PRM2 - DUAL PASSIVE RING MODULATOR
The PRM2 is a passive Dual Ring Modulator. At it's core it is a standard ring modulator utilizing audio transformers with balanced Primary and Secondary impedance and a 4 diode "ring". 2 switches per ring modulator (Amputate) are added in
line of 2 of the 4 diodes. These switches remove the diode from the circuit, creating a +/-/half wave rectifier between the carrier and input. This configuration can lend to complex rhythmic and unbalanced modulations, depending on the
frequencies of both the carrier and input.
The PCB was designed to hold either the audio transformer that ships with all kits, or a Hammond 107N. Aside from being a
higher end transformer, the primary and secondary are drastically different (10k Primary, 600 Secondary Impedance). For
standard ring modulation, the input can be attenuated with the trimmer to better match the secondary, or, for the reason
I originally started designing this circuit in the first place, was how awesome it sounded with the input over-saturated by the
transformer. Unfortunately this transformer does not work well with the +/- rectification as it results in either the carrier
or the input dramatically overpowers the other signal and it's not useful at all. I opted to keep this option in the design, so
if someone wanted to take advantage of it, they could build one of the ring modulators with the 107N transformer and skip
the Amputate switches. Also, they are extremely expensive ($18+ a piece!).
6hp
+12V 0mA
-12V 0mA
line of 2 of the 4 diodes. These switches remove the diode from the circuit, creating a +/-/half wave rectifier between the carrier and input. This configuration can lend to complex rhythmic and unbalanced modulations, depending on the
frequencies of both the carrier and input.
The PCB was designed to hold either the audio transformer that ships with all kits, or a Hammond 107N. Aside from being a
higher end transformer, the primary and secondary are drastically different (10k Primary, 600 Secondary Impedance). For
standard ring modulation, the input can be attenuated with the trimmer to better match the secondary, or, for the reason
I originally started designing this circuit in the first place, was how awesome it sounded with the input over-saturated by the
transformer. Unfortunately this transformer does not work well with the +/- rectification as it results in either the carrier
or the input dramatically overpowers the other signal and it's not useful at all. I opted to keep this option in the design, so
if someone wanted to take advantage of it, they could build one of the ring modulators with the 107N transformer and skip
the Amputate switches. Also, they are extremely expensive ($18+ a piece!).
6hp
+12V 0mA
-12V 0mA
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As with the VG2, this is a good kit for a beginner since it is a passive circuit.
It is best to assemble in this order:
1. Diodes
It is best if the diodes are matched, so if you are using diodes other than the ones supplied in the kits, be sure to order more than you need. With a DMM set to diode, meter the voltage at each diode and write it down. Try to find diodes close enough to each other. The readings will be in mV. The ones supplied with the kits are purchased from a reel. The benefit to this is they are manufactured at the same time and already are within .001-.003 mV of each other.
Remove the diodes from the tape and bend only one of the legs. I find it easiest to bend the side without the white line (refer to the above picture).
Remove the diodes from the tape and bend only one of the legs. I find it easiest to bend the side without the white line (refer to the above picture).
Insert them into the 4 LED footprints (yes, even an LED can be used instead). Be sure to put the leg with the white line in the cathode side of the LED. This is the side that has a line. There is a small drawing of the diode orientation on the PCB. Refer to the picture above for proper placement. Once all 8 diodes are inserted, flip it over and solder them in. you may need to bend some of the legs of the diodes to hold them in place. When done, clip the legs, but be sure to keep 2 of the clipped legs.
2. Jumper (or add) the trimmer
2. Jumper (or add) the trimmer
Take two of the clipped legs from the diodes and bend them in half, then insert them where the 10k trimmer is. You want to be sure to jumper the 2 that have the white loop next to it. Refer to the above picture. If you are using the 107N transformers and wish to adjust the input impedance, install a trimmer here instead. A right angle single turn will work best.
3. Transformers
The transformers supplied with the kits have 2 mounting tabs at each end. You will want to clip these off so they sit flat on the PCB.
3. Transformers
The transformers supplied with the kits have 2 mounting tabs at each end. You will want to clip these off so they sit flat on the PCB.
The transformer footprint is slightly smaller than the transformers, but they will fit fine. You want to make sure that you line up the P on the transformer with the side of the footprint that has a P above pin 1. Make sure that it looks like the pictures below.
4. Jacks and switches
Once everything is soldered in on the backside, flip the circuit board around and install the 6 jacks and 4 switches. Once installed, put the panel and and secure it with the 6 knurled nuts, but only hand tighten. Now, flip the module upside down and make sure the 4 switches are resting evenly on the panel. DO NOT set it on a flat surface to solder. The switch levers will push them up and will cause them to get soldered unevenly. Use a cup (or the like) to hold the module up, but allowing the switches to rest freely. Solder everything up ,
5. Testing
Now, make sure all switches are in the up (all 4 diodes ON), send a sine or triangle wave into the carrier and a saw wave to the input and the output to a mixer. Adjust the frequency of the carrier, then the input and make sure you are getting classic ring mod sounds. Then, switch one of the diodes OFF. Again, adjust the carrier and input frequencies. Next, swith the other diode OFF and repeat. Try different combinations with different waves and frequencies.
The best way to take advantage of the "Amputate" switches is by applying a DC offset to the carrier. I enjoy mixing the output of an Envelope Generator (MN Maths in particular) and the carrier signal and sending the output to the carrier, and turning one or both of the Amputate switches off. Super crunchy. Even better, send the output through a compressor (MI Streams works great) and squash the crap out of it. Using a MN Pressure Points works great in this scenario as you can adjust the frequencies of both carrier and input with each contact pad.
Enjoy!
Notes on the transformers
After much testing (and totally wasting several hundred dollars) I have come to the conclusion that there is absolutely no benefit to the Hammond 107N or T. As I have found, the transformers supplied in the kits sound better!!! So please, DO NOT BUY THE 107N!
T̶h̶e̶ ̶P̶C̶B̶ ̶f̶o̶o̶t̶p̶r̶i̶n̶t̶ ̶f̶o̶r̶ ̶t̶h̶e̶ ̶t̶r̶a̶n̶s̶f̶o̶r̶m̶e̶r̶s̶ ̶i̶s̶ ̶d̶e̶s̶i̶g̶n̶e̶d̶ ̶t̶o̶ ̶h̶o̶l̶d̶ ̶a̶ ̶H̶a̶m̶m̶o̶n̶d̶ ̶1̶0̶7̶N̶.̶ ̶ ̶T̶h̶i̶s̶ ̶i̶s̶ ̶a̶ ̶h̶i̶g̶h̶e̶r̶ ̶q̶u̶a̶l̶i̶t̶y̶ ̶t̶r̶a̶n̶s̶f̶o̶r̶m̶e̶r̶,̶ ̶b̶u̶t̶ ̶w̶i̶t̶h̶ ̶t̶w̶o̶ ̶n̶e̶g̶a̶t̶i̶v̶e̶s̶.̶
1. S̶u̶p̶e̶r̶ ̶f̶u̶c̶k̶i̶n̶g̶ ̶e̶x̶p̶e̶n̶s̶i̶v̶e̶.̶ ̶ ̶J̶u̶s̶t̶ ̶1̶ ̶i̶s̶ ̶a̶b̶o̶u̶t̶ ̶$̶1̶8̶ ̶a̶n̶d̶ ̶y̶o̶u̶ ̶n̶e̶e̶d̶ ̶4̶!̶
2. T̶h̶e̶ ̶P̶r̶i̶m̶a̶r̶y̶ ̶a̶n̶d̶ ̶S̶e̶c̶o̶n̶d̶a̶r̶y̶ ̶a̶r̶e̶ ̶n̶o̶t̶ ̶m̶a̶t̶c̶h̶e̶d̶.̶ ̶ ̶A̶s̶ ̶a̶ ̶s̶t̶a̶n̶d̶a̶r̶d̶ ̶R̶i̶n̶g̶ ̶M̶o̶d̶u̶l̶a̶t̶o̶r̶,̶ ̶t̶h̶i̶s̶ ̶w̶o̶r̶k̶s̶ ̶t̶o̶ ̶a̶n̶ ̶a̶d̶v̶a̶n̶t̶a̶g̶e̶ ̶a̶s̶ ̶i̶t̶ ̶r̶e̶a̶l̶l̶y̶ ̶c̶r̶u̶n̶c̶h̶e̶s̶ ̶t̶h̶e̶ ̶i̶n̶p̶u̶t̶ ̶a̶n̶d̶ ̶l̶e̶n̶d̶s̶ ̶t̶o̶ ̶s̶o̶m̶e̶ ̶g̶r̶e̶a̶t̶ ̶h̶a̶r̶m̶o̶n̶i̶c̶s̶.̶ ̶ ̶U̶n̶f̶o̶r̶t̶u̶n̶a̶t̶e̶l̶y̶ ̶t̶h̶i̶s̶ ̶d̶o̶e̶s̶ ̶n̶o̶t̶ ̶w̶o̶r̶k̶ ̶e̶v̶e̶r̶y̶ ̶w̶i̶l̶l̶ ̶w̶i̶t̶h̶ ̶t̶h̶e̶ ̶"̶A̶m̶p̶u̶t̶a̶t̶e̶"̶ ̶s̶w̶i̶t̶c̶h̶e̶s̶.̶ ̶ ̶T̶h̶e̶ ̶t̶r̶i̶m̶m̶e̶r̶ ̶c̶o̶u̶l̶d̶ ̶b̶e̶ ̶u̶s̶e̶d̶ ̶t̶o̶ ̶h̶e̶l̶p̶ ̶b̶a̶l̶a̶n̶c̶e̶ ̶i̶t̶ ̶o̶u̶t̶ ̶b̶e̶t̶t̶e̶r̶.̶ ̶ ̶
T̶h̶e̶r̶e̶ ̶i̶s̶ ̶t̶h̶e̶ ̶H̶a̶m̶m̶o̶n̶d̶ ̶1̶0̶7̶T̶ ̶w̶i̶t̶h̶ ̶h̶a̶s̶ ̶t̶h̶e̶ ̶s̶a̶m̶e̶ ̶i̶m̶p̶e̶d̶a̶n̶c̶e̶ ̶a̶s̶ ̶t̶h̶e̶ ̶o̶n̶e̶ ̶t̶h̶a̶t̶ ̶s̶h̶i̶p̶s̶ ̶w̶i̶t̶h̶ ̶t̶h̶e̶ ̶k̶i̶t̶,̶ ̶b̶u̶t̶ ̶a̶s̶ ̶o̶f̶ ̶n̶o̶w̶ ̶I̶ ̶h̶a̶v̶e̶ ̶n̶o̶t̶ ̶t̶e̶s̶t̶e̶d̶ ̶t̶h̶i̶s̶ ̶t̶r̶a̶n̶s̶f̶o̶r̶m̶e̶r̶,̶ ̶b̶u̶t̶ ̶I̶ ̶d̶i̶d̶ ̶j̶u̶s̶t̶ ̶p̶u̶t̶ ̶a̶n̶ ̶o̶r̶d̶e̶r̶ ̶i̶n̶ ̶f̶o̶r̶ ̶o̶n̶e̶.̶ ̶ ̶I̶ ̶w̶i̶l̶l̶ ̶u̶p̶d̶a̶t̶e̶ ̶t̶h̶i̶s̶ ̶o̶n̶c̶e̶ ̶I̶ ̶h̶a̶v̶e̶ ̶f̶u̶l̶l̶y̶ ̶t̶e̶s̶t̶e̶d̶ ̶i̶t̶.̶ ̶ ̶T̶h̶i̶s̶ ̶c̶o̶u̶l̶d̶ ̶b̶e̶ ̶a̶ ̶p̶e̶r̶f̶e̶c̶t̶ ̶a̶l̶t̶e̶r̶n̶a̶t̶i̶v̶e̶ ̶t̶o̶ ̶t̶h̶e̶ ̶o̶n̶e̶s̶ ̶s̶u̶p̶p̶l̶i̶e̶d̶ ̶w̶i̶t̶h̶ ̶t̶h̶e̶ ̶k̶i̶t̶ ̶a̶n̶d̶ ̶h̶o̶p̶e̶f̶u̶l̶l̶y̶ ̶y̶i̶e̶l̶d̶ ̶s̶u̶p̶e̶r̶i̶o̶r̶ ̶r̶e̶s̶u̶l̶t̶s̶.̶
Notes on the diodes
For the best results, you will need to use matched diodes. The diodes supplied with the kit are purchased from a reel. The benefit to this is they are already matched as they are manufactured all at the same time. Any diode can be used though, even LED's. But when selecting a diode, order more than needed and go through and test each one, then use the ones that are closest to each other. This can be done with a basic DMM. Switch the meter to diode. Black probe to lead with orientation line and red probe to other lead. Write down the voltage (will be mV). Keep doing this until you find 4 that are the closest to each other.
