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R2XL1 

 5  

The next component in line is R4. This 1K resistor in combination with R3 

and R5 sets the gain of the first inverting opamp stage (U1:C). An inverting 
opamp will take the signal presented on its input and flip the polarity of the sig-
nal on its output giving you the inverse value of the original. In our case,  the 
resulting output signal from the opamp (pin 8) will be opposite in polarity to 
that of the original input signal on the left hand side of R4. The amplitude of 
the signal will also change depending on the gain of the circuit. The formula 
for determining the gain in this circuit is given by Av = -Rf / Ri, where Ri is the 
input resistance of R4 and Rf is the feedback resistance of R3 + R5 together. 
If we want to find the maximum gain of this stage, we can take our 1,000 (1K) 
ohm input resistor and divide its value by our 10,000 (10K) ohm pot and 100 
ohm feedback resistors added together (10,100 or 10.1K ohms). This works 
out to a maximum gain of -10.1 (the negative value just means it is inverted). 
How does this affect our signal? Take for example a +1V input present at R4. 
Multiply the input signal value by the calculated gain factor (+1V x -10.1) to 
obtain -10.1 volts on the output (pin 8) of the amplifier. That wasn’t so hard 
was it? 

Let’s move on. The signal output from pin 8 (U1:C) then goes through two 

more opamp stages (U1:A and U1:B) for processing before we’re done! One 
of these stages has a familiar topology. Take a look at U1:B. It’s another in-
verting opamp using resistors of R1 and R2 to set its gain. Use the formula 
from before to figure out for yourself what the gain has been set for. We’ll con-
firm in a moment if you are correct. 

The other opamp (U1:A ) is configured as a non-inverting amplifier. A non-

inverting opamp does just what it sounds like, it preserves the original signal 
polarity while offering the ability to amplify the signal (increase or decrease its 
amplitude). The formula for determining the gain of this configuration is given 
by Av = 1+ Rf / Ri, where Ri is the input resistance (0 ohms), and Rf is the 
feedback resistance (0 ohms). Since there are no input or feedback resistors, 
the gain works out to be 1 for this stage. This type of circuit is commonly 
called a Voltage Follower (for obvious reasons) and it acts as a buffer. 

Both stages U1:A and U1:B have their gain set to 1 and –1 respectively (did 

you get –1 for the gain of the inverting amplifier?). Because one opamp is in-
verting and the other is not, their outputs are always opposite of one another. 
The end results is a combined gain of 2 for these two opamps together. How 
does that work? Let’s analyze this. If the output of our first stage (U1:C) is +1 
volt (to make the math easy) and it is amplified by the inverting amplifier (U1:
B) with a gain of –1, its output will be –1 Volt. When the same 1V input is ap-
plied to the non-inverting stage (U1:A) with a gain of 1, its output will be 1 Volt. 
Looking across the outputs of both amps (pins 1 and 7) the difference be-
tween the two works out to be 1 - (-1) = 2 Volts. Hey… that’s pretty neat! 

Armed with the information that our first stage (U1:C) has a maximum gain 

of 10.1 and the second stage (U1:A and U1:B) has a fixed gain of 2, we can 

Summary of Contents for RCA to XLR Converter R2XL1

Page 1: ...n types from RCA to XLR it also gives you the added advantage of independent channel gain control for the proper levels Powered by a 12VAC wall power transformer for ground isolation Stereo Mono switc...

Page 2: ...Thermometer LC1 Inductance Capacitance Meter RAMSEY AMATEUR RADIO KITS DDF1 Doppler Direction Finder HR Series HF All Mode Receivers QRP Series HF CW Transmitters CW7 CW Keyer CPO3 Code Practice Oscil...

Page 3: ...t 7 Schematic Diagram 8 Parts Layout Diagram 9 Learn as You Build 10 Assembly 12 Using the R2XL1 15 Professional Audio Wiring 16 Custom Case Assembly 17 Troubleshooting 18 Warranty 19 KIT ASSEMBLY AND...

Page 4: ...tereo Mono switch It takes the au dio presented on the right input and sends it to both left and right XLR amplifi ers when pressed in This allows you to drive a professional stereo audio de vice from...

Page 5: ...ng resistors of R1 and R2 to set its gain Use the formula from before to figure out for yourself what the gain has been set for We ll con firm in a moment if you are correct The other opamp U1 A is co...

Page 6: ...omplish this we use a bridge rectifier consisting of D1 4 to take the AC input voltage and convert it to positive DC pulses This directly is too noisy for our application so C12 was added to smooth th...

Page 7: ...2 4 7 8 10 2 10K ohm resistors brown black orange R13 14 2 100 ohm resistors brown black brown R3 9 2 560 ohm resistors green blue brown R6 12 Capacitors 2 0 01 uF Ceramic capacitors marked 103 C9 10...

Page 8: ...R2XL1 8...

Page 9: ...R2XL1 9 R2XL1 PARTS LAYOUT DIAGRAM...

Page 10: ...leads and the pads simultaneously Apply the solder to the the pad when the junction is hot enough to melt the solder The finished joint should look like a drop of water on paper somewhat soaked in Mou...

Page 11: ...ure the part is mounted flush to the PC board unless otherwise noted 3 Orient it correctly follow the PC board drawing and the written directions for all parts especially when there s a right way and...

Page 12: ...ientation again 5 Install D6 another 1N4002 diode Orientation must be correct or we will get no negative supply Note how this is placed between two large capaci tors Imagine trying to install this aft...

Page 13: ...o change it now Just make sure that the side NOT marked negative is in the same side marked positive on the board 20 Install C8 another 10 uF electrolytic capacitor Again check polarity 21 Install R14...

Page 14: ...nical soundness 34 Install J6 our 2 5 mm AC power jack 35 Install C11 a 470 uF electrolytic capacitor Check orientation just in case you forgot 36 Install C12 another 470 uF electrolytic capacitor 37...

Page 15: ...as your primary audio gain control Since we built in a lot of gain it is too difficult to adjust on the fly Even worse there are two controls to tweak making it even harder to keep these at the same...

Page 16: ...ent standards dictate that XLR connectors should be wired as follows Ground pin 1 White Pin 2 Black Pin 3 Sometimes you will find red instead of white Both ends of the cable are wired in the same orde...

Page 17: ...ceive years worth of enjoyment using talking about and remembering the fun you had building your kit In short TAKE YOUR TIME when assembling the enclosure This is the part that you and your friends wi...

Page 18: ...terference SOLUTION Here is where R6 and R12 come into play The two 560 ohm green blue brown resistors that were left out of the normal construction steps may need to be installed With long cable runs...

Page 19: ...h be assured that the 1K ohm resistors are actually the missing 10 K parts Hum m m I guess the red band really does look orange Ramsey Electronics project kits are packed with pride in the USA If you...

Page 20: ...SEY ELECTRONICS INC 590 Fishers Station Drive Victor New York 14564 Phone 585 924 4560 Fax 585 924 4555 www ramseykits com REQUIRED TOOLS Soldering Iron Ramsey WLC100 Thin Rosin Core Solder Ramsey RTS...

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