Muzishare X7: Replacing the Power Caps and Choke.
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- Опубліковано 26 тра 2023
- This video covers replacing the 2 large 450V rated power caps with some 500V ones. The power supply caps see well over 450V on startup and the first cap runs at 452V, so it's worth considering replacing these if you are working inside the amp. I also replaced the marginally rated 180ma choke with a 250ma one more suited to a push pull KT88 amplifier.
I also removed the headphone jack wiring, which allows the output transformers to be wired directly to the speaker jacks. This improves the ground path for the output signal. Otherwise, the ground wiring seems quite good in this amp and is completely "Star ground" wired!
Here is a link to the KT88-z tubes:
youdaelectronics.com/products...
The power caps I used are:
mou.sr/43sjTUG
Here we go with another popular made in China KT88 Push Pull Vacuum Tube Amplifier. This one was sent in for repairs of the biasing/meter circuit and a full review + mods just like we did on the Wilsenton R8. So far I'm impressed with the quality of the build and we will do sound and measurement tests in future videos.
You can buy this amp here:
amzn.to/3HbkEse
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I love the way you do your job and the arguments you offer for every change you make! This is very important
Looking forward to the sound critique.
Great work Stephe. Can't wait for the sound test!
This is a great way to learn about these Amps, I have two, it’s a shame they didn’t make the Amp with the higher rated components or lower for the resistors you mentioned. I’m not Sure I’m ready to take the soldering to the Amp yet, but I can see why it would be worth doing! Interesting to know about the pop when switching off, one of mine does the same. Can’t wait for the next one to see what you think it sounds like.
Actually that slight pop is the triode/ultralinear relay clicking to triode on shut down. You hear the same thing switching from UL to triode with the amp powered up. No easy way to fix that, but honestly isn't hurting anything.
I have the X7 also. I replaced the coupling caps with V-Cap Odams with great results.
Really enjoy your detailed explanations.
I guess I'll tackle the choke and power caps next.
I got my first solder sucker last week and it worked surprisingly well. It made changing the caps in my Hood 1969 amp really easy.
Which one did you get?
@@SkunkieDesignsElectronics I got one that is blue plastic with yellow button and plunger end (13 inches long) from temu for $6.50. I was worried that the hot solder would melt the plastic but it wasn't a problem. It took just one go to remove the solder from most joins. I soon learnt I had to aim it away from my work area when depressing the plunger as that also ejects the solidified solder. I also got a smaller, mostly metal one for $2.50 but it locked up on me after a couple of uses so I ended up sticking with the bigger plastic one.
I am really excited for your listening test of the X7 versus the R8 🙂 as I am happy owner of the X7.
So far I like what I am hearing!
@@SkunkieDesignsElectronics Yes I love mine, too! My first tube amp 😍😍. I allways had little doubts if it was the right decision to buy the muzishare X7 and not the willsenten R8 as there is only one test review in the internet where somebody told he heard both amps in comparision and told the R8 was better because the bass was more impressing. I am happy with my X7, escpecially in triode mode. And I am really looking forward to your impressions about your sound impressions. To me you are the most competent Person in hifi world regarding tube gear. It is so relaxing see you solder and talking about tube amps...😍😍
It is going to be interesting to compare to the R8
Right. That both use tubes to feed the voltage to the front end tubes, and think it's going to come down to: does a 12AX7 sound better or worse than a 6SL7. I bet it does.
Hey! Just found your channel and I really enjoy your work. I was wondering if you ever worry about putting too much heat from the soldering iron on the PC boards.
I've never had any issues.
Stumbled on this channel having come across Muzishare X7 and trying to get into tube amps. I must say I love the content. Thanks. Would the the logic for disconnecting the ground wires from headphone board be to remove all the excess unnecessary circuitry? Simple and sophisticated?
Exactly, why have all that excess small wire in the signal path if you never intend to use headphones. Plus it corrects grounding issues.
@@SkunkieDesignsElectronics thanks so much. I think I might just start on Muzishare X7 and enjoy the mods.
@Skunkie Designs Electronics - I have this amp and the factory recommends the bias at .040ma but I have it bias at .045ma, and it really makes difference. I am tempted to go to .050ma, but I would need to upgrade the choke first.
What difference did you notice?
@@SkunkieDesignsElectronics increase in clarity while sounding smoother those too are usually at odds but that’s the only way I can describe them
Thanks, I will play around with that. The frequency response and power look the same, but that doesn't mean they sound the same.
Time to review X9! I am wondering if it's better than X9 or it's just more powerful... 🤔😊
Nice video, I'd try adding a large film cap in parallel with those electrolytics. I've had great results adding 6.8uf solen caps in parallel to 470uf power caps.
That's something for folks to play with.
At 5:16 when you are removing the headphone jack ground wires I notice one going to the Pre In switch on the front. Did you ground that somewhere?
Not sure about that, I don't recall any wire going there but it's been a while!
Stephe, I replaced the caps and choke as you demonstrated here and I actually think it improved the sound on the X7, tighter mid base, and a cleaner high end. Maybe the new choke helped along with the caps. For me, I am running the X7 in a bi-amped configuration with a Conrad Johnson Premier Two pre-amp along with a Sonographe (CJ) active crossover and a solid state Sonographe amp on the bottom going to CJ/Fusion speakers. Anyway, the mod took the pre-in functionality out on the X7. I understand the issues around using the pre-in mode on the X7 but would like to restore the functionality and remove passing signal through the X7 volume control. Do you think this can be done without re-installing all the headphone stuff? Thanks!
Sure. Honestly if that was my goal and you feel comfortable modding the amp, simply wire a pair of input jacks directly to the grids of the input tubes and bypass ALL of that wiring, switches, volume control etc.
Thanks, I'll take a look and see if it's something I want to do. I did find the post that indicated to run the prein switch to ground. I did it and it fixed it. Right now it's sound the best since owning he amp.. Maybe best to leave well enough alone, but that's not my style...
Hello. Changed choke to 250mA. Raised the bias current to 55-60mA. Shuguang kt-88z tubes. I don’t notice a big difference in the sound (what did this give you? They write that as the current increases, the anode voltage decreases...
It's not a "big difference". What I noticed was more bass slam, i.e. the drum hits and other hard hitting bass notes were improved. On a push pull amp, unlike what happens with an SE amp, increasing the bias doesn't increase the power. At some point we run out of big differences and start down the path of smaller ones :)
Serious question: is there any tube amplifier that does not need safety modifications? Thank you
Most of these cheap made in China tube amps have issues.
Hello Skunkie,
I would like to apply your ideas for modifications to my Murishare X7 amplifier, thank you for the sharing :)
If I apply the changes myself to my disconnected amplifier from the sector, do I risk an electric shock ? What are the precautions to be taken please ? Thanks ...
Gilles.
Mainly make sure the amp has been unplugged for at least 30 minutes and then using only one hand, carefully double check there is no voltage left stored in any of the large filter caps.
@@SkunkieDesignsElectronics Thank you for the info !
I ordered all the parts at MOUSER and I will have to start the changes very soon when I have a little time!
A big thank you to you Stephe, I admire what you do, take care of yourself!
Gilles from Paris
Hello. I removed the wiring from the headphones, as in your video, and the pre in input stopped working. Where did I go wrong?
Found) if you want to leave the prein, you need to connect the top contact of its switch to negative plug!
Do you mean negative ground?
@@rkks43928 Yes, you should hear the relay click.
So the cap was drained first I suppose?
This is why I have a warning at the start of every mod video. People need to understand and follow all safety practices, which includes draining the voltage from caps before working on an amp. I do not repeat all safety information in every video, that would double the length of every video.
Hello Skunkie...with all the crazy amount of filter capacitor s to choose from I was curious what made you decide to use those TDK Epcos capacitor s...I figured with the quality of Mundorf why the Epcos...thank you
There aren't a lot of 500V+ 470UF caps to choose from at mouser. I looked for long life, 105deg as the main factors and the same physical diameter. These also have low ESR and are at a good price point. Given these power supply cap IMHO have very little impact on the sound, I don't see the value is spending $$$ here. If someone does want to spend some $$$, you could parallel these 200-200 caps.
www.partsconnexion.com/MUNDORF-70428.html
Fantastic Skunkie...that makes total sense, high voltage and high temp caps right on Skunkie I didn't even know TDK made capacitor s lol I'm still learning,
They other key point to remember is predicted life is based mainly off temp. Using a 105c cap rated for 3000 hours vs a 85c cap rated at 3000 hours, the 105c cap is going to last WAY longer if they both see temps of 60c. I just recently been looking at ESR, and using a low ESR cap can eliminate the need to bypass a large filter cap with a film cap.