Modifying the Xiang Sheng 708B [56K!!!!] - Page 2 - Head-Fi: Covering Headphones, Earphones and Portable Audio

penguindude · 02-12-2007, 09:58 PM

Hey dcheming, how is the ALPS 100kax2 potentiometer treating you? Is it much better than the stock one?

Nvm, already answered.

zer061zer0 · 02-13-2007, 03:06 AM

Originally Posted by dcheming

Hey laxx,

So do you know how to solder and desolder? This amp is easy to mod since it has so much room inside. You could just start with the simple mods like the 4 input/output resistors and the 2 coupling caps. If you plan on working inside this amp at all I'd highly recommend adding the bleeder resistors to the big 330uF filter caps first for safety reasons. I'll help you out as much as I can with your mods if you run into any problems or if you have any questions.

zer061zer0,

The full list of all the resistors and their wattage ratings are near the top of post# 1 right under the schematic. For R102,202 I'd recommend using a 5 watt non-inductive wire-wound (NIWW) type since they have very low noise. Vishay Dale makes a 33K 5W in their CW-5 series, but I haven't found a source for these yet over here. All I've been able to find in 33K are some 12W Mills which are way to big, but you might have better luck finding a 33K 5W NIWW where you live.

Oops sorry i miss that..thanks anyway

Miller-8 · 02-14-2007, 09:06 AM

Does removing the the front tube improve sound?

dcheming · 02-15-2007, 01:43 AM

I didn't notice any improvement in sound when I took mine out. The 6N1 in the front window shares it's heater supply with the 6Z4 rectifier tube only and the three audio tubes have there own dedicated heater winding.

dcheming · 02-15-2007, 01:56 AM

I finally picked up a 6X4 rectifier tube today. I was planning on building an adapter to use this tube in place of the 6Z4, but they didn't have any 7-pin sockets there. Since I really want to try this much better tube today I've decided to just modify the socket pins on the PS board itself. This mod is pretty easy since the two pins that need to be swapped are in the perfect place to do so. The only thing that I'm worried about is that the heater in the 6X4 draws 600mA which is right at the limit of what the heater winding is rated for. Hopefully the transformer can handle it.

I'll post my listening impressions later on tonight when I get it done.

zer061zer0 · 02-15-2007, 02:05 AM

Originally Posted by dcheming

I finally picked up a 6X4 rectifier tube today. I was planning on building an adapter to use this tube in place of the 6Z4, but they didn't have any 7-pin sockets there. Since I really want to try this much better tube today I've decided to just modify the socket pins on the PS board itself. This mod is pretty easy since the two pins that need to be swapped are in the perfect place to do so. The only thing that I'm worried about is that the heater in the 6X4 draws 600mA which is right at the limit of what the heater winding is rated for. Hopefully the transformer can handle it.

I'll post my listening impressions later on tonight when I get it done.

Pictures pictures pictures

Chops · 02-15-2007, 02:46 AM

Cool dcheming! I hope that transformer doesn't give you any problems. I'd really hate to hear that it burned up or something.

BTW, look how serious I'm getting with all of this modding! Donated by my father who has about half a dozen different types of these MMs.

Chops · 02-15-2007, 02:54 AM

And the various clip-on tips for the probes.

jink · 02-15-2007, 06:55 AM

What an amazing thread, you are a wonderful tutorial writer! I did not understand about 70% of the posts, but the pictures are nothing short of incredible. What a high level of detail, this amp doesn't have anything left to improve now! Thanks for the good read. =)

That must sound amazing, the best amp I have heard is a go-vibe. I have yet to spend the money to experience a tube amp or a spendy solid state amp.

dcheming · 02-15-2007, 10:02 AM

Thanks for the kind words guys.

I was worried that I posted too many pics, but this page doesn't take that long at all to load, with a cable connection at least. My goal with this thread is to make it as easy as possible for anyone looking to mod this amp to find the info that they need. I still have a few more mods that I want to do so I'll be adding additional sections as those progress. If anyone needs more detailed info on what I've already done or if you just have a question feel free to ask.

zer061zer0,

I didn't get a chance to play around with the new rectifier since I was working on another project all night. I'm definitely doing it tomorrow though and I'll be posting detailed pics of the mod procedure to use the 6X4.

Chops,

If the transformer does burn up then I'll have to get one of those Hammonds that we were talking about earlier.

That's a pretty sweet DMM you got there; blows away my cheap Velleman for sure. You're lucky your dad has so many of them. Even though it's huge I prefer them that way since you can stack it neatly on your workbench shelf as you get more test equipment later.

I also picked up a bunch of different valued 5W and 10W resistors from Norvac today. After I get the 6X4 up and running tomorrow I'm going to play around with adjusting the heater voltage for the audio tubes some more. I'm sure the heater voltage feeding the 6X4 will be too high also so I'll adjust it as well.