Stereomour vs. Paramount

[Paul Folbrecht]

I started a thread with the same title nearly a year ago.  I was looking for amps for a horn system.  No more horns - back to Audio Note AN/Es (HE), for good.

I bought a used Stereomour, pro-built with Mundorf caps.  I am really amazed by how good it is.  Without direct A-B'ing, t is among the best amps I've ever had, and I've had some pricey amps.

Here is my question: In terms of real-world power & drive, how do the two amps differ?  In my large room 3.5W is marginal.  It is *enough*, but pretty much just enough.  The Paramount is rated .5W less.  At these power levels, this might matter.

OTOH the Paramount has the mono advantage: one PS per channel.

So, are there appreciable differences in SPL/drive between the 2A3 Paramount and 2A3 Stereomour?

 

[johnsonad]

Paul, you have been through more gear than most people in a lifetime. Is an opinion going to matter vs. your experience?

Edited for not reading your post well enough the first time.

The nice part about the Paramount is that you can use your 12AT7's from your current amp or the standard 5670 with simple mods.  There are others to experiment with too like the 6SN7 if you can sacrifice the gain. 

 

[Paul Folbrecht]

I'm not looking for opinions, really, but information from the guys that designed the amps.

I'm not asking about 2A3 vs. 300B but the relative drive abilities of the Paramount & the Stereomour both using 2A3s.

You're right, though - I'm probably being a bit anal.  I just want to hear that the Paramount has at least as good as drive of the Stereomour (despite the lower wattage rating) before I commit to building them.

 

[Paul Joppa]

Tough question, because the differences are not primarily power - 3.5 watts is after all only 0.67dB.

The plate choke to load impedance ratio in Paramount is 1.6 times greater, which means deeper, cleaner bass - 2/3 octave. The output transformer will go lower before saturation, as well (if you need it I'll do the calculation, but it's Friday night and I've had a couple drinks so I won't try right now!).

The Paramount has a shunt-regulated driver, which improves the clarity and perceived "effortlessness" especially in the bass. It is also direct coupled, which has a similar effect - not to mention, a better tolerance of overdrive (no "blocking"). And it has capacitorless DC filament power (choke filter) which reduces hum. These are the features that are more significant IMHO that just power capability.

 

[JamieMcC]

Hi hope you don't mind but I am also interested learning a bit more about the Stereomour & Paramount amps and have a newbie question.

I note both amps have options to use different tubes but have the 2A3 in common. Would you mind throwing some light on what might be considered the main difference or advantages in reconfiguring of the two amps with their alternate tube options overt the standard build.

Are the changes for speaker load matching, alternate preferences of presentation?

A/ Stereomour 2A3 vs configure with the 45 Tube?

B/ Paramount 300b vs configured with the 2A3 Tube?

Thanks

Jamie

 

[Paul Joppa]

The Stereomour is designed around the 2A3, and the Paramount around the 300B. The variations are adaptations for those who really want them, but they are not the original design target.

We don't make a specifically 45-powered amp because there are no affordable modern production 45 tubes, but we have many customers who believe the 45 does, or can, sound better than the 2A3 - in spite of producing about half as much power. Owing to some design apects of the Stereomour, dating from its earliest incarnation as the Paramour, it is easily adapted to run a 45 at a good operating point. In Paramour II and now in Stereomour, we have provided specific adaptation instructions so they could be built either way. But you still have to come up with the 45s yourself!

The Paramount has a similar legacy from earlier products. "Afterglow" was the second power amp (released in 1997 when the business was still called Electronic Tonalities, before Bottlehead was adopted). It was a high-end design by John Tucker and had direct coupling between driver and power tube. Variants on that design have been in the product line for many of the succeeding 17 hears. Because the power supply voltage and the output transformer impedance of the 300B Paramount were suitable for this topology, we provided that option. It's too esoteric a design to support a fully separate product, but the Paramount adaptation keeps it available for those who really want it. I don't, incidentally, recommend it unless you are pretty knowledgeable because direct coupling is less reliable and more high-maintenance that capacitive coupling. It is a higher-performing 2A3, with direct coupling, DC filament power, and shunt-regulated driver power distinguishing it from the Stereomour. It also has higher internal voltages, requires regular maintenance of the operating point, and has the potential to damage output tubes if you don't use the latest version and follow the turn-on/turn-off protocol carefully.

Our customer base has evolved beyond the initial hard-core experimenters, as the availability and popularity of SET amplifiers has expanded over the last 20 years. So these levels of flexibility are becoming less important.

Hope that helps clarify things!

 

[JamieMcC]

Paul, thanks for the reply, the bit of background info is both interesting and helpful.

 

[Paul Folbrecht]

Tough question, because the differences are not primarily power - 3.5 watts is after all only 0.67dB.

A trivial difference, to be sure.   (People often say "only 3 dB" as if that's inconsequential, but in fact 3 dB makes all the difference in the world sometimes!  It's the difference between the 'right' volume and one does not create the illusion.  But, 2/3rds of dB - yeah, that's inconsequential, I'd say.)

The plate choke to load impedance ratio in Paramount is 1.6 times greater, which means deeper, cleaner bass - 2/3 octave. The output transformer will go lower before saturation, as well (if you need it I'll do the calculation, but it's Friday night and I've had a couple drinks so I won't try right now!).

The bass of the Stereomore is pretty good - noticeably tighter than the 300B Parabee's.  And my AN/Es do have good output into the 20s corner-loaded as they are.

Are you saying the -3 dB point is a full 2/3rds octave lower in the Paramount?

The Paramount has a shunt-regulated driver, which improves the clarity and perceived "effortlessness" especially in the bass. It is also direct coupled, which has a similar effect - not to mention, a better tolerance of overdrive (no "blocking"). And it has capacitorless DC filament power (choke filter) which reduces hum. These are the features that are more significant IMHO that just power capability.

Could you make any attempt to quantify this effect on clarity?  Are we talking big difference or small difference?

I have read your treatises on doing DC heating right.  I believe you probably have a great solution that does not "suck the life out of the amp" as seems to happen.  OTOH, the Stereomour's hum level is extremely low.

I don't, incidentally, recommend it unless you are pretty knowledgeable because direct coupling is less reliable and more high-maintenance that capacitive coupling... It also has higher internal voltages, requires regular maintenance of the operating point...

Paul, I think you just sold me on the Stereomour after all.  I need amps that are close to maintenance-free.

Right now I'm at a place with the Stereomour anyway where there's no real reason to change.  It sounds superb and I love the value aspect. 

(I want an audio system that is suitable for 'the masses' - one that many people hopefully can afford or could afford if the world were a bit more sane.  A system that gets 90% of what's possible in the ultra-high-end and demonstrates to people who know nothing but iPods what the beauty of reproduced music can be, at a price that will not shock.)

 

[Paul Folbrecht]

Paul, a related question about the Stereomour - would you expect much advantage to using a pair of them, one per channel, with each amp vertically bi-amping one speaker?

(Ya, that's about as unfair a question as can be - how would you really know unless you'd tried it with my AN/E speakers?  But I'm askin' anyway - sorry...)

 

[Paul Joppa]

Paul, a related question about the Stereomour - would you expect much advantage to using a pair of them, one per channel, with each amp vertically bi-amping one speaker?

(Ya, that's about as unfair a question as can be - how would you really know unless you'd tried it with my AN/E speakers?  But I'm askin' anyway - sorry...)

Thanks for saving me the trouble - you nailed it!  :^)

Bi-amping has two meanings. The most effective is to use a line-level crossover before the amplifiers, so each amp is relieved of voltage and current demands outside its passband. The problem is, you need an entirely new crossover design, since the individual drivers have complex impedance functions which are part of the original speaker level design.

It's much less effective (but much more practical) to drive each amp full-range, feeding the speaker-level crossover sections independently. This does not reduce the voltage demand, but it does reduce the current demand, out of band. I assume this is what you are asking about.

For the AN-E (measurements here: http://www.stereophile.com/content/audio-note-e-lexus-signature-loudspeaker-measurements ) the crossover is about 3kHz, so the woofer uses probably 90% or more of the amplifier capacity. There will be little to gain there. The tweeter amp might be a bit cleaner without the bass load. If you did this, I would insert a high-pass filter before the tweeter amp at around 1kHz; this won't affect the crossover but will remove a lot of bass from the treble amp. This can be as simple as a 0.0016uF capacitor before the treble-side volume control. It could maintain some clarity when the bass amp is in overload.

You could also replace the level control with a balance control to adjust the bass/treble balance. But then, AN has already done this to their taste!

So, my best guess is probably audible but probably subtle at best.

I would certainly ask Audio Note about biamping before jumping in - they probably have a position on the subject which is better informed than anyone else's.

While you're at it - ask them about crossover upgrades, if you have the standard crossover with nonpolar electrolytic capacitors. That might make even more difference.

 

[Paul Folbrecht]

Paul,

I would also expect the performance increase in passive bi-amping to be small - the bigger increase in my little 'plan' would likely be from devoting one chassis/PS per channel.  But, if you're doing that, bi-wiring L-R to W-T makes sense.

As reported once in 6Moons, the Living Voice folks found identical passive bi-amping of their speakers - which are very similar in topology, etc., to the Audio Notes - worthwhile enough to merit another pair of ~$75K Kondo monoblocks to do just that in the factory showroom (!).  That is actually what had me think of this, probably.

I wouldn't think of trying to adjust the crossover balance this way.

 

[Paul Joppa]

Guess I should have pointed out that you can parallel the inputs and put the outputs in series to get 7 watts from a monoblock Stereomour  :^) it doubles the load impedance, but you start with 2-4-8-16, so the end result is 4-8-16-32 ohm taps. Real easy to make balanced outputs that way, too. There's your 3dB, incidentally ...

 

[Paul Folbrecht]

Guess I should have pointed out that you can parallel the inputs and put the outputs in series to get 7 watts from a monoblock Stereomour  :^) it doubles the load impedance, but you start with 2-4-8-16, so the end result is 4-8-16-32 ohm taps. Real easy to make balanced outputs that way, too. There's your 3dB, incidentally ...

Playing a Les Nubians track last night with a prominent upright bass line at loud volume, I finally ran into the Stereomour's power limits. 

Sounds like I should indeed consider another Stereomour kit.  Thanks.

(I would guess there is a bit of a loss of purity running the amp like a parallel SET, but nothing's free.)

 

[Paul Joppa]

From an electrical engineering perspective, it makes best sense to parallel current sources, and to put voltage sources in series. Since triodes are more like voltage sources than current sources, I recommend putting them in series rather than in parallel. Pentodes and tetrodes (and FETS and transistors) are more like current sources, and they make sense in parallel.

Incidentally, in normal push-pull amplifiers the output tubes are essentially in series ...  :^)

 

[Paul Folbrecht]

From an electrical engineering perspective, it makes best sense to parallel current sources, and to put voltage sources in series. Since triodes are more like voltage sources than current sources, I recommend putting them in series rather than in parallel. Pentodes and tetrodes (and FETS and transistors) are more like current sources, and they make sense in parallel.

Incidentally, in normal push-pull amplifiers the output tubes are essentially in series ...  :^)

Oh - so what you suggested previously isn't really turning the Stereomour into a "parallel SET" (as I said).  That'd be why you specifically said "outputs in series".  Got it now.

What does running the outputs in series do to the THD profile and sound in general?  I would guess tube matching is not super-critical in this application either (as it is with PSET where one tube can hog all the current in many designs anyway).

 

[Paul Joppa]

THD should be the average of the two parts. The rest of your post is pretty much the way I see it too.

 

[Doc B]

I've been running as as many as four amps this way for 6 years and I find little to fault from a performance standpoint.

 

[Paul Folbrecht]

Hi Paul,

Well, the 10% sale came at an opportune time and I've ordered my second Stereomour kit today.  Could you please post instructions on how to convert the amp to a series-wired monoblock?  (Assume that I'm really stupid...)

 

[Paul Folbrecht]

The Paramount has a similar legacy from earlier products. "Afterglow" was the second power amp (released in 1997 when the business was still called Electronic Tonalities, before Bottlehead was adopted). It was a high-end design by John Tucker and had direct coupling between driver and power tube. Variants on that design have been in the product line for many of the succeeding 17 hears. Because the power supply voltage and the output transformer impedance of the 300B Paramount were suitable for this topology, we provided that option. It's too esoteric a design to support a fully separate product, but the Paramount adaptation keeps it available for those who really want it. I don't, incidentally, recommend it unless you are pretty knowledgeable because direct coupling is less reliable and more high-maintenance that capacitive coupling. It is a higher-performing 2A3, with direct coupling, DC filament power, and shunt-regulated driver power distinguishing it from the Stereomour. It also has higher internal voltages, requires regular maintenance of the operating point, and has the potential to damage output tubes if you don't use the latest version and follow the turn-on/turn-off protocol carefully.

Hi again Paul.  I am now actually leaning to building the 2A3 Paramounts.  The Stereomour is so good that an increase in performance is very intriguing.

When you say that the amps "require regular maintenance of the operating point", what do you mean?  What would there be to adjust?

I once had a Fi 2A3 which is direct-coupled and also Fi 45 monos and there was no maintenance required.

Thanks!

 

[Paul Joppa]

In direct coupled designs the driver plate is directly connected to the power tube grid, so that voltage affects the operating point of both tubes. The driver usually (at least in my designs) has plenty of headroom and can tolerate a range of plate voltages, but the power tube can't if you want to get the best out of it.

For this reason, the current (v1.1) Paramount incorporates the "soft-start" upgrade board, which has and adjustable driver cathode voltage. The optimum adjustment is dependent on your power line voltage so you have to calculate it, and then you must check it and re-balance if the tube drifts too far - IHMO, +/-5% or about +/-10v. In the present design that means taking the amp to the test area, turning it over, connecting a meter, and adjusting a trimpot on the PC board. Inconvenient, but as I said this was not the primary design application. I guess, like reel-to-reel tape, this is a design for geeks!

To my ears, a cap coupled amp with a really excellent coupling capacitor, and operated within its power capabilities, is audibly comparable to direct coupling. These days I am more enamored of a fully shunt regulated power supply for that last bit of nuance. There is no such current product but I AM working on it!