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please help! my amp volume is decreasing suddenly

Started by jeansen, August 18, 2008, 09:50:36 AM

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jeansen

hello, i'm new here and really glad to find this forum... :) i really need help for my amp here..i have a solid state amp Hughes& Kettner blue edition 30 r , i already had it for 3 years now and i really like this amp, an amazing practise amp <3)...but a few days ago, this amp having trouble :( ..the volume is decreasing suddenly in both channel: clean and lead channel and it always synchronized...(if my clean channel volume is decreasing, the lead channel is also decreasing,..visa versa..) it sounds like that there is a sound that want to goes out but it can't ... this problem came in no precise time and paroxysm...sometimes in the middle of my playing and sometimes it already came just as i start turning on the amp volume...

i have tried to isolate the problem by using my amp's "return" to know if the damage is on the preamp or power amp, but i think the power amp is still ok..(the "master" volume is still in perfect condition and no volume decreasing there)....
i also use another guitar and cable or even using another amp to find if the problem is on my guitar or cable but i found that my guitar and the cable are just fine...i also always keep my amp away from the wall to keep a proper ventilation for my amp..

and then, yesterday, i found that i can have the volume back to normal if i turn the volume knob to the maximum position or strum really hard to the strings of my guitar...so as an example: if i have my volume decreasing in some position(x position), then i can fix it if i turn the volume knob to maximum position and the amp volume is back to normal...(if i turn the knob to x position again, the volume produced by my amp is normal for the x position again) ......but then i found also that it won't stay long, the problem will come again and again...

what's wrong with my amp? i have never use my amp too loud or too harsh..i even rarely use this amp, it spends more time in the box then out in my room ( it because of my busy schedules i have for the last 2 years)

btw, is the problem is on the preamp?  ??? is this a problem that i can handle by myself? cause i'm thinking that it is because of a dirty pot or dirty input..is it possible? i'm thinking this because few a days ago, i didn't put my amp to the box and i also put this amp uncovered in my room and i let my cable stay plugged in the input socket..can it be the cause of this problem? if it is, how can i clean the input socket and the pot? could you give me the steps on how to do it? and is there any cautions or danger for my amp that i need to know for doing this?

another question : a few days ago, i also use this amp for playing my acoustic electric nylon guitar ...could it also be the cause?

sorry, i am asking a lot of question and emotional words, i am a newbie on a world of amp and i really love this amp....this amp is so important for me...
please help....thx u :) :)

teemuk

That sounds like a contact problem, meaning either something is dirty/corroded or a solder joint has failed. It's likely one of the potentiometers. Since you can "cure" the problem by applying some stress to one of the potentiometers (therefore re-establishing the weakened contact), the one in question would be my first suspect. Or it could be the input jack. - These things are sometimes hard to pinpoint exactly. Try cleaning the potentiometers and jacks with some contact spray and if that does not help inspect their solder joints to see if they have gone bad. (You may need a magnifier glass for that). If it's just a contact problem it should be a moderately easy thing to fix.

Jack1962

Teemuk is absolutly correct, this is a most common problem, dig in and start cleaning and looking , it mostly is that pot , I would start by throwin some heat to it right away.

                                             Rock On

jeansen

#3
hello, Teemuk and jack1962.thx u for replying  and so concern..thx a lot.. :)
but if you don't mind, i need to ask you some questions again because of my poor english and poor knowledge about electronics...

1.
QuoteSince you can "cure" the problem by applying some stress to one of the potentiometers (therefore re-establishing the weakened contact), the one in question would be my first suspect.
Teemuk, i'm sorry to bother u, but can you please explain me more detail about that sentence..? cause i don't really understand what u mean there... :) what do you mean by the word "stress" and what did i've done that you called as "re-establishing the weakened contact"?
and what do you mean by the sentence " the one in question" ?

2.
QuoteI would start by throwin some heat to it right away.
jack1962, what do you mean by " throwing some "heat"? sorry for botering you too.. :)

3. ....and please show me how can i apply the contact cleaner to the pots and (especially) to the input jack? sorry for asking so dumb question , i'm a newbie in amp world..thank you so much..

btw, just wanna say ...i'm really happy to meet u all and proud to be in this community...thx a lot again... <3)

warm  regards,
Jeansen  :)

Jack1962

Heat up the solder joints on the pot.

                                Rock On

jeansen

#5
QuoteHeat up the solder joints on the pot.
hi!!  :) thx u for the reply, jack1962.. :) i understand now...ok, i will clean first before checking and then heating up the solder joints, like you n Teemuk suggested..thx u so much ...but i have another questions....
1. how can i apply the contact cleaner and clean the jack input? and should i open my amp's case for cleaning the pot?

2. and, i'm just curious, why is the volume decreasing is always synchronized ? ( if my clean channel volume is decreasing, the lead channel is also decreasing at the same time,..visa versa..) is the clean volume and lead volume are connected directly so when either one pot is dirty, the other one will be affected too although this other one is not dirty?
thx u for so concern... :)


btw, i'm still waiting for Teemuk's answers too... :) thx u

warm regards, Jeansen  :)

teemuk

What I meant is that somewhere in your amplifier is a dirty or loose mechanical contact that causes the volume to fade out. When you apply physical stress to the potentiometer (by turning it fully clockwise) the weakened contact is once again restored and the signal level returns back to normal. However, only temporarily since the contact begins to weaken again as soon as you remove the stress from the potentiometer. This causality indicates that the problem with the weak contact is very likely in the said potentiometer.

First things first, you need to open up your amp and inspect it. Quite frankly, you should have done it already. Potentiometers are cleaned by spraying contact cleaner to their resistive strip after which you turn the potentiometer's shaft back and forth a few times so that the potentiometer's wiper (which is attached to the shaft) moves back and forth on the resistive strip hence cleaning it. Now, construction of potentiometers varies a lot and some of them are sealed so well that it is virtually impossible to access their inner parts. No, you can't clean the potentiometers via the front panel. Usually the metal case of the potentiometer has some kind of an opening that you can use to spray the contact cleaner inside but you really need to open up your amp and find out.

In cases where cleaning is impossible or does not help the only choice is to replace the entire potentiometer with a new one. Before you do this it is usually convenient to be 99.9 percent sure that the problem was exactly a dirty potentiometer and not something else. Often in case of contact problems there is a strong chance that the potentiometer is not dirty, just has a broken contact in its solder joints. You need to inspect them first if cleaning does not help. Note that in many amps you need to do quite a bit of dismantling to actually access the solder joints of the potentiometers located beneath the circuit board. Also, many PC board-mounted potentiometers need to be exactly certain type to fit in to the board. If your soldering skills are not good you can easily overheat the joints and lift out the circuit board traces, which will be a b*t** to repair.

Seeing the circuit diagram would answer whether the clean and lead volume are connected directly. At this point it seems very likely.

Jack1962

There you have it Teemuk , has once again brought it to ya.

                               Rock On

jeansen

hi..Teemuk and Jack...thx a lot for the more detail explanations, clearer for me now...i'll try all of your advices tonight..if i have a problem, i'll post a question again if u don't mind. :) :)
thx u so much...btw, how can i clean the input jack also? thx u

J M Fahey

You can squirt a *very* small amount of contact cleaner into the input jack, and them move a plug in/out 10/20 times. This will physically clean the rust/mold/dirt that disturbs good contact. Afterwards, you can "touch up"the solder joints to make sure there are no cracks, which are very probable since this is thesingle most abused jack in the amp. Basically: the same that Teemuk and Jack suggested, applied to this jack.
Good luck.
JM.

jeansen

hello...thx u for the replies, guys....thx u so much... :) I have tried advices from all of you on cleaning the pots and the jack input a few days ago and i found it doesn't work and i luckily have a quick chance to took my amp to the official dealer of HK in my country few days ago..and have it fixed...no problems for this two days ;)
the repairman said that it wasn't because of the dirty pot or input , but like the one that Teemuk has said before...there was a loose solder joints and then he fixed it and all come back to normal... <3)

but, now i am questioning something:
i rarely use this amp and i have never play it quiet loud ( never pull the volume or distortion to max position) and i always keep my amp into the box every time i finished practising..so, how can my amp have a loose solder joint? my friend said it might be happened because of rust? is it true? please reply...thx u :)


btw, for JM Fahey : what did you mean by "touch up" the solder joints? please explain it to me...i have a bad english, sorry. :-[..thx u :)

jeansen

hi..why no one answer my question?  :'( i really would like to know why can my amp had a loose solder joint, even though i rarely overused my amp (i even rarely use my amp :P)....and what should i do to avoid that problem again and to maintain my amp in the top performance in the future? please reply,Teemuk and others...thx u :) :)

J M Fahey

Hi Jeansen. Whay your repairman did, what I call "touch up" is just getting a small/fine tip soldering iron (30/40W), very clean tip, and some thin, good quality solder wire (preferably around 0,7mm) and very briefly re-solder suspect solder joints, adding the tiniest amount of solder possible (just for the rosin core/flux, rather than  the metal itself). The idea is to get any "cold" or cracked solder joint "re-joined" , NOT to make a blob , a messy joint or even worse a short to some nearby track or pad nor melt any plastic nearby. What is your original language?
JM

jeansen

hi...JM Fahey, sorry for replying so late..i haven't got the chance to reply because of my awful internet connection i have a few days ago...thx for replying..i understand it now ..thx u so much... :) btw, my original language is Malay and Indonesia languange.. :)

btw, i'm still needing advice on this question.... :)

Quotei really would like to know :
1. why can my amp had a loose solder joint, even though i rarely overused my amp (i even rarely use my amp)?

2. ..and what should i do to avoid that problem again and to maintain my amp in the top performance in the future?

if Teemuk and others don't mind, please help answer this questions...i really want to upgrade my knowledge about amp maintanance and repairing...thx u :)

teemuk

A solder joint is not a mechanically sturdy connection. If a component is mounted in such way that it is held on place only by its soldering the said solder connection will easily break from a slightest stress such as turning the potentiometer (in case of potentiometers) or plugging in a plug (in case of jacks). When a solder joint breaks you no longer have a proper (low-resistance) connection between the circuit board and the component and the result is intermittency. Components that endure physical stress (e.g. heavy components, switches and aforementioned resistors and jacks) should always be fixed on place by a sturdier mounting method than just the solder on the legs of the component in question. Such method is, for example, mounting them to the metal panel of the chassis or something similar, where the task of supporting the component is no longer resting on the shoulders of the solder joint only. Unfortunately, in many amps this "golden rule" is neglected more or less. This is because such method of construction requires more manual labour, which costs extra. Not a good thing if you want to put out an affordable product.