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Doge 8 Clarity: 12AT7 replacement for phono stage

Hello fellow enthusiasts... My apologies in advance for the noob question.

I've put together my first all tube system, as far as preamp and amp combo is concerned. Looking to see IF replacing the phono section's 12AX7 (Mullard ECC81) tubes with lower gain 12AT7 in my Doge 8 Clarity 2017 ed. will help lower the "hiss"/ tube rush coming off with my current set up. Doge's phono setting is on MM (using Bob's Device Sky 20 SUT), Phono: 47k, tried both normal and low sensitivity, (- 8) gain reduction, but "hiss" is still audible from my seat 7' away from the speakers. 

I'm looking at replacement tubes from Upscale - Mullard 6201 which they claim to be the "quiet" ones. Not sure if it will help in lowering the hiss I've described.

Doge's line level still holds the stock 12AT7 tubes and to me - they sound nice as the reviews online says. I'm sure it can do better with tube rolling. No audible hiss from my seat. Switching between any line level onto phono input clearly augments the hiss.

To take advantage of Doge's much improved line level over the phono, I've utilized my only external phono stage - Schiit Mani. Not ideal but i can handle that better than deal with the hiss using the Doge's internal phono stage. I've contemplated on just upgrading to a nicer phono stage but that's another topic.

So, will it work to replace the 12AX7 with lower gain tubes 12AT7 to decrease hiss in my system? 

Thank you in advice for your time and responses.

Current system:
Rega P3 (2016), NEO ttpsu, DV 20X2L
Schiit Mani to line level vs Bob's Device Sky 20 to phono level
Doge 8 Clarity 2017 ed.
Mystere PA11 
KEF R3 on stands



oyie2000
jbhiller's avatar
jbhiller
1,403 posts
 
@oyie2000 and gilles130, 

I have a Doge 8 Clarity the 2021 edition.  I, too, have hiss in the otherwise magnificent sounding phono stage.  I've swamped some tubes that aren't noisy in other preamp stages (but not phono).  

I really want to resolve this issue because the phono stage is not an afterthought in this product.  It has it's own preamp section of all tubes (no OPAMPs--not that those are bad).  It is rivaling my Manley Chinook and if I can ditch the hiss, I can sell the Chinook (which is awesome) and reduce things by a box. 

The hiss is constant in power, volume, etc.  It sounds like super pleasant but loud white noise.  It has a “shhhhhhhh” sound that is constant with no electrical variance, buzzing, etc.  Just smooth and very loud. 

Now, as atmasphere indicated, the hiss goes down a bit during play so maybe I can just live with it.  

I think I've tried all sorts of loading to no avail.  I sent an email to Marc with Doge.  Let's see what he says.  This is a great product.  The line stage is super!
chrisnchin
2 posts
 
@jbhiller any updates from Doge.  Have you resolved this hiss issue?
dirt13k
3 posts
 
I just received my Doge 8 Charity 2022 Special Edition. It has Brimar 6060 and TAD 7025 tubes I’m using the MC phono stage with a Rega Apheta 2. I also have a bad hiss.
This is my first tube gear Iv got a lot of good info from this forum.
Is it really just tubes that cause this ?

Yes @jbhiller was Doge able to help or did you have any success?
jbhiller's avatar
jbhiller
1,403 posts
 

I did have some success lowering the hiss, but it's still there. 

Now, let me say this.  It's not a problem when playing music. And, I haven't had my Manley Chinook back in the system since breaking in the Doge.  I run a Kiseki Purpleheart MC cartridge on it.  It's really a strong all tube phono stage.  Even my Chinook uses OP Amps on the power side of things. 

 

atmasphere's avatar
atmasphere
11,800 posts
 

I just received my Doge 8 Charity 2022 Special Edition. It has Brimar 6060 and TAD 7025 tubes I’m using the MC phono stage with a Rega Apheta 2. I also have a bad hiss.
This is my first tube gear Iv got a lot of good info from this forum.
Is it really just tubes that cause this ?

Mostly. In any high performance vacuum tube product, the tubes have to be hand-picked. I know a lot of NOS tubes are preferred over new tubes because of the sound. But something to keep in mind: people have been scouring the world looking for low noise NOS tubes for the last 50 years.

For that reason its highly unlikely that the NOS tubes you're using are actually quiet. If you really want quiet tubes, these days they will have to be new. And hand picked for low noise.

You might have to do the hand-picking yourself. Most 'tested' tubes really aren't screened that much IME. So buy about 20 of the tube you want, and then start at the input section of the phono circuit- replace the input tube in one channel only. Warm up the preamp and wait about a minute. Is the new tube quieter than the other channel? If no put it in the reject pile, shut off the preamp and try again.

If yes, tap on the tube. If you hear a loud noise in the speaker, reject the tube. If you hear something but its not loud, keep it and then repeat this process for the other channel.

If you run into a tube that is a lot quieter in the other channel, that means that your first pick wasn't all that quiet- return to that channel and repeat the process.

In this way its sort of like a ladder of steps you take to grade the tubes and you'll wind up with a pile of rejects. They might be good for other locations in the audio chain, just not the input of a phono section. If you don't need them though, send them back for a refund immediately.

Remember to shut the preamp off prior to removing and replacing a tube! Otherwise damage to speakers or your amps could result!

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