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Old 22nd June 2013, 10:56 AM   #11
qusp is offline qusp  Australia
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Quote:
These transformers are hard to argue with and actually have a better frequency response and less phase shift and certainly less distortion than do most high end circuits typically found in use for this purpose.
you may like transformers, thats cool, I have enjoyed them in this role myself from time to time, but the above is simply not true. its trivially easy to better frequency response and linearity of transformers with solid state buffers/line drivers.

the driving factors for TX output are simplicity, isolation and they cope well with glitch noise ie. they dont oscillate or pass on the noise of some of these dacs produce, because they LACK the frequency response/bandwidth. that can be seen as a plus of course; as is their pleasing low order distortion spectra can be.

Last edited by qusp; 22nd June 2013 at 11:05 AM.
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Old 22nd June 2013, 06:44 PM   #12
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Originally Posted by audiorado View Post
Hi...
...I just saw this thread and want to ask for some help.I just buy a pair of this Lundahl transformers and made a passive output for my dac.I just pick up direct analog out from dac legs and feed this to Lundahl transformers in serial 1+1:1+1!!.But I dont know if I need some load resistor on the secondary(output) side of the transformers.The signal will go from dac to my solid state amp that have 20 Kohm input impedance.Plese for help.Im dealing for the first time with transformers on output.
Hi audiorado, The rule I use is if it is 600 Ohms primary and 600 Ohms secondary then terminate it with 600 Ohm resistor across the secondary. Now having said that the Lundahls are a different beast. For Lundahl LL1690 I used a 41 K Ohm resistor and the datasheet zoebel. A zoebel is a series resistor with cap across the secondary and is used as compensation. Have you checked the datasheet? When I get a chance I'll look at it. In any event you should have a fixed load on it for the dac as the resistance is reflected to the primary. Hope that helps. Dave
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Old 22nd June 2013, 08:48 PM   #13
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Thumbs up Transformer

Hi audiorado, For the LL1527.... I'd go 1K series resistor to pin 1 dac +, 1 K series resistor to pin 3, dac -. You can think of these as safety resistors. Hang 5-10 K resistor across pin 5 to 7. The best square wave response occurs with 3-4 K load across the secondary. 20K Ohms is pretty low however that should work fine. Hope that helps..... Dave
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Old 23rd June 2013, 10:34 PM   #14
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Default Dac CS4390+Lundahl LL1527 output stage.....

Hi Dave.....
...thanks a lot for your answer.Becouse Im dealing for the first time with output transformers I will be happy to become so many info as posibile,before start to solder and modify the dac board.In the mine time I have become the answer from Lundahl to,and he says that it is not necessery to put any resistor on the secondary site of the transformer.In fact he say me,that the best way would it be to conect the dac direct output with transformer on input and than the transformer output direct to rca conectors with any aditional components.So now Im a litle confused,becose I dont know what to do.I just want to give the transformer the best posibile conditions to work at hes best.
Sorry for my poor english lenguage.But I hope Dave you will understund me.
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Old 23rd June 2013, 11:50 PM   #15
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1527_7xl.pdf
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Old 24th June 2013, 12:29 PM   #16
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Cool DAC CS4390+lundahl LL1527 passive output

Thanks guys for all answers.So I made the modification to my dac board and the results are:I have use the RC network on the center tap to graund with 10Kohm+22uF paralel on the primary site like this did Andrea Ciuffoli-On the secondary site of transformer I first put the load resisitor 10Kohmfrom + output to - output in paralel and than ground this to the ground.The sound was verry verry good,for the first time I ask my self why I have not try this before and have always try to buy bether opamps and bether tubes for other output stages options.But now coms,than I have put the 10Kohm resisitor from secondary site away and conect the transformer directly with my rca pin conectors.Oh my God,what is happened here,I have in no way espect such improvement in sound.Now the sound is full of dynamic,with verry havy bass,a lot of volume in the middle in verry plesant high octave.But there is a - site to.If I rotate my volume control all the way up and there is ni music playing I hear some hum in my speakers.I try to do this in other option to with load resistor conected and than grounded,but in this option there is no hum at all from my speakers only dead silence.So now my question is,why is there a hum in my speakers when I not conect the load resistor(and gound it) on the secondary site.It is no hum when I conect this,but in this case I feel that the transformer limited somehow the sound,becose with load resistor the sound have lite bass and the music is a litle bit thin and the high frequency a litle bit bright,but like I say,no hum from speakers.Plese dont understund me wrong,this hum when is there is not verry loud,but it is there and on my 98Db sistem I can hear this from the 3 meter distance.
Plese for help and response what this mean now.
Rado
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Old 27th June 2013, 11:16 PM   #17
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Originally Posted by audiorado View Post
Thanks guys for all answers.So I made the modification to my dac board and the results are:I have use the RC network on the center tap to graund with 10Kohm+22uF paralel on the primary site like this did Andrea Ciuffoli-On the secondary site of transformer I first put the load resisitor 10Kohmfrom + output to - output in paralel and than ground this to the ground.The sound was verry verry good,for the first time I ask my self why I have not try this before and have always try to buy bether opamps and bether tubes for other output stages options.But now coms,than I have put the 10Kohm resisitor from secondary site away and conect the transformer directly with my rca pin conectors.Oh my God,what is happened here,I have in no way espect such improvement in sound.Now the sound is full of dynamic,with verry havy bass,a lot of volume in the middle in verry plesant high octave.But there is a - site to.If I rotate my volume control all the way up and there is ni music playing I hear some hum in my speakers.I try to do this in other option to with load resistor conected and than grounded,but in this option there is no hum at all from my speakers only dead silence.So now my question is,why is there a hum in my speakers when I not conect the load resistor(and gound it) on the secondary site.It is no hum when I conect this,but in this case I feel that the transformer limited somehow the sound,becose with load resistor the sound have lite bass and the music is a litle bit thin and the high frequency a litle bit bright,but like I say,no hum from speakers.Plese dont understund me wrong,this hum when is there is not verry loud,but it is there and on my 98Db sistem I can hear this from the 3 meter distance.
Plese for help and response what this mean now.
Rado
Hi, I had a similar issue with an Edcor. The fix is to put a 5K to 10 K Ohm resistor from the output side (RCA ground) back to the ground side on the dac. I'd go to the common point (ground) on the power supply. The reason is this is a balanced dac. The resistor sets a reference point for ground and the noise should be gone. Worked for me.... Dave
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Old 6th July 2013, 08:14 PM   #18
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Originally Posted by AudioLapDance View Post
Give it up for da man!

Andrea Ciuffoli DAC 1.0

Attachment 355569

DAC 1.0

Old school, baby!
I think I have one of those demo boards, if someone wants it, I'll be glad to trade it for whatever you think it might be worth.

Sheldon
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Old 9th July 2013, 09:32 AM   #19
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Default DAC CS4390+lundahl LL1527 passive output

Hi Dave and other Guys...
...thanks a lot for all answers.And yes Dave your sugestions work best.Dave if you could be so nice,can you tell me if I can use this Lundahl transformers with TDA1543 dac to??I just become some dac board from my good friend with TDA1543 in non oversampling mode with direct output via capacitor(47uF electrolitic).Si I would use now in the place of the output capacitors this lundahl LL1527 transformers.Is this posibile??And if yes,would I need some aditional parts (resitors,capacitors)on the primary or secondary site of the transformers??

Rado
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Old 9th July 2013, 12:29 PM   #20
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Since a few weeks I'm listening to the DAC-END R (es9018) with a LL1684 as output stage: sounds fabulous !
Those transformers make it so easy to convert the balanced output of a DAC to SE and add some additional benefits (isolation, filter)
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Last edited by danny_66; 9th July 2013 at 12:32 PM.
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