It often gets louder when it warms up. It takes some time for the bias current to reach its maximum.
I was able to completely get rid of mechanical hum from the toriods in my M2X mono blocks. I have a huge DC-blocker at mains but it was not that which did the trick. The trick was to ensure 100% symmetry at the secondary. So sinus at secondary has exactly same positive and negative "half-waves". One of the thinks that did it was to ensure the two feed forward voltage drops over the rectifier diodes in positive and negative half has exactly same voltage drop. My theory is that DC in toroid can also be introduced at secondary if there is a bit of asymmetry. I also changed toriods to some very expensive ones but it was never the toriods which was the problem. I am sure I can get all toriods to hum 🙂
I was able to completely get rid of mechanical hum from the toriods in my M2X mono blocks. I have a huge DC-blocker at mains but it was not that which did the trick. The trick was to ensure 100% symmetry at the secondary. So sinus at secondary has exactly same positive and negative "half-waves". One of the thinks that did it was to ensure the two feed forward voltage drops over the rectifier diodes in positive and negative half has exactly same voltage drop. My theory is that DC in toroid can also be introduced at secondary if there is a bit of asymmetry. I also changed toriods to some very expensive ones but it was never the toriods which was the problem. I am sure I can get all toriods to hum 🙂
My Dealer [Audio Emotion in Scotland] wants me to test the voltage of my mains. How do I do that?
Could you elobarate/explain that a bit closer? Especially the part about equal voltage drop. Drop across diodes yes, but how did you adjust?
Andy Cine, just so you know when you report back to your dealer, it’s normal to have some fluctuation on the main. Here 110 to 125v is considered « normal » where the standard is 120v. Your amp should perform perfectly fine even if the main is not spot on.
Would this do the trick?
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You could also use one of these - gives you voltage and also power:
Power meter
even tested by clive:
Clive
Of course you could use a Digital Multimeter and with some additional circuitry then also measure the DC-Offset but that is probably too dangerous, if you are new to this.
Power meter
even tested by clive:
Clive
Of course you could use a Digital Multimeter and with some additional circuitry then also measure the DC-Offset but that is probably too dangerous, if you are new to this.
Hi Guys, the latest update is that my dealer Audio Emotion [Scotland], is sending me a multimeter next week to check my mains voltage. They tell me that Pass Labs are "sensitive to this". This sure is a big hassle before I can enjoy my new amp!
I'm being told to set the Multimeter to "AC500" to test my mains voltage. If I don't fry myself, I'll continue this sorry saga to the bitter end.
Thank you. I shall ask my dealer if this would be OK. It would be easier for me than the multimeter they want to send me and probably a lot safer for me too!
It was a long "story". I will try to make it short.
For mains 230 VAC I used a PS-Audio power plant so I had a regulated pure sinus at 230.8 VAC. Then I could easy measure the changes I made to the PSU at the secondary of the transformer. I used the DIY Store universal PSU PCB. I tried SIC diodes (those had much too much feed forward voltage that were very temp dependent). I also tried standard 35A bridges. What did the trick was to use old type Schottky rectifier diodes. I used IXYS DSSK80-0045B. Those are double diodes and with universal PCB they will be paralleled by the layout. Those have very low feed forward voltage. I guess two in parallel will give about 0.1V. First I had an idea to "pair them" but ended up just try it and it turned out to be a success. I got equal size positive and negative sinus halfwaves at secondary. After this the toriods where silent. Also my -+ rails vent from -+ 21.x V to -+23.x and within 0.1V so very symmetric. I also removed the NTC at primary to avoid anything that will change with temperature. The diodes are "overkill" but worked in my case. Just using the power plant did not remove the mechanical hum at all. I think why it worked with the diodes without pairing them is that even a 10% difference in feed forward voltage would not give that much difference. Or maybe I was just lucky 🙂
It could be interesting to know if the theory is correct that by creating asymmetry at secondary then DC is introduced at secondary windings and can create mechanical hum by the forces in the core/windings. It would be easy to try to introduce 4 serial diodes in one half and keep the usual two to rectify the other half and then pull a lot of current.
Boyz, you're cluttering thread with technical things
it isn't about that
it isn't about that
Yes, it was a bit cluttered by technical things.
My suggesting would be to bring the amps to the dealer. Plug it in. Wait for warm-up of the amps. If they hum then ask the dealer to fix it.
To measure the mains "at home" using a multi-meter (and not looking at the curve form with scope) will give nothing. It will just give the dealer an excuse to blame the mains.
My suggesting would be to bring the amps to the dealer. Plug it in. Wait for warm-up of the amps. If they hum then ask the dealer to fix it.
To measure the mains "at home" using a multi-meter (and not looking at the curve form with scope) will give nothing. It will just give the dealer an excuse to blame the mains.
Update: Multimeter readings of my UK mains varied between 239v - 243v. My Dealer [Audio Emotion, Scotland], having very kindly sent me the multimeter, is now in the process of sending me a Habotest Socket Tester. Will I ever be able to get my Pass Labs INT-25 working as it should? When I worked in Hi-Fi Retail, I could never imagine putting a customer through this torture. Music should be something that brings joy and peace. I've had four months of madness!
The Dealer will keep you busy until the warranty is expired 🙂