Domesticating & Documenting the Little Bear

the thin end of the wedge
Coffee Phil
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Re: Domesticating & Documenting the Little Bear

Post by Coffee Phil » 10 Sep 2018 01:28

Hi Glenn,

Here is the story. The LB has a gain of ~ 50 dB @ 1 KHz which is somewhat high for a MM phono stage. The RIAA accuracy is fair as supplied, but there is room for improvement. I designed a new feedback network to give ~ 40 dB of gain @ 1 KHz. The RIAA accuracy was not very good at the low end. I assumed that there was insufficient open loop gain to support 40 dB gain with a feedback network network assuming infinite open loop gain so I altered some of the values to achieve good RIAA accuracy. The values which I posted for the 40 dB network gave good results which I posted. I would not be upset if you duplicated that network. I then set out to design a 30 dB gain network assuming the RIAA accuracy come out well with no “tweaking”. It turned out the 30 dB also was off. I then dug out Mr. Lipshitt’s paper and discovered the error in my design method. About the same time Mr. Layton posted values which he calculated using Mr. Lipshitt’s is equations. I have yet to re-do the calculations using Lipshitt’s equations but it is on my to do list. I would expect that Mr. Layton’s values for both 30 dB and 40 dB should work fine. If I remember his 40 dB values are close to my empirically tweaked values so I believe them. I have not yet tried either of his networks.

I’m pretty sure you should be able to use either of his networks and get good results.

Phil

Glenn Gavryluk wrote:Hello again,still no replies yet so I'll post again.
I'm looking todo the riaa mod and I've found the list of part on this forum but can someone please let me know what goes where?
I know it's the small orange disk caps that need replacing but what is the order for replacing these?..again, I'm no electrical engineer but can do basic soldering etc. So if some one can tell me what to do exactly that would be great! Also I'm no good at reading scematic. Also I ask this as I've gotten confused with coffee phil- he made a new riaa then said not to use it!..then mentioned he was making a new one!...which should I do!?...t. leytons or coffee phil mod?..anyone any advice?...which is best. Please help..

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Re: Domesticating & Documenting the Little Bear

Post by Glenn Gavryluk » 10 Sep 2018 05:36

That's excellent phil, thank you for all your time and effort with this LB.It's been invaluable reference for all of us...I have previously been through various pages on this forum,can you remember with page I can find the schematic for this?...I have a friend who will help me figure it all out.

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Re: Domesticating & Documenting the Little Bear

Post by otanica » 16 Sep 2018 23:31

Hi
I have a version 2.0 T10 I want to apply the Layton 40db mod. I ve tried searching this thread and cannot find the actual documentation. Can someone point me in the right direction.
Currently the preamp overloads my small powered speakers and they clip harshly especially low notes when playing new 180gm records.

Thanks
Brad

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Re: Domesticating & Documenting the Little Bear

Post by hurdy_gurdyman » 21 Dec 2018 21:41

Greetings Little Bear club members,

Just spent a few days reading this entire thread. Whew! I'm not new to tubes, seeing as I've been using them since about 1969 as a 12 year old budding audiophile. It's been a great ride since then in spite of lowish income.
I ordered a LB 2.5 a few days ago, as well as some Soviet era tubes. Looking forward to hearing it. I do plan to do the 40 dB mod someday when finances allow. I'm very comfortable with a soldering iron and reading schematics. It would be nice to have the schematic and pictures all in one section. I'd hate to start over on this thread and try to find the pics (if there are any for the 2.5). Is the 2.5 PC board the same as the 2.2?

I just sold my new Yaqin MS12 phono pre after using it for about 5 months. Badly rolled off highs and 2 dimensional sound stage. Junk. I bought it over the LB because Yaqin amps have a good reputation. Hope this Little Bear is a BIG improvement.

I'm using a Douk A9 amp (modded) and an old 70's Yamaha integrated for a phono and line pre. Hope to buy a decent line level pre to replace it someday and have all tubes again. My last all tube stereo, a Scott LK48b died a few years back and I am missing an all tube system.

Dave :mrgreen:

Coffee Phil
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Re: Domesticating & Documenting the Little Bear

Post by Coffee Phil » 21 Dec 2018 22:20

Hi Dave,

The latest LB which I have experience with it the version 2.2. It is very similar to the early one at the start of this thread, except for the ability to use 12AX7 tubes.

The comment on ground loops and shielding apply to it as well as to the earlier version. As supplied it has ~50 dB gain @ 1 kHz which is on the high side for a MM phono stage. My recommendation is to use either Mr. Layton's 40 dB values which he derived using Mr. Lipshitz equations, or my values which came from a different method and were tweaked to get better RIAA accuracy. DO NOT use my 30 dB values! They are in error.

I also show a method of re-biasing the output stage to address a complaint of distortion at low frequencies and large signals. Using a 40 dB network will reduce the likelihood of the distortion issue so I would not bother unless you are driving long cables or a low impedance load.

I agree it would be nice if someone would consolidate the schemos and make a BOM for the mods, but I'm too busy now.

Phil

hurdy_gurdyman wrote:
21 Dec 2018 21:41
Greetings Little Bear club members,

Just spent a few days reading this entire thread. Whew! I'm not new to tubes, seeing as I've been using them since about 1969 as a 12 year old budding audiophile. It's been a great ride since then in spite of lowish income.
I ordered a LB 2.5 a few days ago, as well as some Soviet era tubes. Looking forward to hearing it. I do plan to do the 40 dB mod someday when finances allow. I'm very comfortable with a soldering iron and reading schematics. It would be nice to have the schematic and pictures all in one section. I'd hate to start over on this thread and try to find the pics (if there are any for the 2.5). Is the 2.5 PC board the same as the 2.2?

I just sold my new Yaqin MS12 phono pre after using it for about 5 months. Badly rolled off highs and 2 dimensional sound stage. Junk. I bought it over the LB because Yaqin amps have a good reputation. Hope this Little Bear is a BIG improvement.

I'm using a Douk A9 amp (modded) and an old 70's Yamaha integrated for a phono and line pre. Hope to buy a decent line level pre to replace it someday and have all tubes again. My last all tube stereo, a Scott LK48b died a few years back and I am missing an all tube system.

Dave :mrgreen:

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Re: Domesticating & Documenting the Little Bear

Post by hurdy_gurdyman » 21 Dec 2018 23:43

Coffee Phil wrote:
21 Dec 2018 22:20
Hi Dave,

The latest LB which I have experience with it the version 2.2. It is very similar to the early one at the start of this thread, except for the ability to use 12AX7 tubes.

The comment on ground loops and shielding apply to it as well as to the earlier version. As supplied it has ~50 dB gain @ 1 kHz which is on the high side for a MM phono stage. My recommendation is to use either Mr. Layton's 40 dB values which he derived using Mr. Lipshitz equations, or my values which came from a different method and were tweaked to get better RIAA accuracy. DO NOT use my 30 dB values! They are in error.

I also show a method of re-biasing the output stage to address a complaint of distortion at low frequencies and large signals. Using a 40 dB network will reduce the likelihood of the distortion issue so I would not bother unless you are driving long cables or a low impedance load.

I agree it would be nice if someone would consolidate the schemos and make a BOM for the mods, but I'm too busy now.

Phil
Hi Phil,

My two fav cartridges I own, a Grado G-1+ and a Shure V15 RS (a disguised V15VxMR using HE stylus) both have 3mV output, so may work OK with the stock gain. I'll probably, at some point, install the 40 dB circuit. We'll see.

Dave

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Re: Domesticating & Documenting the Little Bear

Post by hurdy_gurdyman » 22 Dec 2018 00:27

Curious, has anyone done a direct comparison of the Little Bear T10 to a Hagerman Bugle 2? I have a friend that advised me to go the Bugle route. However, I chose the tube route. Just wondering what the difference in sound may be.

Dave

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Re: Domesticating & Documenting the Little Bear

Post by hurdy_gurdyman » 26 Dec 2018 18:19

My Little Bear came in the mail today. First off, I ordered a 2.5, but I received a 2.6. I have no complaint about that. However, the case isn't the pretty clear acrylic one, but is instead one made of soft flexible plastic that is a matte finish, like wax paper. Looks cheap. Guess they got tired of cases breaking.

I assembled it. Very little, about normal for a tube preamp. No complaints there. I did a voltage check on the tranny (by the way, my house voltage is 117 VAC. Rectifier heater voltage is 5.9 volts, which is fine. The 12AX& heater voltage is 17 volts. A bit higher than the 115 I was hoping to see. I ordered some diodes several days ago. When they get here, I'll insert a pair in the circuit and see how much of a voltage drop I get.

The sound is excellent right from the get-go. Beats the 70's era Yamaha's phono stage I was using. I plan to get a tubed line level preamp so I can take the Yamaha right out of the stereo altogether.

Time to make coffee and sit back for some enjoyable listening, starting with some Brubeck and Desmond. :)

Dave :mrgreen:

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Re: Domesticating & Documenting the Little Bear

Post by hurdy_gurdyman » 26 Dec 2018 20:09

Been listening for a couple of hours now. The hum level isn't noticeable while the record is playing, but is very noticeable with no record playing. This is listening at the normal listening seat. I have some copper foil due to come in at any time. When it and the diodes I ordered get here, I plan to put foil on the bottom and both ends and the backside, and grounding to the ground post. Should lower it even more.

I sent a note to the seller, Doukstore, to see if I can purchase an acrylic cabinet for it. The matte plastic it came with just plain looks cheap.

It didn't come with rubber feet, so will have to find some.

Dave

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Re: Domesticating & Documenting the Little Bear

Post by hurdy_gurdyman » 26 Dec 2018 21:19

Did some tube rolling. Took all three Chinese tubes out and replaced #1 and #3 with new Sovteks, and # 2 with an old stock Baldwin. Hum level went WAY down. Can't hear it from the listening seat. The music sounds cleaner, with more apparent detail to the highs. I have some Russian tubes headed this way that I will experiment with.

BTW, listening with a Shure V15 RS (disguised Shure V15VxMR, only with JICO hyper-elliptical stylus). This is mounted in a 1966 Garrard Lab 80 mk-1 transition turntable. Amplifier is a Douk BOYUU A9 that has been modded (a bit of internal local feedback added, and a couple of resistors added to heater circuit to cut hum). Speakers are 8" Wild Burro Betsy drivers in a Caintuck Audio open baffles sitting on 15" H-frame open baffles driven with Rythmik plate amp crossed at 80 Hz, 4th order. Dang good sound coming out of those speakers right now. :)

Back to drinking coffee and listening. 8)

Dave :mrgreen:

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Re: Domesticating & Documenting the Little Bear

Post by hurdy_gurdyman » 26 Dec 2018 22:11

Russian 6h2n tubes came in today's mail. Just tried them. Hum is a bit lower yet, not much more than my tube amp has by itself. Very acceptable. Will have to listen to them and the 12ax7s a few days before judging which I like better.

Even without being broke in yet, I can hardly believe how much better things sound now than with the Yaqin MS-12B I had, and the preamp of my Yamaha integrated. Still going through the line amp of the Yamaha. Hope to fix that after the first of the year.

Dave

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Re: Domesticating & Documenting the Little Bear

Post by hurdy_gurdyman » 30 Dec 2018 03:05

After a few days of listening, I decided I like the Russian 6h2n tubes better than the Sovtek and Baldwin 12ax7's. They have more apparent detail on the top end (at least as far top as my 63 year old ears can hear). This thing sounds so good that I almost don't resent the cheap matte plastic case. I did send a message to doukstore asking about an acrylic case, but haven't heard anything back yet.

Dave

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Re: Domesticating & Documenting the Little Bear

Post by cobrabucket » 30 Dec 2018 07:04

Glad to hear it! I love the Russian 6h2n tubes I got for mine. Was considering trying a 7N7 w. an adapter. This would be ok, right?

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Re: Domesticating & Documenting the Little Bear

Post by T68 » 30 Dec 2018 08:40

Hi all!
I'm looking into getting an external phono preamp and the Little Bear looks interesting.
I'm gonna try catch up on this thread but maybe you guys can help me with some newbie questions.
- What are the main differences between a t10 and a t11? Is the t11 worth the extra money?
- Some t10 seem to have open sides. Is this safe (thinking of risk of shorting and electrical shocks)?
- Do the LB work fine on 220 voltage / 50hz?
- Which vendor on eBay can you recommend? Rather buy from EU warehouse if possible to avoid import fees.
- My TT and amp are vintage with 5 pole din connectors. Would it work to use din-to-rca adaptors with the LB on both incoming and outgoing signal?

Anything else to consider when going with the Bear?
Thanks for input!
/T

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Re: Domesticating & Documenting the Little Bear

Post by cminor7b5 » 30 Dec 2018 17:08

T68: I just looked on ebay at the listings for Doukstore. I believe Doukstore is the ebay storefront of the manufacturer but I could be wrong.

Current prices for:
Little Bear T10 New Tube Phono Preamp Pre-Amplifier MM Turntable RIAA HiFi V2.6 US $148.15

2018 Little Bear T11 Vacuum Tube Phono Turntable Preamplifier MM RIAA Preamp New US $180.48

I own a T11 which I received in Feb 2018. I am very happy with it. I upgraded the stock tubes to inexpensive Russian tubes via an Ebay dealer. I still have not tried 12ax7 tubes in the T11.

My understanding is that the T11 is T10 in a shielded case with a volume control. I strongly recommend the T11 for the shielded case alone.

Douk Audio MM/MC RIAA Tube Phono Stage Turntable Preamp HiFi Stereo Preamplifier https://www.ebay.ca/itm/Douk-Audio-MM-M ... :rk:5:pf:0 would be the next step up from the T11 imo.

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