Hi,

I intend to begin with a simple setup by using 5V DC supply and a step up tranny to directly connect B-II to Amp. I have a few queries,

1. Would 5VDC 400mA supply be sufficient?

2. Can I connection OUT_- and OUT_+ together to the transformer SE Input pin?
2. What is the impedence out from B-II? The tranny input impedence specified to be between 2~6 ohm. If its higher, any suggestion to better match it?
3. Would 28dB step up provide acceptable gain level?

Thanks for the advise

Edited by user Sunday, January 30, 2011 7:12:30 PM(UTC)  | Reason: Not specified

That is what I did when I first got the BII: http://hifiduino.files.w...com/2010/03/p1020573.jpg
The input plug, I salvaged from another board and the components are just used to filter noise. I adjusted it to 5.4V but 5V should work fine. Just make sure the transformer is regulated and measure it with a resistor to simulate ~400mA of load. Do not exceed 5.5V.

DO NOT connect +Out and -Out. Use +Out and GND.

Just to be clear. As long as the primary is not connected to GND it is perfectly ok to use +OUT and -OUT, one into each lead of the primary. When done this way there will be no differential DC, but there will be ~1.65V common mode DC.

You would not want to use just +OUT and GND unless you use a capacitor to block the DC.

You also would not connect +OUT and -OUT to the same lead (short them).

Edited by user Tuesday, February 1, 2011 2:07:11 PM(UTC)  | Reason: Not specified

You are going to have to track down the source of the hum. Its either a ground loop or EMI. It not really realted to the DAC itself.

Russ,

Could you comment the grounding between primary and secondary and affect on galvanic isolation and EMI/RFI.

It seems that if the grounds were not tied together, EMI/RFI would be 'amplified' by trannies. On the other hand, when grounds are tied together, no galvanic isolation thus ground loop would contaminate the signal.

Thanks for your insight into the tradeoffs and tips to overcome this.

I.C :O

May I know the best practices for grounding the DAC, and should the power ground be lifted? Thanks

To get yourself a IVY or Legato I/V-stage in place of the transformer seems a fairly viable option.....
It will not make your Sowter work in the application, but it may make you stop trying :)

Hi Russ,
I’m Stefano Mainardi from Italy and this is my first post! I bought a Buffalo II DAC with Placid and Placid BP power supplies and a Legato I/V stage, just to start :-).
My goal is to build a transformer I/V stage and I think your Buffalo II is the perfect base for that kind of experiments: first of all, to use a transformer connected between OUT+ and OUT- I need to be
sure to get the same offset voltage/current at both terminals. In this way there will be no DC current flowing into the primary winding…Did you ever measured the differences between the offsets
( (Offset_out+) – (offset_out-) )? With no or very small DC offset I can use a “standard” interstage transformer (usually with no gapped core) , otherwise I’ll need to think about a different kind of
transformer to avoid the “evil” effects of saturation. Or I can consider a transformer designed for push pull application with the common tap connected to GND. What do you think about these solutions, even if you say you don't want to use transformers? :-) And what about the primary impedance/reflected impedance? I’m thinking of connecting the secondary windings (balanced) directly to the preamp (4K input impedance) with a transformer’s turn ratio of 1. You say it’s better to keep the impedance seen by the DAC output reasonably low for THD+N issues so, if it’s possible, it would be better to buy a transformer with low impedance windings. Am I right? I’m a little confused about this issue, it’s the first time I work with this kind of connections/devices. Last thing: why don't use the primary winding resistance as I/V resistor? In many cases I saw a low value resistor in parallel to the primary windings...
Thanks in advance.
Regards
Stefano

PS: sorry for my english!

Hi NicMac,
I'm going to compare the two solutions, so I'll keep you informed about my tests. But I need to wait for al least 2 months because Buffalo II, Placid and Legato are on their way to my home. :-) I too have no experience with transformer, but I think it should be the best way to do the I/V conversion, no active components, no selected and matched components, no power supply issues. Sure enough, the transformer must be designed and made very well.
Stefano