Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Transformer coupled outputs for a dac?
New Posts  All Forums:Forum Nav:

Transformer coupled outputs for a dac?

post #1 of 12
Thread Starter 

I've been reading up on this thread alot:

http://www.diyaudio.com/forums/digital-line-level/137976-experience-diy-dac.html

over at DIYaudio for a DIY dac board from ebay, the popular choice seems to be putting transformers and some resistors in the output of the DAC chip, skipping op amps and any other output stage, after trying to sift through the thread(almost 400 pages) I'm not feeling very enlightened, and any post I make in there gets skipped over, so I thought I'd try my luck posting it here...I don't really understand transformers in the signal path so forgive me if this is a stupid question.

 

Are transformer coupled outputs really significantly better than a good output stage with good op amps or discrete op amps?

post #2 of 12

 

Quote:
Originally Posted by iamthecheese View Post

 

Are transformer coupled outputs really significantly better than a good output stage with good op amps or discrete op amps?


Its a great idea. Let me (try) to answer the question then go on...

 

Define "better" tongue_smile.gif Measurements guys are quick to jump on the fact that Active output stages DO measure better than transformers. BUT there is something simple & elegant about the whole thing. 

 

Now there are some cool things going on with transformers that are harder to achieve with active stages. Mainly that transformers are EASY to make ground-loop-proof. They also go back and forth between SE and balanced very effortlessly. After that its really just following the "simpler is better" school of thought, which is not too hard to get behind. 

 

Each school of thought has its advantages. 

 

Unless Im reading the thread over there wrong they are using a Voltage output DAC chip, which has op-amps IN the DAC chip. Sorry to bust the bubble. The good news is that all the associated stuff around the opamps is (are?) matched to tolerances MUCH better than you could do with discrete gear. 

 

A couple pics of my Zhalou 2.5a with Edcor output transformers:

 

e37ee013_DSC_0004.JPG

 

744fd1d1_DSC_0003.JPG

 

I have made some changes since these pics were taken, but nothing major. I got different ratio transformers (originally 10K:600, now 2.4K:600) and added a simple RC filter network in front of the transformers to roll things off around 40Khz.

post #3 of 12

Just finished reading about Sheldon Stokes latest Dac.

http://getinthewoodchipper.com/?p=302

 

 

I am listening to the loaner Neko Audio D100 Mk2  PCM1794A Dac with Jensen transformer output. This is one of the best sounding Dacs I have ever listened to. Period. THE best actually.

http://www.nekoaudio.com/

 

 

Another place to find a schematic of an already implemented circuit using transformers would be www.kandkaudio.com

http://www.kandkaudio.com/schematics.html

 

 

Totally agreed with Nikongod. Throw the measurements out the window. Try something different, and simple, and listen for yourself.

post #4 of 12
Quote:
Originally Posted by nikongod View Post

I got different ratio transformers (originally 10K:600, now 2.4K:600)...

 

Just curious, why are you using step-downs?

 

Also, there's the transformer-as-passive-I/V-converter approach for current output DACs.

 

se

 

 

 

 

post #5 of 12

 

Quote:
Originally Posted by Steve Eddy View Post

Just curious, why are you using step-downs?

 


I dont need as much voltage swing as the DAC chip puts out, so I figured Id trade it for long-cable driving and the ability to run a whole bunch of amps at meets. 

post #6 of 12
Quote:
Originally Posted by nikongod View Post


I dont need as much voltage swing as the DAC chip puts out, so I figured Id trade it for long-cable driving and the ability to run a whole bunch of amps at meets. 

 

Ah, gotcha.

 

Thanks.

 

se

 


 

 

post #7 of 12

^when he's not borrowing signal from other folks....

 

 

tongue_smile.gif

post #8 of 12

You had to bring *THAT* up. :facepalm: 

 

The Zhalou actually works with The Silver Ghost now. 

post #9 of 12

Yes, well, there is only so much equipment one can carry in a suitcase.wink.gif

 

 

I wonder if anyone would like to take a stab at the worthiness of amorphous, or other types of, transformers that could be used in this situation. 

 

Experiences. Even if by friends. 

post #10 of 12
Thread Starter 

So how do different impedance ratios effect the operation of a dac?

More specifically if I'm planning to use it with an EHHA rev A I'll be building this summer as well.

 

Also, are transformers still applicable with current out dacs like the PCM17xx series?

post #11 of 12

I just tested my dac with Sowter transformers and the results were stunning. My system now has amaizing detail in all frequencies and volume levels.  I think the thing everyone is missing in this is that they are so quick to blame opamps or capacitors for problems with digital audio.  I feel now that all my depression with digital audio has nothing to do with opamps or capacitors in the circuits, they are in certain other places in my system.  My take on this whole thing is the way digital audio is filtered is flawed.  When you ad a filter to the output opamp you pass a signal that is filtered (44.1 K and higher) back to the negative input of the opamp so it will cancel any digital signal left in the audio. New dacs have this filtering internally and should have no problems with less filtering on the output. The problem with this filtering is that it attacks any signal that has a verticle beginning or end, and the filter due to the capacitor (no matter how good) effects the filter phasing that is subtracted from the total audio signal wich effects all frequencies. If we use a transformer on the output stage we can get a filter from its bandwidth, and good ones are phase correct to 2 degrees when a capacitor is commonly 90 degrees.  also a transformer can have a banwidth of 10 to 30,000 + or - 0.25 db.  A good tranformer has better specifications than any other piece of geer in your system. 

post #12 of 12

I think transformers can be very useful as a voltage gain stage. I can recommend reading this thread: http://www.diyaudio.com/forums/twisted-pear/164294-buffalo-ii-transformers.html. Some people claim that Sabre loaded on 0.5Ohm silver wire resistor followed by a transformer and tube stage is the best sounding DAC ever! :-)

New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Transformer coupled outputs for a dac?