Yaqin VK-2100 tube integrated amp

gforce

New Member
Yaqin VK 2100 follow-up. AK denisons : IDEAS ?
Later that week: Still sounds great. Still makes weird sounds. Runs at high temp. ...And the lid is in contact directly with a really ugly little transformer, WHICH HUMS AND BUZZES hard enough to compete with a Vibe. NO interior cover over power trans. If you would be so kind to look at this link:
http://hi-end.on9mart.com/products/amplifiers/integ_amp/AI-YQ-VK2100/YQ-VK2100_09.jpg

Is this like your amp's interior: Second COVER OVER THE POWER SUPPLY? See the red RING THROUGH THE VENTS? Does yours have a RED TOROIDAL TRANFORMER ? Thanks for your time. Paul Whistler.bc.eh
 
I have one, I bought it elsewhere.

Transformers seem vary from country to country, no mine is square-ish.

No internal cover, that may vary with transformer dimensions. Or, as it is made with parts that foreign company's outsource to China, it may have to do with availability.

No hum ether, I'm listening to it now, it's very quiet.

I've compared notes with MJarve who also owns one. They run hotish. I just walked over to mine and put my hand on the case over the heat sink, warms but I could count to ten and still keep it there, but I'm only driving it about at about 1/3 power. It's gotten hotter cranked, but I could still go three or four seconds before wanting to remove my hand.

Mike added some air vents to his.

Did you buy it new? If so, contact the seller.
 
I found, at least in my case, that the solid-state power amp section was biased rather absurdly high. I re-calibrated mine to ~15mV (had been over 80mV in one channel and ~30mV in the other). Cooled down the heatsinks right quick. Of course it still gets hot above the tube area (as I would expect).

As Holst mentioned, I also added some more venting to the bottom of my unit, lined up with the heatsink fins. Again, that helped quite a bit.

My unit does not have the internal secondary enclosure for the PT. I believe that was more common with the first version, as all the units I have seen since then have an EI core transformer with no secondary enclosure (though I have seen photos of US market units with the secondary enclosure and toroid PT).

Another way to tell first generation from the second is whether it takes only 6N1/6N1π tubes or if it can accept 12AT7/12AU7's as well.

I did have an issue with the PT vibrating on mine, which I rectified by installing little bump-on feet on top of it to press against the cover. I can no longer hear or feel the chassis vibrate.

As I mentioned in my initial posts on the VK-2100, the design is solid, but execution could have used some work. I also noted that I was less than impressed with the sheet-metal work on it, and that remains a valid criticism in my view, though the typically low cost did mean they had to cut something somewhere. Given the choices, I'm glad they traded a sub-standard enclosure for better internal components. If you want cake and to eat cake, you have to spend a lot more.

One more thing I might mention is that I removed those ungodly little wire tube retainers from the sockets, which seemed to eliminate some peculiar hums I was getting from my speakers. That's to say nothing of the tubes themselves, one of which on my unit became microphonic, though a handy idler tire from a VCR cured that.

If you (or Holst for that matter) would like help in biasing the power amp, I'd be glad to assist.
 
You can check the circuit board to find out what generation yours is. Mine shipped with 6N1's but it states on the board what tubes can be rolled into what sockets. The lid on mine is as hefty as the Luxman D-373 that is currently sitting next to it.

...again, I think it's variations from run to run.
 
You can check the circuit board to find out what generation yours is. Mine shipped with 6N1's but it states on the board what tubes can be rolled into what sockets. The lid on mine is as hefty as the Luxman D-373 that is currently sitting next to it.

...again, I think it's variations from run to run.

Indeed, that would appear to be the case.

I am satisfied with Yaqin enough that the new amp I ordered last week was made by them. For the same price, I could have gotten something pretty good from a more reputable brand, but in my case it is more about about the quality of the sound than the name on the front.
 
Yaqin VK 2100 ...Please excuse my hum

Been meaning to post this for some time. Found the hum. It was in the floor lamp's transformer. So - amp on and lamp off. Two months on and what a great deal for $325 = to my door in a week.
 
hi guys, im still a novice at this. i think my vk2100 has its bias set too high in one channel.
the right heatsink gets stupidly hot while the other is cool. when i got it i checked the dc offset and managed to adjust it.

now this might sound like a stupid question,
im sure the bias needs adjusting but im not sure where to measure it from?
could anyone point me in the right direction?

thanks
jimmy
 
If you can post a close-up picture of the amp section, I would be glad to help you. I sold mine, and so have nothing to guide you with. It's actually pretty simple- just taking a reading across the emitter resistor- but I did find better test points than trying to cram both leads in that small area.
 
Okay- this should help you out. Be very careful with the leads; if one slips and shorts out something that should not be shorted, you blow the amp. Have a very calm hand doing this.

The other channel will essentially be the same, and you want to balance out both channels within 1-2mV of each other.

Also note that the procedure is somewhat time/temperature dependent. You want to do it when the amp is fully warmed up. Have it idle (that is on, but not really doing anything) for about 1/2 hour with the cover on, but screws removed.

Performing this sort of thing in this amp in particular is a little more dangerous than usual, as there are HIGH VOLTAGES present not far away from where you will be doing this. The amp power rails themselves are only a couple dozen volts, but the power supply for the tubes is in the hundreds of volts. BEWARE!

After you adjust and balance, replace the cover without replacing the screws and start playing some music. Make sure it sounds okay, and let it go at a medium-low volume for about half an hour. After that, stop the music and check the bias again. It should not have drifted or only drifted a little. Re-calibrate if needed, otherwise replace the cover and screws and your set.
 

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thanks m jarve,

your instructions really helped.:thmbsp:
i managed to get both channels to around 16mv , and now after a few hours with the volume cranked the heatsinks only get warm.


thanks again
jimmy
 
Thanks for the tips too !

On mine, I must adjust the bias to 35mv because if I adjust at less there is a buzz in the speakers.
Strange....
 
First of all, thanks for the tip!

Could you also point out where to meisure for DC offset?
I've put some pics on http://speksnijder.org/vk2100 feel free to use any of them.

Does anyone know what tubes really fit the VK2100? It says on the board 2x12AU7 and 2x 12AT7 while all the ads on eBay say 4x6N1. Also, are the tubes auto-biased, or do you have to adjust when replacing them?
 
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First of all, thanks for the tip!

Could you also point out where to meisure for DC offset?
I've put some pics on http://speksnijder.org/vk2100 feel free to use any of them.

Does anyone know what tubes really fit the VK2100? It says on the board 2x12AU7 and 2x 12AT7 while all the ads on eBay say 4x6N1. Also, are the tubes auto-biased, or do you have to adjust when replacing them?

I think it just changes automagically- probably has what would be the screen connection of the 6N1 tied to the CT of the heater taps instead of ground or something. As far as implementation goes, the main difference between a 6N1 and 12A?7 is that the 6N1 basically has its filaments wired in parallel where as the 12A?7 has them in series. And the pin that would be the heater CT on a 12A?7 is the screen on a 6N1.

Usually small signal tubes are not picky about bias like their output counterparts. As long as the pinouts are the same, the voltages are in the ballpark, and the heater taps can supply the appropriate current, everything should be fine.

Checking for offset, just connect your MM to the speaker outputs, preferably with an 8Ω/ >20-watt resistor connected up across the + and -, and adjust the DC offset pot inside to get as close to 0mV as possible, though anything between -50mV and +50mV is acceptable. You will become frustrated, though- as soon as you put the cover on, the DC will drift somewhat, and after it warms up inside, it will drift a lot. So, you want to compensate for this when you have the cover off. If the DC drifts +20mV in one channel after the cover is replaced, and it has warmed up, adjust the DC offset for xmV - 20mV when the cover is off: i.e. the best you can get is ±15mV with the cover off, but it jumps to ±35mV when the cover is replaced, adjust the bias to 15mV±20mV in the appropriate direction so that the offset "drifts" towards 0.
 
Great! Thanks man!

On mine, if I measure bias like you say, black lead on bottom of pic and red on top side, it says -19mV? Are you sure transistor side is +?
Like this:
measure-points-small.jpg

or the other way around?
 
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On that resistor, it would be negative. The idea is that one part of the output stage is constantly pushing out a little current (a + reading across the resistor), while the other part is pulling a little current ( a - reading across the resistor). I normally would have added a ± to the voltages, but I apparently made that edit on my Windows system.

Great! Thanks man!

On mine, if I measure bias like you say, black lead on bottom of pic and red on top side, it says -19mV? Are you sure transistor side is +?
Like this:
measure-points-small.jpg

or the other way around?
 
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