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Zkit Transformer Hum (Read 2054 times)

zeke

Verified Member

Posts: 12

Zkit Transformer Hum
01/18/21 at 22:56:46

Not entirely new but I read through the other posts and my problem looks a little different. My power transformer is humming. It's the Edcor Xpwr008. I've built several Zen amps, some on Steve's circuit board and others P to P. This one is on the circuit board which makes it that much more perplexing since the chances of making an error are greatly reduced.

In any case, the power transformer hums. The unit play but very low. If I turn it up, it distorts. The circuit board is connected to the star ground lug connected to one of the screws holding the power transformer. The ground from the ieec connector also goes to that lug. Speaker binding posts are insulated from the chassis. The inputs show 95K ohms to ground (not sure if that's good) from the signal wire. The pots are touching the aluminum chassis and they show a ground connection and also by a wire to the circuit board. One last item, all the transformers are insulated from the chassis by small rubber washers to curb vibration. The power xformer is just vibrating away...but what is making it do that?

I've been over this several times and am not seeing any physical problems. Voltage from the power transformer is 640 vac with 320vac on each side, as it should be. Filament voltage is 7.3 vac. The voltage at all the checkpoints is within the stated tolerances. I'm at a loss. If anyone has any ideas I'd be most grateful.

PS: Steve Hoffman's review of the Anniversary Zen was awesome. Great Job Mr. Deckert.

Tnx for your help.....

IMG_4643.jpg

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bobc

Senior Member

Posts: 64

Re: Zkit Transformer Hum
Reply #1 - 01/19/21 at 13:22:56

Tough one. I can't see from the picture, but from the wires, it looks like you are using the Edcor OT too. Maybe too obvious, but Is that UL tap on the primary of the OT connected to anything? It shouldn't be.

The transformer has plenty of current capacity for the application.

90% of the time for me, it comes down to a solder joint!

Good luck. Maybe try to check your OT?

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JBzen

Seasoned Member

Posts: 1376

Re: Zkit Transformer Hum
Reply #2 - 01/20/21 at 12:09:45

Did you try a different input tube? Sometimes new tubes can be faulty.

Did you orientate the capacitors shield leads towards ground side of the circuits? How are the OT orientated? 90 degree rotation of one? If done this way, both of these can help eliminate transformer hum.

Just some of my thoughts.

Seems like you had success in the past building. I also did but it can be real frustrating when things just don't work out right. I know! Sometimes walking away giving it a break then return with a fresh clean slate helps in capturing that ah-ha moment.

HTH

John

AMC CD8b>XO3>Cambridge CXN2>ZDAC>ZBOX>braided silver/occ> Zrock2>CSP2+>SE84 milflex copper 25th>9AWG silver/copper braid>lii Crystal 10 in Huijgen cabinets. Ortofon 2M Black>JVC QL-F4/Otari MX5050B2>ZP3. Isolation. AC filtering. Room treatment.

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zeke

Verified Member

Posts: 12

Re: Zkit Transformer Hum
Reply #3 - 01/23/21 at 15:48:22

Thank you all for your replies. I went over this project multiple times and had a friend over with a fresh set of eyes to take a look....nothing stood out. Finally, I disconnected the power transformer from the board, both HV and Filament, and turned it on...it still hums. I have been buying transformers from Edcor for over 7 years and have never had this. I happen to have another XPWR008 in the works with them and when it arrives I'll hook it up on the bench and see what I get. The output on the HV is 40 volts over spec but there must be some other factor (insulation, winding, ?) that is causing this to happen. I'll let everyone know how it turns out.

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zeke Verified Member Posts: 12	Re: Zkit Transformer Hum Reply #4 - 01/27/21 at 20:13:58 Chatted with Brian at Edcor...xformer went back today for evaluation.
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