Raspi 2 and HiFiberry DAC+ coupled to a LM3886T Gain Clone Amp

[aniruddha82]

Amplifier cabinet looks awesome. Where did you get it fabricated from?

Yesterday I could not get my box as the fabrication was not complete :sad: . Spent a good 6 hours with the person. Hopefully...hopefully next weekend it gets done. meanwhile assembled the rest of the boards. The main LM3886T board is still WIP.
Some snaps of the boards in progress

3886T and Main supply board.
The bulky Toroidal
Soft Start Board
The Box Front View..This is still in works.
The Box...Side view
Raspi2+HifiberryDac+


One of the challenges I am facing on main 3886 board is to get matching resistors.

Since the configuration is parallel, their gain should be identical to the extent possible and the factors affecting the gain are RF(200K) and Ri(10K). I have been trying to find a pair of identical match for the board, but it has been in vain. Any suggestions here? The only option I see is to buy a bunch more of resistors and hope that I turn lucky. If anyone has better suggestions, do let me know.

Regards,
Sunil

 

[sunilmani]

Amplifier cabinet looks awesome. Where did you get it fabricated from?

It has been fabricated here in Pune. Went through three elaborate sessions of designing with the fabricator before finalizing. There are loads of minor changes to be done here. Hopefully i would get them by this Sunday.

 

[sunilmani]

Are these resistors regular 1/8W or 1/4W? If yes, they're cheap enough to buy 10-20 pieces each of the same value and hand match them to within a few ohms.

Yes these are 1/4W. Have ordered for 100 pieces. Hope to find 4 sets of identical values.

I was looking for 0.1% tolerance resistors and guess what, the prices were mind boggling for a single piece. So i went ahead and ordered 100 pieces of normal 1/4W , MFR 1% tolerance.

 

[aniruddha82]

Where exactly in Pune and how much did it cost?
I am also in Pune and looking for a proper cabinet for my amplifier.
Thanks in advance

It has been fabricated here in Pune. Went through three elaborate sessions of designing with the fabricator before finalizing. There are loads of minor changes to be done here. Hopefully i would get them by this Sunday.

 

[MaSh]

Any suggestions for a good power source for a raspberry pi3 Digi+ combo. Using the current adaptor that had come with the Pi.

MaSh

Sent from my Redmi Note 3 using Tapatalk

 

[Kannan]

Nothing like using a good quality high capacity power bank.

 

[sunilmani]

Any suggestions for a good power source for a raspberry pi3 Digi+ combo. Using the current adaptor that had come with the Pi.

MaSh

Sent from my Redmi Note 3 using Tapatalk

I have been using a portronics 2A mp power adaptor and it has worked good for me

 

[MaSh]

I have been using a portronics 2A mp power adaptor and it has worked good for me

I guess thats the same as what I got along with the Pi. Its a Proto Centra 5V - 2.0A rated. However, I read some articles online suggesting powering the DiGi+ which in turn would power the Pi via the GPIO pins. I guess need to research more.

MaSh

 

[sunilmani]

Where exactly in Pune and how much did it cost?
I am also in Pune and looking for a proper cabinet for my amplifier.
Thanks in advance

There are two suppliers here in Pune and both are on the outskirts.
1.Jyoti Heat sinks. S.Block, Indrayani Chowk, W-109, MIDC, Bhosari, Pimpri-Chinchwad, Maharashtra 411026. 020 6614 2983
2.Prime Enterprises
SHOP NO- 27, DANGAT INDUSTRIAL ESTATE, BEHIND AURAM ENGINEERING, VADGAON BUDRUK, Pune - 411051, Maharashtra, India. 020 2435 0509

I am yet to get to the payment as the box is not yet complete.

 

[tcpip]

Yes these are 1/4W. Have ordered for 100 pieces. Hope to find 4 sets of identical values.

I was looking for 0.1% tolerance resistors and guess what, the prices were mind boggling for a single piece. So i went ahead and ordered 100 pieces of normal 1/4W , MFR 1% tolerance.

For getting tighter tolerances, I use a trick if I have sufficient PCB space: I simply hook up multiple resistors in parallel. Assuming random distribution of values within the tolerance band, a set of 4 or 10 pieces connected in parallel gives improved tolerance. In other words, 4 resistors of the same nominal value, each 1% tolerance, connected in parallel, may give you 0.5% or better tolerance. Of course, in this case, the nominal value of each resistor will have to be four times the final value I need.

 

[sunilmani]

For getting tighter tolerances, I use a trick if I have sufficient PCB space: I simply hook up multiple resistors in parallel. Assuming random distribution of values within the tolerance band, a set of 4 or 10 pieces connected in parallel gives improved tolerance. In other words, 4 resistors of the same nominal value, each 1% tolerance, connected in parallel, may give you 0.5% or better tolerance. Of course, in this case, the nominal value of each resistor will have to be four times the final value I need.

Good Suggestion - but currently i do not have that kind of PCB space.

 

[sunilmani]

The box has finally come in. Since December i was behind this person to get it done; finally today i have the box. Sharing some snaps of the same -

The front view

The Top View

I could not resist myself and started the mounting and here is how its looking...

Rear view mount in progress

 

[sunilmani]

I am envisaging a problem here. Since the media center is within the box, the power off may not always be controlled and also it may not be preceded with turning off the media center. The result maybe a corrupt database and that would leave Kodi unusable for next time...any thoughts? There are suggestions on super capacitors in some forum...there should be a better way to do this...

 

[sadik]

The Enclosure is looking Beautiful...Very well finished

 

[sunilmani]

The Enclosure is looking Beautiful...Very well finished

Thanks Sadik. I had taken your box as a reference while designing mine. Thank to you for sharing.

 

[jmascreen]

The box has finally come in. Since December i was behind this person to get it done; finally today i have the box. Sharing some snaps of the same -

The front view

The Top View

I could not resist myself and started the mounting and here is how its looking...

Rear view mount in progress

Where did you get the enclosure build in Pune?

 

[sunilmani]

That's covered in the earlier post. please check.

 

[sunilmani]

After a long time, finally found some time to continue the assembly process. Some snaps shared here https://drive.google.com/file/d/0B47c2o9yr3jlRTFBbHU3M29RQTQ/view?usp=sharing

 

[HormusPeston]

Hi Sunil. Very elegant cabinet. As a few forum members had mentioned earlier, the speaker connectors are too close to the AC mains. The cables from at least one of the channels will end up being close to either the AC socket or the transformer. Also, twist the wires to and from the transformer, and those from the bridge rectifier to the filter condensors.

An excellent guide to wiring was written by a member of diyaudio, called Bonsai: http://hifisonix.com/wordpress/wp-c.../How-to-wire-up-a-Power-Amplifier_Updated.pdf

Cheers,
~hp

 

[tcpip]

After a long time, finally found some time to continue the assembly process. Some snaps shared here https://drive.google.com/file/d/0B47c2o9yr3jlRTFBbHU3M29RQTQ/view?usp=sharing

I am able to see just one photo. Are there more?

In general (I'm no expert), I would suggest keeping all mains power related components close to the mains IEC inlet. So, the transformer, rectifier, and smoothing caps should be closely clustered near that area. Helps to keep the low voltage stuff clear of any EMI etc.

I've seen some large commercial amps which have the trafo in the centre of the chassis, but those guys have the ability to do a much more compact design than what a DIYer can do.