I said - or other device. That means all of SE stages. Where single active device doing any amplification. Other circuits, You mentioned does not amplifying stages, but with "gain" <=+1... Please...
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Hi bisesik,
Looking forward to getting a pair of transformers from you, looks like you have done some great work.
Have you done any measurements or do you have any impressions on having the IV resistor on the primary side of the transformer instead of the secondary?
I will try both ways but was curious what your findings have been.
Ryan
Looking forward to getting a pair of transformers from you, looks like you have done some great work.
Have you done any measurements or do you have any impressions on having the IV resistor on the primary side of the transformer instead of the secondary?
I will try both ways but was curious what your findings have been.
Ryan
Indeed good question 
Let it be DACs that have a current output. In my understanding, these are DACs whose the best quality of the output signal are achieved when working on a load that tends to zero. In the ideal case, this is a short circuit. In this case, the DAC "feels" good, it gives a signal in maximum quality. OK, the DAC itself is doing fine, but we still wants to get a signal from DAC at a sufficient volume We are forced to bother the DAC a bit by loading it onto non-zero resistance to get a sufficient signal voltage. It is well known i/v converter. The lower its value, the better in general, but the quieter the useful signal. Thus, a certain balance is required between the minimum impedance and sufficient loudness. Too quiet signal can be too close to the PSU noise. Too loud signal will force DAC itself to be out of best condition. Compromises. Well, as always and in everything.
So what is all this for? A current transformer is required. The current transformer should ideally have zero primary resistance and a sufficient reactance for linear frequency response at low frequencies (let it be 20 Hz).
Let's compare the two options for a 1:4 transformer.
1. The i/v resistor is located on the primary side. Let it be 100 ohms. Suppose a 0.1V signal is highlighted. We get (0.1 * 4) 0.4V after the transformer.
The sound will be formed completely on the resistor. The transformer involved just a little in the formation of the signal and works as a voltage transformer. With such small values of the resistor rating, the signal quality will directly depend on the quality and sound properties of the material of which the resistor itself is made. Commonly such resistors are expensive enough on market.
Amount of unwanted DC voltage applied to the DAC output is equal to which is generated on the 100 Ohm resistor.
2. The i/v resistor is located on the secondary side. In order for the DAC to see the same 100 Ohms, it is necessary to set 100 * (4 ^ 2) = 100 * 16 = 1.6 kOhm. We get the same 0.4V after the transformer. However, the sound will be formed mostly inside the transformer itself, and the quality of the resistor is already fading into the background, since its denomination is already 16 times higher than in the first case.
Amount of unwanted DC voltage applied to the DAC output is equal to which is generated on the primary winding active resistance (~5 ohms.)
BTW, here are some tips from Sowter:
The I/V resistor across the secondary of the transformer instead of the primary has yeilded the best result according to some customers
We recommend that the I/V resistor is placed across the secondary of the transformer
So, I recommend to use the i/v resistor across the secondary coil too
Let it be DACs that have a current output. In my understanding, these are DACs whose the best quality of the output signal are achieved when working on a load that tends to zero. In the ideal case, this is a short circuit. In this case, the DAC "feels" good, it gives a signal in maximum quality. OK, the DAC itself is doing fine, but we still wants to get a signal from DAC at a sufficient volume
We are forced to bother the DAC a bit by loading it onto non-zero resistance to get a sufficient signal voltage. It is well known i/v converter. The lower its value, the better in general, but the quieter the useful signal. Thus, a certain balance is required between the minimum impedance and sufficient loudness. Too quiet signal can be too close to the PSU noise. Too loud signal will force DAC itself to be out of best condition. Compromises. Well, as always and in everything. So what is all this for? A current transformer is required. The current transformer should ideally have zero primary resistance and a sufficient reactance for linear frequency response at low frequencies (let it be 20 Hz).
Let's compare the two options for a 1:4 transformer.
1. The i/v resistor is located on the primary side. Let it be 100 ohms. Suppose a 0.1V signal is highlighted. We get (0.1 * 4) 0.4V after the transformer.
The sound will be formed completely on the resistor. The transformer involved just a little in the formation of the signal and works as a voltage transformer. With such small values of the resistor rating, the signal quality will directly depend on the quality and sound properties of the material of which the resistor itself is made. Commonly such resistors are expensive enough on market.
Amount of unwanted DC voltage applied to the DAC output is equal to which is generated on the 100 Ohm resistor.
2. The i/v resistor is located on the secondary side. In order for the DAC to see the same 100 Ohms, it is necessary to set 100 * (4 ^ 2) = 100 * 16 = 1.6 kOhm. We get the same 0.4V after the transformer. However, the sound will be formed mostly inside the transformer itself, and the quality of the resistor is already fading into the background, since its denomination is already 16 times higher than in the first case.
Amount of unwanted DC voltage applied to the DAC output is equal to which is generated on the primary winding active resistance (~5 ohms.)
BTW, here are some tips from Sowter:
The I/V resistor across the secondary of the transformer instead of the primary has yeilded the best result according to some customers
We recommend that the I/V resistor is placed across the secondary of the transformer
So, I recommend to use the i/v resistor across the secondary coil too
Thanks for your reply.
The main advantage in putting the IV on the primary in my case is I can null the current offset of my DAC (TDA1541A in differential mode) by applying it to the CT between the two primary coils, the opposing current flow is then canceled out in the transformer along with any noise.
But, as I said I will try both ways and see what sound I like best.
Ryan
The main advantage in putting the IV on the primary in my case is I can null the current offset of my DAC (TDA1541A in differential mode) by applying it to the CT between the two primary coils, the opposing current flow is then canceled out in the transformer along with any noise.
But, as I said I will try both ways and see what sound I like best.
Ryan
Well, this will happen by itself and without resistors in the primary coils. Just checked
There is no need to eliminate bias by other ways. The simple connection between Iout+ and Iout- of two in series connected primary windings, the central terminal of which is connected to the ground, gives exactly the same result.True, but there may be a small improvement in having exactly 0V DC on the DAC output. May I ask what the DC resistance for the primary coils are?
In my case I will have 4mA current offset to deal with so this may cause significant voltage offset - which may or may not affect the sound... Ill have to have a play around with it soon.
In my case I will have 4mA current offset to deal with so this may cause significant voltage offset - which may or may not affect the sound... Ill have to have a play around with it soon.
Hi!
I have builded up my DSC board (with PPY Reclocker for BBB) and have tested it on Roon (DSD512) for both types of transformers. Defenitely sounds better with step-up transformer. Think I will find the needed turns ratio very soon
Hello bisesik,
You have a chance to try both ak449x and dsc dac with your transformers which one do you preffer in the means of SQ.
Could you elaborate more on the wiring as the ak4499 outputs are a little unusual compared to other chips. In my DAC changing value of 360R resistor in AKM's Recomended ak4499 IV stage did not affect output levels.
Im wanting to try passive resistor IVs but sure how to go about it.
