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Output transformers for DACs
Output transformers for DACs
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Old 18th December 2019, 01:23 PM   #351
nounouchet is offline nounouchet  France
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Output transformers for DACs
Bisesik, Lemon,


Thank you for your answers.
It's clear form me with the schematic.

With Jensen transformer a use 600 ohm resistor accross the secondary, hence my question.


nounouchet
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Old 19th December 2019, 06:31 AM   #352
lemon is offline lemon  Greece
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The transformer manufacturer on datasheet, describes if there is need a secondary parallel resistor for better flat FR.
The best will achieved with a FFT that you can try different next stage input resistance and make yours experiments.
A Lundahl LL1545A needs a secondary zobel network to flatting the FR, the 1:1 bisesik not.
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Old 22nd December 2019, 01:33 PM   #353
randytsuch is offline randytsuch  United States
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Output transformers for DACs
I have a question on my transformer (1:2+2) and the original ian adapter board.

so it looks like the board and transformer layout support either two 2+2 secondaries or one 4 secondary.

If primary is on bottom, the 4 secondary is on top, and the 2+2 secondaries are on the sides.

The rework instructions I'm looking at look correct if you have one 4 secondary, but incorrect for j3 if you have 2+2 secondaries.
I think you should cut the trace to the secondary closest to j3, and jumper from the pad you just isolated to bottom pin of j3.

Does that make sense?

Randy
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Old 22nd December 2019, 01:55 PM   #354
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Output transformers for DACs
Hi Randy! Is it about XLR polarity?
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Old 22nd December 2019, 02:22 PM   #355
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Output transformers for DACs
If it is about wrong XLR polarity, then yes, in case of 2+2 version it should be like you described:
Ian'DAC_HAT_bisesik_polarity_fault_2_2.jpg

Sorry Randy, I forgot that there was 1:2+2 version for you.


P.S. For all other users: if you do not know about this issue (via PM), then just ignore it, because this wrong XLR polarity connection was corrected in the next PCB revision..
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Old 22nd December 2019, 02:44 PM   #356
randytsuch is offline randytsuch  United States
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Output transformers for DACs
Quote:
Originally Posted by bisesik View Post
If it is about wrong XLR polarity, then yes, in case of 2+2 version it should be like you described:
Attachment 804043

Sorry Randy, I forgot that there was 1:2+2 version for you.


P.S. For all other users: if you do not know about this issue (via PM), then just ignore it, because this wrong XLR polarity connection was corrected in the next PCB revision..
Thanks for confirming. I actually added one other jumper to make both sides the same, but since I guess I'm the only one with a 2+2 and first board no one else will care.

BTW, I have been using RCA's, and didn't realize I was missing two jumpers until this morning. I added those too, but a couple of the holes are messed up so I had to jumper them too.
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Old 27th December 2019, 08:17 AM   #357
Zoran is offline Zoran  Serbia
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Quote:
Originally Posted by bisesik View Post
Yes, across the secondary coil - to stabilize the output impedance for all the frequency range. Kind of i/v resistor in common terms.
Maybe the use of ONLY one output in same time is allowed. Other XLR or RCA should not been even connected with a cable. Because IF booth outputs are plugged in Rinput from next device will take a part in output circuit? As well as capacitance of cables... About 100pF typically probably more with connectors. In reverse step transfer that capacitance will transfer directly to the primary to the DAC outputs?
...
I want to say that in this configuration og secondary, only one cable should be used. XLR or RCA. Other unused output should be disconnected from any cable.
...
Worst case is that booth cables are connected from output of the transformer to inputs on preamps to choose with selector which one to use...
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Old 27th December 2019, 08:18 AM   #358
Zoran is offline Zoran  Serbia
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It is not specific for the these transformers but for any other used in this way.
.
Another thing, If I may, the core is probably without gap. So like it said there is any even slight offset DC difference at the primary taps is not good.
It that way, when we turn on DAC device, some imbalances in the circuit almost always causing DC offset at the output But in very short time until the circuit stabilized. Even these short "bursts" of delta offset at the output of dac and input to primary, can affect the sensitive high permeability, gapless transformer.
.
From my experience that could be avoided in dac power supply unit. Just make the supply have slow reaching level on power ON. About second or 2. Almost with every regulator it can be done. And in some regulators data-sheets we have examples how to.
.
That approach is also good to get rid of clicks and pops, avoiding mute relays and muting circuits, when turning ON device
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Last edited by Zoran; 27th December 2019 at 08:39 AM.
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Old 27th December 2019, 08:48 AM   #359
bisesik is offline bisesik  Kazakhstan
Output transformers for DACs
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Output transformers for DACs
Quote:
Originally Posted by Zoran View Post
...only one cable should be used. XLR or RCA. Other unused output should be disconnected from any cable.
I agree and believe it is useful instuction for any audio equipment which can work simulataneously to both types of outputs, no matter if there are transformers or any other components are used before connectors.
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Old 27th December 2019, 08:50 AM   #360
Zoran is offline Zoran  Serbia
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Sorry that I am wtriting 3rd post...
But it is good to know that we have difference with current output DACs versus Voltage ouput dacs.
Current output DACs with Riv used Shifting Voltage phase to -180deg. Opposite phase.
Positive digital DATA input DAC - Dac output current at Riv - giving -180deg Voltage output.
So it is need to check this and make transfprmer shift phase back into right pase output 0deg
.
Volttage output DAC has outputs are already marked as in phase or/and in phase. So only shifting element is transformer. Also it is good to check with simple measurements just to be sure. If it is outphase switch the secondary taps?
.
It is easely can be spotted by measuring Step response (more clear). Step response IF the ouputs are correct phase always should be firs going into positive Y axis. If the step response going into negative Y the output is outphase, and signal with -180deg going into the system.
.
(With exeption of Single ended tube (or other device) pramps - all single ended Gain stages shifting the phase -180deg.)
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Last edited by Zoran; 27th December 2019 at 09:05 AM.
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