Yeah the power cord that comes with the 708 is one of the smallest/cheapest that I've ever seen. I threw it in the trash! I found some nice 14ga heavily shielded 6ft IEC power cords at an awesome electronics store when I lived in Houston. These cords were surplus and cost $2.99 ea so I bought about 10 of them! Well today I did some more mods. I completely removed the output RCA's and the cheap wire going to them. I will replace these eventually, but I don't really need the preamp function right now and I was just getting tired of looking at them. Then I used the same Belden Teflon wire to replace the headphone wire to the jack. While I had the board that the power switch and the 1/4" jack are on removed, I noticed that there are some 10ohm resisters in series to the jack. I just happened to have some NTE 2W metal oxides so I replaced these. On this note, a lot of the resistors and caps in my amp are kind of damaged/scratched/dented. I plan on replacing all of the resistors that are in the signal path first with something nice like RIKEN carbons. For coupling and preamp out, my 708 uses the red WIMA MKS caps. According to the opinion of many, these metallized polyester caps are crap and shouldn't be used for audio. Some WIMA FKP polypropylene film/foils would be a lot nicer and are the same shape/style. I would much rather try some Mundorf M-Cap Zn or Multicap RTX instead though. Changing these WIMA's and some of the resistors are going to be my next mod. At this point I would definitely say that this amp blows away my previous method of powering my 580's. My amp only has about 10 hours on it so I'm not going to be very critical about the sound right now, but I am very impressed with it so far for the money! Nugget, I totally agree about not feeling bad about cracking this cheap amp open and pulling stuff out. I want to see how far I can take this little amp, within a reasonable budget of course. Modding is great stress relief from classes! I'm taking pictures of every step for before and after comparisons. If any one is interested I will try to post some.

Quote:



Yes please post them!

Damn right I want to see some pictures! Any of the mods make a particularly large difference? I can see starting with some new RCA jacks and a new power cord. And some new tubes, o/c.

Now if I could only find an electronics shop in New York that sells this stuff; mail-order is a PITA with my microscopic mailbox and work schedule.

Well as far as what made the biggest change, I'd say it was the tubes so far. The new wire, RCA's, and resistor seemed to have helped too, but since I'm not familiar with this amps sound yet I can't say by how much. Plus it's barely even started the break-in period. I want to get about 50 hours on it before I do any other mods. From here on out the mods will start making a much bigger difference on the sound so I want to be able to decipher if it is better or worse.

Nugget, couldn't you just get your mail-order parts sent to you at work? Ok, so I have plenty of photos and I can use Photoshop to resize them from 2.5MB to ?? I read somewhere that pics here need to be scaled to 25kB but that there was a way around this. Also how do I post the pics directly in the post, instead of as a link? I've never really posted pics before so I'm new at this. Could someone help me with these, I would appreciate it.

jamato8 started a great mod thread for the Wooaudio 3 and it has a lot of great info in it. Definitely worth checking out.
http://www6.head-fi.org/forums/showt...ight=wooaudio3

You can upload pics to ImageShack and then direct-link them in your posts.

Thanks Nugget! I'm taking a few more right now so I try it out in a few minutes.

I just realized that I have some 1.25uF 400V mylar caps in my parts bin. I can't hold back; I'm going to bypass the headphone output caps with them. The stock output caps are polar electrolytics by the way! Not exactly the best choice to pass audio through.

Well it's not a huge difference, but these cheap Mylar caps opened up the sound a bit. A bit more detail from the midrange on up. I'm not sure if these are metallized or are film/foil, but they are only temporary anyway. They cost me $1.25 each surplus. One of these caps is about a 1/4" away from the back 6922 so I hope heat will not be a problem, but I'll keep an eye on it.

Very clean work. I like. I figure I'll let mine burn in before I really start whacking away at it, though.

Incidentally, where do you find your tubes?

Thank you; doing quality work brings me satisfaction, which is why I find it so hard to leave things alone. I'm also going to try to let it burn in more before doing anything else. However, the 15% off sale at Parts Connexion ends on the 30th so I might at least order some parts.

The 6N3 is still the stock tube. The RCA 6922's I got from drarthurwells. I'm in the process of looking for 6N3 replacements so I'll let you know if I find any good looking deals.

Hey everyone!

Okay, my own little 708B has made it to London from China (thanks Leshele), and although I only had a couple of hours on the weekend to play with it, here are my initial impressions and tests.

The package I got was nicely wrapped, was the right voltage, and also contained the correct power cord to plug it in immediately. The cable/plug might not be audiophile quiality, but I can't estimate yet of what magnitude sound can improve through a better cable (I'm thinking not much). I do have a Belkin mains filter which does a few rudimentary things like surge protection and a bit of isolation of the attached components, and that's good enough for now.

So, I unscrewed the amp to make sure all the tubes are nicely flush in their sockets, left the cover off (since I wanted to do some tube rolling), and then switched the whole thing on and gave it a listen. First impression: balance is off everything sounded like it was too far left. A quick switch of the two driver tubes and the balance flipped to the other side. This probably means the tubes aren't well matched, which isn't great (if you're looking for the amp to work well out of the box) but no biggie (you could always adjust balance in the player, or change the tubes which I wanted to do anyways).

So, out went the two Chinese 6N11s to be replaced by a matched pair of 6N23P-EBs. These worked flawlessly with perfect balance from the start, which was the main improvement I was listening for, and the sound seemed to fill out a bit more as well. As a side note, please don't expect any fancy audiophile lingo for describing sound here. The sound before was a bit thinner before, and became a bit fuller with the Russian tubes, in fact noticeably so.

Since the other 6DJ8esque tubes I"m trying to get haven't arrived yet, the next thing to be played with was the 6N3 sitting in front of the two drivers. This was already doing a good job I felt, but I had 3 more different types of tubes to play with here: a 6N3P-E, a 6N3P-DR, and an RCA 5670 from 1961. The first of these tubes was worse than the Chinese original; it created a massive hum, and quickly exited the amp. The other two tubes are pretty good, I didn't get any hum out of them until I turned up the amp to more than half maximum volume (which is too loud for listening for > 10 seconds with my headphones). In hum, there was a minute advantage for the RCA tube, though it might just be my imagination. The more noticeable difference was that the RCA tube seems comparatively neutral, while the DR one emphasizes the highs a bit too much and sacrifices bass. It could well be that I should just give it 10-20 hours to burn in, but I haven't had that time yet, so my current favourite is the RCA tube. Hopefully I'll have some more time next weekend to do more listening and said burning in. I cleaned all the tube contacts with deoxit before socketing them, which probably has all of 0.03% effect on sound, but gives my mind a nice cosy feeling anyways

Compared to the headphone-out from the Diyeden GM modified, I've noticed two improvements (and might see more as time progresses). The first is that highs no longer all have a slight reverberation to them (minor but noticeable), and the second is that bass sounds a lot more abrupt then before (I think this is also referred to as a tighter or drier bass).

My listening was done with some piano music (Mitsuko Uchida playing the Mozart Sonatas, Dick Hyman playing Duke Ellington), Vivaldi's Four Seasons (Deutsche Grammophon), Pink Floyd - The Wall (MFSL), and a bit of 2RaumWohnung. I'll try out a few more flavours of music when I get the chance to see how things have changed from before

Hey Nugget, I was wondering if you could please take some pics of the inside of your amp and post them. I was just looking at the pic that drarthurwells posted at the beginning of this thread and I noticed that the main board with the tubes on it has a much different layout of it's caps. The headphone output caps look much larger than the ones in mine. The pre out caps are also different from the WIMA's in mine. The other electrolytics are also layed out differently. The big red resistors in his are not in mine either. My 708 just uses metal oxides throughout. I would like to know if your unit is like mine since we got them around the same time.

I'm looking forward to when you start doing mods on yours. It will be nice to have someone to bounce ideas off of. Having two sets of ears listening to the same mod will be helpful.

I'm keen to do some modding to my 708B, but I have my brother's kids staying currently so I won't be opening the covers on my 708B again for a few days at least.

Quote:



How long have you had your 708 for? It'd be great to have a small group of people doing mods. We could cover much more ground this way as far a variety in parts goes.
My unit does not have any hum, but it does have a small amount of hiss that grows with volume. I know this is common in cheap tube equipment, but I'm researching the various ways to make it dead quite. I also noticed in drarthurwells pic that his unit has a ground wire from the IEC jack to the case. Mine doesn't have any ground wire at all! Only the signal ground goes to the case. I'm going to check into this more as it kind of worries me if this amp is not grounded properly.