Hello. I have been the proud owner of a Yaqin MC10-L for about three weeks now. It is replacing an older Pioneer Elite solid state amp. Overall I LOVE it. It is a gorgeous amp and I am sure that many of you hear have an appreciation for just how beautiful tubes are. I am somewhat familiar with electronics (took it in high school and tinkered around as a teen) but there is a LOT to know about tubes. I have spent most of the day reading up on them. My dad is a tube guy but from a guitar players perspective. He was thinking about getting me some upgraded tubes for Christmas (or soon thereafter). Here are some specs on the amp:
"The Yaqin MC-10L, according to my friend Stuart who's an electronics and audiophile guru, is a very simple design that's quite similar to the Dynaco ST70, a classic audiophile tube amp sold from the 1950s into the 1970s. Output power is about 52 watts (at 8 ohms) per channel using four EL-34-B tubes for the power amplification stage and four 6N1's, a common Russian/Chinese tube, for the preamp section. (There are speaker connectors on the back to run it at 4 or 8 ohms.)"
from this page:
coolcatdaddy: Yaqin MC-10L Amp - An initial review
There is a comment on that page suggesting uppgrades:
"Bob L said... I picked up an MC-10L from the same seller around Christmas time. I thought it was amazing, until I rolled some Russian 6n1p's into the preamp stage and some EH 6CA7's into the output stage...wow, what a difference. Upgrade the tubes on that bad boy coolcatdaddy, you dont know what youre missing"
But my sent me this link warning against the 6N1ps:
Print Page - Replacement Tubes for Chinese 6n1
He said they run hot.
I am open to any suggestions and would just love any pointers to technical info. I like the idea of toying with the sound with different tubes and I can't deny that some tubes are just prettier than others. I know that is a minor concern but I could just stare at my amp all day.
I don't quite understand why one tube would replace another and why one would be better than another. I don't want to endanger the amp (although it was a hell of a deal) but would like to have fun with it.
Also it sound great as is IMO. I hear some tiny bits of background noise but turning it off and on has seemed to resolve it. The amp and new speakers have been playing 24/7 on opinions that I should "burn in" both.
The new speakers I bought to go with the new amp are some Focal 716Vs. I love the sound of them as well.
While I am at it here are some pictures of my new gear. The input device is a Roku M2000 Soundbridge. I have been going back and re-encoding my entire library to FLAC for the new setup.
bedroom audio
"The Yaqin MC-10L, according to my friend Stuart who's an electronics and audiophile guru, is a very simple design that's quite similar to the Dynaco ST70, a classic audiophile tube amp sold from the 1950s into the 1970s. Output power is about 52 watts (at 8 ohms) per channel using four EL-34-B tubes for the power amplification stage and four 6N1's, a common Russian/Chinese tube, for the preamp section. (There are speaker connectors on the back to run it at 4 or 8 ohms.)"
from this page:
coolcatdaddy: Yaqin MC-10L Amp - An initial review
There is a comment on that page suggesting uppgrades:
"Bob L said... I picked up an MC-10L from the same seller around Christmas time. I thought it was amazing, until I rolled some Russian 6n1p's into the preamp stage and some EH 6CA7's into the output stage...wow, what a difference. Upgrade the tubes on that bad boy coolcatdaddy, you dont know what youre missing"
But my sent me this link warning against the 6N1ps:
Print Page - Replacement Tubes for Chinese 6n1
He said they run hot.
I am open to any suggestions and would just love any pointers to technical info. I like the idea of toying with the sound with different tubes and I can't deny that some tubes are just prettier than others. I know that is a minor concern but I could just stare at my amp all day.
I don't quite understand why one tube would replace another and why one would be better than another. I don't want to endanger the amp (although it was a hell of a deal) but would like to have fun with it.
Also it sound great as is IMO. I hear some tiny bits of background noise but turning it off and on has seemed to resolve it. The amp and new speakers have been playing 24/7 on opinions that I should "burn in" both.
The new speakers I bought to go with the new amp are some Focal 716Vs. I love the sound of them as well.
While I am at it here are some pictures of my new gear. The input device is a Roku M2000 Soundbridge. I have been going back and re-encoding my entire library to FLAC for the new setup.
bedroom audio
An externally hosted image should be here but it was not working when we last tested it.
I've repaired these and can say that they are better than many Chinese amps. (Build and performance).
Glad to see you have the later version with the holes for bias adjustment. As the output valves/tubes age you will need to check this.
Underneath those transformer covers are conventional EI transformers, but they are of a fairly reasonable size.
Like several other Chinese amps, most imports into the UK are rated at 220v. When run at 240v, they get stinking hot. Hopefully your mains is closer to 110v than 120v.
Glad to see you have the later version with the holes for bias adjustment. As the output valves/tubes age you will need to check this.
Underneath those transformer covers are conventional EI transformers, but they are of a fairly reasonable size.
Like several other Chinese amps, most imports into the UK are rated at 220v. When run at 240v, they get stinking hot. Hopefully your mains is closer to 110v than 120v.
What is a conventional EI transformer? They seem very heavy as most of the weight is on the back end. Don't all household currents fluctuate in America between 110 and 120? Is one better than another? Is there anything I can do about that? And any suggestions on tubes themselves? I did the bias adjustment when I got the amp although I don't really have a clear idea what that is doing. Thanks.
The round transformer covers imply that the transformers are toroidal (doughnut shaped); EI transformers are more conventional looking with a vertical or horizontal stack of laminations with the coil windings inside. The core laminations in an EI tranformer are actually "E" and "I" shaped. Since you appear to be keen on getting a tube lesson, search this forum for EI transformers and toroidal transformers. In general, toroidal transformers can be smaller for a given power rating, are more efficient, but saturate abruptly when overdriven.
Residential mains power has slowly crept up a little over the decades.
If the transformer primary windings are designed for 110V (US) or 220V (EU, etc) the amp with run a little hot (above it's nominal power ratings) when the mains voltage in your house is higher (which is typical today, usually 120V) and can sometimes run the tubes a little closer to their power limit. The amp will run a little hot, produce more output power, sometimes sound better, and have a slightly reduced tube life.
Adjusting the bias pot (voltage adj) adjusts the idle current through the output tubes by changing the negative voltage on the control grid of the tubes. Your amp is fixed bias, another interesting thing to search for here.
I am pretty sure my amp does have bias adjustments. You don't even need to take the cover off. There are holes for the probes for each vallve and its corresponding pot. The first thing I did when I uppacked it is do a bias adjustment.
Here is the guide I followed to do the bias adjustment:
http://yaqin.slickpepper.org.uk/wp-content/uploads/2008/06/mc-10l_bias_adjustment.pdf
Although in the guide you need to take the cover off the newer ones have the holes.
Here is a picture showing the holes:
I have been looking for more specs on the transformer. They do not appear to be torioids:
"First of all, I was a little disconcerted about the seeming hollowness of the cans over the transformers, particularly the outputs. It was my assumption that such large cans hid hideously small iron. The amp has good heft to it, so I figured that Yaqin latched to the age old trick of increasing mass by installing thick plates or even lead bars (I have seen that before). Well, I was dead wrong. While the transformers are not toroid, as one would expect from the cans, they are generously large and of exceptional quality. The individual laminations are incredibly thin, which (based on experience) is a Good Thing™."
And a (bad) Chinese translation from a dealer:
"Output transformer uses the Japanese import audio frequency
special-purpose silicon steel plate (0.35mm thick) and the high strength enamel- insulated wire
and specially circles the system craft manufacture, causes this machine frequency sound width,
high guarantees this machine, center, the low frequency timbre good, insightful is powerful. "
I will definitely do some reading now as you suggested. But still no suggestions for tubes?
Hi.
When Boywonder said that your amp has fixed bias, he did not mean non adjustable. A separate negative power supply is connected to the tubes grids and this is what you are adjusting. This is in contrast to the more usual cathode bias where the voltage drop across a resistor from 0 volts to the tubes cathode makes the cathode more positive than the grid which is held at 0 volts.
Cheers.
Rolf.
P.S.
Wish I had as big a vinyl collection as you!
When Boywonder said that your amp has fixed bias, he did not mean non adjustable. A separate negative power supply is connected to the tubes grids and this is what you are adjusting. This is in contrast to the more usual cathode bias where the voltage drop across a resistor from 0 volts to the tubes cathode makes the cathode more positive than the grid which is held at 0 volts.
Cheers.
Rolf.
P.S.
Wish I had as big a vinyl collection as you!
Exactly. Although it's counter-intuitive, fixed bias means you can adjust the bias current/voltage (with pots) and cathode bias does not have the adjustment.
Don't waste your money chasing the vinyl hype.
You'll spend a fortune for cartridges and tone arms only to play garbage pressings. Unless you want to listen to so called "audiophile" recordings that often are lousy performances by mediocre talent.
Then there is the total Voodoo nonsense that passes for good mechanical design of the turntable purveyors.Just go back to reel to reel tape. Or just be satisfied with CD.
I went that route...had various Koetsu cart. three were in fact especially wound by Mr. Sugano to match the tonearm - turntable that I bought from him directly at CES. Then a series of Madrigal pieces of junk hanging off the tonearm adding mass while masquerading as phono cartridges.. All the while chasing this mystical scent I could have been spending money to buy music to listen to.
Music is vastly more important than equipment... one is the excuse for the other!
Opera for all...............music est totus!
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Welcome to Tubophilia.............a never recovered from way of being.
Sorry bad night at "Black Rock" as it were.
My point was just enjoy your music which is why you have the equipment.
Of course for those fleeting...and make NO mistake they will be far between, few and fleeting, moments of Nirvana or what you will, one forgives all in the enveloping splendor............ (even purple prose).
But the yellow brick (boulder) grooved plasic road is vastly over hyped. Now much of the music recorded in the "golden days" is not. And that should the nexus we seek.
Fortunately there are many re-releases of some of these performances in current consumer formats. Now if we can drive a market for everything being released in FLAC as well as off the shelf disks those carefully guarded master tape libraries will yet pave the road toward music Oneness.
Harvey Rosenberg would be in his "hog heaven"!
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Unlike solid state, vacuum tubes are low gain devices. How a circuit performs is partially determined by the characteristics of the active device used. Transistors have so much gain that circuit performance is almost totally determined by circuit externals. Unless you need some special property, one transistor is as good as any other so long as the transistors in question can process the signal frequencies. I've done lots of projects with "transistors anonymous" I picked up at the local Rat Shack. "Transistor rolling" accomplishes nothing.
If that amp is based on the Dynaco-ST70 design, then tube rolling is something I wouldn't bother with. The inclusion of gNFB also serves the purpose of making the performance more independent of individual component selection. It's the open loop designs that don't include NFB that are most likely to sound different with different tubes and/or passive components.
You might need to tweak your NFB compensation. That sounds like an intermittent high frequency oscillation. I had the same thing happen with a solid state design I did once. Every once in a while, you'd hear a slight "tick, tick, tick" in the background that cleared up with power cycling., O'scoping revealed that this amp would occasionally make like a QRP rig and put out 3.54MHz sine waves. Some NFB loop compensation was needed to fix that.
Different speeks have different impedances, and yours might be triggering an instability. You'll need patience and an o'scope to track that down.
Going down a similar path. Bought the cheap 10 watter. Also classic long-tail splitter and push-pull with feedback from output side. Not as smooth as I expected, so I ordered NOS 6YA7's to replace the splitter 62N's as the forums all seem to blame them. Just came so I can't provide any responce. I have a long list of ideas to play with from ground topology, bias levels, regulation etc. So I hav eheard, they can be made quite nice.
Hi there. Thanks for the info. I have spent all week trying to read up on how tubes work (great guides in the noob section here) but have a ways today. I don't know what and NFB or gNFB is or what an open loop design is. I can include the schematic and maybe you can confirm this. I had already come close to deciding on the Tung Sol EL34Bs as the output tube replacement and am narrowing it down on the preamp tubes. I will immediately start looking into what an NFB is or an "open loop design" but apparently a lot of people due upgrade the tubes in this amp. Even if sticking with the same tube would one brand be better than another? Say a NOS vs. a new well known made tube?
Here are a couple more quotes from MC-10L users:
"Some of my friends and i own the Yaqin MC10L and it is a very good amp. But the original tubes (EL34b)are a bit microphonic so a little humm heared in the speakers. We all changed the EL34b tubes for JJ KT77 or EH 6CA7 and the humm is gone. The other tubes are very good."
Here is the schematic:
An externally hosted image should be here but it was not working when we last tested it.
and a ton more pics/schematics from the same page:
Index of /lez/YAQIN MC10
"Just starting to understand tube circuits" - same here...
V2 is the phase splitter known as a long tailed pair The circuit around V1 doesn't look right, where is the B+ for pin 6?
Ian.
V2 is the phase splitter known as a long tailed pair The circuit around V1 doesn't look right, where is the B+ for pin 6?
Ian.
I don't understand enough to see what you think is wrong. Here is another one. Maybe this one is right? the first one the author said they "corrected" some things.
An externally hosted image should be here but it was not working when we last tested it.
The first schematic looks ok to me, it is just a weirdly drawn SRPP which is turn is direct coupled to a long tailed (differential pair) phase inverter. (see explanation of how this works below)
There is global negative feedback (gnfb) in this design taken from between the 8 ohm secondary of the output transformer and ground which is fed back to the cathode of that srpp input stage.
R106 and C103 form a low pass filter that removes the ac signal but not the dc voltage from the grid, this triode in the phase splitter actually has a grid grounded for the ac signal and is driven by its cathode which in turn is driven by the other section's cathode - this creates the non-inverted phase of the phase splitter output (V2-6). The output from V2-1 is inverted because this stage looks like a standard inverting (common cathode) voltage amplifier stage. The plate loads are asymmetrical because the "long tail" (30K resistor to gnd) isn't really all that long and some signal losses occur in the cathode coupling.. The two grids in the phase inverter must be at approximately the same dc potential which is the other function that R106 and C103 provide - biasing both triodes correctly relative to one another since their cathodes are tied together. (Note for this reason that a triode with well matched sections is a good idea in this stage so that both sections operate at about the same point on their characteristic curves.)
This design looks pretty reasonable to me, rolling tubes should net a significant improvement in sound quality even though gnfb is used - the levels are not likely to be more than 20dB or so - so tube differences whilst not night and day will still be audible. What this means is that closed loop gain [gain with global feedback] is about 1/10th that of the amplifier's open loop gain [gain without global feedback connected] The difference between the two is the feedback ratio which can be expressed as dB or as a numeric ratio [not usually done]. Basically the gain is reduced to 1/10th of its open loop value, and this simplistically speaking this reduces distortion, output impedance, the effects of internal noise sources by the same amount. It also has some positive effect on the bandwidth and flatness of response of the amplifier.
Note: I strongly recommend Newbs purchase a copy post haste of Morgan Jone's "Valve Amplifiers 3rd Edition" It will give you a solid grounding and makes IMHO a fun read for anyone interested in tube audio.
There is global negative feedback (gnfb) in this design taken from between the 8 ohm secondary of the output transformer and ground which is fed back to the cathode of that srpp input stage.
R106 and C103 form a low pass filter that removes the ac signal but not the dc voltage from the grid, this triode in the phase splitter actually has a grid grounded for the ac signal and is driven by its cathode which in turn is driven by the other section's cathode - this creates the non-inverted phase of the phase splitter output (V2-6). The output from V2-1 is inverted because this stage looks like a standard inverting (common cathode) voltage amplifier stage. The plate loads are asymmetrical because the "long tail" (30K resistor to gnd) isn't really all that long and some signal losses occur in the cathode coupling.. The two grids in the phase inverter must be at approximately the same dc potential which is the other function that R106 and C103 provide - biasing both triodes correctly relative to one another since their cathodes are tied together. (Note for this reason that a triode with well matched sections is a good idea in this stage so that both sections operate at about the same point on their characteristic curves.)
This design looks pretty reasonable to me, rolling tubes should net a significant improvement in sound quality even though gnfb is used - the levels are not likely to be more than 20dB or so - so tube differences whilst not night and day will still be audible. What this means is that closed loop gain [gain with global feedback] is about 1/10th that of the amplifier's open loop gain [gain without global feedback connected] The difference between the two is the feedback ratio which can be expressed as dB or as a numeric ratio [not usually done]. Basically the gain is reduced to 1/10th of its open loop value, and this simplistically speaking this reduces distortion, output impedance, the effects of internal noise sources by the same amount. It also has some positive effect on the bandwidth and flatness of response of the amplifier.
Note: I strongly recommend Newbs purchase a copy post haste of Morgan Jone's "Valve Amplifiers 3rd Edition" It will give you a solid grounding and makes IMHO a fun read for anyone interested in tube audio.
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Very happy with the sound though.
NFB: Negative Feedback
gNFB: Global Negative Feedback
Open Loop Design: The operation of the circuit with the feedback not applied. Having a clean open loop design is much better than a poorly performing design which relies on the NFB to correct and conceal that poor open loop performance. This can force the measurements to look good, but there is a considerable sonic penalty to relying on large amounts of NFB to hide your mistakes.
In that schemo, the gNFB is taken from the secondary of the output xfmr, and fed back to the cathode of the first voltage preamp.
The connection of the screen grids of the finals to taps on the primary of the OPT (Output Transformer) is local NFB since it's applied to that stage only. Here's another way to apply local NFB: Vixen Main Schemo. Here, R33-34 feedback the signals at the plates of the 807s to the grid of the 6SN7 cathode followers (C9-10 are DC blocking capacitors) and are scaled so that the feedback voltage is 10% of that found at the plates. This accomplishes the same thing as the Ultralinear connection, and serves to linearize the output stage as well as reducing its effective plate resistance.
No simple answers to that. Back in "the day" good, bad and indifferent vacuum tubes rolled off the assembly lines by the tens of thousands every day. NOS is not always the magic word, especially when it comes to military rejects. Some of those tubes were just plain awful. There is also some excellent new stock available as well. I've used new production Sovtek 6SL7s and 6SN7s and found them to be excellent. Even though the design was done against RCA plate characteristics, the Sovtek's operated with very little measured discrepancies from the design nominal values. So these Sovtek tubes adhere to the design specs quite closely. Also, the Sovtek's were not microphonic at all. There are a lot of NOS 6SN7s that are very microphonic.
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