DAC With No Output Stage

[Mark Allen]

I have been building a CS-4398 DAC that has no output stage. It uses instead a pair of Lundahl transformers driven directly off the output of the DAC itself. The one I have here that is now running sounds unbelievable, convincing me beyond a doubt that no output stage is the better choice. 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. I highly reccomend it and although the cost is a bit high for the transformers you certainly won't be disappointed. Has anyone else tried this or built a DAC this way yet?

Mark

 

[hazard500]

I have been building a CS-4398 DAC that has no output stage. It uses instead a pair of Lundahl transformers driven directly off the output of the DAC itself. The one I have here that is now running sounds unbelievable, convincing me beyond a doubt that no output stage is the better choice. 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. I highly reccomend it and although the cost is a bit high for the transformers you certainly won't be disappointed. Has anyone else tried this or built a DAC this way yet?

Mark

Yep, I've been running this configuration for over 10 years - it was a published DIY tweak back then and was popular in my local DIY group. I used to have have a Cirrus Logic demo board, CS4390 (24 bit/48kHz), the demo board was nice enough to have convenient test points straight off the DAC output which I fed into a Lundahl 1527XL tranny. In 2004 I updated to a CS4398 demo board, and transferred the tranny's to this new DAC. It sounds excellent, and I agree that no output stage is better than any active stage. The trannies are now around $95 each in Australia, but its still way cheaper than building a valve output stage. A solid state stage could be built for less than $200 but not sure that it would sound as good as this.

 

[Pano]

Me too, for several years. Just about everything but Lundhal. I love it. The Cirrus chips seem particularly happy with a transformer output.

It's easy and sounds great. Measures well, too.

 

[Ryssen]

It uses instead a pair of Lundahl transformers driven directly off the output of the DAC itself.

What Lundahl trafo are you using?

 

[jean-paul]

Me too. I used Haufe and Neutrik transformers with very good results. Since ES9023 and FN1242a both can not drive these transformers as well as I would like them to I am selling a few of those boards in the Swap Meet.

CS4397/8 sound the best with transformers IMO.

 

[ReinoutdV]

TDA1541A + transformers

Hi Mark,

same here ! Although i use the TDA1541A as DAC....i also prefer the transformer output stage.

In the DIY-kit there was an opamp option (AD844) and a tube option (6DJ8 or 6C45) but both are inferior to good transformers. First i used "basic" transformers and that was already serious good. Then i found Silvercore (www.silvercore.de) who made 1:20 steup-ups for me....really great !

Included some pictures of the DAC-PSB (yes....currently plain in the open and ABSOLUTELY no hummmmmm). The 2 small coils you will notice on one side of the PCB are actual home made I/V-resistors.
The stainless steel casings are the Silvercore trannies.

Regards, Reinout

 

[Mark Allen]

What Lundahl trafo are you using?

The LL-1690 line transformer. I mean this DAC is absolutely stunning and I can't see why people waste their time doing anything else. The dac uses a CS-8416 input receiver... CS8421 Sample rate converter and a CS-4398 DAC all in TSSOP packages. It's all surface mount stuff for the most part but I'm used to SMT so no big deal. I can't post the schematic because I am not the designer. I was lucky enough to get one pcb from him. There is a link to what the prototype looks like here... CS4398 DAC
Note that mine is slightly different, this is the prototype board. The Lundahl's are 148 USD each in the States. Pricy but well worth it!
Mark

 

[audiorado]

Audio Dac CS4390 with lundahl LL1527 output transformers

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.

 

[Torchwood421]

Transformer output

Yes... I am doing this too. I have the Sheldon Stokes CS8416/CS8421/CS4398 with the LL1690's. Nice. Also got awesome results with a TDA1541A S1 Crown dac using Edcor XSM 600/600 transformers after the I/V. Here is a link to that.... http://www.diyaudio.com/forums/digi...220p-b-will-take-som-time-66.html#post3529449 My TDA is my best dac to date.

 

[AudioLapDance]

Yep, I've been running this configuration for over 10 years - it was a published DIY tweak back then and was popular in my local DIY group. I used to have have a Cirrus Logic demo board, CS4390 (24 bit/48kHz), the demo board was nice enough to have convenient test points straight off the DAC output which I fed into a Lundahl 1527XL tranny. In 2004 I updated to a CS4398 demo board, and transferred the tranny's to this new DAC. It sounds excellent, and I agree that no output stage is better than any active stage. The trannies are now around $95 each in Australia, but its still way cheaper than building a valve output stage. A solid state stage could be built for less than $200 but not sure that it would sound as good as this.

Give it up for da man!

Andrea Ciuffoli DAC 1.0



DAC 1.0

Old school, baby!

 

[qusp]

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.

 

[Torchwood421]

Transformer

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

 

[Torchwood421]

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

 

[audiorado]

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.

 

[AudioLapDance]

View attachment 1527_7xl.pdf

 

[audiorado]

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

 

[Torchwood421]

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

 

[stokessd]

Give it up for da man!

Andrea Ciuffoli DAC 1.0

View 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

 

[audiorado]

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

 

[danny_66]

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)