Using a 1+1 : 1+1 transformer as 1:1, do you connect the primaries/secondaries in series or in parallell?
Why?
Why?
Is anyone with transformer output using a HF ultrasonic filter as well? If so, what is the design?
The transformers that I'm using supposedly roll off around 100kHz, but depending on the noise of the particular DAC chip it could be beneficial to filter further down toward the audio band. Any thoughts w/r to HF noise component of Buf analog output?
Hi everybody,
I'm waiting for my BII DAC looking around for some nice transformer to use in the output stage. I contacted Jensen, Sowter and Lundahl asking for the best choice for what I'm doing. They told me that my bigger problem is the input impedance of my preamp (I'd like to use the following connections: DAC->transformer primary->transformer sec ->preamp input) that's "only" 4K...but I can see that Lundahl LL1527 works at its best with 4K load, so I think it could be the best choice for me...but what kind of problems could arise with low preamp impedance? This is my first design with transformers, so I'm asking you if my calculations are right or not. With LL1527A, primary windings in parallel and sec windings in series, I have 90 Ohms in parallel with 4K and the DAC will see (dynamically) something like 22Ohm reflected by the secondary. But in this calculations, where must I consider the primary impedance? In series with the 195Ohms (equivalent series resistance of ESS9018)? How can I calculate the out voltage at the preamp input? In this case I have a 1:2 turn ratio...Last thing: I can see that there are people using a resistor across the secondary, to lower the reflected impedance in order to let the DAC work better (hopefully) in terms of THD+N. But, stated the best behaviour of LL1527 with 3-4K impedance, is it a good move?
Thanks in advance.
Regards
Stefano
I'm waiting for my BII DAC looking around for some nice transformer to use in the output stage. I contacted Jensen, Sowter and Lundahl asking for the best choice for what I'm doing. They told me that my bigger problem is the input impedance of my preamp (I'd like to use the following connections: DAC->transformer primary->transformer sec ->preamp input) that's "only" 4K...but I can see that Lundahl LL1527 works at its best with 4K load, so I think it could be the best choice for me...but what kind of problems could arise with low preamp impedance? This is my first design with transformers, so I'm asking you if my calculations are right or not. With LL1527A, primary windings in parallel and sec windings in series, I have 90 Ohms in parallel with 4K and the DAC will see (dynamically) something like 22Ohm reflected by the secondary. But in this calculations, where must I consider the primary impedance? In series with the 195Ohms (equivalent series resistance of ESS9018)? How can I calculate the out voltage at the preamp input? In this case I have a 1:2 turn ratio...Last thing: I can see that there are people using a resistor across the secondary, to lower the reflected impedance in order to let the DAC work better (hopefully) in terms of THD+N. But, stated the best behaviour of LL1527 with 3-4K impedance, is it a good move?
Thanks in advance.
Regards
Stefano
At the moment i listen Buffalo II with LL1517 directly connected with 1kohm
in secondary, thanks Rosendorfer and Tyimo. Plenty of detail and dynamic,
i will try different load and transformer lately, but now i can't stop to listen...
in secondary, thanks Rosendorfer and Tyimo. Plenty of detail and dynamic,
i will try different load and transformer lately, but now i can't stop to listen...
I'm using the LL1588 with a 2:1 ratio at the moment.
No extra resistors what so ever and it stiull sound good.
Later I guess I'll hook it up to a tone generator and dial in the optimum load but for now I'm just enjoying the music. 😀
I don't really know what the optimum load impedance is supposed to be for the LL1588?
No extra resistors what so ever and it stiull sound good.
Later I guess I'll hook it up to a tone generator and dial in the optimum load but for now I'm just enjoying the music. 😀
I don't really know what the optimum load impedance is supposed to be for the LL1588?
Sabre32 DAC should be used in voltage mode when using transformers. I tried step-up trafos (expensive amorph LL1931 in 1:16 and 1:8 config) with current mode but effect wasn't good (high THD of low freq). Then I tried LL7901 (1:1, 2:1) with voltage mode - better, then I tried Jensen JT-11P-1 - best transformer effect (many people choose Jensens as the best trafo for Sabre32).
Anyway if you want to achieve THE BEST results forget transformers. Use your BuffaloII with tubes directly - results are incredible - every transformer give you worse results.
Anyway if you want to achieve THE BEST results forget transformers. Use your BuffaloII with tubes directly - results are incredible - every transformer give you worse results.
Played with cinemags step-ups with low IV resistor and 10k:10k... soundwise I prefer probably 10k:10k. I am on a very different opinion ... I do suggest transformers and tubes.
@Gluca
Did you make any THD measuremnts (espiecially for low frequency eg. 50Hz) with RMAA or similar?
Last days i tried this BuffaloII output stage configurations:
1. passive stage using Jensen JT-11P-1
2. Jensen -> SRPP based on 6N30P supertube
3. DAC directly to SRPP
4. DAC directly to tube diffirential preamplifier (PP->SE on 2 triodes+ current cource in cathodes a than cathode follower to lower output impedance)
all tested with 6C33C tube amplifier.
Results: definetely best and similar efect with 3 and 4, when using Jensens very good but there is something missing, some very low level details.
Seriously I did prefere passive stage because of simplicity no PSU, no bunch of cables etc but unfortunetally even the most sophisticated transformer degrade sound a bit..
Another option is DAC-> tube and transformer output from anode but I can't lose more money for transformers...
Did you make any THD measuremnts (espiecially for low frequency eg. 50Hz) with RMAA or similar?
Last days i tried this BuffaloII output stage configurations:
1. passive stage using Jensen JT-11P-1
2. Jensen -> SRPP based on 6N30P supertube
3. DAC directly to SRPP
4. DAC directly to tube diffirential preamplifier (PP->SE on 2 triodes+ current cource in cathodes a than cathode follower to lower output impedance)
all tested with 6C33C tube amplifier.
Results: definetely best and similar efect with 3 and 4, when using Jensens very good but there is something missing, some very low level details.
Seriously I did prefere passive stage because of simplicity no PSU, no bunch of cables etc but unfortunetally even the most sophisticated transformer degrade sound a bit..
Another option is DAC-> tube and transformer output from anode but I can't lose more money for transformers...
Last edited:
No measurements taken, I can go down to 60dB only due to the limited resolution of my o/scope so I would not see any difference. Do you have numbers to share? That would be interesting. I do use transformer at the output too ...
Gianluca
Gianluca
I've made measurments using RMAA and my crappy onboard sound card.
This is comparsion of LL1931 step-up (1:16, current mode) and LL7901 (2:1, voltage mode)
http://www.fotosik.pl/pokaz_obrazek/pelny/f05c802424b7bba3.html
I'm going to buy some good quality external USB sound card (like E-MU 0202) and make measurments again.
This is comparsion of LL1931 step-up (1:16, current mode) and LL7901 (2:1, voltage mode)
http://www.fotosik.pl/pokaz_obrazek/pelny/f05c802424b7bba3.html
I'm going to buy some good quality external USB sound card (like E-MU 0202) and make measurments again.
yes, 2nd harmonic at low frequency. things get much better at higher freqs. that dipends on the signal level too. I guess you were away from saturation anyway.
Yes THD problem is mainly for low freq. I use about 5dBu so not worry about saturation.
Have you got some DS of your cinemag 10k:10k trafos?
here is for Jensens http://www.jensen-transformers.com/datashts/11p1.pdf
Have you got some DS of your cinemag 10k:10k trafos?
here is for Jensens http://www.jensen-transformers.com/datashts/11p1.pdf
15/15B datasheet
5dBu at 50Hz might be very close to saturation for a small step-up transformer, that might explain the odd graphs/results.
5dBu at 50Hz might be very close to saturation for a small step-up transformer, that might explain the odd graphs/results.
5dBu concern voltage mode and LL7901 trafo (2:1), with current mode and step-up trafo DAC see about 5ohm (~1,5ohm DCR+ reflected resistance from secondaries) so signal level was much lower
got it.
I am using 1:36 step up with 5.5ohm IV resistor (sum of everything). what value is your IV resistor?
I am using 1:36 step up with 5.5ohm IV resistor (sum of everything). what value is your IV resistor?
- Status
- Not open for further replies.