*** The DIY Audio Thread ***

[adamau5]

lol, how the dreaded m word can be considered a competitor to anyone is beyond me. worst shop ever.

 

[Smeeble]

Yep, thought it was quite funny that it actually blocked it out, they have never had a part I needed lol

 

[Mr. Brightside]

The tools I needed before I could build my BantamDAC arrived today, so I've now finished building it.


I've plugged it into my laptop and Windows picks it up OK and installs the drivers. I can play music in Windows, but get no output from the DAC. I've followed the troubleshooting guide on the BantamDAC website and found that the problem is that there isn't 4.75V coming out of the second regulator. It also gets pretty warm when plugged in.


Anyone got any ideas what's gone wrong?


Cheers,
Mr. Brightside

 

[p4radox]

I'm assuming you've checked its orientation? Make sure its connections have continuity to ground and supply (the USB's 5V line?).

Apart from that, just double check everything else I guess...

 

[Mr. Brightside]

Cheers for the reply.

It is indeed the right way around, and it does have 5V at its input and is grounded. I've doubled checked everything, and have also bridged the two bits of track that have to be bridged according to the assembly guide (was a bug in the PCB artwork).

I checked the output of the second regulator and while it isn't 4.75V, there is a voltage of about 0.1V across it - combined with the fact it gets very warm - would that suggest I've got a short somewhere creating a very large load for the second regulator to drive, hence the low voltage and high heat output?

 

[p4radox]

I'm not familiar with the schematic, but a short could probably cause that kind of behaviour.

Have you checked for continuity to ground from the regulator's output? That'd conclusively prove/eliminate this possibility.

 

[Mr. Brightside]

Have you checked for continuity to ground from the regulator's output? That'd conclusively prove/eliminate this possibility.

Good plan, will do that tomorrow. Cheers.

 

[adamau5]

first thing i would do is reflow anything that looks dodge, and particularly reflow the regulator.

 

[Mr. Brightside]

I already tried reflowing the regulator yesterday and I checked everything else at the time too. I've just checked for continuity to ground from the regulator's output... there is Just trying to work out where it is now. Ideas?

 

[Mr. Brightside]

Just done a bit more checking with the multimeter. Output from the regulator is 0.12V everywhere it should be 4.75 except across L5 (http://www.diyforums.org/BantamDAC/layout/BantamDAClaybottom.jpg) - on the PCM side of L5 it drops to essentially 0V (whereas across the other inductors, there is no drop).

Either the PCM is fried, or there is some invisible short on the board somewhere

 

[Mr. Brightside]

I've just removed L5, disconnecting VCCR from any power supply and now when measuring the voltage across the second regulator I get 2.9V

 

[Mr. Brightside]

When I remove L5, L6, L7 and L8 (http://www.diyforums.org/BantamDAC/schematic/BantamDACsch100.png) I get 4.75V where expected. I then added one inductor at a time back and kept measuing the voltage from the 4.75V regulator - it progressively fell to 0.12V as I added inductors back. I'm going to call it a morning now because I can't think what else to try so, yes, ideas would be much appreciated

 

[adamau5]

ok, the inductors are in series to the dac chip, which suggests a bridge at the chip.

check with a magnifying glass for and small bridges, and maybe consider reflowing the dac chip (horrible job). The regulator is obviously working ok.

 

[Mr. Brightside]

I did check for bridges with a magnifying glass and couldn't see any that would matter (there's a bridge pins 15 and 16 but they both go to ground anyway). I suppose reflowing is the only thing left to try.

What are the chances I fried the DAC chip yesterday by spending too long soldering it to the board and thus heating it up too much? Is that something that can happen?

 

[adamau5]

thery are pretty sturdy, I remember when i first built an alien dac, the poor thing was horribly abused and it worked perfectly.

also, if its recognised by the pc, the most fragile bit survived your soldering... so i guess its probably ok. The question is did it survive being shorted

 

[Dr.EM]

Very nice finish on your amp Adam!

 

[adamau5]

cheers - Schaeffer is expensive, but the finish is worth it.

 

[J1234]

nice build !


also here are some snaps on the starving student proto board i just did

http://homepage.ntlworld.com/y.a.k.a/Starving%20student%20amp%20prototype/sshproto1.jpeg[/IG]
[IMG]http://homepage.ntlworld.com/y.a.k.a/Starving%20student%20amp%20prototype/sshproto2.jpeg[/IG]
[IMG]http://homepage.ntlworld.com/y.a.k.a/Starving%20student%20amp%20prototype/sshproto3.jpeg[/IG]

the pot had a broken leg, i manged to work round it by soldering the remaining legs, sticking the broken in the hole and soldered the broken bit the the other end
[IMG]http://homepage.ntlworld.com/y.a.k.a/Starving%20student%20amp%20prototype/sshproto4%20potfix.jpeg[/IG]


easier than the p2p one i made, now the hard bit which i the case work[/QUOTE]

Ooo, where did you get that from?

 

[Yaka]

headfi forums, tomb did a run of proto boards. he should a the final boards ready in a month or so. they will be listed on beezar.com boards and tubes will sold matched. for some reason its hotter than both my p2p builds other peeps have reported the same.

 

[J1234]

Cool, cheers.

Still got some tubes left over from my P2P build, they're impossible to get hold off now.