Hi guys
I've not been feeling very well this week, so progress is slow. I am still waiting for the new SD card reader to arrive to be able to show you pics of the thing.
I've ripped out the small PCB that was part of the original Cambridge Audio CDP I've repurposed the chassis of as it had a fault I think was the power switch, and reworked all the mains section by fitting an IEC socket from a broken PC PSU and rewiring all the grounding connections, rewiring the EMI filter board and fitting a new power switch, it all now works as it should, I just need to add an inline fuse holder when it arrives in the post.
The thing works again now, sounds about the same as before, maybe slightly better. However there is still a hum, it's a little quieter than before but still there, I have a feeling it's a grounding issue or may need to add a filter cap.
Photos will be much better at explaining this than words, hopefully the SD card reader arrives in the next day or two.
I've not been feeling very well this week, so progress is slow. I am still waiting for the new SD card reader to arrive to be able to show you pics of the thing.
I've ripped out the small PCB that was part of the original Cambridge Audio CDP I've repurposed the chassis of as it had a fault I think was the power switch, and reworked all the mains section by fitting an IEC socket from a broken PC PSU and rewiring all the grounding connections, rewiring the EMI filter board and fitting a new power switch, it all now works as it should, I just need to add an inline fuse holder when it arrives in the post.
The thing works again now, sounds about the same as before, maybe slightly better. However there is still a hum, it's a little quieter than before but still there, I have a feeling it's a grounding issue or may need to add a filter cap.
Photos will be much better at explaining this than words, hopefully the SD card reader arrives in the next day or two.
Last edited:
I saw this upgrade done to a Cambridge Audio CD player, exactly the same power board as the one I ripped out (except mine didn't have an IEC socket, it had a hardwired 2-core cable), I just wondered what people's thoughts were on this upgrade, a couple of filter caps is very simple to do and from what the guy wrote, should make a significant difference:
Modifying the Cambridge Audio D500 CD Player
Modifying the Cambridge Audio D500 CD Player
Last edited:
Power filtering can make a big difference with some equipment in some cases. Part of it depends on what is on the power lines locally where you are. If the power is dirty, there are various power conditioners that have been made to use with audio gear. You plug the conditioner into the wall socket, then plug the audio gear into the conditioner. Some power conditioners are very effective and many are rather poor. Sometimes good used ones can be found on ebay.
Yes, I've seen those conditioners. The thing is, there's no hum at all when I use my Yamaha amp with DAC built in so I am pretty sure the issue is with the DAC I've built.
I've bought a cheap oscilloscope, the DSO138 model, so maybe I can analyse the current at various points in my DAC and figure out the source of the hum:
Review: Mini Scope | Elektor Magazine
I've bought a cheap oscilloscope, the DSO138 model, so maybe I can analyse the current at various points in my DAC and figure out the source of the hum:
Review: Mini Scope | Elektor Magazine
Ian, please do get a 10:1 probe for that, they are very cheap on Amazon or ebay. Read the voltage rating stuff carefully. A switchable probe on the wrong setting, or the wrong probe type of can be very dangerous when investigating power line related issues, or if used with any other high voltage circuitry. Besides higher voltage, a 10:1 probe also has a calibration adjustment on it to give flat frequency response. Clip leads with a BNC connector aren't able to give that valuable feature.
Last edited:
I've added a second 0.47uF MKP safety cap, this one directly across the live terminals of the IEC socket and I think it has reduced the hum, but only by a small amount and the hum is still clearly audible.
Hopefully my new SD card reader will turn up this week and I can post pictures so you can see how I've got this thing connected up and hopefully help me identify the issue causing the hum. I'm fairly sure it's an RFI/EMI filtering issue, if not, it's imperfect grounding, probably a simple fix, just need to diagnose it.
Hopefully my new SD card reader will turn up this week and I can post pictures so you can see how I've got this thing connected up and hopefully help me identify the issue causing the hum. I'm fairly sure it's an RFI/EMI filtering issue, if not, it's imperfect grounding, probably a simple fix, just need to diagnose it.
I happened to have some small ferrite rings, about 10mm in diameter and I've added a total of 7 of those to anywhere I could fit one between the IEC socket and the transformer. No change at all in the hum,which leads me away from thinking it's an RFI/EMI issue and towards it being a grounding issue. Most annoying because aside from the hum, it sounds pretty good.
Here's how I originally had things configured for my initial test:
I had retained the original power input board, with power switch and fuse. After the initial test I added an EMI filter board, grounding wires and some banks of smoothing caps. This didn't work as I had problems with a loud hum, then an intermittent fault that would stop the thing powering up altogether that I traced to the power input PCB and was probably the power switch.
So I decided to rip that power board out, cut a square hole in the back to mount an IEC socket from an old PC PSU and rewire the AC input altogether. This works fine, but there is a low hum. I've added a couple of filter caps and some ferrite rings since this picture, to little effect.
Here's a couple of pics of one of the banks of smoothing capacitors I built, this one is for a dual rail supply to the analogue output stage, the one for the DAC board is basically one half of this for a single rail supply, the caps are Phillips 2200uF, 16V with an Arcotronics 0.1uF MKP just before the output.
I had retained the original power input board, with power switch and fuse. After the initial test I added an EMI filter board, grounding wires and some banks of smoothing caps. This didn't work as I had problems with a loud hum, then an intermittent fault that would stop the thing powering up altogether that I traced to the power input PCB and was probably the power switch.
So I decided to rip that power board out, cut a square hole in the back to mount an IEC socket from an old PC PSU and rewire the AC input altogether. This works fine, but there is a low hum. I've added a couple of filter caps and some ferrite rings since this picture, to little effect.
Here's a couple of pics of one of the banks of smoothing capacitors I built, this one is for a dual rail supply to the analogue output stage, the one for the DAC board is basically one half of this for a single rail supply, the caps are Phillips 2200uF, 16V with an Arcotronics 0.1uF MKP just before the output.
Attachments
I'll take some better pics tomorrow to show what I've done to try to get rid of the hum, but in the meantime I've annotated this picture to hopefully make things clearer.
The green lines show the grounding wires I have fitted. I've also marked where I placed the two filter caps, one directly across the live terminals of the IEC socket, the other across the live terminals of the input to the EM filter board. I've also added a total of 7 ferrite rings to the AC mains wires. None of this has done much if anything to get rid of the hum which sounds to me like it's at 50hz, which is the frequency of mains AC here in Britain. I don't think it's dirty AC input as I don't get any hum at all when using my Yamaha Amp/DAC, only when using this thing I've built.
The green lines show the grounding wires I have fitted. I've also marked where I placed the two filter caps, one directly across the live terminals of the IEC socket, the other across the live terminals of the input to the EM filter board. I've also added a total of 7 ferrite rings to the AC mains wires. None of this has done much if anything to get rid of the hum which sounds to me like it's at 50hz, which is the frequency of mains AC here in Britain. I don't think it's dirty AC input as I don't get any hum at all when using my Yamaha Amp/DAC, only when using this thing I've built.
What drives the dac input, and what does the dac output connect to? How are you hearing hum, from an amplifier somewhere?
Assuming there is an input device and an output device for the dac, you could try disconnecting the input, disconnecting the output, then turn on the dac and the power amp. Any hum? Touch the amp input ground to the dac ground, Any hum? Plug in the amp to the dac output, any hum? Touch the input device ground to the dac ground, any hum...etc, etc.
Assuming there is an input device and an output device for the dac, you could try disconnecting the input, disconnecting the output, then turn on the dac and the power amp. Any hum? Touch the amp input ground to the dac ground, Any hum? Plug in the amp to the dac output, any hum? Touch the input device ground to the dac ground, any hum...etc, etc.
Last edited:
May I suggest you try rerouting your wiring and layout:
You have switched live running straight over the top of your EMI filter which is not going to help.
Perhaps rotate the EMI board 90 degrees so you can have the input ac close to the IEC, the switched Live on the LH side and the filtered AC on the RH side. (Separation of dirty/clean AC).
Rotate the Transformer 180 degrees and keep the input AC lines short and direct from the EMI board. You appear to have the transformer primary winding wires running in part under the DAC?
Consider then moving the earth star point closer to the IEC so you can drop Earth straight from IEC - Star - EMI, then route the remaining earths to the Star keeping those cables well away from the transformer and AC lines.
I'm not sure if connecting the capacitors in parallel across the two ends of the input is beneficial.
AC wires have a magnetic field radiating from them so always avoid running them close to anything you don't want noise induced in - low level signal lines for example. Try orienting the power connectors for the shortest and most direct route possible.
I've attached a dodgy MSPaint diagram to help explain what I mean.
You have switched live running straight over the top of your EMI filter which is not going to help.
Perhaps rotate the EMI board 90 degrees so you can have the input ac close to the IEC, the switched Live on the LH side and the filtered AC on the RH side. (Separation of dirty/clean AC).
Rotate the Transformer 180 degrees and keep the input AC lines short and direct from the EMI board. You appear to have the transformer primary winding wires running in part under the DAC?
Consider then moving the earth star point closer to the IEC so you can drop Earth straight from IEC - Star - EMI, then route the remaining earths to the Star keeping those cables well away from the transformer and AC lines.
I'm not sure if connecting the capacitors in parallel across the two ends of the input is beneficial.
AC wires have a magnetic field radiating from them so always avoid running them close to anything you don't want noise induced in - low level signal lines for example. Try orienting the power connectors for the shortest and most direct route possible.
I've attached a dodgy MSPaint diagram to help explain what I mean.
Attachments
Dammit, I typed a long and detailed reply then lost connection to the site and lost the reply.
Thanks for the guidance guys, the hum is 50hz, which is the mains AC frequency here, I hear it through the amp.
The DAC is getting it's input from my PC via TOSlink.
I wrote a lengthy piece in reply, and right not, at 4.50am, I can't be bothered rewriting it all, so I'll simply say that I will get my thinking cap on and work out how to rearrange the layout as suggested to minimise cable runs and organise things better. I'll take photos of my proposed new layout before remounting anything, drilling holes etc.
Bed time, will get back to you with more detail on the morrow.
Thanks for the guidance guys, the hum is 50hz, which is the mains AC frequency here, I hear it through the amp.
The DAC is getting it's input from my PC via TOSlink.
I wrote a lengthy piece in reply, and right not, at 4.50am, I can't be bothered rewriting it all, so I'll simply say that I will get my thinking cap on and work out how to rearrange the layout as suggested to minimise cable runs and organise things better. I'll take photos of my proposed new layout before remounting anything, drilling holes etc.
Bed time, will get back to you with more detail on the morrow.
How is the dac pcb earthed? I can see the brown and blue, is one of these also earthed (ie is it a single sided supply or isi it a split supply of + 0 - ?
If so I can't see the 0v going to the earth point.
So have you connected the 0v to the earth terminal along with the 0v of the capacitor bank?
I did have a mains hum issue a few years ago and if my memory serves me, it was because the coaxial digital input of my dac used an isolating transformer so there was no earth continuity to the cd player.
This is normal since when every thing is earthed, it avoids hum loops.
But the Teac cd player was not earthed, it used a separate 12v psu. I found that connecting the coax socket on my dac to ground cured it.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.