[tubegroove]

Hello All, I am very recent owner of a new RM-10MkII which Roger made for me after very patiently responding to my many questions (and some of my misconceptions as well!  ).  I also surfed this forum a fair bit during the research process. Many of the posts here were helpful in answering questions and understanding the product better, so thanks to all the members for their posts
I use it with a TVC Passive pre from Music First Audio (with MkII transformers) and Green Mountain Audio Callisto bookshelf speakers, which are a very easy 4ohm load.  Right out of the box I couldn't help but wonder if such a small sized amp would throw a big sound.  Roger said its small but feisty and he was right!  No worries on that count.  Its still settling down in my system but I like what I hear initially. I get good freq extension at both ends of the spectrum and a nice midrange. Oh and its also the quietest tube amp by a mile and a half that I have ever had in my set up!
I connected the speakers to the obvious 4ohm tap but have been curious about "light loading".  Roger suggested that I try the 4 and 8 ohm taps simultaneously as minus and plus respectively and ignore the 0 tap (which, if I understood him correct, would be the equivalent of a 2ohm tap, or light loading position for a 4ohm speaker).
Has anyone tried this on their 4 ohm speaker? In my experience, with 2ohm equivalent light loading, the bass improves in definition,and while the mids and highs sound very clean, for some reason sound restrained and distant.  Can't imagine why.  Thinking of persisting for a bit with this setting.  Any inputs would be appreciated.  Thanks

[Ralph]

Hello All, I am very recent owner of a new RM-10MkII which Roger made for me after very patiently responding to my many questions (and some of my misconceptions as well!  ).  I also surfed this forum a fair bit during the research process. Many of the posts here were helpful in answering questions and understanding the product better, so thanks to all the members for their posts
I use it with a TVC Passive pre from Music First Audio (with MkII transformers) and Green Mountain Audio Callisto bookshelf speakers, which are a very easy 4ohm load.  Right out of the box I couldn't help but wonder if such a small sized amp would throw a big sound.  Roger said its small but feisty and he was right!  No worries on that count.  Its still settling down in my system but I like what I hear initially. I get good freq extension at both ends of the spectrum and a nice midrange. Oh and its also the quietest tube amp by a mile and a half that I have ever had in my set up!
I connected the speakers to the obvious 4ohm tap but have been curious about "light loading".  Roger suggested that I try the 4 and 8 ohm taps simultaneously as minus and plus respectively and ignore the 0 tap (which, if I understood him correct, would be the equivalent of a 2ohm tap, or light loading position for a 4ohm speaker).
Has anyone tried this on their 4 ohm speaker? In my experience, with 2ohm equivalent light loading, the bass improves in definition,and while the mids and highs sound very clean, for some reason sound restrained and distant.  Can't imagine why.  Thinking of persisting for a bit with this setting.  Any inputs would be appreciated.  Thanks

I am currently running my Sequels (4 ohm nominal) on the 2-ohm tap of my RM-9 and the sound has increased in clarity and bass solidity. Although the power output does diminish, according to Roger, the current increases, so that the volume is more than adequate at this setting. Roger had suggested this to me and he was absolutely right!

Ralph Steinberg

[tubegroove]

Ralph, thanks for sharing your experience.  I find it particularly interesting (reading your other post under the "speaker cable for RM-9 thread) that you eventually went back to the 2ohm tap.  I have been listening on the 4ohm tap thus far but plan to give the effective 2ohm tap another shot (when I get some time to listen at length to do a A/B) - I did note the enhanced clarity and bass firmness when I briefly tried the 2ohm tap, but the volume level seemed to drop too much - but that could have been a result of some new cables that were in my system at the time.

[Ralph]

My initial impression of the sound on the 2-ohm tap was one of an anemic, thin sound, lacking body and natural warmth. The problem turned out to be speaker placement! I moved the Sequels about 6 inches further out from the rear wall and presto! In your case, it is possible that new cables might be reacting differently to the lower impedance load. Does your RM-10 have adjustable gain/feedback, as the RM-9 does?
Ralph

[Ralph]

One other thought: Going to the 2-ohm tap along with maximum feedback (LO gain setting) does indeed change the sound greatly. As feedback increases and load impedance decreases, all sense of congestion and overload in loud passages disappears. In its place is a sense of openness, tranparency and sheer effortlessness, along with what sounds like a greatly expanded dynamic range. Is it possible that you were hearing actually a loss of congestion and opacity rather than a loss of power? I'd be interested to hear your impressions and thoughts.

Ralph

[tubegroove]

Ralph
The RM10 does not have any controls for feedback etc.  Its all hard wired into the circuit.  I never thought of  speaker placement as a variable! Maybe I will experiment with that as well (but that tends to be more tricky).  One change I might try is how I treat the 8ohm and 4ohm tap.  Right I call the 8ohm +ve and the 4ohm -ve.  I will try reversing that as well.  My DAC inverts the signal phase so the end polarity at the amp out might make a difference (I am guessing now)

[Ralph]

Well, since I have dipole speakers, placement is very critical. In fact, I have to use tape measure and a bubble leveler, otherwise both the soundstage and the sound itself deteriorate. The better the system, the more fine adjustments will affect it. Let us know how reversing the cables might affect the sound upon light loading.
Best,
Ralph

[Roger A. Modjeski]

It appears you guys are having fun.

[pehare]

Roger...does light loading the RM 10 effectively create class A amplification up to a certain power level on an 8 ohm speaker?  I've never owned another tube amp that sounded better on the 4 ohm taps than 8 with my speakers which are an easy 8 to 10 ohm load....

[Roger A. Modjeski]

Roger...does light loading the RM 10 effectively create class A amplification up to a certain power level on an 8 ohm speaker?  I've never owned another tube amp that sounded better on the 4 ohm taps than 8 with my speakers which are an easy 8 to 10 ohm load....

Yes, light loading doubles the class A range and in that range the distortion can be 5-10 times lower. Every amp I have made benefits from it.

[tubegroove]

Roger,
Btw, what is the standard Class A range for the RM10?
Also, how much power is the amp expected to lose when I move from the 4ohm to the effective 2ohm tap on the RM10?
Thanks

[Roger A. Modjeski]

Roger,
Btw, what is the standard Class A range for the RM10?
Also, how much power is the amp expected to lose when I move from the 4ohm to the effective 2ohm tap on the RM10?
Thanks

The class A range with a load equal to the tap is around 10 watts. You can connect your bias meter while playing music and when the reading increases say 10% you are out of class A. An analog meter would be best or a digital with a bar.

Each step you go down in light loading reduces the output voltage 3 DB and the power to half. The 4-8 tap is 2 steps down.

[tubegroove]

Thanks, this is helpful information. I use a 4ohm speaker.  I assume this 4ohm load on the 4ohm tap will have the advantage of the full 35W/ch.  Also as I understand it, the 4-8 tap is therefore only 1 step down in my set up.  If so, then following what you have explained, does the amp effectively become a 17.5W/ch (half power) with the 4ohm load connected to the 4-8 tap?  I recall reading on the MR website that the only penalty so to speak of light loading is a 20% loss in power.
Also, since the Class A range (4ohm load on the 4ohm tap) is ~10W and since light loading doubles the Class A range, would I be accurate in assuming all 17.5W be in Class A (4ohm load on 4-8tap)?
................Just trying to reconcile the different bits of information in my mind 

[tubegroove]

Ralph,
I finally managed to get behind the RM10 and swap the speaker cables to the 4-8ohm tap (an injured right hand was holding me back).  This time I connected the -ve to the 8ohm (the last time I connected the +ve).  Its early days since I just made the change, but I think it sounds better (for whatever reasons) that my first attempt at light loading  - could even be my imagination since I am more used to the amp in general 
I do need to turn up the volume knob several notches so trying to determine if I have enough watts to play with (it should be enough for pretty much most of my music, is my guess). 
Will share more details as I listen more...

[tubegroove]

Is a shift from 4ohm load on 4ohm tap to 4ohm on 4-8tap one step down (ie power down to half or 17.5W)?

[Roger A. Modjeski]

Is a shift from 4ohm load on 4ohm tap to 4ohm on 4-8tap one step down (ie power down to half or 17.5W)?

Half power is about right. What matters is do you like the sound that way.

[Ralph]

Ralph,
I finally managed to get behind the RM10 and swap the speaker cables to the 4-8ohm tap (an injured right hand was holding me back).  This time I connected the -ve to the 8ohm (the last time I connected the +ve).  Its early days since I just made the change, but I think it sounds better (for whatever reasons) that my first attempt at light loading  - could even be my imagination since I am more used to the amp in general 
I do need to turn up the volume knob several notches so trying to determine if I have enough watts to play with (it should be enough for pretty much most of my music, is my guess). 
Will share more details as I listen more...

Great news! My thought was that reversing the leads with the +ve on the 4 ohm tap would more effectively light load the amp. Roger, does this make sense?
Ralph

[Ralph]

Dear Roger:
While we're on the subject of power, I get the impression that you don't buy into all the hype that certain reviewers in magazines like The Absolute Sound parrot about how it is necessary to have as much amplifier power as possible, and that speaker manufacturers underestimate the power requirements of their speakers. I seem to remember a statement of yours about "wasted watts." I am beginning to think that you are absolutely correct in this; contrasting the rather bass-heavy, congested sound that I would get from my older Counterpoint SA 20 (200 wpc) and even with the RM 9 connected at the 8 ohm taps and HI gain with the greater transparency, naturalness and bass impact (when called for) that I now get convinces me that sheer brute power output is way overrated. It may well be that part of the difference is the increase in the Class A range that you mentioned. All I know is that at the current settings, I get simply MUSIC from my system, rather than "impressive hifi."
Ralph

[tubegroove]

Half power is about right. What matters is do you like the sound that way.

Yes, I believe I like the sound better using the 4-8tap.  Thanks for sharing that tip with me 

[Roger A. Modjeski]

Dear Roger:
While we're on the subject of power, I get the impression that you don't buy into all the hype that certain reviewers in magazines like The Absolute Sound parrot about how it is necessary to have as much amplifier power as possible, and that speaker manufacturers underestimate the power requirements of their speakers. I seem to remember a statement of yours about "wasted watts." I am beginning to think that you are absolutely correct in this; contrasting the rather bass-heavy, congested sound that I would get from my older Counterpoint SA 20 (200 wpc) and even with the RM 9 connected at the 8 ohm taps and HI gain with the greater transparency, naturalness and bass impact (when called for) that I now get convinces me that sheer brute power output is way overrated. It may well be that part of the difference is the increase in the Class A range that you mentioned. All I know is that at the current settings, I get simply MUSIC from my system, rather than "impressive hifi."
Ralph

Ralph, you are correct, I do not buy the notion that one must have unlimited power. One must remember that the majority of writers of TAS are not very technical or interested in circuit design. They just listen to stuff and write. As to speaker manufacturer's they more likely overestimate the Sound pressure levels (SPL) that most of us listen at. Speaker sensitivities have gotten higher over the past 10 years and many listeners, myself included, have found that the better the resolution of our system is, the lower volume is required to hear everything. If you compute the level of a 90 dB/watt speaker and a 100 watt amplifier you get 110 dB SPL. Many of us listen at 70-80 dB SPL which means we only need one tenth of a watt for that speaker.

As many of you know, I started Audio Art in Richmond Virginia in 1976. We had big listening rooms, Magnepan MG-2s and SAE electronics in one listening room. I would often put on the vinyl brought or selected by the customer, show him to the volume control, tell him to turn it up as much as he liked because the 100-250 watt SAE amp could not blow up the MG-2s. Then I closed the door and left the room.  The house we were using for our store was built in 1865 and had one foot thick brick walls. I often heard some pretty loud sound coming through that I would estimate to be 110 dB SPL.

We also had a room devoted entirely to Electrostatic speakers and high quality tube amps. In that room sensible customers could hear every detail at 80 dB. In that room I could stay and visit with customers.

I have been swimming against the tide of high power for some time now. The little RM-10 surprises people in it's ability to drive a wide range of speakers. It has plenty of headroom

If you listen below one watt it matters not if you have 19 watts of headroom or 99 watts. You need some headroom but consider the following: I have looked at a lot of CDs on the oscilloscope. A large number of them actually show clipping of the source material. In Willie Nelson's Stardust, there are several places where the drum rim-shot are clipped. I would say the headroom on that CD is about minus 6 dB. The guy who re-mastered that should be fired. I have the same recording on vinyl and it doesn't clip. Perhaps this is one of the reasons that vinyl is coming back. Digital is not a bad medium but it is being abused by producers, artists and recording engineers. With over 100 dB of dynamic range and a master tape with at best 70 dB range, why do you have to remaster the CD into clipping? I have often said that when you notice a CD plays significantly louder than others it is severely compressed or clipped.

Even if we have great source material The concept of unlimited headroom is a false one. Weather by choice or necessity, TAS has taken on reviewing the most expensive equipment out there. In the September 2011 edition Robert Harley, being about the only technical guy they have, had the task of reviewing a 1000 watt mono-bloc amplifier that costs $140,000 a pair. He felt that SET (single ended triode) amps have a more palpable and direct communication in the midrange. Later he mentioned that although the bass was deeply extended and powerful it was not the last word in fullness and heft. Well, SETs are generally low powered so there goes the unlimited headroom notion and that a very expensive amplifier is the absolute best.

I've been promoting "Light Loading" because it improves the low power range of a high powered amp. I see that several members here are trying it out with good results. Indeed when you put an 8 ohm speaker on the 4 ohm tap it sounds better because now you have a 20 watt amplifier with a larger class A region, more damping and flatter response. I have measured and heard the difference. Since the RM-10 is capable of over 35 watts per channel, you still have the option of that power should you need it for a party by simply using the 8 ohm tap.