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BPA300 mono block

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#224
Alex88,
I have always wanted to know the function of the variable trimpot on the input to the lm3886. When I built the amps from your first group buy I never got much response from that pot. My dc offset was high on all 4 amps.
Did you ever have oscillation problems. Tad
 
#225
How high is your DC offset? before I adjust the trim pot the DC was about 20-30mV, after adjustment I can get it down to 9mV

When you adjust the DC offset of one LM3886, the DC offset will change on other LM3886, so you have to report the process until all chips has the same DC offset

I built 4 boards and never have oscillation problem. Please try to match the resistor at your best since it will affect gain of each chip.
 
#227
alexw88 said:
How high is your DC offset? before I adjust the trim pot the DC was about 20-30mV, after adjustment I can get it down to 9mV

When you adjust the DC offset of one LM3886, the DC offset will change on other LM3886, so you have to report the process until all chips has the same DC offset

I built 4 boards and never have oscillation problem. Please try to match the resistor at your best since it will affect gain of each chip.
Click to expand...


Hi there,

Well I finished my bpa-s with the Lundhll 1545A...... all good 4 a loooong time now.

I built 4 pcb's around each transformers and i drive 1 pcb 300 for the mid and one for the high's.

just amazed!!! it's enough to make a party in a 100 sq meter room!!!

I found the offset problem too, but if you shorten the inputs, than you can make the adjustment easy... they don't interact soo much...

Will make another run from these pcb-s in jan/feb... so there will be a group-buy op here ..... they will be cheap. with the SMD parts on board.

BTW Alex88 When had you best performance?? Offset around the limit (9 mV) or around zero???

And wich lundahll input/output gave you best result (I use the R4U and L4B)

I would like to make an unregulated snubberised PSU for it. did you made any upgrade? like MUR 860 diodes or snubbbed psu??

what about the star-ground.... on your page (www.shine7.com) you don't use star-ground at all. no "star-power"either!!!

It's uses 50 watt per module (remember 4 pcb's in module) without anything connected to the source. I used really big sinks, since there are 2 pcb's per sink. but even these are about 45 celsius when it's no signal. are all of these are normal, or I should fine-tune something??

and ther was no way to make all the 8 pcb-s to the same offset... there where a few interesting things happenend.... like there where pcb-s wich made 2 chips output to 10-12 Vots!!!! and the third one to negatie 20-24 Volts!!!! I had 3 of these boards... some failure of the chips? or what coud this make?? any idea???


a few had stared like -40 to -170 mV some couldn't be tuned to the positive range.... some could. and I had 1 board like this but in the positive range... to high starting.... never went under 17 mVolts.

I made first 20 boards... I've gave up wit 5-6 of them. I fried one in last week durin' re-wire.

I changed the 0.2R to 0.15R..... but there was no way to find the 0,1% tolerance from ANY of the required parts.

But there is no noise.... minimal hiss..... about 1mV at the output. And THEY Rocks the house with my MTM bastards!

Thanks for the shematics again Alex
 
#229
ccschua said:
wonder how is the sound quality compared to other amp such as 2030 and 7294 and others in terms of dynamics, detail, resolution, accuracy, vocal and atmosphere.
Click to expand...


Sorry, but I can't give you answers for this...... but all I know, It's sounds GOOOOOOOOOOOOOOD 🙂

All the people, who heard, was amazed

My system sounds like a "studio reference" only "MUUUUCH better and louder" as one of my sound-enginer friend told me :devilr:
 
#232
Just a little remark here. I saw Alex88 original amp design on the internet and bought his first set of boards. This was my first amplifier build and really took my time and chose the best parts I could afford.
The end result is something truly great. The sound detail and the mid to highs is as clear an precise as any amp I have every heard. I have been a Mcintosh owner most of my life and this little chipamp is as good or better than them.
Alex did a very good job on the board layout and the construction is quite easy. Well maybe the little SMD parts were tedious.
I never quite understood what the small potentiometers job was or how it affected the circuit. The amps just sound good. If you are not use to hearing the fingers sliding across the strings on a harp or guitar you will hear them now. The small whispers that a fllute player makes as he plays and the faint TING of the cymbals are all there. The plucking sounds on the bass guitar comes through with scary detail. Some folks might not like this but it is in the music, you just have not been hearing it.

Remember to use a really large heatsink. This design puts out quite a bit of heat.
 
#234
help neeeded

hey alex, great work man, the pcb itself looks so great.
only one thing , i live in india (Mumbai), has any body from here purchased any pcbs from you, it is not possible for me to buy the pcb from you due to the cost factor.
i would be greatful if you could share the gerber files for bpa300 monoblock.
any way keepup the grat work
 
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