Music Reference Price List and Specific info on the EM-7 Series

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Roger A. Modjeski

Since my web guy is busy for awhile with other things I am posting the new price list here. Please feel free to continue this thread with any questions you may have.
Music Reference Price List  2007

Amplifiers:

EM7 Stereo 2.5 watt/channel SE power amp.    $750
EM7 Stereo 5 watt/channel SE power amp.      $925
EM7 12 Watt Monobloc (each)         $950
Stereo 5 and Mono 12 can be supplied any voltage at no extra charge.

245 45 or PX4 based Deluxe Stereo 4 watt/channel        $6,000
245.1  45 based Stereo 4 watt/channel less output tubes      $1,850

RM-10 MK II    35 watt/channel Push-pull EL-84/6BQ5       $1,950   
RM-200 MK II 100 watt/channel Push-pull KT-88         $4,200
RM-300 MK II 300 watt Monobloc Push-pull (each)      $4,750

Preamps:

Pot in a Box                  $135
2 Input Toggle Pot in a Box            $195   
3-6 Input Rotary Pot in a Box add $25 per input to above
Volume and Balance with multiple inputs        (call)

C4 Preamp 2 inputs with Regulated Power Supply   $850
Additional inputs up to 6, add $25 per pair.

RM 4+ 6DJ8/6922 Passive RIAA phono preamp          $950
RM 4 Our classic, first product Head Amp          $750
RM 4 and RM 4+ Two Box M/C phono system                $1,600

Speaker Systems:

The FE-103 Single Driver Speaker (each)             $225
Two Knob EQ in a box (variable frequency and level) $250
Fixed EQ in a Box*                       $150
EQ in the EM7 or C4 preamp*               $100

The ESL-1 Integrated Speaker System         $6,500

*This Passive EQ brings body and fleshes out the lower midrange of speakers lacking in that area. It improves our speaker and other hi-efficiency speakers markedly. No more thin lower midrange to suffer through. The difference is startling.


« Last Edit: 23 Aug 2007, 11:28 pm by Roger A. Modjeski »

Roger A. Modjeski

The EM7 Series Amplifiers

This series based on the 6EM7 and 13EM7 encompasses 3 distinctly different applications denoted by their power rating in watts per channel.  We rate at 5% distortion while most other makers rate at 10% or above. In most cases, they don’t even show these specifications. We go so far as to have a published curve that you can see at: http://www.ramlabs-musicreference.com/emlframe.html. Though drawn for the our 245.1 amplifier, the shape of the curve applies to the EM7 line also.

The EM7-2.5, 5 and 12 look the same from the front but have sets of connections on the back as to number of input and output terminals. We have a single thumb screw on top to allow entry with no tools at all. This makes biasing the 5 and 12 very easy. The 2.5 needs no adjustment ever.

EM7-2.5 The original EM7 now with external, easy to change output impedance selection. This is the perfect starter amp for those curious about SETs. Cathode bias requires no adjustment when changing tubes.  It simply takes care of itself. This is called “auto bias, cathode bias or self bias”.


EM7-5.0 Same circuit as the 2.5 but with a larger, higher voltage power transformer. To achieve higher power the bias is easily measured and adjusted to get the best performance from the EM7 tube. This is often called “fixed” bias, which is a confusing term because you can vary it. Since the EM7 is a very stable tube you don’t have to check or adjust it more than every few months.


EM7-12 Our top performing EM7 SET amplifier. Both the power transformer and output transformer are of increased size and power capability. This amplifier has more power, lower distortion and lower noise than typical 300B amplifiers.

FAQs..... Actually, I made them up, but ask a good question and see your answer here next time I update.

Why the use the EM7 tube? The 6EM7 and 13EM7 are identical except for filament voltage, one being 6.3 and the other 13.0. Since the filament winding is 13 volts, either tube can be used by reconnecting the filaments in series for the 6 and parallel for the 13.  This highly evolved tube was specifically designed to be a vertical amplifier and output tube in large color televisions. The vertical output amplifier is a single ended, class A amplifier with a gapped output transformer, cathode bias and high current capability. To do this job it had to be both stable and linear. If not, you would be calling the service man all too often to re-adjust the vertical height (gain) and linearity (bias) on the back of your TV set.  The cathode is indirectly heated so there is no hum pot to null as in most Directly Heated Triode (DHT) amplifiers. The large cathode emits a lot of electrons thus increasing its current and power output capabilities. Low saturation voltage makes it more efficient than DHTs, which have large losses (3 times as much) at maximum current.

Are these real Single Ended Triode (SET) amplifiers? Yes, all three are single ended. Furthermore, the EM7 tube is a real triode, not a triode connected pentode e.g., KT-66, KT-88, EL-34, EL-84, 6L6.    When a pentode is triode connected the screen grid “catches” a fair percentage of the electrons coming from the cathode. It catches them before they get to the plate, so all your electrons are not arriving at the same time as they do in a true triode. The suppressor grid (3rd grid in a pentode) causes an additional problem as it turns back some of the electrons that are headed to the plate.  Furthermore, to fit these grids into the structure the plate has to be moved 9 times farther out (numbers obtained from physical measurements on a EM7 Vs KT-88) In terms of ruggedness the EM7 is a champ. The top mica is twice as thick as the KT-88 and the glass is many times stronger. It took quite an effort to break one open to measure the dimensions. The design of the EM7 makes it one of the most efficient triodes ever made.

Why is there only 1 tube per channel in the stereo amplifier, where’s the driver tube? 
 It’s in the same bottle as the output tube. The EM7 is a dual triode where the two sections are different by design. The more familiar 6SN7 and 6SL7 are “twin triodes” where both sections are identical. The driver section of the EM7 is the well-liked 6SL7 driver. The output section, however, is quite unique. Where the driver section is capable of 1.4 watts dissipation, the output section is rated at 10 watts (that’s dissipation, not output, but it does relate to output).  The output section has a gain and output impedance almost identical to the 300B (mu=4, Rp=750 ohms). Rather interesting for two tubes with 30 years between them.

How can you get 5 watts out of a single EM7 output section where a 300B only gets a few more but has a 40 watt dissipation and a much larger bulb? The EM7 is a very efficient tube that could not have been made in the 1930’s. During WWII and beyond there were many advances in tube design and tube materials. The now popular 6DJ8/6922 is another post war tube. While it was designed as a RF amplifier in a color television, it makes a great audio tube. We owe a lot to color television and the tubes designed for it. The driver tube in the 245.1 is another popular color TV tube. Imagine what tubes might have been created if solid state TV had not come to pass. Sony was the first overseas company to buy a license from Bell Labs to make transistors and the rest is history.

Does this tube have long life? When I visited the Sylvania (Phillips) tube factory in Altoona, PA. I spent a full day conversing with the man who had managed the plant for the past 25 years. On the subject of reliability he stated “During the color TV era, our target lifetime was 10,000 hours minimum and we achieved that in many tubes”. Upon reflecting back to my days as a TV repairman I replaced very few vertical tubes. I made a point of noticing which tubes were original in the older sets and which tubes were replaced more often.  I also noted which tubes stayed in my tube caddy and which were restocked often. 

Is this tube easy to get and inexpensive? Yes to both. You can find them in small lots on eBay or get a matched pair from RAM TUBE WORKS for $60. If you decide on the eBay route you will have to buy several to several dozen and match them for gain and current. I have a stock of several thousand and test them in lots of 100-300. The larger the batch, the better the matches. 300Bs are also easy to get but several hundred dollars a pair.

What kind of speakers should I use with these amplifiers? There are many good choices and efficiency is not the only thing that matters. Your preferred listening level is more important than speaker efficiency.  I have customers who listen as low as 65 dB SPL (Sound Pressure Level). They could use a very low (80 dB is about the lowest made) efficiently speaker and be very happy. Customers who like to listen at 95 dB need a much more efficient speaker (95 dB and up). Radio Shack has re-introduced their analog SPL meter. It’s the most important thing you can buy to guide you on your journey at any power level. If you can report your peak SPL levels and speaker sensitivity I can accurately tell you how much power you need and what amplifier will be the best for your application. You can do this yourself also. If your SPL (at 1 meter from your speaker) is equal to your speaker’s sensitivity then you need one watt. If it’s 3 dB higher you need 2 watts. Each time you add 3 dB over the sensitivity of your speaker you double the power required. Going in the other direction, for every 3 dB lower than your SPL at 1 meter you need half the power. If you listen to a 85 dB speaker at 75 dB SPL you need only 0.1 watts.  Also measure at your listening position to get your average listening level preference.


Roger A. Modjeski

Hi,


I am finalizing the EM7 5 watt/ch stereo and 12 watt mono designs. The circuit and transformer designs are finalized and I am at the point where "features" are being determined.

On first and second runs of the original amp I included things I find useful. For a small amp I felt a High Pass filter would be useful to those who want to use the amp for a midrange or treble application in a multi way speaker. It makes a big difference to remove the bass information from the amplifier if it is not playing that range. Those of you who have two or three way systems where there are multiple speaker posts will appreciate the following. . When you disconnect the strapping and drive the lower frequencies from one amp and the higher frequencies from another amp you are only getting a small part if the advantage of Bi-amping. The woofer amp still sees the HF (high frequency) information and the Treble amplifier still sees the LF (low frequency) information. The harmonic, and more importantly the Inter Modulation (IM) distortion has not been reduced at all. This is because the treble amplifier still sees the large voltage swings due to the bass portion of the signal and the bass amplifier still has to handle the high frequency information, which it would rather not.

The only solution to this dilemma is to do the filtering before the amplifier inputs. An even lager  improvement can be obtained by disconnecting the drivers from their original crossover and going directly to their terminals. I cannot stress enough that this rather simple modification is many times more significant than any cable change. When you get right down to it, any quality speaker should have these terminals available on the outside as an option.

Most speaker designers make a big deal out of the quality of their crossover components. I do appreciate that small nonpolar electrolytics have been eliminated from most crossovers but there are still hundreds of feet of wire wound into chokes, sometimes with iron or ferrite cores. Why not bypass all this stuff??

The only reason that crossovers exist at all in multi way speakers is that manufacturers want to make things very simple, easy to hook up and not raise too many questions among owners. I will go on record here; you are missing a great improvement in your speaker if you do not go to the trouble of properly setting up a multi amp system. Once on this path there are many further refinements that come at low cost. For instance you can easily vary the output balance from one driver to another with a simple volume control on the amp itself. Imagine two or 3 amplifiers sitting in your rack, each playing only it’s frequency range, each with a volume control and each of a proper power level that is commensurate with the driver's needs.  Do you know how many speaker makers have to "pad down" the tweeter or midrange with big power resistors to balance it with the woofer? Do you see that this could be dealt with much more effectively by controlling the signal before it goes through the amp. In addition you can select amps of different virtues for each driver. Consider a solid stage amplifier for the woofer. We wouldn’t care about its midrange sound as it will never play the midrange. Similarly for the tweeter we might use a small single-ended amp for its lush midrange and easy point treble.


That brings us to why I put 2 sets of input jacks on the first run of EM7 amplifiers. Jeffery used them quite effectively having been aware of the points I made above for quite some time. He use two EM7’s configured in this manner to run his multiway system . I encourage others to try this and I am happy to answer questions that may arise. I would also be interested in hearing what your speaker maker may have has to say as to your desire to try this out.

The other feature that was added on the second run was to make the speaker output multi-impedance but not in the traditional way. Traditional impedance taps have unused copper on anything but the top tap. The EM7 output transformer has two secondary sections. They can be wired in series or parallel. Due to the fact that twice the output voltage (series connection) results in 4 times the impedance I have selected roughly 16 ohms for the series connection and 4 ohms becomes the parallel connection (4 to 1 ratio). I find the series impedance is the best choice for most applications. It doesn’t cost much to have to double the output jacks as long as simple ones are acceptable. On the other hand, some users might rather have only one set of jacks internally wired for high or low impedance or simply 8 ohms which will cover most applications.  I have built two special order EM7s with 8 ohm only as requested.

On the subject of special orders we can build your amp in any wood you want.  We have two customers who have sent us a nice piece of Brazilian Rosewood that they happen to have.  We carry Cardas connectors and can install others if you care to supply them. There is a small additional charge and time required for these specials which we can discuss by phone or email.

Our standard connectors for all amps are very nice gold Tiffany style input jacks we had made for us and brass binding posts of our own design. The smaller amps have #8 brass stud and thumb screw and the mono has the same connectors we use on the RM-200 which are ¼ inch stud and brass ½ hex cap.

The questions are these:

1. How many users are interested in filtered inputs? We can filter the inputs for High Pass (tweeter), Low Pass (woofer)  or Band Pass (midrange). For anyone developing his own speaker this would eliminate the difficult task of crossover design.

2. How useful is making  high-low impedance selection external and easy to change? I would love to hear the findings of users who have tried this out.

3. Any other features you might desire?

jrebman

  • Full Member
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The only solution to this dilemma is to do the filtering before the amplifier inputs. An even lager  improvement can be obtained by disconnecting the drivers from their original crossover and going directly to their terminals. I cannot stress enough that this rather simple modification is many times more significant than any cable change. When you get right down to it, any quality speaker should have these terminals available on the outside as an option.
Roger, I did just this with a small system I built back in the early 80s -- pretty decent results even using crappy little chip amps (much smaller than the ones folks think of as "chip amps" of today.)

That brings us to why I put 2 sets of input jacks on the first run of EM7 amplifiers. Jeffery used them quite effectively having been aware of the points I made above for quite some time. He use two EM7’s configured in this manner to run his multiway system . I encourage others to try this and I am happy to answer questions that may arise. I would also be interested in hearing what your speaker maker may have has to say as to your desire to try this out.


The questions are these:

1. How many users are interested in filtered inputs? We can filter the inputs for High Pass (tweeter), Low Pass (woofer)  or Band Pass (midrange). For anyone developing his own speaker this would eliminate the difficult task of crossover design.

2. How useful is making  high-low impedance selection external and easy to change? I would love to hear the findings of users who have tried this out.

3. Any other features you might desire?


I'd like to pick this up again if you don't mind.

My first question is about whether or not you think it is better for passive filtering at the amp inputs or preamp outputs vs. active filtering between preamp (or source) and the power amps that handle each part of the spectrum ( or are directly connected to the drivers in this case)?

After that, the next thing to deal with is relative levels of each speaker, and as you mentioned, this is easy to do with individual attenuators on the amps.

The one thing that I'm mostly curious about is again related to active or passive filtering, and finding some sort of suitable means of adjusting the relative phase of the drivers, and also being able to tune the frequency overlap points (and slopes?) for best driver integration and coherence?

This is all very interesting to me and I can think of any number of 2-way speaker systems that could b very easily adapted to this approach, but the one question that remains is how to get the drivers in proper phase relationship.

As for point 2 above, unless you are moving your amps around or switching speakers a lot, you would probably quickly find what tap works best and pretty much leave it at that.  At least that has been my experience as once the proper tap is found (and it is almost always the 8 ohm tap) there really is no more need to change it.

and for 3 -- it would be totally cool to have the little pre available with two ssets of filtered outputs for each part of the spectrum (and adjustments as necessary) so that you could pretty much have an off-the-shelf, compact solution for building a system with direct, band-limited amplification for each driver in a 2-way speaker.

I'd buy that and use my dyna ST-35 for the bottom end and an EM-7 for the tweeters.  2 inputs on the pre, and I'd be a happy camper (talking about my office system here.)  Ok, a headphone jack would be nice too :-)

If interior real estate in the preamp is an issue, how about another matching box with the electronic crossover in it -- 1 set of pre inputs and two outputs as above?

Maybe I'm dreaming here, but I would truly love to do this for a second system.

-- Jim

Roger A. Modjeski

Jim,

That's a lot to cover. Let's start with filters. In general 6 and 12 dB/octave filters are possible in a passive box, but 12 dB requires a 10 to 1 or better spread between the output impedance of the pre and input of the power amp. For example 10 k pre out, 100K main in. Steeper slopes need buffers.

6 dB/octave are most easily built into one unit or the other. Active crossovers are not bad in any way and a lot better than chokes and caps in speakers. I know it may be a stretch for many readers to believe how much of an improvement can be made by eliminating them. I realize it's much easier to hook up some new fancy cable and get excited about the improvement. We all like to do the things that are easy. I hope to find some brave soles here who will go into their speakers and do the right thing. Even better, ask the maker of the speakers to sell you one without a crossover. All you want is terminals taking you right to the drivers.

As to phase, you can count on less phase shift in an active crossover than a speaker level passive one.

As to amp output impedance, I have provided this in both the standard format of taps and the improved format of series/parallel which uses all the wire all the time. I find all the taps useful, not just the 8 ohm.

Two filtered outputs at 6 dB/octave are easy. Anything steeper requires more tubes. With 6 dB/octave there are no phase problems at all. This is the only slope for which phase is correct through the crossover point.

IkeH

Question on EM 7-5.0
« Reply #5 on: 22 Aug 2007, 10:15 pm »
Hi Roger,

As an owner of RM-5II and RM-9 since 1989, I am a great fan of you and your products, I am so delighted that you his circle.   You have given me a very helpful advice when I called you about my amps. and now such discussions can be shared.

I am very intrigued with the EM 7-5.0 amp. and I would like to consider it for my second system (I would never think to replace RM-5/RM-9 in my main system    :wink:)  In the amplifer description, you wrote that 2.5 W model  has "auto bias" and 5.0 W model has "adjustable bias" and I am wondering how easily it could be adjusted by a user (i.e. would the cover need to be taken off, how would be measured, how do I know what would be the right setting -I presume there may be a tube to tube variation?) 

Thank you,
Isaku     



Whitese

I am interested and maybe others are as well in having a phono pre in the same style chasis as the C-4 pre/EM7 amp...any others?  I already emailed Roger asking if its possible.

that would be one killer sounding and looking setup!

Roger A. Modjeski

The main difficulty with this request is shielding the circuitry and tubes so that the hum and noise pick-up will be minimum. In these circuits an exposed tube on a metal chassis can still pick up hum. Put you hand on an  exposed tube while the system is playing and you will hear hum because your hand acts as an antenna. Exposed tubes are OK if your location is hum free, but I don't want to count on that. One could put a shield on the tube but they are not much to look at. We could put the whole thing including the tubes inside the box and shield the interior.

On the other hand, if you did not need to see the tubes we could put the two phone tubes inside the C-4 and the line and regulator tubes outside as they are now. We would likely have a separate power supply at that point, again to minimize the hum. I am a fanatic when it comes to circuits being quiet. if we want to go whole hog the power supply would be in a matching box with tube rectifier and tube regulator. 

What we have right now is the RM-4 + Passive EQ RIAA preamp that sells for $950. It is in a metal box about the size of the EM-7, same height and about 2 inches longer. I hope to find time to take a picture today or tomorrow.

The RM-4+ is also available with up to 5 additional inputs and a volume control. The line section is passive and there is a power switch to turn off the power to the phone when you aren't listening to vinyl. We have several available with different numbers of inputs. For those whose sources are Vinyl and CD only we have one with a toggle switch for the two inputs for $1000. Given what is being charged for phone these days, this is a bargin. I just saw a phone preamp with op-amps reviewed by Michael Fremer in Sept. Stereophile (pg 25) selling for $960 with two op-amps and a dozen resistors and caps. I assure you the RM-4+ sounds better and costs far more to build. He reviews two other units, another solid state for $2500 and a tube one for $4950.

In that same Stereophile on page 68 is an interesting review by Michael Fremer on the Musical Fidelity Supercharger. I am pleased to report that the RM-200 is still his reference tube amp since the review in April 2002.








Eric

Roger,

What is the significance of your Avatar?

Roger A. Modjeski

That's the little picture, right?  It's from "The School of Athens" a copy of which was the backdrop for our stage at Old Cabell Hall at the University of Virginia. I spent many hours there recording performances, playing the stage piano and working on the E.M. Skinner pipe organ. Word was that it was the oldest Skinner signed by the old man himself that still had the original console and pipework.

Eric

That is great. Cool story