VAGP voltage?

[Alan]

Hi
ive just got my radeon 9600 pro 256mb and immediately voided my warranty by
overclocking it...
ive got on well and got a good boost from overclocking it...
i overclocked the VCORE and VRAM seperately as i have always done... but
untill not i havnt afforded a good pc, having just recently got a new pc
without a graphics card i bunged in a pci jobby but now i have this AGP
one...
i overclocked the memory untill i got artifacts and have done the core
untill i got black dot things... then i pulled back... (thats the right way
to do it is it not?) and seem to have found the sweety spot for my card...
in my bios there is an 'AGP voltage' setting and it sets the voltage for the
AGP... the default seems to be 1.5 volts and its upable to 1.8 volts...

my Q is what does this do?
can it help me overclock more?
if i up it what are the dangers for my PC?

my system is:
Athlon 2800+ @ 3000+ speeds
Jetway N2PAP400 Ultra motherboard
Peak ATI Radeon 9600 Pro 256mb
512mb Ram
20 gb ATA133 harddisk (maxtor fireball)
Q-Tec 550 wat PSU

thanks in advance

alan

 

[Tony C]

Yeah, it seems very odd that you can change the AGP voltage when everyone
swears that by doing so you only risk damaging your card and that it cant
help you overclock your card more. Something about the card will just
"down"convert the voltage to 1.5v..only if u made a mod to the card
physically could anything be achieved. Yet I remember reading some site
once saying they had artifacts, then turned the voltage up to 1.6v to get
things working... seems bogus to me..anyone else have any input?

 

[Sham B]

generally, in digital systems, higher voltages result in cleaner signals,
which is why upping the voltage usually increases the maximim possible
overclock on your CPU and mainboard memory. This works because the higher
voltages give increased stability (stronger and cleaner signals, so
transisters can reach their levels quicker). The higher voltages also
result in increased heat, so you have to add more cooling to cater for this.

Now, I know this works for the cpu and main memory (I do it on my PC), but
for the AGP card, it is slightly more complicated, because most high
performance cards have some sort of power supply filtering on them. the
filtering will probably reject the additional voltages before it gets to the
GPU (there is usually very little excess heat dissipation in stock GPU
coolers, so upping the voltage and then overclocking using the stock cooler
would be a sure way to kill the card - unless the voltage was limited).

Almost paradoxically though, the limiting factor with a GPU as opposed to a
CPU) is heat (it is much harder to dissipate heat from a GPU because the
space for the cooler is limited, and airflow is less optimum), so *reducing*
the voltage can actually have more benefit - the GFX card filtering cannot
create voltage that isnt there, so this time the undervoltage *does* get to
the GPU. As long as the GPU can actually maintain correct running at the
reduced voltage (some cannot, and noise in the PC and PSU quality can become
very important here), you can overclock higher because your card runs
slightly cooler.

The upshot of all this theory of course is to just try it - if your
mainboard supports undervoltages (many do not) give it a try. Unlike
overvoltage, you cannot kill your GPU with undervoltage. If you want to
overvoltage the card (and especially if this is so you can overclock more
aggressively) you really should remove the stock cooler and put a better one
on first just in case it actually works and the GPU really does see the
additional voltage. As I say though, this is unlikely to happen... unless
you specifically mod the card to overclome the filtering. (you usually
attach a wire across two points on the card so the +V rail bypasses the
filtering to do this)

Be aware when overvoltaging that, although most mainboards limit your max
value to somethign that will not normally kill your hardware, some
mainboards assume you know what you are doing, and allow you to overvoltage
far beyond spec. In particular, shuttle mainboards allow you to overvoltage
your CPU to dangerously high core voltages. this si a good thing for the
savvy overclocker.... but if you are not, pop!

Hope that helps.

S

 

[Alan]

generally, in digital systems, higher voltages result in cleaner signals,
which is why upping the voltage usually increases the maximim possible
overclock on your CPU and mainboard memory. This works because the higher
voltages give increased stability (stronger and cleaner signals, so
transisters can reach their levels quicker). The higher voltages also
result in increased heat, so you have to add more cooling to cater for this.

Now, I know this works for the cpu and main memory (I do it on my PC), but
for the AGP card, it is slightly more complicated, because most high
performance cards have some sort of power supply filtering on them. the
filtering will probably reject the additional voltages before it gets to the
GPU (there is usually very little excess heat dissipation in stock GPU
coolers, so upping the voltage and then overclocking using the stock cooler
would be a sure way to kill the card - unless the voltage was limited).

Almost paradoxically though, the limiting factor with a GPU as opposed to a
CPU) is heat (it is much harder to dissipate heat from a GPU because the
space for the cooler is limited, and airflow is less optimum), so *reducing*
the voltage can actually have more benefit - the GFX card filtering cannot
create voltage that isnt there, so this time the undervoltage *does* get to
the GPU. As long as the GPU can actually maintain correct running at the
reduced voltage (some cannot, and noise in the PC and PSU quality can become
very important here), you can overclock higher because your card runs
slightly cooler.

The upshot of all this theory of course is to just try it - if your
mainboard supports undervoltages (many do not) give it a try. Unlike
overvoltage, you cannot kill your GPU with undervoltage. If you want to
overvoltage the card (and especially if this is so you can overclock more

aggressively) you really should remove the stock cooler and put a better one
on first just in case it actually works and the GPU really does see the
additional voltage. As I say though, this is unlikely to happen... unless
you specifically mod the card to overclome the filtering. (you usually
attach a wire across two points on the card so the +V rail bypasses the
filtering to do this)

Be aware when overvoltaging that, although most mainboards limit your max
value to somethign that will not normally kill your hardware, some
mainboards assume you know what you are doing, and allow you to overvoltage
far beyond spec. In particular, shuttle mainboards allow you to overvoltage
your CPU to dangerously high core voltages. this si a good thing for the
savvy overclocker.... but if you are not, pop!

Hope that helps.

many thanks to the 2 of you that replied
ill just leave that setting alone, i dont think the benefit will be worth
the risk of damaging things...

interestingly my memory does not overclock very well on this card...
i start getting artifacts at only 30mhz (60mhz theoretical) more then the
default...
however the core will go a long long way to about +85 mhz...

what causes black dots?
too much heat or what?

alan

 

[Sham B]

Yeah, its normal for memory to be the limiting factor. Memory just doesnt
get that hot even when its overheating, so heatsinks are less useful for
cooling(unlike a GPU, which will fry as soon as it is without the
heatsink)... generally, you are reliant on the quality of your memory more
than good cooling. you cant really cool memory much, and if you try, the
effects are minimal (the physics of it mean that something that is cool is
harder to cool further, whereas something that is white hot will get cooler
very easily... its all about temperature differences - when the temp diff is
greatest, the heat has 'somewhere to go'...usually warming up the
surrounding air).

The black dots are overheating and/or that the memory just isnt fast enough
and is hitting its operating limits. The memory is starting to fail at the
clock speed you are setting it to, and is sending zeros (or rather, not
sending anything in time for the GPU).

S