Mr. Lin
Lunatic Member
Recently I temporarily switched over from the Little Dot I+ to my Head Box SE, for reasons I won't get into here because it's not relevant. Over the past week I've grown to really enjoy the strengths of the Pro-Ject amp, which, while not necessarily better than the I+, can still hold its own in the presence of that tube (hybrid) headphone amp I like so much.
The Head Box SE has advantages that fit many solid state stereotypes, like sharper transient attacks, excellent instrument separation and definition, lots of detail, taut, controlled lower frequencies, and a drier, more neutral and sober sonic presentation (IMO). It works very well with classical music, which is what I'm listening to exclusively these days.
The Head Box SE (from here on to be referred to as "HB SE") is actually two headphone amps in one box, so two people could listen at the same time with different headphones. This feature is of no use to me, I only bought the HB SE because at the time Music Direct was trying to get rid of them (mine's the original black version as you'll see momentarily), and therefore priced them at $200 instead of $300.
Inside the HB SE is a 4508 JRC dual op-amp. I researched this a bit, and it turns out it's a very generic, run-of-the-mill op-amp. This puzzled me since every other part of the amp is of high quality. While researching, I also came across some posts in another audio forum about someone's experience changing out the op-amps in his HB SE. But I should note that, according to the pictures, his version must be older because it seems to have lower quality components in it. This person explained that he was initially "underwhelmed" by the performance of the amp, but that installing a better op-amp changed that dramatically for the better.
If you've read my I+ thread you know I have no shortage of audio-grade op-amps on hand.
So tonight I decided to have at it.
Let me start by saying I had a hell of a time getting into this thing. I approached this task thinking "This will be easy!", just open it up, de-solder, re-solder, install new op-amp, close it up, and voila! No.
After trying to open it with several specialty electronics tools, announcing a complete list of every curse word I know, and, as my girlfriend later put it, throwing a "hissy fit" (and some tools), I discovered that one can remove the two volume knobs and one selector knob on the faceplate, and this allows you to slide the PCB and bottom metal plate out of the aluminum chassis.
ara:
Here's what the HB SE looks like:
Here are two pictures of what it looks like nude, the second one is the side I worked on (I didn't replace both op-amps because I never use the first headphone jack), and you can see the op-amp that was my target, between what I assume are two bypass caps:
Truth be told, removing the stock op-amp wasn't much of a problem at all, although de-soldering is rarely fun. I have the tools and experience, so it was over with quickly.
In these pictures you see the newly-installed 8 DIP socket, and the underside, where I direct your attention to the fact that the soldering I did is much shinier than the stock soldering. That's not because I'm better at soldering, it's because I use Cardas "Quad-Eutectic" solder, which I swear by. Perfect joints every time:
Finally, I selected the beloved TI OPA2107 op-amp to try first, and installed it.
I put everything back together, plugged it in, and the "power on" indicating LED did not light up. :sigh: Fortunately, I quickly figured out that, due to the less than precise way this amps chassis was originally assembled, I had put the faceplate back on in a manner which partially covers the LED.
I hooked it up to the Naim CDP, and to my relief it worked, so I was happy. What I wasn't happy about was discovering that the still-stock number one headphone jack now only had sound in the right channel. This amp has been on loan for years to a family member, and when I got it back a couple months ago I recall having issues with that side, which is why I switched to the right side. I don't know what it is, but I'm disappointed because I was hoping to switch back and forth so I could compare the upgraded side with the stock side. Oh well.
It's hard for me to say exactly what's improved, although I can say with a fair amount of confidence that there's now more micro-detail, which makes instruments sound a little more like the real thing. The background also seems "blacker" somehow, but I'm at a loss as to why that would be.
Overall it was worth the headache, but I'm not finished yet. I intend to go back in and do some resonance damping, namely with a few electrolytic capacitors. Also, in the penultimate picture above you can see a bag of diodes in the bottom left corner. I got these from Japan years ago but never used any of them, and they're supposedly some of the best diodes around for audio purposes, so once I can verify that they're of the proper value I'll probably install them in a couple key places. And possibly some re-wiring as well.
Then, of course, I have about 8 or 9 other types of dual op-amps to try out. It may very well be the case that the 2107 is not an ideal op-amp for this particular circuit and application.
...
The Head Box SE has advantages that fit many solid state stereotypes, like sharper transient attacks, excellent instrument separation and definition, lots of detail, taut, controlled lower frequencies, and a drier, more neutral and sober sonic presentation (IMO). It works very well with classical music, which is what I'm listening to exclusively these days.
The Head Box SE (from here on to be referred to as "HB SE") is actually two headphone amps in one box, so two people could listen at the same time with different headphones. This feature is of no use to me, I only bought the HB SE because at the time Music Direct was trying to get rid of them (mine's the original black version as you'll see momentarily), and therefore priced them at $200 instead of $300.
Inside the HB SE is a 4508 JRC dual op-amp. I researched this a bit, and it turns out it's a very generic, run-of-the-mill op-amp. This puzzled me since every other part of the amp is of high quality. While researching, I also came across some posts in another audio forum about someone's experience changing out the op-amps in his HB SE. But I should note that, according to the pictures, his version must be older because it seems to have lower quality components in it. This person explained that he was initially "underwhelmed" by the performance of the amp, but that installing a better op-amp changed that dramatically for the better.
If you've read my I+ thread you know I have no shortage of audio-grade op-amps on hand.
So tonight I decided to have at it.Let me start by saying I had a hell of a time getting into this thing. I approached this task thinking "This will be easy!", just open it up, de-solder, re-solder, install new op-amp, close it up, and voila! No.
After trying to open it with several specialty electronics tools, announcing a complete list of every curse word I know, and, as my girlfriend later put it, throwing a "hissy fit" (and some tools), I discovered that one can remove the two volume knobs and one selector knob on the faceplate, and this allows you to slide the PCB and bottom metal plate out of the aluminum chassis.
ara:Here's what the HB SE looks like:
Here are two pictures of what it looks like nude, the second one is the side I worked on (I didn't replace both op-amps because I never use the first headphone jack), and you can see the op-amp that was my target, between what I assume are two bypass caps:
Truth be told, removing the stock op-amp wasn't much of a problem at all, although de-soldering is rarely fun. I have the tools and experience, so it was over with quickly.
In these pictures you see the newly-installed 8 DIP socket, and the underside, where I direct your attention to the fact that the soldering I did is much shinier than the stock soldering. That's not because I'm better at soldering, it's because I use Cardas "Quad-Eutectic" solder, which I swear by. Perfect joints every time:
Finally, I selected the beloved TI OPA2107 op-amp to try first, and installed it.
I put everything back together, plugged it in, and the "power on" indicating LED did not light up. :sigh: Fortunately, I quickly figured out that, due to the less than precise way this amps chassis was originally assembled, I had put the faceplate back on in a manner which partially covers the LED.
I hooked it up to the Naim CDP, and to my relief it worked, so I was happy. What I wasn't happy about was discovering that the still-stock number one headphone jack now only had sound in the right channel. This amp has been on loan for years to a family member, and when I got it back a couple months ago I recall having issues with that side, which is why I switched to the right side. I don't know what it is, but I'm disappointed because I was hoping to switch back and forth so I could compare the upgraded side with the stock side. Oh well.
It's hard for me to say exactly what's improved, although I can say with a fair amount of confidence that there's now more micro-detail, which makes instruments sound a little more like the real thing. The background also seems "blacker" somehow, but I'm at a loss as to why that would be.
Overall it was worth the headache, but I'm not finished yet. I intend to go back in and do some resonance damping, namely with a few electrolytic capacitors. Also, in the penultimate picture above you can see a bag of diodes in the bottom left corner. I got these from Japan years ago but never used any of them, and they're supposedly some of the best diodes around for audio purposes, so once I can verify that they're of the proper value I'll probably install them in a couple key places. And possibly some re-wiring as well.
Then, of course, I have about 8 or 9 other types of dual op-amps to try out.
It may very well be the case that the 2107 is not an ideal op-amp for this particular circuit and application....
Last edited:
