Sunday, July 12, 2020

Keeping the Technics SA-GX910 (or SA-GX710) running cool - Fan mod with speed control

In today's post, I would like to share a mod that I just did to my old-time favourite Technics receiver: the Technics SA-GX910. Before going into deeper into this mod, here is a little history on these receivers and why they are (still) one of my favourite receiver. 


This receiver is a top-of-the-line from Technics from the early 90's (1991 to be exact). Many agree that is not only a great sounding receiver, but also a great looking one. With it's graphic equalizer and many MANY buttons, you can fully customize the sound to your liking without the need of going in out of menus like in today's received. Plus, you can monitor all the settings in the gorgeous VFG display. 

The lower end model SA-GX505 (also a great sounding receiver!)

A few models of the Technics SA-GX series, more specifically released from 1990 to 1994, feature a gorgeous large VFD display with a graphic equalizer. I love graphic equalizers! Not much for the sounding adjusting capabilities, but it mesmerizes me to look at the bouncing flash lights moving according to each music frequency! It looks like I am not alone: check some Techmoan videos on this topic (and if you don't know Matt's videos, check it out, he has a great channel!).  

Well, back to these receivers, like it's bigger brother GX910, the lower end models SA-GX505 and SA-GX710 are also excellent sounding/looking units and much more easier to find than the 910. More info on Technics receivers can be found here:

SA-GX910 - Note the huge amount of buttons on it - I love it!

The 2 (two) optical inputs for DAT/CD are separated from all other 7 (seven) analog inputs

The SA-GX910 was the highest-end receiver model launched by the Japanese brand in 1991 with an MSRP of USD 1,000 (or about USD 1,900 in today's money). It features a very high-tech (for 1991) 2 (yes two!) optical inputs for DAT/CD, one of which I now use to connect my MiniDisc unit. 

If you are curious as to why I'm still using a 1991 receiver and many other early 90's audio equipment, the answer is simple, because they are: 
  • very, very powerful; 
  • built like a tank;
  • extremely reliable (made in Japan with high-end components);
  • they look better than today's receivers and ultimately.. 
  • they also sound better!  
Don't get me wrong, I also have a brand new, fully featured Yamaha RX-A780 with all its modern bells and whistles (AirPlay, Bluetooth, etc). When it comes to video and multi-channel audio (DTS X, Dolby Atmos, Dolby Digital EX are fun!), you need a new receiver capable of interpreting these audio codecs and protocols. However, when listening to good-old stereo sources, such as my turntable, cassettes (yes, they can also sound good with the proper equipment!), CD, MD, it is hard to beat an older high-end receiver such as this one - please read this article from 2011 for more insight why many agree that older receivers are better than newer ones


Now, what makes the SA-GX910 sound great - the "new Class A" Technics amplifier (see advantages of class A amplifiers) comes at a price: class A amplifiers are not power efficient. Meaning, these units will inherently run very hot. Running hot is especially worse in the case of the more powerful models GX710 and GX910. 

Technics designed most receivers (including the SA-GX series) with a fan that is programmed to run only when the volume reaches around 50-60% of the maximum output. I bet that like me, 99% of the listeners would use their unit without ever reaching 50% of the maximum volume as these units are incredibly power and can get VERY loud! Therefore, unless you are throwing a big party for 20+ people in a gymnasium of some kind and blasting the speakers, you will never note the fan kicking in!

Despite the fact that the units all have beefy static cooler fins dissipating heat from the power hungry amplifiers transistors, if you are listening the unit at lower volumes, you won't see the fan active meaning that the unit will get very, very hot. After about 1 hour running at 20-25% volume, the unit can easily get so hot that you can't touch its top surface - especially on the top left corner near the VFD display. A common issue with these units is that the VFD display can become dim due to solder joint cracks due to the heating/cooling cycle. Thus, if you want to use the unit for prolonged time (over 30-40min at a time), avoid the risk of solder cracks, components fatigue, etc - you need to modify the standard stock fan.

After researching a lot in other audio forums and in the net in general, I was inspired by a video where the user "samtherecordman" installed a computer fan in his TX-50 Technics receiver to fix this very same issue. 


(*) you could tap directly into the 12V DC from the original transformer as well avoiding the need to buy a power supply, but I preferred to keep a dedicated separate circuit to power this mod to avoid any interference of the fan motor with the original circuits.

Before you start, first assemble and test everything all components on a bench to ensure the fan and it's speed control works as intended:

Now, to the SA-GX unit:

1- First remove the 6 screws holding the top cover in place. Enjoy the complex Japanese design and assembly that still works after 30 years:)

2- Unplug the original fan plug from the board (near the main transformer). 
3- Removing the stock fan: note where the hold clips are located and use a small flat screw driver to carefully unlock the clips. Remove the stock fan by pulling it from the outside of the back cover.
4- Carefully measure and mark the holes where the new fan will be fixed. 
5- Carefully drill the marked holes in the back case (important: make sure you contain the metal shavings from entering the unit! - use a plastic bag with scotch tape to capture this). Make sure to protect the circuit boards and cooler fins to avoid being touched by the drill bit when drilling the mounting holes.

6-  Drill the hole for the PWM speed control board on top of the Dolby board. This board will allow you to turn on/off the fan and adjust its speed to your liking in terms of temperature/noise levels. Hint, I drilled the "UL registered" symbol as it has the exact diameter I needed for the PWM potentiometer. Install the the PWM meter know through the hole:

7- Install the Noctua rubber mounts on the fan:

8- Solder the AC input of the 120VAC to 12VDC power supply to the inside connector of one of the switched outputs of the receiver. This will allow the fans to run only when the unit is on. Connect the power supply DC output and the fan to the PWM control board.

9- Everything connected should look like this:

Note: I added kapton tape to the PWM board just as an extra insulation precaution

 10. Testing everything before closing it:

11- The final result from the back (you can/should cut the excess rubber from the fan mounts:



Fine tuning the fan speed: If I keep the fan at maximum speed the unit runs completely cool - cold to the touch at all times! After fiddling with different fan speeds, I adjusted to about 40% of maximum rpm and the units is just slightly warm even after a 4 hours of operation. And, at this speed the fan noise is basically unnoticeable even between quieter music tracks, so I found this to be the best noise/temperature compromise.

The other 2 separate graphic equalizers on the video are a topic for another post!


  1. Great Post. I am thankful to you for sharing this post. This is very useful for me and as well as for others. Your article is very well written and unique. please keep sharing such posts. eaton vfd

  2. Thank you Segate Controls for your kind and motivational words! Keep me posted if you decided to perform this mod as well.