Little Bear Tube Phono Pre??

[OneyedK]

And what country may that be?

(I for one say that the LPS version of the Sovtek is prone to hum, but this may not be a problem as the little bear has DC heating voltage)
WA<WB<WC : gain

 

[jurmaan]

I'm from Poland and since I can get some tubes from my native resellers I want to avoid buying from abroad or something.

Oh and my voltages are 6.7 and 16.5. So these also qualify for the diodes mod ?

 

[OneyedK]

TAD from Germany are very trustworthy...

You can do the diode mod, but as long as the heater voltage doesn't go over 110% of 6.3V, you're pretty safe...

 

[eltech]

It is my considered opinion that you are either crazy or I got a bad set of tubes... Switching them out for nos Soviet tubes was like night and day. The Chinese tubes went straight into the trash. Everything else here is spot on. I used perforated aluminum to make a cage and some copper mesh to make tube shields. The hum is now acceptable. This preamp sounds Tony the Tiger GREAT!

I can only speak for the tubes I got with two little bear REV 1 boards.
All 6 tubes were consistent (all the same) and both sound the same. The quality is good and the sound is outstanding. Possibly your tubes were not good. Can you describe the sound of your Chinese tubes, and how long did you run them for?

I found the Chinese tubes needed about 8 hours before sounding really good. At first turn on they sounded a bit thin.

I gave the Russian tubes about 16 hours and they were still lifeless, and had no high frequency extension, and the bass was muffled sounding.

 

[eltech]

What more about the hum. It seems that waving my hand around the tubes doesn't make any difference. What I found strange that, when I was turning my record to other side and all I could hear at the time was the hum, I could hear the hum changing to louder or quieter, like switching. It wasn't triggered by me in any way. I observed that it kinda happened "on it's own"

P.S. Sorry for my english but I don't use it on a daily basis

Hello Jurmaan, to get rid of the hum, you need to put the phono stage into a sealed metal box. Wrapping wire / turning it in different directions etc, will not get rid of the hum.

So anyone who intends to buy this kit take note of what I'm saying. Its a great kit, but if you have high expectations, then you must put it into a Faraday cage (sealed metal box)

 

[fetor56]

Hello Jurmaan, to get rid of the hum, you need to put the phono stage into a sealed metal box. Wrapping wire / turning it in different directions etc, will not get rid of the hum.

So anyone who intends to buy this kit take note of what I'm saying. Its a great kit, but if you have high expectations, then you must put it into a Faraday cage (sealed metal box)

This sealed metal box eltech,i'm assuming it needs to be connected to Earth?

 

[eltech]

This sealed metal box eltech,i'm assuming it needs to be connected to Earth?

Yes, it must be connected to earth.
I've attached pictures of my re-purposed vintage cassette deck which now houses the little bear.

The cassette drawer and VU meters have been blocked off with metal joining sheets which I bought from the hardware store for about $2.00 each.
They are riveted to the chassis.

The chassis is connected to mains ground. The turntable earth wire connects to the screw in the case.

I used an old cassette deck chassis because:
1) the cassette deck didn't work because the belt was broken
2) It was free.
3) its high enough to fit the tubes
4) if you buy a metal chassis off ebay it costs $100 delivered.
5) it does the job.
6) Total cost including RCA connectors = $12
7) It is recycling something that would otherwise go to landfill

.....Now enjoying the sound of silence

 

[eltech]

I also mounted the transformer in a wooden box, and run the secondary wires into the case separately.

I've built one with the transformer inside the case, and one with external transformers.

I never did an AB comparison to see if one has lower noise. But I feel better with the transformer outside the case.

For saftey, the cables are retained using cable glands.

Happy new year!

 

[Poultrygeist]

Good job!

You can still fashion a face plate to cover the front and it wouldn't look like a repurposed cassette deck.

I'd take the measurements to Lowes and have them cut a piece of clear acrylic. Then spray the back side gloss black and you'll have a handsome face plate in piano black.

The acrylic must be totally lint free before spraying or it'll show. Stainless steel mounting screws would add some nice contrast and detail.

 

[OneyedK]

I found the Chinese tubes needed about 8 hours before sounding really good. At first turn on they sounded a bit thin.

I gave the Russian tubes about 16 hours and they were still lifeless, and had no high frequency extension, and the bass was muffled sounding.

The Chinese tubes were microphonic AND noisy... Something that doesn't cure over time.
The Russians were great from day one. Maybe you simply got a bad set... It's not because they are Russian that they are automatically good.
Same goes for the Chinese, not because they are Chinese that they are automatically bad.
Use your ears and measurement equipment and decide.

When I need 6N1 or 6N2's, I prefer the Russian manufactured tubes.
For ECC81 (12AT7) and ECC83 (12AX7) I buy a batch of JJ tubes and select them myself.
For all other I often rely on the Premium Select tubes from TAD, wich are Chinese production tubes.
--> For rectifiers, I only trust NOS.

 

[eltech]

I agree with you that microphonic and noisy tubes wont get any better. I also agree that you cant keep using them because going by your description, it would make listening un-enjoyable.

I just wonder if you are being so enthusiastic about these Russian tubes because when you first put them in, that they worked, and in comparison to your Chinese ones that obviously didn't work due to microphonics and noise, then ergo, the Russian ones are great tubes? I also wonder that if you had received working Chinese tubes to compare to the Russian ones, that you may actually prefer the Chinese tubes as I do?

As it so happens, I did use my oscilloscope and ears. The Russian tubes picked up less airborne noise (checking on the scope - good) , but simply had no top end or dynamics (ears - bad)

The Chinese tubes I got are some of the best tubes I've ever heard period.
Perhaps I got lucky and you got unlucky?

I've heard quite a few Russian tubes of the 6n1p / 6n2p /6n3p variety (I also use them in my DAC) and I can identify a common trait with them that they often have a tight upper mid, and rolled off top end.
Not all of them, but the vast majority that I tried. I don't think the ones I got are defective. They just seem to have the common trait that I am familiar with.
I have heard one or two that were "open and airy" sounding, but still not in the same league as the Chinese ones that came with my Little Bear.
The Russian NOS tubes on ebay come from one of three factories. In my experience the factory and the year of manufacture does make quite a difference.

The Chinese tubes I received, I would describe as the perfect tube. - Not microphonic / open / airy / quiet / tonally balanced / grain-free / extended but not emphasized top end / have explosive dynamics.

My advice to people is to listen to the Chinese tubes first, and if proven to sound good and have no microphonics then leave them.
If proven defective (eg. microphonic) then contact the ebay seller and ask for replacements.

I've said what I have to say. Its simply good advice - effectively, if it ain't broke don't fix it. (alternately, if it is broke, do fix it)
I didn't want to get into an argument with anyone, I just wanted to share my positive experience with the Chinese tubes. I think very highly of them as you can probably tell by now. I'd be really sad if people were just throwing out their working Chinese tubes without giving them at least 8 hours of run-in, and a good listen.
If you are happy with your Russian tubes, then great, I'm happy that you are enjoying your little bear as much as I am.

 

[fetor56]

Sound advice eltech....when i get mine i'll first listed to it & see if the hum bothers me.If it does (and it probably will) i'll run the unit for approx 10hrs and see how the valves sound to my hearing.Next step would be to enclose the little bear in a metal enclosure.I'll see how much heat it generates....too much and i'll perforate the enclosure top.Replacement valves may possibly be in the future....possibly.

 

[williwoods]

This is a question for a friend of mine that just bought one of these. He isn't an AK user yet. Hopefully someone who has put one of these together can answer this pretty easily.

Where do you connect this wire (see the attached pics).

he says that he has connected everything else, but cant figure out where this wire goes.

thanks

w

 

[batman7349]

That must be the "Pro" version. It looks like a wire on ground portion of the PCB, but I don't know where they expect you to connect it. My T10 does not have one and my input resistors are labeled R16 & R17, whereas the ones in your picture appear to be R4 & R5 as well as some sort of selector switch. Sorry I can't help.

 

[batman7349]

I have finally finished my Little Bear and have it in my system. Pretty quiet after all the mods. I Connected the floating shield pin on #9 for the 3 x 6N2 to ground. Added diodes to get the 6.3V & 15V respectively. Added copper tape from a stained glass supply store to the top cover. Grounded the transformer. Added 200K ohm resistors in parallel with the 62K ohm resistors to get 47k load on 16 & R17. Replaced the power cord. Replace the two .1uf with K40Y PIO capacitors. I built a metal pan out of the side of an old tower computer, then mounted it inside an oak 1 X 3 box. If I find 4 .47uf K40Y 400V PIO capacitors I will do that mod also but so far I have only found 200V caps. It is now running with a 3 tube Yuan Jing preamp/buffer into a Dynaco ST70 and then into a pair of GR Research X-LS Encores with Mills resistors and Sonicaps, also have an HSU VT3 for a little bottom end punch.

I do have some microphonics after about 1/3 volume so a set of Russian 6N2P-EV tubes are on the way. I have not found a 6Z4P-EV yet.

 

[fetor56]

This is a question for a friend of mine that just bought one of these. He isn't an AK user yet. Hopefully someone who has put one of these together can answer this pretty easily.

Where do you connect this wire (see the attached pics).

he says that he has connected everything else, but cant figure out where this wire goes.

thanks

w

Looks to be the black ground that grounds the transformer,now standard on the Pro .

 

[fetor56]

Well done batman.
Hope when i get my Pro version i don't need to go to such mods.

 

[Poultrygeist]

Great job batman

Nicely matched wood.

 

[batman7349]

Thanks Poultrygeist! I built the cabinet to hold the system the week before. Now to build some produce crates to hold about 800 vinyl LP's that have been in storage since about 1983....

 

[jurmaan]

Well… I noticed another problem with mine. Was just sittin' listening to "shine on you crazy diamond" with my headphones on and in the last 1/4 of the track there is a saxophone line along with clear guitar line. So the guitar notes are ok but when the saxophone appears or other "mid-range noises" I can hear some crackling in the background. This doesn't appear on my other preamp so i suppose it's not record's fault. Any idea's what it might be ?


Oh… and one litthe offtopic question. I'm having some problems with volume on my right channell. Can this be a faulty cardrige ?