[alvaroenoht]

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.

to do this mod, you will have to feed the heater filament in a separate circuit.

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 have been working on the schematics during my lunch break. The b4-x is already balanced. the circuit is balanced in the sense that each channel has an independent power supply, preamp stage and the output stage runs two opamps in parallel per channel!, the components selected seem to be of good quality too. I havent check how they grounded the 3.5 but the 2.5jack is just in parallel with the 3.5 so you should be able to listen from both outputs at the same time.
Perhaps if we remove the 3.5 jack and remove the common ground at the output the sound will improve. I am more focused in the power supply part for now since I want to be able to increase battery time.
I noticed the dc jack is directly connected to the battery and I assume that it has a switch that shuts down a relay that cuts down power to the unit when inserted. I dont think is safe to bypass that relay and use it while connected since it doesnt have a bms and that can damage the battery, but an external battery could be used. it has 5 caps in total for smothing the power one shared before the dc to dc converters and 2 after each channel for the -12v and + 12v rails. A further improvement could be to up the voltage to 16 or 18v, but thats basically redoing the whole unit, not worth it imo.

The suggestion of having separate power supplies for the heaters I dont think is good since the heaters only need 6 volts and they dont care about ripple or noise, most heaters in big units use ac.

 

[alvaroenoht]

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.

yeah! you basically have to redo the board. if you can find a dual mini sub pentode with 2 dual opamps you could get this circuit done in the same space.

 

[DBaldock9]

to do this mod, you will have to feed the heater filament in a separate circuit.


I have been working on the schematics during my lunch break. The b4-x is already balanced. the circuit is balanced in the sense that each channel has an independent power supply, preamp stage and the output stage runs two opamps in parallel per channel!, the components selected seem to be of good quality too. I havent check how they grounded the 3.5 but the 2.5jack is just in parallel with the 3.5 so you should be able to listen from both outputs at the same time.
Perhaps if we remove the 3.5 jack and remove the common ground at the output the sound will improve. I am more focused in the power supply part for now since I want to be able to increase battery time.
I noticed the dc jack is directly connected to the battery and I assume that it has a switch that shuts down a relay that cuts down power to the unit when inserted. I dont think is safe to bypass that relay and use it while connected since it doesnt have a bms and that can damage the battery, but an external battery could be used. it has 5 caps in total for smothing the power one shared before the dc to dc converters and 2 after each channel for the -12v and + 12v rails. A further improvement could be to up the voltage to 16 or 18v, but thats basically redoing the whole unit, not worth it imo.

The suggestion of having separate power supplies for the heaters I dont think is good since the heaters only need 6 volts and they dont care about ripple or noise, most heaters in big units use ac.

(Emphasis added)

Is that a Battery Management System?
If so, I think it's built into the Charger/Power Supply - since it has an LED that changes from Red (while charging) to Green (when charged).

The idea I've got, is to break the 12VDC circuit after the battery, and use a second power input port, fed through a switch, so that either the Aux low-noise linear 12VDC, or the Battery can feed the amplifier circuit.

 

[alvaroenoht]

(Emphasis added)

Is that a Battery Management System?
If so, I think it's built into the Charger/Power Supply - since it has an LED that changes from Red (while charging) to Green (when charged).

The idea I've got, is to break the 12VDC circuit after the battery, and use a second power input port, fed through a switch, so that either the Aux low-noise linear 12VDC, or the Battery can feed the amplifier circuit.

yes the bms is inside the power brick. That will certainly work. I think you can avoid the switch if you add a relay that cuts the battery and use the aux, But I dont know if there is enough space there.

 

[alvaroenoht]

btw how is the sound with the sparkos?? I was reading the specs and they recommend 18 volts. the little bear voltage won't be optimal for it.

 

[DBaldock9]

btw how is the sound with the sparkos?? I was reading the specs and they recommend 18 volts. the little bear voltage won't be optimal for it.

On their SS3601/SS3602 Engineering Data Sheet, ±18VDC is listed as the maximum recommended supply voltage, but the typical supply voltage is ±12VDC, and the minimum supply voltage is ±6VDC.

I'm currently listening to my LZ A4 earphones on the Balanced output of my B4-X (2x Sparkos SS3602), with the input coming from my Topping D70 DAC - watching Christmas Movies on the Hallmark Channel. It all sounds great, although the Sparkos is not a high current op-amp (rated for 15mA Class A / 40mA Class AB @±12VDC).

 

[Bosk]

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.

Either of those options sound like they'd be next to impossible to complete inside the existing case and would be quite involving to perform. I guess the pertinent question would be how much sonic improvement would be likely and if that would justify the time and expense on parts. It certainly seems like there's a number of other areas of lower-hanging fruit that could be looked at first.

For instance, and again my knowledge of electronics is limited so I wouldn't know where to begin suggesting complex circuit changes, here are a few ideas of other things we B4-X owners could potentially improve: (the concept stage is always the most fun because work is completed instantly and ideas are free)

1. How about replacing any resistors & film caps in the signal path? Only problem with film caps it the upper-tier audiophile varieties tend to be very large & potentially worth more than the amp itself. As for resistors, I'm not sure if 0.6W is enough for the releant areas of this circuit but I used these in a TDA1543 DAC once and observed a very obvious improvement:
https://www.partsconnexion.com/vishay-z-foil-tx2575-series-radial-resistors.html

2. What about replacing the volume potentiometer with a stepped attenuator? Not a big Khozmo or similar unless the amp was going to be re-housed, but could something like this fit in the existing case? (don't know if 100k is the right value, just an example of the type I had in mind):
https://www.ebay.com.au/itm/DACT-Ty...m420431cfe5:g:uDsAAOSwizhdqBiW&frcectupt=true

3. Would there be a benefit to either upgrading the trimpots with higher-quality versions or even replacing them entirely with fixed resistors of the optimum tested value?

4. The power supply electrolytic caps could be replaced with nicer ones like Elna Silmic IIs, ideally in much beefier values, but the B4-X seems to have even less room back there than the B4 so again that might be mod requiring a new case. (a common theme emerges)

5. This is where my poor electrical theory will probably become very evident but might there be some benefit to "extending" the ground plane somehow, or doing a better job of connecting it to the case if it is already? Many Astell & Kern users have speculated the sonic differences in the higher-end models are partly due to the differing case materials which I've read are generally connected to the ground plane, copper for example possibly having a benefit over alumnium. This is really just my layman's way of saying "hey maybe grounding is important and could we improve that somehow?".

6. Oh and lastly -again straying into new case territory- in an ideal world it'd be nice to replace the output jack with a high quality 4.4mm Pentaconn jack. Not sure how much sonic difference that'd make.

 

[seamon]

Either of those options sound like they'd be next to impossible to complete inside the existing case and would be quite involving to perform. I guess the pertinent question would be how much sonic improvement would be likely and if that would justify the time and expense on parts. It certainly seems like there's a number of other areas of lower-hanging fruit that could be looked at first.

For instance, and again my knowledge of electronics is limited so I wouldn't know where to begin suggesting complex circuit changes, here are a few ideas of other things we B4-X owners could potentially improve: (the concept stage is always the most fun because work is completed instantly and ideas are free)

1. How about replacing any resistors & film caps in the signal path? Only problem with film caps it the upper-tier audiophile varieties tend to be very large & potentially worth more than the amp itself. As for resistors, I'm not sure if 0.6W is enough for the releant areas of this circuit but I used these in a TDA1543 DAC once and observed a very obvious improvement:
https://www.partsconnexion.com/vishay-z-foil-tx2575-series-radial-resistors.html

2. What about replacing the volume potentiometer with a stepped attenuator? Not a big Khozmo or similar unless the amp was going to be re-housed, but could something like this fit in the existing case? (don't know if 100k is the right value, just an example of the type I had in mind):
https://www.ebay.com.au/itm/DACT-Ty...m420431cfe5:g:uDsAAOSwizhdqBiW&frcectupt=true

3. Would there be a benefit to either upgrading the trimpots with higher-quality versions or even replacing them entirely with fixed resistors of the optimum tested value?

4. The power supply electrolytic caps could be replaced with nicer ones like Elna Silmic IIs, ideally in much beefier values, but the B4-X seems to have even less room back there than the B4 so again that might be mod requiring a new case. (a common theme emerges)

5. This is where my poor electrical theory will probably become very evident but might there be some benefit to "extending" the ground plane somehow, or doing a better job of connecting it to the case if it is already? Many Astell & Kern users have speculated the sonic differences in the higher-end models are partly due to the differing case materials which I've read are generally connected to the ground plane, copper for example possibly having a benefit over alumnium. This is really just my layman's way of saying "hey maybe grounding is important and could we improve that somehow?".

6. Oh and lastly -again straying into new case territory- in an ideal world it'd be nice to replace the output jack with a high quality 4.4mm Pentaconn jack. Not sure how much sonic difference that'd make.

At that point, just get a better portable tube amp? Oriolus BA300s mkii
Edit: The Oriolus amp is also part of a stack that uses premium components: 9038Pro in the DAC, Alps Pot on the SS AMP and there were some audiophile grade components when I inspected the PCB. Also, swappable opamps at all points.

 

[DBaldock9]

Either of those options sound like they'd be next to impossible to complete inside the existing case and would be quite involving to perform. I guess the pertinent question would be how much sonic improvement would be likely and if that would justify the time and expense on parts. It certainly seems like there's a number of other areas of lower-hanging fruit that could be looked at first.

For instance, and again my knowledge of electronics is limited so I wouldn't know where to begin suggesting complex circuit changes, here are a few ideas of other things we B4-X owners could potentially improve: (the concept stage is always the most fun because work is completed instantly and ideas are free)

1. How about replacing any resistors & film caps in the signal path? Only problem with film caps it the upper-tier audiophile varieties tend to be very large & potentially worth more than the amp itself. As for resistors, I'm not sure if 0.6W is enough for the releant areas of this circuit but I used these in a TDA1543 DAC once and observed a very obvious improvement:
https://www.partsconnexion.com/vishay-z-foil-tx2575-series-radial-resistors.html

2. What about replacing the volume potentiometer with a stepped attenuator? Not a big Khozmo or similar unless the amp was going to be re-housed, but could something like this fit in the existing case? (don't know if 100k is the right value, just an example of the type I had in mind):
https://www.ebay.com.au/itm/DACT-Ty...m420431cfe5:g:uDsAAOSwizhdqBiW&frcectupt=true

3. Would there be a benefit to either upgrading the trimpots with higher-quality versions or even replacing them entirely with fixed resistors of the optimum tested value?

4. The power supply electrolytic caps could be replaced with nicer ones like Elna Silmic IIs, ideally in much beefier values, but the B4-X seems to have even less room back there than the B4 so again that might be mod requiring a new case. (a common theme emerges)

5. This is where my poor electrical theory will probably become very evident but might there be some benefit to "extending" the ground plane somehow, or doing a better job of connecting it to the case if it is already? Many Astell & Kern users have speculated the sonic differences in the higher-end models are partly due to the differing case materials which I've read are generally connected to the ground plane, copper for example possibly having a benefit over alumnium. This is really just my layman's way of saying "hey maybe grounding is important and could we improve that somehow?".

6. Oh and lastly -again straying into new case territory- in an ideal world it'd be nice to replace the output jack with a high quality 4.4mm Pentaconn jack. Not sure how much sonic difference that'd make.

Just realized that I forgot one critical component, that every fully balanced amp requires - a 4-gang Potentiometer, to control the L+, L-, R+, R- signals.

For #2, It will need to be a 4-gang stepped attenuator.

For #3, The trimpots probably need to remain, since every tube is different, and may also need adjusting as it ages.

For #5, I did add a GND wire around the Volume Control shaft, so that when the nut is tightened, the "front" panel is solidly grounded.

For #6, I recently looked, but haven't been able to find the chassis mount Pentaconn jacks for sale on AliExpress or in Google Searches - and only the one VERY EXPENSIVE ($66.75 each) listing on eBay. A number of vendors sell the cable mount Plugs, and some have the cable mount Jacks - but the chassis mount jacks aren't readily available to the general public.

 

[Bosk]

At that point, just get a better portable tube amp? Oriolus BA300s mkii
Edit: The Oriolus amp is also part of a stack that uses premium components: 9038Pro in the DAC, Alps Pot on the SS AMP and there were some audiophile grade components when I inspected the PCB. Also, swappable opamps at all points.

Thanks for letting me know! This was the first I've heard of that amp, having been out of the hobby for a couple of years.

So I just put in an order for one on Aliexpress, they're on special for AU$460. (roughly US$337)
https://www.aliexpress.com/item/330...earchweb0_0,searchweb201602_,searchweb201603_

I'll compare it with the B4-X once it arrives and let you guys know my findings.

 

[seamon]

Thanks for letting me know! This was the first I've heard of that amp, having been out of the hobby for a couple of years.

So I just put in an order for one on Aliexpress, they're on special for AU$460. (roughly US$337)
https://www.aliexpress.com/item/330...earchweb0_0,searchweb201602_,searchweb201603_

I'll compare it with the B4-X once it arrives and let you guys know my findings.

Perfect. Please let us know how they compare ASAP!

 

[DBaldock9]

At that point, just get a better portable tube amp? Oriolus BA300s mkii
Edit: The Oriolus amp is also part of a stack that uses premium components: 9038Pro in the DAC, Alps Pot on the SS AMP and there were some audiophile grade components when I inspected the PCB. Also, swappable opamps at all points.

Unfortunately, there appears to be several different Oriolus BA300S amp models.
The way to tell them apart, is to see where the jacks are mounted, and whether there's a power LED.
Since the B300S doesn't have a Volume Control, it's not exactly equivalent to the B4-X.
And, the B300S is Balanced Input to Balanced Output ***ONLY***, so I don't think you can directly connect an Unbalanced signal (like a phone) to the Input.
.
I came across this video comparison of the Oriolus B300S & Little Bear B4-X (but I haven't watched it yet) -
.

 

[Barndoor]

Unfortunately, there appears to be several different Oriolus BA300S amp models.
The way to tell them apart, is to see where the jacks are mounted, and whether there's a power LED.
Since the B300S doesn't have a Volume Control, it's not exactly equivalent to the B4-X.
And, the B300S is Balanced Input to Balanced Output ***ONLY***, so I don't think you can directly connect an Unbalanced signal (like a phone) to the Input.
.
I came across this video comparison of the Oriolus B300S & Little Bear B4-X (but I haven't watched it yet) -
.

Looks like he has replaced the chips in his little bear. Burson v5i maybe?

 

[seamon]

Unfortunately, there appears to be several different Oriolus BA300S amp models.
The way to tell them apart, is to see where the jacks are mounted, and whether there's a power LED.
Since the B300S doesn't have a Volume Control, it's not exactly equivalent to the B4-X.
And, the B300S is Balanced Input to Balanced Output ***ONLY***, so I don't think you can directly connect an Unbalanced signal (like a phone) to the Input.
.
I came across this video comparison of the Oriolus B300S & Little Bear B4-X (but I haven't watched it yet) -
.

There are 2 Oriolus BA300s Models - mki and mkii. I have both and currently selling the mki after getting mkii.
mki was designed as a amp for the Sony ZX300 DAP I believe. mkii was designed to be a preamp between their BD20 DAC and BA20 AMP. I have the entire stack with me.

The difference between mki and mkii is that mki boosts the signal by +3dB. mki has 3 stages - Tube Stage, Opamp gain stage and Opamp Buffer stage. mkii skips the gain stage and only has a tube stage + Opamp Buffer stage.

Sonically, mkii is warmer and has a more tubey sound.

Looks like he has replaced the chips in his little bear. Burson v5i maybe?

Yep looks to be Burson V5i

 

[seamon]

Unfortunately, there appears to be several different Oriolus BA300S amp models.
The way to tell them apart, is to see where the jacks are mounted, and whether there's a power LED.
Since the B300S doesn't have a Volume Control, it's not exactly equivalent to the B4-X.
And, the B300S is Balanced Input to Balanced Output ***ONLY***, so I don't think you can directly connect an Unbalanced signal (like a phone) to the Input.
.
I came across this video comparison of the Oriolus B300S & Little Bear B4-X (but I haven't watched it yet) -
.

Also, you can connect an Unbalanced Output from a phone (3.5mm) to the Balanced Input on the BA300s(4.4mm). You need a custom cable for that.
Source: Have a custom cable for exactly this purpose.