[Tubo]

Greetings,

I joined AC a couple of weeks ago and I just received a new Teac amplifier last Friday. Initial impressions with LS3/5A's are good! You guys have good ears!':)'

Here is my first question: Are Tripath amps digital, as Tripath claims, or are they analogue, as some AA inmates say? For example, AA member lne937s writes,

"First of all- the terminology "digital" is wrong. Class D/PWM (Pulse Width Modulation) switching amps are not digital. They switch on and off at full power an analogue signal at a very high rate (+300khz). The width of the pulse is modulated which is sent through filters to generate the audio signal. The pulse is analogue and is modulated through analogue circuits."

On the other hand, Tripath's website has a white paper which states,

"Tripath Class-T technology uses both analog circuitry and Tripath’s Digital Power Processing algorithms that modulate the input signal with a high-frequency switching pattern... The modulated signal is sent to output transistors then through a low-pass filter (external to the Tripath amplifier) that demodulates it to recover an amplified version of the audio input.

"In a Tripath amplifier there is an input stage that provides analog input signal buffering.  The output of this stage drives the Digital Power Processing TM block.  This block contains an adaptive signal conditioning processor, a digital conversion function, mute control, overload handling, fault detection, predictive processing and qualification logic functions.  The output of the DPP TM block controls a power output stage that drives a speaker through an output filter."

Can somebody explain this? Is Tripath saying that there is an ADC and a DAC within the Tripath chip? Vinnie?

Thanks for your help.

Al Lau  

[NealH]

Probabaly switching amplifier is the more appropriate phrase for this amplifier.  Often terms are applied broadly and, viewing this broadly one could make an argument that the Tripath is digital - to an extent.  

The Tact has a switching output also so, in this respect it's no different than a Tripath or other class "D" switching type amplifier.

The Tact does appear to skip one conversion stage though, if fed directly from a transport's digital output.  It takes a digital sample and, using it's built in algorithms converts this to a class "D" type switching output signal.  Filters are also included to remove most of the out-of-band artifacts, and passing on the amplified version of the original signal - just as in the Tripath.  

Does this necessarily mean the Tact is better?  Not really.  If all things are equal then I could accept the argument however, in audio designs things are seldom, if ever equal.  Tact enters the arena with a decided  advantage, and they appear to make well of this advantage, but it does not mean it will automatically be the best approach when comparing different system configurations.  In most cases maybe, but not always.  It's always possible that some other implementation of the specific modulation algorithm could offset the advantage of one less input conversion.

[Vinnie R.]

Probabaly switching amplifier is the more appropriate phrase for this amplifier.  Often terms are applied broadly and, viewing this broadly one could make an argument that the Tripath is digital - to an extent.  

I agree with rnhood...it can be a little confusing.  

I view a "real digital amp" as an amplifier that inputs a digital signal, amplifies it in the digital domain, and outputs an amplied digital signal.

Tripath technology is more of a "hybrid" type amplifier.

Class-T amplification inputs an analog signal (from your source or preamp), buffers it, and then it passes to what they call a DPP section that modulates this analog signal with their proprietary switching algorithms (which does NOT convert it to a traditional PWM signal...it is more like spread-spectrum) that are variants of adaptive/predictive algorithms use in the telecom field, believe it or not.  The output of their DPP section is what drives the transistor power output stage, and then similarly to Class-D, this amplified switching pattern is passed out of the Tripath chip and filtered via an external low-pass filter to recover and amplified version of the anlog input signal.

Can somebody explain this? Is Tripath saying that there is an ADC and a DAC within the Tripath chip? Vinnie?

Well, there is kind of an ADC inside the chip, but there is not a DAC inside the chip.  The output of the chip is a switching pattern that must pass through a low-pass filter (that is external to the chip) to demodulate the amplified version of the input.  

Hope this helps,

[JeffB]

Vinnie states:
"I view a "real digital amp" as an amplifier that inputs a digital signal, amplifies it in the digital domain, and outputs an amplied digital signal. "

I have to say that, to me, this makes no sense at all.  The digital(1s and 0s) describe the waveform, but they say nothing about the volume of  the waveform.  The 1s and 0s describe a waveform with 65536 discrete amplitude steps, but nothing is stated about how loud the 65536th step is.  I think an amplified digital signal is an invalid statement.

I think of it this way.  An amplifier simply moderates the current delivered from a power supply in such a way that the current flow mimicks the input signal at the desired volume.  If the moderation is performed using digital circuitry then it could be considered a digital amp.  But the flow of current from the power supply to the speakers is always an analog process.

[Vinnie R.]

I think of it this way. An amplifier simply moderates the current delivered from a power supply in such a way that the current flow mimicks the input signal at the desired volume. If the moderation is performed using digital circuitry then it could be considered a digital amp. But the flow of current from the power supply to the speakers is always an analog process....

Yes, this is true and understood.  My point is that I consider a true digital amplifier is one that amplifies a digital signal (amplifies the 0's and 1's).  This may be invalid in terms of an audio amplifier, because we all know that loudspeaker drivers require an analog electrical signal to reproduce sound, not discrete symbols of a real digital signal.  I was just saying that in the strictest sense, I say a digital amplifier amplifies a digital signal ...something you would find in the telecom industry (ex. a regenerative repeaters, which inputs and outputs digital signals!).

In audio land, we're talking about the ouput of a "switching amplifier," which is a modulated analog signal (Class D, Class T, whatever).

Sorry for the confusion, but regarding what Tubo was asking about Tripath, I'd say his answer is correct.

An amplifier simply moderates the current delivered from a power supply in such a way that the current flow mimicks the input signal at the desired volume. If the moderation is...

This makes no sense to me at all!  I never heard of an amplifier that moderates anything!    I hope you know I'm just kidding with you, Jeff.  

Thanks for posting,

[ekovalsky]

The Tact has a switching output also so, in this respect it's no different than a Tripath or other class "D" switching type amplifier.

The Tact does appear to skip one conversion stage though, if fed directly from a transport's digital output.  It takes a digital sample and, using it's built ...

In my system, a TacT RCS 2.2X feeding two S2150 amps via digital link outperformed a dCs Elgar Plus feeding a Jeff Rowland 302/4 ICEpower amp through an high quality XLR interconnect.  This is with the TacT in bypass mode, i.e. without any parEQ or room correction and without a preamp between the dCs & JRDG.  The dCs is designed to drive power amps directly.

My point is that the all-digital TacT system probably does offer benefits over other switch mode amps that take only analog inputs.   Something else that helps the TacT is that it has no volume control -- atteuation is achieved by lowering the voltage of the power supply rails which is very clever.  

My TacT S2150s don't have an analog input, so I cannot compare them with other amps when driving from a DAC or analog preamp.

Besides TacT, BOZ, and Lyngdorf Audio (nee TacT dK), Spectron is introducing two digital-input switch mode amps later this year.  Behold of Germany offers them also but unfortunately the prices are in Burmester and MBL territory.

[JeffB]

Vinnie,

If it helps any with your joking, I develop software for a living.  When it comes to amplifiers I have to speak at a very high level, because I know nothing of their guts.

--Jeff