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Old 4th March 2012, 08:47 PM   #321
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If you have the parts, give it a try and let us know how it works.

I have recently tried a new Buffalo and transformer setup and can report success. I am using a pair of Jensen 4:1 step down transformers directly from the DAC. It is loaded with 2.7k resistor, which paralleled with my amp input impedance works out to be equal to the 2.4k that is required. I am really pleased with the sound.

I have an Emotiva amp that it is used with that has high gain so I needed to step down the signal. I found the -12dB that these transformers attenuate helpful. At full volume the signal is quite loud but listenable. This works out to about 50W into my speakers.

I am using a volumite for the volume control. Prior to this setup I have used both Legato 3.1 and IVY. I thought these were very good, particularly Legato SE, but there was a little grain at lower volumes, where I listen quite often. The transformer eliminates this and has a nice smooth sound at low volumes. I think this might be attributed to the high common mode noise rejection of the transformers, plus with the attenuation the DAC is outputting more signal. I also tried the transformer as balanced to SE conversion on the output of Legato but found this to be a little thin or lacking bass. Midrange was a little too pronounced.

I am quite happy with this combo. Although I still plan to do some more experimenting...
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Old 5th March 2012, 01:34 AM   #322
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Lowering the gain of the previous two output stages will likely yield similar (or maybe better) results.
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Old 5th March 2012, 11:21 AM   #323
RollE2k is offline RollE2k  Sweden
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Now i have looked things up a bit more, and i will be using transformer, lundahl probably. haven't decided on model yet.. but Russ/Brian have recommended a little bit higher primary impedance right?
Also im thinking that i will either runt just a pure transformer in 2:1 ratio, because i won't need more than approx 1.1v RMS out, and it should be above that with 2:1 ratio.

Now i'm thinking - would it be better running this way that Joe suggested earlier:
Click the image to open in full size.
But lowering the parallel loads to maybe 14-15R?
And as said earlier this should be loaded with my Single ended 16k input on the secondary. Will the second one sound better or worse?
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Old 5th March 2012, 05:26 PM   #324
Gluca is offline Gluca  Italy
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the primary winding should be floating (ie not connected to GND)
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Old 5th March 2012, 05:48 PM   #325
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Quote:
Originally Posted by Gluca View Post
the primary winding should be floating (ie not connected to GND)
It can be, but it actually works just fine to reference it to GND as he did. One could try it both ways and see what they prefer.
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Old 5th March 2012, 07:57 PM   #326
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I've got my dual mono up and running. I'm using the Feastrex 1:1 transformers and my resistors are 10 ohms. I tied the resistors to ground (as in the diagram) and it plays (very) nicely.

Output after the transformer is only 200mv, but I have it running into a tube stage of about 20 db gain (goint to try a 6H30Pi-DR and a 6H6P - doing listening tests now) to get the (approx.) 2v output.

Been playing if for a few days now as I am still breaking in the output caps in the tube output stage (Mundorf 2.2UF Silver/Gold/Oil).

My ears are Very very happy.

.... note to Gianluca.... I have my Eimac project on the shelf.... got just a little bit afraid of working with 1200VDC ;^)

JD
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Old 6th March 2012, 02:46 AM   #327
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Quote:
Originally Posted by RollE2k View Post
Now i'm thinking - would it be better running this way that Joe suggested earlier:
Click the image to open in full size.
But lowering the parallel loads to maybe 14-15R?
And as said earlier this should be loaded with my Single ended 16k input on the secondary. Will the second one sound better or worse?
I can't say whether it will sound better or worse, but there will be trade offs. Transformers for different audio functions are wound differently. Each type is optimized for its function. A 1:10 step up transformer is probably either for mic input or MC step up. They will likely work best with circuits optimized for those applications. I decided I was using the transformer primarily for balanced to single ended conversion and selected one that was optimized for that task.

Don't forget that the two resistors will be in parallel with your reflected impedance through the transformer (16k / 10^2 = 160) which will lower output a little. The DAC will be loaded with 2x22R in parallel with 160R, or about 34R.

Going directly into a 2:1 transformer will be similar output, except the stepdown transformer impedance would be 2^2 x 16k. With this case the DAC would be loaded with 64k. The DAC will be in voltage mode with both cases, but I would think that it might perform better into a higher load. Also in either case, its probably best to follow the recommendations for output load and damping circuit requirements.

You may have better luck finding different options for 1:1 or 2:1 transformers too. I am interested to hear what you decide to do in the end.

Quote:
Originally Posted by Russ White
Lowering the gain of the previous two output stages will likely yield similar (or maybe better) results.
I will give this a try Russ. I keep getting a bigger smile on my face with each change. Which would you recommend adjusting, the I/V stage or the SE conversion? I have a feeling that it might be the I/V stage but a confirmation would be great. I also have a breadboard of matched transistors that I intend to try to build a homemade version of Ventus (sans buffer). Now all I need is more free time...
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Old 6th March 2012, 06:07 PM   #328
Gluca is offline Gluca  Italy
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Quote:
Originally Posted by Jeffrey Davison View Post

.... note to Gianluca.... I have my Eimac project on the shelf.... got just a little bit afraid of working with 1200VDC ;^)

JD
AH! I was (am) tempted to stick a 75TL just after the ESS ... yummi.
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Old 15th March 2012, 01:46 PM   #329
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Using a 1:10 output transformer it mean that a 10Kohm load is converted on primary like a 10000 / (10 * 10) = 100ohm.
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Old 15th March 2012, 01:52 PM   #330
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Using DAC with a single power supply like ESS, Crystal, WM8740, WM8741, AKM4396, PCM1794 should be necessary a RC network to skip DC bias otherwise the output transformer can saturates the core.
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