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Xiansheng 708B headphone tube amp - Page 7

post #91 of 413
9/27/06 at 4:48am


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post #92 of 413
9/27/06 at 6:22am

Moremore

More more up up...very interesting what are you doing right now!
Can you make the full photo inside again...please!
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post #93 of 413
9/28/06 at 2:17am

Parts Connexion

Well I finally decided on the parts for my PC order:

RIKEN carbon films for the input resistors and all the cathode bias resistors

Auricaps for the interstage coupling caps

Mundorf M-Caps for the power supply bypass caps

ALPS Blue Velvet potentiometer

I spent a bit more money than I wanted to, but I gotta take advantage of the sale right. Going to phone it in tomorrow at lunch.
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post #94 of 413
9/29/06 at 2:39am
Thread Starter 
Quote:
Originally Posted by Gradofan2
It's a bit confusing... is the E5 + BADA + SA5000's still the "best there is"... or is that now the Saturn + BADA + K701's... or what?

I know you've ranked your amps and gear for us... but... can you assign a relative point value to them (i.e. 10, 9, 8, etc.) to give us a sense of how great the difference is??? I mean is the BADA a 10, and the 708B a 6, and the Ming Da a 5, or what? I'm sure that would be helpful to a lot of us "vicarious audiophiles."

Also - do you know where a "vicarious audiophile" can pick up the CT Silver Reference II's for a bargain price (i.e. cheap)??? $550 for IC's is a bit ridiculous - no cable can possibly make that much difference - which is precisely why I have the CT Silver IC's.

Thanks,
GF2

First, let me correct a previous evaluation of the Sylvania JAN 6DJ8 or 6922 tube. They are slightly richer in tone than the RCA I recommended, but have slightly less detail and clarity. Some will prefer one and some the other, but they are good with the 708B.

The SA5000 was superior (to me) than the HD650 - particularly in detail, imaging, and instrument separation.

Then I got the K701, which not better than the SA5000 in some ways, was better overall than either the HD650 and SA5000. Yes the K701 is the best headphone currently available and produced. Now someone will remind me of this statement when I say, in the future, the HD700 are the best headphones.

Then people told me of trouble driving the K701s with some amps - never had this problem with the amps I owned.

The E5 remains a great high resolution CDP. More detail and beter imaging and image separation than the Rega Apollo, but the Apollo is not as lean in tone and is smoother. Then I got the Saturn which is better than either the E5 or the Apollo.

ICs are important. Have heard good things about DH Labs (very inexpensive) but never owned them. The TweekGeek CT Silver ICs are great for a low cost - can't beat them for the bucks. My Silver Reference II ICs are great for higher cost, and yes, give slightly more transparency than the CT Silvers. They are no longer available but you can buy them as the Acoustic zen Silver Reference II at Audiogon at times for $500 used but excellent. Are they worth $500? The WTB connectors alone cost $50 each ($200 total for the one meter pair of ICs). The audible improvement is definite but slight. Wolfe Audio uses connectors that cost maybe $200 or so each. He sold out his stock of 8 WTB connectors to me for use in making my ICs, as he went with the higher priced ones. I am sure his current cables are fantastic.

I still prefer the Bada PH12 - have blown mosfets from tube changing but these are cheap and not hard to replace. Some people will prefer other amps at the same or even lower price level.

The Chinese amps I have owned generally rank in sound quality with their price. But some may not agree. The MC66AE was very lush and enjoyable - great sound, but somewhat un-natural in timbre. Some people will prefer the rich timbre to a natural timbre. Some people will prefer the MC66AE to the Bada PH12 - I don't.

The 708B is great for $200 - but lacks the weighty fullness of the either the MC66AE or the Bada. The G&W T2.6F has great detail, imaging, and image separation, but has some leanness of tone (the Sylvania JAN 6922 tubes help here). The T2.6F reminds me of the Raptor but not quite as lean as the Raptor. The ASL MG III has some real good qualities which I did not explore in tube changes so I don't know this amp really well.

I could be happy with any of these amps - I just keep going back to the Bada as more natural and realistic overall. This is not a big difference and others will prefer some of the other amps that I have owned to the Bada.

So, did I fail to answer your question to the degree you expected?
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post #95 of 413
9/29/06 at 11:42am

That Helps...

That helps...

I realize it's moreless what you've said before... but, it seems to be a little more clearly articulated.

Although only the perspective of one reviewer, I think what really helps in such comparisons is a rating scale for various qualities - because it provides a relative context for differences (e.g. how much more leaness, or weight, bass, treble, soundstage, etc. 1 to 10 scale). A slight difference may be difficult to discern and may not justify a much higher price (e.g. between the CT Silver cables and the CT Silver Reference II cables, etc. - perhaps the CTS's are an 8 and the CTSR II's are a 10, etc.)

But... your clarification does provide some context and clarification.

Of course... I realize... in the end... the only way for others to judge... is to try each themselves.

Thanks!
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post #96 of 413
9/30/06 at 5:14am

Different Rectifier Tube

As we all know there are very few replacement choices when it come to the mini 6Z4 rectifier tube. Whereas the mini 6X4 has the normal range of NOS and current-production to chose from. The 6X4 uses the same heater voltage as the 6Z4, but two of the pins would need to be switched on the 708B's PCB to use it. The reason I'm posting this is that I'm going to design a new PCB to use the 6X4 instead and I'm curious if any other 708B owners here would be interested in going in on this with me to reduce the cost. I would prefer to get this professionally made for me somewhere instead of using prototyping board. I plan on reusing all the parts that are already on the stock PS board; the only change would be the rectifier tube. Let me know if you're interested.

Since the transformer is made for 110VAC instead of 120VAC , my heater voltage is running pretty high. I measure 7.54V instead of the proper 6.3V. I really don't want to shorten the life of my tubes, so now I really want to build a regulated DC heater supply for this amp. I'm looking into the various ways of doing this and all the pros/cons of each method. It would also be nice to build this with a "standby" setting to keep the heaters idling at ~4V to significantly reduce warm-up time and more importantly avoid both cathode poisoning and stripping. I would probably replace the push-button power switch with a 3 position rotary switch. The first position would be "Off", the second would be "Standby", and the third would be "On". This setup would avoid having to drill a hole for a second toggle and would eliminate turning things on in the wrong order.

It would be great to get both of these PCB's made together which is the route I will probably go.
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post #97 of 413
10/1/06 at 4:31am
Well I just hooked my 580's back directly to my soundcard out and I don't know if I like what the 708B has been doing to the sound. The amp does have better tone and much more impactful bass, but there is a harshness in the treble that fatigues me quite quickly, especially on cymbals. I don't have this problem with my soundcard out and I've listened through it for 8 hours straight many times before with very little fatigue. I'm not sure if it's the tubes I'm using or the actual circuit design itself. I still need to change the 6N3 for something better. The RCA 6922's help, but I imagine the gain tube would make a bigger difference. Can any 708 owners make a comment on there amps treble properties?
I really like what tubes do to the sound and I would love to get this amp sounding the way I think it ought to, but I'm just trying to figure out if it's worth it making a bunch of expensive mods to maybe get it there if it's not the tubes that are the problem. Should I just move on to a fundamentally better better design? Any comments from more experienced tube-headfiers?
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post #98 of 413
10/1/06 at 12:44pm
Quote:
Originally Posted by dcheming
As we all know there are very few replacement choices when it come to the mini 6Z4 rectifier tube. Whereas the mini 6X4 has the normal range of NOS and current-production to chose from. The 6X4 uses the same heater voltage as the 6Z4, but two of the pins would need to be switched on the 708B's PCB to use it. The reason I'm posting this is that I'm going to design a new PCB to use the 6X4 instead and I'm curious if any other 708B owners here would be interested in going in on this with me to reduce the cost. I would prefer to get this professionally made for me somewhere instead of using prototyping board. I plan on reusing all the parts that are already on the stock PS board; the only change would be the rectifier tube. Let me know if you're interested.
Unless you're willing to drill a hole in the top of the case and have a tube sticking out, you're going to need to mount the 6X4 horizontally (at least if you're going to use a Mullard). The 6X4 is a taller tube, and won't fit in the case. It's going to be a more complex operation than simply redoing the existing board with different pinouts.
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post #99 of 413
10/1/06 at 5:30pm
I don't think I'd be wanting to do those power supply mods myself, I've got about ten 6Z4s (no 6X4s) and my amp is running on 240V. Mostly planning cheaper mods as I wanted to spend my money on other gear.
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post #100 of 413
10/1/06 at 6:57pm
Thread Starter 
Quote:
Originally Posted by dcheming
Well I just hooked my 580's back directly to my soundcard out and I don't know if I like what the 708B has been doing to the sound. The amp does have better tone and much more impactful bass, but there is a harshness in the treble that fatigues me quite quickly, especially on cymbals. I don't have this problem with my soundcard out and I've listened through it for 8 hours straight many times before with very little fatigue. I'm not sure if it's the tubes I'm using or the actual circuit design itself. I still need to change the 6N3 for something better. The RCA 6922's help, but I imagine the gain tube would make a bigger difference. Can any 708 owners make a comment on there amps treble properties?
I really like what tubes do to the sound and I would love to get this amp sounding the way I think it ought to, but I'm just trying to figure out if it's worth it making a bunch of expensive mods to maybe get it there if it's not the tubes that are the problem. Should I just move on to a fundamentally better better design? Any comments from more experienced tube-headfiers?
Are you talking about the 708B unmodded?

Your soundcard may have some treble rolloff that reduces distortion from your digital source.

I changed my 6N3 stock tube for a Russian 6N3P EB and it seemed to have a slight improvement - not as much as I expected though and the improvement may have been just imagined - need more time to tell for sure. One odd thing is that the stock 6N3 has no markings on it at all - not sure it is a Chinese tube - though the other stock tubes are Chinese. The construction of the 6N3 that came with the amp looks like that of the Russian 6N3P EB.

Botom line: My stock 6N3 tube may in fact be a Russian 6N3P tube which is why it sounds close to (or the same as) the Russian 6N3P EB.

BTW - I tried 5 new 6N3P EB tubes I just got and three had hum problems. Others have noted hum problems with replacing the 6N3 with other tubes. Very unusual.

One fault of the 708B is some glare in the timbre of tones in the upper midrange and some harshness with high energy treble material. This is no problem most of the time - just with some CDs or some program material on a CD. Better caps could help here I believe.
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post #101 of 413
10/1/06 at 7:43pm
Thank guys for your replies. It's all too easy to get frustrated with audio equipment, and I definitely was last night.

The diagram that I saw for the 6X4 showed it being a 1/4" taller than the 6Z4. If I move the wires to the top of the PS PCB then I might be able to lower the board down enough to make it fit under the top cover. I might also be able to find a lower profile socket to gain a bit more clearance. I guess the best thing to do would be to just order a cheap 6X4 and check to see if I could make it work.

Yeah my 708B is pretty much stock right now. Just the signal wire and a pair of resistors have been changed. I don't think my sound card has any treble rolloff as I don't notice any on my monitors or when using the same HP directly from it.

The 6N3 in mine does have what looks like Chinese letters on it and also a 6N3-J designation under them. I have some other types on they way from my sister so I'll see how these sound instead. Hopefully there will be no hum.

The glare problem is not fully present on every song, but a few songs really are noticeably harsh. Makes me turn down the volume when it happens. I'm really hoping the caps that are on the way will help alleviate this. I guess my only option right now is to just sit and wait for the parts to get here and try them out. I am going to install them in steps instead of all at once to see if I can narrow down this glare to one part or area. I'll report my impressions when the parts get here next week. Man, waiting on mail-order sucks!
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post #102 of 413
10/1/06 at 8:48pm
Thread Starter 
I hope you will upgrade in stages and evaluate in each stage:

Stage one: most important basic upgrades - describe what these are and the results

Stage two: additional upgrades and describe per above

Stage three: whole hog suggestions


If you change out the 6Z4 for the 6X4 you need only drill a 6 mm hole on the top cover to allow the tube tip to clear - likely will extend not much above the level of the top - poses no electrical danger and ventilates the heat for better cooling.

I think this could improve the sound as the 6X4 rectifier is likley better, and rectifiers do indeed influence the sound quality even though some people say they shouldn't. I changed the Chinese rectifier tube in my home preamp to a NOS RCA 5Z4 and got an improvement, and then to a Ken Rad 5Z4 and got even more improvement.
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post #103 of 413
10/1/06 at 9:32pm
Quote:
Originally Posted by dcheming
The 6N3 in mine does have what looks like Chinese letters on it and also a 6N3-J designation under them. I have some other types on they way from my sister so I'll see how these sound instead. Hopefully there will be no hum.
All the tubes that came in my 708b except the 6Z4 have the same logo and are all labeled with the type code, i.e. 6N1, 6N3, 6N11. The original 6Z4 looked cloudy and old and had no markings on it. The extra 6Z4s I own look more like the others in the amp and have the same logo, these are made by Shuguang in China.
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post #104 of 413
10/2/06 at 12:54am
Well I just did an experiment with my input cable setup. My sound-card has balanced XLR outs and I've just been using cables that have the "hot" signal and the ground going to an RCA plug. I have some cheap in-line impedance converting transformers that convert bal XLR's to unbalanced RCA's. Well when I used these converters and a RCA cable to go to the 708, the hiss that I normally hear with nothing playing was reduced in level by about four time! These also seemed to help with the high frequency problems as well. However since they are cheap transformers they really colored the mids and made the bass extremely hollow sounding. Nevertheless, this has shown me that the impedance miss-match that I'm getting by using my simple XLR to RCA cables is causing a lot of problems in my setup. I should have known better!

So I'm going to need to either build a pair of active BAL-to-SE kits or use some nice transformers like Lundahls. I would much rather prefer to go with the transformers, but I think this route might cost too much. Can anybody here recommend a high quality active BAL/SE kit? Even some links to some schematics for a circuit would be helpful too.

Damn I wish I had a CD player to try the 708 out SE, but all I have is an X-Box which is way to loud when turned on.
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post #105 of 413
10/3/06 at 11:52pm

New Power Wire and Switch

Just finished putting in a 15 amp toggle switch and some 12ga power wire:











I also mounted the transformer on some 3/8" spacers to get more airflow underneath, but mostly did it because I think it looks better raised up a bit. I used stainless steel fasteners for this:



Like I said, I love upgrading things!
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