Analog Stages and CDPs

[steve]

Steve,
            I was thinking that a TVC could be used in lieu of the analog board in a CDP. I personally did not experience any problems with the TVC as far as gain, use of long ICs, freq. bal issues. Resonance problems yes. When the Trannie was mounted on Ebony and the sides treated with BHP they seemed to go away. The quality of the trannie is key. A balanced double "C" core or "R" core done right should be just fine. What I do not understand is how to get the voltage required to drive the Amp directly from the CDP I described.

rollo
           

Hi Rollo,

  In place of the analog stage is worth a try. Like you said, will depend on the quality of the tranny, frequency balance etc.

Signal voltage may not be a problem since bypassing the analog stage only lowers the gain about 6-8db, might check your machine. Either a good active preamp or integrated amp should work.

[_Scotty_]

rollo, see this link as for an explanation of resonance. http://stereophile.com/solidpreamps/106sonic/index4.html
The transformer interacts with the load and can produce a number of problems.
The rising distortion at low frequenciies illustrates why the bass dynamics and extension seem lacking.
Transformers don't conduct DC and as the frequency decreases the transformers distortion rises.
The peaking at ultrasonic frequencies is the resonance effect that Steve was referring to.
The characteristics the TVC exhibits in the course of measurement for the review are typical of a transformer. The device is simple enough that basic physics and electrical parameters can be used to describe its' behavior.
Scotty

[steve]

rollo, see this link as for an explanation of resonance. http://stereophile.com/solidpreamps/106sonic/index4.html
The transformer interacts with the load and can produce a number of problems.
The rising distortion at low frequenciies illustrates why the bass dynamics and extension seem lacking.
Transformers don't conduct DC and as the frequency decreases the transformers distortion rises.
The peaking at ultrasonic frequencies is the resonance effect that Steve was referring to.
The characteristics the TVC exhibits in the course of measurement for the review are typical of a transformer. The device is simple enough that basic physics and electrical parameters can be used to describe its' behavior.
Scotty

Hi Scotty,

     There is even more Scotty. The capacitance that the secondary sees (stray, interconnect etc.) is multiplied by the ratio of the primary to secondary. So as the ratio increases (lowering the volume setting) the capacitance the primary sees, and the source sees is increased. Even slight variances in this capacitance changes the high frequency response that one hears.

Too much inductance, or not enough high frequency response due to lack of good interleaving will cause the frequency tonal balance to be off.

Of course we are talking just the transformer, just the volume control. We have not even discussed the following preamp gainstage, which is located in the amplifier.

Take care.

[richidoo]

Is lack of current a significant issue here? For use as output stage in a CDP, you would only have the DAC chip itself as current source to power everything up to the next active stage, including cable capacitance, load resistance, tranny losses, etc. A great DAC like TI's PCM1704, makes 1.2ma output current. Will it clip if loaded more than it's rating?  Is that enough current for typical source component's typical load? Opamps that can drive 200 feet of rubber cable at 600ohms still only make 26ma, so maybe in a purist system with load carefully considered, 1.2 ma from the DAC is enough??

Will amplifying the DAC's output voltage with a transformer further reduce DAC's current drive, by raising impedance I assume?     rollo, I encourage you to proceed with your experiment, but I wanna understand what these guys are talking about while they are on the line
Thanks

[steve]

The resonant peaks are typical for different volume settings. Those resonant peaks affect the highs, causing degradation, a tweeking/brightness of the highs on down.