I found a computer power cord in the shop and asked the broker if I could give it a try. At first he was reluctant, but then allowed me to try. It acted as if it had a stuck key; I knew this could be a much bigger issue than just a key; so I talked to him and got a really good deal on it! This parts kit was essential for bands who were on the road with one of these beasts, so I was told. This came from a former employee that worked in the Moog Trumansburg Factory.

He included with this auction lot several Moog schematic blueprints and an EMU modular catalog!!! I hope to get my Moog back in pristine working condition here shortly. Meanwhile, I finally took some photos of these schematics that I have framed and hanging in my man-cave. Here are some more schematics and a great article. If you have any of these, or have images or links to others, please post in the comments; I would love to see more!

SDIYClass#2 - The 3 dollar LoPass Gate - Make your own Vactrol!

These look great framed and beer game simulation solution on the walls! Thanks for sharing these photos. Hi David. How has the Synthasystem project been selling? He has my Microcon clone that has done well for him. So could you provide a better scan of the B blue print? These are precious finds you have … Thanks.

moog filter schematic

Your email address will not be published. This site uses Akismet to reduce spam. Learn how your comment data is processed. Thanks again for making these schematics available.

What do you think? Cancel reply Your email address will not be published.The filter is arguably the element of a synthesizer that does the most to define its character.

Words like squelchybrassycreamygritty and so on are often used to describe their impact, and reading those adjectives in this context probably made you think of a few specific synths. Perusing the various offerings in both the fixed architecture and eurorack markets presents a perplexing plethora of jargon.

To make matters worse, many of these terms overlap, as manufacturers will often use different names to describe the same feature.

So what makes all these filters different and how does that affect the way a synthesizer will sound? The low pass sometimes referred to as high cut filter is the most common type of synthesizer filter. As its name suggests it allows low frequencies to pass through, which can be useful for taming an abrasive top end.

High pass or low cut filters do the opposite, letting the high frequencies through while cutting out the more rumbly tones. Mix a high pass with a low pass and you get either a band pass or a notch filter, depending on how they are arranged.

A band pass allows only a narrow band of the frequency spectrum to pass through while the rest is filtered out. Notch is the opposite, filtering out only a narrow band of the frequency spectrum. A coffee filter, on the other hand, separates the ground beans from your coffee I threw that one in just to see if you were paying attention.

There is also the more rare and mysterious All Pass filter.

moog filter schematic

If everything is allowed to pass through then what exactly is filtered? In this case the entire signal is passed through but shifted in phase and blended with the original signal. At the filter cutoff point the phase shift is ninety degrees. The resulting phase cancellation causes an effect that sounds similar to a phaser or flanger. Similarly, comb filtering, which is the term for the actual result of a phaser, flanger, or chorus, is caused by blending the original signal with a slightly delayed version of itself which creates a series of notches through phase cancellation.

The length of the delay determines where in the frequency spectrum the notches occur. Varying the amount of the delay time is what creates the swishy jet plane effect.

The cutoff frequency is the point in the spectrum where the filtering takes effect.View all our schematics on our main schematics page here. The schematic shows the path of electricity, the components it will pass through, and the layout of those components. But it also demonstrates the aesthetic of the artist and the structural beauty of the design.

This strange duality embodies the nature of the schematic. They are a documentation of the history and progression of his innovation in an artistic and beautiful format. We are progressively sharing schematics in our archive for your examination, learning, and enjoyment.

The archival process required to insure that these documents can be properly shared is very detailed, process-oriented, and thus requires copious time and resources. Please consider donating here to assist us so that we can continue to preserve and share our vast collection. Post a comment if you have any further information about the people, devices, or rich history of these documents!

Moog Co. What the heck was Bob up to here? This is a power supply for the original device made for Herb Deutsch. This document is of incredible historic importance, as it is one of the first Moog synthesizer power source designs. We are honored to steward, preserve, and share it with you. The least glamorous of the series: the power supply. However, this particular schematic is exciting because of its age.

Drawn this early init is probably the initial design for the modular power source. In this piece, the movements of dancers in proximity to technology triggered sound samples in an integration of music, dance, and real-time composition. This schematic is likely associated with the creation of this technology.

Also included are some notes Bob took in regard to the design and improvement of the device used in the performance. Compare the two and see if you can spot the differences! This schematic is relatively early drawn inand is for the design of the B oscillator module. Above is a schematic for the high pass filter. When used in conjunction with the low pass filter, it made a very pleasant-sounding band pass filter.

This document not only shows the circuit traces but but also has the components written in in pencil, providing a functional portrayal of the module.The Model D also set standards that were imitated by most other manufacturers that came after — The left-to-right layout of oscillator, filter and envelope controls, the idea of pitch bend and modulation control wheels to the left of the keyboard and the basic signal and control paths along with some of the front panel terminology.

If there is one impression that describes the physical experience of the Minimoog it is that it is solid and substantial.

The knowledge and experience that Moog had accumulated from building their modular systems translated very well into the Minimoog. It was the machine that was intended to take the synthesiser out of the studio and onto the stage and Moog did this very well indeed, the Minimoog has an impressive sonic palette without being too complicated or too limited with some clever features — One of the oscillators is set up to double as a low frequency oscillator, turning it from being a sound source to a control source.

The Minimoog is quite simple internally, easy to access and service. The front panel controls are large, solid and of good quality. The mains transformer and secondary power supply boards can be seen in the images above. Below the black transformer on the LHS you can see the small circuit board that contains the power rectifier diodes and filtering capacitors.

To the right of the image is the power supply board. Note the two large gold heat sink fins for removing heat from the two transistors that are bolted to the corners of the fins — One transistor provided the positive 10 Volt supply, the other the negative 10 Volt supply. Together they produce the symmetrical 10V-0VV power that is needed throughout the synth.

In the centre of the image you can see pairs of little black transistors that are connected by a white thermal paste. This is common in analog synths, particularly in oscillators when it is desirable to keep the two transistors that are wired as a symmetrical circuit as close to the same temperature as possible so that they drift with temperature change at the same rate.

The noise generator uses a transistor junction wired in such a way as to produce noise which then passes through three filter stages to produce white, pink and red noise. This board has been re-capped at some point — the cylindrical electrolytic capacitors on the board are a newer type. They can change the timing of certain circuits too.

The oscillator board, located on the right hand side of the synth when looking from the rear. A closer view of the CV mixing section of the oscillator board. They are the round white components with the black caps. Further to the left are the components that make up the wave shapers that produce the pulse and triangle waves. The sparse dual envelope generator board. Synths this age often have odd modifications added over the years. This one is on the envelope generator board.

The filter is usually what first comes to mind when conversation turns to the sound of the Minimoog, or indeed the sound of any Moog synthesiser. Despite these transistors and capacitors looking every one of their forty-plus years they are still working perfectly.That is the question.

Saving species is essentially a forever-type FAQ on Coronavirus and Mefi : check before posting, cite sources; how to block content by tags.

moog filter schematic

Oddly attractive images even if like me you can't read a circuit diagram to save yourself. Behringer tents their fingers menacingly. I think you can buy T-shirts printed with the diode ladder schematic. Of course, most of this stuff has been getting ripped off since forever. Analogue circuitry is pretty easy to reverse-engineer if you've got it in front of you. Based on a series of wide-ranging oral history interviews done with family members, colleagues, and contemporaries, and done in partnership with the Asheville, N.

From the words of Herbert Deutsch and Bernie Worrell to Shirleigh Moog, David Borden, and many others, and featuring rare Moog instruments such as a vacuum tube theremina Trumansburg-era Minimoogand an early Moog amplifier of which only three were ever sold.

I remember back in high school I found a theremin schematic that Bob drew, and someone put on the internet. But that one was hand draw, these are fancy style drafted for production.

Look: a car speaker in a drum posted by bdc34 at AM on March 13, [ 1 favorite ]. Majestic display of music nerdery. Yup Moog very famously sued ARP - and possibly some other companies over the years - for imitation of their classic filter design. Here's one - not drawn by Bob though.

Haha I didn't see that somebody else was talking about this. Gotta point out the Moog filter is a transistor ladder design though. Look: a car speaker in a drum posted by bdc34 at PM on March 13 That's mind blowing.

I suppose he's using the thing as a gigantic microphone but why not just use an actual-factual microphone? Or at least a smaller speaker? Rip apart an old Guitar Hero drum controller and it's going to be a plastic plate with one of those piezoelectric musical x-mas card speakers under it. I actually repaired my own Rockband drum set a few times using parts from greeting cards.

Look: a car speaker in a drum Questlove used to have his kick drum mic'd with a subkick mic. Tags Moog. Share Twitter Facebook.Of the voltage-controlled audio filter topologies, there are few. This piques my interest in such a circuit—clearly, a voltage-controlled filter VCF is a useful, maybe even an essential, element in audio circuits!

And with all the creativity of 20th-century analog engineers, the fact that these circuits are scarce is fascinating. Why are there so few topologies? Why don't any of the existing topologies look much like filters? Voltage-controlled filters or VCFs were a mainstay of the analog synthesizer. The most common configuration, arguably, uses the operational transconductance amplifier OTA based filter, with such ICs as the LM and the LM being popular choices. But one filter stands above the rest, for being creative, effective, and I have on good authority audibly "brilliant".

This is the Moog ladder filter. Without further ado, let's take a look at the Moog filter, roughly as it appeared in the Moog Prodigy. Audio input is applied to Q1, feedback for resonance, also known as emphasis in electronic music is applied to Q2, and the other transistors are in pairs, tied at the base, with capacitors shunting their emitters. The output is taken as the voltage across the top-most capacitor. To simplify this a little bit, we can with some care remove the biasing components, and we get the schematic shown in Figure 2.

This is only slightly misleading, because of course the bases are not floating, but are held at constant potential through a divider. Let's just look at the circuit. The cutoff-frequency control for the circuit is a current, I biasapplied to a differential pair Q1-Q2.

Moog Modular Schematic Blueprints :: Obliq Museum

Changing I bias causes the bias current of the transistors to change, for the whole network. Neglecting base currents i. The transistors in a pair share the same base voltage but have different emitter currents. Because the small-signal currents are different, the small-signal v be for the transistors will be different, and so a potential will develop across the emitter capacitor. The capacitor, being a frequency-dependent reactance, gives rise to the filtering effect.I have been collecting copies of Moog patents, those invented by Robert Moog and as well as those assigned to Moog Music, Inc.

I present them here along with some hopefully entertaining commentary. I think it is interesting how the guts of some great synthesizer circuitry is described so well in patents, yet not covered in books or articles to any great extent.

Sure, patents are the way to protect this sort of intellectual property in a business with some competition, but these patents speak volumes about the approaches the engineers were taking in creating some breakthrough musical instruments. At the very least the patents, as well as other synthesizer patents, supply remarkable lessons in not only how to design analog circuitry, but also in how to build a great musical instrument.

Analyzing the Moog Filter

The USPTO links are the official ones, and include database information such as which patents reference this one as well as the text of the patent and scans of the patent in tiff format. The Pat2Pdf service automatically provides a nice pfd file from the tiff scans. Possibly the most famous electronic music patent ever, this is the guts of the circuitry for the Moog A voltage-controlled low-pass filter, the Moog B voltage-controlled high-pass filter and the Moog C filter coupler.

This filter is certainly well known for its characteristic sound, but I want to point out some of the breakthrough concepts behind it. First, voltage-tuning a filter over a wide range is a difficult electrical engineering problem. How do you do it?

Synthesis Essentials: Know Your Filters

Electrical circuits don't normally work that way. Bob Moog looked to the emitter resistance of balanced pairs of transistors -- the emitter resistance can be varied exponentially over a wide range and the symmetry of the balanced circuit cancels out most of the control signal and even-order harmonic distortion. The four-single-pole-low-pass-sections-with-feedback approach was not typically used for filter designs at the time, but it addresses these issues perfectly.

For comparison, the peaking frequency for the traditional 2-pole biquad filter is not the same as the filter's tuned frequency, although the two approach each other toward oscillation.

The transfer functions of the low-pass and high-pass filters are:. As feedback is applied, the four poles split out, literally in the shape of an "X" and move apart 90 o from each other. At a feedback factor of 4. Bob Moog's design does all this with a remarkably simple circuit that performs well, and any inaccuracies it does have provide a lot of character to the sound. The filter can be overdriven in a musically pleasing way as all the transistor stages clip gradually.

So this is a killer design from many angles. The B high-pass filter is the electrical brother of the low-pass filter, although the schematics look very different from a distance.

The high-pass filter does not have a feedback path and thus no resonance control; perhaps there are stability issues here. On the other hand, the Moog AES article below mentions employing a small amount of feedback to sharpen up the response curve. The C filter coupler is the obvious way of doubling up a low-pass VCF and a high-pass VCF in series for a bandpass filter or in parallel for a band reject filter with individual controls of center frequency and bandwidth.

Roland and other companies have produced diode ladder filters using diodes as the tuning elements instead of transistors, presumably as a "way around the patent".

moog filter schematic

The diodes do not separate the capacitor sections from each other like the transistors do, so the diode-based ladder filters have their poles scattered along the x axis instead of all at the same location.

They sound different, their cutoff slope is much more gradual, and they require a lot more feedback to oscillate. This is the patent for the Bode Frequency Shifter manufactured by Moog and available as module Full schematics are included in the Moog modular service manual. The patent schematic and the sevice manual schematic are very similiar although the patent has, as expected, far less circuit detail.

The basic idea is an implementation of the trigonometric identity for the cosine of the sum of two angles to shift the frequency up:.

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