My first mod! (Entech 203.2)

[mwallace573]

Inspired by this thread, I decided to take the plunge and attempt a few mods to my Entech 203.2. I am happy to say that they went off without a hitch.

Here we have the 203.2 board pre mod. Sorry for the somewhat fuzzy picture but my camera was a bit funky at the time. I had already snipped the front LED wires when I took this picture.



The mods I attempted were to attach some connectors to the front panel so I could remove the panel without having to desolder the wires every time. I also decided to switch out the opamp to a LM4562 as mentioned in this thread, so that meant that I was going to have to install a DIP socket.

This was the first time I've attempted a real mod outside of a simple recable, so I decided to take a few precautions. The main thing I did was get something to practice on; namely a busted soundcard that I purchased from a small computer shop. I also got the card because it had the connectors I would need for the LED mod.

Here is a picture of the board after I removed the OPA2134, which I decided to save in case I wanted to bring the DAC back to it's stock configuration, as opposed to snipping the connectors as was mentioned in the thread that inspired me to do this in the first place.


I didn't notice that hole was clogged until I took the picture. Needless to say I cleaned it out before I continued.

Next I went about psyching myself up for the main event, which was installing the DIP socket, which is Mouser p/n 575-113308. I used silver solder and a shakier hand than I would have liked, but it still went a lot smoother than I expected.

Here's a picture of the board post socket installation, with the LM4562 sitting next to the board. Doesn't it look lovely?



Edit: Decided to add a pic of the back of the board. A bit low light but good enough.



After that, things were pretty uneventful. I attached two pin connectors that I removed from the old soundcard that I practiced on, and ripped off a couple of computer case LED wires (the kind that run from a motherboard to computer case) to attach between the board and panel LED.



The case gave me a little fight before I was able to close it up, but nothing I couldn't handle.

Effects of the opamp switch are subtle but noticeable. Highs and mids are improved, and the bass seems to be unaffected. Bass guitars do sound very nice though. I can't say anything more specific right now. I'll need a little more time with it before I can say something definite. All I can say for certain is it sounds very nice.

Well, that's my story. Feel free to chime in with your Entech mods. I heard about a "Wildmonkeysects Filter mod", but searching turned up nothing. Any info about that mod would be appreciated.

[joe_cool]

Wow, nice job on the opamp removal. How did you get the chip off the board without damage?

[UglyJoe]

I second that question.

[mwallace573]

Originally Posted by joe_cool

Wow, nice job on the opamp removal. How did you get the chip off the board without damage?

Very carefully.

First I applied a generous amount of flux to the points where the opamp was attached to the underside the board. My iron never touched the top of the board. I then used a desoldering braid and removed as much of the old solder as I could, making a circle around the opamps "legs" as I did so. I made certain to keep the iron on the board for as little time as possible. Every once in a while I would grab the top of the opamp and wiggle it a little to see which of the 8 points were loose, then focus on the points that were still snug. After that, it was pretty much a repeat of the above steps until it came out. Nothing too complex. Just a little time consuming. It took me about 5 minutes to get it out.

For the record I used a 30 watt Rat Shack iron.

Edit: Turns out the stock opamp was a lost cause before I took it out. When Entech/Monster put the thing together, they decided to shorten the legs/connectors on the opamp when they soldered it in place, making them too short to make a good contact with my DIP socket. It will still work, but I have to push the chip down to get a connection. Guess I'm gonna check and see if BB will give a free sample or two.

[holland]

check the DC offset. You may have oscillation with the LM4562. I recall someone else (joe cool I think) modded with a LM4562 and had some issues.

[mwallace573]

Originally Posted by holland

check the DC offset. You may have oscillation with the LM4562. I recall someone else (joe cool I think) modded with a LM4562 and had some issues.

That's the first I've heard of that. How do you go about checking the DC offset?

[holland]

joe_cool modded a 205.2, same internals, basically. It was mentioned in passing.

http://www.head-fi.org/forums/showpo...4&postcount=31

Measuring DC offset. Check the DC voltage of the opamp out relative to ground. I don't know enough about the Entech to say whether or not power on without a source will enable the circuit or not.

Anyway, on the opamp, check pin 1 relative to ground and pin 7 relative to ground. You probably don't want anything larger than 0.3mV.

[colonelkernel8]

No 4562 problems here.

I took my Entech 203.2 mods a little further, I replaced every film cap in the unit with a Wima cap.

[joe_cool]

My problems with LM4562 and LM6172 were on the 205 DAC, which has a discrete class A buffer and a muting relay after the opamp.

The 203 uses a ~600-ohm resistor between the opamp and a muting transistor (x2 for stereo).

To measure the offsets for left and right channel, unplug the RCA cables and measure the voltage on the jack, from inner (signal) to outer (ground) conductor. You will need to apply a SPDIF signal to unmute the circuit. Anything less than 10 mv is expected. Higher offsets may be a problem for some amps but not for others. Offsets larger than 50 mv usually indicate a problem.

If DIYers want to try opamps which are not specified for +/- 15 volts on the power supply (like the AD8620) they should change the voltage regulators from 78L15 and 79L15 to 78L12 and 79L12. They are not expensive.

In my opinion, a significant factor in getting the best from these DACs is using a special high-grade SPDIF cable. Get one at minimum 1.5 meter long (5 feet is what I use) and get one designed for digital audio. Regular 75-ohm video cables will work but they will not give the fast rise times needed to minimize jitter.

[mwallace573]

Originally Posted by colonelkernel8

No 4562 problems here.

I took my Entech 203.2 mods a little further, I replaced every film cap in the unit with a Wima cap.

That sounds like fun. What effect did it have on the sound?

[colonelkernel8]

Originally Posted by mwallace573

That sounds like fun. What effect did it have on the sound?

Probably nothing, but it looks nice.

[Dept_of_Alchemy]

Originally Posted by mwallace573

That sounds like fun. What effect did it have on the sound?

x2

[fordgtlover]

Nice job!

Originally Posted by colonelkernel8

Probably nothing, but it looks nice.

Pics?


I replace the opamps, and the electrolytic caps in my Silverstone EB-01 with Panasonic FMs.

Pics here:
What was the first computer you ever used?