzo » Sat Oct 31, 2009 7:10 pm

A scope used for biasing? High fidelity amplifiers want the lowest possible distortion so they can more faithfully RE-produce the sound amplified through them. Guitar amps are not reproducers of sound, they are part of your instrument. Distortion is not only inevitable, it is usually desired.

Using a scope to set bias implies, I am assuming, that your tech is setting bias for least crossover distortion. In a guitar amp, the general consensus is to set bias by dissipation of the power tubes. If you are burning up power tubes, back off on that bias.

The bias test points built into this amp monitor the bias VOLTAGE, not current. Most of us consider that useless, HOWEVER, when set to factory specification by those test points, the result is a cooler tube that should last a lot longer.

Just for the sake of science, try setting the amp to factory spec, not some latter day "better" method. See how it works out.

Hiss is a product of gain. The more gain there is, the more hiss there will be. if the level of hiss changes, all other things remaining the same, then something in the amp or tubes is also changing.

Hiss is not hum, so ground loops are not causing hiss. They cause hum.

You can localize the source of your hiss. Do ANY controls have ANY effect on the sound of the hiss? If you can turn it up and down or change the tone of it with a panel control, then that means the hiss is coming from a point in the system BEFORE that control. Likewise, if a control has zero effect, then the hiss is coming in after that control. I don;t doubt the preamp is mainly responsible, that is where most of your gain lies.

Does the noise gate control on your amp have any effect on this hiss? Ask your tech if the noise gate circuit has been removed or disabled. Some guys take them out. They may prefer it without the noise gate, but it is noiser that way. Or perhaps that is the issue, your noise gate circuit has an intermittent connection or part.

I have attached a noise service buttetin from the factory, ask your tech if this has been performed or incorporated into the amp. It seems to be manufacture date sensitive.

Ive read an artical that suggests the main pcb in the JSX is rated at 63vdc but the Filter Capacitors installed are only rated at 60vdc... This means as the tubes start to age and draw a little more current we are going to have a problem... And you know what the Hiss gets louder as time passes...

Well, 63v is a standard cap rating. There may be some 60v rated caps out there, but I have never seen any. In the bias circuit, which is where we would find such caps, the main bias filter uses two of them in series, so that means 126v rating effectively, and the remaining one is across the bias voltage, which is a lot lower than 60v. I am not at all aware of the relationship of tubes aging, drawing more current and somehow that causes stress on the bias caps?????

I am aware that in times past some JJ power tubes did have narrower pins, but was unaware that continues. Easy to check with a micrometer.

You are using the EL34, an not the E34L, is that right?

I like the Winged C tubes, myself. And Marshall ships them in recent amps.

Just what is the nature of the tube failures you report as short life? Are we talking power tubes or preamp tubes? Are the tubes actually failing? Or is this a situation where you hear the hiss, send it in for service, they stick in new tubes, and the whole thing repeats every couple months? In which case what you are calling short tube life is really more a matter of a recurring problem that the techs always try to solve by swapping tubes. MAybe? if that is it, the tubes are probably fine, and it is the act of swapping them out that "fixes" the amp.
PV JSX noise bulletin.pdf
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Re: JSX Hiss, unwanted noise and tube life issues...

Postby CastleJoe » Sat Oct 31, 2009 8:42 pm

Thanks Enzo...

Yeah no one has ever Biased the amp via the test points...

The amp has only ever been Biased by approved Peavey techs or Peavey Aust. them selves... So I dont need to go through how to Bias the amp.. If these guys dont know what there doing well... What can I say... They all use Scopes to find the sweet spot so to speak...

Ive always used the JJ EL34's (not EL34L's)... Im going to try the Winged "C" EL34's this time around though...

Having said all that if I messure at the test points to see where its at, it reads 45.. And if EuroTubes are right.. in EL34 Bias mode the tubes noramaly run hot and its possible to fry them.. But Im not drawing any conclusions on this...

The amp has already been Biased by Peavey Aust. to Factory defualts (Thats what they told me) and it run ok for a while then.. the same ol crap happened...

Biasing the amp does not appear to be the issue here...

I do understand the difference between the Hum and Hiss....I was just trying to give everyone an idea of how the amps setup...

The Noise Gate on the amp is set to 10, but the issue remains...(Hiss and short tube life that is)

Then Amps gate helps take the edge off for sure, but its still real noisy.

The Hiss is loud enough to effect the way the gate opperates.. That is you need to set the gate to clamp fairly hard... But this means its effecting the sensativity of my playing, soft or light picking wont come through.. And Guitar volume needs to be above half way... Sucks...

Hey thanks for the JSX Noise Bulletin, Ill pass it on to the Tech...But yeah I think mines had it done...

As far as Filter Cap and Plate resistor questions, Im just trying to thriough things out there to try to determine whats going wrong.

At the end of the day:

1. Peavey or approved Techs are setting up/servicing the amp (biasing and replacing the tubes)

2. There is an ongoing issue with white noise (Hiss) and short tube life. For two years now.

3. There is random crackling coming from the amp (according to the tube store web site the Plate resistor could be at fault? I dont know)

4. The Filter Cap question is just me trying work out if this could be a possible root cause for the problem. Thats all

5. I just dont want to have to fork out for tubes every three months, considering Im only playing through the unit 6 hours a month. JJ have said the tubes should last 1 -1.5 years based on my useage...

6. I can no longer stand playing with Hiss mixed into my guitar tone. I understand there should be an acceptable level of Hiss coming from a high gain amp. But thats not what were talking about here.

I am convinced that there is an issue that is effecting either the bias proccess of the amp and/or something is causing the bias to ulter over a short time that is killing my tubes.. I just dont know what this could be and any suggestions are welcome... I just dont want to go over the whole how to bais thing again...

Sorry if I come accross a little harsh Im just getting frustrated with this whole experiance...


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Re: JSX Hiss, unwanted noise and tube life issues...

Postby CastleJoe » Sat Oct 31, 2009 9:24 pm

Guys your not going to believe this.. I pulled the chassis to have a look for the Added cap as per the Noise Gate Enhancement document Enzo sent me..

And Guess What...??

Its not bloody there.... WTF? Ive sent this to Peavey Aust Twice complaining of Noise and Hiss and they send it back to me and say there is nothing wrong with the amp... And its been to a number of Peavey approved techs...

Makes me think how hard have people been looking at this amp, and how seriously are people taking me...

So I guess this is going to resolve my Hiss issue.. Now to work on the Tube life issue. What could be effecting my tube life, except an incorrectly Biased amp?

Im going to buy a Weber Bias probe from EuroTubes and Bias it myself maybe? Icant seem to be able to trust anyone to get this sorted...

Thanks again Enzo.. What a Champ... :D

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby JamesPaul » Sat Oct 31, 2009 9:34 pm

CastleJoe wrote:...

Thanks again Enzo.. What a Champ... :D

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby Classic30inCincy » Sat Oct 31, 2009 9:49 pm

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby avirox » Sat Oct 31, 2009 11:35 pm

O.o now that is a freaky discovery

Just something to note, though: the noise gate has no effect on the clean channel whatsoever; it only works on the crunch and ultra channels, so if you are getting hissing on Clean then the missing cap is probably not the cause (though who knows, I'm no technician..).

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby CastleJoe » Sat Oct 31, 2009 11:57 pm

Hey Guys...

Sorry, but I need to backup on my last post... The board the noise gate mod applies to board 72101012... I was looking for a cap like in the picture of the noise gate document...

Ive got board 72101012C, and there is a cap on the board between R21 and D2...

Dam...Must be the modified board with the cap already on it... Sorry guys...Still in search of a solution for my dramas....

Ive added two images: The first shows the cap. The second shows the Power Tube sokets.. They seem to be getting real hot.. Can someone tell me if this is normal.. The PCB board appears to bubble in places.. Real small..

Anyway Thanks again guys...
TubeSockets.jpg (273.53 KiB) Viewed 3813 times
CapImg.jpg (147.16 KiB) Viewed 3813 times

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby CastleJoe » Sun Nov 01, 2009 12:07 am

One more thing.. It looks like Ive got revision C of the original board.. So what else other than the Noise gate mod has changed since the original? Where Ive got the 3rd revision and the Noise Gate mod was added almost imediately after sales of the amp started...

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby Van Noord » Sun Nov 01, 2009 1:43 am

The way your amps noise gate is working is very strange. You say it cuts off your playing? And continues to hiss when set to 10?
First off, the built in "noise gate" on the amp has absolutely no clamping or gating abilities. It's labeled a "gate" but should be called a suppressor. It is simply a hiss eliminator.
My JSX is a 2004 model that I've had for close to 5 years and the gate rids my amp of a huge amount of hiss without affecting the tone or dynamics.

In all honesty, stop using those dreadful new production JJ power tubes. Loads of people are having problems with them.
If you want a good reliable EL34 then try out Svetlana, Electro Harmonix or Ruby tubes.


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Re: JSX Hiss, unwanted noise and tube life issues...

Postby CastleJoe » Sun Nov 01, 2009 1:37 am

Yeah going to use the Svetlana (SED Winded C) EL34's...

The gate I was talking about when clamping was the Boss NS-2 which is in the loop.. I need this as well..That is in addition to the amps gate set at 10.. because the amps gate (filter) has no effect on the clean channel...

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby KTB » Sun Nov 01, 2009 11:52 am

The noise gate of this amp is nothing more than two bak to back diodes going to a 1Meg pot. The preamp topology is the reason for the noise not tubes or biasing. Every stage has a bypass cap which also adds to the gain and gain and noise are proportional as to frequency and this amp has all 3. Lots of frequency shaping and mid band rolloffs are involved but with the exception of the 2nd gain stage which uses a 470n bypass capacitor the other stages are basic Fender topology and no Cathode followers or direct coupled circuits to add to tube count. Cascaded stages are noisy so a noise gate is needed but the on board one should be turned off while using the other..

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby CastleJoe » Sun Nov 01, 2009 6:05 pm

Hey KTB or anyone else,

Can you think of an reasons why when the amp is retubed it sounds awesome.. But in a very short time the Hiss starts to get bad, And the life of my Power Tubes is short?

When the amp is re-tubed I can back the gate off on the amp to about 5, no probs.. For about a week or so and then the Hiss starts to get worse and setings need to change..

Aventually I cant run the Ultras gain past 3 - 4 because it just becomes un-usable... I used to be able to crack this up to about 7 - 8 no probs and have the things sound amazing... But over a short period of time breakup becomes earlier each time I play it, and my dials need to change to maintain a tone that is usable..

Something has changed in the amp.. It nolonger seems to be performing consistantly over time.. I know you should expect some degrading in the tone over a fair period of time, as its a tube amp... But Im forking out for tube refits all the time and its driving me nuts...

When thHiss starts to creep in you can hear clipping in the signal, especially if you step on the Wah.. Brings it right out.. And the random Crackling???

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Re: JSX Hiss, unwanted noise and tube life issues...

Postby CharlieP » Sun Nov 01, 2009 6:26 pm

Maybe your bias is too hot. I am not familiar with the bias of your amp. I have read that some Peavey and/or Fender amps should be best biased with a bias meter and not on the test points. It seems some of them are too hot even tho the test point method shows OK. You may want to check in to this. If it is hot then that would make the tubes not last. Sound good for a short time and eventually burn up.
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Re: JSX Hiss, unwanted noise and tube life issues...

Postby electroman » Sun Nov 01, 2009 8:48 pm


For biasing I never use the scope method, by doing this you are tring to remove the notch or cross over point. However tring to do this may cause you to push the amplifier out of the class it was deigned to run in and it may be running.

I use winged c's 6L6's and el34's and never have problems with them. For biasing industry standards are anywhere between 50% to 70% of tube operation. I bias at 60% so my calaculation would be:

EL34 =25 watts at 60% = 15watts
Plate voltage = 480aprox
15/480 = 31.25mA This current will be equal 31.25 mV measured on your meter with a bias probe using a 1ohm measuring resistor. (Ohms Law)

Your calculation may differ a little depending on the spec of your bias probe.


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