Phono 3 / RFI problems

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eagwok33
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Phono 3 / RFI problems

Unread post by eagwok33 » Sun Feb 10, 2019 10:32 pm

When I purchased the Phono 3 last year (I use a phono 3 with one BBPSU), I had it set by Richard to MC mode.

Originally, I bought a phono 2 mm version in late 2017, which I used with my BBPSU and a dedicated MC step-up transformer. The music this MM version made was fantastic to my ears! :-). (Read my report from Dec. 2017 in the NVA review section on page 17). RFI-noise was not discernible with the MM version, there was only a slight hum detectable as I listen with a high efficient horn ls. I could reduce this hum by floating (no earth connection) the BBPSU. (The only thing this MM version didn't like was a mobile phone in the listening room as this caused some interference noise through my speakers. But I never have my mobile phone with me, when I listen to music - so no problem... :))

Then I had my Phono 2 set to MC by Richard and on the way back to Austria the case of the Phono 2 MC was damaged during transport. Hooked up to my system it sounded very good, but there was RFI-noise heard over my horn ls-system. Richard immediately offered to take the phono 2 back as apparently the transport damage caused some internal problems, too.) As at that time, also the phono 3 was newly available, I decided to upgrade my returned Phono 2 to a Phono 3 MC version set for usage with one BBPSU only.

This Phono 3 MC version made it safe to my house and the musical enjoyment started again (see my feedback in the review section on Page 20). The only negative was - as before with the Phono 2 MC - RFI-noise with the Phono 3 MC version connected to my system over the horn speakers. The RFI-noise was at that time less audible then with the Phono 2. This noise became a bit stronger over time (sometimes it is better, sometimes it's worse) and in the meantime the musical pleasure I had at the beginning and especially with the Phono 2 set to MM is no longer there.

It seems to me that something isn’t 100% right with my Phono 3 MC. I wonder if due to my 98dB efficient speakers, the super minimalistic design Richard uses for his phono stages would be better served with a Phono 3 set to MM-mode and dedicated step-up than set to MC-mode?

Has someone here in the forum with high sensitive speakers encountered similar RFI-noise problems with a NVA phono stage in MC mode?

My other two phono stages (Graham Slee Revelation and pimped EAR 834) don't have such a RFI problem with the same MC cartridges connected (Lyra Skala and AT OCC30) through my Lenco L75 / Schick 12" tonearm combo.

I tend to ask Richard to have a look at the phono 3 unit and return it for inspection.

Question to Richard:
Can there be something done to get the phono 3 to be less prone to RFI-noise ithout sacrificing the musical qualities?

Feedback highly appreciated!

Thanks,
Norbert
Norbert

Tubes and Vinyl rule, Music rocks! :icon-wink:

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Dr Bunsen Honeydew
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Re: Phono 3 / RFI problems

Unread post by Dr Bunsen Honeydew » Sun Feb 10, 2019 10:47 pm

SPL is SPL - too efficient, turn it down. The problem is voltage gain and interference. With MM there is less voltage gain so a very low background RF is not audible. MC has about 10 times as much voltage gain so it is showing up the RF.

Two cures 1 stop the thing that is giving you the RF, 2 cure or comp (filter) the RF. Try ferrite rings, or I can fit a 1000pf cap on the input instead of 470pf. Fit a BMU (stops it if it is mains borne), even changing mains socket or equipment position can change this pick up.

Finally if all else fails go back to MM, there are some very good ones, including high output MC (same gain as MM).

EDIT - and one I forgot. A wire from the outside (earth side) of a phono plug wired to a mains plug with a earth (only wire to earth terminal) plug in where you think you have a good earthed socket, or attach it to a cold water pipe (metal to metal). Plug the phono plug into a spare pre amp input or output.

eagwok33
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Re: Phono 3 / RFI problems

Unread post by eagwok33 » Mon Feb 11, 2019 1:41 pm

Thank you Richard for your response and tips.
Dr Bunsen Honeydew wrote:
Sun Feb 10, 2019 10:47 pm

Two cures 1 stop the thing that is giving you the RF, 2 cure or comp (filter) the RF. Try ferrite rings, or I can fit a 1000pf cap on the input instead of 470pf. Fit a BMU (stops it if it is mains borne), even changing mains socket or equipment position can change this pick up.

Finally if all else fails go back to MM, there are some very good ones, including high output MC (same gain as MM).
ad cure 1: Not easy to find the thing that is giving me the RF. I had the earth connection in our rented apartment checked and no fault could be found.
A friend brought his new Graham Slee Accession MC stage lately to my house (60dB gain for MC usage) and this one had no detectable RFI problems.
ad cure 2: I will try to connect the BBPSU to a different wall outlet in my room. Ferrite rings I can try, too. Should I place them best over the power cable of the BBPSU (near the BBPSU) or the two power cables connected to the Phono 3?

Regarding BMU: It doesn't sound like a mains born problem as no other equipment shows this RFI-noise with volume of preamp fully up.

To go back to MM is definitely fine with me. I consider this currently and come back to you if the change of power socket and ferrite rings don't work.

Regarding your separate earth cable tip: I tried this out - as you told me about this trick some time ago - and connected it to different wall sockets in my room and the earth side of cinch socket on preamp without success with regard to the RFI-noise.
Norbert

Tubes and Vinyl rule, Music rocks! :icon-wink:

CaterhamKev
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Re: Phono 3 / RFI problems

Unread post by CaterhamKev » Mon Feb 11, 2019 1:50 pm

I thought the answer is obvious? You need a grounding box.
Of course I am joking....

Is there a tasteful/simple way to add a bit of an RFI shield to the outside of the box?

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savvypaul
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Re: Phono 3 / RFI problems

Unread post by savvypaul » Mon Feb 11, 2019 2:07 pm

Constant hum or a flicking / chuffing noise?
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Daniel Quinn
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Re: Phono 3 / RFI problems

Unread post by Daniel Quinn » Mon Feb 11, 2019 2:34 pm

Do you have a sky q box ?

if so try turning this off at the mains.

eagwok33
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Re: Phono 3 / RFI problems

Unread post by eagwok33 » Mon Feb 11, 2019 3:19 pm

CaterhamKev wrote:
Mon Feb 11, 2019 1:50 pm
I thought the answer is obvious? You need a grounding box.
Of course I am joking....
Indeed... :) nah, no money for such questionable gadgets...
CaterhamKev wrote:
Mon Feb 11, 2019 1:50 pm
Is there a tasteful/simple way to add a bit of an RFI shield to the outside of the box?
Thanks for the tip Kev!
Thought about that, but my experience with such RFI shields is unfortunately that it is degrading the music in most cases. And often not the nicest to look at. Will give it another thought...
Norbert

Tubes and Vinyl rule, Music rocks! :icon-wink:

eagwok33
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Re: Phono 3 / RFI problems

Unread post by eagwok33 » Mon Feb 11, 2019 3:25 pm

savvypaul wrote:
Mon Feb 11, 2019 2:07 pm
Constant hum or a flicking / chuffing noise?
Thanks Paul!
Not a constant hum. It's more like a faint radio interference, but not that strong that you hear someone talk or hear faint music. Don't know if this can be described as "flicking / chuffing noise".
Norbert

Tubes and Vinyl rule, Music rocks! :icon-wink:

eagwok33
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Joined: Wed Nov 01, 2017 9:18 pm
Austria

Re: Phono 3 / RFI problems

Unread post by eagwok33 » Mon Feb 11, 2019 3:28 pm

Daniel Quinn wrote:
Mon Feb 11, 2019 2:34 pm
Do you have a sky q box ?

if so try turning this off at the mains.
Thanks Daniel!
No Sky box or something similar in our apartment. (TV is most of the time off anyway)
Norbert

Tubes and Vinyl rule, Music rocks! :icon-wink:

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Andy-831
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Re: Phono 3 / RFI problems

Unread post by Andy-831 » Mon Feb 11, 2019 4:36 pm

When I was struggling with finding the "right spot" for my Phono 2 I temporarily wrapped it in tinfoil to act as a Faraday Cage which seemed to work until I found a spot far enough away from the other electronics to allow it to be removed.

Not an elegant solution I accept but reassuring enough to give you the confidence that a solution did exist.
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301 / 3012 / Shure M75 + Jico SAS
401 / PU7 / AT33ev
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