Muzishare X7: Repair Diagnostics and Initial Impressions

[@califmike2003]

Muzishare makes a good quality and sounding amps.

[@cameronwilson8561]

So glad you are doing a video on this amp. I bought one about two years ago, so far been pretty happy with it. One of the stock KT88s died a few months into using it, but I was planning on replacing them anyway. I have also read on many forums that the bias switch can be problematic. Hope you make a full series on this amp too. 👍

[@SkunkieDesignsElectronics]

Maybe I should look for a replacement for that too then if others found them to be a problem?

[@normbal]

Not that I’m considering buying one, but, having gone through your mods for my R8 - WOW! This is going to be fun to just watch and learn. Dying to know which pots you go for to replace the bias trimmers. Thanks.

[@jamesparrish2928]

Great video Skunkie! Learning a lot as we go through this one.

[@andrewp9725]

Awesome! Can’t wait to see this series evolve keep up the great work!

[@SkunkieDesignsElectronics]

Parts are on the way. The bias pot upgrades should work on an R8 too and I have a plan to make them less sensitive.

[@frankgeeraerts6243]

Yes Steph many of these amplifiers suffer from commercial implications/limitations . Low quality bias pots ( they will go wrong at a given day ) ..........no protection when they go wrong, operation voltages of power supply capacitors to low at normal line voltages and line AC can swing even above the nominal voltage ! High quality ( pro use ) do often have also a marking on the capacitor , for example : 500 V /550 V surge ! Exessive long wiring ( often low quality wires ) on inputs to selector etc Another observation are the use of gridstoppers (witch is good) but the gridstopper must be mounted direcitly to to the pinout of the gid of the tube , resistor solderd with shortest lead as possible direct to the pin . ( old school practice ) When working with a tube rectifier one must avoid hot switching , so to switch this one on and of when testing , the rectifier ( for the input tubes I suppose ) must be pulled out or it must cool down between on/off switching . After correctingrepair/modificatins ..........the final pricetag of buing such an amplifier will be substantial higher than the initial one when purchased , .........but it can also be fun to do a better job than the factory build stock one...........and as you ecperienced when testing the output tubes who are always expensive , the need to buy garanteed new quality matched tubes and the temptation / curiosity of tube rolling as well as considering the purchase of rare and very expensive nos noval tubes ............. In the end it is a choice ..........when you are aware wht itb means to buy an amplifier on a budget and why some higher quality amplifiers are more expensive.......but when you like doing things your own way it may be a good starting point to do a better job like you practice as long as someone is aware of vall the implications it will have on his budget .. Have a very nice day and thank youfor the nice and informative upload.

[@flyingmattyboy]

Looking forward to see how this goes Skunkie. Thanks for the excellent videos.

[@cobar5342]

Great dissection Stephe

[@MD-wk3gj]

Glad to hear so many positive comments from Stephe about this amp. I wanted either the Willsenson R8 or R300 based on other reviews and honestly prefer the look but as someone with zero experience doing the repairs/upgrades I don’t think that is wise. So far this one seems to be a winner and for the money might be the best deal currently in the market…am I wrong Stephe? I will say listening to the small suggestions by Stephe on doing this or that better I compare it to any contractor I’ve ever met. They always have their opinions. It may be right or not but typically small suggestions are preferences or ideal upgrades. There is nothing wrong with that and I’ve noticed Stephe tends to be reasonable at clarifying “I’d rather…” or something like that.

[@Crmsnraider]

Another great video Skunkie! Looking forward to this, I keep learning new things here *thumbsup*

[@jamesmcmillan6350]

I demoed the R8 and the Muzishare and have had it for 2 years. I rolled my tubes for the rectifier I chose Mullurd reissue GZ34's, For preamp a NOS Tungram 12ax7 and 2 GE five star 5814a's and I replaced the KT-88's with 4 matched Gold Lion Reissues .... My wife still thinks I paid over 3500 for it. By the way the headphone amp is very good and I do use it. The phono preamp is serviceable but a Schiit Mani is and upgrade. I am planning to take it in to my local shop and upgrade the caps and I have a crackle when I turn the vol up that goes away immediately so I need to spray it. It sounds really good with both my Q acoustics and my Klipsch ... I will continue to watch your series.

[@SkunkieDesignsElectronics]

I just started listening to it, burning in a set of KT88-z power tubes and rolled a EH 7025 into the 12AX7 slot (low noise 12AX7) and like what I am hearing. I plan on doing a back to back listening session this weekend with an R8.

[@jamesmcmillan6350]

@@SkunkieDesignsElectronics would you check out the "pre-amp bypass" on front left of amp and use another preamp and see what you think?

[@nevillegoddard4966]

Very cool! I bet there's a nice glow emanating from it in low lighting! Nearly looks like mundorf capacitors in it? It's gonna be interesting to see what you think of its performance. I'm gonna look for the next installment!

[@twitchbook-1]

thanks and have a good one

[@milosbicanin9231]

hi Skunkie, a friend recommended E80CC tube instead of 12AU7/ECC82 as much better sounding , but it draws 0.6 amp instead of 0.3 in current on the cathodes. I have no idea if the power transformer can deliver that extra current. What is your opinion on that?

[@SkunkieDesignsElectronics]

Just keep an eye on the transformer temp, I have no idea either as they don't publish ratings.

[@EsotericArctos]

I think having the bias pots recessed is a good idea. You don't need to change bias all the time. Once set, it can be left alone for a long time, unless changing the tubes. I always change bias pots to recessed kind so they dont get accidentally moved. People move their amps, or reach around to change wiring. The tubes are not always hot during these times, so can be easy to move a non-recessed pot. I believe testing of these amps is on a 220 / 110 style system instead of the 240/120 system, which would be why the voltage on the B+ is about 20V higher than what would be appropriate for those filter caps. In China, it tests below 450V even with no load. I am in Australia, where the voltage can be as high as 250V, and I too have seen the B+ exceed the specs of the filters, but I have also seen the manufacture of these amps and when tested in China, the B+ doesnt exceed the rating of the caps.

[@SkunkieDesignsElectronics]

But they KNOW they are mainly selling these for export so should have internal voltages below what the parts are rated for.

[@electronicmusic6609]

Hi. Thanks for all this info. Can you make a video to explain us how to make vu-metre more sensitive ? Thank you for your work 🙏🏽🙏🏽🙏🏽

[@SkunkieDesignsElectronics]

Sorry, I no longer have this amp to work on or make videos with.

[@bob_mosavo]

Thanks 😊

[@aquaescape411]

So the matched tube set part. Do you match each side, all four , or something else (like inner and outer tubes)?

[@SkunkieDesignsElectronics]

I want to see matched pairs on the same channel for a push pull amp.

[@mddawson1]

I realise that this is probably not possible due to space constraints inside tube amps but would a stepped attenuator for the tube bias be more reliable or would the steps prevent accurate biasing of the tubes?

[@SkunkieDesignsElectronics]

yeah the steps would likely be problematic. I wanna study this circuit and see if there is a way for the trimmer to be way less touchy too.

[@ptg01]

So cool....

[@burkhardhalfmann9539]

Heyoh Stephie! I am happy owner of the X7 and I have got a question regarding the BIAS current. You mentioned that the BIAS current with 40 mA is "supercold biased" for a KT88 and that the sound might be different or maybe better with a "hotter" BIAS > 40 mA. But the choke is designed for 180 mA and this limits the BIAS current to ~ 45 mA max each Power tube. If I would change the choke to 250 mA (~ 62.5 mA max each power tube) the power transformer needs to be capable of the higher Power. I could ask Connie from Newsong distrubutor (she is really nice) what kind of power transformer is in the amp and what is the maximum allowed BIAS current if the choke is upgraded to 250 mA regarding the maximum allowed power of the power transformer. Do you think I really need to replace the 450 V capacitors to a higher Voltage when I run it with e.g. 60 mA Bias current? Does the Voltage over the capacitors rise when I rise the BIAS current? In general how does it affect the life span of the KT88s running with a higher BIAS? Is there a recommended BIAS not to exceed e.g. 55 mA or something else for a KT88? Do you think it might affect any other parts critically in the amp running with a higher BIAS ? That was a lot of questions... Just want to get your point of view and not a legal binding advice ;-) It is my first tube amplifier and I dont want to make any changes that might destroy the amp...

[@SkunkieDesignsElectronics]

Running the amp for 5-10 minutes with the tubes biased at 50-60ma isn't going to "kill" any parts and you can see if it changes the sound in a way you like. The voltage over the caps in really unrelated to bias and in fact raising the bias will lover the voltage they see a little bit. The main issue is the voltage they see goes over the spec on start up. You can see the bias vs tube spec using this calculator, even at 60ma it's only 70ish percent. Changing the bias doesn't change the power, it changes how deep into the power used the amp stays in class A and can impact the bass response. robrobinette.com/Tube_Bias_Calculator.htm

[@burkhardhalfmann9539]

@@SkunkieDesignsElectronics ah many thanks for the link 👍. So the only thing I have to do is to measure the plate-to-cathode voltage between the Pins (tubes installed) and type it in and press calculate or did you allready measure or know the plate-to-cathode voltage? What I still don't understand is that a push-pull amp can operate in class A mode. I thought only single ended amps with one power tube each channel are class A. Is only one power tube of 2 used at low volumes in push pull tube amps?

[@SkunkieDesignsElectronics]

way too complex to explain in a YT comment. Class A and single ended are different things. Single ended is always class A but push pull is normally class AB but they can also be class A

[@MsGreenEys]

Hello, is it worth investing $1000 in the Muzishare X7 to eliminate all problems and buy selected tubes? Or would you rather buy an expensive $2500 tube amp? Kind regards, Ludovic

[@SkunkieDesignsElectronics]

A) I haven't listened to whatever $2500 amp you are talking about so how could I know? B) yes, the stock tubes don't sound good. Most commercial "budget" i.e. under $5000 amps come with mediocre at best tubes and need upgrading. At the price point you are buying a high power tube amp, it's gonna be a budget model with issues related to cost cutting. Understand that the wholesale price of this amp is likely under $700-800, if that. It's like expecting a Mercedes at used Kia prices.

[@mddawson1]

I just read that Muzishare and Willsenton are made in the same factory. This would explain the layout/construction similarities.

[@SkunkieDesignsElectronics]

See that makes sense!

[@mddawson1]

@@SkunkieDesignsElectronics This was posted on the Steve Hoffman Music Forums with a copy of product certification for Muzishare and Line Magnetic. Quote: "From what I've been able to gather, Zhuhai Meishi Audio Equipment Co., Ltd. of Guangdong, China manufactures Line Magnetic, Muzishare, Willsenton, Boyuu, Reisong, and possibly Cayin as well."

[@SkunkieDesignsElectronics]

See now that seems odd given the poor design and performance the Reisong products I have tested have been. Both the A12 and the A50 were really bad out of the box.

[@mddawson1]

@@SkunkieDesignsElectronics Maybe they do OEM work for other companies?

[@moodyga40]

should fit a CL80 NTC

[@frankgeeraerts6243]

YES

[@petegaslondon]

Croweded? Yeah I see what you mean - mind you I've seen far worse layouts, and sure wouldnt turn my nose up at one of these to play with :) Mind you when it gets to 4 figures I get to thinking 'bout what I could BUILD for that - sure its way cheap for Audiophile class amp of that kinda power (if the transfomers are good) but ... I get to thinking what I could BUILD for that budget :) Be way interested in how the transformers hold up with high powerd bass freq's - eg are the big metal casings ALL transfromer, or is there something smaller within ;) ??

[@SkunkieDesignsElectronics]

After working on the R8 with the larger octal tube sockets, it's a lot more crowded up there :)

[@petegaslondon]

Yeah I get you - I could never relate to 6SN7s, octals for signal stages - it always seemed a waste of space ;) but it sure DOES leave more room to manouvre ! Please, see what you can do with this guy, and if poss, test low freq extension at power? Potted tranfomers sure LOOK lovely - but you ask yourself how much is 'transfomer' and how much just 'pot' ?

[@SkunkieDesignsElectronics]

I will be doing the same tests I did on the R8 and will compare.

[@1mctous]

I would take the cheap phono stage out of the circuit and make it another line level input.

[@SkunkieDesignsElectronics]

You could and/or do that and use an external phono stage. I am curious what it sounds like compared to my tube EAR834 clone.

[@bobbyfeatherstone2834]

Why not just add extensions to the shafts of the existing pots?

[@SkunkieDesignsElectronics]

I was more concerned about the quality, I've seen these pots fail in other amps that use this brand of pot.

[@bobbyfeatherstone2834]

Gotcha! I just got home with my X7 abt. 4 hrs ago, is it ok to run it a little right out of the box? Or should I change out those big resistors first?

[@SkunkieDesignsElectronics]

Sure, these are much less likely to run away like the R8 can.

[@bobbyfeatherstone2834]

@@SkunkieDesignsElectronics Gosh thanks! Can you please recommend a tube preamp that would be a good fit? I am running a Linn/Sondek LP 12, stock Sure tonearm, GRADO cartridge with no other markings, I don't know if the Grado is moving coil or what? How can I tell? I am considering the DOUK or FOSI, amps I'd like to stay @ around a hundred bucks or so but will go a little higher if it's worth it . Speakers are Celestion Ditton 110 or Mission 700's Please advise.Are there any preamps out there with 12AX7/7025's? I'm a guitar player so I i already got a boatload of those laying around. Love the channel! Thanks for your help.

[@SkunkieDesignsElectronics]

For a phono pre-amp, the EAR834 clone is good. The little bear pre-amp I did a series on is also really decent, these all use 12AX7/7025 tubes.

[@interesting7906]

The shortcuts taken in the power supply and poor quality bias pots is really unacceptable. This is unsafe. What type/brand resistors and caps do you recommend? There are not alot of 550VDC electrolytics out there.

[@SkunkieDesignsElectronics]

I'm going with 500V TDK I found on mouser that are similar size to these, should fit right in these brackets. At least these bias pots have fail safe resistors!