[abernardi]

Hi Everybody,
  I've been reading this circle for a few months now and you guys (with the help of some great reviews) inspired me to pick up a used Sensation M901.  It's very exciting, I'm coming back into audio after a 10 year hiatus and things have certainly changed.  This time around I'm focusing on putting together a GREAT sounding stereo system for little $$$.  The Sensation is a great "bang-for-the-buck" piece of gear!  I'm just about to pull the trigger on a pair of exquisite speakers made by "Avlar".  Avlar never quite got off the ground, but they made a fantastic speaker.  It's a variant on the Heil AMT that goes all the way down to 500Hz.  If you know this driver, it's very open and extends way, way up and is very sensitive (100db/1W).
  So I took the Sensation M901, w/Sonicaps platinum bypass, Dodd tube buffer with the standard tube and batteries (btw, it has over 100 hours on it from the previous owner), to the store and we hooked it up to the Avlars.  The owner had heard of Virtue but never actually heard one.  One of the salesmen was pretty skeptical about the battery.  I just smiled because even without hearing it yet, I was pretty certain based on what I've read here, that they were going to be blown away. 
   The first thing I noticed was the beautifully smooth and silky low end.  We looked at each other and the owner paused and just said..."Good amp."  It was one of those short observations that meant much more than a long critique.  We ran into a snag right away, not the amp's fault, but the speakers had the wrong AMT's in them.  They were tuned for the bigger speaker model, so the high end was greatly exaggerated.  And of course, so was the noise floor.  We swapped the speakers out for a pair of GoldenEars towers nearby and everything was balanced right, though while very good sounding, the GoldenEars couldn't quite reach the sense of reality that the Avlars presented.
   So, here's my concern and a question.  The noise floor was still noticeable.  It was a slight hiss that could be heard from the sitting position.  Not loud but once you're focused on it, it's there.  You could also hear it in the quite sections of the recorded material.  We were listening to a Dianna Krall cut, very sparse, lots of long pauses and the hiss was apparent.  Now I've read thru a lot of posts here and understand there is a certain amount of noise that can come from the tripath chip and the tube buffer and that it's very susceptible to magnetic fields, RF, etc.  I didn't know that at the time, so I'll have to play with it next time I go to the store.  The question I have is, under most conditions the hiss will not be noticeable with most music.  Is this because the material is just louder than the noise floor, or does the noise floor actually drop?  I'm curious because there seems to be so much effort put into getting the signal to the speaker as pure as possible and if the noise floor is still there, though inaudible, couldn't it still have some kind of detrimental effect?  Smearing, etc?
   The other thing I noticed was after about 20 min. there was a very high pitched hum or tone, faint but there.  I think the batteries were probably getting low, that's my guess.  I plugged them into their AC regenerator and it went away, but was replaced by an even higher pitched, but fainter hum.  The batteries were fully charged when I received the amp, but it sat for about a week before I hooked it up.  Is it normal for the batteries to lose their charge in that time?
   Anyway, overall, I'm really pleased with this amp.  Even with the bad driver, I could tell the detail was there and it wasn't harsh (comparatively).  Hopefully this weekend I'll be able to do it again with the right drivers and take them home.  Thanks for the great work Virtue!

[virtue]

Welcome!

Yes, the amp is not absolutely silent.  It's very dependent on the tubes you use but is not absolutely silent with the buffer turned off either.  On very sensitive speakers you will hear it more; most customers barely notice it. 

Yes, the amp whines when the batteries get very low.

Yes, you'll hear a rustling on the buffer version when you change volume.  It's startling at first, strange later on.  We never figured out how to get rid of it... never planned on putting a buffer inside the unit when we designed it.  It was fortuitous in many respects.

Maybe running a buffer outside the amp, before ithe signal reaches the POT would work, not sure.  Gary sells an external buffer.

Yes, it's a great sounding amp! 

Hope you grow to love our work, the good, the bad, the ugly.

Seth

[Jason T]

Cami has found that moving the power wire for the buffer around can reduce the noise floor significantly.
play with it a little and you should notice an improvement

[abernardi]

You know, concerning the rustling pot, now that i think of it, it sounds exactly like a dirty pot.  I haven't come across one for some time because I thought the technology had changed.  The cure was simple, just quickly rotate the pot back and forth a few times and it clears out the oxidation or dirt.  If it's really dirty there's a cleaning spray you can use.  Maybe that's what's going on with this amp.  I'll have to try it next time I hook it up.  Anyone try this?

[virtue]

It's been tried and it helps - a little.  It's a combination of routine oxidation with the ultra-high impedence buffer. We went with solid-state pots on the THREE to avoid stuff like this.

[oskar]

I have a non-buffered battery Sensation. My speakers are 90db sens. With the volume pot wide open I hear absolutely.... nothing. That's with my ear next to the driver. Have you tried turning off the buffer?

[marvda1]

how about an update adam?  try a phono grade tube from upscale audio.  maybe a mullard or rtf 12au7.
marvin

[Mama Virtue]

The power wire (usually orange, runs to the monster power cap) on most units does not have a lot of extra length to move a whole lot. The best thing to do for that "fix" is to turn the amp with buffer on, volume up until you can hear the hiss either easily without moving closer to the speakers or to have it up enough that when you move close to one or the other you've notice a difference. try anything from putting the wire as close to the chip board as possible, moving it up and over components etc. However, the solder joint is somewhat delicate (or should I say the wire) so move slowly and carefully. Once you find the "sweet" spot (lowest hiss) leave the wire in that position (may even need to tie it in place...carefully of course  ). You may notice less rustle in the volume knob as well. IF you have a wire long enough, try running/pulling it along the face as much as possible.

All amps have the wire in what we found to be the quietest position before shipping. That doesn't mean it didn't move out of place during shipping  And yes, many customers have found upgrading the tube itself to a better, higher end tube than the stock tube helps significantly. Tom Brink and others have discovered quite a few of these quieter tubes.

Also, do you have the stock 24V/65W power supply? If you do please unplug the batteries (after proper power down) and plug in the PSU. Is there still the whine? If there is, we can rule out low batteries. If you don't have the stock 24V PSU, I'll send you one.

Lastly what battery charger do you have? Is it a Soneil charger? If it's not please email me at cami@virtueaudio.com

[virtue]

Trust me, I'm not thrilled at all with the "piano tuning" recommendation above.  Moving internal wires by hand on a live system is not prudent and continual trial and error sucks.  Use a wooden chopstick or something, please!

I've challenged Gary to come up with a new way to wire the buffer and upgrade options that are compelling enough to justify a mail-back upgrade.

We'll see what he comes up with. 

[tabrink]

 
I have probably swapped more tubes than I have hairs on my head and some are dead quiet (Psvane/ Sylvania)  and some get a little noisy at times. I can tell you that with any tube if I just go and fire up the Sensation after a shut down it is going to be 30-60 minutes before it gets very quiet. Most definitely when your batteries are low the noise can be significant. I can tell no difference keeping the charger continuously plugged in or separating from the power conditioner. Indeed if you are solely on battery and notice background noise just plug in the charger and wait thirty  minutes and you will notice the noise went away. I personally have never turned the buffer off so have no clue what eliminating the tube might offer.
I can tell you IF I shut down my Sensation (seldom) I always fire up it a few hours before listening along with whatever DAC I am using and it will be dead silent. If you are walking in and cold starting your Sensations they are going to be noisy for 30-60 minutes and then the joy begins.
I have also found this to be true of nearly every DAC I have owned.
Best,
Tom

[abernardi]

Tabrink - "Ahh, I see!", said the blind man.

I completely forgot about warm-up.  Hopefully later this week I'll go down to the store again and check all this out.  Maybe I could hear the whine change because the AMT is so sensitive?  Or maybe it was just a function of low batteries.  More to come

Mama Virtue - I do have the Soneil charger for the batteries.  I also have a GPE 24V - 2500mA 60VA charger, I assume that's the stock charger.  I will try your suggestions, but I'm also nervous about poking around a live amp feeding expensive speakers.  As to turning the volume up until you hear the hiss, the volume makes no difference.  The hiss was at a constant level regardless of the volume knob position. 

Once I get the system set up at home, I'll start playing with tubes.  That being said, this is the first time I've had any tube equipment.  I think my father had a decent Scott or Fisher tube receiver, but that was many years ago and I only remember the glow in the box (and the TV).  Anyway, I have some fundamental questions, please don't laugh...

why is it called rolling tubes? 

I heard tubes should be treated like tungsten bulbs, don't touch them with bare hands because the oil from you skin will damage the glass.  Is that true?

I assume that tubes get pretty hot, should the amp be given any extra room to breathe?

I did know about the 30 min. warmup, just forgot.  Is it ok to leave the unit on?  Is it preferable?  There's debate on solid state equipment about that.  Some say leave it on because the stress of powering up multiple times will burn something out sooner than just leaving it on.  Is that the same with tubes?

   THANKS!

[Mama Virtue]

Mama Virtue - I do have the Soneil charger for the batteries.  I also have a GPE 24V - 2500mA 60VA charger, I assume that's the stock charger.  I will try your suggestions, but I'm also nervous about poking around a live amp feeding expensive speakers.  As to turning the volume up until you hear the hiss, the volume makes no difference.  The hiss was at a constant level regardless of the volume knob position. 

I assume that tubes get pretty hot, should the amp be given any extra room to breathe?
   THANKS!

Honestly as I said, all amps have the wire in the best position, so it's mostly a last resort option. Try everything else first (new tubes etc)
My advice to all of our customers, whether its adjusting something or replacing something: if you're the least bit hesitant, or slightly uncomfortable, DON'T do it.
It's not worth raising your stress levels

In case no one has mentioned, the noise level of the buffer drops significantly after 150 hrs. The buffer breaks in, tube breaks in and the whole amp breaks in. We recommend at least 100 hrs with the stock amp. Since this unit is used you can probably assume it has somewhere from 50-200 hrs, if not more. I would suggest turning it on and leaving it on (can leave volume down) for several days before you go back to the store in case it has less hours. (assuming you have speakers currently)


IMO all gear should be given room to breathe. Electronics generally get warm or even hot and without sufficient air space around the unit, heat builds up. Just as your computer should have plenty of space for the fans to actually circulate the hot air out of the machine, and even though most gear doesn't actually have fans (far as I know...can't see all you guys being able to stand hearing that in the background) 3-6 inches of room next to the right side of the Sensation (heat sink/buffer side) is probably a good idea.We have never had an amp overheat, but most people have units stacked on shelves which obviously provides plenty of air circulation.