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Xiansheng 708B headphone tube amp - Page 12

post #166 of 413
So how much sound improvement should I get out of this? The total so far is $153.65 not including the ELNA caps that I need to get from you. I am debating if this is worth it since the amp cost about the same price.

Please pm so I can get those ELNA from you.

Thanks!
post #167 of 413
You really don't have to do everything mentioned to improve the sound. I feel that the two biggest improvements were the ALPS pot and the Auricaps.

I've put about $110 worth of parts in mine and don't regret doing so. A few of these where just for cosmetic reasons, but if you just want to get the biggest improvement per dollar spent then maybe you could just start with the important stuff first like the pot, resistors, wire, RCA jacks, headphone output caps, and the interstage caps. These are the weakest links and should be around $80 total. I know that this is a good fraction of the cost of the amp, but one of the reasons why the 708B is so cheap is due to the low cost of the internals. You can always just do this in small steps to see if you think it's worth it.

If you measure a low DC output on your source then you can get rid of the input caps completely. This is a gamble though because your source might develop higher DC someday and that would then destroy your cans, but the best cap is no cap.
post #168 of 413
3 Hours and a six pack later...I've finally added the input selector switch. I just went with a GC 3PDT mini toggle switch instead of the TOCOS one I was planning on using; I didn't want to wait two more weeks for shipping. All I have to do now is order a 1/4"-40 tap from ICS Cutting Tools and then I'll be able to mount the switch underneath the volume knob.





This was by far the best mod I've done so far since I go back and forth between my CD player and computer/Xbox daily.
post #169 of 413
Quote:
Originally Posted by dcheming View Post
3 Hours and a six pack later...I've finally added the input selector switch. I just went with a GC 3PDT mini toggle switch instead of the TOCOS one I was planning on using; I didn't want to wait two more weeks for shipping. All I have to do now is order a 1/4"-40 tap from ICS Cutting Tools and then I'll be able to mount the switch underneath the volume knob.





This was by far the best mod I've done so far since I go back and forth between my CD player and computer/Xbox daily.

Hi Dcheming,

You have got some serious mod over there. Was wondering if for the volume knob, is there any other option besides going for a blue velvet, i figured that i might spoilt the stuff with my half past six skills on the machine.

Would also like to check with you if u have any idea of this amp also by Xiangsheng, the H-02A.
post #170 of 413
Yeah I guess the list of mods is getting fairly big.

The Blue Velvet is a good deal for $18, but you can surely do better and there is enough space to use pretty much anything. The ALPS Black Beauty would probably be better (if you can find one), not sure though as I've never used one. A TKD CP2511 would be nice too. Above these would be the various stepped attenuators, but I would never put something that nice in a cheap amp like the 708B.

The Xiang Sheng H-02A looks interesting being a 2×30W hybrid amplifier, but I'm not familiar with it though. How much does it cost? Considering the low quality parts and the 110v transformers used in XS equipment, I'd pass personally. I would much rather build something like a Charlize amp kit with quality parts instead.
post #171 of 413
Thread Starter 
I would love to hear your modded 708B - bet it is terrific.
post #172 of 413
You should look for one of the fake ALPS stepped attenuators. One came in my amp, and although I would have much rathered a real one I dont think you can argue much with its ability to preform.
post #173 of 413
Quote:
Originally Posted by drarthurwells View Post
I would love to hear your modded 708B - bet it is terrific.
Well if we ever run into each other at a meet, I'm bringing it for sure.
post #174 of 413
Quote:
Originally Posted by dcheming View Post
Yeah I guess the list of mods is getting fairly big.

The Blue Velvet is a good deal for $18, but you can surely do better and there is enough space to use pretty much anything. The ALPS Black Beauty would probably be better (if you can find one), not sure though as I've never used one. A TKD CP2511 would be nice too. Above these would be the various stepped attenuators, but I would never put something that nice in a cheap amp like the 708B.

The Xiang Sheng H-02A looks interesting being a 2×30W hybrid amplifier, but I'm not familiar with it though. How much does it cost? Considering the low quality parts and the 110v transformers used in XS equipment, I'd pass personally. I would much rather build something like a Charlize amp kit with quality parts instead.

Its cost slightly lesser then the 708B, but its sound rather bad. I just gotten mine recently, cos a frd brought it in for me. its almost immediate after a few days of listenning i started changing some parts. Yes, the Xiangsheng products are utilising a lot of cheap parts, even the caps looks used.

I am again modding my 708B after having successful modded some stuff recently. The below are some of the mods that a frd of mine did for me:
some caps change to polyproplene ones, and resistor change



as well as tubes rolling




Will proceed to some 2nd stage mod myself soon...
post #175 of 413
Some work in progress pictures, ahahhaaaa....



dcheming, i might need ur help in areas such as recabling, changing the headphone out, on/off swtich and the volume pot.

Do have the model no. of the swtichcraft headphone out?

I would also like to know what is a good value for the powersupply caps(the one with the rectifier) to go up to.
The default ones are rated at 330uf/450v, and i am thinking of increasing te value, i did the same with the H-02A and did hear some improvement, I would need to know what a range i can go up to for the XS708B.

As for the other ecaps in the other areas, i am thinking of changing them to better ones or maybe higher value ones as well. what do u thinking will be a good and safe value to go up to. Are Rubycon ecaps good enough, cos the high voltage caps are quite difficult to find over here on my side.

Lastly can i also request to have a picture of the wiring to the ur volume pot, might be using another pot with 6 poles but i am quite unsure abt the connections. Same goes to the connections to the on/off swtich and headphone jack.

Many thanks in advance..

Regards,
Marcus
post #176 of 413
That doesn't surprise me that the H-02A sounds bad. It might have some potential, but I don't know if it would even be worth buying considering the overall low quality of everything inside XS amps. I'm also starting to think that they must utilize used parts. The stock RCA jacks on mine where horrendous, most of the ecaps were dented and scratched, and a lot of the resistors are chipped and scratched.

Those Vishay caps look nice! They're massive.

What type of resistors did you use?

I really want to try some Fairchild Stealth diodes in the PS soon.

I don't know if I'd change the values of the ecaps. I would be worried about how that would affect the circuit. If anything I'd just upgrade their quality, but use the same uF value. Maybe someone more knowledgeable can comment on this.

Which Rubycon series are you referring too? They make some excellent ecaps in a variety of series, but they are mainly lower voltage it seems. For the two PS ecaps (the big 330uF and the 33uf) you can use whatever you want as long as it's rated for 450v. Nichicon, Xicon, Vishay/Sprague, United Chemi-Con, and Mallory all offer caps in both these values rated at 450v and are available from places like Mouser.

Unfortunately the Switchcraft 1/4" jack doesn't have a part number on it, but as long as it will fit through the 8mm front panel you can use whatever. I'll try to find out the PN for it.

The pin-out for the volume pot will depend on which one you use. The only wiring diagram I have is the one that came with my ALPS RK27. When you finally get one I'll help you figure out how to hook it up properly.

For the switch I went with a GC #35-024 On-On 3PDT mini toggle. I think the easiest way to explain the wiring procedure would be to draw some pictures so give me some time. It's not hard at all, just hard to describe; a picture is worth a 1000 words right?

Do you have a PayPal account Marcus? If you'll pay shipping I could send you a small parcel containing the harder to find parts like the ELNA caps, the HV ecaps, and the TRS jack. I could also include a GC switch and the cheap NTE resistors for the PS if you'd like. PM me if you're interested.
post #177 of 413
Here are the labeled pics to show how to hook up the input selecting toggle switch.





I think that this is pretty self-explanatory but I'll write it out anyways:
L1 is the left channel of input 1.
G1 is the ground of input 1.
R1 is the right channel of input 1.

L2 is the left channel of input 2.
G2 is the ground of input 2.
R2 is the right channel of input 2.

L is the selected left "output" to the volume pot.
G is the selected ground to the volume pot.
R is the selected right "output" to the volume pot.

Assuming that you'll be mounting it on the front panel, when the handle is to the left this will be input 1 if you wire everything as it's labeled in the two pics. Honestly you could probably just use a 2PDT switch and make the grounds of both inputs common. I wanted to avoid any possibility of ground loops or crosstalk between sources so I opted to switch between the grounds as well.
post #178 of 413
Hi Dcheming,

Thanks for the really informative picture. This really helps a lot. I just saw a similar swtich the other day and I guess i will be getting it to form the 2nd pair of RCA input.

I also used some cat5e cables, teflon coated i think, but i am thinking of using some 24awg silver plated wires also teflon coated, for the grounding of the rca and and perhaps other ground for other areas as well. I cant remember where i read that silver plated cables actuallly helps in a faster discharge resulting in some improvement which i cannot recall, not sure if u could verify this.

Will be posting some pics of what i have done so far soon....
post #179 of 413
Some pictures of the parts removed.





Detaching pcb for replacement.






Will have to check with Dcheming, the purpose of this wire connecting to the 2 hooks holding onto the wire holding onto the tubes, it seems that they are giving some charge and there are some sparks when i am disconnecting some parts nearby, have the same thing happening when i was tube rolling the last time too. Just a quick one and luckily nothing was shorted.

post #180 of 413
Hi Dcheming,

When changing the power cables, did u just cut of at one end and joint it to the thicker power cables by means of soldering and cover them up with the heat shrink?
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