ebay DAC

Bizzie · Post by **Bizzie** » Thu May 10, 2012 4:21 pm

I've set up the dac with the two xformers that I have and discovered that I had installed one of the electrolytics the wrong way round when it started venting from the top this is in the power supply area, after changing the cap I fired it up again and the power led came on and the coax led came on then the coax led went out and stayed out and the usb led came on.

I've tried it with my squeezebox using the coax and isn't any sound at all but using usb from my macbook it works just fine and sounds pretty good.

I tried reflowing any joint that look the least bit dodgy but now I'm stuck or is there some way I'm supposed to switch it from usb to coax there are not instructions with it but I'd have thought that there should be some sort of switching.

Bizzie · Post by **Bizzie** » Fri May 11, 2012 4:55 pm

Tried emailing the ebay vendor about this and asked if thers some way to get it to switch between the inputs he just said no switch is needed and to check i have the components in the right place which i'd already done so it looks like I'm stuffed with this I don't know where to start looking for the problem.

pre65 · Post by **pre65** » Wed Dec 19, 2012 12:22 am

On the AK4393 like I use the output has 3 terminals, L - R and ground.

My ground wire is connected to the grounds (bodies) of the two output phonos. Should there be any other connection to the output phono grounds ? (ie mains earth ?)

Post by **Nick** » Wed Dec 19, 2012 8:55 am

Its up to you, either take it to earth, or to earth via a small resistor, or leave it floating and ground it in the following amp/preamp.

I would go for the small resistor, I dont like things floating if there is not a good reason (and I can't think of one).

pre65 · Post by **pre65** » Wed Dec 19, 2012 9:24 am

Thanks Nick.

Small resistor ? Something around 50-100R ?

When I measured the DAC on the bench yesterday there seemed to be a small voltage on the ground wire from PCB to output phono.(no interconnect connected)

Should that be ?

pre65 · Post by **pre65** » Wed Dec 19, 2012 9:38 am

And also,

what about the input phono ground ? At the moment it's just connected to the coax shield of the coax wire to the PCB and thence to the PCB itself the other end.

Does that need the same treatment ?

Post by **Nick** » Wed Dec 19, 2012 9:56 am

pre65 wrote:Thanks Nick.

Small resistor ? Something around 50-100R ?

When I measured the DAC on the bench yesterday there seemed to be a small voltage on the ground wire from PCB to output phono.(no interconnect connected)

Should that be ?

Depends on if the board is standard, the dac has a vcc/2 DC offset 2.5v in this case), but the buffer/filter should remove that, but you don't say what size of small you are using in your measurement.

Post by **Nick** » Wed Dec 19, 2012 9:59 am

pre65 wrote:And also,

what about the input phono ground ? At the moment it's just connected to the coax shield of the coax wire to the PCB and thence to the PCB itself the other end.

Does that need the same treatment ?

The two grounds are the same, so if you link the phono out ground to earth, the input will also be there.

Its one of the things I have added to the digital board I plan to play with, some isolation transformers at the front, so the input can float. The USB module will also be in front of electronic isolation, and the analog output will be via a transformer, so it will all be doing it sown thing earth wise

pre65 · Post by **pre65** » Wed Dec 19, 2012 10:18 am

Right, I've done some measurements on the output phonos. Input and output phonos open.

Phono ground to

LH = AC 14mv
DC 2.8mv

RH = AC 14mv
DC 7.9mv

Phono ground to IEC earth

AC = 10.75v
DC = varies (DMM) from 0-3mv no steady reading

DAC is standard apart from LM4562 op amp.

Post by **Nick** » Wed Dec 19, 2012 10:49 am

ok, the output offset is probably just the untrimmed offset from the op amps. the voltage to earth is whatever it feels like being.

Remember, voltage is a potential DIFFERENCE, but for a difference to make any sense, they must have a reference in common. By connecting the two points with your meter, then you have created a 10M or so link, and you are measuring the voltage across that 10M or so. It doesnt mean anything.

pre65 · Post by **pre65** » Wed Dec 19, 2012 10:50 am

Nick wrote:ok, the output offset is probably just the untrimmed offset from the op amps. the voltage to earth is whatever it feels like being.

Remember, voltage is a potential DIFFERENCE, but for a difference to make any sense, they must have a reference in common. By connecting the two points with your meter, then you have created a 10M or so link, and you are measuring the voltage across that 10M or so. It doesnt mean anything.

That's good then. Thanks for the help.

Bizzie · Post by **Bizzie** » Sat Apr 06, 2013 2:42 pm

As mentioned in thread about Andrew's 6.3v indirect heater boards I have built an AK9346 mini DAC with a Broskie unbalancer as an output stage which is now about sorted and sounding really good to my ears, but I want to be able to switch inputs to use this with a CD player and a Squeezebox is it ok to just put a simple spdt switch in the input from the RCA connector or will this degrade the digital signal too much.

simon · Post by **simon** » Sat Apr 06, 2013 8:36 pm

I've built a Broskie cathode follower (Unbalancer without gain stage) to use with my Buffalo II DAC and I'm very impressed too. I'm using 5687s, but it took a big step forward when I shunt regged the HT. Are you using one of Broskie's excellent PCBs, and which valves are you using?

Bizzie · Post by **Bizzie** » Sat Apr 06, 2013 10:45 pm

Not using the PCB they're always out of stock I've wired point to point its not that difficult evenI can do it

I'm using mullard ecc82 and russian 6H6n using the unbalancer rather than just the cathode follower part gives a little bit of gain which seems to be needed with this DAC.

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