Hello to everyone. First of all, I just want to tell you that your forum is very inspiring and was also the reason why I decided to build my CHIPAMP. However I got a problem with the hum in my MyREF amplifier. Since I have finished my amplifier, I was not able to get rid of the hum in the speakers. First of all, the hum which was present in the speakers correlated with the hum of the transformer (it was changing periodically). I used the mains DC filter, to get rid of it. The hum is now constant, but still present. For signal input, I am using Audinst HUD mx-1. .... See photo of the amplifier. I will be grateful for any recommendation. Thanks.
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Sorry, I'm not knowledgeable enough on this circuit to offer help. Do you have pics with better lighting so we can more clearly see the wiring details?
I don't think it's hum related, but I'd definitely move that ground connection from the toroid bolt to a dedicated chassis connection close to the power entry/filter.
Do you have hum when you short the inputs? Or move the toroid further away?
I think I've read that with the current MyRef dual toroids are usually required for hum-free operation.
Hopefully others have some good advice.
BK
I don't think it's hum related, but I'd definitely move that ground connection from the toroid bolt to a dedicated chassis connection close to the power entry/filter.
Do you have hum when you short the inputs? Or move the toroid further away?
I think I've read that with the current MyRef dual toroids are usually required for hum-free operation.
Hopefully others have some good advice.
BK
You MUST remove that connection from the transformer securing bolt.
It is acting as a shorted turn and injecting a large AC current into the Protective Earth.
Use Green/Yellow for the Protective Earth. That the standard colour in many countries.
Yes, there is a mains fuse in the IEC socket. I removed protection earth from the transformer securing bolt, but the hum is still present. I will change the wire according to norms tomorrow.
Have a look at Peranders' DC blocker. They are not expensive.
You will see he has given the option for multiple Bypass Diodes on his PCB. The diodes limit the maximum voltage that can ever appear across the DC blocking capacitors (they still sit at mains voltage).
With two series connected diodes in each direction bypassing very high current, (maybe during start up, or during some abusive incident), you may find that the diode Vf jumps upto 1V per device. That equates to 2Vpk across the capacitors. 5V rated capacitors will do, I chose small 16V 3300uF electros for my first few DCblockers. Recently I bought 10V 4700uF and these work just as well. 10off in series/parallel pass sufficient current to never allow the diodes to turn on during all normal operation of 100+100W stereo power amplifiers.
You will see he has given the option for multiple Bypass Diodes on his PCB. The diodes limit the maximum voltage that can ever appear across the DC blocking capacitors (they still sit at mains voltage).
With two series connected diodes in each direction bypassing very high current, (maybe during start up, or during some abusive incident), you may find that the diode Vf jumps upto 1V per device. That equates to 2Vpk across the capacitors. 5V rated capacitors will do, I chose small 16V 3300uF electros for my first few DCblockers. Recently I bought 10V 4700uF and these work just as well. 10off in series/parallel pass sufficient current to never allow the diodes to turn on during all normal operation of 100+100W stereo power amplifiers.
Some current can leak to the case. That makes the electro can a MAINS VOLTAGE component.
Once the lid is on you may adopt the attitude that no one can be harmed. The fuses will save everybody.
I think differently. The rules allow one to adopt single insulation inside a protective enclosure. But I adopt double insulation for all the mains cabling inside my enclosures. That same rule applies in the UK for ALL mains cabling in a house, even those behind your plasterboard.
Well, I ve just tried the approach which I found there: Mains DC and Transformers Anyway DC filter is working fine, the hum which is present after the source is connected is the main problem.
You're getting some good advice and have some things to follow up with.
When I suggested shorting the inputs, I meant disconnect the RCA interconnects AND short at the chassis connector. You can cut off the ends of some throw-away RCAs for this. Such "shorting plugs" can come in handy. Alternatively you can short the inputs at the boards themselves depending how you soldered up your board. If it hums with inputs shorted it leaves no doubt the issue is with the amp.
Your chassis RCA connectors are isolated from the chassis and verified as such after install, correct?
BK
Well. Right now the huge buzz is present when there is no input (It has appeared after I disconnect signal cables on the PCB and attached them again). When I connect the input, the hum is the same as it was before. It s like pure ghostery to me. I was reading about HBRR+HBRL but I am not quite sure about it. Should I put an 10 ohm resistor to the series with an output ground?
This sounds like there's a mis-wire somewhere. A few things to check (please remove power first):
- Are the transformer secondaries paired correctly and are they connected to the correct terminals on the PCB?
- Are the input leads coming from the input jacks connected correctly? Signal lead to signal in, return lead to signal common?
- As has already been asked, are the input RCA (I presume) jacks isolated from the chassis?
Are you sure there is DC on your mains AC? Try removing the DC blocker circuit. The fewer unknowns in the equation, the more likely a solution can be found.
- Are the transformer secondaries paired correctly and are they connected to the correct terminals on the PCB?
- Are the input leads coming from the input jacks connected correctly? Signal lead to signal in, return lead to signal common?
- As has already been asked, are the input RCA (I presume) jacks isolated from the chassis?
Are you sure there is DC on your mains AC? Try removing the DC blocker circuit. The fewer unknowns in the equation, the more likely a solution can be found.
Secondaries of the transformer are paired correctly to the correct terminals. Input is also connected correctly. RCA are isolated from the chassis. I was manipulating with the input cables from the RCA connector leading to the PCB, and it seems like the hum depends also on their location within the space.... strange ....
I am sure there is a DC in the mains, toroid used to have periodical noise, after I attached DC filter, periodical noise has disappeared.
I am sure there is a DC in the mains, toroid used to have periodical noise, after I attached DC filter, periodical noise has disappeared.
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