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-   -   LM3886 running inverting only and bridged - for 8 Ohms only (http://www.diyaudio.com/forums/chip-amps/222519-lm3886-running-inverting-only-bridged-8-ohms-only.html)

astx 30th October 2012 01:37 PM

LM3886 running inverting only and bridged - for 8 Ohms only
 
10 Attachment(s)
Dear diy'ers,

attached you can find my diy version of a very good and warm sounding 4 channel gainclone based on LM4562 and 2 x LM3886.
Feel free to re-use my schematics and pcb for DIY!
To manage mains there is a pic microcontroller based control circuit.

Best regards,

Toni

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astx 30th October 2012 01:55 PM

4 Attachment(s)
some more pictures:

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AndrewT 30th October 2012 02:13 PM

I'm not allowed to put in the word I am thinking !!!

I had a post written and clicked on a pic. The Forum downloaded a revised page with the pic. When I returned to where I was, my post was lost.
Why does the Forum sometimes on clicking superimpose the pic alongside where one currently is and at other times take one to a new page?

AndrewT 30th October 2012 02:18 PM

How about adding a note that the decoupling caps Cs are located on the amp PCBs and not as shown on the PSU schematic.

How does output offset vary with time from start up and/or with temperature?

Can you include details of the MCU operation and how we can duplicate that functionality?

Why does the FFT show both 50Hz and 60Hz and the harmonics of both?

And congrats on the super drawings.

Clever use of the sawn in half heatsink to fit all 4 amplifiers inside your chassis and still give adequate cooling. Nice.

I have a similar sink but it's only 50mm tall. If instead of having 12 @ 50mm I had 6 @ 100mm high I would never have any cooling problems. What height is your extrusion?

astx 30th October 2012 02:21 PM

Dear AndrewT,

thank you for your response - but I am not responsible for any forum problems ...
:confused:

If you have any comment on the project - try again to post your ideas.
:)

Regards,
Toni

geraldfryjr 30th October 2012 02:22 PM

I like this method of design and is the way I have been planing driving my chipamp design for a BTL configuration.
Thanks for posting the THD graphs.

Cheers!!!

jer :)

astx 30th October 2012 02:52 PM

Quote:

Originally Posted by AndrewT (Post 3220999)
How about adding a note that the decoupling caps Cs are located on the amp PCBs and not as shown on the PSU schematic.

How does output offset vary with time from start up and/or with temperature?

Can you include details of the MCU operational and how we can duplicate that functionality?

Why does the FFT show both 50Hz and 50Hz and the harmonics of both?

And congrats on the super drawings.


Many questions in one post ...

1) The "PSU" that you mean are the bypass capacitors already located on the amplifier pcb. As we have here 2 types of GND (power GND and analog GND) I have decided to draw this an the amp circuit.

2) I have built 4 amplifiers and the output DC offset varies from 1mV to 35 mV. As the amp warms up the DC offset is getting lower. The DC offset depends mainly on the LM4562 input stage. If one would match/check the used input opamps, there would be nearly no DC offset as the two LM3886 are galvanically coupled to the input/inverter stage.

3) Maybe someday you will find the firmware and C source-code using SDCC compiler to self edit the firmware. As the "mains inrush controller" is not directly needed for this project, I will open a new thread if there is enough interest on it.
What is controlled by the MCU/inrush controller (which itself is always powered by a small PSU):
  • Controls the 2 mains relays to suppress inrush current. Supports two high power toroids. Timing is configurable. (typically 250ms delay)
  • mute signal during power on/off.
  • power on/off button (on switch or push button with power state saving in eeprom)
  • external power on/off (e.g.: needs additional optocoupler)
  • 3 configurable temperature sensors (e.g.: left/right heatsink; case temperature)
  • DC speaker controll - emergency power off - locked
  • RS232-TTL-Level-Interface for configuration only or for connection to another MCU (e.g.: to support IR remote control, Voltage sensors etc.)
4) The 50Hz and its harmonics are introduced by the measurement setup: PC running ARTA/STEPS and using an ASUS Xonar Essence STX Soundcard. During measurements a Hameg HM1507 OSC was also connected. The amp itself is totally silent with shorted inputs.

Thank you,

Toni

astx 30th October 2012 03:09 PM

Quote:

Originally Posted by AndrewT (Post 3220999)

Clever use of the sawn in half heatsink to fit all 4 amplifiers inside your chassis and still give adequate cooling. Nice.

I have a similar sink but it's only 50mm tall. If instead of having 12 @ 50mm I had 6 @ 100mm high I would never have any cooling problems. What height is your extrusion?

Dear AndrewT,

sorry I have overseen your last question:
The heat sink model: KS216-100E (0.4 K/W) before "saw in action". Size: 216x83x100mm.
An LR24 stateful variable active crossover divides the signal before amp input into bass and mid/treble (crossover point 400Hz). So the heat sinks are big enough as only 2 amplifiers are providing high power.

Regards,
Toni

astx 30th October 2012 04:02 PM

1 Attachment(s)
Quote:

Originally Posted by geraldfryjr (Post 3221005)
I like this method of design and is the way I have been planing driving my chipamp design for a BTL configuration.
Thanks for posting the THD graphs.

Cheers!!!

jer :)

Dear jer,

you mean you already have a similar design ...

Regards, Toni


Attachment 309176

astx 30th October 2012 05:05 PM

Quote:

Originally Posted by AndrewT (Post 3220999)
Why does the FFT show both 50Hz and 60Hz and the harmonics of both?

Dear AndrewT,

about the 50 Hz: our mains is running 50Hz. I thought about the 60Hz artefacts and the only source with 60Hz:
The connected LCD monitor get it's video signal with 60Hz refresh ... could it be the video card generating a sharp 60 Hz pulse?

Regards, Toni


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