MultiAmp V.3 multichannel biological amplifier system

 

In our choice there are three different amplifier systems. This page describes the MultiAmp amplifier family. Our other amplifier products are BioAmp, and LinearAmp families. All of them are up-to-date, easy to use, highly reliable, microprocessor-controlled constructions. We manufacture three different amplifier families, because the three product lines are optimized for different application fields. Please read through the appropriate descriptions for the details.

 

MultiAmp is a modular, expandable, multichannel biological amplifier.

 

MultiAmp amplifier family is especially powerful in multichannel applications, since such a level of reliability and flexibility is unthinkable in other analogue amplifiers. And the top of all that, our MultiAmp amplifier system offers a very reasonable price level in comparison to the number of channels. The most important aim during its development is to remove all that features (and the appropriate circuits) what are substituted in the biological data acqisition software packages today. In this way the size of the circuits can be decreased, and as a result, the number of the channels can be increased.

 

An example: the smallest (8-channel) MultiAmp system:

 

        Click on the picture to get it in full size

 

 

MultiAmp's main fields of applications:

 

    - EEG Brain Mapping

    - Current-Source Density

    - Cortical Depth Mapping

    - Multichannel recording from brain slices

    - Chronic multichannel recording

 

 

The modular structure of the MultiAmp system:

 

The number of the amplifier channels can be configured in multiples of 8. Actually there are two different amplifier units in our choice. One of the amplifier units is an 8-channel equipment, and the other amplifier unit is a 16-channel equipment, where the 16 channels are divided into two 8-channel parts, and they can be programmed independently. In the future there will be introduced a 32-channel amplifier unit, too. The Power Supply unit is a separate equipment. From one Power Supply unit a maximum number of 64 amplifier channels can be powered. Certainly, more than 64 amplifier channels are also can be installed in one recording system, but for higher (more than 64) channel numbers, more than one Power Supply unit should be installed. The following list shows the necessary elements to order according to the number of the amplifier channels:

    8-channel system: one Power Supply unit, and one 8-channel MultiAmp amplifier unit

    16-channel system: one Power Supply unit, and one 16-channel MultiAmp amplifier unit

    24-channel system: one Power Supply unit, one 16-channel, and one 8-channel MultiAmp amplifier units

    32-channel system: one Power Supply unit, and two 16-channel MultiAmp amplifier units

    48-channel system: one Power Supply unit, and three 16-channel MultiAmp amplifier units

    64-channel system: one Power Supply unit, and four 16-channel MultiAmp amplifier units

    128-channel system: two Power Supply units, and eight 16-channel MultiAmp amplifier units

 

MultiAmp is a programmable amplifier, but it has no sampling circuits in the signal path at all. In other words, it is controlled by a built-in microcontroller, or a remote computer, but it has got only high-performance, low noise, low distortion analogue amplifier circuits. This feature is indispensable when you use averaging techniques to process its output signals. The internal microcontroller, and the optional digital port (which offers remote control facility from a PC) are optically isolated from the amplifier stages. In this way we could connect all the advantages of high accuracy analogue amplifier circuits, and easy usage of digital control.

 

Although MultiAmp is a programmable equipment, it does not need a separate computer to work. According to this fact, it can be used as a stand-alone amplifier (while possessing an optional serial port to communicate with a PC). This stand-alone feature is very comfortable, because the computer is always given, but it should be used to collect, and to process the experimental data. MultiAmp's microcontroller on the front panel has got a 3-button keypad, and menu-driven internal software, so it is very friendly to use.

 

 

Technical data:

 

In the MultiAmp system the High Pass Filter has got 4 possible positions, and the Gain have got 8 possible positions. The Low Pass Filter is fixed at 8 kHz in the analog circuitry by default. You can order your MultiAmp manufactured with other Low Pass filter setting, as well. The actual High Pass Filter, and Gain values, realised during the manufacturing process can be ordered with the default parameters, but they can be requested with special values, to meet any special requirements, as well. The default values for the Filter and Gain sections are listed below.

 

High Pass Filter

0.0126 Hz (12.64 s)
0.16 Hz (1 s)
1 Hz

100 Hz

 

Low Pass Filter

8 kHz

 

Gain
200
500
1,000
2,000
5,000
10,000
20,000
50,000

 

The MultiAmp system must not be used in human experiments, because it has not got European permission for human applications.

 

The complete User Manual of the MultiAmp amplifier system is available for download.

 

 

Noise considerations:

 

The noise level of MultiAmp was measured in two different arrangements. In both arrangements the 8-channel monopolar (single-ended) headstages were used. The inputs signals of the headstages were generated by a battery-powered square wave generator. The output impedance of this generator is 470 Ohms. The measured noise voltages were referred to the input of the headstage (in other words, they were measured at the output, but they were calculated to the input, divided by the actual Gain). We found, that the circuits after the headstage in MultiAmp have negligible effect for the total noise characteristics. The difference between the two noise measuring arrangements was the bandwidth.

 

1) MultiAmp was used on its natural way, the bandwidth was 8 kHz.

 

        Input noise RMS voltage: less than 50 microVolts    (200 microVolts peak-to-peak)

 

2) External low pass filter (2-pole, passive) was connected to the outputs of MultiAmp, and the bandwidth was limited by this filter to 1 kHz.

 

        Input noise RMS voltage: less than 10 microVolts    (40 microVolts peak-to-peak)

 

We removed the switcheable low pass filter circuits completely from MultiAmp when the first version was designed in 2006, and we would like to keep this strategy during the development of new versions, too. The low pass filter is an essential part in every amplifiers (referring to the sampling-law of Shannon). Low pass filters are used in the two other amplifier families of Supertech. A Bessel-type filter works in BioAmp, and an 8-pole, precision Bessel-type low pass filter works in LinearAmp. We decided to remove it from our newest amplifier construction MultiAmp, because the best biological data acquisition programs on the market use a brand new method (they can do it, because the computers are very fast). They sample with a very high, presettable frequency, they make an on-line low pass filtering on-the-fly, but they log the data on the hard disk with a smaller sampling rate (determined by the software low pass filter setting). This method is spreading nowadays. If you are considering to buy a MultiAmp, you should check the availability of this feature in the data acquisition program you use.

 

If you are not satisfied with the fixed 8 kHz of bandwidth, you have got three possibilities to modify it:

 

A) Low Pass Filter function can be carried out in the data acquisition software with on-line digital low pass filtering. If your DAQ software does not support digital Low Pass Filter function, you can choose from the following two options.

 

B) The bandwidth of MultiAmp can be limited internally in the amplifier during the manufacturing process. You can order any lower frequency limit, to meet any special requirements. This possibility provides a little bit better (approximately 2 dB better) signal to noise ratio than option C, but the limited bandwidth can be modified in the factory only.

 

C) The bandwidth of MultiAmp can be limited externally, with additional, passive low pass filter boxes. From the ribbon cable output connectors of MultiAmp all the outputs are driven to small boxes containing 8-channels of low pass filters. These external filter boxes provide the possibility to remove them by yourself anytime later. They can be necessary to remove, if you will need higher bandwidth in the future.

 

The difference between amplifier models mostly depends on the quality of the design. Such features as hum noise, square wave transient response, phase response, frequency domain characteristics, ability of parasite oscillations, thermal stability, reliability, etc. are responsibility of the designer. But there is no real difference in the signal to noise ratios of biological amplifiers manufactured by different firms. The signal to noise ratio depends on the internal design of the operational (and instrumentational) amplifier integrated circuits. The race of the smaller electronic noise is a race of the semiconductor manufacturers. The designer can only choose from the good amplifiers, from the leader semiconductor factories.

 

 

Ground topology:

 

There is a general design method in the high gain amplifiers, what is applied in MultiAmp, as well. Usually in the biological amplifiers (as in our amplifiers, too, if optical isolators are not used) the Input GND, and Output GND points are connected together internally. The ohmic resistance between them is less than 0.05 Ohms. However they are signed as different points, because in the interior of the amplifier the ground network forms a linear topology, not a single-point GND (as it is adviced in the text-books). The suppression of the hum noise is better, if the ground line follows the signal line linearly according to the increasing signal amplitudes from the input to the output. To establish a single-point shielding ground is a good solution at the output end of the signal ground line. Unfortunately the security ground wires are also connected to the metal enclosures of the equipments. The security ground wires are usually hum noise sources for the biological amplifiers (because they usually drive some mains-frequency fault currents from other equipments, from other rooms), but they must not be disconnected, they are compulsory to be used. If you use a mains isolation transformer with symmetrical secondary coil, you can eliminate the disadvantage of the security ground (if in your lab it is allowed to use, please check the local rules). The vibration isolation table, the manipulators, the Faraday-cage, metal parts in the Faraday-cage, the oscilloscope, the PC, the Output GND of the amplifier, and the real, separated signal ground line (coming from the earth directly, if it is available) should be connected to this single-point shielding ground. But the ground point of the biological target (the slice chamber, or the body of the amimal) should be isolated from the shielding ground point (special care should be taken with the metal parts close to the target in the Faraday-cage). The Input GND point of the amplifier is used to provide a low impedance ground to the biological object only. The Input GND point to the biological object is the GND pin at the input of the headstage.

 

 

8-channel amplifier unit of the MultiAmp system:

 

            Click on the picture to get it in full size

 

 

16-channel amplifier unit of the MultiAmp system:

 

            Click on the picture to get it in full size

 

 

Power Supply unit (up to 64 channels) of the MultiAmp system:

 

            Click on the picture to get it in full size

 

 

Headstages

 

All MultiAmp amplifiers have got multi-purpose connectors for external headstages. This method gives an opportunity to use various types of input modules to meet all the future demands. Actually there are 8-channel monopolar (single-ended), and 8-channel differential headstages for MultiAmp in our standard choice, but we have been continuously working on new circuit versions to support more sophisticated applications, as well.

 

There are some applications, where the most important aspect is the size of the headstage (e.g. freely moving mice, and neonatal rats). For such applications we have developed 8-channel, and 16-channel interfaces to connect smaller headstages to the MultiAmp system.

 

If you can not find the appropriate headstage model for your special task in our actual choice, we could develop a special headstage especially for you. It is our method, how we can improve the features of our equipments. We collect all the notices and feedbacks of our customers, and we implement their knowledge into the features of MultiAmp.

 

8-channel monopolar headstage:

               

 

Click on the picture to get it in full size

 

 

Connectors

 

The pin assignment of the 20-pin, 2.00 mm wire connector, what is used to connect the 8-channel headstage to the MultiAmp, and the 37-pin SUB-D connector, what is used between the Power Supply unit, and the MultiAmp amplifier units are not published here. The user must not connect any other equipment into these connectors, only the appropriate products (manufactured by SUPERTECH) should be connected. However, if you are interested to know them, please call, or email us: office@superte.ch

 

The Downloadable pin assignment of the 10-pin, 2.00 mm input wire connector of the 8-channel monopolar headstage of MultiAmp amplifier is available.

 

The Downloadable pin assignment of the 20-pin, 2.54 mm output wire connector of each 8-channel output sections of the MultiAmp amplifier is available.