Hi guys,
I have a weird issue with an Audio System X-ION 280.2. It similar to audio_system_f2-190 in the attached pdf, but not exact. I've used those schematics as a referance.
There is crossover distortion once You apply any load to it. Goes for both channels. If there is no load applied the sinewave behaves differently. There is distortion on the bottom half and the top half is being chopped off.
Rails are exactly the same and correct +-50v, +/- 15 are present, There seems to be some issue with the bias, at least to my understanding, but using the bias knob make little to no difference, there is almost no increase in current draw between min and max position. And i've repaired amp like this before, this is not correct behaviour.
I've changed already the LL4148B diodes and the Zeners but with no avail.
Any idea what can cause this issue for both channels at the same time ?
I have a weird issue with an Audio System X-ION 280.2. It similar to audio_system_f2-190 in the attached pdf, but not exact. I've used those schematics as a referance.
There is crossover distortion once You apply any load to it. Goes for both channels. If there is no load applied the sinewave behaves differently. There is distortion on the bottom half and the top half is being chopped off.
Rails are exactly the same and correct +-50v, +/- 15 are present, There seems to be some issue with the bias, at least to my understanding, but using the bias knob make little to no difference, there is almost no increase in current draw between min and max position. And i've repaired amp like this before, this is not correct behaviour.
I've changed already the LL4148B diodes and the Zeners but with no avail.
Any idea what can cause this issue for both channels at the same time ?
Attachments
That sounds to me like there is no drive current to the lower half of the FETs.
I would pay attention to R20/30 and Q12/16 (if this is as your amplifier is).
I would pay attention to R20/30 and Q12/16 (if this is as your amplifier is).
Using the secondary ground for the reference (black probe), what's the DCV on each end of R160 and R161 (4 voltages)?
These are different amps from different series same brand. They are similar as much as for the way they work (general schematic approach). You can check both of them here:
https://amp-performance.de/en/806-Audio-System-Twister-F2-190.html
https://amp-performance.de/en/1154-Audio-System-X-ION-280-2.html
All resistors measure in tolerance, checked that already.
What You are saying make sense but to happen for both channels at the same time, very unlikely.
https://amp-performance.de/en/806-Audio-System-Twister-F2-190.html
https://amp-performance.de/en/1154-Audio-System-X-ION-280-2.html
All resistors measure in tolerance, checked that already.
What You are saying make sense but to happen for both channels at the same time, very unlikely.
R 161 = one end -3.9v and other end -3.9v (2mv across the resistor)
R 160 = one end +4.1v and other end +4.1v (2mv across the resistor)
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All resistors?
If not all, check R84 and R85 to confirm within tolerance.
Measure the DCV directly across R160 and R161. Having 0v across one of the resistors seems odd.
If not all, check R84 and R85 to confirm within tolerance.
Measure the DCV directly across R160 and R161. Having 0v across one of the resistors seems odd.
Perry I've edited my previous post.
Measure the DCV directly across R160 and R161. Having 0v across one of the resistors seems odd. = 2mv across both
R84 and R85 to confirm within tolerance. = 10k as they are supposed to be.
Measure the DCV directly across R160 and R161. Having 0v across one of the resistors seems odd. = 2mv across both
R84 and R85 to confirm within tolerance. = 10k as they are supposed to be.
Removed Q9. Is Q9 a mute transistor ? Bias pots are working now.
Voltage did increase a bit.
Now it is:
R 161 = 3.3mv (across the resistor)
R 160 = 2.7mv (across the resistor)
With Q9 removed I've noticed at the speaker output terminals, if I increase the gain a bit, even with no RCA plugged in, there is self-excitation or self-oscillation and my power supply goes into protect as current draw exceeds 10A. There is no difference if there is a load at the speaker terminals or not.
Voltage did increase a bit.
Now it is:
R 161 = 3.3mv (across the resistor)
R 160 = 2.7mv (across the resistor)
With Q9 removed I've noticed at the speaker output terminals, if I increase the gain a bit, even with no RCA plugged in, there is self-excitation or self-oscillation and my power supply goes into protect as current draw exceeds 10A. There is no difference if there is a load at the speaker terminals or not.
Attachments
Yes, part of the muting circuit. Was the transistor leaky/shorted?
If the gain is left at the lowest level, will it work normally?
Does it oscillate if you switch the LPF in?
Is the protect LED lit?
If the gain is left at the lowest level, will it work normally?
Does it oscillate if you switch the LPF in?
Is the protect LED lit?
Yes, part of the muting circuit. Was the transistor leaky/shorted? = leaky, is that a NPN transistor BC850 ?
If the gain is left at the lowest level, will it work normally? = yes it does, couple of volts rms are fine, a bit over it and it's going bad
Does it oscillate if you switch the LPF in? = no, it does not. But the switch makes a tremendous pop sound whenever i press it, like almost ground to rail to ground DC for a moment and current draw at that point maxes out again. I've already tried to clean up all of the pots/knobs/switches couple of times with contact cleaner.
Is the protect LED lit? = flashes for moment, exactly when the current draw maxes out. I think this is due to my power supply going in protect and lowering the voltage ?
If the gain is left at the lowest level, will it work normally? = yes it does, couple of volts rms are fine, a bit over it and it's going bad
Does it oscillate if you switch the LPF in? = no, it does not. But the switch makes a tremendous pop sound whenever i press it, like almost ground to rail to ground DC for a moment and current draw at that point maxes out again. I've already tried to clean up all of the pots/knobs/switches couple of times with contact cleaner.
Is the protect LED lit? = flashes for moment, exactly when the current draw maxes out. I think this is due to my power supply going in protect and lowering the voltage ?
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For the part number, that would be likely. The information I have is incomplete. The other common 2G is a PNP and yours is an NPN.
So, is the fault related to the position of the gain control or is is related to the input/output level? This is why I stress not using the gain control to adjust the level of the amp output when troubleshooting. Use the volume/level control on the signal source.
Is the shield ground of the signal source grounded? That can sometimes be an issue (if not grounded).
Are there any op-amps with excessive DC offset on their output terminals?
So, is the fault related to the position of the gain control or is is related to the input/output level? This is why I stress not using the gain control to adjust the level of the amp output when troubleshooting. Use the volume/level control on the signal source.
Is the shield ground of the signal source grounded? That can sometimes be an issue (if not grounded).
Are there any op-amps with excessive DC offset on their output terminals?
Okay....sorry about that,
I took apart the switches and the knobs left them in isopropyl alcohol for some time. Fitted them back. I don't have any more oscillation except when i'm using the LPF button. At some point in it's travel from on to off and off to on, it introduces the oscillation again for a brief moment. If you hold the switch at that specific position oscillation stays present. The popping sound whenever you use the LPF button is also still present. I think the button itself is damaged.
After all of that I've retested using only the volume/level control on the signal source (Q9 is still lifted).
Channel A is fine, i've even tested it with 4 and 2 ohms loads, no issue whatsoever till clipping.
Channel B - clean sinewave with no load till clipping. But when you attach a load it plays with a bit of distortion, And if the sinewave goes above 5vrms, it goes into protect. So there is an issue with channel B. I'm attaching a picture how does the sinewave starts to look like at around 5vrms. Using the bias adjustment does not help.
I use a signal source a laptop running on its battery or a portable player.
I took apart the switches and the knobs left them in isopropyl alcohol for some time. Fitted them back. I don't have any more oscillation except when i'm using the LPF button. At some point in it's travel from on to off and off to on, it introduces the oscillation again for a brief moment. If you hold the switch at that specific position oscillation stays present. The popping sound whenever you use the LPF button is also still present. I think the button itself is damaged.
After all of that I've retested using only the volume/level control on the signal source (Q9 is still lifted).
Channel A is fine, i've even tested it with 4 and 2 ohms loads, no issue whatsoever till clipping.
Channel B - clean sinewave with no load till clipping. But when you attach a load it plays with a bit of distortion, And if the sinewave goes above 5vrms, it goes into protect. So there is an issue with channel B. I'm attaching a picture how does the sinewave starts to look like at around 5vrms. Using the bias adjustment does not help.
I use a signal source a laptop running on its battery or a portable player.
Attachments
If you run a jumper from the primary ground to the RCA shield ground, does it make a difference?
Using an isolated signal source can lead to liability issues, especially if the transformer has a primary to secondary short that you will miss with an isolated shield. The shorted transformer can damage the customer's signal source (head unit) and can possibly cause a fire by burning the RCA cables from the amp all the way to the head unit. It's happened before. You have to protect your signal source but that's easy to do.
Using an isolated signal source can lead to liability issues, especially if the transformer has a primary to secondary short that you will miss with an isolated shield. The shorted transformer can damage the customer's signal source (head unit) and can possibly cause a fire by burning the RCA cables from the amp all the way to the head unit. It's happened before. You have to protect your signal source but that's easy to do.
If you run a jumper from the primary ground to the RCA shield ground, does it make a difference? = makes it even more distorted and amp goes into protect after 2 seconds.
What should I use at my bench table as a signal source in order to be more inline with car conditions ?
What should I use at my bench table as a signal source in order to be more inline with car conditions ?
An amplifier shouldn't have a problem with a grounded shield since virtually all head units have grounded shields.
I use a standard head unit but you can use anything but I strongly recommend using a grounded shield. If you have the tutorial, item 11 on the Equipment page shows what you need to protect the signal source. If not, I can explain it, if you want me to.
Is there any DC on the RCA shields?
on any of the speaker terminals?
Is the noise coming from the preamp section or is it being generated in the output stage? It sounds like it's preamp if the problem goes away in LP mode.
I use a standard head unit but you can use anything but I strongly recommend using a grounded shield. If you have the tutorial, item 11 on the Equipment page shows what you need to protect the signal source. If not, I can explain it, if you want me to.
Is there any DC on the RCA shields?
on any of the speaker terminals?
Is the noise coming from the preamp section or is it being generated in the output stage? It sounds like it's preamp if the problem goes away in LP mode.
I have the guide, i will check it.
Is there any DC on the RCA shields? = No
on any of the speaker terminals? = No.
Is the noise coming from the preamp section or is it being generated in the output stage? It sounds like it's preamp if the problem goes away in LP mode. = LP minimizes it, but doesn't get rid of it, if i turn it off, there is even more distortion at the sinewave. I don't think it's the preamp section. I think it's the output section.
If it's only present above certain threshold value of voltage or current (5vrms, 4ohm in my case) and a load attached, sounds to me like a transistor cannot supply enough current or is not being properly driven.
Is there any DC on the RCA shields? = No
on any of the speaker terminals? = No.
Is the noise coming from the preamp section or is it being generated in the output stage? It sounds like it's preamp if the problem goes away in LP mode. = LP minimizes it, but doesn't get rid of it, if i turn it off, there is even more distortion at the sinewave. I don't think it's the preamp section. I think it's the output section.
If it's only present above certain threshold value of voltage or current (5vrms, 4ohm in my case) and a load attached, sounds to me like a transistor cannot supply enough current or is not being properly driven.
Can you swap signal between channels using jumpers at C150/C250? to confirm that the problem is the output stage and not the preamp?
Just did that. Issue stays at the Channel B. So it's the output stage. And it's presenting itself only when a load is applied.