Archive for the ‘Mining Hardware’ Category


Today we have built a 6-card mining rig using Gigabyte GeForce GTX 750 Ti (N75TOC-2GI) video cards that are based on the latest Nvidia Maxwell architecture promising very good performance for mining with low power usage. Our own initial tests of the GeForce GTX 750 Ti as a single card for mining have shown very promising results as well, so we’ve decided to see what we can expect from a mining rig and put together 6 cards with PCI-E x1-x1 extenders on an AsRock H81 Pro BTC motherboard with Intel Celeron G1820 CPU and 4GB of RAM running Windows 7.


The result we’ve got from the 6-card mining rig for mining Scrypt with CUDAminer was a total of 1480 KHS as hashrate. Then after overclocking the video cards to the maximum stable result we managed to get (+135 MHz for the GPU and +610 MHz for the video memory) we’ve managed to increase the total hashrate to about 1615 KHS. We went as far as to increase the power target limit from the default 38.5W by modifying the video BIOS of the cards. With the modified video BIOS we have managed to get slightly more than 1700 KHS with a lot of extra power used by the whole system that made it not worth it the so little extra increase in the hashrate. Just to be sure that the x1-x1 PCI-E risers (not powered) might be the cause of slight performance drop we’ve replaced them with x1-x16 USB 3.0 powered extenders, though that did not change the performance we got from the cards.

The Gigabyte GeForce GTX 750 Ti video cards we used for the mining rig do have an external PCI-E power connector, however it seems that unlike AMD graphics with OpenCL, when using Nvidia-based GPUs with CUDA for mining the use of a x1 PCI-E lane to access the video card does introduce slight performance drop and if you multiply the 10-15 KHS less per card for a 6-card mining rig it is not so little. So it is important to know that if you are going to build a GTX 750 Ti-based mining rig you will be getting slightly lower hashrate if you are using PCI-E extenders as compared to what you will get with cards inserted in x16 PCI-E slot directly. Also there is some variation between cards in terms of the maximum overclock supported that results in different maximum frequencies that you can achieve, for example if one card is able to do +135/+700 MHz for the GPU/VRAM the second one could be maximum +100/+600. This means that in a 6-card mining rig you will need to either sync all of the cards and use the same lower settings for overclocking the GPUs to ensure they will run stable or to not have the settings synced and find the maximum for each of the cards.

Another interesting thing we have noticed is that while the use of T5x24 kernel for a single card with CUDAminer for best results, for a 6-card mining rig the use of T10x24 might sometimes provide slightly higher hashrate than T5x24, so you should try with both and see what works better in your individual case. Tomorrow we are going to be doing some more testing of the 6-card GTX 750 Ti mining rig that will be focused mostly on the power consumption as this is also a very important thing when talking about crypto currency mining.


The Block Erupter Cube Bitcoin ASICs are the latest products (though already a few months old) to come out from the company ASICMiner – the same company that made the small USB sticks for mining Bitcoins. These ASIC devices are capable of 32 to 38 GHS (stock and overclocked) and come with a small form factor, but with a relatively high power consumption to be good choice to continue mining for much longer. We got our hands on one of these devices and decided to check it out and report some interesting things we’ve found out about it and that you will probably not find anywhere else. Like for example the thermal images of the miner in action that you can see above that give interesting insight into the operation of the miner. You can see that inside of the device can get pretty hot, while the outside aluminum case remains pretty cool, so the cooling is apparently quite effective in moving air through the chips to keep them operating problem free even when overclocked, even though the chips temperature can go as high as 80 degrees Celsius. Another interesting finding is that the safety fuse on the back of the device can get pretty hot, so e careful with the fuse while the device is working.


The inside of the Block Erupter Cube Bitcoin ASIC consists of a main control board and six modules with chips, each of the boards with chips has 16 chips and the total number of chips inside the device is 96. These are the same chips that are found on the Block Erupter USB devices, so they are not very power efficient nowadays as compared to other alternative solutions available. As you can see the idle power consumption of the ASICMiner Block Erupter Cube is 130W and having the device overclocked to run at 38 GHS the power consumption can go up to about 350W (measured at the power outlet). The high power consumption is with the relatively low hashrate already is what is making these a bit outdated and in a few more jumps in the Bitcoin difficulty.


The Block Erupter Cube devices comes with a built-in web management interface that also allows you to switch between the normal and overclocked operation mode with a click of a button. The web interface lets you enter the pool settings, so the device can operate without the need of a computer, however it only supports getwork and not stratum. And with stratum pools you need to use a stratum proxy in order to be able to connect to a stratum pool and that needs to be installed on a computer. We have managed to get about 37 GHS stable hashrate from the unit we have tested in the overclocked state and it was running stable and reliable for the whole week of testing that we did. And while the Block Erupter Cube ASIC miners do have some specifics, they do look nice and well built and already can be found quite cheap, pretty soon there will no be much point in mining for Bitcoins with them, unless you don’t pay for the electricity used. So do not get very tempted by a too attractive price for a Cube miner and better consider another ASIC alternative for mining Bitcoins that provides higher hashrate and uses less power.


Yesterday in our first impressions from the Gridseed 5-chip Scrypt ASIC device we have shared that the modified version of the cpuminer software is not reporting local hashrate. This is a problem as you can hardly know what is your current hashrate, especially when you start overclocking the device to get some extra performance out of it. You need to rely on information reported by the pool about your worker’s current hashrate, but these tend to often report lower or inaccurate results than actual hasrate. This is due to the fact that pools base the reported hashrate on the submitted shares for a given period of time, so result can vary. We can report that the average hasrate we are getting from our 5-chip Gridseed DualMiner ASIC device in terms of Scrypt mining performance to be hovering around 300 KHS with the stock frequency of 600 MHz that the five Gridschip GC3355 chips inside run at.

We could get the chips to run at about 850 MHz, but they were giving out quite a few HW errors, at least visually as the cpuminer software does not report actual number of stale shares or HW errors that the device makes. Seeing a lot of the red error messages means you are probably getting a lot of HW errors and should try reducing the clock frequency with 50 MHz or more. With 800 MHz the device was running more stable with much less HW errors, however this result was achieved with the use of the standard cpuminer software supplied with the device. Apparently this version of cpuminer had a bug and did not disable the BTC core and as a result mining Scrypt only you can get up to about 60W power consumption. By using the newer fixed cpuminer for Gridseed the power usage got down to the 8-9W range and we could overclock the device at 850 MHz with more stable results and very few HW errors. With 850MHz clock we got pools to report hashrate going up to about 400 KHS which is definitely a nice improvement though the newer version of the cpuminer still does not report local hashrate, so it is hard to get more realistic rate for the performance of the device when overclocked.

If you wan to overclock the Gridseed ASIC devices you need to use one fo the preset frequency values as they will not accept just about any frequency that you send to them. The lst of accepted frequencies consists of the following values: 250, 400, 450, 500, 550, 600 (default), 650, 700, 750, 800, 850 and 900 MHz. It is possible that with the version of cpuminer linked above that ensures low power consumption the ASIC devices may be ale to run pretty stable even at 900 MHz, however we still haven’t extensively tested that. Still even when using 850 MHz with about 400 KHS does not sound bad at all as compared to the claimed stock 300 KHS at 600 MHz.