Well I'm not going to write a massive hand hold dissertation with this upgrade because it's not that hard but has it's difficult moments just like any other mod I suppose.
I'd put this DIY Upgrade projects difficulty level at a 3 out of 5. Annoying level at 3.5 of 5.
Ok to start you need an allen key (for the chassis bolts) a drill (cordless is fine), 10 mm metal drill bit, soldering iron, solder,about 1 ft worth of decent 20 or 22 gauge hook up wire (the better the quality, the better the result) some channel locks or open box wrench (for the nut that holds the pot to the faceplate), some wire strippers and some side cutters. If you have none of these tools or have no idea what some of them are.....forget about doing this mod or any others.....and seek out a tech savvy pal...you'll thank yourself later for being so wise.
This mod is straight forward as far as what you have to do so the technical aspects of it are as simple as simple can be.
Step 1 : Take the 6 bolts holding the lid on ....out
Your done
....OK no your not. Now with that lid off look at the area where the pot is located and make note of the VOL VOR pads. These are the pads that you will use for the STEPS pot wiring (just 3 of them L+ GND and R +).
I already have the Alps pot free from the face plate in this pic so pay no attention to it...the pic is to show the pads you need to be aware of for the stepped pot's wiring.
Step 2 : Remove that stock black volume knob. I had very little in the way of a tool that can handle such a large diameter knob and this sucker is on there tight so if you are able to get this bugger off (LOL) with just hand strength alone ...well that's just excellent Mongo !!!
I had to use an old standby trick I used years ago ....I have a medium size pair of super old vise grip pliers that come in handy when all else fails. The trick is not to destroy that knob with the steel teeth of the vise grips.Wrap the teeth of the vise grips in electrical tape and set up the vise grips to just have enough lock on the knob to allow you to rock it off the Alps shaft. Once you have that stock knob off use your open end box wrench (12mm I think) to loosen the nut on the pot shaft ...from there you can use your fingers to get it off (along with it's washer). Remove the Alps pot and it's wiring and set aside. How you decide to remove the wiring from the pcb is your choice. Whatever is easiest and safe for the pcb pads will suffice.
Step 3: Take your drill with the 10 mm bit installed and enlarge the hole so that the stepped pot will slide through. You don't want the hole to tight or to loose since you'll need some tension or grip by the hole to help you with keeping the stepped pot from moving freely when you turn the knob (after the washer and nut have been snugged up near the end of the mod). You'll have to shave a little more material than 10 mm (not a lot more though) ...but test fit the pot each time you take out a little material. Cut off the key way tab that sticks out on the front of the stepped pot casing with your side cutters (nibble it down until it's flush with the rest of the poly casing). You'll note the same key way tab has been sheared off the Alps.
Before you can test fit you need to detach the faceplate (not entirely) from the chassis box. Go to next step for this....
Here's a pic of the drilled out .....well you know...
Step 4: In order the free the faceplate from the rest of the chassis you simply make note of the screws used to hold the faceplate to the L/R pillars at the front. 2 screws on each side and 2 underneath so 6 in total. Take those out and the faceplate is now free from the chassis. Be careful with it as the wiring to the headphone jack is now taking the tension of the faceplate when you lean it forward for the test fit of the stepped pot into your newly drilled out hole. Make sure you get all the metal shavings out of the chassis box interior (I use a small cut up fridge magnet for this) so they can't cause any problems later. Once you have the hole the right size pull the stepped pot out and set the C-2C aside for now (remember to put the faceplate back into place to take the tension off the jack wiring, you don't have to bolt it back in place it should stay on it's own).
Step 5: Wiring the stepped pot. This is where you prep your wiring ( I used 22 gauge stranded silver plated copper in Teflon) by cutting your 1 ft section into 3 x 4 inch lengths. Once you have your 3 wires cut strip 1/8 in of insulation off each end and then tin those with your soldering iron/solder of choice. I use bog standard stuff for this (Kester 60/40 or something like that) it doesn't matter all that much IMO. If you have some silver solder then by all means use it. Solder the 3 wires to the stepped pot in the following locations.....make sure you do not have any overlap or shorts to another tab or component. The tinned leads and pre tinned tabs are all the solder you need. You just need to heat up the connection for a good joint. Make sure you have a solid good connection before moving onto the next spot.
Step 6: Once you have the three leads properly secured to the pot the next step is to solder these to the VOL/VOR pads we saw in the first pic. Here is a pic for the correct wiring locations for those 3 leads.
You'll note 2 gnd pads on the pcb. You only need to use one of them for the single gnd lead of the stepped pot...so take your pick. You can loosely mount the stepped pot before soldering these in or you can do that after. It's your preference. You'll have to see if the wiring length allows such an option.
Once you have the 3 leads soldered to the correct pcb pads you can now mount the pot. The key way notch you removed earlier with allow you to easily mount the stepped pot flush with the back of the faceplate.
Once you have it in place put the washer and nut back on and only finger tighten for now. You will still need to rotate the pot for best positioning (least amount of tension on the leads etc).
Your on the home stretch now.................
Step 7 : Ok now that you have the pot oriented so that it has clearance on the back side (those brass screws that hold it together don't hit the Nover cap on the left hand side) and you are satisfied there is no tension on the 3 leads...take your wrench and tighten the nut on the faceplate. It doesn't have to be super tight but tight enough that the pot won't rotate when you adjust the volume. Now it's time to double check your wiring before bolting the faceplate back onto the chassis. Everything good ? Then it's time to bolt it back on to the chassis using the 6 screws you removed earlier.
Now that you have the faceplate bolted back onto the chassis securely you can now put that lovely new silver knob to use. Rotate the stepped pot all the way to the left (represents min volume). Since the pot has 23 steps and almost turns 360 degrees you can experiment a little with placement of the knob indicator. I stuck with 7 o'clock as the starting point but note that the end point will be 6 o'clock when using that starting point. It's up to you where or how you want it to look.
Use thumbs to force the knob on (the fingers on the faceplate backside for leverage). Be careful and keep the knob straight when pushing it into place. The silver knob is deeper than the black one so it will stick out a little further once all the way on. It's a tight fit. Do not use a mallet or hammer to knock this sucker into place...that is sure fire recipe for disaster for the knob and the pot. IMO at least.
Anyway once you have the knob on there as far as you can get it to go your C-2C should look similar to this
Step 8: Testing the function of the new pot. If all is fine then you can bolt the chassis lid back into place.
Congrats on a successful pot transplant....sit back and enjoy the new life you've just given your C-2C. The SQ improvement is immediately apparent.
Enjoy !
Peete.
Stepped Attenuator DIY upgrade for the Audio-gd C-2C (new chassis)
