Introduction
Op-Amps i.e. Operational Amplifier are the fundamental building block of Analog electronics and more specifically Audio & Video systems, Analog to Digital Converters , Digital to Analog Converters , Active Filters , RF systems , and the list goes on. Op-Amps are virtually everywhere! Basically what an Op-Amps does is that it amplifies the input signal and the regenerates the amplified version of the input signal at its output. The way an Op-Amp regenerates the input signal at its output is dependent on many of its parameters. Ideally, we would want an Op-Amp to regenerate the input signal of any frequency with maximum fidelity along with maximum noise rejection at input side. But in real world this is not the case i.e. practically Op-Amps have their own limitations. Some of these limitations might not be of any concern, given its below or above a certain threshold, for a particular application. For example in Audio systems , using an uber high bandwidth Op-Amp gives no practical advantage over using a medium/high bandwidth Op-Amp.
In this article we will go through some key Op-Amp parameters. Also do note that this article is completely from the specification point of view. Its a very basic guide to Op-Amp Specs for fellow PC & Gaming Enthusiasts who might be new to Op-Amps and stuff. For Audio characteristics you may refer the product page Here.
In Audio devices Op-Amps are generally used as pre-amplifiers , low power amplifiers i.e. headset amplifiers, in distortion pedals, etc. As far as Audio is concerned we would like an Op-Amp to have low distortion , low noise floor , high input noise rejection. If I am correct then Audio Op-Amps for G1.Sniper are used in the last stage of the audio pipeline. The inclusion of such an amplification device like the Op-Amps means more clarity and loudness in sound at the output.
The G1.Sniper 5 motherboard comes with an ‘OP-AMP Upgrade Kit‘ which includes :
- OPA2134(on board) – By Burr Brown, now owned by Texas Instruments.
- LM4562 – By National Semiconductor, now owned by Texas Instruments.
Now lets see what ‘OP-AMP Premium Upgrade Kit’ is all about and check how these Op-Amps rank from spec perspective.
The ‘Op-Amp Premium Upgrade Kit‘ is for G1.Sniper 5 Motherboard which is sold separately for $79.9 (MSRP) and the Bundled Op-Amp ICs are :
- AD827J – By Analog Devices.
- LT1358C – By Linear Technology.
- OPA2111K – By Burr Brown, now owned by Texas Instruments.
A closer look at the kit
ICs and the extractor :
OPA2111K :
LT1358 :
AD827 :
Here is a list of “Certified Op-Amps” – OPA2314 , OPA2111 , OPA2107 , OPA2604 , OPA2227 , LM4562 , LM49720 , NE5532 , JRC4558 , LT1358C , OPA2111K. These Opamps are basically pin compatible Op-Amps having similar voltage specs.
Inside the Specs
Now lets compare some important specs of these Op-Amps in the Premium Upgrade Kit.
Specification conditions : Vcc = +/-15Vdc , Temperature = +25 Deg.C unless otherwise mentioned.
1) Bandwidth(BW) or Gain Bandwith(GBW) : This is simply gives how the gain of the Op-Amp varies as we change the frequency of input signal. At high frequencies the gain starts to drop. The Bandwidth graph tells us what all frequency signals can pass through the device without any significant signal attenuation(i.e. reduction in amplitude in simple terms) for a fixed gain value. Generally audio grade Op-Amps have this around 2 to 10 Mhz or above. Anything above say 15Mhz might not give any practical advantage over say 10Mhz GBW for audio applications.
| AD827J | LT1358C | OPA2111K |
| 50Mhz | 25Mhz | 2Mhz |
Here AD827 and LT1358 have high Bandwidth than what is required while OPA2111 has considerably low bandwidth in comparison but then even 2Mhz is not bad considering Audio frequency range of around 10Hz to 22Khz.
2) Slew Rate : This tells us how much fast the voltage can change at the output of the Op-Amp. We can also consider this as the speed of the Op-Amp. If input signal is changing faster than what an Op-Amp can handle then that would induce unwanted distortion in the output signal and it would not be able to faithfully regenerate the input signal at its output i.e. we will have a loss in fidelity. A slew rate of around 10V/us or higher is really good for audio grade op-amps.
| AD827J | LT1358C | OPA2111K |
| 300V/us | 600V/us | 2V/us |
Even here AD827 and LT1358 have crazy high Slew Rates than what is required.
3) Common Mode Rejection – CMR(or CMRR) : Common Mode Rejection gives the Common Mode Signal/Noise Rejection capability of an Op-Amp. Common Mode Signal/Noise is the Noise induced at both of the Op-Amp’s input simultaneously. An Op-Amp ‘magically!’ rejects this Common Mode Signal and only lets the difference between its input pass through to the ouput. For our purposes we would want a minumum CMR of 80dB or higher.
| AD827J | LT1358C | OPA2111K |
| 95dB | 97dB | 110dB |
CMR for each of the three is impressive.
4) Input Voltage Noise Density : This might be one the confusing parameters which has weird units like “Nano-Volts per Root-Hertz” i.e V/rt-Hz. In simple words – it actually gives RMS Noise Voltage over a frequency range. For our purposes we would want this parameter as low as possible. For the curious types , you can check out the “Opamp Input Voltage Noise Tutorial” by Dave at EEVBlog.
| AD827J | LT1358C | OPA2111K |
| 15nV/rt-Hz | 8nV/rt-Hz | 6nV/rt-Hz |
5) Input Offset Voltage & Current : Both of these parameters contribute to DC offsets at the output and hence we need both of them to be as low as possible. Ideally when we apply zero Volts at both of Op-Amp’s input we would get exact Zero Volts at the output , but in reality this is not the case. Practically you would need some finite difference in voltage between the two inputs to make the output zero and this required difference in voltage is Input offset Voltage. This input offset voltage starts to drift off and increases as the temperature increase hence the drift also must be low. Input Offset current is the difference between the input bias currents at the input terminals. Input offset current shows up as an offset voltage at the output and many times it can add more offset voltage at the output than Input offset voltage alone.
Input offset Voltage (Max) :
| AD827J | LT1358C | OPA2111K |
| 4mV | 0.6mV | 0.3mV |
Input Offset Current (Typ) :
| AD827J | LT1358C | OPA2111K |
| 50nA | 40nA | 3pA |
3pA is pretty low indeed!
Note : There are still many other reasons and factors , inherent to the design of the Op-Amp , which can induce additional Noise , Distortions and Offsets at the ouptut. Precision Audio Grade Op-Amps having Ultra low Noise & Distortion Audio Op-Amps are specially designed to reduce these – for example AD8599 , LM4562 , etc..
Conclusion
Firstly we welcome this step taken by Gigabyte. By introducing the Op-Amp Upgrade kit Gigabyte has given end-user the ability to change the Op-Amp – not only the bundled ones but also any other compatible audio grade Op-Amp of one’s choice. Audiophiles would love this freedom to swap on borad Op-Amps. I would I have loved it even more if Gigabyte would have included “jellybean-ish” 1 or 2 more Op-Amps which are famous amongst audiophile and DIY community like NE5532 , AD8599 instead of say AD827. But then on the good side, the motherboard comes with OPA2134 as an on-board ‘default’ Op-Amp and is a good performer indeed! OPA2134 is yet another well known Op-Amp amongst DIYers and Audiophiles. And then there’s LM4562 too!
Finally, talking about the price – it seems to be a bit on the higher side!. After doing a price check on Digikey and Mouser – Price must have been in $55-65 range – considering GB would be buying these in bulk and then selling them as Premium Upgrades , or am I wrong? On the other side buying them from the distributor in low quantity(1x) and getting them shipped can cost you around $60-80. Hardcore Audiophiles and Audio-freaks would be interested in buying the Premium Op-Amp Upgrade kit or they might even source these and other Op-Amps on their own!