Fresh Fizz

Have you thought about an explanation of the sweet spot in a more dynamic way? An electromagnetic pickup causes a comb filter effect. The notches and peaks of the comb filter depend on where the pickup is positioned. At the sweet spot you've found there are 6 comb filters tuned to their respective open strings. Maybe you should compare it to tuning the carrier frequency of a ring modulator to the key you're playing in. FF

The most likely is that your power valves are not a matched pair. They draw different currents at rest. As a result of this the remaining hum after rectification isn't cancelled out at the output transformer. You can check the currents through the power valves by measuring the voltage across the cathode resistors (& no input signal) and applying Ohm's law. Should be somewhere around 35 - 40 mA. 2 solutions: use a matched pair of output valves or use some bias circuitry with a trimpot per valve. cheers, FF

It's a miracle that nothing burnt through. Is it because of the valve rectifier (GZ34)? Are the kathode resistors bigger than 1 ohm (some kinda class A setup)? The 5F6A bias(& power) conversion should solve your problem when using 5881s. Since you're experimenting with 6L6s the bias setup requirements could be different. I'm looking at a Fender vibrolux 6G11-A schematic. It has 365 volts at the anode and -36 volts as bias input. FF

So you're the owner of a Dukane 1c460. (PA, rackmount) I found something of the Dukane 1u460. (PA, head) So you need to check if it's based on the same schematic. I wouldn't be surprised if your Dukane is the result of a u46025F6A(Bassman) conversion that went wrong. If I have understood it well the flickr link provides enough info to get the Dukane working as a Bassman. flickr not flikker cheers FF

Well...could you expand on this aspect then because I'm not understanding I suspect. To me there seems to be a logic flaw. If a driver is putting out enough EMF to move the string, any magnetic sensor is going to sense this fluctuating EMF resulting in oscillation or squeal, no? If the cancellation of the two driver coils is complete, then there will be not enough EMF to move a string surely? I can kind of see the idea of having the two drivers separated but my experiments in sandwich designs and similar things never could overcome this kind of intrinsic quality problem... I'm not that keen on studying patents these days either, though the referencing of the Moog thing and not studying it for at least the 10 minutes it took to get the general gist of it and see that there have even with this information some false assumptions seems neglectful. The basic thing is much as I described and proposed years ago, sample and hold and activating things exactly as described in the "driver engine" idea so that interactions that they describe between close drivers and sensors are eliminated through the sequencing of activation. I mentioned the name Moog like: Moog did it so we could do it. The false assumptions are yours. I spent more than 10 minutes on the Moog patent and watched several YouTube clips to get an idea of its performance. I'm not familiar with your "driver engine" idea, but if you say that it works on the same principles as the Moog then why you don't understand? FF

@psw #1: My road to success is trial and error, develop some basic idea, build an early prototype and then figure out why it doesn't work. I'd rather not study patents, too boring. #2:'Our old school' sustainers make use of 2 separate transducers (driver and sensor) which operate continuously. The Moog kind of sustainer uses only one transducer. But the transducer cannot do both functions at the same time therefore this kind of sustainer needs a technique to switch between the two functions. Col's sandwich stack and my version deal with another issue, the big difference that exists between signal levels in driver and sensor mode. The combined sandwich drivers have a hum cancelling effect on the sensor coil. This should greatly reduce the interference of the decaying signal across the driver coils (right after the switching) with the signal across the sensor coil. #3: Well, the goal is mentioned in the topic title. Figure out how it could be done and then ,if possible, build it. Hexaphonic is always an option but in an experimental stage you want to keep it as simple as possible. #4: ? #5 and 6: No need for improvement! Going fishing all day isn't better than going to a shop and buy a fish. Same goes for carving a bear out of wood instead of watching a real one in the wild. Cheers FF

Thanks for the replies guys. I myself have a lot of doubts if this could work. But as RM2488 mentioned it's already been done by Moog. So it's theoretically as possible as me building a guitar and winning the GOTM competition. Some of the issues mentioned I even haven't thought of. I want to share some other idea I have after reading your comments. What I am thinking of is using 3 coils. Two driver coils (bifilar wound) and one sensor coil. Both driver coils have their own driver amp. One of the amps has the signal inverted (inverting opamp, coil leads swapped). The switching should work like this: 1. driver mode: 100% non-inverting amp, 0% inverting amp 2. sensor mode: non-inverting amps switches to 50%, inverting amp switches to 50%. PRO's(?): no single driver coil that runs idle (100% to 0%) side effects of switching up & down should offset one another. If the level of the inverting amp exceeds that of the non-inverting amp there should be string damping. Cheers FF

You could try to use less overdrive/gain. That way you can vary the sound a bit more by changing the way you hit the strings (soft/hard picking). a case of lack of practice. More callus will keep the heartbeat away That sounds good! How about some: polyphonic fuzz some extreme eq settings, like ultra deep or twangy bass strings or fixed wah wah setting per string. Cheers FF

Hi folks, Since Hideki entered the PG forum with the Moog Guitar patent: here I have been thinking if it's possible to build a sustainer that uses the sustainer coil in a duo function: as driver as well as sensor. I took the liberty to copy col's last post from McSeem's hexaphonic project. hmm... thinking out loud time... Yes, like back in the good old days. I have no idea whatsoever. The first thing I would want to know is what a chopped signal does to a string. Could be as simple as a ring modulator driven by a 196 Hz sine wave and a 2 kHz block wave as carrier signal. The ring mod signal goes to the sustainer driver in neck position. Then I use my bridge pickup to listen what my open G-string sounds like. (Clean ?) The way I see it 2 things need to happen. 1. Switching from sensor mode to drive mode 2. Delaying the signal picked up in sensor mode and use that signal in drive mode. Yes, the switching frequency is a problem. Our driver coils are not able to handle high frequencies too well. Cheers, FF

Donald Tillman's java applet is a great tool: here. FF

Hmm, it doesnt look simple either. You probably will use analog switches to connect different filters. Besides, what happens in case there's a signal from two or more strings? Just connect two filters in parallel? In my opinion it's not that hard to build a true hex system. You can order pickup coils from Paul Rubinstein, for example, and use 3 minimal-circuit stereo power amps, such as LM4952, which has a DC gain control. Not sure about namely this one, but I'm sure there's a simple and compact IC solution. No analog switches, just different filters for different channels and a single-pole sustain pot. Well, plus maybe 6 single FET preamps. But anyways, it's nothing compared to that monster circuity Moog guitar. I was truly impressed by that. No, there is a fat chance nothing concrete will come out of this. After having built an ordinary sustainer with AGC I want to do something more experimental. But I want to stick with my high impedance humbuckers as signal source. My idea is to use overdrive instead of AGC and use low pass filters after the overdrive. Perhaps another way of achieving a filter effect depending on which string is played is to put a low pass filter before an auto-wah. I understand your question about the parallel filters. But I want to keep it as simple as possible. I want the device to sustain the lowest frequency it can 'find'. And I wonder if it's possible to build a basic mono Moog. I don't think it's pulse-width modulation. Couldn't it be time division multiplexing (and demultiplexing)? Using an oscillator and some CMOS switches, could that work? Switch between pickup and driver function? I only don't understand why the Moog doesn't sound fizzy while the sustainer signal is that much truncated. Cheers FF

Yes, the building of the hex magnetic and all the necessary circuitry inside your guitar is an impressive piece of work. I myself am thinking of a solution which enables me to stick with the mono guitar pickup. Like adding 6 coils whose only function is to sense which string is being picked/ sustaining. And filter the sustainer signal according to this information. Basically a analogue and poor man's hexaphonic. And it works under linux. FF

To me it seems that the hex magnetic gives a more pleasant sounding feedback. With my own sustainer (with magnetic pickup) I don't get higher than the 3rd harmonic. The hex piezo seems to be able to give you all the higher harmonics you need. I have some questions. OK, you might as well interpret it as a request for more sound clips 1. What is the phase relationship between the sustainer driver and the hex piezo? For a magnetic pickup it's all about position,polarity and electrical properties of the coils, what's it like for a piezo? 2. How does the sustainer device perform when a mix of hex magnetic and hex piezo is used as input? Do you get a more versatile or balanced sustainer by combining the hex mag with the hex piezo? 3. What does it sound like when the hex magnetic is used as sustainer input and the hex piezo as output (to amp or DI)? Or vice versa? Cheers, FF

I'm glad to hear this from you, al s. I was starting to think there was something wrong with my hearing. Or taste. So much progression and innovation, and we're only at page 2! FF

I see Thanks for the information! So it's applying a low pass filter, reversing the frame, applying the low pass filter once again, reversing the frame. So the phase shifting caused by the filter will be zero. Clever. It's not that ridiculous after all to distort the signal that goes to the sustainer driver. I tried that for my first sustainer device. But it didn't work well with monophonic pickup and driver. (too much bandwidth, cannot filter per string, intermodulation) A problem with distortion is that it's reacting fast. Especially in higher fretting positions. When using a limiter with a long release time the signal first sags right after the string is picked before it goes into sustain. I tried the procedure you described for myself. So far it could be done the analogue way. With 24 dB /octave low pass filters and eventually some all pass filters to compensate phase differences. But I understand you work one step at a time. I'm very curious how you will take this project to the next level. The delay does 2 things. It eases the problems you have with squealing. It works as a comb filter, it really disturbs the phase relationship between driver and pickup. (lowest frequency with a 180 degrees phase shift: 1 / 0.020 / 2 = 25 Hz) Some fundamentals are out of phase. Cheers FF

Of course you need 6 noise gates (3), one for each string. No need to build 6 separate side-chains. But on the other hand, why not? Cheers FF

I don't see a simple solution. Since you are the programmer over here you could write some program that does the following: 1.Send the signal through a low pass filter (24db/octave). 2.Then the signal goes to a comparator. If the signal from the low pass exceeds the reference voltage the comparator's logical level changes ( 0 to 1 or vice versa). 3. When the comparator's logical level is changed a noise gate will switch off drastically reducing the signal. So what you've done is create a side-chain (1,2). Only the noise gate (3) is in the signal path. Of course you don't need to build this in 6-fold. You mix the signals from the 6 piezos into one signal. By the way, somewhere else you mentioned some other problem you have with silencing the 'unplayed' strings. If you send some tiny portion of the overall mixed signal to all of the 6 sustainer driver amps it could be just enough to snow under the process of spontaneously developing sustain on 'unplayed' strings. Hope this helps a bit FF

Clip 1: very nice sustain McSeem! Clip2: the same + some very nice Mustaine! May that shitty guitar playing of yours Rust In Peace. Which song does it remind me of? Perhaps you could tell what's in the sustainer's feedback loop apart from the double filter. Limiters, eq? Is the double filtering meant to deal with phase differences caused by the low pass filter or does it compensate phase differences between hex pickup and sustainer driver? Time counter-motion sounds very mysterious to me. Cheers FF

About the harmonics. It matters whether it is for melody (lead guitar) or backing (chords). Pinched harmonics (lead guitar) are played on top of the backing while in case of the hexaphonic sustainer sustaining with higher harmonics you lose the fundamentals and the relationship with the original chord. Of course you can play all of the 12 notes as a melody note. But a wrong harmonic in a chord just sounds wrong! Carrilons have bells that produce a 'minor' sound. Major chords played by these bells sound weird! Cheers, FF

It's harmonic if the 3rd or 5th harmonic are built on the fundamental of a major chord (like both E-strings in E major). E major 3rd on b: f#, 9 5th on b: d#, maj 7 3rd on g#: d#, maj 7 5th on g#: c, 6- e minor wrong 5th harmonic on e! g#, maj 3 3rd on b: f#, 9 5th on b: d#, maj 7 3rd on g: d, 6 5th on g: b, 5 I would say you need to avoid the 5th harmonic to occur. You get too strange combinations (maj 3 and maj 7 in minor chords, 6- in major). The low pass filters (per string adjusted) have to be steep enough to filter out the 5th harmonic of the open strings sufficiently but not to weaken the fundamentals in higher fretting positions too much. Yes, keep going! FF

Nice tutorial! Should be a sticky thread. So if I understand you well this hexaphonic sustainer driver will eventually replace the neck humbucker? . But until now you only have driven the strings from above (like an E-bow)? I don't want to sound negative but if you're going to drive from below using too much power could become a problem (string rattling). Cheers FF

Yes, a current amp and connected like you assumed, or I could stick an inverting opamp in front of the LM386 to increase the open loop gain (inverting opamp as mixer of input and feedback line). Perhaps the open loop gain has to be a bit more than 200? I don't know if I'm right, but this is what I was thinking: Let's say we have a tap at 10%. (upper coil 90%, bottom coil 10%) Total self inductance is 1.2 mH, resistance is 8 ohms. First component of self inductance based on ratio of turns compared to total amount of turns Upper coil is (0.9)² x 1.2 mH = 0.81 x 1.2 mH Bottom coil is (0.1)² x 1.2 mH = 0.01 x 1.2 mH But the total self inductance is 1.2 mH, not 0.82 x 1.2 mH Mutual inductance is 1 - (0.81 + 0.01) x 1.2 mH = 0.18 x 1.2 mH Mutual inductance equally divided across both of the coils is added Upper coil : (0.9 x 0.18 + 0.81) x 1.2 mH = 0.972 x 1.2 mH Bottom coil: (0.1 x 0.18 + 0.01) x 1.2 mH = 0.028 x 1.2 mH For low frequencies (if open loop gain = ∞ ) gain = 11 For high frequencies gain = 0.972 / 0.028 + 1 = 35.7 So there will be some compensation at high frequencies but never more than 35.7/11 times (some 10 dB) My next driver will have a tap so I can check this out. No man overboard if this idea proves out to be totally incorrect. Take it easy, guys. Cheers FF

Congratulations, McSeem! You build with the speed of light, truly amazing. I love the sound of your hexaphonic pickup. It's hard to believe it's not eq-ed, it's so clear. Well, I never built one, so what do I know about it. The way you constructed the hexaphonic with the adjustable string alignment looks very neat. Of course I would like to know more about the hexaphonic, how it's constructed and about the coils electrical properties. And a lot more. You presented a lot of information at once. (Thank you.) I need to study and let it sink in. How was your experience with the hexaphonic as sustainer driver? And when you're bored you may throw it in my direction Cheers FF

@col and psw what if one of you guys started a new general sustainer driver discussions topic? And keep this thread for lm386 related issues only. FF

That makes sense, but then why does a zobel network help ? What is it about the amp that requires it to feed a resistive load? cheers Col Some stability issue, keeping the load impedance low and real: Boucherot cell I've never bothered to try but perhaps the zobel could be omitted. With a tiny LM386 there isn't that much at stake. The self resonance of the driver must be in the hundreds of kiloherzes. I can remember Hank McSpank wasn't able to trace the resonance frequency when performing tests for the piggyback driver. And the self inductance of the driver coil isn't that dangerously high. It's nothing compared to that of the primary coil of an output transformer of a valve amp. If a valve amp isn't loaded with speakers or a dummy load then the induction voltages can destroy the output transformer or power valves. More like this: cheers FF