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Hissy Phono stage...

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Hissy Phono stage...

Postby JollyJeweller » 23 Feb 2012 12:09

Chaps.
As you may know , I've gone all tubey....
I had a Tom Evans Groove + SRX phono stage that was starless and bible black quiet, now I'm using a Luxman 38 SQu with a built in phono stage, which above 50% volume gets a bit hissy , no hum, just hiss.
Is this normal for a valve phono stage?
I'm also pondering a SUT, as the Mantis only puts out 0.30 mv which I gather is pretty low, any thoughts?
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Re: Hissy Phono stage...

Postby Dr Pan K » 23 Feb 2012 12:36

luxman states that a step up transformer is integrated in the phono design..

have u tried connecting y tom evans to the luxman line input ?
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Re: Hissy Phono stage...

Postby JollyJeweller » 23 Feb 2012 12:45

Dr Pan K wrote:luxman states that a step up transformer is integrated in the phono design..

have u tried connecting y tom evans to the luxman line input ?


Hi Pan.
The Tom Evans is sold now.
The 38 does have 3 phono inputs, a MM , and 2 x M/C , but I think the output on the Mantis is a bit low even for those 2 M/C inputs.
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Re: Hissy Phono stage...

Postby Dr Pan K » 23 Feb 2012 13:12

i believe the low MC setting is more than enough for the .3 mantis.

it should deliver decent dB at aprox 10-11 oclock volume knob.

and, at least in theory, the lux38 has a very fine phono stage.. i have no personal experience with the specific model.

do u have any other carts to test with ? maybe MM ?
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Re: Hissy Phono stage...

Postby Hanuman » 23 Feb 2012 13:20

Indications from the measurements taken for the Stereophile review (http://www.stereophile.com/content/luxm ... asurements) are that it's not the quietest phono pre-amp around. 0.3mV is only slightly lower than average but it also looks to me that the gain of the Luxman's phono inputs is not particularly high. It evidently has a very good overload margin so the idea of using an external SUT into the MM input is not a bad one.
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Re: Hissy Phono stage...

Postby pivot » 23 Feb 2012 16:40

Tubes natrually have some thermal noise - nature of the beast - but a correctly designed circuit should not be intrusively noisy

Looks like 12AX7/ECC83 are the gain stages for phono. What brand of tube is used?

There can be a fair amount of variation between brands of 12AX7. Electro Harmionic are current manufactured Russian tubes that should be fairly quiet. Try some tube rolling? If you already have EH onboard maybe try some JJs or Svetlanas?
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Re: Hissy Phono stage...

Postby JollyJeweller » 23 Feb 2012 17:29

I've resisted the temptation to take the top off and have a look inside, but guess with tube amps it's de rigueur!
I'll have a rummage around and let you know what brand tubes are being used.
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Re: Hissy Phono stage...

Postby JollyJeweller » 24 Feb 2012 16:14

pivot wrote:Tubes natrually have some thermal noise - nature of the beast - but a correctly designed circuit should not be intrusively noisy

Looks like 12AX7/ECC83 are the gain stages for phono. What brand of tube is used?

There can be a fair amount of variation between brands of 12AX7. Electro Harmionic are current manufactured Russian tubes that should be fairly quiet. Try some tube rolling? If you already have EH onboard maybe try some JJs or Svetlanas?


OK...image here.
4 x EL34, Eastern Harmonics.
The other 7 are non branded, only have the Luxman L on them.
Of the 7, 4 are 82's , 3 being uncovered, and 1 has a black spring loaded cover on it.
The other 3 , all of which have black covers, are 83's.
The Luxman website says its the other way around, 4 x 83s and 3 x 82s.
Image

I'm a little confused.
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Re: Hissy Phono stage...

Postby Hanuman » 24 Feb 2012 17:55

It seems to me that this amplifier is brand new? Now I've tube-rolled with the best of them in the past but rolling a spanking new product? Surely the designers and builders deserve a bit more respect than that. Maybe you bought the wrong product for your needs. You did audition it, I presume?
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Re: Hissy Phono stage...

Postby luckydog » 24 Feb 2012 17:59

Hi JJ. Much depends on whether the noise source is internal to a valve, or in the circuit. The former can sometimes be addressed by valve variants/substitutions, with lower anode resistance. But doing it blind, ie w/o a schematic, isn't too clever and might end in tears.

Generally, it's tough but achievable to obtain low noise valve preamp designs. Perhaps take it up with Luxman and/or the dealer, because noise shouldn't be notable ?
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Re: Hissy Phono stage...

Postby pivot » 24 Feb 2012 20:32

Hanuman wrote:..... Now I've tube-rolled with the best of them in the past but rolling a spanking new product? Surely the designers and builders deserve a bit more respect than that. .....?


Assuming the designer not an accountant desided on the tube brand. Not always a correct assumption. Design may have spec'ed 12AX7 and the pencil pushers saw they could get Chinese 12AX7s for a lot less then JJs or EH or?

Swapping tubes, if you stay with the right/same tube type, should not do any harm. Even brand new tubes from a decent source can have the occasional "skunk" in the batch.

Tube rolling is something to try not a guaranteed fix. Careful tube rolling is part of the fun of owning tube gear isn't it?
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Re: Hissy Phono stage...

Postby pivot » 24 Feb 2012 20:49

JollyJeweller wrote:[4 x EL34, Eastern Harmonics.
The other 7 are non branded, only have the Luxman L on them.
Of the 7, 4 are 82's , 3 being uncovered, and 1 has a black spring loaded cover on it.
The other 3 , all of which have black covers, are 83's.
The Luxman website says its the other way around, 4 x 83s and 3 x 82s.

I'm a little confused.


The covers are shielded tube sockets - odds are they are on the tubes in the phono section at least and line level preamp perhaps.

Is there a schematic in the owners manual?
Kevin R-M

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Re: Hissy Phono stage...

Postby JollyJeweller » 27 Feb 2012 11:03

Hanuman wrote:It seems to me that this amplifier is brand new? Now I've tube-rolled with the best of them in the past but rolling a spanking new product? Surely the designers and builders deserve a bit more respect than that. Maybe you bought the wrong product for your needs. You did audition it, I presume?


Hi.
I think you've misunderstood the spirit of my post.
I love the amp, and I love the sound.
I would like, however, to reduce the amount of noise on the phono stage, it's not critical , but it's a "would like"...
As Pivot said, I'll bet the original spec was for better AX and AU7's , and a Japanese accountant reduced the spec to save a few Yen.
I'll look at rolling those , see if it reduces the noise floor a bit.
Thanks.
Neil.
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