Soekris' DAC implementations

[Curious Fitz]

The soekris dam1021 is native voltage out, with a output impedance of 640 ohm from the raw output and 10 ohm from the balanced buffered output. No I-V converter is needed.

Aha! So, out of interest/curiosity (thus the name) - if you were to add an output transformer to the raw output, would a 640 Ohm to 640 Ohm transformer be a good choice...?

 

[soekris]

Aha! So, out of interest/curiosity (thus the name) - if you were to add an output transformer to the raw output, would a 640 Ohm to 640 Ohm transformer be a good choice...?

It's probably much easier to find 600 ohm types And I don't think the difference is enough to matter.... Be aware as even as transformers are specified for 600 ohm use, you get lower distortion at low frequencies when driving by lower source impedance....

Not that I used to be fond of transformers, but research for another project have enlightened me a little....

 

[spikestabber]

It's probably much easier to find 600 ohm types And I don't think the difference is enough to matter.... Be aware as even as transformers are specified for 600 ohm use, you get lower distortion at low frequencies when driving by lower source impedance....

Not that I used to be fond of transformers, but research for another project have enlightened me a little....

You must be very experienced with them given all the ethernet implementations.

 

[Curious Fitz]

It's probably much easier to find 600 ohm types And I don't think the difference is enough to matter.... Be aware as even as transformers are specified for 600 ohm use, you get lower distortion at low frequencies when driving by lower source impedance....

Not that I used to be fond of transformers, but research for another project have enlightened me a little....

Thanks soekris

Yes - 600:600 would be easier to find!

Please could you explain

Be aware as even as transformers are specified for 600 ohm use, you get lower distortion at low frequencies when driving by lower source impedance....

in a bit more detail in relation to the DAM? I'm a bit of a newbie!

I have heard a lot of people mention utilising an output transformer between the DAC out and power / integrated amp can have a lovely effect on the sound...

I don't have the knowledge or experience myself, but, was looking into whether I should pursue this train of thought with the DAM board.

If so: what recommendations of transformers would you give?

Thanks soekris

also: any recommendations on getting the 3.3V necessary for the i2s input please?

 

[soekris]

You must be very experienced with them given all the ethernet implementations.

I have quite some experince with ethernet transformers, actually I started out with ARCnet transformers, if anybody rememeber ARCnet.... But I meant to say: Not that I used to be fond of Audio Transformers ... but you probably knew....

Thanks soekris

Yes - 600:600 would be easier to find!

Please could you explain in a bit more detail in relation to the DAM? I'm a bit of a newbie!

I have heard a lot of people mention utilising an output transformer between the DAC out and power / integrated amp can have a lovely effect on the sound...

I don't have the knowledge or experience myself, but, was looking into whether I should pursue this train of thought with the DAM board.

If so: what recommendations of transformers would you give?

Thanks soekris

also: any recommendations on getting the 3.3V necessary for the i2s input please?

It's something about basic core behavior at lower frequencies, don't know the specifics as I have never used audio transformers.... But when you look at t.ex. a Jensen Transformers datasheet you would notice that low frequency THD increases with higher Rs, higher level and smaller cores....

So my recommendation would be a premium 600:600 audio transformer, like Jensen or Lundahl, with the largest core you're willing to pay for....

Best source 3.3V for I2S input would be the I2S source power.

 

[RollE2k]

Lundahl LL1690 is probably about as good as it gets for phase splitter in a 2:1+1 setup.
LL1544A would probably also work, but i have never tried that transformer...it's almost half the price.

 

[quantran]

If we use a transformer here, it only acts as a low pass filter and there is no other benefit. I think this DAC doesn't need more filtering.

 

[Curious Fitz]

It's something about basic core behavior at lower frequencies, don't know the specifics as I have never used audio transformers.... But when you look at t.ex. a Jensen Transformers datasheet you would notice that low frequency THD increases with higher Rs, higher level and smaller cores....

So my recommendation would be a premium 600:600 audio transformer, like Jensen or Lundahl, with the largest core you're willing to pay for...

Thanks soekris

Best source 3.3V for I2S input would be the I2S source power.

I'm thinking of using this board to provide the I2S input to the DAM board, should I attempt to find a 3.3V output from it/do you have any advice on using a board such as this please?

http://www.diyaudio.com/forums/digital-line-level/267948-soekris-s-dac-implementations-100.html#post4984687

 

[RollE2k]

If we use a transformer here, it only acts as a low pass filter and there is no other benefit. I think this DAC doesn't need more filtering.

What about phase splitter, and isolation?
There is pretty much always positive (and negative) aspects of everything - so it's a matter of what you perfer.
In this case i would myself rather buy a secondary board if balanced is the primary thing your are looking for.

 

[Julf]

What about phase splitter, and isolation?
There is pretty much always positive (and negative) aspects of everything - so it's a matter of what you perfer.
In this case i would myself rather buy a secondary board if balanced is the primary thing your are looking for.

Isolation is occasionally a good idea, but if you want to use a balanced connection, it is the input end that is important, not the output (driving a balanced, differential connection and input from an unbalanced output still gives most of the benefits of a fully balanced setup).

 

[RollE2k]

Isolation is occasionally a good idea, but if you want to use a balanced connection, it is the input end that is important, not the output (driving a balanced, differential connection and input from an unbalanced output still gives most of the benefits of a fully balanced setup).

If the following stage is a native balanced, it is of benefit...
But why would a transformer phase splitter be worse than op-amp phase splitter that is there today? I would say it have more benefits, except the THD measurements....

 

[Julf]

But why would a transformer phase splitter be worse than op-amp phase splitter that is there today? I would say it have more benefits, except the THD measurements....

THD, IM, and limited frequency range are the main downsides. Galvanic isolation is the only real upside. Do you need that?

 

[quantran]

If you use a 600:600 transformer why not connect dirrectly to the raw Vout? Isolation is only useful for those who need such feature (pro gears use it a lot but not really needed for home use). Most preamps with a balanced input also have single end inputs.

 

[Julf]

Most preamps with a balanced input also have single end inputs.

And a balanced, differential input can of course perfectly well be driven by an unbalanced signal - the input doesn't care.

 

[Curious Fitz]

If you use a 600:600 transformer why not connect dirrectly to the raw Vout?

Yes - the raw output was my original suggestion to keep things 'pure' (but I'm a mere newbie!) - however, you mentioned:

If we use a transformer here, it only acts as a low pass filter and there is no other benefit. I think this DAC doesn't need more filtering.

?

In your opinion, if adding to the raw output, what sort (if any) of transformer would you suggest?

 

[batteryman]

Aha! So, out of interest/curiosity (thus the name) - if you were to add an output transformer to the raw output, would a 640 Ohm to 640 Ohm transformer be a good choice...?

If you want to use a transformer then use a Bifilar wound balanced type connected to the balanced outputs with no ground connection.

I use a Sowter 9545 for the simple reason that bifilar winding means the common mode rejection is high so any unwanted common mode noise on the output of a dac cancels. It is this, just as much as noisy ground isolation that is the reason for using a transformer in my opinion.

Sowter Type 9545 DAC INTERFACE TRANSFORMER

 

[Curious Fitz]

If you want to use a transformer then use a Bifilar wound balanced type connected to the balanced outputs with no ground connection.

I use a Sowter 9545 for the simple reason that bifilar winding means the common mode rejection is high so any unwanted common mode noise on the output of a dac cancels. It is this, just as much as noisy ground isolation that is the reason for using a transformer in my opinion.

Sowter Type 9545 DAC INTERFACE TRANSFORMER

Very interesting batteryman

What about from the raw output please? If I wanted to use that output, what would your suggestions be please?

 

[batteryman]

Very interesting batteryman

What about from the raw output please? If I wanted to use that output, what would your suggestions be please?

The transformer may work on the raw outputs but 640R output impedance will affect the frequency response because the 9545 is designed for low impedance dac outputs.

 

[RollE2k]

THD, IM, and limited frequency range are the main downsides. Galvanic isolation is the only real upside. Do you need that?

Limited fequency rangers is really not a problem with a good transformer like LL1690, check datasheet.
Also if THD is what matters most, then why are we even looking at a R-2R dac? At least that is the way i have feel about audio all the time..

I have a pre-amp with both input and output transformer (k&k audio style linestage) sounds wonderful, and i have not yet found a reason to replace it.

There is often alot to get from galvaniserad isolation when it comes to current flows.

What i'm trying to say is that people shouldnt be so fast to dismiss transformers without even trying then.

 

[quantran]

Yes - the raw output was my original suggestion to keep things 'pure' (but I'm a mere newbie!) - however, you mentioned:

?

In your opinion, if adding to the raw output, what sort (if any) of transformer would you suggest?

No, I do not suggest any transformer. I am not sure why you read that I suggest to use transformers. I think it's best to add a buffer, solid state or tube depending on your preference.