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Old 15th February 2014, 10:35 AM   #521
Ryssen is offline Ryssen  Sweden
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Now let me understand this: I connected directly to the output of 30mV rms (with the 3 ohm resistors as shown in the diagram) my amp, but even at low volume there is distortion. Why?
If you take the signal before the tubestage,is there distortion there to?


Another question,can I use the 330 ohms resistors even if I use the "unballancer" with differential tube input.(without a trafo)
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Old 27th May 2014, 03:25 AM   #522
zz1969 is offline zz1969  Russian Federation
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Originally Posted by Joe Rasmussen View Post
Interesting question, but simple answer. Since the Secondary load is relatively high, the DAC hardly sees the DC resistance of the transformer, if it is reasonably low. I used a 1:1 transformer with a lot higher DCR than that and yet was under 100 Ohm.

The DAC will see the 330R at all times and very little in parallel.

Lundahl 1517 will be OK.

BTW, hate to be pedantic, there is no such thing as Ohms, it is always Ohm (no "s") whether singular or plural.

Cheers, Joe
Hi Joe,

if using 2 DACs in dual mono, should we use 3 Ohm or 1.5 Ohm resistors? (in a variant with transformers and a tube stage)

Rgds,
Evgeny
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Old 27th May 2014, 06:42 AM   #523
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Hi Joe,

if using 2 DACs in dual mono, should we use 3 Ohm or 1.5 Ohm resistors? (in a variant with transformers and a tube stage)

Rgds,
Evgeny
Often that is the case, if you are dumping twice the current, it will produce double the voltage.
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Old 27th May 2014, 03:04 PM   #524
zz1969 is offline zz1969  Russian Federation
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Hi Joe, thanks for a quick reply.
I am using your D setup at the moment: dual mono B-III with 1.5 Ohm resistors, Sowter 3603 transformers and an Aikido tube stage with 6N2P input and 6CG7 output tubes. Sounds good, for me better than any transistor output stage I tried. Thanks.
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Old 27th March 2015, 06:13 AM   #525
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Morning good folks

I would like to bring life into this old thread again.

I have read this thread over and over again and there is still so many questions left unanswered!
I have a Buffalo III dac which I experiment with (like every one else in this thread )

For now I have finished a tube gain stage and I'm ready to experiment with Joe Rasmussen's suggestion to load the Sabre dac with 3R to ground or even lower (I have borrowed 2 Lundahl 1984 1:1) but: First of all I was thinking: Why use a transformer 1:1. The signal has to be gained after 3R of course like 50-70 times..
Would't it be enough to load the dac, put in a high quality cap between dac and tube gain stage?
What role does this 1:1 transformer actually have if the if the signal has to gained pretty much?

I had this theory - Why not use an Lundahl ribbon mic transformer like : LL1927A :http://www.lundahl.se/pdf/1927A.pdf
Or LL2913 :
http://www.lundahl.se/pdf/2913.pdf

And together with the exstremly low dcR of the primary it would be possible to let the dac see a very low impedance without "killing" the signal to ground with these very small resistors! And the gain after transformer would not have to be as high like in a riaa preamp - You guys follow me?

Ok, I send a mail for the swedish distributor of Lundahl with my theory Mr. Peter Buddee and he friendly replyed that he would have to ask Mr. Kevin Carter at K&K.
Kevin provided a quick respond: Ribbon transformers do not have enough induction in the primary to make a good bass respond from a source of 195 ohm like the ES9018!!
All right I can understand that - But where is the limit then? Lundahl dosen't provide us with the primary induction in there hole program.
Some people in this thread have tried the LL1941 and LL1933 both mc trannys with a pretty low dcR on primary and in my world it meens that the primary induction also would be low! And according to the datasheets they have to work from a source below 50 ohm

As you folks problerbly can see, I'm a little confused..
It seems like this thread has turn out from transformers as output stage to transformers with a gain output stage - So why use a 1:1 when we still load the dac with small resistors and gain after?
It would make sence to me to use a 1:16 or greater transformer to raise the signal from dac which must around 5mV with 0,5 ohm resistors to ground. That will give arround 80mV there just have to be gained about 25 times to reach 2V output - Please correct me if I'm on totally wrong path here

Anybody who want's to kick in with some useful facts are more than welcome

Joe Rasmussen - Marek - Gluca - RollE2K - Mars2
I can see that you guys have tried step-up's.. What do you think of my thoughts ?

If money was of no concern I would buy 2 pcs. of these LL1674 1:4 - LL2913 1:37 - LL1927A 1:55 - LL1941 1:16 - LL7902 1:4 just to try them all out!!

But a daytime carpenter job in Denmark, well it does not make you financially rich

Please let me hear from you all again
Best regards
Henrik
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Old 27th March 2015, 10:29 AM   #526
Marek is offline Marek  Poland
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What role does this 1:1 transformer actually have if the if the signal has to gained pretty much?
desymetization, HF filtering and ground separation.

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Lundahl dosen't provide us with the primary induction in there hole program.
Some people in this thread have tried the LL1941 and LL1933 both mc trannys with a pretty low dcR on primary and in my world it meens that the primary induction also would be low! And according to the datasheets they have to work from a source below 50 ohm
You're right, inductance od primary winding has to match output impedance of DAC. So in case of ES9018 you have to use at least 200:XXX trafo, not 50:XXX.
And you right, my LL1931 trafo has too low inductance for ES9018 - as you mentioned it is designed for 50ohm source - I got great sound BUT with lack of lower bass...

My goal for using step-up trafo (LL1931 in 1:8 turns ratio config) was to ommit one stage of active amplification, driving power tube amplifier ( 2 stage: VT-25+GM70 ) directly with DAC+step-up.
With standard amplifier you don't need such gain so you may consider lower (1:1 max to 1:4) turns ratio.
Note that with higher turns ratio there is a problem with output impedance because O_imp= I_imp * (turns_ratio)^2.

I'm not using any load resistors letting ES9018 to work with "voltage mode" because I really can't see any real advantages to work with "current mode" except some better -dB numbers which are negligible to me.

If money was no object I would order a custom supermalloy trafo from SAC Thailand with SILK Nano winding technology SAC Thailand

Marek
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Old 27th March 2015, 11:46 AM   #527
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I'm not using any load resistors letting ES9018 to work with "voltage mode" because I really can't see any real advantages to work with "current mode" except some better -dB numbers which are negligible to me.
Than why not to use direct voltage output from the dac?
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Old 27th March 2015, 12:37 PM   #528
Marek is offline Marek  Poland
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desymetization, HF filtering and ground separation.
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Old 27th March 2015, 01:39 PM   #529
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What do you mean by desymetization? Is there a need to filter HF, does the signal from dac is 'dirty'? Perhaps you mean HF cut off?

The main reason to use transformer more likely is to convert balanced to unbalanced output signal.
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Old 27th March 2015, 02:40 PM   #530
Marek is offline Marek  Poland
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desymetrization = balanced to unbalanced conversion.
Yes, signal from delta sigma DAC is 'dirty', it contains lot of HF noise (mainly from noise shaping process) which unfiltered will demodulate on nonlinearities into the audio band. It must be filtered out.
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