[Aurora13]

Hi Steve,

I'm going to buy a Tact TCS Mk.II with 3 Tact S2150's (curently have one S2150). What is the best way to connect my HTPC to it?

USB Off-Ramp Turbo 2? And if yes what connector options should I use (S2150/TCS accepts for S/PDIF both RCA and AES/EBU):

1. Captive S/PDIF coaxial cable with copper Eichmann Bullet-RCA Plug (standard)
2. Captive S/PDIF coaxial BNC output instead of Bullet-plug (75 ohm Neutrik BNC)- no charge
3. AES/EBU output instead of S/PDIF coax - $150 additional
4. RCA jack instead of captive cable - $15 additional
5. AES/EBU jack instead of captive cable (must also have option 3) - $25 additional
6. Nextgen copper 75 ohm plug on captive cable - $120 additional
7. Nextgen copper 75 ohm jack - $60 additional

Or should I wait, because I read somewhere you were making a I2S interface for Tact equipment?

Thanks in advance for your advise.

[audioengr]

Hi Steve,

I'm going to buy a Tact TCS Mk.II with 3 Tact S2150's (curently have one S2150). What is the best way to connect my HTPC to it?

USB Off-Ramp Turbo 2? And if yes what connector options should I use (S2150/TCS accepts for S/PDIF both RCA and AES/EBU):

1. Captive S/PDIF coaxial cable with copper Eichmann Bullet-RCA Plug (standard)
2. Captive S/PDIF coaxial BNC output instead of Bullet-plug (75 ohm Neutrik BNC)- no charge
3. AES/EBU output instead of S/PDIF coax - $150 additional
4. RCA jack instead of captive cable - $15 additional
5. AES/EBU jack instead of captive cable (must also have option 3) - $25 additional
6. Nextgen copper 75 ohm plug on captive cable - $120 additional
7. Nextgen copper 75 ohm jack - $60 additional

Or should I wait, because I read somewhere you were making a I2S interface for Tact equipment?

Thanks in advance for your advise.

Tact is one of the pieces that I'm interested in developing an I2S interface for.  I have had other inquiries like yours.  I can Kludge one in quickly using my current Off-Ramp I2S board, but in order for you to have the full functionality, I will probably have to install switches for selection between 16/44.1 and 24/96.  Also, depending on the chips used inside and the "mute" controls, there may be a hazard of DC or loud pops on the outputs if you were to suddenly pull the USB cable or the power to the Off-Ramp board (say if you were powering it from a battery externally).  These are the things that make the "quick and dirty" I2S interface somewhat hazardous and not very user friendly.

This is why I have designed special I2S interface boards and flex-circuits for the AirPort Express, the DEQX, my Spoiler DAC and the Benchmark DAC-1.

Therefore, if you want a bullet-proof solution that sounds great right now, I would recommend the Off-Ramp Turbo 2 with captive AES cable or AES jack.  The captive cable is preferred, but it is only about 1 foot long.

Steve N.

[welwynnick]

How would that work? 

On the face of it, it makes a great deal of sense.  The usual audiophile configuration using one of the increasingly common digital power amps is: Transport -> DAC -> Controller -> Power Amp.  The first interface may be SPDIF or even I²S, but the others will be analogue, which is ironic given the digital final stage.  So the TACT combo could avoid the redundant DAC and ADC stages if the digital Controller -> Power Amp interface is used.

Sounds very promising, but I'm curious about the implementation.  A digital power amp is a bit like a DAC in itself - just a speaker level DAC, rather than a line level one.  But when a DAC takes a digital audio stream from a player, it is taking the timing information from the player - either in the bit stream, or in bit/word clock timing data being fed forwards from the transport to the DAC. 

TACT combo or integrated amps are different because they take digital audio inputs.  If you add an I²S input, Steve, what timing information will be used to drive the output switching stage?  With most digital amps I believe this comes from an internal clock, but won't there be a clash between the I²S clock from the transport and the amp's own clock?

BR,   Nick

[audioengr]

How would that work? 

Sounds very promising, but I'm curious about the implementation.  A digital power amp is a bit like a DAC in itself - just a speaker level DAC, rather than a line level one.  But when a DAC takes a digital audio stream from a player, it is taking the timing information from the player - either in the bit stream, or in bit/word clock timing data being fed forwards from the transport to the DAC. 

TACT combo or integrated amps are different because they take digital audio inputs.  If you add an I2S input, Steve, what timing information will be used to drive the output switching stage?  With most digital amps I believe this comes from an internal clock, but won't there be a clash between the I2S clock from the transport and the amp's own clock?

The clock that is currently derived from the S/PDIF data stream will instead be directly delivered to the DAC chips inside from the I2S interface.  This is how all of my I2S interfaces work.  The normal output of the S/PDIF receiver is just replaced with the I2S interface.  If you look at both of these interfaces running on a scope they look identical.  To the TACT, the I2S interface just seems like another S/PDIF interface.

The clock that is used for the switching amp function is probably an entirely different one.  This clock is generally in the 500kHz range and may be variable, and asynchronous to the input stream.  The TACT uses a DSP function to capture the input data at very high frequency (probably at least 10 MHz) and convert this to the appropriate pulse-width modulation.  The data from the interface is only coming at a maximum of 96kHz, so each word probably sits in a register waiting for the DSP engine to read it for an eternity compared to the 10MHz DSP frequency.  I'm sure that it looks at a series of sample points and does some math to determine how to change the pulse-width modulation.  Then it has all the time in the world to determine the proper modulation changes to make for the next interval.  Then it looks at the next set of sample points, probably overlapping with the last points to do the calculation.  So, even though the DSP engine is asynchronous to the input stream, it is so much faster that it can wait for a "data word ready" signal and then read each word asynchronously.  Think of it this way:  for each data tick, there are at least 100 CPU ticks.

Steve N.

[jhm731]

Have you worked on TacT equipment?

The amps can take a 192K input signal.

The input signal is upsampled to 384K before conversion.

Clock is 98MHz.

[audioengr]

Have you worked on TacT equipment?

The amps can take a 192K input signal.

The input signal is upsampled to 384K before conversion.

Clock is 98MHz.

No, I have not ... yet. Makes sense to me.  This is what I expected.

steve N.