[DBaldock9]

Very nice, did you notice much improvement? May I also ask if there's any particular benefit to star grounding them?

I didn't really notice any obvious changes in the sound - the tubes are still a bit noisy while they're warming up, and then everything sounds good after a couple of minutes.
.
The capacitors are grounded to the point on the circuit board that's actually labeled as GND.

 

[Bosk]

Well I just performed the mod (yes I'm keen) with some Russian surplus PIO 0.047 caps I had on hand -the Wima's were actually 0.1nF and might've been a little wimpy- and yes there may be a slight improvement particularly in the high frequencies. The soundstage also feels slightly deeper but its difficult to know if that's just my imagination.

With regards to noise, background noise levels were one of the weakest aspects of the stock amp. However things improved dramatically after swapping out the battery and now its virtually silent without that annoying oscillating crackle.

 

[SBMonster]

My unit is just arrived. I’m impressed overall, but I noticed that on higher volume the left side starts to be distorted and it is very noticeable, but the left and right channels are same volume. I also noticed when i switch it on, the left tube lights up faster and a bit brighter than the right one. Could you guys tell me if there is any solution to this?

 

[SBMonster]

Just paired them up for a test.

Looks like they fixed the "Daul" thing, and also the things related to interference caused by cellphones? so far i can't hear any of it.

 

[DBaldock9]

My unit is just arrived. I’m impressed overall, but I noticed that on higher volume the left side starts to be distorted and it is very noticeable, but the left and right channels are same volume. I also noticed when i switch it on, the left tube lights up faster and a bit brighter than the right one. Could you guys tell me if there is any solution to this?

There are two small Pots for each tube, that you can try adjusting a bit - to set the operating point voltage - so they have more equal headroom.

 

[SBMonster]

Thank you for your quick response. Are those the ones on the outside of the tubes or the ones in the middle?
I connected it to my computer also to my iphone. If i turn the volume over 60-70 percent and about 90 on the b4 there is a lot of distortion on both channel. Is this normal? op amp change solves this? I like to listen music loud sometimes, but this thing barely louder(without distortion) than my devices.

 

[DBaldock9]

Thank you for your quick response. Are those the ones on the outside of the tubes or the ones in the middle?
I connected it to my computer also to my iphone. If i turn the volume over 60-70 percent and about 90 on the b4 there is a lot of distortion on both channel. Is this normal? op amp change solves this? I like to listen music loud sometimes, but this thing barely louder(without distortion) than my devices.

There's one Pot on the "outside", and one on the "inside" - for each tube.
I'm not entirely sure which one to start with, when making adjustments.

 

[Bosk]

Would it be a lot of trouble to convert to balanced input? I could purchase a balanced volume pot but the grounds for each channel would need to be separated throughout the amp I'm assuming.

Is 100k the correct potentiometer value?

 

[DBaldock9]

Would it be a lot of trouble to convert to balanced input? I could purchase a balanced volume pot but the grounds for each channel would need to be separated throughout the amp I'm assuming.

Is 100k the correct potentiometer value?

Fully Balanced is literally 4 separate amplifier channels (L+, L-, R+, R-), which probably means 4 tubes, and the 2 dual op-amps.
.
The Potentiometer is just an input attenuator, providing a load for the source.
If it's before the input DC blocking capacitor, then the value doesn't need to be considered, as far as affecting the bias voltages on the tube circuit.

 

[Bosk]

Fully Balanced is literally 4 separate amplifier channels (L+, L-, R+, R-), which probably means 4 tubes, and the 2 dual op-amps.
.
The Potentiometer is just an input attenuator, providing a load for the source.
If it's before the input DC blocking capacitor, then the value doesn't need to be considered, as far as affecting the bias voltages on the tube circuit.

Thanks for clearing that up, it would definitely be a project far beyond my skill level. Back on firmer ground would you happen to know the value of the potentiometer or can you advise me on how I'd go about measuring it with a multimeter please?

I've considered replacing it with a stepped attenuator -having had great results with them before- but will probably opt for a higher-quality volume pot instead as the amp adds so much gain to a DAP in line-out mode that I listen fairly close to the minimum point after channels are matched and would be concerned even a 47 step attenuator would lack enough levels of usable volume before things just get too loud.

 

[alvaroenoht]

Thank you for your quick response. Are those the ones on the outside of the tubes or the ones in the middle?
I connected it to my computer also to my iphone. If i turn the volume over 60-70 percent and about 90 on the b4 there is a lot of distortion on both channel. Is this normal? op amp change solves this? I like to listen music loud sometimes, but this thing barely louder(without distortion) than my devices.

Hi! I have the same problem. I cant pass 2 o clock without getting tons of distortion. The left is also out of balance. I know it can be adjusted with the pots but I just compensate on the source. But the distortion I read is fixed with better opamps. I have 2 OPA1622 on their way and hope this solves the problem.

 

[Bosk]

I recently put in orders for a Penon Totem 3.5mm interconnect and a new IEM cable (CEMA Tianwaitian) along with another Little Bear B4-X amp. I plan to mod the second one differently and now have some insurance in case the worst should happen and I kill the first board.

Links to the cables:
https://penonaudio.com/audio-cable/3.5mm-cable/penon-totem-audio-cable.html
https://www.aliexpress.com/item/1005001446578292.html


This will be my first experience with palladium-plated cables and the results should be interesting. Meanwhile the resistors I ordered for the B4-Xs (plural) arrived today so they'll be replacing those Dales shortly.

 

[Bosk]

The new resistors are in place. I used 0.25w Takman Carbon Films, except for the two 2.2k input resistors in the signal path which were replaced with Vishay Z-Foils.

The change has been pronounced and extremely satisfying. There is more detail, a blacker background, the soundstage feels more solid and believable, but most of all everything flows much better and it sounds more like listening to music rather than an audio system trying to reproduce music. The lazy description would be a more analog sound, with a significant amount of digital grit swept away. This effect is consistent with my experience using Z-Foils in a TDA1543 DAC a number of years ago. At US$16 per resistor I have difficulty justifying using them outside the signal path, but along it they are absolutely worth the money. Very highly recommended mod.

I've decided to keep the amp in its' original case rather than build a larger one for it, (though the 5500mAh battery is far too large to fit so that will rest underneath in traditional DAP/AMP sandwich fashion) and plan to destroy the input traces on the PCB from the 3.5mm jack to the OP-AMP and replace them with OCC wiring, (plenty of room inside the case under the PCB provided wire gauge isn't too large) however that leaves those dubious WIMA input capacitors. Unfortunately all decent audiophile 2.2uF film caps are enormous by comparison, I could mount some on top of the case towards the rear and then trail the wires inside but that would nullify having the amp packed a snug little case to some extent. I'm mindful that just as diminishing returns are a reality when buying increasingly expensive off-the-shelf gear, so is the reverse when you start modding stuff - the more you remove junk from the signal path the more cumulative benefit is to be gained from each additional step, so naturally I'm tempted.

 

[allaces305]

Can anyone please help me with barrel/ tip size of the charging cable that fits the B4-X perfectly....i lost the original charger and need to by a universal charger that brings many sized tips..... Thank you in advance.

 

[DBaldock9]

Can anyone please help me with barrel/ tip size of the charging cable that fits the B4-X perfectly....i lost the original charger and need to by a universal charger that brings many sized tips..... Thank you in advance.

NOTE: You need to buy a Li-Ion charger, and not just a generic 12.6V charger.
Last year, I bought a spare 12.6V @ 1A Li-Ion charger (to use at work) from Amazon - but it's not available any longer.
The size of the plug is 3.5mm x 1.35mm.