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I tried replacing the 6N3 with a russian 6N3P-EV(EB) but they increased the buzz and didn't improve the sound. Also tried replacing the 6n11's with two Sylvania JAN 6DJ8 but one channel was much louder than the other. Anyway they didn't seem to have a very big effect on the sound signature.
There's more info on the Xiang Sheng in this thread by the way if you hadn't seen it already: FS: Hornet RSA Modified
The Russian 6n23p-eb(ev) is supposed to be a good replacement for the 6n11 I read but my experience with the Sylvania 6DJ8 made me feel sound quality would not improve greatly from replacing the 6n11's.
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--------------------------------------------------- "Eagles may soar, but weasels don't get sucked into jet engines."
John Benfield
Welcome aboard, thanks for adding your mods and pics to this thread.
It's a shame that all the units seem to only have 110/220V transformers. Your measured heater voltages of 7.0-7.2V while on 240V are pretty much how mine where when on 120V.
I also was a bit surprised to see that this amp is not grounded. From what I gather they did this as a cheap way to prevent ground loop issues. I was hesitant to add a ground wire since I didn't know what effect it would have on the amp. Next time I fire up my soldering iron I'll properly ground it for piece of mind.
Correcting the B+ voltage is something I never got around to. Last time I checked it was at around 215V. I have to drive 80miles to get suitable resistors so it's been put it off long enough to have been forgotten about.
The stock phono sockets on my amp where undersized as well. New standard gold plated jacks are so cheap anyways I would of replaced them regardless.
The two electrolytic caps on my amp and on a few others where dented also. I wonder where Xiang Sheng gets their high-quality components.
From my limited tube rolling experience, changing the 6N3 tube seems to make more difference than the 6N11's, but I'd still recommend upgrading the 6N11's as well.
That's a nice little PCB for the pot. Definitely easier than soldering directly to the pins. My old stock pot was pretty bad on the balance issue. Also it seems like it was a linear pot which is why it would get loud super fast. Concerning the deafening hum when you plugged in your Senns, that's what I was worried about with grounding the chassis. I'll have to try it with the resister or maybe a ground loop breaker.
That sucks about the high prices on the Musicaps. At least SONIQS SAX are polypropylene. I want to step up to a film and foil cap eventually, either PP or polystyrene.
I don't think it's necessarily that your CD player has a loud output. The problem is that the gain of the XS is extremely high. There really isn't an easy way to lower the gain of this amp aside from building a potential divider on the input.
It looks like they used different signal wire in your amp. The stock stuff in mine had white insulation.
Welcome aboard, thanks for adding your mods and pics to this thread.
Thanks, no problem!
It's a shame that all the units seem to only have 110/220V transformers. Your measured heater voltages of 7.0-7.2V while on 240V are pretty much how mine where when on 120V.
I did ask the seller about this, and got the reply I expected - that it'll run on 240, which to be fair, it does. I used it for the first few weeks on a variac set at 220V, until I got the voltages back.
Correcting the B+ voltage is something I never got around to. Last time I checked it was at around 215V. I have to drive 80miles to get suitable resistors so it's been put it off long enough to have been forgotten about.
Doing electronics as a hobby in the UK has become so expensive recently. My local store has just closed after about 80years of service, they were great for finding all sorts of goodies. We have a Maplins, but that's turned into a toyshop. So, I'm left with the alternative of finding bits on ebay, or lashing out at least £30 per order with RS, Farnell or Rapid, often for a handful of resistors.
From my limited tube rolling experience, changing the 6N3 tube seems to make more difference than the 6N11's, but I'd still recommend upgrading the 6N11's as well.
...maybe I'll try that too?
That's a nice little PCB for the pot. Definitely easier than soldering directly to the pins. My old stock pot was pretty bad on the balance issue. Also it seems like it was a linear pot which is why it would get loud super fast. Concerning the deafening hum when you plugged in your Senns, that's what I was worried about with grounding the chassis. I'll have to try it with the resister or maybe a ground loop breaker.
The PCB machine is a useful bit of kit, but it can be a PITA to use!
It looks like they used different signal wire in your amp. The stock stuff in mine had white insulation.
I might change the signal wiring, and I'm also tempted to replace the PCB with the mains switch and headphone jack. For some reason I'm not too happy about them both being on the same PCB.
Something else I've been investigating with another project is putting a 120ohm NTC themister in series with the mains feed to the transformer. This should reduce the inital inrush current until the thermister is at running temperature. It'll need to be mounted in a ceramic terminal block, as it will probably run at about 110C. The only downside is that it will drop a few volts, so may need the heater/HT voltages sorting again.
I've now got a fluted 28mm aluminium knob to replace the plastic one, and finally fitted the cover back on it!
Looking at this page really brings back some fond memories, so looking forward to listening to my XS as I havent been home for quite a while.
I think the 6dj8 does have an impact on the sound, I uses the 6x4 with a slyvannia 5670(6n3) and 6dj8(6n11) and i believe that there is a sharper edge given to the music (if memory serves me correctly). although the sharpness was slowly tone down over time.
I was getting a lot of distortion and way too much gain from my 708B, so did an Internet search to see what might be out there and found this thread.
I have now done most of the mods recommended on this thread and am generally pleased with the results, although I have what I think is a better way of doing some parts of the process, although I also have a problem with (UK) 50 Hz mains cycle hum.
Hopefully these are not related
My main difference with the orthodoxy on this thread is that you can get transformers with multi-tapped primaries fairly easily over here. So in order to adjust the working voltage of the pre-amp from 220v to 240v (same applies to get US 120v to 110v) all you need to do is fit in a small (20 - 30VA) transformer, wire the input mains between the 240v and 0v connection and use the 220v tap and the 0v to feed the existing toroidal transformer in the pre-amp. There is comfortably enough space in the case to house such a transformer at the back next to the mains input. Attachment 10482
You need to rotate the PSU board 90 degrees (caps to the rear works best) and by slicing off a small portion of the rear of the audio board and jumpering a couple of severed connections, that can still be fitted on 3 of its 4 original mounting screws. Attachment 10488
This avoids the need to adjust the heater voltages for the valves with resistors and gets the main DC voltage to the right level.
I am trying to post some photos, but with a 25kB limit, I am having trouble; cosmetically my fully modified version looks pretty similar to the original, it just has better components more or less throughout. Attachment 10486
I have a much more detailed resolution version of the photo if anyone has an idea how or where to post it.
Apart from the extra transformer, another practical measure was to stick my soldering iron into the rear of the original volume control knob until the plastic of the mounting hole got a bit soggy, then rammed it firmly onto the ALPS pot and let the plastic re-set. You need to keep it a) straight and b) central, but really this worked like a charm and avoids the need to use nasty Radio Shack knobs. Attachment 10485
All the distortion has gone and the gain is now manageable. I can just about listen to the pre-amp output at full volume (it is still quite loud); on headphones, full volume is perfectly acceptable without risking inner ear damage.
I added an Earth (Ground) connection from the front panel and the case body to the Earth pin of the mains input (somebody on the thread did something similar). However, I ended up with very loud 50Hz mains hum and had to install an earth-lift switch at the rear to optionally connect or disconnect this. Attachment 10487
Even with the earth pin of the mains input totally disconnected from anything, I still get a fairly noticeable mains hum. I have not done anything to specifically Earth the ALPS Blue Velvet pot (I am not sure I know how I would do that, but I noticed some other posters had trouble in this area).
This is very interesting ........as I mentioned I've a small amount of hum on the right channel [left is silent] ....what appears to have made a considerable improvement was just changing the 6n3. The vol pot has made little or no difference to the hum level.
Not certain I like the extra transformer idea...20va seems rather small and could compromise the current capacity of the psu ....not that it won't work its just my experience that when you fit bigger tranny's things always sound better.
i used to have some hums after i XS recase project, but its gone after i added a earth and also short the gnd pin on the volume pot, not sure if it works for you but hope it helps.
Linear Mode
