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Output transformers for DACs

Hi Kevin. I suppose, should be like on drawing

For chromenuts.jpg
 
Hi Ivan

Thank you for your response.

I think I understand your diagram for a single D3 board.

Could you show me how the wiring would work with the two D3 boards I have set up as dual mono?

I have attached a picture. They are stacked and one board is used to process either the left or right channel.

Also, should any of the jumpers be removed or changed to use the transformers with my dual mono boards?

I don’t know what value resistors are installed between R1a and R1b or R2a and R2b yet.

Regards
Kevin
 

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Kevin, I forgot that tubo's version was with two primary coils. That is why the previous drawing is wrong. That is why I was a bit confused regarding your wish to try DualMono setup. I think you mean the differential connection when talking about using of 2 D3 boards, right?
So, to correct the previous drawing, for SE mode (single TDA1541A) it is needed to connect this way:

For chromenuts_corr.jpg

For dual mono (differential connection) you will need to follow this drawing:

For chromenuts_corr_bal.jpg

Regarding R1a, R1b, R2a, R2b - there is no need to use them as you have already the installed R1 and R2 resistors 11kOhm. R1 and R2 are the i/v resistors that replaced your R35/R36 resistors on D3 boards. If you want to try i/v resistors on R35/R36 places on the D3 boards, then the exact same signal can be achieved using:
11k/484=~22 Ohm

ps this PCB board relates to this circuit and it is a kind of versatile board for my transformers:
Output transformers for DACs

pps. You should understand that the output impedance after such transformers will be determined by the transformation ratio and in your case will be equal to the value of the resistor R1/R2 - it is 11kOhm.
 
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Hi Bisesik, I have read all the 3d.
I am interested in purchasing your transformers.
I would like to use them in a Behringer DEQ2496 as the input to the A / D conversion (AKM 5393VS) and in a Cambridge DacMagic (azur) DAC as an output to the Wolfson WM8740a DAC.

In the DEQ2496 I enter "XLR Analogic Input" with XLR-Rca adapters (source signal unbalanced).
In the DacMagic I come out of the XLR outputs with homemade XLR-Rca adapter cables because I enter in two different amps.
On the XLR pin2 + pin1 go to one amp (50K input) + pair of speakers, pin3 + pin1 go to the other amp (47K input) + pair of speakers (reverse polarity which I then straighten by turning the speaker wires).
Both amps have unbalanced inputs.
I hope I have explained.
My English is not good.
Do you have any solution for me?

Many thanks 🙂
 
On the XLR pin2 + pin1 go to one amp (50K input) + pair of speakers, pin3 + pin1 go to the other amp (47K input) + pair of speakers (reverse polarity which I then straighten by turning the speaker wires).
On the edge of madness :hypno1:

But it is your way, OK 🙄
Nothing extraordinary actually except of unsimmetrical load on positive and negative poles of your DAC XLR output.

Anyway, I can make transformers for AK5393 or WM8740. Actually it should be the same pairs 10k:10k transformers. Nothing extraordinary again.
 
Thanks for the reply Ivan.
Do you think the unbalanced 47k / 50k load could be a problem?
Basically, would then be 4 equal 10k / 10k transformers the most suitable?
As for the DacMagic which also has an Rca output, would there be a way to keep it always "under" the transformers?
What is the current price of transformers?
Are there any pcbs to facilitate assembly / layout?
Thanks!
 
Do you think the unbalanced 47k / 50k load could be a problem?
You have 47k load between + and - (let's imagine virtual 23.5k to GND from + and 23.5k to GND from -). And there is another load from - to GND of 50k. So +pole is loaded onto 23.5k while - pole is loaded to 23.5k||50k=16k. 23.5k vs 16k. I can not comment, as the sonical expertise at your place is more representative than theoretical points. If OK, then OK 🙂

Basically, would then be 4 equal 10k / 10k transformers the most suitable?
Yes, I think so.

As for the DacMagic which also has an Rca output, would there be a way to keep it always "under" the transformers?
Transformers should be implemented between DAC chip and RCAs/XLRs. If you want to use both RCA and XLRs outputs, then extra DPDT switch will be needed (to choose between XLR and RCA).

What is the current price of transformers?

$170 for pair + shipment + "1/2PPfee". FedEx is most safe and fast, but expensive, ~$80 I can send via national post, but the delivery time is unexpected (safe in terms of money) and can be unpredictable in the scale of international delivery, 2 months and more - is often...

Are there any pcbs to facilitate assembly / layout?
Thanks!

Here is the circuits, CAD, gerbers of versatile PCB for my transformers.

Output transformers for DACs
 
Hi Ivan

Thank you VERY much for your illustration and help.

I hope to have the transformers wired up to test soon.

I just wanted to say that when I measure the impedance at the output of your transformer PCB I get about 150 Ohms with the transformers mounted in circuit.

When the transformers are removed from the board I can measure R1 and R2 and the output as 11k Ohms.

Obviously, the only way the board will ever be operated is with the transformers mounted.

This confuses me about the 11k load you say is created on the output of the transformers?...or the output of the transformer PCB?

I am planning to try making my own wire wound iv resistors to place before the transformers.

I will remove R1 and R2 when I put these iv resistors in place on the output of the D3 PCB.

I’m wondering what the load will be at the output of the transfomer PCB in this scenario.

Regards
Kevin
 
Hi Kevin,
as we talking about music, then it relates to the AC, not DC. The inductive impedance of the coils of transformers is huge compared to DC-resistance. In terms of DAC - no matter where to put the i/v resistor. Before the transformer or after it except of the value. 11k on the secondary means that it will be reflected to the primary side as 11k/484 =23 Ohm. So you can use 23 Ohm across the primary coil or 11k across the secondary coil to get the same amplitude. The output impedance will be the same for both situations and equal to 11k.
 
You have 47k load between + and - (let's imagine virtual 23.5k to GND from + and 23.5k to GND from -). And there is another load from - to GND of 50k. So +pole is loaded onto 23.5k while - pole is loaded to 23.5k||50k=16k. 23.5k vs 16k. I can not comment, as the sonical expertise at your place is more representative than theoretical points. If OK, then OK 🙂

Yes, I think so.

Transformers should be implemented between DAC chip and RCAs/XLRs. If you want to use both RCA and XLRs outputs, then extra DPDT switch will be needed (to choose between XLR and RCA).

$170 for pair + shipment + "1/2PPfee". FedEx is most safe and fast, but expensive, ~$80 I can send via national post, but the delivery time is unexpected (safe in terms of money) and can be unpredictable in the scale of international delivery, 2 months and more - is often...

Here is the circuits, CAD, gerbers of versatile PCB for my transformers.

Output transformers for DACs

Thanks for the informations!
I had a question. Because some have 600ohm transformers in the same design: 600ohm ... and instead you recommend 10k: 10k. Excuse the beginner question! Thanks
 
Thanks for the informations!
I had a question. Because some have 600ohm transformers in the same design: 600ohm ... and instead you recommend 10k: 10k. Excuse the beginner question! Thanks

According to information from table ELECTRICAL CHARACTERISTICS from WM8740 datasheet, the 600 Ohm is the minimum possible load impedance but the output voltage level is presented there for 10k load. AK5393 according to its datasheet have the input impedance of 4kOhm, again it is not even close the 600 Ohm.
If you want to leave all the OPs (buffers) after 8740 and before 5393 then 600:600 is OK (no need to open devices, RCA-RCA or XLR-XLR connections then). And no matter in this case "who" is the DAC and ADC chips, as you dealing with the interstage between the OPs - one only pair of 600:600 transformers is needed then as a separate interstage device.
 
It is not exact so actually. He have transformers with another turns ratio (much higher) and I hope he will try soon another version (much less turns ratio) which I have sent to him 5 months ago. Australian post are unimaginable guys :whazzat:

Finally! They arrived! Its a Christmas miracle!

I've had some time to have a play around with these lower ratio (0.5+0.5:4 - is this correct Ivan? Its been so long since I ordered them.) transformers that have just arrived and they sound a little clearer than the high ratio ones (1+1:37+37).

The THD measurements I made had the same result for both versions (0.5+0.5:4 and 1+1:37+37) running in a balanced config using a total of 4 DACs.

A 20Hz sine wave played through the DAC gave these results with my less than perfect (pretty crap) test setup-

4Vpp :
- 2nd @-58dBr
- 3rd @ -32dBr
- 4th @ -63dBr
- 5th @ -40dBr
- 7th @ -47dBr
- 9th @ -55dBr

2Vpp :
- 2nd @ -59dBr
- 3rd @ -32dBr
- 4th @ -65dBr
- 5th @ -53dBr
- 7th @ -55dBr
- 9th @ -55dBr

Overall I like the sound at about 2Vpp, so this leaves me needing slightly more gain for some recordings - I think its time to make a BA-3 preamp or something similar.

The dominant 3rd harmonic at a level of 2Vpp is not overly noticeable - seems to give an ever so slight edge to the sound but still a very enjoyable, clean and clear listening experience.

The odd harmonics at a level of 4Vpp was a little too much for my likings.

When I set the level to about 1Vpp the THD dropped below 1% (if I calculated properly) but at this level I found the SNR started to suffer.

I've also been testing single ended mode using only 1 DAC (instead of 4 running is differential mode) and the sound is very nice. I think the 2nd harmonic being higher masks the 3rd and gives a little touch of bloom to the music.

I also did listening tests to compare the difference between 2 and 4 DACs running in differential/balanced config - and the sound of 4 DACs sounded slightly more dynamic.
 
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Thank you for your response, Ryan!
That transformers are 0.5+0.5:6.
Your measurements are OK I think. If THD graphs needed here, then let me know, I will try to find them on PC to show...

Couple hours ago I came back from listening of my DAC (1541A) in big horns system. Despite of the big THD difference compared to the modern DACs, TDA1541A is the best device I heard in terms of music emotions delivery and meaning. If you still need the audiophile things (you know all that attributes: depth, scene, dynamics, details, naturallenes, etc) - then all you need is just to switch from music to that attributes - they are absolutely on their highest level, but it is so hard to switch from the music, which is entering you and takes your mind away...
 
Thank you for your response, Ryan!
That transformers are 0.5+0.5:6.
Your measurements are OK I think. If THD graphs needed here, then let me know, I will try to find them on PC to show...
I think my measurements are probably not too accurate as the noise floor is at around -75dBr - so the noise is probably adding to the results quite a bit.

Couple hours ago I came back from listening of my DAC (1541A) in big horns system. Despite of the big THD difference compared to the modern DACs, TDA1541A is the best device I heard in terms of music emotions delivery and meaning. If you still need the audiophile things (you know all that attributes: depth, scene, dynamics, details, naturallenes, etc) - then all you need is just to switch from music to that attributes - they are absolutely on their highest level, but it is so hard to switch from the music, which is entering you and takes your mind away...

Yeah I think the sound of a well sorted TDA1541A is hard to beat, there is something quite unique about the way it involves and draws you in to the music.
 
Hello, just to share my experience with 0.5+0.5 : 22 transformers on a SM5865 DAC Chips. They are really superb , sound is more transparent and 3D than ever before. Tried many kinds of Opamps on my DAC output - none of them can compare to this transparency. Of course i have weak output ( 0,47V) and a driver / buffer is needed to match my amp impedance, but once everything is set right - the potential of this transformer i/v is superb. Bravo!
SM5865 — ImgBB
 
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It seems you should have bought a 1:4 transformer. A buffer is not a solution, because it will give you no gain, and it is not easy to make a high quality stage with low gain and low output impedance.

The beauty of transformers is that you should not need anything else.