Power Plant Premium Hum with Power Amp

I picked up a used Power Plant Premium (PPP) power regenerator. I have a Zen Mystery Amp (ZMA) from Decware http://www.decware.com/newsite/MYSTERY.html and the ZMA hums mechanically when it is plugged into the PPP. The hum seems to be coming from the transformers or the capacitors. There is no hum coming through the speakers. This tells me the ZMA is not happy and I stopped using the PPP. I have removed all inputs to the PPP except for the ZMA and I still get the hum. I removed all inputs to the ZMA and I still get the hum. I have swapped “premium” power cables with no effect. I have tried Multiwave on and off. No other unit in my system hums when connected that I can tell, but no other unit has such a beefy power supply. This is a tube amp with “a massive power supply with caps so large it is possible to eliminate the choke and any dropping resistors feeding the output stage”. I use a TrippLite i500 isolation transformer and I have no hum at all.

Anyone suggestions?

Welcome, normd!

My first thought as I started reading is that some amp transformers, especially in tube amps, do not like multiwave. But you already tried multiwave on and off.

My only other idea is to make sure the unit is supply the amp with 120V. My recollection is that once the PPP is warmed up the inboard display is fairly accurate. Voltage can be adjusted and perhaps someone played with it before.

Forum member lonson has a nice collection of wonderful Decware bits. My hope is he will see this and have a suggestion for you.

Thanks. I measured 118v on the output. Do I need to adjust it to 120? I do believe that someone has adjusted the PPP voltage before me. I connect with Lon on another board and he has not had any hum problems with the Regenerators and Decware amps.

I’ll call PSA tomorrow.

Some transformers are sensitive to voltage. It is possible this is causing the transformer hum.

It would be good to talk to PS Audio about adjusting the voltage. My recollection on the PPP that there is a little adjustment screw on the underside of the unit. You first adjust the display to match the incoming voltage, and then separately adjust the output to 120V. I do not recall the specifics of the procedure other than making sure the unit is warmed up and stable.

I’m sure PS Audio can talk you through it. All you need is a multi-meter and a small screwdriver/hex key.

Please let us know what you learn.

I hope this solves your issue.

I believe transformer hum can also be caused by DC voltage on the line. I don’t know how to test for that, or what might be causing it.

Exactly. It is likely DC voltage on the line, something the PPP was not able to correct for. Newer Power Plants do.

Thanks Paul! It seems my only options are to use my PPP for everything but my power amp, which defeats the purpose, or get a P5.

Is that about right?

Unfortunately, yes. Though if I understand the problem, it hums with or without the PPP. Or did I misunderstand? If not, there’s no harm and plenty of benefit keeping it attached to the PPP.

I have absolutely no hum from the power amp when it is plugged into the wall or an isolation transformer (i500) - dead quiet. The amp only hums when plugged into the PPP, even with nothing else attached.

I have reports from others that are using the P5 with my amp successfully, but now I am wary of getting a P5 since I may have a DC voltage problem.

It’s puzzling Norm, as I reported on the Decware forums I’ve used a P300, a Power Plant Premier, a P5 and a P10 with Decware amps (though not the Zen Mystery Amp) and components and had no hum issues. I guess Paul may be right. The only time I had a hum issue was traced back to the cable tv coaxial cable and was only on the input I used in my DAC for the DVR; I fixed that with an inline filter (which I now don’t have to use when Time Warner became Spectrum and some neighborhood repairs were made to transformers and lines).

The Zen Mystery Amp has MASSIVE power supply capacitors, I mean MASSIVE. Steve Deckert, the designer/builder says this in conjunction with the voltage regulation tubes removes the need for line conditioning or possibly regeneration. Lonely Raven who is on this forum and the Decware forum reports that he hears no to very very little difference with his Zen Mystery Amp plugged into the wall or plugged into his P10. So perhaps you’re not missing much at all if you plug the amp into the wall and use the Premier for all other components. Do you hear improvement (around/outside of the hum) to the amp with the PPP?

@normd if your amplifier doesn’t hum when plugged directly in to a power socket then you do not have a ‘dc’ on mains issue.


I continue to encourage adjusting the voltage.

Many thanks for all the input and responses. This is quite an active and helpful group. Pretty cool to have Paul himself respond!

I can adjust the output voltage to 120V using the pot on the bottom. The display then reads 122V. The service manual has an adjustment to calibrate the display to the input and output voltages. Unfortunately, the adjustments do not work. Perusing their forum and confirmed by Jeremy, the PPP is in failure mode. See the link below. I still have the hum, which is another indication.


I am not going to spend $500 to get it fixed on top of the purchase price.

Based on this, I have contacted the seller for a refund and I am on the lookout for a P5.

Thanks for the update. An unfortunate end result, but at least you can return the unit and move on. The P5 is a large improvement over the PPP so this is another plus.

Sorry to read that result Norm, but now at least you know.

Bummer. Since it is in failure mode I wonder if the PPP itself could be adding DC to the line to account for the hum. I would have thought it would just pass the AC unchanged but who knows.

Possible, but this seems unlikely. Multiwave can cause some transformers to hum, but it seems equally implausible that the unit would invoke multiwave in failure mode.

Whatever the cause, it is good in the case as it encouraged Norm to investigate and he discovered the problem with his unit.

So far the seller refuses to accept that there is a problem with the PPP since it allegedly worked fine in his system. However, with the hum problem and the fact that I cannot calibrate the display output voltage reading, I am convinced something is not right with the unit. I have no hum when my amp is plugged into the wall socket. I only have the hum when the amp is plugged into the PPP. PSA Service is perplexed. I refuse to use the unit in my system.

At the sellers request I am sending the PPP to PSA for diagnostics. This seems like a waste of time and energy on my part. This should not be my problem.

I am not going to invest any more money in this aged unit. I opted to use it as a trade in on a new P5.

Thanks to everyone for the input and advise.