Xiansheng 708B headphone tube amp - Page 9

Total in that pic was about $88. This was ordered from PC during the 15% off sale and we don't have sales tax here in OR(), so it would be a bit more than this in reality.

I'm doing this round of mods in stages and taking notes in between. The Auricaps went in first and then I listened for a hour and a half. These helped a lot with the treble harshness. Distorted guitars and cymbals were a lot more clear. They also seemed to tighten up the bass a bit, which surprised me. Overall the sound was more detailed, but also smoother which is a nice combo.

As of right now the Riken's are also in and I'm listening as I type. They seem to have brought a bit of an edge back to the treble unfortunately, but I want to give them some time to burn in more before I make more comments.

I'm going to wait a few days until I put the ALPS in to see what happens with the Riken's. I just realized that I'm almost out of solder! I need to drive to the nearest electronics store 30 miles away in Salem this weekend to get more.

So far in this entire modding project I would say the Auricaps have made the biggest difference. My recommendations at this point in the game would be to replace the RCA's, the signal wiring, the inter-stage coupling caps, and the tubes. For me that totals to about $42 in parts. All the other stuff that I've done so far I can't say made a worthwhile difference. I'll post further impressions in time.

Thanks DCheming. Wow seems that this little amp after some extensive mods gonna cost a lot!

Just finished putting everything in. First things first; the three part swaps that made the biggest difference were the ALPS potentiometer, the Auricap inter-stage capacitors, and the ELNA headphone output capacitors.

I feel the ALPS made the most noticeable difference, but the Auricaps were in as well at that point, so some of the improvement was the combination of the two. The ALPS helped a lot not only with overall resolution, but also with soundstage clarity. The instruments are easier to locate, sound more natural, and on songs that have little details such as echos that are way off to the side are much more audible now. Reverb sounds much sweeter too.

Both the Auricaps and the ELNA's made the sound more detailed and smoother. Distorted electric guitars and cymbals are way less harsh than they were before. The Auricaps seemed to tighten up the bass some too.

I'm pretty happy with how it's sounding right now. This is what I spent on the parts that I'd recommend for the biggest improvement:

ALPS 100k - $18 ea
Auricap 0.22uF - $15 pr


I got the ELNA 100uF 250V caps for about $3 a piece. I'm using two in parallel for each channel. I also swapped the Riken input resistors out for NTE metal films. I liked the more organic sound of the Riken carbon films, but they where adding an edge to the treble which was bothering me. So I'd either leave in the stock input resistors or go with some nice metal films.

I also changed the 22uF power supply bypass electrolytics for some 33uF Gemcons. I did this because the caps that came with my amp where dented and scratched almost through the aluminum case. I didn't notice any improvement with these in though.

I also rotated the power supply board around 180 degrees. This works out better for wiring and I think it makes the layout of the inside look more balanced. I re-soldered all the power wires to the top of the boards instead of underneath.

Be aware that the ALPS is not a direct drop in. It will require the mounting hole to be enlarged slightly. I did this carefully with a round file because I didn't have the proper size drill bit. Also the little stub that prevents the pots body from rotating is further out than the one on the stock pot, so a new hole will have to be drilled for this. I mounted my ALPS with the pins facing up, so this little hole was drilled on the right side of the shaft.

So overall the clarity has significantly improved, the sound is a lot smoother, and most of the harshness is gone. I will be listening all night so I'll see how fatigue compares to how it used to be. With the two crucial mods I mention above as well as new headphone output caps, RCA jacks, signal wiring, and tubes, one can get a huge improvement in sound for around $70. This just reiterates to me how important quality components are, especially when listening with something as sensitive as headphones.

That's some gorgeous work. Next might as well try building one from scratch!

I'm awaiting some new tubes from drarthurwells, will drop those in ASA they arrive. Other than that, I've come to the painful realization that my schedule won't allow for too much DIY goodness in the immediate future....

Two new Russian 6N23P-EB and a Soviet-era 6N3P-EB just rolled in, and hot damn are they an improvement. My current setup has more weaknesses than I can count, so I was worried that I wouldn't notice a difference. Boy, was I wrong. The amp is now more musical, faster, more detailed, and more refined, especially in the treble. I don't have the advanced audiophile vocabulary that some of you folks do, so the best way I can describe it is that stock the sound came at you and with the new tubes it surrounds you.

Thanks to Doc Wells for the tubes. Now to (eventually) replace some of the other parts!

Man, I really need to replace the cheap 6N3 in my amp. It's extremely microphonic and I'm getting a a high pitched whining sound sometimes. I put together a cheap isolation table using two 2"x2"x12" step-stones with a 12" inner-tube between them and a 13"x13" piece of carpet to go under the bottom stone. This helps a lot with the flimsy computer desk that I'm using right now. So you got the 6N3P-EB from drarthurwells too? I need to get some kind of replacement asap.

I'm going to take the 708B to an audio shop down the street and listen to it with a NAD C542 this weekend. I want to see how good it sounds with a nice source feeding it. I've been letting it play as much as possible these last couple days to burn in all the new parts and I'm hoping to get another 25 to 35 hours on it before listening to the NAD.

Nugget, it's a shame you don't live closer to me, I'd be more than happy to do some surgery on your amp as I have quite a bit of free time right now. I'm glad to hear you got an nice improvement with the new tubes.

Yeah, I'm waiting for a chance to break out the soldering iron, but I just don't see it happening for a while. As my wife put it when I was swapping the tubes last night, and managed to short a charged capacitor with a piece of the stock bent-wire "tube-restraining-system" leading to a loud pop, "Why are you always trying to break things or kill yourself?"

I didn't have any microphonics problems, but one of the stock 6922s had a crackling problem at anything approaching higher volumes. Very noticeable in quieter passages, completely destroying the dynamics of the music.

I did the same thing with one of the bent-wire restrainers when I first put the tubes back in and got a big spark. I just took them all out after that, but I'll probably install them back in when I finally put the cover back on.

dcheming, may I ask what were the original caps and resistors that were inside the 708b?

Robfow, all the resistors that I've replaced were just cheap, generic metal-film types; 1k for the input, 1k for the 6N3 cathode bias, and 10R for the headphone jack.

The power supply bypass caps were SHL 22uF 400V electrolytics.

The interstage coupling caps were WIMA 0.22uF 400V metallized polyester.

The preamp output also uses these exact same WIMA caps too.

The headphone output used KME 150uF 200V electrolytics.

The volume pot was a cheap WL 100k carbon type.

Thanks dcheming. I'm deciding what to get to replace those. I bought mine second hand and the previous owner had already replaced the volume pot with a Alps 100k.

Hi guys, I am now currently modding my Xiang Sheng, after hugely being motivated by what you guys had done.

I am a real newbie to this, and was wondering if any of you have the schematic for Xiang Sheng.

Appreciate it a lot. Thanks!

zer061zer0, I do have a schematic drawn out, but I don't have a scanner. I could try to take a picture of it and see if it is readable. The 708B uses pretty much the same layout as the Morgan Jones amp, but most of the component values are different. Here's the link to the MJ amp for reference:

http://www.headwize.com/projects/sho...=cmoy5_prj.htm

I'm pretty happy now with the overall sound I'm getting from the amp. I still need to swap the 6N3 though. I just picked up a NAD C521BEE cd player this weekend and I'm going to mod it of course. I just downloaded the service manual to help with that. The sound of this player is not bad, but I know it can do better. So this will be an on-going project these next few weeks.

It will be nice to have someone else do some mods to the 708B also to get a second opinion. If you have any questions I might be able help and I have a ton of pics that I'd be able to use to help explain things with. So what are you thinking of doing first?

Thanks Dcheming! I would appreciate that greatly!

Actually, I have not done any modding to my 708B. I do not have any experience in DIY modding, and have no background in electronics.

I do have some one who is helping me with my modding. Was thinking of changing some of the in and output caps. Also, my right channel output suddenly went kaput yesterday, so i will also be changing the RCA plugs for it? Would like to change the on/off switch to maybe a solid toggle switch, and some of the internal wires too.