New Little Bear Pro v2.5 breakdown

[StylinLP]

Hey all, I just received my Little Bear Pro v2.5 tube phono preamp. The quality of the parts are much much higher than I would have expected for what little the guy sells these from China. My buddy got one as well and we are both impressed. Even the glossy black circuit board looks like its good quality. As you can see from the photo's its for a bit of copper and gold plating but not everywhere. The tube sockets are not copper...
I noticed they didn't bother to wash the Flux off the circuit board. So that's the 1st thing I will need to do before putting the transformer in and trying it. Tomorrow I will clean it then get it together by night time and give it a listen. In the meantime, here is a list of the parts it came with.

I will be asking for recommendations on taking every part of this baby to the next level. Replacing everything. I will be asking for recommendations.

Rubycon Nichicon capacitors

x3 - 68uF 450v 105c (circuit board is marked 400v)
x1 - 100uF 450v (circuit board is marked 400v)
x2 - 4700uF 35v (circuit board is marked 50v this is bad?)
x2 - 220uF 50v

x4 - WIMA MKS4 .47 100v
x2 WIMA MKP10 .1uF 400v

 

[StylinLP]

Here are the 12AX7 chinese tubes and the transformer that was sent with the Little Bear

 

[phalanger]

Hey all, I just received my Little Bear Pro v2.5 tube phono preamp. The quality of the parts are much much higher than I would have expected for what little the guy sells these from China. My buddy got one as well and we are both impressed. Even the glossy black circuit board looks like its good quality. As you can see from the photo's its for a bit of copper and gold plating but not everywhere. The tube sockets are not copper...
I noticed they didn't bother to wash the Flux off the circuit board. So that's the 1st thing I will need to do before putting the transformer in and trying it. Tomorrow I will clean it then get it together by night time and give it a listen. In the meantime, here is a list of the parts it came with.

I will be asking for recommendations on taking every part of this baby to the next level. Replacing everything. I will be asking for recommendations.

Rubycon Nichicon capacitors

x3 - 68uF 450v 105c (circuit board is marked 400v)
x1 - 100uF 450v (circuit board is marked 400v)
x2 - 4700uF 35v (circuit board is marked 50v this is bad?)
x2 - 220uF 50v

x4 - WIMA MKS4 .47 100v
x2 WIMA MKP10 .1uF 400v

If the components are really of the brands indicated then I see no reason to replace them. Unfortunately with Chinese ebay offers that's always the question as counterfeits are not uncommon.

 

[StylinLP]

I've soldered in Rubycon Capacitors before and they are definately the real thing. I'm think the WIMA are too but I don't know for sure. Based on all the feedback and responses from this Chinese seller he seems very honest and trustworthy. He even responded to my questions while on vacation and added more information. He has improved this model a number of times based on all the American users feedback. I'm happy with the quality. But I'm looking at Mundorf caps and audio note resisters and oossibly copper tube sockets

 

[phalanger]

I've soldered in Rubycon Capacitors before and they are definately the real thing. I'm sire the WIMA are too but I don't know for sure. Based on all the feedback and responses from this Chinese seller he seems very honest and trustworthy. He even responded to my questions while on vacation with add i quite information. He has improved this model a number of times based on all American users feedback. I'm happy with the quality. But I'm looking at Mundorf caps and audio note resistors and possibly copper tube sockets

If they are real then WIMAs (especially the MKP10's) are very capable caps already, no less good than regular Mundorf M-Cap. I'd say in this class of preamp, there's probably limited gain to be had from replacing already good components by slightly better ones. The tubes are another matter though

 

[vinylkid58]

The tube sockets are not copper...

Copper oxidizes, which isn't a good thing when you want to retain good contact with something electrical. That's why copper is usually plated with tin or silver or nickel.

I will be asking for recommendations on taking every part of this baby to the next level. Replacing everything. I will be asking for recommendations.

If you're going to do that, why not just build from scratch.

jeff

 

[StylinLP]

Well, about my history...I compelted my 1st two learning to solder kits from ENCO last month and worked 1st try. Then I bought the ENCO Tri Power supply kit and that turned out working perfect 1st try. Now I am restoring an original Atari 2600 heavy sixer and adding a composite and svideo video kit. Almost done with that. My next learning project will be recapping a pair of Wharfedale W90 speakers and then this Little Bear Phono tube preamp. After im done with all that I am thinking of buying an audio kit to learn. Im far away from building something from scratch. There is no way in a million years I could design one. It would have to be a kit.

 

[StylinLP]

Can anyone answer me about rectifiers? The Little Bear comes with the 6Z4 with 7 pins. But these tubes I found on ebay below have only 5 pins? Also, I was not able to find any Russian. Any advice on a better rectifier?

SLEEVE OF 5 SYLVANIA JAN 6Z4/84 TUBES $25
http://www.ebay.com/itm/SLEEVE-OF-5...612?pt=LH_DefaultDomain_0&hash=item2546d1d4f4

SYLVANIA JAN 6Z4/84 TUBES
http://www.ebay.com/itm/SYLVANIA-JA...bfd77b&pid=100010&rk=3&rkt=24&sd=160101946612

RAYTHEON 6Z4/84 4-PILLER RADIO TUBE $5
http://www.ebay.com/itm/1-RAYTHEON-...333?pt=LH_DefaultDomain_0&hash=item5670d311ed

Strong NOS GE FAT Bottle Black Plate D Getter 84 / 6Z4 Tube
http://www.ebay.com/itm/Strong-NOS-...990?pt=LH_DefaultDomain_0&hash=item19e45b38e6

 

[vinylkid58]

The big old Sylvania 84's are a completely different tube as far as the basing is concerned. What you want is the good old american 6X4. Here is an explanation of how to convert your board:

If anyone is curious about the rectifier mod, its fairly straight forward. Cut pin 7, bend it upward away from the board, and with a piece of wire connect it to pin 5 on top of the board. Flip it over, and link pin 6 and 7 together underneath. Insert 6X4 rectifier. Done. I refuse to pay $10 for a chinese tube when I can get a NOS american one for $5

jeff

 

[StylinLP]

Vinylkid, thanks, that is exactly what I wanted. I remember some chat about that subject on the other thread but it wasn't entirely clear. I thought something was broken and people were helping.

Can anyone tell me which resistors are in the signal path? Which exact resister numbers on the board? I want to replace them with AudioNote or Mundorf.

 

[StylinLP]

Photos of the circuit board showing [hopefully] the resistors in the audio signal path.

 

[phalanger]

Photos of the circuit board showing [hopefully] the resistors in the audio signal path.

Your picture shows the resistors, but not the copper traces
Best way is to just ask the seller for a schematic.

Although I don't expect there will be an audible difference from swapping out the resistors. Audionote resistors seems over the top for a simple pre like this. That's the sort of thing that might start to make sense when everything else is already superb in design and execution. Not to say anything negative about this phono preamp, but it is a humble design with a very simple onboard power supply and cheap transformer, there are probably a dozen other bottlenecks before the quality of the resistors becomes a meaningful issue.

That said, if you really want to practice your soldering and meanwhile waste some good money on boutique resistors, the ones surrounding the red WIMA caps and the ones near the in/out will be most likely in the signal path

 

[vinylkid58]

Best way is to just ask the seller for a schematic.

Just google EAR 834p.

jeff

 

[StylinLP]

Phalanger, I see what your saying. Well, playing around and learning electronics is one reason too. Some of the boutique electronic sellers like Parts Connexion has a big %50 to %85 off sale one a bunch of components including resistors. Spending $20 to $30 is nothing to me but it would be fun to see if there is an improvement. Problem is that I have no idea if these resistors are .5 watt, 1 watt or 2 watts. But I do know how to read the color bars on the resisters to get the values which are already printed on the circuit board.

The capacitors are easy to do and there is big sales on those as well. Its not like im going to buy $100 caps or anything...

The 3 12AX7 tubes that came with the unit will be used for now. I want to hear what they sound like for at least 20 hours. Then I was thinking of jumping on a Gold Lion 12AX7 New deal of a matched 3 set. They sell for about $100. Unless I can get a better recommendation for the money.

Last thing to do is the Rectifier mod as mentioned in this thread then choose a US made NOS tube with 5 pins. I figured I would stick with the ceramic sockets as is but wonder if I can Craig Detoxit clean then ProGold or is that a bad thing to do?

Has anyone tried making a walled cage of copper sheets to drop down over the transformer? Would that help with the hum?

 

[phalanger]

So have you tried the phono pre yet? I'm curious how it performs.

About the transformer hum, do you mean it causes hum in the audio circuit or do you mean mechanical hum from vibrating?

 

[StylinLP]

No not yet, alergies the last few days. I will get it together by tomorrow night.

But, my buddy got a little bear v2.5 and his is having hum problems as well. He will be trying to re-orientate the transformer to see how that effects the hum. I read the "bells" need to be pointed away from the signal circuit. He hasn't tried copper tape yet.

 

[Aligauld]

Can anyone answer me about rectifiers? The Little Bear comes with the 6Z4 with 7 pins. But these tubes I found on ebay below have only 5 pins? Also, I was not able to find any Russian. Any advice on a better rectifier?

SLEEVE OF 5 SYLVANIA JAN 6Z4/84 TUBES $25
http://www.ebay.com/itm/SLEEVE-OF-5...612?pt=LH_DefaultDomain_0&hash=item2546d1d4f4

SYLVANIA JAN 6Z4/84 TUBES
http://www.ebay.com/itm/SYLVANIA-JA...bfd77b&pid=100010&rk=3&rkt=24&sd=160101946612

RAYTHEON 6Z4/84 4-PILLER RADIO TUBE $5
http://www.ebay.com/itm/1-RAYTHEON-...333?pt=LH_DefaultDomain_0&hash=item5670d311ed

Strong NOS GE FAT Bottle Black Plate D Getter 84 / 6Z4 Tube
http://www.ebay.com/itm/Strong-NOS-...990?pt=LH_DefaultDomain_0&hash=item19e45b38e6

Hi there,
If you do a search for 6C4P-EV (EZ90 6X4) you should find some.
These are black anode Soviet military grade and are a direct replacement for the Chinese 6Z4.
I purchased some of these last year for the Little Bear and they work perfectly

 

[rothwellaudio]

Has anyone tried making a walled cage of copper sheets to drop down over the transformer? Would that help with the hum?

Copper isn't a magnetic material and so has no effect on magnetic fields.

 

[fetor56]

This works....#472
http://www.audiokarma.org/forums/showthread.php?t=550392&highlight=Little+Bear+Preamp&page=32

 

[StylinLP]

Oh yea, Tube shields. Well, I ordered Herbies Tube Dampers which come highly regarded. They dont shield the tubes.

Last night I spent a considerable ammount of time cleaning all the flux off the circuit board. Word of advice. Get a cleaning brush or tooth brush. I did it with just electronics Q-Tips and paper towel. The blew if all the lint off with my air compressor. Tonight I will put the thing together and measure the output voltages of the transformer if I can figure out how with my new nice Extec 330 multimeter lol