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Old 31st May 2011, 10:37 PM   #1
tony Ma is offline tony Ma  United States
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Default Mods Xiang Sheng 728A

Hi all,

I just want input for this Xiang Sheng 728A I want to mods it
This amp using 12AT7×2pcs, 12AU7×2pcs, 6Z4×2pcs
My questions should I change
  • Tube to brand telfunken / mullard or any suggestions
  • Upgrading Capacitor? Which one I should upgrade
tks
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File Type: jpg 728 Schematic.jpg (56.6 KB, 601 views)
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Old 22nd June 2012, 03:03 AM   #2
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Hi Tony,

This unit is very very popular in China. It sells around 15 units a month. However, it seems that it hasn't really made its way among foreigners.
I just ordered mine yesterday and I am going to HK to pick it up next week.
Did you find any info with regards to mods? By speaking with the factory I understand that they have already improved a lot of the weak components from the 1 st version (the one from 2006) in the new model (including the tubes from 6N1 to 12AT7).
The lady from the factory said that their clients are actually quite happy with the stock tubes.

FYI, these are a few of the tubes that the unit can cope with (according to them):
12AT7 can be replaced with ECC81, 6201, 12AT7GT, etc.
12AU7 can be replaced with ECC82, 6N10, 6189, 12AU7GT, etc.

Did you try any other tube? Any mods?

Happy with the unit?

Thanks,
Serge
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Old 23rd June 2012, 03:09 AM   #3
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I stumbled upon this unit. I am trying to not buy it! Here is a good review but in Spanish. Perhaps Google translate will help. Also in that thread, is a link to a really thorough upgrade of a similar unit...

Análisis de un amplificador chino
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Old 6th October 2016, 04:57 AM   #4
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Default PARAGON AUDIO (FRANCIS JANSZ)

Quote:
Originally Posted by sergedc View Post
Hi Tony,

This unit is very very popular in China. It sells around 15 units a month. However, it seems that it hasn't really made its way among foreigners.
I just ordered mine yesterday and I am going to HK to pick it up next week.
Did you find any info with regards to mods? By speaking with the factory I understand that they have already improved a lot of the weak components from the 1 st version (the one from 2006) in the new model (including the tubes from 6N1 to 12AT7).
The lady from the factory said that their clients are actually quite happy with the stock tubes.

FYI, these are a few of the tubes that the unit can cope with (according to them):
12AT7 can be replaced with ECC81, 6201, 12AT7GT, etc.
12AU7 can be replaced with ECC82, 6N10, 6189, 12AU7GT, etc.

Did you try any other tube? Any mods?

Happy with the unit?

Thanks,
Serge
Dear SERGE,
I have bought the XIANG SHENG DAC CONVERTER, And was very happy with it and Compared it with THE BRITISH MADE MUSICAL FIDELITY and THE MAKINGSTOCH DAC, I believe that it sounded a little better in the MIDRANGE And lacked a little in The Bottom end, But Value for money ALL in ALL it is Well Built and Very Pleasent on Hearing test We had 10 Listerners all blind folded, when conducting the listening test, 6 out of 10 Prefered THE DAC From XIANG SHENG, 4 out of Ten commented that it was lacking a bit on the Bottom End, 7 out of Ten Loved The High's
, and after running several test , 7 out of 10 Stated that they will Buy The Same DAC Converter. 3 out of 10 Immediately placed orders From MR: YOUNG LEE. and 3 Out of 10 Also placed orders FOR THE DAC and The 728 A Pre AMP That Includes. me, as I just placed my order on the 5/10/16, and should get delivery in around 10 working days. Once I get my unit I will first try it for a few months before Replacing The Better Tubes and Changing The Caps to Same Value Caps with AUDYN CAPS, and also Change The OUTPUT Wires With SOLID CORE TREATED WIRES. as advised by my Technician, I believe this will make this unit sound great and could be rated with Pre Amps that Cost around $:3,500 to around $4,500, And all in all This Pre AMP can be bought for about $375 USD and The upGrade could Cost Around $ 230, USD Total Cost for a Good Sounding PRE AMP will be around $ 605 USD, in comparission to Spending $ around $:4,000,
I personelly will be Happy to spend $:605 instead of Spending $4,000 To Get The same Results.
I think that This Pre amp is a Very good buy.
Kind Rgds
Francis Jansz
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Old 28th October 2016, 07:07 AM   #5
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I Just Got Delivery of My XIANG SHENG 728 A PRE AMP. I have just opened the Box and Noticed That There are 2 OUTPUT LINES ON The BACK PANEL 1 HIGH OUTPUT and 1 LOW Output, THE ADMIN OFFICER has Advised me That I Can Connect The HIGH FULL SPECTRUM Iine Out to My LUXMAN A 2003 3 WAY all TUBE ACTIVE CROSSOVER INPUT.
AND I can Also Connect The PRE AMP LOW OUTPUT Line To My POWERED SUBWOOFER and Both Outputs WILL Work Safely without any Signal Loss.
I was also Told That This PRE amp is Not in CLASS A Operation, Now I would like to know if There is ANY MODIFICATIONS THAT CAN BE DONE TO RUN IT IN CLASS A OPERATION. if So I would like to know what alterations i will have to do by a quallified technician.
This Will help me to get the results i need .
Kind Rgds
Francis Jansz
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Old 28th October 2016, 07:12 AM   #6
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Default fRANCIS jANSZ

How can I Modify The Xiang Sheng 728 A Pre Amp to Operate in CLASS A .
Please Advise of What Modifications are needed.
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Old 14th January 2017, 11:23 PM   #7
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Quote:
Originally Posted by Francis Jansz View Post
Dear SERGE,
I have bought the XIANG SHENG DAC CONVERTER, And was very happy with it and Compared it with THE BRITISH MADE MUSICAL FIDELITY and THE MAKINGSTOCH DAC, I believe that it sounded a little better in the MIDRANGE And lacked a little in The Bottom end, But Value for money ALL in ALL it is Well Built and Very Pleasent on Hearing test We had 10 Listerners all blind folded, when conducting the listening test, 6 out of 10 Prefered THE DAC From XIANG SHENG, 4 out of Ten commented that it was lacking a bit on the Bottom End, 7 out of Ten Loved The High's
, and after running several test , 7 out of 10 Stated that they will Buy The Same DAC Converter. 3 out of 10 Immediately placed orders From MR: YOUNG LEE. and 3 Out of 10 Also placed orders FOR THE DAC and The 728 A Pre AMP That Includes. me, as I just placed my order on the 5/10/16, and should get delivery in around 10 working days. Once I get my unit I will first try it for a few months before Replacing The Better Tubes and Changing The Caps to Same Value Caps with AUDYN CAPS, and also Change The OUTPUT Wires With SOLID CORE TREATED WIRES. as advised by my Technician, I believe this will make this unit sound great and could be rated with Pre Amps that Cost around $:3,500 to around $4,500, And all in all This Pre AMP can be bought for about $375 USD and The upGrade could Cost Around $ 230, USD Total Cost for a Good Sounding PRE AMP will be around $ 605 USD, in comparission to Spending $ around $:4,000,
I personelly will be Happy to spend $:605 instead of Spending $4,000 To Get The same Results.
I think that This Pre amp is a Very good buy.
Kind Rgds
Francis Jansz
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Old 14th January 2017, 11:32 PM   #8
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Dear Friend,
I took your ADVISE and Bought the XIANG SHENG 728 A Pre AMP, My Technician Checked it out and Stated that This Pre Amp is in CLASS B and not in CLASS A, Please inform me if This is Correct, I have just Connecting it to my System and it Sounds O K for now, Once I use it for a Few Months, I intend Replacing The Caps to The AUDYN Caps and Intend Replacing The OUTPUT WIRES to The Solid Core Wires as Recommended by you. , Should this be a Class B Pre AMP what do I have to Change to make it Run in CLASS A, Your thoughts will be Appreciated, and my Technician was Also not Happy with The POWER SUPPLY on This Pre Amp, I would like your Comments my Friend,
Regards
Francis Jansz
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Old 15th January 2017, 06:36 PM   #9
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I would very much hope that some of the issues brought up here have meanwhile been fixed. The original design as of about 5 years ago (I guess) appears to have been very flawed... undocumented built-in (non-bypassable?) loudness, high output impedance, excessive rectifier and SRPP tube wear, potentially out-of-spec heater voltage depending on what your line voltage is. And it looks like they used heaps of old carbon composition resistors that have not aged well. I agree, no amount of voodoo parts would save this mess.

Since you have a tech at hand, I suggest you have him check all the issues brought up, including the out-of-spec resistors. Maybe he can also produce something resembling a legible, complete schematic - at which point it should also be possible to decide whether the circuit really operates in Class B anywhere, though TBH I rather doubt it. It just doesn't make much sense for a tube preamp.

Chinese audio manufacturers have improved a lot in recent times, and with the 2 outputs it seems that several changes have been implemented, so it is quite possible that the current design is actually OK... but I'd really want to verify that. The original design seemed aimed primarily at gullible audiophools on the hunt for a "bargain". Spectacular...ly bad.

Someone should poke a moderator to have this moved over to Tubes / Valves.
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Old 17th February 2017, 06:03 AM   #10
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tube preamps run in class A. Class B means part of the time the tube does not conduct,
as in push-pull.
hi/lo needs defining - is this hi voltage output AND low voltage output OR
high freq output and low freq output. my guess is the former.
in any case, you are feeding it to a cross over so you don't need both.
the circuit in the OP is not totally correct - it shows only one output.
there is nothing wrong with the power supply.
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