Domesticating & Documenting the Little Bear

the thin end of the wedge
T68
senior member
senior member
Sweden
Posts: 426
Joined: 11 Jul 2018 18:41

Re: Domesticating & Documenting the Little Bear

Post by T68 » 30 Dec 2018 23:52

Thanks for good info, cminor!
Sounds wise to go for the t11 with the shielded case.
Also good to hear that it can be upgraded with a simple change of tubes. I'm no wiz with a soldering iron :-).

lentulus
junior member
junior member
Russia
Posts: 5
Joined: 01 Jan 2018 09:08
Location: Russia

Re: Domesticating & Documenting the Little Bear

Post by lentulus » 08 Feb 2019 05:17

I have little bear 2.5 with 6n2 tubes. When I changed the tubes, my hand touched some part on the board and I received an unpleasant electric shock. Power at this moment was not connected. After this, my little bear stopped working. 6n2 tubes do not work. On the Internet, I found the schema of a little bear version 2.2, but did not find version 2.5. If someone has it, I would be grateful for the help.

JoeJester
junior member
junior member
Posts: 11
Joined: 11 Apr 2017 13:06

Re: Domesticating & Documenting the Little Bear

Post by JoeJester » 10 Feb 2019 06:21

Take clear pictures of both the component side and the foil side.

ver 2.5 may have added a new, minor feature.

You can find pictures of both on the internet, and see if the components are the same and what the differences are.

lentulus
junior member
junior member
Russia
Posts: 5
Joined: 01 Jan 2018 09:08
Location: Russia

Re: Domesticating & Documenting the Little Bear

Post by lentulus » 10 Feb 2019 14:23

The problem was solved. The preamp did not work due to poor contact with one tube.

T68
senior member
senior member
Sweden
Posts: 426
Joined: 11 Jul 2018 18:41

Re: Domesticating & Documenting the Little Bear

Post by T68 » 11 Feb 2019 05:38

Good to read that it wasn't any more serious problem, lentulus.
Besides this, how is the t10 2.5 working out for you? I'm a little curious since I just ordered that model for myself.
Hopefully it will arrive in a couple of weeks (slow boat from China and all that :-) )

lentulus
junior member
junior member
Russia
Posts: 5
Joined: 01 Jan 2018 09:08
Location: Russia

Re: Domesticating & Documenting the Little Bear

Post by lentulus » 14 Feb 2019 07:50

T68, it's hard for me to compare, since this is my first preamp. I am generally pleased with him. On the advice of many users, I replaced the 6N2 tubes with the Russian 6N2P -EV and the sound became clearer and more voluminous. However, my overall audio system has problems with low bass. Most likely it is the fault of the Technics p30 cartridge or the fact that I connected the preamp to the home theater system.

T68
senior member
senior member
Sweden
Posts: 426
Joined: 11 Jul 2018 18:41

Re: Domesticating & Documenting the Little Bear

Post by T68 » 24 Feb 2019 17:07

Well, right after I placed my order back in January the seller went off on holiday. He got back a week ago and arranged the free shipment right away. And now it's already on Swedish turf. Impressive!
Hope Swedish customs is nice :-)
With a bit of luck I might be rocking (hopefully not humming) the little bear t10 by this weekend.

MadhaviPrem
Posts: 1
Joined: 27 Apr 2009 14:11
Location: Earth

Re: Domesticating & Documenting the Little Bear

Post by MadhaviPrem » 06 Mar 2019 07:45

Hi
Just got myself one 2.61 Version. I want to upgrade the power transformer. I live in Greece and here there is a very good transformer maker.
My transformer is toroidal 50VA Primary 0- 230V and Secondary 0-15V , 0-6.3V and rectifier 200V-0-200V .
My question is nowhere I can find current requirements.
Does anybody know how much current capacity is needed at each secondary? 1A ,2A or 50mA ?
If any expert throw some light on this.
Thanks in advance

ROY_H
member
member
Posts: 32
Joined: 14 Mar 2013 18:22

Re: Domesticating & Documenting the Little Bear

Post by ROY_H » 28 Aug 2019 17:39

This is my first posting here though I have been working my way through all of this long thread (well, almost all. I left out the discussion pages on motorbikes !)
It’s been an arduous but worthwhile marathon and special thanks to CoffeePhil for his very pragmatic and fascinating comments about the Little Bear.
Now apologies for what’s going to be a long posting but I hope my experiences will be useful. I purchased my LB just before I found this thread and received it just as I was getting to some of the interesting mods. I received a V2.62. The difference from the V2.6 appears to be that the on-board connections from the transformer are now headers with the appropriate connections already on the transformer leads. Less chance of wrong wiring-up. The transformer supplied was an EI type and it came with 12AX7B valves and screening cans.
Everything powered up well and the sound was great (previously had a Linsley-Hood op-amp based phono stage home-assembled) and no problems with hum. However, I sourced some Russian 6N2Ps and on installing three I had hum like never before. I tried all sorts of earthing strategies with no success so went back to the 12AXs and normality returned. Cut a long story short, looks like one of the Russian valves was a dud so I carefully picked out three good ones and it’s now as good as silent at all sensible volume levels even without the screening cans (looks better without them anyway)
My next stage was an itch to try one of the RIAA revisions so I decided to go for the 40dB T. Layton mod. I’m experienced at soldering having built amps and pre-amps in the past so felt confident. I’ve got a temp. selective soldering iron, solder sucker, heat sink pliers and yards of fine-gauge silver-based solder!
Next decision was choice of components. Resistors were easy. I purchased strips of twenty of boyh values in 1% 1/4W metal film. Using a Beckman multimeter I choose the two resistors of each value which a. closely matched the required value b. Closely matched each other, thus ensuring balance.
The capacitors were a puzzle initially. 5% ceramics were initial choice but very expensive and trying to find the right set of values to match the criteria was hard. I opted to purchase a bulk package of 10% 50V disc ceramics which had 20 each of 50 values! It was only a fiver delivered and I reasoned I could find the correct values by measurement. I bought a multi-function tester from China a while back and this measures capacitance amongst other parameters. Clearly, I didn’t know how ACCURATE it was (though it measured very close to the nominal values of all the ones I tested at both ends of the range) but aimed for PRECISION to again achieve balance between channels. Using this I found two 1nF which measured 900pF + 5pF and the 250pF I achieved by two 220pF and two 30pF again measuring the values and then measuring a pair combined to achieve + 5pF. I piggy backed the 900pF onto the 3M9 resistor before soldering all the components onto the board.
Results? Well, it all worked (good start) and the sound? I can only say that IMHO it is the best sound I’ve ever had out of my system EVER. Everything was clear, well separated. The stereo image was as wide as I’ve ever heard it and the overall effect was outside the speakers and 3-dimensional. As a final test, my wife remarked (without knowing what I’d done) that there was no way CDs sounded as real and open as the sound we were hearing from this.
Bottom line, if you feel confident on doing this, go for it. My cost for the components was less than £10 and time about an hour and I’m convinced I have a phono pre-amp to rival some very expensive alternatives.
Way back in the early ‘70s, Ivor Tiefenbrun formed Linn products with his turntable and told everybody that the key to good sound was the source which at the time was revolutionary. I believe the LB with these mods proves this!

Coffee Phil
vinyl addict
vinyl addict
United States of America
Posts: 5783
Joined: 20 Sep 2008 08:22
Location: California

Re: Domesticating & Documenting the Little Bear

Post by Coffee Phil » 28 Aug 2019 18:20

Hi Roy,

Congratulations on the successful mod! I believe that getting a cap meter and combining caps to get the values which you need is the easiest, most cost effective way to get the caps when you are doing a one off item. One word of caution however. Make sure the caps are COG. X7R is less good but if you are measuring them they are less expensive and smaller in the larger values. Avoid Z5U like the plague for this purpose. They are unstable with respective to temperature, and voltage and can be micro-phonic. They are suitable for bypass and coupling only.

Phil

ROY_H
member
member
Posts: 32
Joined: 14 Mar 2013 18:22

Re: Domesticating & Documenting the Little Bear

Post by ROY_H » 28 Aug 2019 19:16

Hi Phil. Thanks for the comments, hope my post is useful to some! Re the caps, I'm afraid I don't know their designation and presume there's no way of determining from markings. As they were bought as a bulk package who knows!!
If as I use the pre-amp I start noticing any aberrant behaviour I'll start considering looking into obtaining your suggested types but at the moment it's indicating that this really is the route to go with this beast. The improvement over the (already good) original is marked.
Incidentally, the cap meter was very cheap and having done repeat measurements on the same caps of different values the reproducibility was very good which gave me confidence it was on the right lines. It also measures resistors (including the 3M9s I used) and inductors as well as it's key role for transistors. well worth keeping in the tool drawer!

T68
senior member
senior member
Sweden
Posts: 426
Joined: 11 Jul 2018 18:41

Re: Domesticating & Documenting the Little Bear

Post by T68 » 30 Aug 2019 16:24

Good to read about your successful mod, Roy!
Any chance of seeing som pics of how and where you did it on the board? Would be much appreciated!

ROY_H
member
member
Posts: 32
Joined: 14 Mar 2013 18:22

Re: Domesticating & Documenting the Little Bear

Post by ROY_H » 31 Aug 2019 15:46

I did take a few pictures as I did the mod as I thought it might be useful reference to anyone else who might fancy it, so here goes !
20190817_135739.jpg
(119.89 KiB) Downloaded 60 times
20190817_135937.jpg
(107.07 KiB) Downloaded 58 times
20190817_140449.jpg
(91.26000000000001 KiB) Downloaded 57 times
20190817_140457.jpg
(95.54000000000001 KiB) Downloaded 55 times
20190817_140604.jpg
(134.95 KiB) Downloaded 55 times

ROY_H
member
member
Posts: 32
Joined: 14 Mar 2013 18:22

Re: Domesticating & Documenting the Little Bear

Post by ROY_H » 31 Aug 2019 15:47

And the final two!
20190817_141154.jpg
(96.15000000000001 KiB) Downloaded 54 times
20190817_142606.jpg
(96.45 KiB) Downloaded 53 times

T68
senior member
senior member
Sweden
Posts: 426
Joined: 11 Jul 2018 18:41

Re: Domesticating & Documenting the Little Bear

Post by T68 » 01 Sep 2019 22:03

Thanks for the pics!

Post Reply