Modifying the Xiang Sheng 708B [56K!!!!]

[dcheming]

Wow, quite a bit happened since I was last here.

It's good to have you back Charles. Bummer about the computer virus causing so much trouble. Congrats on the new job though. I've also been making plans to put together a nice two channel system since I'll be moving to San Francisco this summer. Hopefully we'll find a place big enough to have a proper setup.

Those Onix X-Statik look interesting. Open baffle speakers have some serious benefits, but bass depth and weight is usually a problem. So the hybrid approach makes a lot of sense. I've been thinking about something like the GR Research OB-7 kit, but I'd really want to hear one first before spending that much on parts. I'm also considering some Magnepan 1.6s, but again I would need to spend some more time with them first.

Since you sold your 701s and have some HD600s on the way you'll be able to use a smaller uF cap on the outputs. Have you tried those Solen 51uF caps purely as output caps? Even though Solens aren't really that great I still much prefer them to the ELNA e-caps. Of course your Mundorf e-caps are likely much better than the ELNAs I was using so YMMV.

Cloth Ears and jrhill, please feel free to add as many pics and impressions/thoughts/ideas to this thread as you want. I'd like this thread to as diverse a source of info as possible. That and I just enjoy seeing other DIYers work.

[Chops]

Originally Posted by dcheming

Wow, quite a bit happened since I was last here.

It's good to have you back Charles. Bummer about the computer virus causing so much trouble. Congrats on the new job though. I've also been making plans to put together a nice two channel system since I'll be moving to San Francisco this summer. Hopefully we'll find a place big enough to have a proper setup.

Those Onix X-Statik look interesting. Open baffle speakers have some serious benefits, but bass depth and weight is usually a problem. So the hybrid approach makes a lot of sense. I've been thinking about something like the GR Research OB-7 kit, but I'd really want to hear one first before spending that much on parts. I'm also considering some Magnepan 1.6s, but again I would need to spend some more time with them first.

Since you sold your 701s and have some HD600s on the way you'll be able to use a smaller uF cap on the outputs. Have you tried those Solen 51uF caps purely as output caps? Even though Solens aren't really that great I still much prefer them to the ELNA e-caps. Of course your Mundorf e-caps are likely much better than the ELNAs I was using so YMMV.

Cloth Ears and jrhill, please feel free to add as many pics and impressions/thoughts/ideas to this thread as you want. I'd like this thread to as diverse a source of info as possible. That and I just enjoy seeing other DIYers work.

Just to get this out of the way first... You're back!! LOL

Yeah, the whole PC virus bit sucked as I didn't only lose my own site, but also a client's! But he was fading out his business anyway so it didn't both him too much.

The X-Statik's are more than just interesting, they are phenomenal! I just got them in yesterday and have had them going non-stop since 3:30pm yesterday. I was just blasting the hell out of them for the first time a few minutes ago with a pipe organ CD. All I can say is WOW! Definately more than my money's worth on these babies!

I was originally going to get those OB-7 from GR (Danny Richie), which also helped design and DID design the crossovers in the X-Statik. The reason I didn't is because I suck at wood work. I mean, I can do it, but it looks like b u t t when I'm done with it.

I can tell you this, don't think about those OB-7's. JUST BUY THEM AND BUILD THEM! Trust me on this. They use 5.25" woofers where mine uses 6.5" woofers, and his uses a ribbon tweeter where mine uses a 1" soft dome. But the major thing is that the OB-7 uses 4 woofers in the sealed enclosure and uses premium caps in the crossover networks. I only have 2 woofers in the sealed enclosure and decent caps. Plus with the OB-7, you can upgrade the drivers for a small fee and have more output, lower distorsion, lower bass and higher power handling. I've had Maggies before and they don't stand a chance against these X-Statik's. The OB-7's are most likely even better!!

BTW, I have the matching X-Voce center channel coming as well. Just ordered it today.

Yep, I have the HD600's coming. As far as the amp though, I think I'm going to leave it as is until I make the move to a new chassis, which I am going to do. Then I'll have it to where it's easy to switch out caps, kind of like what you did in your NAD cdp.

And to the new guys on the block, please do post pics and comments. Every little bit helps!

Now for just a little bit of off topic eye-candy to motivate Derek!

[Cloth Ears]

A question from a "tube-newb" (I'm copy-writing that, hands off...). Someone mentioned that the 6Z4's out there were all the same (or close to it). A quick search found this

which looks like the original and this

which looks rather different. One by RCA and one by Westinghouse. Different, or the same in different shape (leopard changing its spots, maybe?).

I took some photos (and have a schematic that I'm going to transcribe) from last night - although I think James has already started making changes based on Morgan Jones' Mini amplifier circuit. But I probably won't be able to get to them until the weekend. Definitely work in progress.

[Chops]

There's two different types of 6Z4's out there. The ones you pulled up are the American versions. The Chinese version is the one in our amps. Two totally different tube types, however they might be designed the same internally. I guess if you changed out the tube socket, it might work, but don't quote me on that.

Derek would be the one to ask.

[glitch39]

the american 6z4's are tall. so even if you change out the socket, it won't fit the case. the chinese 6z4 is almost like the size of a 12ax7

[Chops]

Originally Posted by glitch39

the american 6z4's are tall. so even if you change out the socket, it won't fit the case. the chinese 6z4 is almost like the size of a 12ax7

Well, for one thing, the American 6Z4 is an entirely different tube which also happens to be a full size tube. IF, you wanted to convert over to this tube (if you even can), you would have to relocate it anyway and use a new chassis as the 708B chassis has no room for it, let alone it being taller than the chassis.

[Cloth Ears]

Originally Posted by Chops

Well, for one thing, the American 6Z4 is an entirely different tube which also happens to be a full size tube. IF, you wanted to convert over to this tube (if you even can), you would have to relocate it anyway and use a new chassis as the 708B chassis has no room for it, let alone it being taller than the chassis.

Thanks, Chops - pictures can fool you (the RCA looked the same size).

I've managed to take the following pictures of the work in progress, but I'd have to leave it to James to explain exactly what's been done. Please excuse the crappy photography...

James circuit diagram of what's currently been done.

One picture from above.

Another picture from above.

And a picture showing the (temporary) set-up for testing headphone jacks and volume controls.

Since these were taken on Thursday night he's looking at changing it to be closer to the Morgan James (with feedback) amp posted by Chu Moy (I hope I spelled that right!) somewhere on the WWW. This 708B circuit seems to resemble it in a lot of ways - which probably accounts for why it sounds so good for so little (imagine a $200 Earmax Pro).

[Chops]

Originally Posted by Cloth Ears

Thanks, Chops - pictures can fool you (the RCA looked the same size).

I've managed to take the following pictures of the work in progress, but I'd have to leave it to James to explain exactly what's been done. Please excuse the crappy photography...

James circuit diagram of what's currently been done.

One picture from above.

Another picture from above.

And a picture showing the (temporary) set-up for testing headphone jacks and volume controls.

Since these were taken on Thursday night he's looking at changing it to be closer to the Morgan James (with feedback) amp posted by Chu Moy (I hope I spelled that right!) somewhere on the WWW. This 708B circuit seems to resemble it in a lot of ways - which probably accounts for why it sounds so good for so little (imagine a $200 Earmax Pro).

Sorry for the delay, been busy with work and doing research on my new vehicle (swapped cars with one of my bro's just for the heck of it!). Looking to do lots of mods to it... Imagine that! LOL

Anyway, you amp looks pretty nice, though I'm not too sure what's up with all the duct tape everywhere. Aussie's electrical tape?


BTW, my new cans came in a few days ago and I've had them running the entire time. They have 80 hrs on them so far and are starting to really open up. Man, I forgot how good these 600's sounded!




And just for fun, here's another shot of my amp with the 51uF Solen's along with the 100+100uF Mundie's.

[Cloth Ears]

Originally Posted by Chops

Anyway, you amp looks pretty nice, though I'm not too sure what's up with all the duct tape everywhere. Aussie's electrical tape?

BTW, my new cans came in a few days ago and I've had them running the entire time. They have 80 hrs on them so far and are starting to really open up. Man, I forgot how good these 600's sounded!

The duct tape is there for 2 reasons. First, electrical safety - all the 240v wires have been covered pending sealing them up later. Second, to hold the caps (and other stuff in place). Eventually it'll come off and be replaced by heat-shrink or proper mounts.

Still waiting on 2 pairs of 6DJ8's from different places, a GE JAN 5670 and a triplet of Chinese military 6Z4's (to see if we can get any better sounding). And some other Sangamo, Sprague and PIO (Russian) 0.22uF caps for trying out in the 3 places where they're used. And 3 different volume pots, a cheap one, an ALPS blue and a 24 stop stepped attenuator.

We may have to redo the baord before we finish...

Pictures and the new circuit when we get closer to finalising it.

[dcheming]

So yeah, as Chops said there's the full-size 6Z4 as well as the mini 6Z4 that's used in the XS. I have no idea why they share the same number. As was mentioned there's no way to fit such a large tube inside the case. Also I doubt the power transformer could handle the heater current since it can barely handle the 6X4 I put in, which draws slightly more than the stock mini 6Z4.

I'm interested to hear your impressions on the three different volume pots. I was considering rigging up a switch setup to compare pots with but never got around to it.

Chops, what kind of car did you borrow? I've done this before too with cars and bikes of friends. Such a great way to experience new machines for free.