Digitimer now offers three different models of isolated amplifier designed for clinical or human research use, which at first glance might seem confusing, so how do you choose the right amplifier for your application?

When selecting an amplifier for evoked potential, EMG or EEG applications, the number of channels is usually the foremost priority, but it is also important that other specifications such as the maximum amplifier gain and the variety of high and low pass filter settings are also considered.  Each of our isolated amplifiers has been developed to meet the needs of specific users and while our amplifiers are designed to be “general purpose”, each amplifier has features that make it more suitable for a particular type of recording.

Fortunately, with a little knowledge of the intended application, its technical or signal conditioning requirements and any local ethical/regulatory restrictions, it is usually easy to identify the most appropriate human-safe amplifier for your needs.

Is a medically certified amplifier absolutely necessary?

The answer to this question can dramatically simplify the product selection process, as well as reduce costs, so it is a good one to consider from the outset.  If you have an absolute requirement for medically approved isolated amplifier, certified within the UK/EU for patient use during diagnostic testing or treatment, then the 8-Channel D360 is the ONLY medically certified amplifier Digitimer currently manufactures.

However, bear in mind that patient use does not necessarily require a medical device, although local ethical approval for a research study involving patients may be harder to obtain if you do not use a medically approved amplifier.

How Many Channels Are You Recording?

If your application is research-based and you only need one or possibly two channels of EMG measurements, for instance for nerve or muscle excitability testing using electrical stimulation and QtracW threshold tracking techniques, then the D440-2 is the perfect amplifier for this.

For recording more than 2 channels in a human research setting, then you can opt for the D440-4, the new D360R-4 or the original D360.

Once you have determined how many channels you need and whether the device has to be medically approved, the decision making process gets a little more complex, but below, we compare the features of the D360, the new D360R-4, D440-4 amplifiers.  Armed with these comparisons you should be in a better position to choose the right amplifier for you.

The 8 Channel D360 versus the NEW D360R-4

One of the main drivers in the development of the new D360R-4, was to produce a high performance research amplifier which matched the capabilities of our “gold standard” D360, but delivered at roughly half the cost.

Unfortunately, halving the number of channels doesn’t simply lead to a 50% reduction in development or manufacturing costs, so this did mean that some of the more advanced features of the D360 were not included in the D360R-4, however, development of the D360R-4 did give us the opportunity to make several improvements in terms of software and hardware usability.

Here is a comprehensive list of the major differences between these two high performance isolated amplifiers:-

• Unlike the D360, the D360R-4 is not designed, certified as or intended to be used as a medical device.
• The D360R-4 has four differential channels, whereas the D360 has eight.
• The D360 allows for internal linking of electrode inputs of the same polarity, so they share electrodes, the D360R does not and such linking would have to be undertaken using external wired connections.
• Electrode impedance checking is NOT available with the D360R-4.  If impedance checking is required, we do offer our D175 handheld impedance meter.
• The D360R-4 software allows channel settings to be “linked”, but only permits one linked group, whereas the D360 allows for multiple independent groups.
• The D360 software permits channel re-naming, allowing different recording sites to be identified by a text entry.  The D360R-4 numerically identifies channels.
• The D360 features a protocol manager that allows different user accounts to save and recall settings for different recording montages.  With the D360R-4, this is simplified, with all saved protocols stored in the same location, irrespective of the Windows user account.
• When connecting to the host PC, the D360R-4 uses a standard USB cable and does not need a serial port or additional USB serial adaptor.
• Unlike the D360, the D360R-4 notch filter auto-selects to 50Hz or 60Hz depending on the mains frequency.  This makes the D360R-4 a far better traveller, as you can use it in regions with 50Hz or 60Hz mains supplies with no effect on notch filter performance.
• The headstage cable for the D360R-4 is completely detachable, making it easy to replace in the event of damage during use.
• The D360R-4 Client Software and API are fully compatible with 64bit installations of data acquisition software, such as CED Spike2/Signal.  When controlling the D360 from Spike2 or Signal, these programs need to be installed as 32bit applications, which may be less convenient.
• The D360R-4 is more compact than the D360 and designed for use on a desk or bench.  It does not have 19″ equipment rack mounting capabilities.

The D440-4 versus the NEW D360R-4

For research applications that need up to 4 channels, then it is important to compare the D360R-4 and the D440-4.

• Importantly, the D440-4 has a maximum gain of x20,000 versus x3,000,000 for the D360R-4, making it suitable for standard EMG measurements, but unsuitable for recording low amplitude responses such as auditory evoked responses and EEG.  For more demanding low amplitude applications, choose the D360R-4.
• Recording of AC or DC signals is possible with the D440-4, but the D360R-4 has a low cut filter minimum setting of 0.05Hz, which means it is only suitable for AC-coupled signals.
• The D440-4 has far more limited options for the high/low pass filters and lacks a 50/60Hz mains notch filter.
• The D360R-4 has a remote preamplifier headstage which makes it more appropriate for applications which might require greater mobility or the shortest possible electrode leads.
• The remote headstage of the D360R-4 also make it more appropriate for use with setups that involve magnetic stimulation, as the main D360R-4 amplifier may be located more distant from the stimulating coil during use, while the preamplifier headstage is near the recording site.
• Only one D440 amplifier can be connected to a single host PC, limiting a recording system to four channels.  Multiple D360R-4 amplifiers may be connected to one host PC, allowing for expansion of D360R-4 amplifier systems over time, to 8, 12 or even more channels.

Needless to say, if you have read this far and are still confused by the features our amplifiers provide, then just give us a call or send us an Email, as our experts will be happy to guide you through the selection process.