Audio i2e

Frequently asked questions about AG1.0 / The PURR

Does the AG1.0 change the sound of my guitar (...if there are no capacitors in the input no gain is selected...) ?
If the AG1.0 is switched off, a relay connects the input directly to the output. All other circuit parts of the AG1.0 are disconnected. The sound of the guitar (... including the connected cable to the amplifier ...) will not be changed at all in this case. If the AG1.0 is switched on, but there are no capacitances in the input and no amplification activated (both rotary switches on position "0"), the following condition results: The guitar pickup is no longer loaded with the capacity of the cable to the amplifier but only with the relatively high input resistance (typically 1MOhm) and the very small "natural" input capacitance (typically 15pF) of the AG1.0 and the capacity of the patch cable (<100pF). This shifts the resonance of the pickup to higher frequencies. The guitar sounds more "airy". That's the only change the guitar signal experiences. The rest of the circuit is sound-neutral and does not change the sound of the guitar.

Why is the difference with / without AG1.0 more distinct with some guitars as with others ?
Decisive is the inductance of the pickup. If I want to achieve a high output, I make many turns on my pickup. This also results in a high inductance. The resonant frequency now results essentially from this inductance of the pickup and the capacity of the cable. With high inductance, the resonance is quite deep, even with a short cable, and the longer the cable gets, the farther it moves down and attenuates the higher frequencies. For pickups with lower inductance (= low output power), there is some "more headroom" in the length of the cable since the short cable response is still relatively high and a longer cable still allows more levels than a large pickup inductance.
This is very clear in one of our test guitars, a T-Style with serial pickup in the neck position and a powerful DM-type on the bridge. With 6m long cable, the heights of the neck pickup are only slightly attenuated, but the bridge pickup experiences a whole new freshness with the
AG1.0.  

Why does the AG1.0 has no input for an external power supply ?
There is simply no room for an external voltage input!
The preferred application of the
AG1.0 is to be mounted in close proximity to the guitar (... on the guitar strap ...). Here an external voltage input does not make sense anyway. Of course, the AG1.0 can also be mounted on the effect board, e.g. only to use the buffer or booster function. Here, an external voltage input could make sense, but the power consumption is so low (battery life more than 500 hours), that even with this type of application, the absence of an external voltage input is acceptable.

Do you use the "good" field effect transistors in the AG1.0 or just the "bad" operational amplifiers ?
We actually use an operational amplifier in the AG1.0! But not all operational amplifiers are "evil".
The
AG1.0 is not about changing the guitar signal in the sound and, for example, Add harmonics. The signal should pass through the AG1.0 as uninfluenced as possible (... of course except for the adjustment of the resonance of the pickup ...). The dynamic range should be as large as possible despite the operating voltage of "only" 9V, especially if the input signal is large and still a gain was set. The power consumption should remain minimal. The input impedance should be as large as possible, the output impedance as small as possible. And it should be almost arbitrarily long cables to drive. These specifications are best fulfilled with an operational amplifier. However, not with any cheap field, forest and meadow OP, but only with a high-quality representative of its kind, with lowest power consumption despite high cut-off frequency, high input resistance and rail-to-rail capability. In other devices, if we use the sound of e.g. By using enhancement with harmonics, we use the "good" field effect transistors and avoid the use of "evil" operational amplifiers.  

Why does the AG1.0 needs a microprocessor ?
Some functions, such as the monitoring and display of the state of the battery or the control of the bypass relay, are actually beneficial to do through a small microprocessor with appropriate software. In particular, even if the power consumption should be minimized. The slightly higher price compared to a discrete solution is justified by optimal function, low power consumption and small footprint.

Do i have to fix the AG1.0 at my guitar strap or can i integrate it in my pedal board ?
Of course, the AG1.0 can also be integrated in the pedal board. However, the function of shifting the resonance of the pickup by means of switchable capacitors tends to fade into the background (... after all, a relatively long cable is probably already connected to the guitar itself ...). But the AG1.0 is also as a pure buffer or booster an excellent solution and surpasses so many other pedal.

What is the difference between the AG1.0 and a "normal" buffer/booster for the pedal board ?
Capacitive loading of the PickUp is first of all from the guitar cable itself, but of course also from the sum of all the short patch cables, which connect my possibly not a few effects devices. The sum of the patch cords can quickly reach or even exceed the capacity of the actual guitar cable. A buffer / booster as the first device on my pedal board makes sense of course: The influence of all subsequent patch cables is kept away from the pickup of my guitar. At least this load is then no longer relevant ... But the long guitar cable to the buffer / booster on my board still loads my pickup! This can only be avoided by using a buffer directly on the guitar itself ... e.g. through the AG1.0. And this not only separates the load on the guitar cable from the pickup, but of course also the patch cables. The buffer on the board becomes redundant, ..   

What do you think about the myth of "neutral" buffers ?
There are actually manufacturers who boast of offering a "neutral" buffer. The guitar sound would not be changed by the buffer ...
The fact is: Whether implemented with transistor or operational amplifier, it is really the simplest exercise today to build a buffer that has a linear frequency response in the frequency range of a guitar, ie between 80Hz and 10kHz and has only inaudible self-distortion! At a time when there were only germanium transistors, things looked different. Those who boast about being able to offer a "neutral" buffer today are more likely to struggle with replicating old schematics rather than being familiar with the state of the art nowadays. For us it is not a big topic ... of course the
AG1.0 is a "neutral" buffer. Not worth talking about    

Does the AG1.0 work with my bass ?
Even though the bass is supposed to generate mostly low notes, the overtones play a crucial role in the sound, especially with unpolished strings and plectrum playing. Therefore, the AG1.0 also audibly changes the resonance behavior of the pickups with long cables on the bass. In addition, if the output level is too low, the booster function can be very useful.

Can i use the AG1.0 also with my active guitar ?
The active guitar does not need the function to decouple the resonance of the pickup from the cable. But as a buffer or booster, the AG1.0 can also support active guitar sensibly.

Can i use cable with any length and qualitiy with the AG1.0 now ?
The lowest possible capacity is just one of the quality features of a cable. In addition, however, cables differ in terms of processing, the quality and soldering of connectors, resistance to treading, flexibility, low noise, and so on.
Even if capacity does not matter anymore when using the
AG1.0, the other qualities remain important and cheap cables often do not offer them. However, with the AG1.0 in use, you can essentially focus on the mechanical qualities of the cable (... and will surely find a good cable at a good price ...) and save the hunt for voodoo features and Prices of some dubious manufacturer.
The key to the
AG1.0: Whether good or bad cable, whether long or short cable, whether at home, in the rehearsal room or at the gig, with the AG1.0 the sound of the guitar is always the same!  

What capacitance has the enclosed patch cable ?
The included patch cable has a length of about 30cm and a capacity of about 60pF. 

Why is the AG1.0 relativly expensive ? My xyz pedal can do more costs less ?
The AG1.0 was developed in Germany and is manufactured in relatively small quantities also completely in Germany (including case processing and PCB production). Only high-quality components are used. In fact, the price is based on a still moderate calculation and none of the participants is rich by the AG1.0. Less price is not possible, otherwise we would not be able to pay our rents and then develop new, interesting devices. See in this context also our 2-channel guitar interface ESTE and the amplifier JESS, whose new concepts were not yet so on the market available.

Are you boutique ?
What is boutique? If you're doing a Marshall / Fender circuit diagram for the hundredth time, you've changed some component values ​​slightly, offering a "totally different-sounding" amplifier at an outrageous price, using noisy carbon press resistors and hand-soldered Voodoo capacitors? Or if you imagine a TL071 operational amplifier with diodes in the negative feedback as the non-plus-ultra, of course, in black gunk must be shed, otherwise everyone could see what is behind it, and also plays this great guitarist XYZ this part exclusively, and costs Of course, a multiple of an equivalent brand pedal (the Green ...)?
If the boutique is, then we are not! We do not copy existing equipment and issue it as a novelty, but are always looking for new ways. The focus is always on the instrument, our devices should support, ideally be part of the instrument. Prices are calculated according to quantity and effort fair and not determined with dice.

Why does the battery does last so long in the AG1.0 ?
In fact, the battery in the AG1.0 reaches a running time of more than 500 operating hours, provided it is an alkaline type with about 500mAh (... you can find cheap in the cash department of the largest German discounters ...). The reason for this is simple: The circuit has been designed with optimal power consumption, an extremely low-power OP, a bistable relay for the bypass function and an intelligent battery management based on a small, extremely low-power microprocessor.

Can i use the AG1.0 in conjunction with a passive piezo pickup in an acoustic guitar ?
Piezo pickups are inherently a relatively large capacitance themselves (e.g.,> 20nF). Therefore, the influence of a relatively small capacity of even a long cable (for example, 1nF) is rather small. In this respect, it usually would not need
AG1.0. However, a piezo pickup benefits from the highest possible input resistance of an amplifier (... apart from special piezo amplifiers, keyword charge amplifier ...), as it can only transmit low tones sufficiently. If the amplifier used does not have a sufficiently high input resistance and thus lower tones are rather weak, then the AG1.0 can possibly help. He has an input resistance of at least 1MOhm and is therefore still quite good for the connection of a piezo. The boost function of the AG1.0 may also be useful. He also makes the connected at its output to the amplifier and possibly long cable less susceptible to interference, because he controls it low impedance.
Conclusion: The
AG1.0 is not specifically designed for the requirements of a passive piezo pickup, but depending on the amplifier used (and the quality of the cable used to the amplifier) ​​can improve the frequency response (low frequencies) and the signal to noise ratio. 

The gain selector at the AG1.0 does produce switching noise in the amplifier. Is there something wrong ?
When the Gain control is pressed while the AG1.0 is actively connected to an amplifier, switching noise occurs. This is not a defect, but due to the principle, the gain between 2 positions is always short at "1", corresponding to an open switch (... as in switch position "0"). The Gain control on the AG1.0 is not intended for continuous volume control during active operation, but more than a Gain preset that is once selected for the connected pickup and then not changed during play (... is ever after attachment to the belt also rather impractical ...). Much more should be used for the volume control of the guitar, in particular because this is replaced by the use of the AG1.0 an improved function. As already stated elsewhere, the low-pass behavior of the potentiometer in the guitar is mitigated in conjunction with a long cable, the heights are no longer attenuated as much when turning back the volume as without AG1.0.


i2e'17