Simple LM3886 Amplifier

[saheb11123]

First of I would like to say thanks to some special people who has helped and supported me in many ways that I can't say.

Thanks : Sangram Da(cranky) , Koushik Da(koushik fm) , Amlan Da


It had been a long journey from the very first enquiry till the finish of the build..

I didn't know much about DIY or anything , when I got first introduced to Sangram da, he was like a vast chamber or unverse of knowledge. He still is.
From then on I started learning little by little about the world of audiophiles.


Now coming to the point, this is an simple LM3886 stereo build.
The pcb's are custom etched by amlan da a friend and guide thanks again.
We started off with LM4780 build but that got very complicated and there were certain issues, ultimately the chip got fried.

The pics are attached, Ill be posting the schematic of the pcb at a later time alongwith the components list.

The PSU is a 20-0-20 traffo 5amps rectified by bridged mur680 and with 1 10000uf 63V cap per channel + 2 10uf 63v caps per channel.

Testing the Amp

Finished thing:
Temporarily been kept this way... Will soon get a cabinet made and transferred.

 

[saheb11123]

Need Suggestions of improving power supply

 

[linuxguru]

Need Suggestions of improving power supply

Filter caps look too small - you need something like 6800uF to 10000uF per rail, maybe more for a stereo setup.

You can also consider dispensing with the 50 Hz mains trafo altogether, and using 2x laptop power adapters (say 24V, 3A per rail). It will have less peak power capability than an EI trafo, but it will be much smaller and lighter, which is useful for small bookshelf setups.

Check out my MiniRef 1875 implementation for an example:

http://www.hifivision.com/diy/44488...o-amplifier-built-beginners-6.html#post590177

 

[saheb11123]

Filter caps look too small - you need something like 6800uF to 10000uF per rail, maybe more for a stereo setup.

You can also consider dispensing with the 50 Hz mains trafo altogether, and using 2x laptop power adapters (say 24V, 3A per rail). It will have less peak power capability than an EI trafo, but it will be much smaller and lighter, which is useful for small bookshelf setups.

Check out my MiniRef 1875 implementation for an example:

http://www.hifivision.com/diy/44488...o-amplifier-built-beginners-6.html#post590177

Thank you, but how would i get -ve rail from laptop adapter?
Also can you suggest some capacitor that i should look at? I mean some website from india is preferable, or maybe somewhere where i would procure some good components (locally is also welcome as well as any fm who is selling).

Again thanks for replying and suggesting

 

[saheb11123]

Schematic and PCB :




The component values from my build is a bit different from those here. There is also a feedback resistor which is directly soldered to the 3 and 9 pin .

 

[linuxguru]

Thank you, but how would i get -ve rail from laptop adapter?
Also can you suggest some capacitor that i should look at? I mean some website from india is preferable, or maybe somewhere where i would procure some good components (locally is also welcome as well as any fm who is selling).

Laptop adapter: You'll need two units with isolated secondaries (pretty much all laptop adapters are of this type). Connect -ve of adapter 1 to +ve of adapter 2 to create the power ground. +ve of adapter 1 is the +ve rail, -ve of adapter 2 is the -ve rail, giving (say) +24V/0/-24V rails.

I don't know the electronics market in Kolkata - some other FMs may be able to help. In Mumbai, Bangalore or Chennai, there are several vendors for imported electrolytics. You should be able get Elna, Nippon, Panasonic, Rubycon, Nichicon or other Japanese brands from time to time.

 

[koushik]

Well done, Saheb. Looks good.
Thanks for mentioning my name here, but I haven't contributed anything to this project

Need Suggestions of improving power supply

Down the line,

1) I would change all the capacitors to something of better quality like -
UKA1V101MED1TD - NICHICON - CAPACITOR ALUM ELEC, 100UF, 35V | element14 India

2) Bypass all the capacitors on PS and Amp with polyester capacitors like -
BFC237011474 - VISHAY BC COMPONENTS - CAP, FILM, PET, 470NF, 63V, RAD | element14 India

3) I don't know the quality and value of the VC pot but that should be of correct value and of decent quality.

These would certainly change the timber and texture of the sound to a notch higher.

 

[palka]

Thank you, but how would i get -ve rail from laptop adapter?
Also can you suggest some capacitor that i should look at? I mean some website from india is preferable,

You may look at the following places: Here, & Here.

 

[saheb11123]

Well done, Saheb. Looks good.
Thanks for mentioning my name here, but I haven't contributed anything to this project



Down the line,

1) I would change all the capacitors to something of better quality like -
UKA1V101MED1TD - NICHICON - CAPACITOR ALUM ELEC, 100UF, 35V | element14 India

2) Bypass all the capacitors on PS and Amp with polyester capacitors like -
BFC237011474 - VISHAY BC COMPONENTS - CAP, FILM, PET, 470NF, 63V, RAD | element14 India

3) I don't know the quality and value of the VC pot but that should be of correct value and of decent quality.

These would certainly change the timber and texture of the sound to a notch higher.

There is already one panasonic and two holcos on each pcb:yahoo:hyeah:. And yes few days later I was thinking of changing chadni electrlytic one's with the good nichicon's was only looking on how to source them, and now that you and other FM have pointed out, Im surely going order those.


And even you hadn't contributed the moral support (me whatsapping you and asking you questions and you never said no) that was enough.

 

[saheb11123]

You may look at the following places: Here, & Here.

Thank you for the info it means a lot

 

[koushik]

There is already one panasonic and two holcos on each pcb:yahoo:hyeah:. And yes few days later I was thinking of changing chadni electrlytic one's with the good nichicon's was only looking on how to source them, and now that you and other FM have pointed out, Im surely going order those.


And even you hadn't contributed the moral support (me whatsapping you and asking you questions and you never said no) that was enough.

There are many type of capacitors from same manufacturer. So choosing right one is important. And also don't forget the bypass polyester caps.

 

[saheb11123]

Okay , I have been using the amp from the day i built it, and i have two questions?

1. Whenever anyone switches something on/off in the house (same room or other) i can hear a "phat" sound from the speakers, what is this issue?

2. I can hear a faint "hiss" sound when the amp is on and not playing anything(it is connected to pc), again anyway to eliminate this?



Thanks and regards
Soumyajyoti

 

[koushik]

For the first thing you have to beef up the psu capacitors and bypass them with plastic caps.

For the 2nd one, there are many possibilities. First thing change the source from pc to something else and check if the hiss is still there.

 

[saheb11123]

Whatever the source is , the hiss is still there, tried with both phone and pc.
Can it be caused by the RCA jack?
Do suggest me a uber budget friendly (as low as possible) EP to RCA

 

[omishra]

Can you short input wires (each channel live and ground) of Amp without any source and listen the hiss? From RCA to PCB you need either shielded wire or twisted pair of wires. Wiring and board should be like spider - legs moving away from body, wires moving away from board and not running parallel to PS/in-out wires.

In any case, earth grounded metal chassis is first requirement for quite amp. PS ground (DC '0') should be connected to chassis through 10? or earth isolator.

 

[saheb11123]

Can you short input wires (each channel live and ground) of Amp without any source and listen the hiss? From RCA to PCB you need either shielded wire or twisted pair of wires. Wiring and board should be like spider - legs moving away from body, wires moving away from board and not running parallel to PS/in-out wires.

In any case, earth grounded metal chassis is first requirement for quite amp. PS ground (DC '0') should be connected to chassis through 10? or earth isolator.

Thank You.

 

[amlan_dg]

Hi Saheb,

Put a 220pF ceramic cap parallel to R2 in the schematic.
Use 10uf Muse BP for C1 in the schematic.(calculate -3dB point)
Use 100uF Panasonic FM for local ps decoupling on the board.
Use 100nF polypropylene caps right on the LM pins.
Wiring needs a lot of work, as suggested by omishra.
Amp needs a cabinet.

 

[saheb11123]

The amp is dead quiet now. After breaking in it sounds like living inside a thatrea, to how much spare space i have the sound depth and field is pretty good.

Update : Brought some 15000uf caps (punsumi industrial grade as suggested by cranky)

 

[koushik]

The amp is dead quiet now. After breaking in it sounds like living inside a thatrea, to how much spare space i have the sound depth and field is pretty good.

Good to know that. What worked for you? grounding?

 

[saheb11123]

The earthing was dead. Due to today's rain it repaired itself. The hum was due to cheap RCA cable though.

I didnt do any additional grounding, I just bought the caps today and connected them removing the previous ones.