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post #3721 of 9604
Fitz, would you mind sharing some details on how you did this mod?
post #3722 of 9604
This was a very busy weekend for me, lots of modding and building.

For the building, it'll have to wait a couple of weeks to finish some casework, but the modding I can share now.

I modded both of my DACs, NorthStar m192 and Forte F-50a. I rewired the coax S/PDIF input with real coax cable and replaced one of the RCA inputs with a real 75-ohm BNC.
The analog output stage of the Forte-F50a (which is truly balanced, with the unbalanced output directly running off the balanced outputs) has 4 single-channel opamps in it. I replaced them all with socketed OPA627s (the funniest story, I had 5 OPA627s arrive after being in the mail system for over 2 years!)

NorthStar m192 DAC


Forte F-50a DAC


The BNC was to be used with an EMU 0404 PCI that I planned to mod with a hard-wired coax cable with BNC termination. This mod unfortunately didn't work out. The coax cable was so stiff (20awg solid wire) that when I soldered the it to the card, it lifted the trace and took out two SMD parts (a resistor and a cap). Now I'll be on the hunt for another cheap card with pulse transformer coupled S/PDIF output. That also means I have an "analog-only EMU 0404 PCI" left around, that I'll post for-sale for cheap.
post #3723 of 9604
Quote:
Originally Posted by MASantos View Post
Fitz, would you mind sharing some details on how you did this mod?
Unfortunately I didn't take any pictures of the process, as I did it on a whim and wasn't entirely sure if it would work out, but I'll try to explain how I did it, which may not be the best or most efficient way since I was making it up as I went along.

First you need to dismantle both of the RK40s, which involves removing the back cover piece and grinding down a lip on the main shaft, so that you can pry off the retaining ring and break everything down into its basic components. You can test fit the metal shell to get an idea of how long the shaft will need to be, using the front panel, four middle sections, and one back cover.

Cut the shaft off the extra front panel, and notch it so that it can fit over the tapered end of the other shaft. Use some slow setting epoxy (like JB Weld) to attach the two pieces together, and set them as perfectly straight as possible (you'll have to get creative here, I ended up using a variety of things to adjust the angle of the pieces including pieces of paper and guitar picks). This is the most important step, as even a slight misalignment will result in problems getting the wipers to line up with the tracks properly, which is why I recommend using a slow setting epoxy that gives you plenty of time to make minute adjustments until it's as perfect as you can get it. Once the epoxy has set enough to handle, file or grind it down to match the shape of the shaft, and test fit it in the metal shell (but without the back cover). Be careful when handling it as it has very little mechanical strength at this point. As you turn the shaft from the front, the back end with the extension should stay pretty well centered over the entire rotation. If it's moving all over the place, go ahead and snap the two pieces apart and redo the process. If it stays perfectly centered, or is only very slightly off, you can proceed with strengthening the extension on the shaft.

What I did to give the joint some actual mechanical strength was to cut a groove lengthwise on one of the flat sides of the shaft, most of the way down the length and about halfway deep. Then I put a small steel rod (actually a tiny drill bit, very cheap and the perfect size) inside the groove and epoxied it in. Let the epoxy cure fully before moving on, and once it has file or grind it down flat so the wipers will still be able to slide onto it.

Before you can reassemble everything, you also have to create a spacer to go between the front two and back two wipers. There's two kinds of wipers, differing by how the spacers are on them, and I'll call the one on the front by the knob A and the one on the back B. You'll end up assembling them A, B, A, B, like two pots sitting in line with each other. If you hold the wipers together by themselves, you'll see the middle two are much closer, and you need to make the spacer thick enough to increase the gap to match the others. This can be done however you like, but what I did was wrap some tape around the shaft of a drill bit, and smeared some quick setting epoxy around it. Once it set for a bit, I put the drill bit in my drill press backwards, and held a file to it while it spun, to make the outer edge nice and round. Then I pulled it off the drill bit and tape, and filed the top and bottom edges down until it was the right height.

With the spacer made (and test fitted), you can start assembling the new pot. This is also a perfect time to clean the wipers/tracks and add some faderlube. Assembly should be very straightforward, as everything fits together in a fairly obvious manner. On the back two wipers, as you put them on spin the shaft back and forth a few time to observe the alignment. If the shaft wasn't perfectly straight, you may need to bend the prongs on the wiper assembly to one side or the other (just a gentle nudge with a small screwdriver will usually accomplish it), although it shouldn't need more than 1mm of adjustment.

When you finish putting it all together, you can optionally add a dab of epoxy to lock the last wiper in place against the shaft (in lieu of the original retaining ring), although it's not strictly necessary since the wipers stay in place pretty good on their own. Now you only need some longer screws to close the shell back up, and I chose to retap the back piece for 4-40 screws instead of whatever was originally used, as they'll be much easier to find in such a long length.
post #3724 of 9604
Can you translate that into Portuguese for me?


Very clever work Fitz, but I'm not the least surprised.
post #3725 of 9604
Well, I'm trying to just get this damn amp finished already, and I really wasn't thrilled with the added time and cost to design a relay-based volume control like I was planning, not to mention it would take up a lot of valuable space in the enclosure I want to use (read: the enclosure I bought cheaply a long time ago). You'd be amazed how creative you can get when you have motivating factors like those.
post #3726 of 9604
Quote:
Originally Posted by tomb View Post
Very nice
post #3727 of 9604
Quote:
Originally Posted by Ferrari View Post
The casework for my proto Bijou has come to an end, about 10 months after the amp was playing music for the first time.

Wowzers! Totally amazing. Who wouldn't want to see that beauty every day?

Excellent!
post #3728 of 9604
I have been doing some modding to my PC transports. Here is is insight into the journey.

ChainTech AV-710
This is a great budget soundcard. It offers bit-perfect optical S/PDIF and sports a Wolfson WM8728 DAC.

Lots of mods, mostly input/output regulator caps, DAC PSU caps. The best is obviously the DAC output caps - Muse ES bypassed by Vitamin Q.



EMU 0404 PCI
This card is said to have a very good implementation of coax S/PDIF (nice 75179 pulse transformer). I ripped out the DB15 connector and hard-wired a real coax S/PDIF cable to the output, terminated with BNC.



ESI Juli@
This card has one awesome trick - it allows you to disconnect the DAC board and get direct access to the output of the PCI interface (VIA Envy24HT-S / VT1721). I cut a Cat5e cable and tapped the I2S output from the card. This is now my main transport driving the I2S input of the North Star m192 DAC.



If anybody has an ESI Juli@ and NorthStar m192 DAC, I strongly recommend this as connection. I have an extra breakout cable that I will send to whoever has this combo.
post #3729 of 9604
CMOY with internal regulator and trickle charger I built for a user in my country's local forum.

post #3730 of 9604
Quote:
Originally Posted by TzeYang View Post
CMOY with internal regulator and trickle charger I built for a user in my country's local forum.

Impressive! What opamp did You use?
post #3731 of 9604
OPA2227

I don't know if there's anything better for the CMOY. Any suggestions? I'm usually very impatient when it comes to listening to opamps critically to find out which one's good lol.
post #3732 of 9604
Nice work FallenAngel!
post #3733 of 9604

my BANTAM DAC is built and working!







and to show that it works under linux, here's a 'lsusb -v' (list usb verbose) output:




I am SO surprised that I was able to build this! my eyes are not what they used to be (I'm middle-aged) and it was really challenging to solder this with almost no SMD work experience. I've been doing thru-hole work for over 30 yrs but not really any SMD until right now

plugged it in, looked at my opcom terminal and I see 'burr brown japan' saying hello. hey, that must be my new dac!

thanks to the project team for putting this together. very cost effective DIY.

/bryan
post #3734 of 9604
Quote:
Originally Posted by bhjazz View Post
Wowzers! Totally amazing. Who wouldn't want to see that beauty every day?

Excellent!
Thanks! I do enjoy my Bijou everyday.
post #3735 of 9604
Quote:
Originally Posted by TzeYang View Post
OPA2227

I don't know if there's anything better for the CMOY. Any suggestions? I'm usually very impatient when it comes to listening to opamps critically to find out which one's good lol.
I put 2x OPA227 into my first cmoy and then put OPA2227/OPA227 into my Pimeta. When I put an OPA2107 in to replace the OPA2227, I've been amazed.

I found this list but you always have to weight someone comments with compared to your own impression of the same op-amps.
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