Looking for a bit of guidance on where to start with some debug. I've built a couple of Pass designs before, but starting out debugging with no schematics or idea where to start is a whole new prospect - so advice is very much appreciated!
I have an amplifier which has developed an odd noise - it's actually a car amplifier, but apart from using a switching PSU and having no possibility for 50Hz hum - is probably similar to any other class AB.
With no or very-low signal, it's fine. Zero noise.
With a slightly louder signal, at louder points or when notes hit, it makes a static/white noise over the louder notes
Louder still, and the amplitude baseline exceeds the level when the static starts, and static is constant.
At much louder levels, the noise does not scale, so is to some extent drowned out by the music.
Are there any pointers as to where to start? Electrolytics? PSU section?
I have an amplifier which has developed an odd noise - it's actually a car amplifier, but apart from using a switching PSU and having no possibility for 50Hz hum - is probably similar to any other class AB.
With no or very-low signal, it's fine. Zero noise.
With a slightly louder signal, at louder points or when notes hit, it makes a static/white noise over the louder notes
Louder still, and the amplitude baseline exceeds the level when the static starts, and static is constant.
At much louder levels, the noise does not scale, so is to some extent drowned out by the music.
Are there any pointers as to where to start? Electrolytics? PSU section?
If it is a car amp then I assume it runs off 12 volts DC. The current demands can be very high.
First step would be to scope the incoming 12 volts supply and make sure it stays clean. If that is 100% good then scope the rails in the amp itself.
First step would be to scope the incoming 12 volts supply and make sure it stays clean. If that is 100% good then scope the rails in the amp itself.
I was thinking to start with the power rails. Will probably start there.
Should have also said though - this is not running some silly 18in subwoofer in a box. This amp is actually driving some 2.5in Wideband drivers in the A pillar, and when I say quiet, I mean quiet. But it is connected to a substantial power cable, direct to the battery.
Should have also said though - this is not running some silly 18in subwoofer in a box. This amp is actually driving some 2.5in Wideband drivers in the A pillar, and when I say quiet, I mean quiet. But it is connected to a substantial power cable, direct to the battery.
Ah OK. I thought you meant you were repurposing a car amp for home use 🙂 and I had visions of you running it off a small laptop type PSU...
As its a true car installation then I'm going to move this over to the car amp forum. You should also list the type and model number to assist those used to working on these.
As its a true car installation then I'm going to move this over to the car amp forum. You should also list the type and model number to assist those used to working on these.
Thanks - didn't realise there was a dedicated car section!!
I doubt it is a well known amplifier - it's a Hertz EP4. A pretty modest amp which I've had for a long time, but should be easily up to delivering a good performance in its current application, when working correctly...
The noise is for sure affecting one pair of the four channels. I'm yet to debug for certain if it is on the other pair. I am actively crossing over at 400Hz between the HF wideband drivers (output pair A) and midrange drivers (output pair B). If I disable the crossover and run the midrange drivers full range up to 20khz, I don't hear the static. But it may be that they are not sensitive enough at high frequencies to make the noise, rather than for certain that the B pair are unaffected.
(It might be tempting to comment that it's not worth repairing - and all else being equal, I could well agree. But it is very tightly integrated into the setup as it stands, with cutouts, cable looms, mountings, etc, that would have to be redone to accommodate a new amp. So it is worth a good bit of time and effort to restore.)
I doubt it is a well known amplifier - it's a Hertz EP4. A pretty modest amp which I've had for a long time, but should be easily up to delivering a good performance in its current application, when working correctly...
The noise is for sure affecting one pair of the four channels. I'm yet to debug for certain if it is on the other pair. I am actively crossing over at 400Hz between the HF wideband drivers (output pair A) and midrange drivers (output pair B). If I disable the crossover and run the midrange drivers full range up to 20khz, I don't hear the static. But it may be that they are not sensitive enough at high frequencies to make the noise, rather than for certain that the B pair are unaffected.
(It might be tempting to comment that it's not worth repairing - and all else being equal, I could well agree. But it is very tightly integrated into the setup as it stands, with cutouts, cable looms, mountings, etc, that would have to be redone to accommodate a new amp. So it is worth a good bit of time and effort to restore.)
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That "hiss " could be instability , if you have an oscilloscope check the output which could come from HF generated by the SMPS ( under load ) or a problem with the amplifier itself .
As Mooly says -- what is the make/model otherwise we wont get very far and it will be supposition.
As Mooly says -- what is the make/model otherwise we wont get very far and it will be supposition.
Ah right its a Hertz audio/video amplifier of California not found a schematic yet but some of their advertising speak of mosfets at the output --try increasing the gate resistors value if they are mosfets.
You may need a scope to find the fault unless you could find some intermittent problem like dirty switches or pots.
Service manual, eprom result list | Elektrotanya
Service manual, eprom result list | Elektrotanya
Thanks for the schematic.
I had a look further. It has the issue on all 4 channels, which going off the schematic, and common sense, means it has to be the PSU. I guess it would be a fairly logical and straightforward first step to recap the electrolytics in that section. (I do have a scope to probe it out, but I haven't used it for a few years - which means it is in a fairly inaccessible strata in the garage)
There is one big issue though. See the linked photo. How on earth do I remove the heatsink spring clips? I can't even really pry the bigger ones up at all with a screwdriver, never mind move them. I could Dremel them off, but the swarf would probably mean the whole thing would need a run through the dishwasher. Then I would have to thermal epoxy them back down...
Unless there is an easy trick?
I had a look further. It has the issue on all 4 channels, which going off the schematic, and common sense, means it has to be the PSU. I guess it would be a fairly logical and straightforward first step to recap the electrolytics in that section. (I do have a scope to probe it out, but I haven't used it for a few years - which means it is in a fairly inaccessible strata in the garage)
There is one big issue though. See the linked photo. How on earth do I remove the heatsink spring clips? I can't even really pry the bigger ones up at all with a screwdriver, never mind move them. I could Dremel them off, but the swarf would probably mean the whole thing would need a run through the dishwasher. Then I would have to thermal epoxy them back down...
Unless there is an easy trick?
Sorry , to me at least its a bit dark in your red circled part of the photo and not large enough.
Jl audio 500/1 Transistor clamps
Recapping, if the caps show no signs of leaking or venting, is likely a huge waste of time.
That said, if you see a lot of high frequency ripple on the power supply rail voltage, that would indicate that the rail caps are open or out of tolerance.
Recapping, if the caps show no signs of leaking or venting, is likely a huge waste of time.
That said, if you see a lot of high frequency ripple on the power supply rail voltage, that would indicate that the rail caps are open or out of tolerance.