Hi, not sure if anyone can help,but i now have 2 of the mengyue mini el34 based amps(second one was sent as warranty replacement due to hum), both have a low level hum from what I think is the input (front tranny in picture)transformer.
As i'm a relative newcomer to valves,can anyone advise how this can be eliminated, by modifying the circuit or by any other means. I cannot find a schematic for this amp does anyone have any idea if one exists?
I have enclosed a link to my particular version,its was supplied as a 24w, via ebay,but i've noticed many other chinese sellers listing it as 12w, i'm confused???
Music Angel MENGYUE MINIX3 EL34*2 Class A Integrated Amplifier - $174.82USD : Enjoy music, enjoy hifi audio!, we sell Music Angel,qinpu,yaqin,MeiXing MingDa,Bewitch,Bada Amplifiers, CD player,power amp, preamp
any help much appreciated,
tom.(uk)
As i'm a relative newcomer to valves,can anyone advise how this can be eliminated, by modifying the circuit or by any other means. I cannot find a schematic for this amp does anyone have any idea if one exists?
I have enclosed a link to my particular version,its was supplied as a 24w, via ebay,but i've noticed many other chinese sellers listing it as 12w, i'm confused???
Music Angel MENGYUE MINIX3 EL34*2 Class A Integrated Amplifier - $174.82USD : Enjoy music, enjoy hifi audio!, we sell Music Angel,qinpu,yaqin,MeiXing MingDa,Bewitch,Bada Amplifiers, CD player,power amp, preamp
any help much appreciated,
tom.(uk)
It may be that it runs 12W in triode mode, or 24W in UL or pentode mode. Or maybe just that the 24W version uses Chinese watts.
Do you mean audible hum from the transformer? If so, it certainly isn't an input transformer.
Do you mean audible hum from the transformer? If so, it certainly isn't an input transformer.
Given that it is a single ended EL34 per channel, even 12W has to be Chinese watts.
Front transformer is a power transformer, two OPT behind that.
Front transformer is a power transformer, two OPT behind that.
OK, I didn't look too closely. I thought it might be a triode P-P monobloc. Why do they put the power transformer between the circuit and the OPTs?
Because they do business, to feed their children, and put things which and how they look more impressive. Even when they use 300B on 5 mA idle current, it looks better than say EF...something.
meng el34b
hi jaz,
looking for a simpler remedy to the issue as this is above my head technically,relatively new to tube workings,just wonder if I have been supplied with lower voltage units? Is ther any tests i can make to check what volts its running at, the front tranny is marked up 230v ive been told by a local amp repairer in south wales(uk) to check pins 2 and 7 on el34's these should be at 6.3v ac? Any other checks that may solve the hum issue? I can supply some photos with the base off if this helps?
thanks
tom.
hi jaz,
looking for a simpler remedy to the issue as this is above my head technically,relatively new to tube workings,just wonder if I have been supplied with lower voltage units? Is ther any tests i can make to check what volts its running at, the front tranny is marked up 230v ive been told by a local amp repairer in south wales(uk) to check pins 2 and 7 on el34's these should be at 6.3v ac? Any other checks that may solve the hum issue? I can supply some photos with the base off if this helps?
thanks
tom.
please, note that just because its a small tube amp, it doesn't mean its less dangerous
it could still be voltage above your mains voltage
and you wouldn't test your house mains plugs with your fingers, would you 😀
if you cannot build a similar tube amp, then do not try to repair one either....simply, don't
Tom,
I agree with Tinitus, if you are not familiar with tube circuits or electronics in general, it would be better if you take the unit down to a repair shop and have the tech measure the voltage (should be pretty cheap) or troubleshoot the hum problem (could be expensive).
Having said that, if you still want to try to troubleshoot it yourself, please be very careful... You can put the DVM probes on pins 2 and 7 as the tech suggested and see if the voltage is way over 6.3VAC, it is possible that you are getting more than 230V from your mains and the power transformer was designed to run on 220V (as in China).
Also, just how loud is the hum, can you still hear it when playing the music at moderate levels? Anyway, if you can post some gut shots, they can also provide us with some clues.
Jaz
I agree with Tinitus, if you are not familiar with tube circuits or electronics in general, it would be better if you take the unit down to a repair shop and have the tech measure the voltage (should be pretty cheap) or troubleshoot the hum problem (could be expensive).
Having said that, if you still want to try to troubleshoot it yourself, please be very careful... You can put the DVM probes on pins 2 and 7 as the tech suggested and see if the voltage is way over 6.3VAC, it is possible that you are getting more than 230V from your mains and the power transformer was designed to run on 220V (as in China).
Also, just how loud is the hum, can you still hear it when playing the music at moderate levels? Anyway, if you can post some gut shots, they can also provide us with some clues.
Jaz
hi jaz, the tech I spoke too, didn't seem interested in touching the amp. There are no other tech's local to me, (i'm in Cardiff, uk), the other nearest one's are around 100 miles away so I would need to post,that's if they were interested in the job.
I,ve decided to have a look at it myself, i'm a qualified electrician so know the issues with electrical safety.
All i'm seeking is some guidance as to if this can be sorted, reasonably cheaply,otherwise it may be a case of selling both amps onto somebody that can repair them?
thanks again,
tom.
I,ve decided to have a look at it myself, i'm a qualified electrician so know the issues with electrical safety.
All i'm seeking is some guidance as to if this can be sorted, reasonably cheaply,otherwise it may be a case of selling both amps onto somebody that can repair them?
thanks again,
tom.
hi, I forgot to mention sorry, the hum is of a very low level,but, you can hear it in a queit room with no music playing, as soon as music is played the hum cannot be heard.
Yes a schematic will help, also in this case, I think it is likely that the layout and wiring may be contributing to the excess hum, please post some pictures if you can.
Jaz
Jaz
If a cheap Chinese made amp has a little hum in quiet room that goes away, or is not noticeable, when playing music, I think you got a deal and I don't see what the problem is. What were you expecting for under $200? A dead quiet amp? If it sounds ok when playing, I would leave it alone.
I think you right, probably best to leave alone, I'm may well sell the 2 if anyone is interested, the one amps done about 30 hrs and the other unit has done about an hour, just to check it over.
If anyone is interested let me know?
Thanks
Tom
If anyone is interested let me know?
Thanks
Tom
Here is the schematic diagram of the Meng Yue X3 EL34, with some basic measurements.
I believe someone else has already pointed out that the safety earth is not connected on this amp - this is a safety issue that needs to be taken seriously. If you plan on using this amp, please ensure that the safety earth is connected to the chassis directly or via a diode bridge.
Other than this safety warning, this is actually quite a nice amp to 'hack'. As a minimum, trioded EL34 sound much nicer (to me anyway). There is enough space on the chassis to fit much better output transformers and rework the whole guts, for example a Transcendar 5K SE TT-015 fits nicely using some of the existing mounting holes.
I am currently listening to this Meng X3 with full Power Drive mods: extra +/-150V DC, D3A in triode, 10M45, 2SK3767, fixed bias to EL34 trioded (70mA), Transcendar 5K, Auricaps, 6dB total NFB from secondary.
With these mods the distortion is still pretty high at 3% / 1W, but purely 2nd harmonic, 3rd harmonic is >30dB down.
I believe someone else has already pointed out that the safety earth is not connected on this amp - this is a safety issue that needs to be taken seriously. If you plan on using this amp, please ensure that the safety earth is connected to the chassis directly or via a diode bridge.
Other than this safety warning, this is actually quite a nice amp to 'hack'. As a minimum, trioded EL34 sound much nicer (to me anyway). There is enough space on the chassis to fit much better output transformers and rework the whole guts, for example a Transcendar 5K SE TT-015 fits nicely using some of the existing mounting holes.
I am currently listening to this Meng X3 with full Power Drive mods: extra +/-150V DC, D3A in triode, 10M45, 2SK3767, fixed bias to EL34 trioded (70mA), Transcendar 5K, Auricaps, 6dB total NFB from secondary.
With these mods the distortion is still pretty high at 3% / 1W, but purely 2nd harmonic, 3rd harmonic is >30dB down.
Attachments
Hi, many thanks for the helpful info. Only mod I've done to my amps are the earth to chassis link.
Being a newbie to tubes and electronics in general,(but learning all the time), some of this a little above my head,although I am a qualified electrician so I'm aware of electrical hazards in general.
I'm located in uk, are these or other suitable trannys available in the uk. Did you have hum from the mains tranny with your unit? What would be the costs to mod these as you say, as The trannys alone would be more than a good secondhand uk valve amp or a kit from a reputable seller on here?
Many thanks
Tom
Being a newbie to tubes and electronics in general,(but learning all the time), some of this a little above my head,although I am a qualified electrician so I'm aware of electrical hazards in general.
I'm located in uk, are these or other suitable trannys available in the uk. Did you have hum from the mains tranny with your unit? What would be the costs to mod these as you say, as The trannys alone would be more than a good secondhand uk valve amp or a kit from a reputable seller on here?
Many thanks
Tom
Hi Tom, the output transformers are usually available from ebay, for example check out ebay item 281031361385. These are very good and are well worth the asking price (you can usually get them for $145-170/pair).
The only other suggested 'first priority' mod (IMHO) would be to rewire the EL34's in triode (remove the 68uF G2 filter and 3K G2 feed resistor => G2 is now floating, now connect to A via 330R resistor). This also helps if you decide to keep the original trannys for while (they are far from brilliant, but I have seen and measured much worse 🙂
The power transformer and layout in the X3 is pretty good IMHO, I did not see any evidence of hum induced from power to output iron directly (unlike some other small SE amps I have where the power tranny *does* couple to the outputs). Quick test - listen to the speaker while the amp is warming up. If hum comes up immediately => magnetic coupling. If hum comes up as valves warm up => electrical reason, via output valves, and this can usually be fixed, to different degrees of perfection: chokes in PSU, or adding extra circuitry. Mr Broskie from TubeCad for example has a lot of good articles on how to suppress hum/noise from supply voltage.
Another quick test to make sure there is nothing catastrophically wrong - measure the heater voltage, should be around 6.3V. Also, check the voltage drop on the 2x240R riple fitler series resistors on the PSU board, should be around 120R x 67mA = 8V (make sure the supplier did not 'save' on removing the 240R power resistors), these directly reduce the hum level.
As I said, IMHO these amps have a lot of potential. If nothing else they are a great way to learn about valves for an entry level price, much easier than doing the whole thing from scratch (again, IMHO). I hope you will have lots of fun with them!
Tibor
The only other suggested 'first priority' mod (IMHO) would be to rewire the EL34's in triode (remove the 68uF G2 filter and 3K G2 feed resistor => G2 is now floating, now connect to A via 330R resistor). This also helps if you decide to keep the original trannys for while (they are far from brilliant, but I have seen and measured much worse 🙂
The power transformer and layout in the X3 is pretty good IMHO, I did not see any evidence of hum induced from power to output iron directly (unlike some other small SE amps I have where the power tranny *does* couple to the outputs). Quick test - listen to the speaker while the amp is warming up. If hum comes up immediately => magnetic coupling. If hum comes up as valves warm up => electrical reason, via output valves, and this can usually be fixed, to different degrees of perfection: chokes in PSU, or adding extra circuitry. Mr Broskie from TubeCad for example has a lot of good articles on how to suppress hum/noise from supply voltage.
Another quick test to make sure there is nothing catastrophically wrong - measure the heater voltage, should be around 6.3V. Also, check the voltage drop on the 2x240R riple fitler series resistors on the PSU board, should be around 120R x 67mA = 8V (make sure the supplier did not 'save' on removing the 240R power resistors), these directly reduce the hum level.
As I said, IMHO these amps have a lot of potential. If nothing else they are a great way to learn about valves for an entry level price, much easier than doing the whole thing from scratch (again, IMHO). I hope you will have lots of fun with them!
Tibor
Safety earth connections to a chassis should always be directly wired - never through other components. There may be other components in the path from the safety earth to a signal ground (can be parallel back to back diodes, or resistors, etc), but that is for the purpose of breaking earth loops that may contribute to hum in the signal path.
The safety earth connection to the chassis must be able to withstand a direct short from the AC supply and must be able to pass sufficient current to blow the fuses or to trip the circuit breakers further back along the supply chain.
Would you explain a little more about magnetic coupling and perhaps what might be done to help it? I think I have that issue with an amp I just built. Don't want to otherwise hijack this thread, just a concept I am curious about. Thanks!
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