Music Reference RM-200 MK-I User manual

Music Reference RM-200 MK-I and MK-II
100-Watts Per Channel Stereo Power Amplifier
Owner’s manual
2010
Music Reference/RAM Labs
Santa Barbara, CA
805 687 2236
www.ramlabs-musicreference.com
www.tubeaudiostore.com

2
LINEAGE
The RM200MkI/MkII evolved from Music Reference’s classic RM9, the RM10, and the
state-of-the-art Music Reference RM9 Special Edition. The RM200MkI/MkII achieves a
news standard for musicality in stereo amplification. Using only a single matched pair of
KT88 of 6550 output tubes per channel, the RM200MkI/MkII easily achieves 100 watts per
channel.
Let’s take a few moments to learn what the RM200MkI/MkII achieves relative to a typical
100 watts per channel stereo tube amplifier in terms of True Music Power
TM:
Amplifier
8-Ohm Load
4-Ohm Load
2-Ohm Load
RM200MkI/MkII
112 Watts
145 Watts
125 Watts
Typical Tube
Amplifier
100 Watts
65 Watts
40 Watts
These specifications are all gained with the speakers connected to the 8-Ohm tap, and
represent the amplifier’s True Music Power
TM, not simply the typical RMS rating…
INSTALLING THE TUBES AND SETTING-UP YOUR RM200MkI/MkII
Please remove the tube set from the accessory box found with your RM200MkI/MkII. Note
the “’V’ Number” marked on each tube. With your RM200MkI/MkII turned-off and
unplugged, please insert each tube into its corresponding position/socket as marked on
your RM200MkI/MkII’s top plate.
Please note your RM200MkII has two 70-Amp rated “high in-rush” power switches for long
switch life. One power switch is marked “Master/Forming,” and the other is marked “Play.”
Please make sure both power switches are in the “off” position.
Select a location for your RM200MkI/MkII that provides at least 2-feet of free air space
above your RM200MkI/MkII to allow for adequate ventilation of your RM200MkI/MkII. DO
NOT place your RM200MkI/MkII directly on a carpeted surface.
CONNECTIONS
Plug your RM200MkI/MkII into a 3-prong wall socket. If any other units in your system have
ground pins, we recommend you “float” the grounds of all your other units with an adapter
or “cheater-plug.” However, we recommend that you always ground your RM200MkI/MkII.
We find that the lowest hum is achieved in most systems when only the power amplifier is
grounded, as your power amplifier is the least sensitive component, and has the largest
ground current. You may also wish to defeat polarized 2-prong plugs in your other
components t allow you to reverse the plugs for the lowest noise and best sound. You
should do this systematically with your power amplifier first, followed by your preamplifier,

3
and each of your sources to determine the configuration for each component is your
system. Do not expect large differences in the change of hum…
Connect the INPUT to the LEFT and RIGHT XLR connectors located behind your
RM200MkI/MkII’s transformer cover. Should you be using your RM200MkI/MkII with a
preamplifier or other source that lacks balanced (XLR) inputs, then please use an RCA-to-
XLR adaptor or re-terminate your interconnects with XLR plugs. In accordance with
industry standard, Music Reference defines XLR Pin No. 2 as HOT.
Connect your speaker cables to the brass binding posts located behind your
RM200MkI/MkII’s transformer cover. Note the “Impedance” markings adjacent to each
speaker binding post. Since your RM200MkI/MkII is a fully balanced amplifier from input to
output, you will notice the 4-Ohm and 8-Ohm speaker outputs/binding posts are not ground
referenced. For these two impedances, the speakers are connected to the “+” and the “-“
terminals of the appropriate impedance.
Additionally, 2-Ohm and 1-Ohm speaker taps are provided. These quite low speaker
impedance taps can be very useful for loudspeakers that exhibit very low or unruly
impedances. Feel free to experiment with different impedance connections.
“LIGHT LOADING” YOUR RM200MkI/MkII
You may always connect an 8-Ohm speaker on your RM200MkI/MkII’s 4-Ohm speaker tap,
however, not the other way around. Your RM200MkI/MkII amplifier actually appreciates the
“lighter load,” and the tubes will last longer. As long as your system will play loud enough
without clipping, then “light loading” your RM200MkI/MkII is preferable. Your
RM200mkI/MkII amplifier will also have higher damping (woofer control) and lower
distortion.
Always use the same impedance value for your right and left channel.
TUBES
Your RM200MkI/MkII is factory-equipped with 2-each 6BQ7 driver tubes, and 2-each
matched pairs of KT88 or 6550 output tubes. Each of these tubes has been specially tested
and selected for your RM200MkI/MkII by RAM Labs (www.tubeaudiostore.com) using
specially developed testing and matching procedures that allow you to operate your output
tubes at a higher bias resulting in lower distortion!
Please record the serial number, Bias, and Transconductance (Gm) of each tube (marked
on the label of each tube box) on in the corresponding position on the Tube Seating Chart
located at the end of this owner’s manual. Please refer to these Bias and
Transconductance (Gm) values when ordering replacement tubes from your dealer or RAM
Labs (www.tubeaudiostore.com). Please keep this manual with your most
valued documents. It will be very important should you ever need replacement tubes.

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OUPUT TUBES
The output tubes of your RM200MkI/MkII are set up as matched pairs by RAM Labs
(www.tubeaudiostore.com) for optimum performance when working in push-pull. The two
pairs are matched by RAM Labs (www.tubeaudiostore.com) to less than 10% variation
in bias and transconductance (Gm). Both output tubes in each pair will then share the
workload equally. They will also track evenly as they age and dissipate. For optimum
performance, always use RAM Labs matched output tubes as other vendors only match for
either bias or transconductance, but not both. They also may not test their tubes at the
correct operating values for your RM200MkI/MkII.
BIASING THE OUTPUT TUBES
Your RM200MkI/MkII was fully adjusted and calibrated at our factory. No further
adjustments are necessary.
However, we highly recommend checking the bias of your RM200MkI/MkII’s output
tubes every few months (check tube bias at least twice-a-year).
This is a simple procedure that requires the use of a voltmeter.
Output Tube Bias Values for your RM200MkI/MkII
Tube Types tested and
matched by RAM Labs
mV
(Recommended)
mV
(Maximum)
Genalex KT88 Gold Lions
40
44
RAM KT88
38
42
Shuguang (Chinese) KT88
35
38
6550 WE
38
42
6550 =C=
38
42
Tube Types tested by Others
mV
(Recommended)
mV
(Maximum)
Genalex KT88 Gold Lions
35
38
Sovtek KT88
31
35
Electro Harmonix (EH) KT88
31
35
Shuguang (Chinese) KT88
21
27
6550 WE
31
35
6550 =C=
31
35

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STEP-BY-STEP OUTPUT TUBE BIASING PROCEDURE
RM200MkI/MkII Tube Biasing instructions (written for 4-Ohm speaker tap use):
1. Adjust your voltmeter to read DC volts, 200 milli-Volt range.
2. Turn on your RM200MkI/MkII amplifier and allow your RM200MkI/MkII to fully warm-up
(approximately 15-minutes).
Please note your RM200MkII has two 70-Amp rated “high in-rush” power switches for long
switch life. One power switch is marked “Master/Forming,” and the other is marked “Play.”
Please press the “Master/Forming” power switch to the “on” position first. Then, press the
“Play” power switch to the “on” position, and allow your RM200MkII to fully warm-up
(approximately 15-minutes).
3. To test one channel, please insert the "red"/"positive" (+) probe into the test point
(marked "TP+") closest to the tube to be tested (say "V6"), and place the "black"/"negative"
(-) probe on the (-) 4-Ohm binding post that is connected to your speaker cable and is
closest to the test point ("TP+")/tube you are testing (say "V6"). Please make sure your
probes are making firm contact...
4. Note the Bias Reading of the tube you are testing (say "V6"). (Bias reading should be
between the “Recommended” mV and “Maximum” mV Bias Values listed in the table
above for your RM200MkI/MkII).
5. Then, test the other tube in that same channel (say "V4"), by inserting the "red"/"positive"
(+) probe into the test point (marked "TP+") closest to the tube to be tested (say "V4"), and
place the "black"/"negative" (-) probe on the (+) 4-Ohm binding post that is connected to
your speaker cable and is closest to the test point/tube you are testing (say "V4)."
6. Note the Bias Reading of the tube you are testing (say "V4"). (Bias reading should be
between “Recommended” mV and “Maximum” mV Bias Values listed in the table
above for your RM200MkI/MkII).
7. Please average the two Bias Readings for one channel, and note the "Averaged Bias
Reading" for that channel.
For example, let's assume the Bias Reading for "V6" reads "38mV," and the Bias Reading
for tube "V4" reads "36mV." Then, the "Averaged Bias Reading" would be "37mV."
8. Use a fine flat-head adjustment screwdriver (we recommend a 2.5mm by 55mm
screwdriver) to adjust the Bias of your RM200MkI/MkII so each tube is set to your desired
Bias setting/reading.
For example, let's assume you wish to set the "Average Bias" of your RM200MkI/MkII at
"35mV." And, let's assume the Bias Reading for "V6" reads "38mV," the Bias Reading for
"V4" reads "36mV," and therefore, the "Average Bias Reading" for the right channel is
"37mV."

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To reduce the "Average Bias Reading" from "37mV" to "35mV," please adjust the right
channel Bias pot (ie. "V4," and "V6" output tubes) so that together, both tubes average
"35mV" (ie. set "V6" to read "36mV" and set "V4" to read "34mV").
9. Repeat thee procedures for your left channel (ie. "V5" and "V3" tubes).
10. Roger A. Modjeski recommends setting the Bias of your RM200MkI/MkII amplifier
closer to "Recommended” mV values shown in the table above as this will result in a
slower tube dissipation rate (ie. your output tubes will have longer life)...Our experience
shows that the tube life is 5000-10,000 hours at this bias setting…However, your
RM200MkI/MkII amplifier will produce lower distortion with a Bias setting closer to
"Maximum” mV values shown in the table above.
“CAPACITOR FORMING CIRCUIT” FOR RM200MKII
Your RM200MkII includes the industry’s first “capacitor forming circuit” for a tube amplifier.
This unique circuit allows charging the capacitors in your RM200MkII without energizing
your Rm200MkII’s tubes to maximize the musical performance of your RM200MkII without
prematurely dissipating your tubes to extend their tube life.
EMPLOYING RM200MkII’s “CAPACITOR FORMING CIRCUIT”
Your RM200MkII employs two 70-Amp rated “high in-rush” power switches for long switch
life. One power switch is marked “Master/Forming,” and the other is marked “Play.”
Please press the “Master/Forming” power switch to the “on” position first. The
“Master/Forming” switch in the “on” position charges the capacitors in your RM200MkII at a
higher than normal operating voltage to assure your RM200MkII is always “ready-to-play”
at maximum musical performance.
When you are ready to play your RM200MkII, then please press the “Play” power switch to
the “on” position. The “Play” switch in the “on” position reduces the voltage in your
RM200MkII to the normal operating voltage, and energizes the tubes in your RM200MkII.
Your RM200MkII is ready for “active listening” after a brief tube warm–up period
(approximately 15-minutes).
ADJUSTMENTS, FUSES, TUBE CONSIDERATIONS AND LIFE
CHECKING BIAS
We have designed your RM200MkI/MkII to make tube biasing simple using a voltmeter.
The test points are accessible from the top of your RM200MkI/MkII so you don’t have to
remove anything. You may check the bias as often as you like, and we recommend you
check your RM200MkI/MkII’s tube bias at least twice-a-year. We do not
recommend leaving the meter connected permanently as there is a small risk of damaging

7
an analog meter if a tube shorts or flashes. We suggest a using a digital voltmeter as most
digital voltmeters have excellent protection.
FUSES
The fuses for your RM200MkI/MkII have been carefully specified.
The output tube fuses are ceramic, 5 X 20 mm, 250 mA, slow blow, high-interrupting
(interrupt rating: 1500A@250VAC). Please note that typical fuses have a much lower
interrupt rating of 35A@250VAC, and are not suitable for your RM200MkII.
The mains fuse is 5 x 20 mm standard slow blow, 5.0 Amp (for 120 volt) or 2.5 Amp (for
240 Volt).
For your protection and safety, always replace with identical or comparable fuses. DO
NOT SUBSTITUTE! Using a different fuse will void your warranty. You may order
additional fuses from RAM Labs/Music Reference (www.tubeaudiostore.com) or your
dealer.
WARNING: Do not use “Tuning Fuses”, “IsoClean”, “Furutech” or any of the high-end
fuses as they have already shown that they are unable to protect the tubes and output
transformers. The people making them know nothing about high-interrupting fuses
(interrupt rating: 1500A@250VAC). Roger A. Modjeski was told by one distributor that their
ceramic fuse was equivalent to our high-interrupting ceramic fuse because they were both
ceramic. This is clearly not factual.
TUBES
The six tubes in your RM-200MkI/MkII have been carefully selected by RAM Labs for best
performance. The operating parameters have also been selected to achieve long life and
reliable operation. We suggest replacing with RAM Labs tubes when that time comes.
You may notice a bright flash from the bases of V1 and V2 on turn-on. This is perfectly
normal and does not shorten the life of the tube in any way. The flash is due to the fact that
the filaments are coated to insulate them from the cathode sleeve. In the process of
connecting the tungsten wires to their pins, the coating has been removed. This uncoated
portion has less thermal mass and thus heats quickly, causing the flash. The input tubes
are rated for 10,000 hours and 10,000 turn-on cycles. Therefore, it is perfectly OK to turn
the amplifier off and on again if you are not listening for an hour or more. Although there is
a common myth that tubes do not like to be cycled, I have found it to be without foundation.
Filament failures in well-made tubes are so rare, I can't remember when I last saw one.
You may notice some hum from your speakers if your hand or an AC cord is placed near
V1 or V2. This is normal as the tube is unshielded. If you notice crackling noises, try
cleaning the pins of V1 and V2 with a small brass wire brush and lightly coat the pins with
DeoxIT, use sparingly.

8
SYSTEM NOISE
If you have hum, leave the RM200MkI/MkII grounded and float all the other ground pins on
your other power cords. Those units will now be grounded to the wall through their
interconnects and the hum will be far lower.
To ensure quietest performance, we suggest that your RM200MkI/MkII be properly
grounded, and that your RM200MkI/MkII have a distance of at least one-foot between any
electrical appliance (ie. Preamplifier, TV monitor, power filter, another amplifier). Start with
only having your RM200MkI/MkII grounded in your system. If you are using two amplifiers
in your system (mono-blocking or bi-amping), then float the ground on one of the amplifiers
using a non-polarized 3-prong to 2-prong adapter (“cheater” plug). Sometimes reversing a
2-prong plug will lower hum or improve sound. Experiment with each component in your
system to find which combination works best for you. The differences may be subtle or not
appear at all…
Remember to dress the cables away from your RM200MkI/MkII’s transformers, and any
other source of magnetic fields. If you are still getting hum, check the placement of each of
your components. Are they stacked on top of each other so that the input section of your
preamplifier is directly beneath the power supply of your Digital-Audio-Converter (DAC) or
other source? You want to isolate each component as much as conveniently possible.
Often, an FM tuner connected to the Cable TV system or outside antenna will cause hum in
the entire system due to AC pickup in the coaxial cable coming in. Always disconnect the
tuner audio cables or antenna cable to test for this hum, as it will affect other sources. This
insidious problem can be corrected by installing a “75Ωto 75Ω” isolation transformer that
breaks the ground.
At Music Reference, we recommend keeping interconnects short in length, and having
longer runs of speaker cable. Interconnect impedance should be no more than 20ρF per
running foot, or 200ρF total. You may use any type of interconnect you desire. However,
we do recommend using shielded interconnects especially if the run between your
preamplifier and your amplifier is a long one…
TUBE NOISE
Your RM200MkI/MkII uses specially selected input tubes that are quiet and stable. Tube
noise would be evidenced when sputtering, hissing, spitting, or high frequency ringing
sounds are audible in one channel. To determine the faulty driver tube, listen to your
amplifier to assess what channel emits the tube noise. Then, turn off your amplifier and
exchange the driver tubes left-to-right. Turn your amplifier back on, allow the tubes to warm
up, and check the bias on both channels. If the offending sound has moved to the other
channel, then you know it is time to replace that faulty driver tube. If the sound did not
change channels, then turn your amplifier off, allow the tubes to cool, put the tubes back in
their original positions, and contact your dealer or Music Reference for further assistance.

9
TROUBLE SHOOTING
While it is highly unlikely that you run into all, if any, of these situations, the following are
some test procedures that you should run in the event that your RM200MkI/MkII appears to
misbehave (the vast majority of problems encountered are attributed to noisy tubes and
improper component placement or grounding):
DISTORTION
Output tube distortion usually results from one or more of the output tubes becoming gassy
(having grid leakage). A gassy tube will cause the BIAS to change from the time you turn-
on your RM200MkI/MkII through the first hours or so of operation. A gassy tube draws
extra current when it gets hot and will run even hotter as a consequence. You may feel the
extra thermal heat from the output tube by holding your hand beside the bad (gassy) tube.
NEVER TOUCH A TUBE’S GLASS ENEVLOPE WHILE THE AMPLIFIER IS
OPERATING OR IMMEDIATELY UPON TURN-OFF! SEVERE BURNS WILL
RESULT! Darken the room and look for a part of the gray PLATE area of the tube
GLOWING RED. A gassy tube will also blow fuses when the amplifier is driven hard for
long periods. It is necessary to replace the bad (gassy) tube out of your amplifier, or you
will cause slow damage to the other tube in that pair.
Through our research and published speaker test date, we have found speakers whose
impedance drops markedly below the values stated by the manufacturer. When played
hard for long periods of time, this drop in impedance below the stated value causes
overheating of output tubes and premature gassiness.
We highly recommend using the lowest impedance speaker tap that you can without
experiencing clipping at your listening level. Quite often, a speaker will play louder and
cleaner on the lower impedance speaker tap.
BLOWN FUSES
There are two different types of fuses used in your RM200MkI/MkII: 250mA Slow Blow,
High Interrupting (interrupt rating: 1500A@250VAC) ceramic output tube fuses; and a
5Amp Slow Blow power supply fuse (2.5Amp Slow Blow for 240V mains).
The 250mA Slow Blow, High Interrupting (interrupt rating: 1500A@250VAC) output tube
fuse is in series with that cathode of each output tube. One tube fuse will blow if you have a
lint short, a gassy tube, or a power surge. You may or may not see a flash in the tube at
fault when this occurs…If the fuse blows, then there will be a drop in power on that side,
but sound will still be present. We suggest replacing the 250mA Slow Blow, High
Interrupting tube fuse at least two times before giving up on that tube.
The easiest way to find out if the 250 mA tube fuse is blown is to check the bias. If the tube
fuse is blown, then there will be zero-mV or just a few mV reading. The tubes will still light
because the tube fuse is only for the high voltage and not the heaters.

10
To replace the blown tube fuse, turn your amplifier off, replace the 250mA Slow Blow, High
Interrupting tube fuse, rap the output tube with a pencil, and turn your amplifier back on,
again. If the tube fuse blows immediately, then the tube has a short and needs to be
replaced.
As your amplifier plays for the first couple of hours, check the amount of heat coming off of
the faulty tube by holding your hand approximately 1” away from the tube, and comparing
the heat generated from that tube and the others. Also, watch the plate structure of the tube
to see if there is any change in color from gray to red. Signs of excessive heat, or a glowing
plate structure means that the faulty tube is gassy and should be replaced. Since the output
tubes are in parallel, one gassy tube will cause its partner to get hot also. If after two hours
there are no other instances of blown tube fuses, then sit back, relax, and enjoy your
RM200MkI/MkII.
If the main fuse blows the tubes will not light and the amp will act like it is off or unplugged.
If one pair or two pairs of output tubes do not light but the drivers do the problem is an open
filament, bad tube socket or broken wire beneath the socket. The filaments of the output
tubes are series connected so both must be good to light. The drivers are parallel
connected and light independently.
Visit our home page to learn about the design philosophy of the RM-200MkI/MkII:
http://www.ramlabs-musicreference.com/rm200.html
A brief autobiography of the designer is located at:
http://www.ramlabs-musicreference.com/bio.html
or simply go to our website www.ramlabs-musicreference.com and look under “Articles by
Roger A. Modjeski” in the center of the bottom of our home page.
If you need assistance, then please send an email message to us at roger@ramlabs-
musicreference.com or call us at 805 687-2236.
We have replacement output tubes at $100-$150 per pair and driver tubes at $75 per pair.
Fuses are $3 each or 10 for $20. These are current prices that may change without notice.
These items may be purchased directly from us at our www.tubeaudiostore.com site.