[fabien32]

I recently took delivery of a B4-X and am planning to mod this great little amp. I've already ordered a pair of V5i-Ds, am planning to do the copper shielding tape mod to the interior of the case, and perhaps a few other simple things.

One question, would anyone happen to know which size of silicone o-ring dampeners will fit the 5899 tubes? I figured out 19mm apparently suits 6922s, but these 5899s are virtually half the size. The microphonics in my B4-X are rather severe so its definitely an area I'd like to address.

The microphonics normally can be fix with playing with the adjustment screws that can be found on both sides of the tubes

 

[DBaldock9]

I recently took delivery of a B4-X and am planning to mod this great little amp. I've already ordered a pair of V5i-Ds, am planning to do the copper shielding tape mod to the interior of the case, and perhaps a few other simple things.

One question, would anyone happen to know which size of silicone o-ring dampeners will fit the 5899 tubes? I figured out 19mm apparently suits 6922s, but these 5899s are virtually half the size. The microphonics in my B4-X are rather severe so its definitely an area I'd like to address.

I used these rings, since they fill the gap between the circuit board and the case - https://www.amazon.com/gp/product/B07ZDNHGKG/
.

 

[Aklo09]

Do you have to unsolder the tubes to install rings or they just slip in?

 

[Bosk]

The microphonics normally can be fix with playing with the adjustment screws that can be found on both sides of the tubes

Excellent, I just have three quick questions regarding those screws please.

1. Is it safe to adjust them while power is on and music is playing?
2. Do I need to use a multimeter to adjust them properly?
3. Would reducing the gain increase battery life but worsen sound quality?

Many thanks for helping me out. I know enough electronics to perform basic mods like replacing resistors, connectors etc. but don't understand most of the theory.

I used these rings, since they fill the gap between the circuit board and the case - https://www.amazon.com/gp/product/B07ZDNHGKG/

Fantastic, just what I needed. I'll order some immediately. I'm finding there's a very pronounced ringing when accidentally tapping the sides of the amp.

There's also a very low audible buzzing sound that oscillates from high to low frequencies continuously which is evident through earphones during quiet passages and also a slight channel imbalance, though I'm guessing these are more likely solved by playing with the adjustment screws.

Thanks again for your help.

 

[DBaldock9]

Do you have to unsolder the tubes to install rings or they just slip in?

If your question is for me - Well, I assembled removable tube carrier boards, that plug into the main board, so the tubes were out of the unit when I installed the O-rings.
.
Removable tube carrier (back view) -

.
Removable tube carrier (front view) -

.
Litte Bear B4-X, before O-rings (top view) -

 

[fabien32]

1. Is it safe to adjust them while power is on and music is playing?
2. Do I need to use a multimeter to adjust them properly?
3. Would reducing the gain increase battery life but worsen sound quality?

1.It is safe and even recommend to adjust them when playing
2.no multimeter is needed
3.lowering gain doesn't affect the quality of the sound in general

 

[alvaroenoht]

If your question is for me - Well, I assembled removable tube carrier boards, that plug into the main board, so the tubes were out of the unit when I installed the O-rings.
.
Removable tube carrier (back view) -

.
Removable tube carrier (front view) -

.
Litte Bear B4-X, before O-rings (top view) -

Hi!! nice mod. Where did you get the removable tube carriers?.
Also what type of opamps are those?. I checked and it requires dual opamps per channel. Seems to be driving them in parallel with unity gain. I was thinking about ordering some sparkos 3602, but I am afraid they wont fit, but movin the tubes out of the way maybe will make some space?. Have you mod the power supply?. I was thinking about using a usbc pdb in 12 volts to use it with an external battery bank for longer listening sessions.

 

[Bosk]

1.It is safe and even recommend to adjust them when playing
2.no multimeter is needed
3.lowering gain doesn't affect the quality of the sound in general

Many thanks, I'll try adjusting them and see how it goes!

 

[DBaldock9]

Hi!! nice mod. Where did you get the removable tube carriers?.
Also what type of opamps are those?. I checked and it requires dual opamps per channel. Seems to be driving them in parallel with unity gain. I was thinking about ordering some sparkos 3602, but I am afraid they wont fit, but movin the tubes out of the way maybe will make some space?. Have you mod the power supply?. I was thinking about using a usbc pdb in 12 volts to use it with an external battery bank for longer listening sessions.

The op-amps that are in the photo are OPA-1622 (Dual Op-Amp (VSON-10) on DIP-8 header, ±18VDC), ordered from eBay.
My Sparkos SS3602 did fit in the unmodified B4-X, just barely - with one of them touching the tube on that side.
My main goal in creating the tube carriers, was to move the tubes away from the op-amp sockets.
They were made by ordering a proto-board kit from Amazon, and cutting a couple of pieces to size with an X-Acto thin-kerf saw.
Then I soldered point-to-point wiring from the pins that are soldered to the main board, to the pin sockets for the tubes.
I haven't modified the power supply circuit, yet - but that is in the planning stage.
What I'd like to have, is an "Aux" power input, that is switched in-place of the battery output, so that I can use a low noise linear 12VDC supply for desktop operation, or charge and use the internal battery for portable operation.

 

[alvaroenoht]

The op-amps that are in the photo are OPA-1622 (Dual Op-Amp (VSON-10) on DIP-8 header, ±18VDC), ordered from eBay.
My Sparkos SS3602 did fit in the unmodified B4-X, just barely - with one of them touching the tube on that side.
My main goal in creating the tube carriers, was to move the tubes away from the op-amp sockets.
They were made by ordering a proto-board kit from Amazon, and cutting a couple of pieces to size with an X-Acto thin-kerf saw.
Then I soldered point-to-point wiring from the pins that are soldered to the main board, to the pin sockets for the tubes.
I haven't modified the power supply circuit, yet - but that is in the planning stage.
What I'd like to have, is an "Aux" power input, that is switched in-place of the battery output, so that I can use a low noise linear 12VDC supply for desktop operation, or charge and use the internal battery for portable operation.

great! just ordered mine and I am trying to analyze the circuit from the pictures I find in the internet while mine arrives. I was planning to do exactly what you did! but didnt seem to find anyone that tried to do it. Now that I know it can be done I will focus in the power supply. Please keep us posted with those mods!!

 

[Bosk]

I haven't modified the power supply circuit, yet - but that is in the planning stage.
What I'd like to have, is an "Aux" power input, that is switched in-place of the battery output, so that I can use a low noise linear 12VDC supply for desktop operation, or charge and use the internal battery for portable operation.

Sounds very interesting! Really looking forward to seeing how this turns out.

My electronics knowledge is pretty minimial so this may be a silly question, but would it be beneficial to add a regulator of some kind between the battery and the tubes to stabilize the voltages they're fed and possibly lower the noise floor?

I purchased a couple of 'super regulators' like these from Parts Connexion in the past and found the difference they made in DAC circuits was massive:
https://www.partsconnexion.com/BELLSPX78-85581.html
https://www.partsconnexion.com/NCLASSD-83328.html

 

[alvaroenoht]

Sounds very interesting! Really looking forward to seeing how this turns out.

My electronics knowledge is pretty minimial so this may be a silly question, but would it be beneficial to add a regulator of some kind between the battery and the tubes to stabilize the voltages they're fed and possibly lower the noise floor?

I purchased a couple of 'super regulators' like these from Parts Connexion in the past and found the difference they made in DAC circuits was massive:
https://www.partsconnexion.com/BELLSPX78-85581.html
https://www.partsconnexion.com/NCLASSD-83328.html

The little bear have 2 dc to dc converters / regulators? (Mornsun A1212S) for (+12v and -12v) and some big caps in front to smooth the power (at least that's what it looks from the pictures). That regulator could be beneficial for an external power supply. There is one guy in reddit that did that mod, and he experienced a low hum when powered from a switching power supply, The problem might be the heaters getting dirty power since they are connected in series directly to the battery. I think that's the reason you cant power the little bear and listen to it at the same time because it doesn't have a bms and no filtering in the power input at all.
https://www.reddit.com/r/headphones..._bear_b4x_external_power_mod_a_mixed_success/
I was thinking in using a USB-C PDB at 12 volts like this https://www.amazon.com/SparkFun-Power-Delivery-Board-Distribution/dp/B084RZLTQW and adding a relay to disconnect the battery once the usbc pdb is powered and provide the power from the usb-c unit. that way I can use an external battery to power the b4-x for extended listening and when using more power hungry op/amps providing more amps, but I don't know how dirty the power is going to be. Have to try.
As soon as I get mine I will finish drawing the schematic and post it here to see how we can further improve it.

 

[DBaldock9]

Sounds very interesting! Really looking forward to seeing how this turns out.

My electronics knowledge is pretty minimial so this may be a silly question, but would it be beneficial to add a regulator of some kind between the battery and the tubes to stabilize the voltages they're fed and possibly lower the noise floor?

I purchased a couple of 'super regulators' like these from Parts Connexion in the past and found the difference they made in DAC circuits was massive:
https://www.partsconnexion.com/BELLSPX78-85581.html
https://www.partsconnexion.com/NCLASSD-83328.html

Back on page 20, there's modification shown, which adds regulators to each tube power supply circuit - https://www.head-fi.org/threads/portable-tube-amp-from-china.626237/post-14530910

That's another thing that I'll probably try with my B4-X.

 

[Bosk]

The little bear have 2 dc to dc converters / regulators? (Mornsun A1212S) for (+12v and -12v) and some big caps in front to smooth the power (at least that's what it looks from the pictures). That regulator could be beneficial for an external power supply. There is one guy in reddit that did that mod, and he experienced a low hum when powered from a switching power supply, The problem might be the heaters getting dirty power since they are connected in series directly to the battery. I think that's the reason you cant power the little bear and listen to it at the same time because it doesn't have a bms and no filtering in the power input at all.
https://www.reddit.com/r/headphones..._bear_b4x_external_power_mod_a_mixed_success/
I was thinking in using a USB-C PDB at 12 volts like this https://www.amazon.com/SparkFun-Power-Delivery-Board-Distribution/dp/B084RZLTQW and adding a relay to disconnect the battery once the usbc pdb is powered and provide the power from the usb-c unit. that way I can use an external battery to power the b4-x for extended listening and when using more power hungry op/amps providing more amps, but I don't know how dirty the power is going to be. Have to try.
As soon as I get mine I will finish drawing the schematic and post it here to see how we can further improve it.

That sounds like a really interesting project. I asked the Ebay seller who sold my B4-X for a schematic but was told they can't provide one, so if you could draw a schematic for us that'd be extremely useful!

Back on page 20, there's modification shown, which adds regulators to each tube power supply circuit - https://www.head-fi.org/threads/portable-tube-amp-from-china.626237/post-14530910

That's another thing that I'll probably try with my B4-X.

I'll be very interested to watch your progress. Perhaps a blacker background, better dynamics & imaging would result from more stable voltage being fed to those tubes.

Just spitballing here, but would it be very difficult to mod the 3.5mm input to 2.5mm balanced instead, thereby making the amp fully balanced in the truest sense? I previously owned an ALO CDM and found the difference in performance between running it in single-ended & fully balanced modes was enormous, in the latter it really came alive.

 

[DBaldock9]

That sounds like a really interesting project. I asked the Ebay seller who sold my B4-X for a schematic but was told they can't provide one, so if you could draw a schematic for us that'd be extremely useful!




I'll be very interested to watch your progress. Perhaps a blacker background, better dynamics & imaging would result from more stable voltage being fed to those tubes.

Just spitballing here, but would it be very difficult to mod the 3.5mm input to 2.5mm balanced instead, thereby making the amp fully balanced in the truest sense? I previously owned an ALO CDM and found the difference in performance between running it in single-ended & fully balanced modes was enormous, in the latter it really came alive.

I've got a pair of fully balanced amps - iBasso PB2 Solid-State Portable & Loxjie P20 Tube/Hybrid Desktop.
It would be great if the Little Bear B4-X was fully balanced, but modifying it, in the available space, would be a bit tricky.
.
[A.] If you want to be able to take a Balanced Input, and provide a Balanced Output - then you'll need to make these changes:
1.) Add a 2.5mm TRRS Input Jack
2.) Route the L+, L-, R+, R- signals to the tube pre-amplification circuit (bypassing the phase-splitter that would be needed for [B.])
3.) Add 2 more tubes for Balanced pre-amplification of L+, L-, R+, R-
4.) Reconfigure the current op-amps to be 4 separate buffers (instead of phase-splitters) to drive the Balanced Output
.
[B.] If you want to be able to take a Single-Ended Input, and provide a Balanced Output - then you'll need to make these changes:
1.) Add a phase-splitter at the Input (which is what the current op-amps are doing for the Output) to create the L+, L-, R+, R- signals
2.) Add 2 more tubes for the Balanced pre-amplification of L+, L-, R+, R-
3.) Reconfigure the current op-amps to be 4 separate buffers (instead of phase-splitters) to drive the Balanced Output
.
So the design concepts are fairly simple, but trying to add additional op-amps (w/support circuitry), and tubes (plus voltage regulators for the tubes), while still leaving space to do op-amp rolling - inside the current B4-X case - would probably require creating a completely new main circuit board, along with daughter-boards, so everything fits.