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THE ROGUE 90 STEREO AMPLIFIER REVISITED
Since my original article, the entire circuit board in the Rogue has been
replaced and I have also installed new Electro Harmonix KT88s. For all
practical purposes, it can be considered a new amplifier. I wanted to come
back to this amp and address several issues that its break down in
December precluded.
I feel that I have enough hours on the Rogue at this point to consider it,
once again, broken-in. If further hours provide any notable changes in its
sound or performance, I will certainly report them. For now, though, I feel
that my system is once again performing as the audio gods intended.
The input tubes are still NOS Westinghouse 12AX7s; the 6SN7s are a Philco
and a Hytron of unknown age but good working condition. The Rogue is
silent through the speakers but does have some just-audible hum at its
chassis when the amp is cold. This hum drops in level once the amp is
warmed up but does not entirely disappear. It may be as quiet as it is
possible for it to be. I am still investigating.
As a sound staging junkie, I could not be happier with what I am hearing. I
am getting a wide and deep, very stable sound stage with lots of detail.
Tonally, everything from the highest treble to the lowest mid-bass
frequencies sounds wonderful. (The Rogue handles the frequencies from
80Hz up.) Every CD sounds different and unique, yet the Rogue seems to
get the best possible sound from each of them. The lack of noise makes it
possible to hear the subtlest inflections in the music. Overall, my system is
sounding the best that I have ever heard it. What a relief! After the ups
and downs since December, it is great to be able to sit down and wallow in
the music again.
Unfortunately, I can only wallow so long and then I have to start messing
with things.
TRIODE VERSUS ULTRALINEAR MODE
One of the other things I never got a chance to mess with before the Rogue
broke down was comparing its Triode and Ultralinear modes.
There is a small switch on the back of the amp that selects between the
modes and it can even be switched while the amp is playing, according to
the owner’s manual. I was reluctant to do that but found I could pause my
transport, flip the switch, and be in the other mode in just seconds.
I listened to a variety of CDs while trying out the two modes and found the
difference between them to be very small. Here is what I hear: Triode mode
is, to use a photographic analogy, like using a very minimal diffusion filter to
take your photos. It flatters slightly but when examined closely there is a
small amount of detail missing. I want to stress that fact that I am referring
to a very small amount of detail. I had to listen intensively, knowing which
mode I was in, to even discern this difference.
Based on this comparison, I am going to stay with Ultralinear mode in my
present set up. I do not find the very slight flattering the least bit
necessary. I also like knowing that the amp is capable of achieving its
maximum power, which is one of the reasons I bought it. It is entirely
possible that, with a change in any component, the triode mode may be the
more enjoyable way to listen. We shall see. It is certainly something that I
expect to come back to.
FOUR VERSUS EIGHT OHMS
Once again, I spent time listening to both output connections and found no
difference that I could reliably hear, despite the fact that my speakers are
rated at a four Ohm impedance. I ended up using the eight Ohm taps
simply because the Rogue seems to play slightly louder when my speakers
are connected to them. While I appreciate the economics of making a high
quality tube power amp in the USA, I would be willing to pay slightly more
for the Rogue if they added a third binding post so that either transformer
tap could be tried without having to change its connection from the inside of
the amp. I would even forego the Triode/Ultranlinear capability for this
binding post. Or just punch a hole in the chassis when its being
manufactured so that I can add the binding post myself. I would be happy
with that, too.
PLAYING WITH SOME TUBE DAMPERS
In the June 2006 Hi Fi News, there is an article on tube microphonics written
by Ken Howard. Using a Prima Luna Three preamp and Four power
amplifier, his test set-up allowed him to visually depict the microphonics
present in their tubes with and without damping devices attached to them.
To very briefly summarize his results, the only external tube damper that
actually reduced microphonics was the Tube Ring (www.tuberings.com), a
PTFE ring that is held in place by a titanium circlip. The Tube Ring were no
better, however, than simply putting the tube cage back on the unit. No
other damping devices did anything and nothing affected the microphonics
of the power amplifier tubes.
I have been waiting since last fall to try some inexpensive* silicone damping
rings on the tubes in the Rogue. Despite the results gotten by Mr. Howard,
I felt it was still worthwhile experimenting with them since he did not use
this type of ring and my components/listening room situation might offer
somewhat different results. I am ever the optimist where my system is
concerned.
THE QUESTION
The question that needs to be asked is why should an external damping
ring affect the performance of any tube? The tube guts are inside a glass
envelope in a vacuum so is there any reason to expect that damping the
glass will affect its internals? Isn’t this a bit like sticking blocks of foam
rubber on your car windows in hopes of improving the wheel balance?
As it turns out, the answer is no. I have examined quite a few different
tubes and all of them have some sort of connection between the internals
and the glass envelope. This connection varies from fine wires, to little bent
tabs, to mica rings and rectangles, and all of these connections exist to
center the internal parts. They do this by touching the glass over very small
areas—areas the size of the period at the end of this sentence in some
cases. This connection, however minute, has the potential to allow outside
vibration into the tube via the glass envelope. The energy from these
vibrations can then interact with precision-tolerance parts whose spacing is
very critical.
Let’s not overlook the fact either that vibration also enters the tube via its
socket connection.
This then leads to the question of how much vibration does it actually take
to affect a tube’s performance and at what point is that audible? I am not
sure that there is a clear-cut answer to this.
I can say, that in the case of the Rogue, tapping the tubes sharply with its
biasing tool does not cause any resultant noise from the speakers and each
tap is undoubtedly magnitudes of force higher than anything it will ever see
from external vibrations.
Still, I have the damping rings and I’m not going to happy until I try them
on something.
As I see it, there are three sources of vibration, which can potentially affect
the tubes in an audio component.
ACOUSTIC VIBRATIONS
Vibrations coming through the air and striking the tube are the vibrations
we usually think of when considering tube microphonics. These are probably
the highest energy vibrations acting on the tubes in most rooms and they
can come from any direction in the room. If you are unlucky enough to
have a tube sitting right in a low frequency room mode, it might get a pretty
good working over.
TERRESTRIAL VIBRATIONS
How many earthquakes do you think affect our planet every day? According
to www.infoplease.com the number is right around 8,000. That is not a
typo. While the vast majority of these seismic vibrations are too small to
feel, they are evidently not too small to measure. How many of them have
the energy to affect my Rogue amp’s tubes through the basement floor slab
where it sits on a stand that sits on carpet over padding? I have no idea
but I would expect the number to be pretty low. Still, if you think of your
equipment as being relentlessly shaken** by the planet you live on, you are
absolutely correct.
There are other terrestrial vibrations to consider as well. When your
woofers energize the air, they also affect the floor under them. Don’t
overlook, either, the vibrations rippling out from the refrigerator when it
runs or from other motorized appliances if they share the same floor as
your audio system. I can feel the trash truck stop at our house even down
in the basement listening room. The list is long.
If anything, I think we probably underestimate the energy entering our
systems via the floor beneath them.
INTERNAL VIBRATIONS
If you can hear your power transformer hum, it is feeding vibrations into the
chassis. Even if you can’t hear it hum, it’s still probably feeding some
vibration into the chassis.
From an audio perspective, there just really aren’t any good vibrations.
So given this relentless vibrational assault is there any reason to believe
that some inexpensive silicone damping rings are going to effect any
worthwhile reduction in the energy hitting your tubes? The only way to find
out is to try them.
I installed two damping rings on each tube. To avoid blocking the opening
between the 12AX7 tubes and the chassis, I put both rings on either side of
the uppermost of the two mica centering rings. On the 6SN7s, I put the
rings on the glass as close to the centering structures as I could. The
centering tabs in the KT88s are in the top of the tube and the rings are
made to fit on the large bulge. I put a ring near the top and bottom of each
bulge. Click here for a photo.
It was necessary to remove the tubes to put on the rings. In anticipation of
this, I had removed and reinstalled all the tubes before I started my listening
session to insure that I wasn’t hearing a change due to simply reseating the
tubes. I listened for about an hour to several CD tracks that I thought
would be informative. I shut off the amp for about fifteen minutes to let the
tubes cool enough to install the rings. I let the amp warm back up and re-
listened to the same tracks.
I felt that installing the damping rings resulted in a very small increase in the
silences between notes. The background was blacker by a barely perceptible
amount. Or the dampers made no real difference; it was that hard to tell.
Still, I intend to leave the damping rings on the tubes. While there may not
have been any blatantly obvious improvement in the sound, there was no
harm done to it either. Tube internals are connected to their glass
envelopes as well to their mounting pins. There exists the potential for
these damping rings to do some good, however small.
Also, I leave the chassis cover off of the Rogue since I am frequently
checking bias or playing with input tubes. If the dampers offer the same
benefits that would come from keeping the cover on, that alone makes
using them worthwhile in my situation.
Finally, I am a big believer in what I call the “cumulative effect,” that small,
virtually inaudible improvements will eventually add up to a clearly audible
improvement. At least I live in hope that this is happening.
In the final analysis, these damping rings are inexpensive enough to be
worth experimenting with. Even if the results are not hugely audible***,
they still make sense to try in your own system.
IN CONCLUSION
Other than continuing to look for some interesting 6SN7s to try in the
Rogue Stereo 90 amplifier and listening for any further changes in its sound
as it accumulates hours, I don’t expect to say much more about it. This is a
very fine amplifier. Buying it was a decision that I am happily looking
forward to living with.
Kent Johnson
April 16, 2007
*About $30 for all the rings, which I purchased on eBay. I have plenty of
small tube rings left over.
**Please note how I resisted adding “not stirred.” Or maybe I didn’t.
***Frankly, if installing any sort of damping ring resulted in a huge change
in the sound of a given system, I would suspect that it was a coincidence
and that something else had actually occurred.
****I’ve got to learn how to do actual footnotes.
Since my original article, the entire circuit board in the Rogue has been
replaced and I have also installed new Electro Harmonix KT88s. For all
practical purposes, it can be considered a new amplifier. I wanted to come
back to this amp and address several issues that its break down in
December precluded.
I feel that I have enough hours on the Rogue at this point to consider it,
once again, broken-in. If further hours provide any notable changes in its
sound or performance, I will certainly report them. For now, though, I feel
that my system is once again performing as the audio gods intended.
The input tubes are still NOS Westinghouse 12AX7s; the 6SN7s are a Philco
and a Hytron of unknown age but good working condition. The Rogue is
silent through the speakers but does have some just-audible hum at its
chassis when the amp is cold. This hum drops in level once the amp is
warmed up but does not entirely disappear. It may be as quiet as it is
possible for it to be. I am still investigating.
As a sound staging junkie, I could not be happier with what I am hearing. I
am getting a wide and deep, very stable sound stage with lots of detail.
Tonally, everything from the highest treble to the lowest mid-bass
frequencies sounds wonderful. (The Rogue handles the frequencies from
80Hz up.) Every CD sounds different and unique, yet the Rogue seems to
get the best possible sound from each of them. The lack of noise makes it
possible to hear the subtlest inflections in the music. Overall, my system is
sounding the best that I have ever heard it. What a relief! After the ups
and downs since December, it is great to be able to sit down and wallow in
the music again.
Unfortunately, I can only wallow so long and then I have to start messing
with things.
TRIODE VERSUS ULTRALINEAR MODE
One of the other things I never got a chance to mess with before the Rogue
broke down was comparing its Triode and Ultralinear modes.
There is a small switch on the back of the amp that selects between the
modes and it can even be switched while the amp is playing, according to
the owner’s manual. I was reluctant to do that but found I could pause my
transport, flip the switch, and be in the other mode in just seconds.
I listened to a variety of CDs while trying out the two modes and found the
difference between them to be very small. Here is what I hear: Triode mode
is, to use a photographic analogy, like using a very minimal diffusion filter to
take your photos. It flatters slightly but when examined closely there is a
small amount of detail missing. I want to stress that fact that I am referring
to a very small amount of detail. I had to listen intensively, knowing which
mode I was in, to even discern this difference.
Based on this comparison, I am going to stay with Ultralinear mode in my
present set up. I do not find the very slight flattering the least bit
necessary. I also like knowing that the amp is capable of achieving its
maximum power, which is one of the reasons I bought it. It is entirely
possible that, with a change in any component, the triode mode may be the
more enjoyable way to listen. We shall see. It is certainly something that I
expect to come back to.
FOUR VERSUS EIGHT OHMS
Once again, I spent time listening to both output connections and found no
difference that I could reliably hear, despite the fact that my speakers are
rated at a four Ohm impedance. I ended up using the eight Ohm taps
simply because the Rogue seems to play slightly louder when my speakers
are connected to them. While I appreciate the economics of making a high
quality tube power amp in the USA, I would be willing to pay slightly more
for the Rogue if they added a third binding post so that either transformer
tap could be tried without having to change its connection from the inside of
the amp. I would even forego the Triode/Ultranlinear capability for this
binding post. Or just punch a hole in the chassis when its being
manufactured so that I can add the binding post myself. I would be happy
with that, too.
PLAYING WITH SOME TUBE DAMPERS
In the June 2006 Hi Fi News, there is an article on tube microphonics written
by Ken Howard. Using a Prima Luna Three preamp and Four power
amplifier, his test set-up allowed him to visually depict the microphonics
present in their tubes with and without damping devices attached to them.
To very briefly summarize his results, the only external tube damper that
actually reduced microphonics was the Tube Ring (www.tuberings.com), a
PTFE ring that is held in place by a titanium circlip. The Tube Ring were no
better, however, than simply putting the tube cage back on the unit. No
other damping devices did anything and nothing affected the microphonics
of the power amplifier tubes.
I have been waiting since last fall to try some inexpensive* silicone damping
rings on the tubes in the Rogue. Despite the results gotten by Mr. Howard,
I felt it was still worthwhile experimenting with them since he did not use
this type of ring and my components/listening room situation might offer
somewhat different results. I am ever the optimist where my system is
concerned.
THE QUESTION
The question that needs to be asked is why should an external damping
ring affect the performance of any tube? The tube guts are inside a glass
envelope in a vacuum so is there any reason to expect that damping the
glass will affect its internals? Isn’t this a bit like sticking blocks of foam
rubber on your car windows in hopes of improving the wheel balance?
As it turns out, the answer is no. I have examined quite a few different
tubes and all of them have some sort of connection between the internals
and the glass envelope. This connection varies from fine wires, to little bent
tabs, to mica rings and rectangles, and all of these connections exist to
center the internal parts. They do this by touching the glass over very small
areas—areas the size of the period at the end of this sentence in some
cases. This connection, however minute, has the potential to allow outside
vibration into the tube via the glass envelope. The energy from these
vibrations can then interact with precision-tolerance parts whose spacing is
very critical.
Let’s not overlook the fact either that vibration also enters the tube via its
socket connection.
This then leads to the question of how much vibration does it actually take
to affect a tube’s performance and at what point is that audible? I am not
sure that there is a clear-cut answer to this.
I can say, that in the case of the Rogue, tapping the tubes sharply with its
biasing tool does not cause any resultant noise from the speakers and each
tap is undoubtedly magnitudes of force higher than anything it will ever see
from external vibrations.
Still, I have the damping rings and I’m not going to happy until I try them
on something.
As I see it, there are three sources of vibration, which can potentially affect
the tubes in an audio component.
ACOUSTIC VIBRATIONS
Vibrations coming through the air and striking the tube are the vibrations
we usually think of when considering tube microphonics. These are probably
the highest energy vibrations acting on the tubes in most rooms and they
can come from any direction in the room. If you are unlucky enough to
have a tube sitting right in a low frequency room mode, it might get a pretty
good working over.
TERRESTRIAL VIBRATIONS
How many earthquakes do you think affect our planet every day? According
to www.infoplease.com the number is right around 8,000. That is not a
typo. While the vast majority of these seismic vibrations are too small to
feel, they are evidently not too small to measure. How many of them have
the energy to affect my Rogue amp’s tubes through the basement floor slab
where it sits on a stand that sits on carpet over padding? I have no idea
but I would expect the number to be pretty low. Still, if you think of your
equipment as being relentlessly shaken** by the planet you live on, you are
absolutely correct.
There are other terrestrial vibrations to consider as well. When your
woofers energize the air, they also affect the floor under them. Don’t
overlook, either, the vibrations rippling out from the refrigerator when it
runs or from other motorized appliances if they share the same floor as
your audio system. I can feel the trash truck stop at our house even down
in the basement listening room. The list is long.
If anything, I think we probably underestimate the energy entering our
systems via the floor beneath them.
INTERNAL VIBRATIONS
If you can hear your power transformer hum, it is feeding vibrations into the
chassis. Even if you can’t hear it hum, it’s still probably feeding some
vibration into the chassis.
From an audio perspective, there just really aren’t any good vibrations.
So given this relentless vibrational assault is there any reason to believe
that some inexpensive silicone damping rings are going to effect any
worthwhile reduction in the energy hitting your tubes? The only way to find
out is to try them.
I installed two damping rings on each tube. To avoid blocking the opening
between the 12AX7 tubes and the chassis, I put both rings on either side of
the uppermost of the two mica centering rings. On the 6SN7s, I put the
rings on the glass as close to the centering structures as I could. The
centering tabs in the KT88s are in the top of the tube and the rings are
made to fit on the large bulge. I put a ring near the top and bottom of each
bulge. Click here for a photo.
It was necessary to remove the tubes to put on the rings. In anticipation of
this, I had removed and reinstalled all the tubes before I started my listening
session to insure that I wasn’t hearing a change due to simply reseating the
tubes. I listened for about an hour to several CD tracks that I thought
would be informative. I shut off the amp for about fifteen minutes to let the
tubes cool enough to install the rings. I let the amp warm back up and re-
listened to the same tracks.
I felt that installing the damping rings resulted in a very small increase in the
silences between notes. The background was blacker by a barely perceptible
amount. Or the dampers made no real difference; it was that hard to tell.
Still, I intend to leave the damping rings on the tubes. While there may not
have been any blatantly obvious improvement in the sound, there was no
harm done to it either. Tube internals are connected to their glass
envelopes as well to their mounting pins. There exists the potential for
these damping rings to do some good, however small.
Also, I leave the chassis cover off of the Rogue since I am frequently
checking bias or playing with input tubes. If the dampers offer the same
benefits that would come from keeping the cover on, that alone makes
using them worthwhile in my situation.
Finally, I am a big believer in what I call the “cumulative effect,” that small,
virtually inaudible improvements will eventually add up to a clearly audible
improvement. At least I live in hope that this is happening.
In the final analysis, these damping rings are inexpensive enough to be
worth experimenting with. Even if the results are not hugely audible***,
they still make sense to try in your own system.
IN CONCLUSION
Other than continuing to look for some interesting 6SN7s to try in the
Rogue Stereo 90 amplifier and listening for any further changes in its sound
as it accumulates hours, I don’t expect to say much more about it. This is a
very fine amplifier. Buying it was a decision that I am happily looking
forward to living with.
Kent Johnson
April 16, 2007
*About $30 for all the rings, which I purchased on eBay. I have plenty of
small tube rings left over.
**Please note how I resisted adding “not stirred.” Or maybe I didn’t.
***Frankly, if installing any sort of damping ring resulted in a huge change
in the sound of a given system, I would suspect that it was a coincidence
and that something else had actually occurred.
****I’ve got to learn how to do actual footnotes.