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Somebody asked me while I was still in the process of building it how much it would cost them to get one built for them. I told them they didn't have enough money to get me to do this again . Thanks for the kind words though, I really do appreciate it.

I'm testing some 6H13C's in it right now, but I'll probably put up some more info on the other mods later tonight. I'm not done yet!

Power Supply

This was one of the mods that simply came along for the ride while I was replacing everything else. As far as the power supply caps (both the primary 1000uF ones and secondary 330uF ones), I didn't replace them for any real specific reason by themselves. I wasn't too interested in trying to recycle the now torn up stock capacitors, which had a lot of their sleeving ripped off by the glue that held them down, and cleanly remove all the old wire and resistor leads attached to them. The new Nichicons also happen to all show the side with the least amount of labeling on them, giving a nice uniform black surface. The two power resistors with the primary power supply caps did warrant a replacement though. The ones used in the stock design are rather cheap and with a very thin, flaky coating. Even when it was brand new it was starting to peel off in places, and only got worse the more I tinkered inside the amp. I used some Ohmite resistors for the replacements, which have given me no problems as of yet. These resistors get hot enough to seriously burn you, so they definitely needed to be of sufficient quality so as to not break down. As far as the rest of the power supply (IEC jack, switch, transformer, bridge), I left alone. There wasn't anything to benefit from diving into the cost of replacing the mains side of the power supply, and I have a bad history with 120VAC so I kept my fingers out of it.


Groundloop Breaker

This was a last-minute mod that I added just days before the amp was finished. In fact it was the insulated headphone jack that I had to wait on that had me working until the night before the mini-meet comparison with the LD2+ (see the upcoming Headphone Jack section for more on this). I wasn't experiencing any real problems with a groundloop in my system, but I wanted to have myself protected for when the system gets moved somewhere else. In the stock Darkvoice, the earth ground is connected to the chassis right by the IEC jack, and the signal ground connects to the chassis ground at the headphone jack. By using an insulated headphone jack to separate the earth and signal grounds, and connecting the two via a resistor and capacitor at the back of the amp, I was able to add the groundloop breaker.

As I said before I didn't notice any problems with a groundloop before adding this, but the amp does seem to have an even blacker background now. I'm able to put on the headphones, and not even have a clue if the amp is even on at all, even when turning the volume all the way up with nothing playing. It's immensely enjoyable and almost ethereal the way the music just comes out of the blue.


Tube Sockets

The tube sockets used in the Darkvoice are nothing special. They're about as plain and ordinary as you can get. Unfortunately, this also means they aren't as reliable as they could be either. I'm not too pleased with the specific sockets chosen, given that the pins on them can wiggle freely (by design), and some of the spades don't have a perfectly tight grip, whereas some do. For the smaller input tube, this isn't really a problem, as it can be pushed down and sits nice and stable. The larger output tube is where the problem arose. On certain tubes, especially used ones with groves worn into the pins from previous tube sockets, the Darkvoice wouldn't really grip them evenly or securely, leading to the large tube being able to sit a few different ways, and sometimes be easily rocked from one to another. This caused loud crackling and popping on the signal if the tube was not in the "sweet spot".

My main goal in finding new tube sockets was pins that are permanently fixed in place (no wiggle), and a much stronger gripping mechanism for the tube pins. I only found one kind that really satisfied what I wanted, and of course they had to be much more expensive than any of the ordinary tubes sockets. The ones I used are made of teflon, and use six-pronged gold-plated grips on the tube pins. The difference in inserting/removing tubes is not difficult to notice. Tubes slide in very smoothly without a lot of wiggling back and forth, they sit perfectly flat down against the tube socket without any imbalance, and hold in place completely securely. It actually takes more force to remove the tubes now, but they come out easier with just smooth, steady rocking. All in all this is a very useful upgrade for the constant tuberoller like myself.

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Rest assured knowing that I've just been told that the refinishing is coming along nicely, and he expects to have results approaching the W2002's finish in terms of beauty.

Well given what I assume is the condensed version of your work log in this thread, I wouldn't imagine you'd be at all eager to dive into the same briar patch again . You're very welcome, it's excellent work.

And so it was written "... lead me not into temptation for I am immune. Alas I am a Head-Fi member and temptation now is my constant companion.."

Beautifull work Fitz!

I don't like crossfeed much personally, but your headphones probably respond better to it than mine.

HOLY CRAP!!!
To say I'm impressed doesn't begin to express how I feel when I look at this amp. I'm just seeing this thread for the first time. I'm still away on a job, but got some PC access today. I love the faceplate too! Where did you get that done? You really outdid yourself Fitz!

First, you guys do know that this amp was bought, then Fitz gutted and rebuilt it. Not taking anything away from Fitz, but the credit for the appearance of the amp should go to darkvoice.

Fitz,
Few questions and comments for you. I did skim through the long darkvoice thread, that took a while. I think it would be nice if you moved the schematic from that thread to this one, give people a better understanding of your mods.

Also, it would be nice if you could post part numbers and sources for the parts you used, if you have that information electronically already. Would help anybody thinking of modding the amp.

Would about the coupling caps? I remember you changed those too, but did not see mention of that (or is that yet to come?).

I am thinking about buying this amp, but have not pulled the trigger yet, and if I buy it, I would eventually mod it. I would at least mod the power supply, change the lytics and probably the bridge diodes, and also the coupling caps. But, this brings up the question, if you do all that, are you better off starting with a kit or diy project.
If you had to do this again, would you do it this way (modding a darkvoice)? I know there are advantages to modding an already built amp. In my case, I am pretty sure if I mod something, it will look better than if I build it from scratch. It is also easier to mod an existing product, but it would probably cost money to mod than build from scratch.

Hope I did not ask too many questions,
Randy

Fitz designed and had the face plate made, so I think that alot of it goes to him.
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You're right. I owe you an apology Fitz.

I thought you had just modded an existing face to add the crossfeed. When I took a close look at the faceplate on your amp, it is obviously different from the one on the stock 336.

I don't remember reading in the long thread that you had a custom faceplate made, but I could have missed it because I skimmed though some parts.

So, sorry again. And, now I am REALLY impressed with your work on this project.

Randy

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Yup... that's why this was said in the very first paragraph of the thread.

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The last thing I want to do is assume responsibility for other people trying to do the same mods. None of the final mods were done with the amp already built and all other components in place, so I have no idea how things would work out trying to replace certain parts in situ. I've been toying with the idea of posting some specific guides for the more useful mods, but I'm still not sure about it, since I can't really be sure on how they would turn out doing it in a different order than I did.

People are more than welcome to PM me to talk about parts and installation for some of the mods, as they already have done, but I'm not going to simply post a schematic and BOM and say "have at it." To me, that's just asking for trouble.

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There's still a lot I haven't written up yet. I've spent most of the last week trying to relax with just a little bit of light browsing/posting.

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Would I do it again this way? I don't know. This wasn't a case of simply buying the Darkvoice and then deciding on all these mods at one time and doing them. There was already a lot of modding done before it was gutted, and many of the mods in it now weren't thought up until I was already well along the way of putting it back together. Net cost is an irrelevant factor when talking about paying a premium for parts of relatively minor impact.

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You've got pretty far to go to catch up to another Head-Fier as far as asking questions goes.

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And I really regret making that remark, next time, I will just ask the questions. When I made that remark, I did not realize you had a new face place custom made. I was thinking about when you first added the Fitz mod to your darkvoice, and had added the switch to it. I should have looked at the new pictures more carefully before saying anything.

As for putting up a schematic and PL, I think mods are always a YMMV thing, and whoever mods their gear is taking a chance. To me, you would have no responsibility for mods that did not turn out well, you are just providing information.

But, I see your point about worrying about responsibility for problems, and you have been very nice to share what you have so far.

Randy

If you're 21 and doing work like this I'd love to be around when you reach your 40's to see what creations you've come up with. Fantastic work!

Hrm... it's been a while since I've updated this thread. Guess it's time to get back to making some posts that have a little effort in them, eh?

Part 3 of the mods will be posted here shortly.

Front Panel

There's not much to say about this one, since it has no affect on sound quality. I was very hesitant to actually have a new front panel custom made, since it was more costly than some of the other mods that already had minimal impact themselves. In the end I decided since I was already going all the way with replacing parts internally, I might as well do something to distinguish it externally as well.


Various Resistors

All of the other various low-wattage resistors were replaced with the same Vishay/Dale RN series that were used in the crossfeed module. At the cost for each one, it wasn't worth trying to salvage the old resistors from the removed parts, and hoping the leads would still be long enough to work with any small changes in layout and part placement. Like the power supply, this was another one of the mods that just came along for the ride.


Headphone Jack

I did not originally plan to replace the headphone jack on the Darkvoice, as the one used is perfectly fine by itself. However, when I decided to implement the groundloop breaker, I realized the headphone jack was where the signal and chassis grounds were originally connected. To keep the grounds from direct contact, I would have to replace the headphone jack with an insulated jack. Not just any regular insulated jack either, since the shaft of the headphone jack comes into contact with the front panel, it had to have a nylon bushing and not just insulating washers. The Switchcraft jack I originally wanted to use was essentially impossible to find on short notice, and the shorter one I did find required me to trim back some of the body on it to make it extend far enough forward to work. It still let the headphone plug sit too close to the front panel for my liking, with barely a hair of clearance around it. I ended up replacing the Switchcraft with a Neutrik jack. The Neutrik jack itself fit perfectly, and the different shape actually fit better inside the Darkvoice, but the huge nylon washer had to be cut to almost half its original height.

This doesn't directly have any impact on the sound quality, but it is necessary to realize the benefits of the groundloop breaker, so see the previous section on the groundloop breaker for impressions.


Output Coupling Capacitors

And for the grand finale, the single most impactful mod of them all. If I wasn't able to do this mod, I honestly wouldn't have even bothered with any of the others at all. This was the biggest drawback to having the first version of the Darkvoice, as the output caps are smaller than what is currently being used. Even with the newest versions I still think they're too small to be able to truly advertise the Darkvoice as driving phones as low as 32 ohms, since it rolls off a lot of the sub-bass on those very low impedance phones. I noticed a distinct lack of sub-bass impact when comparing the Darkvoice directly to other amps, to an almost alarming degree of obviousness. With a simulation of the whole Darkvoice circuit, I calculated the -3dB point into the W5000s at around 65Hz. This is simply way, way too high, and definitely explains why they were lacking impact on the Darkvoice.

To get a satisfactory amount of capacitance in this spot, I had pretty much two choices: non-electrolytic caps too big to fit inside the chassis at all, or electrolytic caps. Since having caps hanging out of the bottom of the amp wouldn't work too well for me, I had to go with electrolytics. I chose to use Nichicon KZ Muse caps to gain the necessary amount of capacitance and still be able to fit inside the amp, and Solen SM tin foil caps as a bypass on the electrolytics. To be able to still securely mount the capacitors to the chassis, I had to go with only half the amount of capacitance I originally planned, but it's still more than sufficient. The new -3dB point is around 1.7Hz, which is obviously well clear of anything I'm going to be hearing through the amp.

This one single change completely changed the sound characteristics of the Darkvoice with low impedance phones. Now that it is able to fully drive them, the Darkvoice lives up to its name and can even make the W5000s sound "dark" with certain tube combinations. Admittedly, this does make it less neutral, but it makes it so much more enjoyable to listen to, and doesn't actually sacrifice any detail or clarity in the upper end. It's a difficult thing to describe this kind of change, but I'll expand on it more later.

Fitz, great to hear more about your mods and especially the mod for lower impedence phones. I wish that some of these Chinese manufacturers would build *atleast one* tube amp for Grado's and AT's...but they all seem to have issues with low impedence headphones.

The idea that the W5000's could even seem 'dark' with certain tube combinations is a very intriguing thought to me, when you think of the balance that would bring to that headphone. This is killing me!!