Tube phono stage tube rush question.

[Ramarge3653]

Hi,

I recently picked up an Aesthetix Rhea phono stage and as this being my first tube preamp I have some general questions. Whenever I have my system turned on with no vinyl playing I hear a constant static hiss, and it sounds very similiar to FM static hiss. I've done some research and what I've been told is that this is considered tube rush. Whenever I play a record I cannot hear any audible hiss, it's only if I turn the volume up when no record is playing that I hear this hissing/static sound. As I mentioned this is basically my first experiance with a tube preamp and just figured I would ask if this is normal.

Thanks in advance
-Matt

[Zebbo]

I don't think you'll find any valve phonostage that is silent. The stage you have is a high quality unit so I would expect it to be quieter than most but the valves themselves vary greatly. It is also relative, how high do you have to turn the volume up to hear the hiss from your listening position? If it's way beyond the level you listen at it isn't a problem.

[Ramarge3653]

For example, the loudest I listen to my stereo is at 1 O'clock and I can hear a faint hissing(shhhhhh) starting at 9 0'clock and it's not bothersom and very faint and probably wouldn't notice it unless my ear is about 12 inches from the speakers. When I turn up the volume up on my stereo to 1 o'clock it's definitely noticeable, not terribly loud but defiantly can hear it loudly from my listening position and in the kitchen (same room space). This is my first tube preamp so I have no other judgement as to what the norm is, I just feel that it should be much quieter. This is a used unit and the guy I bought it from said the tubes have around 50 hours on them but I have no way to verify.

Thanks for the reply.

[andyr]

That is why I, for one, use a discrete (as distinct from op-amp based) ss phono stage.

Moreover, my other phono stage (battery-powered, JFET-based) is considerably quieter than my mains-powered one.

I cannot abide hearing either hiss or hum when playing vinyl.

Regards,

Andy

[Ldg]

Valve noise is much maligned, need not be audible. Certainly not above the vinyl groove-stylus noise floor, which should always be the limiting factor.

Are valves intrinsically noisy ? An EF86 small signal audio pentode which has something of a reputation for being noisy, has a noise equivalent figure of about 7nV/sqrtHz. Compared to about 5nV/sqrtHz for a 'low noise' op amp such as an NE5532. The challenge with valves is to keep support circuitry from contributing to overall noise figures in preamps. It can be done, but it can also be mucked up. Same is true in op-amp and discrete designs, but mucking it up is just a doddle in valve circuits.

Strictly, valves of the same type from different manufacturers ought to have the same characteristic parameters upon which noise (internal and external) depends. If there's a significant noise difference between valve manufacturers, chances are other params are different too.

Long live the EF86, design one in today I've no idea what line up the Aesthetix Rhea uses, BTW.

[Ldg]

A quick look at the Aesthetix Rhea reveals it has four gain stages, in 12AX7s plus a 6922 . That's ECC83s plus an ECC88 variant. Selected for low noise, whatever that means (?!)

It's hard to squeeze out much gain from a triode stage. Hence the tradeoff, especially in MC stages, for number of stages versus noise for each stage.

I'm into EF86s at the moment, because they have great gain, and can get it done in fewer stages. Would two stage based on EF86 beat four stage ECC83/88 for noise ? Quite possibly. 75dB is quite a high gain to extract at low noise from a valve preamp anyway.

But the Aesthetix Rhea looks very very nice. I suspect that listening to a tiny trace of the universe being born is no price to pay for the rest of its merits.

Enjoy !

[pivot]

Tubes must have some noise due to the heat needed to make them work BUT a well designed tube or hybrid phono stage should have hiss well below the groove noise of a quiet record.

The most recent tube phono stage I spent any time with was the Bottlehead Seduction I built "bone stock" for a friend. Each channel is two triode (Electro Harmonic 6922 stock) gain stages with passive EQ with 36 db of gain. I have heard nosier factory made solid state gear. Certainly no audible noise at the listening position.

Other side of the coin I found the Bellari 129 Hybrid tube unit I had home briefly had much more "tube rush" for less gain. I would have expected it the other way around. Tube rolling in a NOS Telefunken ridge plate 12AX7 made it quieter but not acceptable IMHO.

In theory all tubes of the same type SHOULD have the same noise floor but tube rolling from back when I played with modifications to Dynaco PAS preamps suggests that reality departs from theory.

Try some careful tube rolling. Word on the street is the Sovtek 12AX7 LPS is one of the quieter 12AX7 tubes currently available. Personnally I have a shoe box full of NOS oldie 12AX7 tubes for playing with so have not heard the new stuff.

What is in there now?

[Ldg]

Actually, noise that arises internally in valves isn't 'thermionic' or related to heat. By and large. It is related to equivalent internal resistances, which is related to parameters of the valve, which is related to geometry and spacing of electrodes. Shape of bits of bent wire, in layman's terms. Amazing, but true.

I love valves. The whole idea of manipulating current in a vacuum with bits of bent wire is so 'essential' and somewhat wonderful.

No dispute that various manufacturers' valves can have somewhat different noise performance. Just that must be asssociated with variation of other parameters too, it's the way it works.

[Ramarge3653]

Thanks for the information. I currently have the stock tubes installed, but I've been reading a lot of forum posts and some say to swap the stock 6922 tube for a Seimen 7308 and the hiss will be almost non existant. I'm not sure how valid this is but it might be worth a shot.

[Hanuman]

Thanks for the information. I currently have the stock tubes installed, but I've been reading a lot of forum posts and some say to swap the stock 6922 tube for a Seimen 7308 and the hiss will be almost non existant. I'm not sure how valid this is but it might be worth a shot.

Small-signal tubes are relatively cheap so why not give it a try. I also had a look at the Rhea's spec. and concluded that it's probably not the quietest tube unit around. A couple of other "tube" units that I know of use a JFET (a transistor) at the lowest-level gain stage, which helps keep the signal-to-noise ratio reasonable. The Steelhead springs to mind. Certainly, if you've been accustomed to good solid-state phono amps you'll find an all-tube unit to be pretty noisy, relatively. I had the opposite experience when I swapped an Audio Research PH3 for the EAR 324 that I currently use. The EAR is silent by comparison.

I have heard the Rhea on a few occasions and can attest that it is really special - I've not been disturbed by any unwanted hiss whenever I've heard one.

[Ldg]

Thanks for the information. I currently have the stock tubes installed, but I've been reading a lot of forum posts and some say to swap the stock 6922 tube for a Seimen 7308 and the hiss will be almost non existant. I'm not sure how valid this is but it might be worth a shot.

AFAIK, the 7308 is a low microphonics version of the ECC88. ie it might have internal rubber dampers and be more structurally supported. Not that the ECC88 is particularly microphonic IME. Spec 7308 shows a bit more heater current than the ECC88, which seems a little odd, perhaps once intended for mobile applications ? ECC88s generally crop up in SRPP and cascode stages, which although they can be early input stages, can be used as the final gain stage, having lowish output impedance. But this is only guesswork on my part !

[Hanuman]

... but I've been reading a lot of forum posts and some say to swap the stock 6922 tube for a Seimen 7308 and the hiss will be almost non existant.

The 6922 is in the buffer and my intuition would lead me to focus on the tubes upstream, particularly the very first gain stage. Long ago I used a 6DJ8/ECC88-based head-amp and I had two handfuls of tubes always on hand to swap depending on the noise-levels of the particular day, which apparently were related to the phase of the moon or other such cosmic influence. My noise manifested as a low-level "bonfire", not the steady hiss you're getting.

[Ldg]

... but I've been reading a lot of forum posts and some say to swap the stock 6922 tube for a Seimen 7308 and the hiss will be almost non existant.

A bit more research reveals 7308 is a 1962 ECC188 equivalent, described in the spec as "long life shock and vibration resistant double triode with anti-microphonic construction."

Spec is here http://www.drtube.com/datasheets/e188cc-philips1962.pdf

Spec noise equivalent resistance for the ECC188/7308 is 250R, versus 300R for a standard ECC88. That's not going to set the world alight by way of improvement. So, by spec, there's not much in it as to broad spectrum hiss performance. But microphonics will be better, though I've never noted that in an ECC88. Perhaps as Hanuman posts, because of its location in the path. Also, the noise Hanuman describes when ECC88 used as an MC first stage sounds like non-ideals anyways perhaps, and not part of theoretical or spec figures perhaps. Desciption seems like flicker noise, which has a strong lf bias, and crackle.

I never knew about ECC188s, so that's a discovery. Not sure I'd be at the front of the line to try, in this case, on paper though there's not much advantage unless microphony is a problem. But, you never know and there may be non-ideals in play too. Cheap and plentiful they certainly aren't !

I agree with hanuman, upstream seems the place to look for noise improvements.

[andyr]

So why would you use tubes in a phono stage at all, if some tube (hybrid!) phono stages use JFETs for the first (extremely low input) gain stage, to reduce noise?

Why not simply use JFETs in the 2nd gain stage too ... to get even less noise (compared to a tubed 2nd stage)?

Regards,

Andy