Salas hotrodded blue DCB1 build

[Salas]

If all is well you burn a mere 1.5W on each output MOSFET now. Just 0.84W on each CCS MOSFET. That metal base is big. If those red pads are Kerafol (ask Tea) then the case to metal thermal resistance is next to nothing. Those parts are 0.83C/W junction to case. Your test build is open also. They possibly glide merrily near room temp.

[AndrewT]

de-rate heatsink for Delta T.
Expect for a 1W into 20C/W at least a temp rise of 30Cdegrees, maybe even as high as 35C.
Ta = 20degC
Ts ~ 50 to 55degC
Tc ~ 51 to 56degC
Tj ~ 52 to 57degC

Ts & Tc @ >50degC is too hot to hold.

Note that for those temperatures, the devices should live for ever.

I design for the two worst case conditions
1.) Survivability if the output is shorted when mains voltage is maximum.
2.) Survivability if zero output current.

[ma_coule]

Originally Posted by ma_coule

Hi Tea-Bag,

any boards and kits left?

Regards,

[dimkasta]

The arduino controller is almost ready.

I used an encoder with button for the manual rotary control allowing 20 steps from 0 to 100%, and an apple remote for IR allowing 100 fast steps. The arduino then controls 2 100K DS1804 digital pots. A led is also dimmed to give a visual indication of the current volume level.
The only things remaining are to replace the second pot (used a 10K accidentally) and then properly implement the muting and test it more.

The digital pot will then control a lightspeed clone. The balance pot will be replaced by a trimmer to allow for more accurate centering since I always use it centered while listening anyway.

I plan on using a separate small toroid for the arduino, and power lightspeed with a single 7805 (no filter caps) from the Vout on the DCB1.

Any thoughts?

[Salas]

Only that it will be an impressive automated DCB1 and that controlling LDRs can be a PITA. Will it carry a backlit color LCD screen?

[dimkasta]

Hehe yeah at first I was thinking to build something like the one in the Buffalo thread in avclub.
But since I won' t need all the DAC stuff I decided that there is no point. The LCD will be an overkill. Just 3 leds for power, 2 sources and volume indication.

I know what you mean about the LDRs... I initially was planning to use separate pot quadruplets for each LDR (100K+1K) to perfectly control the LDR values per step, but it was really a chore... Not to mention the 16 pots (48 digital pins would be required....)

[Salas]

Now the tease part is that we had a DCB1 guy who was swearing by using a dedicated shunt reg for the LSPD part and the sound quality he could achieve VS powering it from a chip reg.

[dimkasta]

Damn... I hate you (not)... I have some SSLV BiBs laying around but no low voltage BJT parts... And I will need an extra toroid for it... Unless I pull AC from the Vin of the DCB1?

[Salas]

Mosfet will go 5V also. You can steal some if you will run it conservatively and your Tx will allow with hot rod and all. Hey don't shoot the messenger, if it even was Malka07 a couple of years ago then I had a total recall flash (not as much as Colin Farrell, but there).

[dimkasta]

I bought a DMM with temp measuring. The cold metal plate was 25,5C before turning it on. Same with the mosfets.
After ~1 hour the fets were at about 31C.

Now I have just boosted it a bit attaching 2 additional 12R @5W resistors on each rail bringing it to ~3,75R.

Here are the measurements

Vout: 9,95V and -9,99V
CSS: 1,412V and 1,391V
Offset: -1,3mV and -0,9mV

and about 20 minutes later

Vout: 9,9V and -9,96V
CSS: 1,411V and 1,392V
Offset: -1,3mV and -1mV

This translates to ~370mA

Still a bit lowish, but it seems to work nicely.
First impression was that the change was very noticeable. The music is more dynamic. The entire spectrum is much more solid and well defined. Highs are very clear, mids and mid highs have more bite and bass is louder and better controlled. And voices are starting to .... holly cr@p

I am getting more and more impressed by it every day