Hi,
I’ll do my best to describe this problem, in the hope that someone can advise what the problem might be.
I’ve owned a very clean (and brilliant) Hitachi SR-804 for around ten years now, and over the last couple of years it has developed a strange fault. The right channel on the amp will run fine for, say, ten minutes a time then right channel VU meter will start flicking up and down the scale like mad whilst a very loud, sub bass sound will be produced through my right hand speaker. If fact, the first time this occurred it blew the driver in my right speaker.
The amp is a US model, I use a step down transformer to use it with UK current. I’ve checked the channel fuses inside the amp, both seem fine. I’ve tried all manner of cable changes, changed the step down transformer, switched the speaker wire etc and it always comes through in the right channel.
The amp will produce this fault whether or not there is any audio going into the amp (ie. the turntable or aux playing any music) and is unaffected by volume/tone controls, switches etc. The VU meter for the right channel will also flickering wildly whether or not the amp volume control is turned up or not.
I’m stumped, I’m sure solving the issue may be beyond me, but I’m trying to ascertain if anyone has experienced a similar fault and what the issue may be before I am concerned with getting it fixed or not. Of course, I’d like to, but if it’s an expensive fix, this may be beyond me at the current time.
Any help would be appreciated.
John
I’ll do my best to describe this problem, in the hope that someone can advise what the problem might be.
I’ve owned a very clean (and brilliant) Hitachi SR-804 for around ten years now, and over the last couple of years it has developed a strange fault. The right channel on the amp will run fine for, say, ten minutes a time then right channel VU meter will start flicking up and down the scale like mad whilst a very loud, sub bass sound will be produced through my right hand speaker. If fact, the first time this occurred it blew the driver in my right speaker.
The amp is a US model, I use a step down transformer to use it with UK current. I’ve checked the channel fuses inside the amp, both seem fine. I’ve tried all manner of cable changes, changed the step down transformer, switched the speaker wire etc and it always comes through in the right channel.
The amp will produce this fault whether or not there is any audio going into the amp (ie. the turntable or aux playing any music) and is unaffected by volume/tone controls, switches etc. The VU meter for the right channel will also flickering wildly whether or not the amp volume control is turned up or not.
I’m stumped, I’m sure solving the issue may be beyond me, but I’m trying to ascertain if anyone has experienced a similar fault and what the issue may be before I am concerned with getting it fixed or not. Of course, I’d like to, but if it’s an expensive fix, this may be beyond me at the current time.
Any help would be appreciated.
John
Hi,
Thanks for your swift reply. Soldering; I can do a bit of. Measuring voltages; wouldn’t know where to start, to be honest!
If it helps, the noise is a sort of deep thudding, almost one per second. If it’s a re cap that’s need, I’m probably going to be better off getting it done professionally I’m imagining? Don’t think that’ll happen in the near future due to the current pandemic, but is it an expensive process from your experience?
Thanks for your swift reply. Soldering; I can do a bit of. Measuring voltages; wouldn’t know where to start, to be honest!
If it helps, the noise is a sort of deep thudding, almost one per second. If it’s a re cap that’s need, I’m probably going to be better off getting it done professionally I’m imagining? Don’t think that’ll happen in the near future due to the current pandemic, but is it an expensive process from your experience?
recap is not expensive and it is easy for an experience diyer.
But if you love your amp and no other amp to use then you better let a pro to repair it.
People has no experience to repair an amp, the result may be a dead amp.
But if you love your amp and no other amp to use then you better let a pro to repair it.
People has no experience to repair an amp, the result may be a dead amp.
This much rather sounds like an intermittency issue, typically bad solder joints or possibly even traces, but could be a transistor going bad as well. For starters, inspect the board for potentially bad solder joints. Everything that gets hot or is heatsink-mounted is especially suspect.
I just picked up one of these and it has the same problem as the OP.
I will be opening it up ASAP to have a look.
sgrossklass, it does seem like an intermittent issue, I have managed to have the unit play perfectly for hours at low-mid volume, but at high volume (wanted to see how it performed) it would act as described. Almost seems a temperature related issue.
I will be opening it up ASAP to have a look.
sgrossklass, it does seem like an intermittent issue, I have managed to have the unit play perfectly for hours at low-mid volume, but at high volume (wanted to see how it performed) it would act as described. Almost seems a temperature related issue.
In addition, I have read and discovered to be true, the low filter when on, stops this from happening. A starting point anyways.
If it is happening after a period of time, and is repeatable, it might be a bad capacitor somewhere. I have an amp that the left channel of the phono pre-amp would quit after 5 minutes. It was repeatable, same fault, always the same period of time after turning it on. Turned out to be a bad capacitor, the worst part is that I fitted it when I recapped it a few years ago 😱
Anyway, replacing the part (and the matching part in the "good" channel") fixed the problem.
Might be a dry solder joint, but would think it is something more consistent (a failing part like capacitor or transistor).
Anyway, replacing the part (and the matching part in the "good" channel") fixed the problem.
Might be a dry solder joint, but would think it is something more consistent (a failing part like capacitor or transistor).
It happens every time the receiver is on, but how long it takes to start varies and the duration it lasts for varies. It does seem to be getting worse i.e. starts sooner after power up and lasts longer in duration, which prompts me to hit the low frequency filter and it stops immediately.
Excuse my ignorance but does this mean the signal is now bypassing the defective part or perhaps it is a low frequency signal causing the issue and the filter effectively eliminates it?
Excuse my ignorance but does this mean the signal is now bypassing the defective part or perhaps it is a low frequency signal causing the issue and the filter effectively eliminates it?
I've repaired last month my old 40 years Pioneer amp and there was a similar VU going up like crazy, it turned out to be a resistor with a broken leg connected to one oft the pre-drivers.
I've only found it when I began removing the pre-drivers for testing.
I've only found it when I began removing the pre-drivers for testing.
That is not likely, all the loudness switch (S604) does is short out a capacitor to remove a low pass filter effect. But it would narrow the problem down to around IC401 or IC601, would suspect a bad capacitor if they are original parts.
Ok, Thanks gannaji, I've heard the term before but never realized what it meant, now I know.
I'm back to work so hopefully I can find some time on the weekend to take a look, after I replace the bulbs in my Onkyo unit.
I'm back to work so hopefully I can find some time on the weekend to take a look, after I replace the bulbs in my Onkyo unit.
gannaji is right! - So is amplidude. When powe supply caps dry out, their capacity goes lower - as in less uF effectively (100uF measures 5uf for example) - then the B+ or B- rail can become modulated by the amp's circuit. As the circuit draws current, the amp starts behaving like a low frequency oscillator. Your bass driver starts pumping back and forth as +/- 50 peaks are being pumped out by the amp. After a while, your voice coils in the speaker will fry - as you describe. It sounds like the put-put of a motorboat...! So YES: start recapping and see if the problem does not go away. - Even if it turns out to be something else, your old amp will benefit from a cap overhaul. Good luck!
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