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Old 16th February 2011, 03:10 PM   #141
markusA is offline markusA  Sweden
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Using a 1+1 : 1+1 transformer as 1:1, do you connect the primaries/secondaries in series or in parallell?
Why?
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Old 16th February 2011, 03:54 PM   #142
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Is anyone with transformer output using a HF ultrasonic filter as well? If so, what is the design?
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Old 16th February 2011, 04:00 PM   #143
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Quote:
Originally Posted by David Garretson View Post
Is anyone with transformer output using a HF ultrasonic filter as well? If so, what is the design?
Don't most transformers take care of that for you (high end roll-off)?
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Old 16th February 2011, 04:07 PM   #144
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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?
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Old 26th February 2011, 07:01 PM   #145
tubeing is offline tubeing  Italy
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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
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Old 3rd March 2011, 04:59 PM   #146
Angelm is offline Angelm  Bulgaria
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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...
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Old 3rd March 2011, 09:39 PM   #147
markusA is offline markusA  Sweden
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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?
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Old 3rd March 2011, 10:17 PM   #148
Marek is offline Marek  Poland
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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.
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Old 3rd March 2011, 10:47 PM   #149
Gluca is offline Gluca  Italy
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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.
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Old 3rd March 2011, 11:30 PM   #150
Marek is offline Marek  Poland
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@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...

Last edited by Marek; 3rd March 2011 at 11:32 PM.
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