AK4396: best solution for output stage

[Bill Fuss]

Yes, it's pretty simple. Just add the recommended load resistor, and dont connect anything to signal ground. It is a differential circuit and does not require a ground reference to work properly. It can also be used with XLRs in a balanced system, it is an inherently balanced circuit.

 

[Puffin]

Would I be right in thinking that I would connect to

Pins 19,20, 23, 24

http://www.datasheetcatalog.org/datasheet/Cirrus_Logic/mXxtsys.pdf

 

[Bill Fuss]

Yes, that's correct.

 

[Puffin]

Thanks.

 

[Puffin]

I have modified a Playstation 1. It uses the AK4309 dac chip. The modifications say that you connect to pins 15 & 16 for L & R output (which I have done) If I was to use transformers, would I connect to pins 11 & 12 as well?

AK4309 pdf, AK4309 description, AK4309 datasheets, AK4309 view ::: ALLDATASHEET :::

 

[Bill Fuss]

I looked at the datasheet, 15 and 16 don't have anything to do with analog output and 16 is a dead leg???

This chip has a large DC offset voltage and a high impedence load requirement so you would need to use coupling caps anyway, kinda sours the intended purpose but still doable. A 10k trafo would be needed with a cap on the leads to 11 and 12 and the other legs to analog ground. You would end up with a little over 1VRMS at the output.

 

[Bill Fuss]

OOPS, 15 is analog ground.

 

[Puffin]

I looked at the datasheet, 15 and 16 don't have anything to do with analog output and 16 is a dead leg???

This chip has a large DC offset voltage and a high impedence load requirement so you would need to use coupling caps anyway, kinda sours the intended purpose but still doable. A 10k trafo would be needed with a cap on the leads to 11 and 12 and the other legs to analog ground. You would end up with a little over 1VRMS at the output.

Yea, i thought it was a bit wierd, but it works?

I note what you say about coupling caps.

 

[audiodesign]

my solutions

Hi-Resolution System 192KHz 24bit with EMU 0404 USB

 

[johnm]

When using an output transformer with the AK4396, does one need to add any resistors/capacitors at all? I have read that the AK chip is somewhat rare in that it produces no 'nasties' so does not need any kind of filter.

How about load resistors on the transformers primary for this chip? This thread seems to indicate that one doesn't need these either? (6th post down):

Audio Asylum Thread Printer

I'll be using a 'Digitec' transformer which is 1:1. No data on ths unfortunately, but more info. here (post 278 onwards) :

http://www.diyaudio.com/forums/digital-line-level/137976-experience-diy-dac-28.html

Cheers,

- John

 

[johnm]

Anyone?

 

[SoNic_real_one]

http://www.asahi-kasei.co.jp/akm/en/product/ak4396/ak4396_f00e.pdf
Page 31, 32, 33 shows filters and on page 34, 35, 36 it is shown how to calculate them. So, yes it needs filters, no matter what the urban legends are saying.

 

[johnm]

Thanks for that info Unfortunately it doesn't mention using output transformers, and I haven't a clue how to work this out alas. Bit of a layman.

There just doesn't seem to be any hard/fast guidelines for people using output transformers with these differential output DACs; everyone uses different configurations it seems.

I guess I'll start with using no load resistors - not necessary for the AK4396 according to K&K Audio/Lundahl: Audio Asylum Thread Printer

For the output filter I'll use the Jensen values as a starting point I guess: http://www.jensen-transformers.com/as/as093.pdf

- John

 

[sendler]

Try it

Thanks for that info Unfortunately it doesn't mention using output transformers, and I haven't a clue how to work this out alas. Bit of a layman.

There just doesn't seem to be any hard/fast guidelines for people using output transformers with these differential output DACs; everyone uses different configurations it seems.

I guess I'll start with using no load resistors - not necessary for the AK4396 according to K&K Audio/Lundahl: Audio Asylum Thread Printer

For the output filter I'll use the Jensen values as a starting point I guess: http://www.jensen-transformers.com/as/as093.pdf

- John

Try it with no filter as it will probably sound much better. I run no filter with just blocking caps and it sounds much better that way than when I was using a passive filter with the caps. The transformers will roll off the ultrasonics much more than the caps already. Some people use 3k swamping resistors across the balanced legs for additional load and this can be done as there is no dc between the legs but there us 2.5vdc between each leg and ground

 

[Bill Fuss]

I guess I'm starting an argument but, do you really think you can hear a single pole filter with an F3 of 150khz.

My Jensen trafos don't start rolling off till well past 220khz so the possibility of damage is very real, depending on the bandwidth of your amps.

If you are confident the 4396 chip is comfortable with a 20-50 ohm DC load on the output pins then go for it without the series Rs.

That's just my opinion, and I may be wrong, as I often am.

Bill

 

[Bill Fuss]

Another very important point, there is a vast difference between input trafos and output trafos. You will see in the LL1690 specs that it is an input trafo and absolutely requires a loading scheme. A trafo designed for output duty has no such requirements, and this is a fact, not conjecture.

 

[johnm]

Thanks for the replies folks. Alot to chew on!

The problem is I don't know anything about the output transformers I'll be using; they're marked Digitec SA and came from the (semi)group buy from this thread from post 278 onwards:

http://www.diyaudio.com/forums/digital-line-level/137976-experience-diy-dac-28.html

I used these transformers with the Gigaworks CS4398 DAC without any components at all and they sounded great. No problems, at least that I could hear...

I know the AK4396 is a different chip altogether, so just want to make sure I don't damage it. I've ordered the components to construct the Jensen filter values, which I hope will be applicable here.

- John

 

[Spartacus]

When using an output transformer with the AK4396, does one need to add any resistors/capacitors at all? I have read that the AK chip is somewhat rare in that it produces no 'nasties' so does not need any kind of filter.

Hello John, small series resistors are needed to isolate the DAC from capacitance, which can cause instability. However there is a balancing act here, as transformers like to be driven from as low an impedance as possible. Try 25R resistors in series on the primary side. Loading the secondary ..... that depends on the type of transformer, as Bill said.

 

[Bill Fuss]

John, I believe those were designed as output trafos. As I recall they have 20 ohm winding resistance, input trafos are generally much higher and almost always have faraday shields. Output trafos don't exhibit resonance peaks so if you have access to a scope and signal generator you could easily test them.

 

[johnm]

Thanks Bill/Spartacus - unfortunately I only possess the most basic of DIY equipment, namely a soldering iron and multi-meter, so I guess I'll have to 'suck it and see' as far as transformer loading/filter is concerned.

The seller of the Digitecs (Franz Gysi) reported good results using 10R resistors in series on the primaries, with 0.33uF between the primary inputs. I guess that's a good place to start?

To be on the safe side I'll use filtering on the secondary side, and for want of a better starting point will use the Jensen combination of 976R - I have 1K - and 1n2 across secondaries. When I can afford it I'll go for a pair of Lundahls or similar where the specs are known.