Yaqin CD3 / Darkvoice 336SE Mods (Coupling Caps)

Parts list so far is looking like:
For the Yaqin CD3:
4x Clarity Cap SA 0.47uF
2x Clarity Cap SA 0.22uF

For the Darkvoice 336SE:
2x Clarity Cap SA 0.47uF
2x Mundorf E-Cap100 100uF
2x (Each) PRP 1% 1W Resistors (1K, 2K, 10K, 1M)
2x (Each) Kiwame 1% 2W Resistor (200R, 30K)
2x Vishay/Dale 1% 25W Resistor (1K)
Alps 100K Blue Velvet Potentiometer

Some things I haven't quite decided on yet:
Maybe new RCA jacks.
Maybe replacing the 220uF/250V caps with nicer Nichicon ones.
Power supply capacitors/resistors

Does anyone have any comments on implementing a cathode bypass capacitor? I would probably use a Elna Silmic II, but I don't know what value or voltage.

Also, does anyone have any comments on using a film to bypass the Mundorf E-Cap? The only other person I've seen using the E-Cap in a Darkvoice amp had it bypassed with an Obligatto film; not sure if it's something I should be looking to do.

Attached shows planned circuit specs (really just has different coupling cap values and a cathode bypass cap), though some values are missing at the moment.

I started taking the innards of the Darkvoice apart tonight.
Some things that were accomplished:

• Removed PCB on filter capacitors. 200R/10W resistors removed (slated to be replaced with Mills 12W)
• Removed gobs of hot glue on input/output wiring and between coupling capacitors
• Desoldered input/output wiring from RCA jack PCB. Removed jacks and PCB (slated to be replaced with nicer jacks and nicer wire)
• Removed big ugly red coupling capacitors (slated to be replaced with Mundorf 100uF bipolar + Clarity Cap SA 1uF)

I haven't yet done any significant work on the bunch of wiring surrounding the tube sockets. That will all be replaced with high-quality solid-core wire down the road. I also need to figure out how to remove the faceplate so that I can replace the headphone jack and potentiometer. I'll probably go with a nicer Neutrik jack and an Alps Blue Velvet pot (debating using 100k instead of 250k). Once I figure out how to systematically disassemble the amp, things will go much faster (not necessarily more smoothly :cheesygrin:)

It's a work in progress. I'll probably swap the capacitors in the Yaqin this weekend to some Sonicaps. That should be significantly easier than working inside the Darkvoice.

Regardless, I'm having fun.

Here (link) is a collection of pictures I took of the insides before I started taking it apart. I will have to take more photos of what it currently looks like inside later.

Made a bit of progress tonight, packing that PCB with new components. The through-holes where the old resistors were were a little small, so I had to get somewhat creative with how to pack them in. I'll end up having the same problem with the Clarity Caps (their leads are at least 16AWG, and those holes look like they won't fit under 20)

Picture of the PCB

Once this is done, I'll have to start taking apart and replacing the wiring and resistors that are point-to-point inside the amp. That should actually be somewhat easier, not having to work around the limitation of desoldering/resoldering a PCB.

Honestly, the most difficult things forthcoming will be replacing the headphone jack and potentiometer. I have yet to figure out how to get access to them.

DefQon wrote: »

Nice mods going on there mate. With regards to accessing the pot and headphone jack. You'll need the appropriate sized tip hex (allen) key to remove all 8 hex screws on the faceplate. Once removed you have full access to the bolted on volume pot and hp jack by removing the washers.

With replacing the pot, make sure you don't end up ordering some custom stepped or ALPs pot as it could end up being too long to fit, especially since the P2P wiring to the front 6SN7 tube cramps things up a bit.

Just another question, what will you be replacing the 6 x 10uf filter caps with?

I figured those 8 hex screws on the faceplate were the key to it, but just by inspection I couldn't tell how to take it apart. I also didn't have the correct size allen key on hand. :sad: Thanks for confirming my suspicions, though! And welcome to Club Polk.

I will be replacing the 3x10uF caps per channel with a 100uF Mundorf bipolar electrolytic cap, bypassed with a Sonicap Gen I 8.9uF film cap. I've heard of one other person using the Mundorf bipolar caps (though they used an Obbligato film as a bypass) to good effect.

DefQon wrote: »

Thanks...

Some pictures would be great. I already have mine fairly modded but the filter caps is something I have not replaced yet as I only use the amp to drive my high impedence HD600's and few other can's.

I've been updating as I've worked my way through the process, including some pics. Above your first post is a picture of the filter cap PCB that I took. It doesn't have the larger Sonicaps in place yet. I'll probably be updating on Friday or Saturday with that board being completely done.

Because the transformer leads were cut so short, soldering them back on to the PCB might prove to be a huge pain. I've been playing with the idea of adding some extension wires onto them to make it easier.

At the end of my mods, I think the only stock things inside will be the tube sockets (though I've honestly debated buying new Belton sockets to drop in) and the electrolytic filter caps along the V+ line.

zingo wrote: »

Enjoy the process! As a guy who's modded many piece of equipment, you don't gain much in resale value, but it's good experience and usually some nice gains in sound quality.

I'm certainly enjoying the process! I've done cable mods before and built the main amps I use in my stereo system (actually I cheated a bit, because those amp boards were pre-built; I just swapped some resistors), but this is the first time I've gone in and done a comprehensive set of mods on an already-assembled piece of equipment.

The people over at Darkvoice didn't make it very easy with their early production runs; they used PCBs in places where it didn't make a whole lot of sense (e.g. on the RCA jacks and on the filter capacitors) and hot glued a lot of things in place. It's a while away, but I'm excited to get it back it reassembled and back in commission.

I still can't for the life of me figure out how to get the face plate off. It seems like there are four screws from the inside of the amp holding it on, not the eight hex key screws surrounding the volume knob. Only three of the hex key screws had nuts on them, and none of them seem to just come out with counterclockwise rotation, as if they aren't actually in a threaded hole. I'm trying to push them from the other side while unscrewing, but it's a bit difficult. Just FYI, they fit 2mm and 5/64" allen wrenches.

I attempted to remove the chassis that carries most of the components of the amp (what the tube sockets are attached to), since it is also held on by four screws, but they are rather soft and tightly fastened, and one of them is now stripped. That tray is actually in the way of accessing three of the hex-key screws from the faceplate.

Here (link) are some pictures illustrating what I'm talking about. If anybody has any suggestions (looking at you DefQon - might have to message you on Head-Fi), they'd be much appreciated.

Still having fun, though. It's gonna be pretty quick once I actually figure out how to replace the potentiometer and headphone jack... Who would've thought the wiring would be the easy part compared to actually disassembling a chassis?

I decided to take a break from the Darkvoice for a bit, thinking that focusing on the Yaqin CD3 might give me something to do for a few days. As it turns out, swapping the coupling caps in the CD3 ended up just about the easiest thing I've ever had to do with a soldering iron. It took all of half an hour to heat up, replace six caps, and cool down.

Picture of final product

Turns out the pot I bought (Noble 249Y) is too deep by about 1.5mm and runs into the front tube socket.

While this would typically be cause for cursing and generally angry behavior, I've found a workaround! Namely, swapping the positions of the headphone jack and potentiometer on the front of the amp.

The potentiometer (provided I drill a hole for the little nub thing they always have) would fit where the headphone jack originally was with 1-2 mm of clearance between it and the bracket for the 220uF electrolytics; likewise, the Neutrik headphone jack I've bought has tons of free space in the center of the chassis without interfering with the tube socket, provided I make the hole in the front of the chassis slightly larger to accommodate the screw that the headphone jack uses.

I think it may just work out in the end. This is nothing compared to the other problems I've had. It just requires a little bit of mechanical work. I have some time to consider my options. This doesn't require any sort of reworking of the aluminum faceplate, in theory. In practice, these things could work out entirely differently.

And this is why I like DIY projects.

Here (link) is what it would look like from the front. No knob, as they are still on their way to me. It looks a bit more assymetric than the "stock" look, but it is technically superior in terms of components. :redface:

Bonus pic: Comparison of potentiometer sizes

trav0810 wrote: »

I have a CD-3 myself, so I am really interested to hear how that turns out.

I've already finished the mods on the CD3 up here. I have to say, the upgrade was worth it to me. It was painless, and it had what I would describe as a tangible effect on the sound - benefits of a quick turnaround time on modding and getting it back in place. :cheesygrin:

Really, the biggest effect I've noticed would be in vocals. The Sonicaps are generally described as having a tangible "midrange bloom", and I have to say I agree in this case. It was a very good upgrade over the stock film caps in terms of vocals.