I try to explain... if i´m wrong , someone can correct me please.
Everything what means higher hashrate is like in overclocking any CPU. This means the frequency gives you the maximum number of calculations the chip can do per second.
You can surley try to set higher frequencies whithout any modifications like with the 5 Chip GSD they come with stock freq of 600 Mhz but you can set easily up to 850 Mhz.
Higher frequency means more calculations per second and more Hashrate. The problem is that with higher frequencies the chip becomes unstable and this result in
HW´s or miscalculations. It´s like someone try to do too many things at the same time , and at one point he can´t handle so many opperations and stuck.
So the goal is to get the chips stable at higher frequencies an they need more Voltage to do this . And of course more voltage and frequency generates more heat. The second problem.
The default Voltage of the GSD Chips is at 1,2 V With the 33K ohm resistor. If you replace this with a 39 K ohm resistor for example the Voltage rise to 1,4 V , so they
handle more stable frequency but also more heat. This you can easily measure at the big yellow caps.
1) Are the modifications #2 and #3 above compatible? I believe that J4bberw0ck put both in place.
The bridge voltmod=1 does the same thing but in other way it affects the 2-bit VID convertor to select another output line, this means it selects another resistance. There are 4 Resistors to set 36k, 30k, 33k, and 27k. With the clasic vmode you choose the 36k resistor istead the 33 k , like an overclock jumper without the need to solder any parts.If you do the vmode and choose the 36k , but you replace the 33k resistor , i think the replace of the 33k is useless and do nothing . The convertor coose only one output.
And of course you need the modifed cgminer and set the voltage=1 parameter. So think this is more like an alternative to solder a resistor.
Maybe J4bberw0ck can tell us more if i forgot something.I only apply the bridge mod to my first gsd 5 chip miner. There are for sure more jumpers and you can influence the output voltage in more ways but for me i think is better to stay with one mod at same time its possible to have unespected effects or that both methods add the voltage change and you have to much output.
2) If both modifications #2 and #3 are performed, is more heat produced at the same hashing frequency?
For me this happens, at the same freq setting you have permanently change the chip voltage if you apply the resistor mod. Higher Voltage means more heat.
3) If both modifications #2 and #3 are performed, is a greater hash rate obtainable overall?
I don´t no any combination of both methods , but both results in increase the chipvoltage to rise higher frequencies at very low Hardware errors. So if you have more Vcore and can set higher Frequency at very low HW this results in higher hash Rate. And have in mind that only the accepted shares counts for the effective hash rate.
There are for sure more "little" things to adjust this and get the best compromise between frequency and HW´s.
I don´t know if there are more benefits if you combine both methods for me more simple to replace just one resistor or to solder just one bridge.
4) If both modifications #2 and #3 are performed, is a greater hash rate obtained at a single frequency?
The effective Hashrate for sure i think, if you have less Hw at the same Frequency , maybe the mining software say the same Hash rate for the same Freq but you get more accepted shares, if there was some HW´s in default mode.
5) If you use an adjustable pot and run at a set hashing frequency, say 925 MHZ, is the heat generated greater if the pot is set to 37.5 KOhm compared to the pot being set at 36 KOhm?
Maybe the difference is not so big but if you set 925 Mhz @ 37.5 K the chips works with higher voltage than when you set 925 Mhz @ 36k. So the power consumption rise with the higher voltage and this produce more heat at the same freq.
So if you don´t want to overclock so much , its better to stay with 36K if this runs stable. Just an example : I have 2 blades , one with 36 K Mod ,one with 39 K mode, the one with 39 K Mode is a little bit faulty so i run them "only" at 900 Mhz. The 36k one runs better so i set 950 Mhz , but even if the 39K one has a lower Freq it produce more or min. the same heat like the 36k one. That´s because this runs with higher voltage.
I hope this helps you a little bit , and maybe someone can complete or correct me if i´m wrong.Especially for the bridge mods you can read here more : ---->
https://bitcointalk.org/index.php?topic=519112.0
