[elvispreasley]

Just got my B4-x. Unfortunately it appears to be from the new batch with a different type of tubes. Unluckily I spent about 40$ on few different pairs of 5899 tubes, thinking to make it replacable on my amp) Well, hope someday I'll find out what to do with them...
The amp came with 2 Burnson V5i op amps (which I also ordered), so I installed them right away. Also I covered the inner part of the amp metal body with faradey tape and put 2 silicone rings on each tubes. Another words, did some basic mod straight out of the box.
I still need more time to realize - do I like the sound with this amp better then with the built in amp of my portable multibit dac/amp (Tento 1866), but I already have one concern. The amp has very noticeable "hiss" noise on the background. When the music is playing it's kinda hard to hear it, so it's not really affecting a lot the overall sound of the amp during this time, but when the music is not playing - the "hiss" noise is really easy to hear. I do have an experience with several tube and hybrid amps, but never ever heard anything like this, as they usually had quite black background. Is this a typical situation with B4-x or my particular amp has some problem, which cause this effect? If there any chance to fix it?

UPD: Just found out that the hiss exists only with low impedance and high sensitivity earbuds/earphones (32 ohm, 115db as a particular example). With 600ohm earbuds, B4-x has fairly black background.

 

[Bosk]

Just got my B4-x. Unfortunately it appears to be from the new batch with a different type of tubes. Unluckily I spent about 40$ on few different pairs of 5899 tubes, thinking to make it replacable on my amp) Well, hope someday I'll find out what to do with them...
The amp came with 2 Burnson V5i op amps (which I also ordered), so I installed them right away. Also I covered the inner part of the amp metal body with faradey tape and put 2 silicone rings on each tubes. Another words, did some basic mod straight out of the box.
I still need more time to realize - do I like the sound with this amp better then with the built in amp of my portable multibit dac/amp (Tento 1866), but I already have one concern. The amp has very noticeable "hiss" noise on the background. When the music is playing it's kinda hard to hear it, so it's not really affecting a lot the overall sound of the amp during this time, but when the music is not playing - the "hiss" noise is really easy to hear. I do have an experience with several tube and hybrid amps, but never ever heard anything like this, as they usually had quite black background. Is this a typical situation with B4-x or my particular amp has some problem, which cause this effect? If there any chance to fix it?

UPD: Just found out that the hiss exists only with low impedance and high sensitivity earbuds/earphones (32 ohm, 115db as a particular example). With 600ohm earbuds, B4-x has fairly black background.

Yes I found there's a huge amount of background electrical noise with the stock amp, which is its' Achilles heel along with poor battery life.

In my case replacing all the stock Dale resistors removed almost all the noise. There's still a little but its so quiet I barely notice it at all.

 

[elvispreasley]

Yes I found there's a huge amount of background electrical noise with the stock amp, which is its' Achilles heel along with poor battery life.

In my case replacing all the stock Dale resistors removed almost all the noise. There's still a little but its so quiet I barely notice it at all.

Are you sure that replacing of the stock resistors - affecting the noise? I mean, it seems like it's all because of the high output impedance of the amplifier, as with high impedance headphones - there is no noise whatsoever. Just don't understand - how the resistors may affect it in such a case?

Meantime, I compared the sound of the build in amp of my Tento 1866 with B4-x and can say for sure that Little Bear significantly improves SQ of my dac/amp. First of all it gives higher volume level, pairing with hard to drive earbuds and cans (like my LCD3). Also it gives more clarity and transparency for the sound, more bass slam and better LF control. The soundstage feel bigger and more airy.
I'm really happy with a performance of this little cheap guy and can highly recomend it for any portable setup. Great performance for such a small money.

 

[Bosk]

Are you sure that replacing of the stock resistors - affecting the noise? I mean, it seems like it's all because of the high output impedance of the amplifier, as with high impedance headphones - there is no noise whatsoever. Just don't understand - how the resistors may affect it in such a case?

Meantime, I compared the sound of the build in amp of my Tento 1866 with B4-x and can say for sure that Little Bear significantly improves SQ of my dac/amp. First of all it gives higher volume level, pairing with hard to drive earbuds and cans (like my LCD3). Also it gives more clarity and transparency for the sound, more bass slam and better LF control. The soundstage feel bigger and more airy.
I'm really happy with a performance of this little cheap guy and can highly recomend it for any portable setup. Great performance for such a small money.

Unfortunately I performed a bunch of mods around the same time - replacing the battery, replacing the electrolytic caps and replacing the resistors. It felt like replacing the resistors had the biggest effect on background noise levels, but all three mods may have contributed. There is still noise remaining but at such a low level it is difficult to noticed especially when playing music.

I like your setup! The B4-X is great value but I feel value goes up exponentially when a few simple changes are made. Once noise levels are reduced & battery life improved it feels like a different product, and when modded to the extent of mine it sounds like an entirely different beast that I've no doubt can compete with any portable amp available.

 

[elvispreasley]

Unfortunately I performed a bunch of mods around the same time - replacing the battery, replacing the electrolytic caps and replacing the resistors. It felt like replacing the resistors had the biggest effect on background noise levels, but all three mods may have contributed. There is still noise remaining but at such a low level it is difficult to noticed especially when playing music.

I like your setup! The B4-X is great value but I feel value goes up exponentially when a few simple changes are made. Once noise levels are reduced & battery life improved it feels like a different product, and when modded to the extent of mine it sounds like an entirely different beast that I've no doubt can compete with any portable amp available.

What kind of battery did you replace on? How long it holds charge now?

 

[Bosk]

What kind of battery did you replace on? How long it holds charge now?

I replaced the stock 1,000mAh battery with one that's 5,500 mAh, and recently took delivery of another that's 10,000 mAh. I haven't timed battery life since, but am guessing it would be 5 or 6 hours as the other mods I've done like changing the op-amps for Burson v6s and installing larger capacitors has increased the battery drain.

 

[elvispreasley]

I replaced the stock 1,000mAh battery with one that's 5,500 mAh, and recently took delivery of another that's 10,000 mAh. I haven't timed battery life since, but am guessing it would be 5 or 6 hours as the other mods I've done like changing the op-amps for Burson v6s and installing larger capacitors has increased the battery drain.

5-6 hours is not really far from the stock 4 hours battery life, but if your mods are draining a lot of power - that's a great result!
What about the size of the battery? Does it fits inside of the B4-x, like the stock one or it stays outside - "powerbank style"?

 

[Bosk]

5-6 hours is not really far from the stock 4 hours battery life, but if your mods are draining a lot of power - that's a great result!
What about the size of the battery? Does it fits inside of the B4-x, like the stock one or it stays outside - "powerbank style"?

The 5,500 mAh battery is slightly smaller than the stock B4-X itself, whereas the 10,000 mAh battery is much larger and about twice as heavy. I'll post more photos of the amp here when I next mod it further.

 

[elvispreasley]

The 5,500 mAh battery is slightly smaller than the stock B4-X itself, whereas the 10,000 mAh battery is much larger and about twice as heavy. I'll post more photos of the amp here when I next mod it further.

You mean that 5500 battery is almost the size of whole B4-X?

 

[Bosk]

You mean that 5500 battery is almost the size of whole B4-X?

That's right, here's a photo of it under my amp that I posted earlier in the thread.

 

[elvispreasley]

That's right, here's a photo of it under my amp that I posted earlier in the thread.

Oh yeh, I've seen this picture, but didn't realize that there is a battery underneath the amp.
That's to extreme to me, to be honest. I'll rather stay with 4 hours battery life, but in a compact form factor)
However I'm saluting to your effort - to push the SQ of B4-x far beyond it's stock limit!

 

[DBaldock9]

I've ordered a set of 8 spare JAN5899 tubes, and some of the 8-Pin miniature tube sockets.

Depending on how difficult it is to get the necessary power supply components, I'm going to give a shot at building a Balanced (4x tubes & 4x op-amps) Amp, based on the B4-X circuit design.
.
Wish I had access to an easy to use circuit board layout program, and an inexpensive board fab shop.

 

[Bosk]

I've ordered a set of 8 spare JAN5899 tubes, and some of the 8-Pin miniature tube sockets.

Depending on how difficult it is to get the necessary power supply components, I'm going to give a shot at building a Balanced (4x tubes & 4x op-amps) Amp, based on the B4-X circuit design.
.
Wish I had access to an easy to use circuit board layout program, and an inexpensive board fab shop.

That sounds awesome!

It’s a very ambitious mod, are also you planning to design a new power supply, perhaps with separate voltage regulation for each tube & op-amp? I do wonder how much untapped potential lies with cleaner power, especially if you plan on running it on mains power perhaps.

I can’t wait to watch your progress.

 

[DBaldock9]

That sounds awesome!

It’s a very ambitious mod, are also you planning to design a new power supply, perhaps with separate voltage regulation for each tube & op-amp? I do wonder how much untapped potential lies with cleaner power, especially if you plan on running it on mains power perhaps.

I can’t wait to watch your progress.

Rather than a mod to my current B4-X - I really want to design a new circuit board, with enough space for the 4x tubes, and clearance around the op-amp sockets for large discrete op-amps. I've got to figure out whether the circuit will require manual switches, to change between Balanced & Single-Ended Input modes.

I was thinking I might use one or two of these 12,500mAH 3.7V batteries - https://www.aliexpress.com/item/33049806489.html
One of these 5V USB chargers / boost modules could provide the power supply input - https://www.amazon.com/daier-Lithium-Li-ion-Battery-Charger/dp/B07SBZZ5SC/
It can also take the 3.7V from the battery, and output a (+) voltage from 4.3V to 27V, at up to 2A.
I'm wondering whether the boost module can be used "floating", so it can provide the (-) voltage rail, as well?

 

[Bosk]

Rather than a mod to my current B4-X - I really want to design a new circuit board, with enough space for the 4x tubes, and clearance around the op-amp sockets for large discrete op-amps. I've got to figure out whether the circuit will require manual switches, to change between Balanced & Single-Ended Input modes.

I was thinking I might use one or two of these 12,500mAH 3.7V batteries - https://www.aliexpress.com/item/33049806489.html
One of these 5V USB chargers / boost modules could provide the power supply input - https://www.amazon.com/daier-Lithium-Li-ion-Battery-Charger/dp/B07SBZZ5SC/
It can also take the 3.7V from the battery, and output a (+) voltage from 4.3V to 27V, at up to 2A.
I'm wondering whether the boost module can be used "floating", so it can provide the (-) voltage rail, as well?

So you'd effectively be building a new amplifier from scratch. Those batteries are certainly very cheap for the amount of power they'd provide, and you'll certainly need quite a bit depending on how much run time you'd be happy with.

Wouldn't you obtain optimum performance by effectively building an entirely separate power supply for each op-amp & tube? Of course that would mean much more space required and power drawn which would could be a consideration depending if plan to build something geuinely portable or more in the transportable category.