PH16X Hum/Buzz

I love my PH16X (built by Roy Mottram) but at normal listening levels I can hear a pronounced 60Hz hum combined with a higher frequency buzz.

The first thing I tried was switching out all four 6922’s and switching out the 12x4 for all new tubes. The noise still persists.

Next I tried measuring a few voltages. F+ to F- was 12.65V and B+ was 176V. That’s within a 1% difference so I doubt Roy’s wiring is wrong. However with the unit open I noticed the transformer itself seemed to be humming and I could also feel the chassis subtlety vibrating. I’ve been told this could be DC offset on my AC lines, but I have no way to test this as far as I know.

Another thing to note is that if I turn on my PH16X the hum only starts once the unit has warmed up and not immediately after being switched on.

What could cause this noise? I love the sound of Roy’s products but I can’t tolerate the hum through the speakers!

Has this noise been there from the beginning, or has it recently started? If you haven't done so already I suggest you temporarily disconnect the phono input to see if the hum goes. The problem may be an earth loop somewhere. Check that the turntable is connected to the earth lug on the chassis, if it is try removing it to see if that helps.
Finally, having eliminated any external culprits, and the problem is related to the PH16 itself, I suggest sending an email to Roy for his advice.

I tried disconnecting the phono input and the hum is still present. I also tried it with and without the ground wire connected.

Does anybody know if an isolation transformer will help?? (Humdinger)

I think  you need to establish the cause of the hum before considering an isolation transformer.

What preamp are you feeding the PH16 into?
I ask because I have seen several posts where people have been using their PH16's directly into a power amp and that would cause the noise you describe.

I feed my PH16 into an SP14 preamp which is connected to a tube power amp and it is completely hum free.

I’m feeding it into an integrated SS amp

Edit: I also tried shorting my the inputs (as per another forum post I read) on my PH16 and the hum persists.

OK that's fine. Then I would try a ground loop isolator. They are inexpensive and might work if a ground loop is the problem

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If the loop is internal to the PH16 send a photo to Roy and he might be able to identify it, but as he assembled it I would be surprised if that was the case.
If a Ground Loop Isolator works and you can't find the source of the hum loop, then maybe consider an upgrade to a Humdinger. Isolators like the one above cost less than $10, so worth a try.

Let me see if I understand the problem as presented:

The SP16 is a phono-head-amp designed to provide the first stage of pre-amplification to a standard magnetic cartridge mounted on a conventional turntable. In turn, it is being fed into a conventional solid-state integrated amp (Make/Model?).  With the 16 turned OFF, but the amp turned ON, there is no perceivable hum or other artifacts.  When the 16 is turned ON, coincidental with the tubes reaching operating temperature, there is a 60 hz hum with an additional higher frequency component.  There is, also, a perceived hum from the mains transformer, and a perceived vibration of the 16 chassis. This hum persists as long as the 16 is on, whether there is signal or not. If this is a correct summary, then I have the following suggestions. They are diagnostic, and may seem a bit odd on first-look, but they have worked for me in the past, more than once. For these suggestions, you will need a GOOD VOM, something auto-ranging and something capable of measuring AC over DC and DC over AC.

   a) With your VOM set on AC volts, measure from the 16 chassis to a good ground – plugged in and on, but NOT connected to the integrated amp. What you are looking for is a hot-chassis, indicative of some failure or short within the amp itself. Anything more than a very few millivolts is too many. Sources of leakage could be a bad transformer, leaking cap or other component to the chassis-ground, bad death-caps and so forth. Also something as simple as a pinched wire.
   b) Do the same with the other components in the system.
   c) It is likely that the turntable has a ground wire. That is NOT a conventional mains-ground, but a means to drain static charge from the cartridge (a small piece of plastic) caused by the vinyl record (a much large piece of plastic) rotating below it. If it is connected to a conventional ground, any potential on that ground will be amplified, first by the SP, and then by the amp. Connect it to either headshell on the RCA plugs from the TT. This will bleed the static into the SP, and eliminate a source of hum.
   d) DC Offset:  A real issue, if exceedingly rare in the US, as there are multiple system grounds between-and-including the end-user and the Utility. This is much more common in Europe, where the system ground may be a considerable distance from the end-user. But in any case: With your VOM set on DC volts, measure at the wall plate. Any DC component, again, of more than a few mv, if any at all, and you have a problem. Please make sure your VOM is designed for this test. If you do have DC volts on your AC line, the sovereign cure is an isolation transformer. That will remove any-and-all DC offset. Nor is there any reason NOT to install one in any case, other than the expense.
  e) A hum-loop isolator should not be necessary in most cases. Except that some ‘modern’ amplifiers not designed with on-board phono stages are also not designed for the isolated ground required by a phono-head-amp (see c) above).  
  f) Lastly – I do not know if the 16 has a tube rectifier. But, if it does, 60 hz hum *typically* is indicative of a faulty/failing rectifier.

Let us know what transpires, and best of luck with it!

For future reference my amp is the Atoll IN100se integrated amp

a) Chassis to ground shows 0.001VAC. I measured with the turntable (plus TT ground wire connected) and integrated amp disconnected.

b)Chassis to ground of my amp shows 0.001VAC as well

c)I’m using a VPI Prime Turntable and I have a wire connected from the ground lug of the tonearm box to the ground lug on the PH16.

d) Did some measurement on my outlet.
Neutral to ground: 0.300VAC (Just stray voltage?)
Hot to ground: 123.4VAC
So the mains voltage in my area seems to be a bit high. Any comments on this?
Hot to ground: 4.4mV DC
The DC component is small.

e) I can email Atoll about how their amp is designed in regards to that. This amp does not come with a phono input

f) I picked up a spare 12x4 rectifier tube and it made no difference

( Connect it to either hadshell on the RCA plugs from the TT.)

PeterW, OP ; let me jump in again. Peter, exactly where are you talking here ? I don't understand AGAIN... Thx pal, Dale

Dale Stevens wrote:( Connect it to either hadshell on the RCA plugs from the TT.)

PeterW, OP ; let me jump in again.  Peter, exactly where are you talking here ? I don't understand AGAIN...  Thx pal,  Dale

Dale:

As follows.
a) remove spade lug on TT ground wire.
b) strip end and tin with solder.
c) solder to the left signal headshell from the TT.

Done.

thermionicvinyl has said he tried disconnecting and shorting the phono inputs and the hum persists so I think we can eliminate the turntable/cartridge from the equation.

I had a look at a build in progress page on the VTA website of the PH16X.  When the top plate is lowered in place, the transformers appear to be only inches away from the sensitive high gain stage with no screening from the transformers. When I built my non X version of the PH16 I partitioned the power supply and transformers from the phono preamp board. For good measure I lined this partition with mumetal sheeting and the amp is totally quiet even when using a moving coil cart via inbuilt SU transformers. The PH16X tubes being outside on top will have some screening from the transformers by the top plate, but a way of testing if this is the source of the problem here is to separate the top plate and enclosure as in the photo and run your amps and see.
Use something more secure than a pencil

Another thing in this photo, at least at this stage in the construction, is the lack of a good electrical connection between the top plate and enclosure. Some paint needs to be scraped away from one screw hole and washer, lock washer, plus screw used to make a good connection. Check your case thermionicvinyl.

The PH16/16X are a good phono preamps and I haven't heard of any other hum issues, but the things I've mentioned above may be worth checking out.

A few things:
   a) A typical MM cartridge makes between 3 & 5 mv. The typical MC cartridge makes between 0.08 & 1.5 mv. If your 4.4 mv DC component, if chopped (very likely) leaks back onto the cartridge via the misplaced ground you will get your persistent hum, and any other artifacts along for the ride.
   b) That turntable ground is not a traditional mains ground, but a static bleed ground – and should be isolated from the mains ground. Hence the suggestion that it be connected to one-or-another headshell from the shielded signal wires from the TT. This will bleed the static charge, but not pick up any mains-related contamination going the other way.
   c) And, of course, mijohn has a valid point. However, one would think that if this were an issue, shielding the power-supply would be an OEM option, not something that had to be done after-the-fact.
   d) If you have the means and methods to try out an isolation transformer, that would eliminate any DC offset, however small. There is no reason not to do so, other than the expense. And if the 16 goes quiet – then your problems are solved.
   e) I am not so sure your integrated amp (looks like a solid device) is a contributing factor unless its internal grounding system is quite unusual. Noting that it is of French origin, that would be no surprise as Euro Utility grounds may be hundreds of meters to several kilometers from the end-user. Emailing them on the concern may give you an answer that has escaped the rest of us.

As always, best of luck with it!

Thermionic
send me an email ( info@tubes4hifi.com ) so we can communicate directly.
Is this hum new or was it there from the beginning?
I won't send out equipment that isnt' dead quiet in my setup.
Hum is usually 120Hz from power supply, or 60Hz from ground loop,
or mechanical vibration from the transformers.
Isolation transformers are known to help if the problem is some strange ground loop between components that can't otherwise be found,
but best practice is of course to plug ALL components into the SAME AC power outlet.
Also, with a DVM set to ohms, check to make sure the top plate has a direct connection (dead short) to earth ground thru the AC input filter.

Hi Roy,
If I recall correctly the hum was always present but it’s more obvious now with my new amp. I think it’s because it has a gain stage. I took a look inside in case anything was loose and I as far as I can tell it’s good. It sounds closer to 60Hz but I can break out RTA if need be. Both components are plugged into the same outlet. Top plate has a solid connection to earth.

I measured my mains voltage (to see if it fluctuates over time) and I got 124.0VAC with a 4.3mVDC component. So it looks like the voltage is consistently high in my area. Are your preamp tolerant of high mains voltage?

I sent an email to Atoll and i’ll update everyone when they reply.

Just picked up an ac isolation transformer today. It’s got two isolated outlets so I plugged the PH16 and the Atoll into both. Hum is still present and no reduction in its volume.

My only guess is my high line voltage is the culprit (would require a variac) or there is something wrong with the phono stage itself. I measured my D3 voltage to be somewhere around 6.9VDC. I don’t know if that’s within the range or not.

I also noticed the power supply board itself humming and not so much the transformers. What could this indicate?

I don’t think your line voltage is the problem. As I understand it, utilities are required to supply you with voltage that doesn’t vary from 120 VAC by more than 5% either way. So that would mean your voltage should be between 114 and 126 VAC. One would hope that all modern domestic electronic equipment, including the PH16, has been designed to cope with that range.

The mechanical humming you’re hearing from the board is more than likely from the transformer being transmitted through the chassis to the PCB as they are quite close to each other.

If your PH16 were mine and I hadn’t found a cause for a hum-loop I would consider doing several things:

1) Test the PH16 with another integrated or preamplifier and if the problem remains move on to steps 2 - 4
2) Replace the two filter caps both labeled C10 on the power supply board.
3) Find a suitable size aluminum box to shield the transformers, or construct a  shield from MU metal sheet.
4) Make sure that I had a really good electrical bond between top plate and enclosure.

But before I did the above I would email the designer and builder of this amp, Roy Mottram, for his ideas on how to fix the problem.

Finding the source of a hum can be a frustrating business, so good luck in your quest!

Let's try to get back to basics:

60 hz hum generally indicates a failing rectifier, or some direct source of mains AC or some component of chopped DC at 60 hz, Any DC-offset should have been eliminated by the isolation transformer. That you have two 12X4s does not necessarily eliminate them from consideration. Do you have the means to test them properly?

120 hz hum generally indicates failing/inadequate filtration (filter caps). Not many of us can tell the difference off-hand. If your VOM has a counter function, or if you have a scope, try determining *FOR SURE* what you have. If, in fact, you have 120 hz hum, start with the filter caps. Your mechanical artifacts are certainly indicative of an overloaded power transformer - which would be the case with partially shorted caps.

Lastly, have you reconfigured the TT ground as suggested?

Examples of 60 Hz and 120 Hz hum/tones.
If it sounds more like 120 Hz I'd definitely replace the filter caps (both labeled C10), as I suggested in step 2 above.
But as Peter says sometimes its hard to tell the difference, so I would replace them anyway.

thermionic and I have been emailing to narrow it down, but if his D3 voltage is low then likely R27 is too large.
D3 voltage needs to be above 20vdc for the HV regulator to take out the hum.

It's good to know you're on the case Roy. I'd be interested to Know what you find.

D3 is indeed low.

Just ordered some high quality power resistors. Hopefully they solve the problem!

Has R27 (1K) drifted off value or has Roy recommended lowering the resistance to get D3 above 20vdc? Has he suggested several values to try?
R27 @ 1K is working well in my PH16, but I would be interested to know what value you settle on. I agree, hopefully this fixes the problem!

The SP10 and SP12 Preamp’s the Roy built that I bought from him both had hum issues. Nothing Roy suggested helped. The SP10 was traded back to Roy in an upgrade to the SP12. I ended up selling the SP12 on AudioKarma the buyer ended up sending it back to Roy and Roy’s excuse was ‘I don’t know what the seller did to it to make it hum when he couldn’t solve the him issue. I didn’t build the preamp. Roy did. The hum wasn’t my fault. I’d never buy a preamp from Roy again.

the PH16 and PH16-X use different power transformers, so the value of R27 is usually either 1K or 2.2K, depending.
R27 is both an RC filter and a voltage drop for excess B+, so it's value is tailored depending on users AC input and power tranformers to get the correct voltage to the B+ regulator.
Seems DogStar had an unusual problem with his system that I couldn't duplicate here, and extremely few buyers have that problem, but it does happen.
His preamp was under warranty for a year, so I would have fixed it for him for free if he bought it assembled from me. I only get 2-3 preamps back a year for service out of hundreds sold,
and about half the time the problem turns out to be a local problem such as house ground or faulty interconnects.
There always seems to be a very few with problems and of course they have the loudest voices, on the forum we discuss more problems than posting great reviews,
those who wound up happy with super good experience. mijohn has a more typical experience, zero hum.
Let's keep the forum for use to help, not to rant complaints, you can send those direct to me if need to vent.