EQUIPMENT FORUMS >> ZP3 / ZMC1,2,3 >> ZP3 hum

Message started by meteoor on 09/18/17 at 19:12:38

Title: ZP3 hum
Post by meteoor on 09/18/17 at 19:12:38

ZP3 phono stage, Torii Mk3 amp
I have a nagging problem with audible hum affected by the volume control on the Torii. It's not severe but noticeable at mid volume with no input signal.

The hum doesn't come from the amp or the phono stage until the interconnect cables are attached at one end to the phono stage. In other words, it happens when those wires are in free air and not connected to the turntable step-up transformer. It can't be the turntable, it doesn't seem like a ground loop. The amp and phono stage are dead quiet until input wires are connected to the phono stage. It happens when everything else near it is turned off or unplugged.

It leads me to believe that the interconnects are acting like an antennae but whether those cables are cheap, high quality, shielded or not - the effect is always the same!

Any ideas on this?
Thanks so much and my apologies if this has been answered before!

Title: Re: ZP3 hum
Post by Archie on 09/18/17 at 19:48:08


What you describe seems to be my issue as well.  Lately I've been contemplating sending my ZP3 back to Steve.  In the past I could live with my hum but with my 0.35mV cart the hum is bad at listening levels -- at least between tracks.  My chain is:  TT, ZMC1, ZP3, CSP3, ZMA.  Everything is very quiet except the ZP3.

I've tested my ZP3 with different TTs and Carts as well as a 1000 ohm resister as a dummy load.  Mine is dead quiet too, when nothing is connected to it.  Since hum is so subjective I've never been sure if this is what the ZP3 should do or if mine is particularly loud.

I'm interested to see if you come up with a solution.  I once thought I found a tube solution but tube rolling has no noticeable effect.

Or are you having a different issue?   :-/

Title: Re: ZP3 hum
Post by meteoor on 09/18/17 at 20:15:13

Thanks Archie. I'll post any developments. I'm not really familiar with the circuitry however, it does seem that the input cable itself is picking up signals and the ZP3 is amplifying them. What I don't understand is how the cable shielding can do much of anything unless it has a separate bond to earth.
Like you, I did every trouble shooting thing I could think of and finally came to this conclusion.

Title: Re: ZP3 hum
Post by meteoor on 09/18/17 at 20:21:41

Archie, have you tested yours with the input cables attached to the ZP3 but loose at the other end? ie. the TT not involved. In my situation, the hum is not audible until cables are connected at one end.

Title: Re: ZP3 hum
Post by Archie on 09/19/17 at 00:46:48

If I understand what you are saying, you have hum with just the cables attached but no source whereas without the cables it is quiet?  I assume the hum is there with the source connected -- otherwise you wouldn't care.

I'll test this tonight.  BTW, I have found almost no difference between shielded and unshielded cables (Decware brands and others).

Title: Re: ZP3 hum
Post by meteoor on 09/19/17 at 13:06:44

Archie, yes, I have the same level of hum when anything is connected to the ZP3 inputs, whether it be the TT/step-up or just the cables alone.
I just had a conversation with a cable expert and he said that testing for hum with "open" cables was invalid as cables, shielded or not, need to be connected at both ends. Having them open ended allows them to act like an antennae, he said.
Oddly though, the hum is exactly the same with open cables or with the TT connected. I've tried every grounding solution but I'm beginning to think that this hum, noticeable when the needle is lifted at moderate volume levels, is characteristic of the ZP3 - UNLESS, there is some grounding issue within the unit.

Title: Re: ZP3 hum
Post by Archie on 09/19/17 at 17:01:53

Yes, with my cables disconnected from the source, they act like an antenna and hum.  The hum is different than when connected but about the same intensity.

As far as whether the ZP3 has inherent hum, many on this Forum report that their ZP3 is quiet.  I do better with my 0.45 mV cart than my 0.35 MV cart since the output of the ZP3 is higher and I use less volume on my ZMA.  When I listen loud, the hum is clearly audible at 30 ft!  I can't say that it colors the music but I figure that it must.  I've also tried all kinds of grounding to no avail.  Unground things are order of magnitude worse.

Title: Re: ZP3 hum
Post by Steve Deckert on 09/20/17 at 01:01:45

The ZP3 actually has no residual hum, as evident when the turntable is disconnected from it.  The hum is coming from the turntable itself.

Below are some tips for chasing hum down to a benign level that I have pulled from other posts.

The Stereo
Switch the stereo to CD or AUX, and with nothing playing, turn the volume up to your normal listening position. If there is no hum now, then we can eliminate the stereo. If there is a hum, powersupply service is probably indicated.

The Phono Preamp
This will require one accessory, a shorting plug. You need to get a couple of standard RCA plugs from Radio Shack for instance, and you need to short the center pin to the outside ground. Now, in place of the turntable, plug the shorting plugs into the phono input. Now, set the stereo to phono and turn the volume up to your normal listening position. If there is no hum now, then we can eliminate the phono preamp or phono stage. If there is a hum, phono stage service is indicated.

The Turntable Wiring
This will require one accessory. a pair of alligator clips. You can also get these at RS. You need to clip together, I.E. short out the left and right cartridge pins. Do this on the back of the cartridge. You needn't remove the cartridge connections. Just connect one pair of clips between the red and green pins and another between the white and blue pins. Now, set the stereo to phono and turn the volume up to your normal listening position. If the hum is gone now, then we can eliminate the turntable wiring. If there is a hum, something is amiss with the turntable wiring. either a bad connection. or perhaps someone has changed the factory wires for some "fancy" wires that do not give sufficient shielding.

The Phono Cartridge
If you've come this far, then the problem must be the phono cartridge.
Most cartridges use hi permeability steel shells to protect the coils from electrical fields that can cause hum. However, not all companies use this system. As such , there are some cartridge brands that are sensitive to external electric fields and will hum. The only solution you have is to replace the offending cartridge. Or, if you love the sound and want to keep it, you will have to play with the location of the turntable and try to minimize hum. Sources of hum fields are power transformers in equipment, wiring in the walls, certain turntable drive motors. Experiment by listening to the hum while you move the tonearm through its arc(cued up!!) and see if you can find a null location that will give you the best results.

Line hum on the phono input is a very common problem, especially for the moving magnet cartridge. Moving coils are less susceptible due to their low impedance.

I am assuming your phono interconnect cable is good, and the plugs and jacks are free of oxidation.

The first thing to look for is the cartridge pin connection. Check for any oxidation or loose connectors. Try to carefully pull each one off the pin, then reconnect, which will at least temporarily break any oxidation. A common error is to incorrectly connect the hot leads to cartridge ground pins. Some cartridges have color coded pins to avoid this problem.

Wht L hot
Red R hot
blue L gnd
Grn R gnd

The cartridge L gnd pin is internally wired to the cartridge body. Make sure the ground wires (blue and green) are connected to the ground pins on the cartridge. Many MM cartridges will produce normal stereo sound when the ground and hots are flipped, but will hum. The next culprit could be "fancy" wiring inside the turntable. The turntable chassis and tone arm should be connected to a dedicated ground wire, and terminate to your pre-amp chassis. If the cartridge ground pins are bridged to the turntable chassis ground (connected together somewhere) then you may have a ground loop problem.

Also here a few other useful tips when everything is working properly, BTW there will always be at least a faint hum at max gain. It is unusual that you would have zero audible hum at full gain, much higher than normal listening level. At normal listening levels, there should be barely audible hum in an extremely quiet room, or none at all. That aside, the TT should be away from all wall warts, and the unsuspecting 12 volt halogen desk lamp, which will emit a 6o hz magnetic field into your cartridge. Also no fluorescent lights, no light dimmers, (notorious for inducing hum) no refrigerators or other heavy electric appliances with electric motors on the same branch circuit. Your turntable should be located away from every other stereo device.. if on a rack, leave an empty shelf space below the turntable.

And from turntablehumreduction.pdf a few more good tips;

1. Plug the amp, preamp, and turntable into the same outlet strip
Voltage differences between system components get amplified. You can minimize undesirable voltage differences by plugging all the components into the same outlet strip. That assures that all of their power is in phase, and that minimizes the voltage differences that result between the components, minimizing hum. This is the single most effective thing you can do to assure low noise.


2. Use good, low ground resistance cables with double shields for
phono inputs. (woven shield plus foil shield)
Even though we’ve done step one, there will still be currents induced onto the phono cable shield. Ohms law tells us that voltage equals current times resistance, so if we want to minimize the voltage, then we must minimize the resistance.
Double shields give us cables that block both hum and radio frequency interference.

3. Make sure the ground connections (the crowns) of the RCA jacks fit snugly at both the preamp and phono ends

4. Make sure that the ground connections are clean (no oxidation).
As in the previous step, freedom from noise means you need low resistance ground connections and wires between the cartridge and the preamp. The system is only as quiet as its noisiest element, so low resistance cables with high resistance contacts for the grounds owing to either a loose fit or connector oxidation will be noisy!

5. Use the shortest practical cable length to connect the phono to the
Long cables have more opportunities to pick up noise. Therefore, you’ll want to use the shortest cables that are practical for your setup.

6. Make a clean, low resistance connection between the turntable
ground and the preamp ground
Most turntables come with a separate green ground wire that should be run to a ground screw on the preamp. Make sure that the connection is tight and clean so it will have low resistance.

7. Keep the tonearm/cartridge away from large magnetic fields like
those generated by large transformers
Remember how much gain the system has at low frequencies? Recall also that the cartridge responds to small magnetic field changes generated by a moving stylus on the LP. External magnetic fields impinging on the cartridge from power equipment will generate hum. Sometimes the hum comes when the arm gets close to the turntable motor. Sometimes an adjacent component creates a magnetic field that creates hum. In such cases, your best defense against hum is to place distance between the source of the magnetic field (hum) and your phono cartridge.

8. Experiment with an additional green wire ground in strategic
An additional wire to a good ground can sometimes help the noise. Where to get a good ground? If the chassis of one component is grounded, then you might run a wire between that grounded chassis and the chassis of some component with a two-wire plug. This is a somewhat advanced skill, and if the idea makes you nervous at all, then don’t do it.

9. Experiment with reversing two-wire plugs
Some components with two-wire plugs are polarized, with a wide blade and a narrow blade. You can’t reverse them. However, a fair number of components have two-wire non-polarized plugs. This is especially true of vintage components. Reversing the way you plug a two-wire non-polarized plug into the power strip can significantly reduce system hum.

Hope that helps!


Title: Re: ZP3 hum
Post by meteoor on 09/20/17 at 01:14:00

Great! Thanks so much, that gives me a lot of working options! I'll follow up!

Title: Re: ZP3 hum
Post by Archie on 09/21/17 at 01:37:06

I did the Phono Preamp test (which is originally from the KAB site) and I got the same hum as when the TT is hooked up (no hum when nothing is hooked up).  I spoke with Steve and he thinks my ZP3 might be on the edge of noisy and with my low output MC cart it stands out.  I think after Decfest dust has cleared I'll send in my ZP3 for an overhaul.

Title: Re: ZP3 hum
Post by Archie on 11/18/17 at 18:57:09

I thought an update to my ZP3 hum situation was in order.  

I sent my ZP3 back to Steve for service and he repaired the input ground.  When I got it back I didn't have any improvement in hum over the speakers but the transformer hum I'd had since new was now gone!   :)  

I recently bought a new Technics 1200G TT (what a work of art and engineering!) and found that while testing with full gain, I could hear persistent noise when the TT was powered on and I had transient noise when the switches were activated.  I should mention that I have also had "motorboating" due to a small computer fan that I run behind my ZMA.  These two noise sources, however, were small compared to the hum/noise I got from my ZP3 (5% maybe) and were not at all audible even at high listening volumes.  The ZP3 hum was readily audible between tracks, even at moderate listening volumes.

Now some good news.

My new TT has a bigger motor than my previous TT and I thought that it might be causing interference since my TT ICs ran along the same path as the TT power cord.  I shifted the cables and my ZMC1 to another location and voila, end of hum and noise -- from everything!  Motorboating gone; TT noise gone; ZP3 hum (75%+) gone!   :D

I thought I'd run down all possibilities in the past.  I have shielded ICs at the TT  (I tried many kinds including Decware) but they made no real difference compared with unshielded ICs.  Where the problem seems to have been was TT IC proximity to power cords that powered devices with motors and proximity to the power outlets.  I can't get my ICs completely away from amplifier power cords since they run side by side in and out of the amps.  Amp power cords do not seem to be a problem though.  I also moved my ZMC1 away from motor power cords and the electrical outlets so this may also be a factor.  However, I had ZP3 noise before introducing a ZMC1 into the chain.

I still think there is a random component to trouble shooting noise but I hope my experience helps others navigate this problem.

I now can say I have a QUIET ZP3.  Steve's repair was necessary but moving cables was the final key.

EDIT:  It just occured to me that my ZP3 noise was happening even when the TT was turned off.  Now I'm thinking that TT IC proximity to the electrical outlets may have been the biggest factor with the noise.

Title: Re: ZP3 hum
Post by Martindfletcher on 11/29/17 at 13:56:18

My best results are from getting the zmc as far from the tone arm as possible.  At 12:00 volume no hum at listening position, very minor right next to speaker with 101db zu druids.   So I can concur as well.  The routing was a pain the ass drilling in my entertainment  center to route the cables in this way but way worth it.  Will take a pick next time I clean up the room, too sore after all the work.

Title: Re: ZP3 hum
Post by Archie on 11/29/17 at 16:32:25

I had the ZMC1 in different places in the past but none changed the hum.  I had given up on that aspect and figured I'd have to live with it.  For me it seems that getting my TT related ICs away from my electrical outlets was the key.  I really don't know for sure why, but moving the ICs 2 feet to the right did the trick!   :D

Title: Re: ZP3 hum
Post by Martindfletcher on 12/01/17 at 04:46:45

I should have also added I need as much distance ~12" as my table allows between the TT and amps at higher than pre extra beverage volumes.

Title: Re: ZP3 hum
Post by atacgene on 12/03/17 at 15:39:14

Hi all, I have exactly the same hum issue, but I suspect the cause in my case is somewhere from my SUT to the ZP3. I know my ZP3 has no hum on its own and also acceptable hum when no SUT is used, so a bit different from the case described by this author (Archie). However, I have noticed that the hum gets much louder if my power supply for the TT is too close to the SUT and so I moved that as far away as possible. (and hum persists even if I unplug that power supply).
Hum is gone if I disconnect the incoming interconnect from SUT to ZM3. (meaning unplug the interconnect from the input  RCA of ZM3. This interconnect is grounded, as without ground the hum his much worse.
But the hum gets worse if these interconnects when plugged in is moved closer to the huge transformer of the Zm3. The design of ZM3 is such that the interconnects is lying next to the tramsformer which can be a flawed design IMO (though I could be ignorant in this!) So hum is reduced if I try to bend the interconnect away from transformer. Eventually I placed a piece of aluminum cover (taken from one of my DIY SUT) between the interconnects and the transformer that really did reduce the hum by 15-20%.
So Archie, this may be a last resort you can try to eliminate the hum further.
For me I may need to find a better SUT (more professional than DIY and not vintage) I have ordered some thicker lead plates to do the shielding better and see if that helps. Lastly I may need to switch my already well shielded interconnect (from Yannis cable) to coaxial version.
Will see how this goes.

Title: Re: ZP3 hum
Post by atacgene on 12/03/17 at 15:42:26

Another solution is to use a fully balanced system from the SUT onwards:

But that requires entire system change which I don't think can be done with ZMP3 + my Torri Jr,, unless STEVE can do it!  See what he thinks  :D

Title: Re: ZP3 hum
Post by Archie on 12/03/17 at 19:26:35


I wonder if some 90 degree adaptors might help get your cables away from the ZP3 transformer.  Previous incarnations of the ZP3 had the RCAs in the front.  Steve moved them for some good reason which I don't remember.  From the start I've had noise from my transformer in the form of vibration that Steve recently fixed (faulty internal ground).  It was shortly after that that I rerouted my ICs and effectively got rid of the speaker hum.  They two could be somehow related and that could be why my earlier attempts to reduce hum by shifting equipment were unsuccessful.  I've tried putting aluminum foil around things as shielding but I never got any improvement.  I'm not sure lead is the right material for RFI shielding.  I'm fairly ignorant about electronics but you might need a grounded Faraday cage type shield to really be effective.

My hum reduction almost seems like magic to me in that a 2 ft move of my ICs brought it down to a non-issue.

Title: Re: ZP3 hum
Post by 4krow on 12/04/17 at 00:36:46

If I may, could I bump into this thread and say that, yes, lead is a great shield for RFI. With tongue in cheek, I am thinking that it would also shield against 60 cycle hum. Funny thing is that hum is usually eliminated where you might not expect, as was the case for moving the IC cables. I am chasing it in a piece of my equipment at the moment, and wouldn't be surprised to find that removing an earth ground or some such thing will be the cure.

Title: Re: ZP3 hum
Post by atacgene on 12/04/17 at 07:02:16

Yes, I think lead is great for shielding, as after all that is what they use in radiology to block all sorts of radiation.
And yes, I never thought of 90 deg RCA, thanks Archie!  I just ordered myself some, except that I cannot find high quality silver ones. Not sure how much interference  I would introduce by adding inferior RCAs along the chain.

Title: Re: ZP3 hum
Post by funch on 12/07/17 at 04:14:22

I'm pretty sure I have a pair of these around. I can check when I get back
home tomorrow.

Title: Re: ZP3 hum
Post by atacgene on 12/07/17 at 05:19:40

THanks, this silver set looks great, though I wonder if that would make much of difference, given the shot distance but then it does feel better using brass/cheap Chinese plugs. And I don't think Decware use silver RCAs either. I just put a pair of bras/gold plated ones from Ebay  90 deg RCA and it works really great! Archie is genius, such simple solution that I could not think of. Well the hum has dropped > 50% (?65%) then the additional lead shield is no longer making much difference, giving only about  5%-10% more benefit. So I suppose Decware should improve on the design of the location of the RCAs, maybe sticking them backwards away from the transformer like most amps do.  So now at listening level, the hum is not that obvious except in very quiet passages. Using my Decware Z stage to adjust the volume around also seem to help reduce the hum a bit too. Thanks guys for all your help!  In future switch to a more prof SUT and maybe using 1:40 step up (now at 1:30) may also help. I am using monocartridge now so will switch to a lower output cartridge later to see if the hum is still tolerable.

Title: Re: ZP3 hum
Post by Archie on 12/08/17 at 17:11:59


How were you using the lead?  I have some thin lead sheets that I might try.

Title: Re: ZP3 hum
Post by Archie on 12/08/17 at 23:57:21

I played around with the lead sheeting a little.  The sheet was about the size of a piece of paper.  With my gains way up (well beyond listening levels) so I could hear hum, I only got any effect when the sheet was held over the 3 front ZP3 tubes.  The lowering of hum was small and would never be heard at listening levels, as was the full gain hum.

I got no change when I put it between the ZP3 transformer and the ICs.

Edit:  The front tubes on my ZP3 are highly microphonic which would explain why sheiling over them cuts noise.  Does anyone know of a simple RF shield that might slip over these tubes and not obstruct heat flow?  I big piece of lead isn't exactly aesthetic.

Title: Re: ZP3 hum
Post by Archie on 12/18/17 at 21:37:42

I found what I think is a very worthwhile addition to my ZP3.  I found an IERC tube shield that cuts down on microphonics, heat and RFI.  Not bad for under 6 bucks a tube!

Here is a link giving some heat rejection information:

Here is a link to the eBay seller I bought from:

I bought enough for my CSP3 and ZMA too.  Those shields fit a bit tight since 9-pin tubes have varying diameters.  On these components I think heat rejection is the only advantage (if it's even an advantage.  Steve thought it could change the sound for good or ill since sound can change with tube heat.)

On my ZP3 I get subtle reduction in audible hum and huge micro-vibration reduction due to how the shield contacts the tube.  Without the shield if I touch the lead tube (with gains up to hear noise better) I get hum.  As I put the shield on the tube I also get hum.  However, as I seat the shield against the metal ZP3 top the hum stops and touching the shield doesn't cause hum.  Prior to these I used rubber o-rings that really did nothing.  These are Mil-Spec parts that are no longer manufactured.  The size needed for the 12AX7 and 12AU7 ZP3 tubes is:  TR6-6020B or MS24233-5. (same shield but different numbers)

Title: Re: ZP3 hum
Post by Jeff of Arabica on 12/19/17 at 04:56:30

Very interesting Archie.  Thanks for sharing this info/experience.  I had experimented with tube shields on the ZMA before with no noticeable benefit.  But, they were of a different, more traditional style tube shield.  These are intriguing being that they are military hardware, but most noteworthy is the hum change once fully seated and contacting the amp top plate.  I just ordered a set to play with myself.  Ill let you now how it goes.

EDIT:  Now that I think of it, I was pondering these Mapleshade tube shields awhile back because they grounded the tube to the amp top plate with a copper strip.  When I spoke to Steve about it at Decfest, he felt doing so might offer an audible benefit.

It seems these shields you've come across are essentially accomplishing the same task of damping and grounding the tube, but in a much cheaper, simpler, and less pretty manner.    

Title: Re: ZP3 hum
Post by Archie on 12/19/17 at 16:10:33

Steve also mentioned to me about making a simple aluminum shield (or buying one of the many available) and soldering a wire that runs to ground.  If the IERC didn't ground by contact I was considering attaching a wire.   The hum reduction is subtle.  It was as if there was a faint overlaying hum of a slightly different frequency that was eliminated.  At this point my hum is negligible anyway but I think any reduction is worthwhile.

The heat rejection of these shield is also impressive.  I think that's what they were designed for in the first place.

I agree that these shields don't seem to do anything (other than heat rejection) on my CSP3 or ZMA.  They do look kind of cool though.  I'd post a picture but I don't use any of the Net services, so I can't.  PM me with an email if you want to see them installed.

Title: Re: ZP3 hum
Post by atacgene on 12/22/17 at 05:15:48

For some strange reason I could not find a reply button on this forum so I could not reply.  Now I found it again!
Archie, my hum is also much reduced to acceptable  level but it is still there. Your magic trick of using the angled RCA works best. The lead shield I use also works, but the effect is not as much now. i still have 2 thick spare ones. My shied is about 3 pieces of 0.3mm pure lead stacked together. I don't know how else we can reduce the hum. Next I would use better shielded interconnects. The shielding of the tube seems interesting and maybe I will try that too.

I also read that a fully balanced SUT actually leads to 0 hum! It makes sense as fully balanced means all the noise signals are cancelled out.
Check out this guy's post:

This may be the ultimate step to do but then one needs to convert the phono amp to balanced as well. However, if one uses the ZBIT to connect the single ended interconnects to the phone, this may work, though I am not sure if the hum will still come back as unbalanced signal passes through the amp. However since the ZP3 does not have hum without SUT, I assume the hum is generated from the SUT, so it seems we just need a fully balanced SUT to get rid of most of the hum.
Has anyone tried fully balanced SUT/Phono?

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