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SE to Balanced will help?

The Sentinel

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Hello!
When pushed all the way up in the preamp gain I am getting 14dB of noise from one of my sources, all others make nothing, zero, nada, of noise at that highest gain of the preamp.
The source that has noise is connected this way:
-Cartridge - Ortofon Quintet Black S (MC low output)
-Tonearm - SAM 12" Calista II
-Turntable - SAM Aldebaran
-Phono preamp - Schiit Mani2 (A lot better than the original Mani in every aspect including the noise floor)
-Main preamp - NAD C165BEE (Deadly silent with all other sources)
-Power Amp - PrimaLuna EVO400 (as said, no noise at all with any other source)
-Speakers - Klipsch Forte IV
-All interconnects and speaker cables are medium quality from audioquest (the red ones)

The noise is like a 60hz hum but I doubt it is electrical hum as the noise is present even with the power supply of the turntable totally disconnected; my guess is that the noise comes from the Mani2 but I really do not want to get in the thing of buying a very expensive phono preamp if a SE->Balanced converter can do the job. Here are my questions:

1) Would a single ended to real balanced/differential converter be able to eliminate the noise if I put it in between the NAD preamp (SE output) and the PrimaLuna (balanced input)?
2) If the answer is "yes", any recommendation for such a converter?

Any suggestion will be highly appreciated!
 

Blumlein 88

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Sounds like the hum is in the phono system. I don't think switching to balanced is likely to help at all. Also, you probably are never going to get the phono part as quiet as everything else. Phono preamps have 50 db or so of gain so any noise is pushed up further. Do you hear the hum at normal listening levels? BTW, when the TT is switched off the cartridge is still connected to the Schiit phono preamp.

Now you may experiment with grounding the TT or phono pre different ways and reduce the hum. If the AQ cables are not coax, you might try some other RCA connects that are coaxial if you have some handy. Do you have the tone arm or TT connected via a ground wire to the Schiit phono grounding lug? Also don't know what other gear the Mani is close to. Having so much gain, sometimes if you can move the Mani to a different location away from other gear it may reduce hum.
 
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radix

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Have you connected the Mani2 ground to the TT, if it supports that?

I'd get some RCA shunts and use those for the TT input the mani2. That will ground the input. If that removes the humm, then you know the problem is 60Hz pickup before the mani. If it does not remove the hum, then its a problem with the mani2 or the cabling.
 

DVDdoug

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I am getting 14dB of noise
Measured where and relative to what? What dB scale?

14dB SPL (acoustic) is too quiet to hear (and generally too quiet to measure).

+14dBFS (digital) would be terrible and unlistenable. -14dBFS would be unlistenable too.
 

BenjaminB

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why using a separate phono amp when the NAD 165 has MC input? One of the main selling arguments for that pre-amp!
OK, one could argue that a separate phono amp close to the turntable should minimize noise. But in this case, clearly not.

Suggest then to test skipping the separate phono amp and just use the NAD. At least as a test, if still 60 Hz hum then you know it is not the phono amp, and so on.

Balanced cables isn't likely to help you - maybe if using in the tone arm but that probably has other consequences.
 
OP
T

The Sentinel

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Sounds like the hum is in the phono system. I don't think switching to balanced is likely to help at all. Also, you probably are never going to get the phono part as quiet as everything else. Phono preamps have 50 db or so of gain so any noise is pushed up further. Do you hear the hum at normal listening levels? BTW, when the TT is switched off the cartridge is still connected to the Schiit phono preamp.

Now you may experiment with grounding the TT or phono pre different ways and reduce the hum. If the AQ cables are not coax, you might try some other RCA connects that are coaxial if you have some handy. Do you have the tone arm or TT connected via a ground wire to the Schiit phono grounding lug? Also don't know what other gear the Mani is close to. Having so much gain, sometimes if you can move the Mani to a different location away from other gear it may reduce hum.
Hello, thanks for replying.
No, the hum is not heard at normal listening levels; only at VERY high gain of the amplifier and I almost never use such amount of voltage.
Yes, I am going to do some testing changing the cables. Yes, there is a ground cable in between the tonearm and the Mani2; both, the tonearm and the Mani are well separated from other gear and/or AC cables.
Well the possibility of the RCA->XLR converter seems like a no-point action. Thanks again!
 
OP
T

The Sentinel

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Have you connected the Mani2 ground to the TT, if it supports that?

I'd get some RCA shunts and use those for the TT input the mani2. That will ground the input. If that removes the humm, then you know the problem is 60Hz pickup before the mani. If it does not remove the hum, then its a problem with the mani2 or the cabling.
Hello, yes, the tonearm has a terminal that is connected to the Mani2 ground.
Those shunts seem like a good way to locate where's the problem, thanks, will do!
 
OP
T

The Sentinel

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Measured where and relative to what? What dB scale?

14dB SPL (acoustic) is too quiet to hear (and generally too quiet to measure).

+14dBFS (digital) would be terrible and unlistenable. -14dBFS would be unlistenable too.
Hello, excellent point, let me elaborate:
At my listening position, using the cheap sound meter app of the iphone, I read an average of 31dB-A; it is a fairly silent room and that is the situation at any time any day fortunately; well, if I set the gain of the preamp to the very maximum, the reading at the iphone goes up to 45dB-A and that noise sounds like 60hz hum. That happens only with the TT selected, no other source does that (2 CD players that go to a DAC before the preamp and two cassette decks that go directly to the preamp). Do I explain myself?
 
OP
T

The Sentinel

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why using a separate phono amp when the NAD 165 has MC input? One of the main selling arguments for that pre-amp!
OK, one could argue that a separate phono amp close to the turntable should minimize noise. But in this case, clearly not.

Suggest then to test skipping the separate phono amp and just use the NAD. At least as a test, if still 60 Hz hum then you know it is not the phono amp, and so on.

Balanced cables isn't likely to help you - maybe if using in the tone arm but that probably has other consequences.
A few years ago I just could not resist the temptation of buying a Schiit Mani and use it instead of the internal phono stage of the NAD preamp; it happened that it improved the sound quality but, still, the noise floor of that Mani was kind of high so I went for the Mani2 and it happened to have lower noise floor and even better sound.
Will do that test tonight, going directly from the TT to the NAD.
Thanks!
 

BenjaminB

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The phono stage is the most suspect, it has a huge gain (50-60 dB) and an external PSU (from the spec " “wall wart” style 16VAC transformer, dual-filtered, regulated +/- 16V rails"). Thus easy for the phono pre-pre-amp to pick up some hum from the PSU.

Considering the price of the phono stage, $149, Schiit must have minimized the BoM (bill of materials), the PSU is an obvious candidate (a bit strange that they use a transformer, a switched PSU would be cheaper and better. Oh well ...).

If the phono stage is identified as the culprit, then there are some different possibilities to act:
1) contact Schiit, request a new, and better, PSU. may work, easy to do.
2) fix a replacement for the PSU, preferably a switched nit, giving +- 16 V. May cost some. Must also have the right connector.
3) improve filtering by adding some capacitors and maybe coils. Requires knowledge!
4) skip the schiit unit, go back to the NAD entirely.
5) ....

I am actually a bit surprised that a separate phono stage for just $149 sounds better than the phono stage in NAD 165.
 

SoNic

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Recently I tackled a similar issue in my headphone amp.
Looking at various schematics of my other electronic devices that didn't have hum, I found out that, in US, the case ground is connected to power receptacle ground and is electrically isolated from signal ground. Between them usually there are some small value capacitors (01.uF to 1uF).
In my case those two ground were tied together in one point. So I decoupled those (lifted the ground basically) and soldered in a 0.68uF capacitor.
The hum vanished.
Now, the devices with external transformers, that have no ground pin in the power socket, should not create those ground loop issues. Dissconect the cables that come into Mani 2 first to see if noise is still there (maybe short the inputs, but it should not be needed).

Otherwise, you might need a ground loop isolator audio transformer.
 
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Blumlein 88

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I noticed in the review here it has a two prong power supply that fits either way. This is a hit or miss procedure, but just plugging it in with reversed polarity will sometimes have lower hum in one direction versus another. I also think expecting zero hum at max volume is something you will struggle to achieve. If it isn't audible at normal listening volumes, I wouldn't let it bother me. The suggestion someone had to short the inputs to the Mani is another good test.
 

drewdawg999

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Is the hum still there if you reduce the gain on the Mani2? I had a similar problem with my phono pre, a MS Nova Phonomena. At 60dB of gain there was a hiss and a hum at about the same levels as you're experiencing, noise floor at around 45dB, which is borderline unacceptable for me. It was audible from the listening position, and during quiet passages of music. It's just something you have to live with, with these levels of gain on your phono pre. My solution was getting a step up transformer and reducing gain to minimum (40dB). Noise is gone and now all is well and my MC setup has never sounded so good. Of course this involves another component (SUTs are a whole other rabbit hole) and another pair of interconnects (which needs to be well shielded).
 

restorer-john

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LOMC means you have about 60-65dB of voltage gain downstream from that transducer. That is >1000 times.

There's not an MC front end on earth that won't make noise and pick up hum at a "VERY high gain" on your amplifier, as you mentioned. Not sure what you are expecting- it 'aint CD.
 

SoNic

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I have used to listen to LP and I even build my own preamp for it with discrete components.
It definitely didn't have power hum at -60dB, but that was after careful grounding and shielding of the coil wires - twisted pair wires inside a shielded cable, one cable per each channel.
 
OP
T

The Sentinel

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The phono stage is the most suspect, it has a huge gain (50-60 dB) and an external PSU (from the spec " “wall wart” style 16VAC transformer, dual-filtered, regulated +/- 16V rails"). Thus easy for the phono pre-pre-amp to pick up some hum from the PSU.

Considering the price of the phono stage, $149, Schiit must have minimized the BoM (bill of materials), the PSU is an obvious candidate (a bit strange that they use a transformer, a switched PSU would be cheaper and better. Oh well ...).

If the phono stage is identified as the culprit, then there are some different possibilities to act:
1) contact Schiit, request a new, and better, PSU. may work, easy to do.
2) fix a replacement for the PSU, preferably a switched nit, giving +- 16 V. May cost some. Must also have the right connector.
3) improve filtering by adding some capacitors and maybe coils. Requires knowledge!
4) skip the schiit unit, go back to the NAD entirely.
5) ....

I am actually a bit surprised that a separate phono stage for just $149 sounds better than the phono stage in NAD 165.
Hello and thanks for replying!
I was not able to change the Mani2 PSU as it is an AC PSU and I don’t have another one at hand. I guess I’m contacting Schiit to ask for a replacement.
I do not think that I am going to look for a replacement on my side, I prefer to wait for Schiit’s answer.
No way that I am going to deal with capacitors or coils!
Yesterdays night I tested the system go in directly to the NAD’s phono stage, and it was even worse!, A big hum came from the speakers at maximum gain of the preamp.
Also, I did several testing, changing the grounding to different locations and the result did not vary for the good.
 
OP
T

The Sentinel

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Is the hum still there if you reduce the gain on the Mani2? I had a similar problem with my phono pre, a MS Nova Phonomena. At 60dB of gain there was a hiss and a hum at about the same levels as you're experiencing, noise floor at around 45dB, which is borderline unacceptable for me. It was audible from the listening position, and during quiet passages of music. It's just something you have to live with, with these levels of gain on your phono pre. My solution was getting a step up transformer and reducing gain to minimum (40dB). Noise is gone and now all is well and my MC setup has never sounded so good. Of course this involves another component (SUTs are a whole other rabbit hole) and another pair of interconnects (which needs to be well shielded).
Well, that seems like a very good idea, thank you very much!
right now with the Mani2 is working with 62dB of gain and I can reduce to 40
 
OP
T

The Sentinel

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LOMC means you have about 60-65dB of voltage gain downstream from that transducer. That is >1000 times.

There's not an MC front end on earth that won't make noise and pick up hum at a "VERY high gain" on your amplifier, as you mentioned. Not sure what you are expecting- it 'aint CD.
Well, you are right on that, maybe my expectation is way too high, actually, I never play vinyl at such a high volume
 
OP
T

The Sentinel

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I have used to listen to LP and I even build my own preamp for it with discrete components.
It definitely didn't have power hum at -60dB, but that was after careful grounding and shielding of the coil wires - twisted pair wires inside a shielded cable, one cable per each channel.
My lack of technical knowledge is what made me buy the preamp, if I had the technical knowledge I would had built mine
 
OP
T

The Sentinel

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Try running an additional ground wire from the Mani to the NAD???

You sometimes have to experiment with ground. Use a piece of wire with bare ends and touch the chassis of all equipment. Sometimes you can solve the problem entirely this way.
One of the many tests that I did today was exactly that one I need didn’t work. Actually, I tested grounding directly to the ground wire that goes in the electrical installation of the house that I am totally certain that is very well grounded to the land. Nothing worked so, I think it is not a grounding issue, but a PSU issue combined with a huge amount of gain, first 62dB at the Mani2 and then all the NAD’s gain way up.
 
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