Solder them to the marked points after scratching the mask or solder on pads sharing the same traces. Also remove everything from the left of the cap bank.
Attachments
As I understand it on a dual rail supply the ground is just a reference. The current should go out on V+ and come back on V-.
Although if you have any local smoothing caps on the channel boards, then the ripple they take out will go out on V+ and come back in on ground (or go out on ground and come back in on V- for the negative side).
Either way, I suspect it doesn't do any harm to have all 3 twisted together, but I'd love to hear other opinions.
[Edit: oops, I wasn't on the last page of the thread. I see AndrewT already addressed this....]
Last edited:
Quite right.
I faced the same issue a couple years ago and this solution has been working for me since. A thick wire from the center tap connected to a solid star ground made at least 6" far from transformer. Both PSU's ground input (shown in my last attachment) taken from star ground. Amp GND taken from star. Speaker return directly to capacitor bank GND (not to star).
For center tapped transformer its easy to implement. For a dual secondary transformer AC1's second wire and AC2's first wire (anti-phase) is soldered to make the center tap. To find the anti-phase wires, join any two wires from the two secondaries and measure AC at the open wires. If 2X secondary voltage is shown then its right and the joint can be used as a center tap, if very low or no AC voltage is shown then its wrong; just open the joint and replace any one of the two wires with the other wire of its respective secondary.
Other than in a full dual mono setup, a loop is bound to occur as long as the RCA grounds get in touch at the source. And in that case it is best to keep the loop far from transformer so that the hum is as low as possible (that's why the star better be far). A loop breaker in its default application is used to break the loop created by the mains earth. For loops created inside the cabinet exclusively in the ground node by using a shared transformer our usual breakers will not be of much help, and IME input ground lift networks have routinely failed to lower hum in this case.
The main difference between the original design and my proposal as in reply to manniraj's post is that in the original design the ground reference is created after rectification by stacking rectifier outputs and I proposed to have it before. Hence the center tap and the off-board bridge modules, because, the same can not be implemented with the on board rectifiers.
Hi Shaan,
I have been searching for this solution for a long time. You have great stuff posted above that comes from your invaluable "lessons-learned". Can you please kindly make a schematic diagram to go with your words here to make it clear? I think that this is going to be a very important and well-used reference if it works.
Thanks,
X
I have been searching for this solution for a long time. You have great stuff posted above that comes from your invaluable "lessons-learned". Can you please kindly make a schematic diagram to go with your words here to make it clear? I think that this is going to be a very important and well-used reference if it works.
Thanks,
X
It's as I posted earlier in the two attached pics. The "TO PSU1/2 GND IN" outputs from the first picture connects to the trace marked "GND" in the second picture. Precautions are are as posted in my last post. A thick wire from the center tap connected to a solid star ground made at least 6" far from transformer. Both PSU's ground input taken from star ground. Amp GND taken from star (not from PSU). Speaker return directly to PSU capacitor bank GND output (not to star). I hope it works for you too.
Attachments
Sorry I missed the earlier post with the schematic, thanks for re-posting it. I have some P2P CRC's that I can use to try this out. Wish I would have know about this when I was having all the problems in this thread. People there kept insisting that going to dual trafo's was the only way to fix it.
I have dual transformers with 0-35,0-35 8A and the crc psu’s made of mur860g. (Using softstart)
Have implemented all sorts of connections and ended up with unresolvable solution (hum)
Don’t know where the problem exists when same amp ran with single transformer and single psu there was no hum, after implementing dual mono there is hum
Observations:
1)When the home ground is connected to chassis/star ground the hum intensity is more - so i removed the home ground to chassis
Question: is the home ground should go to the chassis/star ground?
2)After removing the home ground to chassis there was slight hum, after trying different connections. Finally I could managed to make that hum to get reduced( when the ear is placed near to midrange driver)- like can be heard from less than half feet.
As am not that expert in the diy world, please answer to my question regarding the home ground.
Is the problem with crc psu?
Is the hum common with higher watt amps? (Am using apex fh9hv-150W @8ohms)
Have implemented all sorts of connections and ended up with unresolvable solution (hum)
Don’t know where the problem exists when same amp ran with single transformer and single psu there was no hum, after implementing dual mono there is hum
Observations:
1)When the home ground is connected to chassis/star ground the hum intensity is more - so i removed the home ground to chassis
Question: is the home ground should go to the chassis/star ground?
2)After removing the home ground to chassis there was slight hum, after trying different connections. Finally I could managed to make that hum to get reduced( when the ear is placed near to midrange driver)- like can be heard from less than half feet.
As am not that expert in the diy world, please answer to my question regarding the home ground.
Is the problem with crc psu?
Is the hum common with higher watt amps? (Am using apex fh9hv-150W @8ohms)
Do you still hear the hum when inputs are shorted to each other? If it goes away, the problem is not inherent in the PSU and amp setup but in the source to amp ground loop. I had one DAC that hummed terribly and another by same manufacturer but different model with much less hum. The problem seems to be in how the earth grounds and chassis grounds cause ground loops.
Try a USB DAC that is powered from a laptop running on batteries and see if hum goes away.
Finally, maybe try what Shaan suggests above?
Try a USB DAC that is powered from a laptop running on batteries and see if hum goes away.
Finally, maybe try what Shaan suggests above?
Am using chromecast audio as the source, definitely it’s not the source issue as have used the same source when tried earlier with single psu and single transformer
Inputs shorted to each other means?
I have shorted both the rca socket grounds and the hum is very minimal
Planning to implement following way to solve the home ground issue, hopefully it should solve
https://encrypted-tbn3.gstatic.com/...2pBGfUKZ0eoID6i_MGi6pNHX6VZCXrZdwS9BlMYZYnRDA
Inputs shorted to each other means?
I have shorted both the rca socket grounds and the hum is very minimal
Planning to implement following way to solve the home ground issue, hopefully it should solve
https://encrypted-tbn3.gstatic.com/...2pBGfUKZ0eoID6i_MGi6pNHX6VZCXrZdwS9BlMYZYnRDA
Last edited:
edit: off-topic segment deleted.
You don't need a star ground in a full dual mono setup. The two channels' grounds should not be allowed to come into direct contact except at the far end of the RCA input connectors.
Are you using loop breakers to connect the PSU grounds to chassis? You need two of them.
You don't need a star ground in a full dual mono setup. The two channels' grounds should not be allowed to come into direct contact except at the far end of the RCA input connectors.
Are you using loop breakers to connect the PSU grounds to chassis? You need two of them.
Last edited:
As stated above I will be using the 2 loop breaker and have to check
When checked earlier with others, they suggested to use star grounding and spent so much time in solving the issue.
After spending time in googling finally got above reference
Thanks Shaan for your inputs directly and indirectly
as you gave the solution for my issue with mur860 blown case
That's the standard FW PSU. It's not dual mono. It's shared positive and negative rails from one dual rail PSU. Even though dual cap banks are used, the upper four is for +24v and the lower four is for -24v rail. It does use an independent 15mF cap for each amp as the final smoothing cap though for better stereo separation.
Last edited:
Shorting inputs means connect +ve input to -ve input at the input terminal block.
Interesting. I thought I had seen all the Firstwatt PSU designs, but that one's a little different (and pretty much exactly the same as what I've drawn). It should work, then.
Cheers,
Jeff.
[Edit: Cross-posted before that last message. I think that second schematic is the one people were having trouble with regarding hum and/or buzzing, no?]
Cheers,
Jeff.
[Edit: Cross-posted before that last message. I think that second schematic is the one people were having trouble with regarding hum and/or buzzing, no?]
Last edited: