I'm outfitting a new Antec Solo case for my PC, and have chosen the recommended 120mm Nexus D12SL-12 for Exhaust / CPU, and the 92mm Nexus DF1209-SL3 fans for intake.

I'm running them on 7v by switching the negative pin in the Molex connector to the 5V line, but at 7V I can't get an rpm reading at all.
I have removed the black and red wires from the 3pin connector and running on 12V from the Molex connector this works fine.
At 7V however my Gigabyte GA-MA770T-UD3P motherboard won't get an RPM reading.

On the review pages for these fans there are RPM figures listed down to 5V so this must work somehow:
http://www.silentpcreview.com/article69 ... html#nexus
http://www.silentpcreview.com/article72 ... html#nexus

All advice is appreciated.

RPM sensors work by counting the number of times the sense pin is shorted to ground per minute. When you do the 7V molex mod the sense pin gets shorted to 5V. This doesn't trigger the RPM sensor so it thinks the fan is not spinning. There is no way around this without additional circuitry.

Thanks for the information, I'm going to need another method of reducing the voltage short of using a fan controller.
I would like to be able to monitor RPM to know if there is an issue with a fan.

I think somewhere I've seen info somewhere regarding putting a resistor in the 12V wire to the fan to knock the voltage down.
Since these fans are supposed to be inaudible at around 8V, is there info on SPCR that would let me know what size, type and wattage of resistor would get me to that voltage?

Use a fanmate, they are very cheap. Using resistors would be very inefficient, zener diodes would be better if you need to roll your own. But a fanmate would be better in most cases I think.

A resistor is the cheapest, but you might have to try several. Some 56Ω 0.5W. I used one recently, got a strange effect: after some time the rpm reading was a half of what it should be, and remained that after a restart. Then I put there 24Ω, was good for my needs. And the fan's switching noise, rather audible without the resistor, was gone!

Guess I better start researching zener diodes or fan controllers.

I want to step the voltage down to 4-5 fans (CPU, Exhaust, Intake x1 or 2 and GPU) so a fanmate for all is going to run the same or more than a fan controller. Wondering if most fan controllers come with lots of cable length as there is some distance between the motherboard 3-4 pin connectors, fan mounts and front bays where a controller would go. I have plenty of length on 4pin Molex connectors on the PSU.

Too bad the 7V trick kills the rpm sensor as this was an easy way to get to 7V.

If you could find a US source for something like this, it might be worth trying http://www.watercoolinguk.co.uk/p/Fan-power-adaptor-cable-12V--%3E-7V-03m-with-rpm-lead_20511.html as a cheap way (around $3 US per cable) to get 7V with an rpm reading.

Here is a US source for an inexpensive fan controller that will let you vary the voltage for the fan from 5V to 12V. This controller is $5.00 USD, but if you search around, you may be able to find something slightly less expensive too.

http://www.frozencpu.com/products/13367/bus-260/Gelid_Solutions_Fan_Variable_Speed_Controller_-_FC-FX01.html?tl=g47c17s285

If cable length, or mounting location is a factor, there is always the Aquaero LT, which can be mounted anywhere in the computer and can control up to 4 fans as is, or can be expanded. It comes with 4 temp sensors, and can be expanded to eight, plus a flow sensor (water cooling), etc. You can choose 2-point fan control, or a full (smooth) curve with as many control points as you want for each fan. All control of the LT model is done with some pretty sophisticated software (Aquasuite), so there is no need for a front panel display. The software is only used to monitor and for the initial setting of parameters. The Aquaero controllers then can do what you want without any software at all running in the background.

I have one of these on its way, should be here Monday. If you can hold off about a week, I can post a review of everything it can do (in theory, lots), and how well it does it.

But if you would rather have a controller with a front panel display, there are these Aquaero models:

Aquaero 5 pro (no softkeys, no remote control):http://www.performance-pcs.com/catalog/index.php?main_page=product_info&products_id=30623

Aquaero 5 XT (everything, the works):http://www.frozencpu.com/products/13215/bus-259/Aquacomputer_Aquaero_5_XT_USB_Fan_Controller_Touch_Screen_Graghic_LCD_Liquid_System_Controller_w_Remote.html

The prices for the ones with a panel display are staggering, for a cooling controller, but the LT is reasonable. The LT is only a few dollars more than the Lian Li six-channel controller (knobs, fully manual - you set the speeds, won't increase speeds in response to higher temps unless you twiddle knobs).

Note that my preferred vendor is FrozenCPU, but they are out of stock on the Aquaero controllers. Performance PCs is pretty good too. Will let you know on Monday.

This cable will not get rpm reading. It does exactly what the OP has done already (apparently).

I have used the Zalman adapter cables (RC56, etc) for the odd fan in the past. They are resister based, so they provide an rpm reading without difficulty. However, once you have four or five fans that need to be controlled it probably makes more sense to invest in a fan bus controller.

Thanks for all advice, I'm now looking at various types of fan controllers:

The Zalman ZM-MFC1 Combo bay controller looks nice but it seems this one, and all of the other Zalman fan bay style fan controllers can only provide rpm signals on one 4-pin and one 3-pin fan. If I'm going to get a bay style fan controller I want one that will control at least 4 fans and send rpm signals from all to my motherboard. The current board I have has three 3-pin headers and one 4-pin header.

Any suggestions on bay style controllers that offer voltage control for 4 or more fans with rpm signals from all?
I don't care about temperature features.

The Fanmate 2 or Gelid FC-FX01 are looking better to me, since one of these for each fan will provide 5-12V and also rpm monitoring.
I'm planning on the 120mm Nexus D12SL-12 which is a 3-pin fan on my CPU heatsink and connecting to the 4-pin header on the motherboard.
Will this work with a Zalman Fanmate 2 or Gelid FC-FX01 since they have 3-pin connectors?

Also found some on eBay that appear to be Chinese clones of the Fanmate or FC-FX01, not sure if any of these are worth a try.

There are a lot of 3.5" and 5.25" bay fan controllers if you want to control a lot of fans. One fanmate per fan would probably not be very practical. I have little experience with those, but if I had to recommend one it would be the Scythe "KAZE Q" Fan Controller because the potentiometers have a nice feel and I think it looks sleek.

To get RPM monitoring on every fan you need a more fancy controller. Or you could fix it yourself since ground is now common, unlike when doing the 7v trick. Just draw the RPM sense wire (and possibly ground but this is optional) from the fan to a motherboard header.

Thanks again for all suggestions.

My Antec Solo case is now assembled, I ended up making the Fan Voltage Diode Strip shown here as its cheap and works great:
viewtopic.php?p=109317

I'm also using a two position switch with the low speed running at 7.2V and the high speed at 9.6V, Sort of a Winter silent / Summer very quiet settings.
Between the quieter fans and the soft silicone hard drive mounts it is much quieter than my previous build using an Antec SLK3700AMB which only had hard drive grommets not thick silicone mounts.
I may try the suspension mounts at some time but there is no vibration now from a pretty noisy WDC Black 1TB drive and I can barely hear the seeks.

The problem now is my Gigabyte video card is now the making the most noise, and since its not a three wire fan I have no idea what speed it runs at.
I would like to slow the fan down but since its still under warranty am reluctant to clip into its wires.
I've tried slowing it down in the cards software but its louder than automatic control even on the lowest manual setting.
Below are some pics of the card, fan, the plug on the fan leads and the socket on the board.

Is it possible to get a socket with wires attached so I can just plug the fan in and hook up to my Diode Strip?
Any other suggestions on how to tame the cards noise is appreciated.

My first guess was you did not slow it down, but then it could not be louder than automatic.
I had a Gigabyte 4670, which did not control the fan. I wrote on SPCR, how I made it to control the fan. If your card does control, you don't need any hardware change.
A diobus would be a bad solution, because the card wants all 12V on the fan at load. The difference in power draw idle-load can be very big.

Just brought up the Catalyst Control Center and if I check manual fan control then move the slider from 20-100% and click apply, the difference in noise is huge.
If I set it back to automatic control it gets a bit quieter than 20% but still very audible in a quiet room. I'll try and find your posts on your 4670 to see if I can learn more.

Found this about the Arctic Cooling Accelero S1 VGA Cooler, and the idea of no fan at all sounds nice.
I'll have to see if I can fit it in and what it would block if anything, down side is I'd be voiding my warranty on the card.
http://www.silentpcreview.com/article793-page1.html