gurus req to check out AGC Sustainer Circuit

[psw]

Well the sustainer thread still goes on...127 pages now!!!

Anyway, col has built a version of this circuit into a guitar on vero board...after a mistake discovered with a faulty solder join, it appears to be working, though some noise is still a problem. Noise in this device is a difficult thing...the driver gives off a large amount of EMI / electromagnetic radiation and some parts of the circuitry and instalation is important to look out for.

This circuit, and other means to limit and compress the signal is being looked into, there may be a simpler or other way to achieve the effect.

Otherwise, different driver designs and further testing and further mods to this, may prove it's worth afterall.

In other news sustainer, bancika (DIY Layout Creator, creator) is involved and working on the sustainer... pete

[col_012]

I think there is a better way of achieving the goal that this circuit was intendet to tackle.

The idea is that we want the sustain level and response to be even no matter which string is played and which fret it is played on. There is an enourmous difference in response depending on the magnetic mass of the string and it's tension. Playing higher on the neck makes any string more responsive because it will be closer to the driver - this effect is magnified by a higher action.

Using a normal compressor/limiter circuit doesn't help much because the best it can do is even out the signal sent to the driver - unfortunately the more responsive string/fret combos will obviously respond much better to the same level of driver signal....

The circuit at the top of this thread was an initial attempt to solve this by trying to break the restriction imposed by the feedback loop of a compressor type circuit.

The 'better way' that I'm working with now is:
Rather than trying to 'beat' the feedback loops tendency towards equalizing the signal output - why not incorporate the driver/string/pickup part of this system into the feedback loop (seems obvious now heh.)..
So instead of rectifying the output of the compressor and feeding it back to the start.... take some of the input from the guitar pickup, rectify that and use it to control the AGC amp...
The biggest problem I can see is that the initial attack from a hot pickup can by much larger than the circuit would deal with when it has settles into a steady feedback state... so how to protect the circuit from that initial attack without too much additional circuitry (it has to be as small as possible)...

An additional benefit of this approach over the last on is that it makes adjustment of the response (via a knob on the guitar) much simpler - in the original design, just naively boosting the driver signal would just cause the AGC to limit it further...

Anyway - thats the new plan

btw, is the project guitar forum down just now? I havn't been able to access it for a couple of days ?

cheers

Col

[DDD]

As far as I know the LM13700 (as well as 3080 IC) has too low input impedance. Connecting it directly to the pickup output will kill not only the highs, but the mids, too. The best way is to use the emitter follower before LM13700 or the common emitter stage with gain of about 3 times.
It's not necessary to protect input stages of the ON-BOARD preamp from too high signal levels. They usually can handle it easily without any damage.
Also I have to say that IMO it's impossible to "flatten" sustainer responce with the 9-volt power supply. According to my experience the necessary dynamic range of the amp-driver couple is to be at least 10 times higher than that with the 9-Volt battery. The only way is to use compressor circuitry before your pedal chain or combo amp.
As you can see almost all of the promotional soundclips presented by F@@nandes etc are recorded using high-gain distortion boxes or compressors. The "dry" sustainer sound is quite poor and not impressive at all, isn't it?

[psw]

As you can see almost all of the promotional soundclips presented by F@@nandes etc are recorded using high-gain distortion boxes or compressors. The "dry" sustainer sound is quite poor and not impressive at all, isn't it?

Well, I don't think so. I think most promotion of sustainer technologies are incredibly poor. They use a metal sound because that is what they see as their market...afterall this is feedback, rock and roll right!

The aim of the technology is to create infinite sustain (and related effects) with the preservation of the guitar's natural sound without noise. This can and has been done by both the commercial units and by the DIY sustainers.

What is not so "impressive" is what use the ability to create controled feedback or infinite sustain and use it in new and creative ways. Some of the possibilities are quite subtle...you can use the harmonics mode at a low sensitivity so that when the note begins to decay, the decay fades out at a harmonic, for instance.

Other effects are things like the generation of harmonics greatly extending the range of the instrument; controling the attack of notes by light picking, or simply fretting notes, to create swells; the potential to sustain notes on fretless instruments; the ability to create feedback without loud amplification of distortion, so making such sounds compatable with acoustic instruments; the potential to sustain acoustic instruments through such devices...

None of these potentials rely on distortion. The problem is more, given the potential to do something does not give the imagination or widespread appeal and aceptance of a technology. That said, the most famous and recognisable sustainer sound is featured on U2's with or without you, hardly a distorted or even characteristic lead sound, more a melodic counterpoint not commonly heard.

Also I have to say that IMO it's impossible to "flatten" sustainer responce with the 9-volt power supply. According to my experience the necessary dynamic range of the amp-driver couple is to be at least 10 times higher than that with the 9-Volt battery. The only way is to use compressor circuitry before your pedal chain or combo amp.

I may not quite be understanding what you are saying here. What col is trying to achieve in "flattening" the response could well be addressed by compression of the guitar's output signal. This is another reason for the use of distortion which will naturally compress by clipping and fatten up sustained notes with harmonic distortion. A lot of what is lost, and where perhaps col and I differ, is dynamic range. I wan't the instrument to be able to respond from a wisper to a scream, without the burden of excessive volume or effects. Compression and distortion limits the dynamic range and the expression of the instrument unless used with some subtlety.

What I do find appealing in what col is trying to do is the evening out of hot and dead spots on the guitar. My guitar can sustain notes on all strings and all frets cleanly...and it does this with a 9 volt supply with a current draw from 20-100mA...cols system appears to draw significantly less. Now if it can do this, why could it not lessen the effect for hot spots and thereby creating a more even response. Hence...

The idea is that we want the sustain level and response to be even no matter which string is played and which fret it is played on. There is an enourmous difference in response depending on the magnetic mass of the string and it's tension. Playing higher on the neck makes any string more responsive because it will be closer to the driver - this effect is magnified by a higher action.

Now, compression of the guitar's signal itself will create the illusion of this, but will effect the dynamic range of the whole instrument...it will sound "effected". A violin player would not accept such a restriction on the use of the bow (nor a wind instrument on breath control) that results in limiting the dynamic and expressive qualities of his instrument and technique, and neither should we.

OK...so what does the sustainer sound like? Here is a link to the sustainer sound page over at PG...col has recently posted a clip of what his sustainer sounds like with the discussed circuit...
http://projectguitar.ibforums.com/index.php?showtopic=17852

In relation to dynamic range and the use of the sustainer in a different and clean mode I'd direct you to a couple of improvisations of mine at this link...
http://www.soundclick.com/bands/pagemusic.cfm?bandID=464294

airie
Solo sustainer guitar in fundumental sustain mode. Demonstrates a clean sound with some notes not picked but swells out simply by freting the note. Notice that with multipule notes it is the lowest that sustains through...  
The Yearning
Sustainer sounds woodwind imitation and polyphonic sustain demo  

These were recorded directly to my computer's generic sound card with audacity and my technique timing and the quality of this $50 strat may be suspect...what tracks like this demonstrate what I am trying to get across what I am aiming for which is a large dynamic range and extention of the tonal palete.

Recorded in the same manner, but with a more overdriven sound is the clip I improvised soon after installing this device in the guitar...
Downloadable directly from here... http://users.pandora.be/onelastgoodbye/sounds/beckistan.mp3

What this clip demonstrates is some of the extra body that some distortion provides and how this also serves to even out and fatten up the device in harmonic mode. The first two phrases demonstrate the sound of the modified neck pickup, then the bridge pickup (without sustainer) so as to show the natural sound of the instrument. A more thorough description of the track is posted at the sustainer sounds page.

None of these tracks resemble the kind of music or tone that the promotional material of the companies are putting out, and I think they are selling the device short.

Impressive? Impressed? Well it's really not what I can do with it, but what people could imagine themselves doing with it.

On a side note. I always found it a little strange that an instrument with such popularity as the electric guitar has not a solo (unaccompanied) tradition to draw on. It is rare for the electric guitar to be heard on it's own and is often mixed into a rythm track, a riff or solo feature, but rarely on it's own. Time and again I am drawn back to artists like Jimi Hendrix who was able to provide wonderful tones and textures of clean guitar without huge layers and compression. This was a time when the electric guitar was still a dynamic instrument and capable of a full range of expression (clean, distorted, effected, loud soft and fed back!). Now, only genres such as "Jazz Guitar" and occasionaly in "Country Music" do you even here the guitar on it's own without distortion. Everything is so evened out nowadays that the dynamic range is lost to a great extent, as is the expressive abilities and some of the imagination that could spring from it.

Anyway...enough from me...I hope that future developments in this device will continue and more people will be exposed to the possibilities of the device. I will continue to encourage and work in my own way towards making it more accessable, simplifying it's installation and improving it's performance.

pete

[slacker]

Can anyone explain how to calculate (and change?) the input impedence of the first LM13700 stage of this circuit ?
Would it be possible to give it an impedence high enough so a normal guitar pickup could be connected to it without significant tone sucking - bypassing the input ?

Col

You could probably use the spare darlington to make a high impedance buffer and drive the LM13700 with that.