Hi there.
I'm still a newbie, but I'm trying to learn at home with a couple of amplifiers I'm using as study projects.
1. is an Ariston Amplifer, from 1982. It's pretty rare, and there'a nearly nothing about it online https://pinkfishmedia.net/forum/threads/ariston-amplifier-help-required.220097/.
2. the other two are the more ubiquitous Cambridge Audio A3/A5/P500. Basically the same amplifier. I have two of these, which work but I'm not 100% happy with the resulting sound. I'm debugging a "parasitic" wave form, which seems to hang off the top of a sine wave. Check out the image attached to see what I mean. If anyone can understand what they're seeing, I'd love to learn about it.
As I'm learning I'm going to get myself a Project 3A from Elliot Sound Projects. If I cannot fix my CAs then I'll replace the board with a 3A.
TTFN
I'm still a newbie, but I'm trying to learn at home with a couple of amplifiers I'm using as study projects.
1. is an Ariston Amplifer, from 1982. It's pretty rare, and there'a nearly nothing about it online https://pinkfishmedia.net/forum/threads/ariston-amplifier-help-required.220097/.
2. the other two are the more ubiquitous Cambridge Audio A3/A5/P500. Basically the same amplifier. I have two of these, which work but I'm not 100% happy with the resulting sound. I'm debugging a "parasitic" wave form, which seems to hang off the top of a sine wave. Check out the image attached to see what I mean. If anyone can understand what they're seeing, I'd love to learn about it.
As I'm learning I'm going to get myself a Project 3A from Elliot Sound Projects. If I cannot fix my CAs then I'll replace the board with a 3A.
TTFN
Attachments
What you are seeing looks like high frequency instability/oscillation.
A commercial design (any design) should not exhibit this but seeing this is a commercial amp my first thought would be that it has been worked on before and possibly had parts replaced or removed or incorrect parts fitted.
Check that R211 is OK but beyond that you need to look into any past history and what may have been done to it.
A commercial design (any design) should not exhibit this but seeing this is a commercial amp my first thought would be that it has been worked on before and possibly had parts replaced or removed or incorrect parts fitted.
Check that R211 is OK but beyond that you need to look into any past history and what may have been done to it.
Thanks for your reply. I’ve had this amp since new and this fault I detected earlier last year when I bought the oscilloscope. It was sounding a bit squishy in the mids. It had been used daily for years, connected to a Stream magic listening to internet radio.
Last month I replaced all the electrolytic caps with matching good quality ones. It actually sounds ok playing music. I’ve tried cd and various digital music. It’s lacking bass though so it’s back on the bench.
I’m not denying I might have done it more harm than good, but has 20years service. As I say, it’s a learning project and I’m growing very familiar with the layout against the schematic.
My challenge is understanding how the different sections are supposed to change the wave form and trying to tell where this signal is coming from.
It’s on both channels and it’s not apparently coming from the tone control.
It’s only on the 20hz through 400hz. After that the sine wave looks good though I need a dummy load to work through the noise.
Last month I replaced all the electrolytic caps with matching good quality ones. It actually sounds ok playing music. I’ve tried cd and various digital music. It’s lacking bass though so it’s back on the bench.
I’m not denying I might have done it more harm than good, but has 20years service. As I say, it’s a learning project and I’m growing very familiar with the layout against the schematic.
My challenge is understanding how the different sections are supposed to change the wave form and trying to tell where this signal is coming from.
It’s on both channels and it’s not apparently coming from the tone control.
It’s only on the 20hz through 400hz. After that the sine wave looks good though I need a dummy load to work through the noise.
So did it have this issue as seen on the scope before the recap? In other words can you be 100% sure nothing amiss happened changing the caps?
Given both channels are the same you should look for something common and that could even be something like a missing screw used for grounding somewhere.
Also be certain the scope set up and how and where you connect the ground leads to the amp are not causing any issues. If the scope is mains grounded and if the amp is as well (and any source components) and if you are grounding the scope probe internally somewhere you might be introducing some odd ground loop that could cause this.
The presence of a load should not make any difference to the output signal you see on the scope. If it does then something is amiss somewhere.
Given both channels are the same you should look for something common and that could even be something like a missing screw used for grounding somewhere.
Also be certain the scope set up and how and where you connect the ground leads to the amp are not causing any issues. If the scope is mains grounded and if the amp is as well (and any source components) and if you are grounding the scope probe internally somewhere you might be introducing some odd ground loop that could cause this.
The presence of a load should not make any difference to the output signal you see on the scope. If it does then something is amiss somewhere.
Made progress.
The A5 has the parasitic hum on both channels fairly consistently through a range of low Hz. I tapped around board with a pencil and it goes away, then comes back.
Reflowed every joint in the board. Noted the board is slightly warped. Also noted some dark resistors. Parasitic still there. Tapping the resistors makes it go away. Tapping the input transistors. Thought it was the input lead. Inconsistent. Will replace the resistors on both channels and report back.
The P500 amp has it rather had exactly the same parasitic issue. And then suddenly it didn’t. That had dry joints at the power button. Reflowing fixed that. Using my probe to recheck this wasn’t a power supply. And the parasitic hum goes away. I’ll test it for a few days to make sure it’s really gone.
I’m still feeling this isn’t quite fully understood but it is progress.
Maybe glue the mains caps? They were originally and I didn’t when I replaced them.
The A5 has the parasitic hum on both channels fairly consistently through a range of low Hz. I tapped around board with a pencil and it goes away, then comes back.
Reflowed every joint in the board. Noted the board is slightly warped. Also noted some dark resistors. Parasitic still there. Tapping the resistors makes it go away. Tapping the input transistors. Thought it was the input lead. Inconsistent. Will replace the resistors on both channels and report back.
The P500 amp has it rather had exactly the same parasitic issue. And then suddenly it didn’t. That had dry joints at the power button. Reflowing fixed that. Using my probe to recheck this wasn’t a power supply. And the parasitic hum goes away. I’ll test it for a few days to make sure it’s really gone.
I’m still feeling this isn’t quite fully understood but it is progress.
Maybe glue the mains caps? They were originally and I didn’t when I replaced them.
Darkened resistors are not uncommon if they are run hard. Failure is usually permanent and either sees them going high in value or open circuit. Anything that is tappable suggests in the first instance a bad joint or connection. Crimped wires in plug/sockets can be problematic.