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B-tech BT928, i need some help with modifications. Replace cap

post #1 of 3
Thread Starter 

So i bought this b-tech thing from my work ( got it for cheap )

 

I removed the Tone pot which made a whole lot for the good of the sound quality. The next thing i´m looking to replace is the capacitor for a larger one of better quality. I think i´l start with this since the soldering seems quite easy and it looks to be a good way to start this DIY stuf.

 

I dont know much about these thing, i got basic soldering skills and a decent soldering station. 

 

Can i replace the cap with this one? http://www.amazon.com/Rubycon-Thru-Hole-Electrolytic-Capacitor-Impedance/dp/B0015AAS9W/ref=pd_sbs_indust_7

 

Also, is there any other quite simple thing that i can do to this thing to make it sound better? I know there are a lot of pictures and stuff around the web. But they all seem to complicated for me as for now. 

 

Best regards!

post #2 of 3

Hi there, i can give you an honest guidance on this project, unlike alot of crap, thats been spoken over the years about this little beauti, the bt928 circuit that is, this unit has been designed for a certain market hence the cheap price. Basic amplification for your average punter. However grosley overlooked, & not really talked about anywhere ive seen, is its circuit, which is basic but thats its trump card, its well designed & performs excellent with the NE5532, the main heart of the system. Changing op amps & major circuit changes is a waste of time. This circuit has been used widely, with various minor tweaks, at certain price points, with top notch results ! I could go on, but we'll finish there for now. For your self & all the modding clan, here as follows are four major modifications you need to do first before anything else ! These make the biggest improvement out of all, & no it isnt the caps & resistors !

 

Replace the volume control with one of the famous alps blue potentiometers ( 10k direct swap ) ( 20k input signal resistor will need to be decreased )  

 

Take out the tone control, the two green capacitors & overlooked my most ,the link wire which left in, may create signal path iregularities to one channel ?

 

Buy yourself a good quality:   15v  ( 2a or above ) in line  switch mode regulated power supply

                                                       avail from cpc, rs , farnell ect  

  

 This makes a massive improvement !  Sound quality / balance & distortion levels, The power supply eliminates all noise on the rails, &  power output improved !

 

& this is before you change the resistors & the caps !

 

I would just like to point out that some people have tried to add regulators to the board, this is not necessary, no more power supply mods are required other than a faster diode ( opinions vary ) once you have purchased the above switch mode reg psu.

 

Also overlooked on all the bt928 mods ive seen are the 101 ceramic capacitors been left in place ! These are nasty & no good for audio tuning frequencies, replace them with polystrene 100pf  types.

 

Doing the four modifications above will set you on the way to having an excellent performing audiophile headphone amp ! There are a many more minor mods but times run out for me now ! 

 

good luck !

post #3 of 3

Hello Guys,

 

I've got the same BT928 amp and I've done some modifications. I was interested to start to do some DIY projects and this amp and the posts looked OK for me. And I like to listen the good quality music, so I've decided to give it a go.

I attach photos what I've done. I know it doesn't look beautiful but it was my first project and I've got only a basic soldering set :)

 

So,when I've finished with the job only one side of the headphones had sound and by now it just doesn't work.

It has got the power but no sound comes out.

 

Could anyone give me some help if it possible from this photos what could wrong with it?

 

I've tried to attach photos but the webpage doesn't give me permission.

Any idea for that? :)

 

 

 

Many thanks

 

Baz

 

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