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Mods to "Little bear" T11 phono pre-amp

It does have a bit of a fat round sound to it. Are you still using the Chinese tubes that came with it? The 6N2's that came with mine sounded flat and thin. The first two tubess from left to right are the most important sound wise. I used a JJ ECC83 for the first tube and a couple close tolerance matched military grade GE 12AX7's for the second two I had laying around.
 
Lavane said:
It does have a bit of a fat round sound to it. Are you still using the Chinese tubes that came with it? The 6N2's that came with mine sounded flat and thin. The first two tubess from left to right are the most important sound wise. I used a JJ ECC83 for the first tube and a couple close tolerance matched military grade GE 12AX7's for the second two I had laying around.
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"Fat round sound." I like that. :) We guitarists call it phat. :thumbsup:
 
Lavane said:
It does have a bit of a fat round sound to it. Are you still using the Chinese tubes that came with it? The 6N2's that came with mine sounded flat and thin. The first two tubess from left to right are the most important sound wise. I used a JJ ECC83 for the first tube and a couple close tolerance matched military grade GE 12AX7's for the second two I had laying around.
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I've tried both my Russian 6N2 and quality 12AX7s - still poor.
I suspect I've misunderstood the feedback cap replacement; should I have done the following?
1695374357806.png
 
Stock it appears to have a 100 and a 10 in parallel to make 110. I don't really see any special advantage to doing it one way or the other.

I didn't read this whole thing in detail but my understanding is that none of the values in the feedback circuit were changed, just the type of cap. So swap the 330 for a 330, and swap the 100 + 10 for a 110. Or you could do a 100 + 10 like stock. Same-same. I have done caps in parallel to add up to some specific value that just doesn't exist. Actually used that trick in a Fisher phono EQ, used it on a resistor too. The values specified were not typical, but they could be easily made from commonly available values.

if you swapped the 100+10 for 100+330, thats going to roll off the highs quite a bit I think. It will have more feedback at higher frequencies so less gain at the top.
 
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Not sure what changing from a 100 to a 110 would do. Is this the best phono pre I have ever heard? No but it didn't sound flat and muddy. I never tried the Russian tubes, I used some EH7025 and thought it sounded pretty nice.

Also your cart seems to like a good bit of capacitance, more than normal cables would provide. I would measure the cables with the cart unplugged and add the needed capacitance until you reach the loading it wants.

Optimum Load: 47,000 ohms resistance in parallel with 400 lo 500 picofarads total capacitance per channel.

 
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StepheK said:
Not sure what changing from a 100 to a 110 would do. Is this the best phono pre I have ever heard? No but it didn't sound flat and muddy. I never tried the Russian tubes, I used some EH7025 and thought it sounded pretty nice.

Also your cart seems to like a good bit of capacitance, more than normal cables would provide. I would measure the cables with the cart unplugged and add the needed capacitance until you reach the loading it wants.

Optimum Load: 47,000 ohms resistance in parallel with 400 lo 500 picofarads total capacitance per channel.

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Appreciate the data on the Sure cartridge.
As I suspected, I'd misunderstood the schematic, I've now unsoldered the 330pf cap and deposited in it's correct position (C13/C14).
Extremely pleased with the results, a major improvement and more than worth the cost of the new components.
I've a good collection of 12ax7 type valves so I'm looking forward to rolling a few. Currently using ECC803s in positions 1 & 2 and a 5965 clear top (for sparkle and head room) in position 3. Five Leaves Left is on the Thorens TD125, the guitar detail and Drake's voice are beautifully presented with the detailed bass that I was craving.
Thanks again.
1695402571519.png
 
Cutty Dyer said:
Appreciate the data on the Sure cartridge.
As I suspected, I'd misunderstood the schematic, I've now unsoldered the 330pf cap and deposited in it's correct position (C13/C14).
Extremely pleased with the results, a major improvement and more than worth the cost of the new components.
I've a good collection of 12ax7 type valves so I'm looking forward to rolling a few. Currently using ECC803s in positions 1 & 2 and a 5965 clear top (for sparkle and head room) in position 3. Five Leaves Left is on the Thorens TD125, the guitar detail and Drake's voice are beautifully presented with the detailed bass that I was craving.
Thanks again.
View attachment 2991737
Click to expand...
I'm a big fan of the new production EH7025 tubes for applications like this. Glad you found the problem and like the results!
 
To further enhance the bass and improve RIAA balance I've carried out a further 2 mods (blue call-outs) that I gleaned from the Vinyl Engine "long" thread:
1695797056343.png
The mods get the component values closer to the original EAR design:
1695797157722.png

I recommend these additional changes, the T11 is now performing very well; well beyond my expectations.
 
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The solder pads are so fragile in the first version board I have that I stopped at Stephie's original mods. I'm glad it's working out for you though.
I've found myself playing with phono preamps lately. I started with building a CNC phono preamp. It's a really nice SS preamp with loading selectors and able to use various OP amps. I've been really happy with it. Even with the stpck OP amps having BJT's inside it sounded nice. But swapping them for a set with JFETs was even better.
now I have a PH-10 Z-Mod board using 12AY7's that's a modified Dynaco tube phono board I plan on using in a stand alone build. It's very similar to the version using 6922's in my main system preamp.
 
I quite fancy a JFET SS phono stage, but I'll stick with the improved T11 for now.
Lavane said:
The solder pads are so fragile in the first version board I have that I stopped at Stephie's original mods. I'm glad it's working out for you though.
I've found myself playing with phono preamps lately. I started with building a CNC phono preamp. It's a really nice SS preamp with loading selectors and able to use various OP amps. I've been really happy with it. Even with the stpck OP amps having BJT's inside it sounded nice. But swapping them for a set with JFETs was even better.
now I have a PH-10 Z-Mod board using 12AY7's that's a modified Dynaco tube phono board I plan on using in a stand alone build. It's very similar to the version using 6922's in my main system preamp.
Click to expand...
 
StepheK said:
Not sure what changing from a 100 to a 110 would do. Is this the best phono pre I have ever heard? No but it didn't sound flat and muddy. I never tried the Russian tubes, I used some EH7025 and thought it sounded pretty nice.

Also your cart seems to like a good bit of capacitance, more than normal cables would provide. I would measure the cables with the cart unplugged and add the needed capacitance until you reach the loading it wants.

Optimum Load: 47,000 ohms resistance in parallel with 400 lo 500 picofarads total capacitance per channel.

Click to expand...
I finally got around to following your advice and attempted to meet the capacitance requirements of the Sure cartridge. I added a couple of 320pF capacitors across the RCA inputs (figured the phono cables and capacitance of the LB11 would be in the region of 100pF). The additional caps have returned excellent results, now extremely pleased with the T11, just need to address the slight "hum" I've managed to introduce - will the fiddling never end!
 

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Hi everyone! First post here :) Sorry to resurrect this thread, I didn't want to start another discussion on the same topic...
I purchased a Little Bear T11 that just arrived, I already knew that it could be improved and I'm planning to do so in the near future, but first I have a couple of problems/questions:
- Being a guitar player using tube amps I already had here some ECC83S tubes, and I directly mounted them knowing that they are better then the 6N2 tubes that came in the box. Unfortunately the middle tube doesn't work with the ECC83S (I tried three of them with no success), it doesn't glow nor get warm and no sound is coming out. It works fine with the 6N2 tube. Maybe it's just bad soldering somewhere in the pcb near the tube socket? Or maybe the socket itself or the switch?

- I'm not an electrical engineer but I have some experience with soldering, using multimeter etc as I built myself my Serge Modular Synth, but I never messed with high voltages and I don't want to risk anything: I know that you should discharge capacitors for safety before doing anything else on the circuit (I found this very clear video about that:
) is there anything else I should do before putting my hands on the pcb?

I will enjoy the phono stage as it is for a while, comparing it with the integrated one of my NAD 3120 (with my Thorens TD-160 and Kef Q350 speakers), cranking up the volume of the NAD there is a little noise but it's silent at my loudest listening level; the impression I have after the first hours of listening is that the soundstage is a little wider than with the phono input of the 3120, and music is a little more lively, with a slight mid frequency punch, bass frequency are less pronounced and maybe a little less precise.
Not a huge difference though between the two, I'll do some more A-B comparisons in the next days. Anyway I hope it will improve with StepheK's mods, I'll order the components soon!
 
It may just be a bad solder jount on that socket. Maybe for the switch also.
You can test the switch to make sure it's not faulty once you get the board out using an ohm setting on your multi meter. They are a bit of a puzzle to get apart. But the mods are worth it.
 
Glauco said:
I already had here some ECC83S tubes, and I directly mounted them knowing that they are better then the 6N2 tubes that came in the box. Unfortunately the middle tube doesn't work with the ECC83S (I tried three of them with no success), it doesn't glow nor get warm and no sound is coming out. It works fine with the 6N2 tube. Maybe it's just bad soldering somewhere in the pcb near the tube socket? Or maybe the socket itself or the switch?
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You need to rewire the heater line to use an ECC83 (12AX7) in a 6N2P socket --- and vice versa.

6N2P to 12AX7 wiring.jpg
 
Lavane said:
These phono preamps have a switch for each socket to be able to switch between 12AX7's and 6N2's. If the OP can't get that one socket to play nice with 12AX7's, he can always go with a Russian 6N2-EV.
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A switch is so much better, as several folks I know wanted to either return to the 6N2P from a 12AX7 tryout or a 12AX7 from a 6N2P trial.

Re-soldering that 9-pin socket is a mini nightmare. :(

The triple-mica 6N2P-EV is a long-lasting tube that, in my experience, takes a good amount of time to settle into a pleasant tone. Initially, it's a bit tight-sounding.

6N2P-EV Voskhod - Kaluga.jpg
"Rocket" Voshod 6N2P-EV

6N2P-EV 1960 Reflector.jpg
Reflector 6N2P-EV
 
Mr Boochie said:
A switch is so much better, as several folks I know wanted to either return to the 6N2P from a 12AX7 tryout or a 12AX7 from a 6N2P trial.

Re-soldering that 9-pin socket is a mini nightmare. :(

The triple-mica 6N2P-EV is a long-lasting tube that, in my experience, takes a good amount of time to settle into a pleasant tone. Initially, it's a bit tight-sounding.

View attachment 3324151
"Rocket" Voshod 6N2P-EV

View attachment 3324152
Reflector 6N2P-EV
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I haven't tried the Rockets yet, but the Reflektor's I have. So far I haven't had a bad sounding Reflektor tube yet. Including octal signal and power tubes.
Maybe not the best sounding in some circuits, but never bad sounding.
 
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