Just ordered a Trends 10.1 Class T Digital Amp - A whopping $130

[Deang]

You plug POTs into a VOIP router use a VPN to get to another VOIP router with a POTs plugged into it and talk over it.... analog in, analog out.... is it an analog connection?

No, it's digital. You suck.

[sfogg]

"PWM is not the same purpose as PCM. PWM in these amps creates no digital words or bytes or nibbles or even bits."

PWM is different then PCM so no, there wouldn't be digital words.

If you don't think there are bits look again. What is a bit? It is simply a binary value. If you hooked up your scope to the L/R data feed to the DAC in your CD player what will you see? Nothing more then square waves... a binary value... on or off, high or low..etc..etc. You can correlate those bits if you also look at the L/R data clock and the bit clock and see which square waves are which words and such... but at the root it is all just bits... represented by square waves.

A PWM is also just square waves. Instead of being formed into words for a sample the bits themselves vary in width... the square waves are wider or narrower. PWM is binary... the signal is in one of two states... on or off.

"We wouldn't call an FM Tx/Rx process "digital". PWM and FM and AM are just different modulation schemes."

FM and AM are not binary. They are a linear modulation scheme from their carrier.. the modulation has more then one of two states. That is why they aren't digital. Of course either modulation scheme can carry digital data too.

"In order to have a digital scheme, you have to sample a signal and convert the sample into a binary coded word, or byte or nibble and process those words, bytes and nibbles along a bus, registers and so on."

That is when talking about PCM, PWM is different.

"None of which is involved in a PWM amplifier. That's why there is no DAC or ADC."

Not a PCM DAC or ADC, but there is effectively a PWM A/D and DA in them.

Shawn

[sfogg]

"In order to have a digital scheme, you have to sample a signal and
convert the sample into a binary coded word, or byte or nibble and
process those words, bytes and nibbles along a bus, registers and so
on."

That is when talking about PCM, PWM is different."

For another example of a digital system that doesn't code into words check out Sony's DSD system which is used on SACD. Be warned you will read lots of marketing hype about it.

Shawn

[DrWho]

Mike Wyatt, Audio Magnus, says that Trends is now working on a preamp. Now, if only we could find a Dobly/DTS package with 7.1 we'd have a winner.

How bout 7.1 with active bi-/tri-amping? I think one will be due out sometime around Christmas of this year... []

[DrWho]

"In order to have a digital scheme, you have to sample a signal and

convert the sample into a binary coded word, or byte or nibble and

process those words, bytes and nibbles along a bus, registers and so

on."

That is when talking about PCM, PWM is different."

For

another example of a digital system that doesn't code into words check

out Sony's DSD system which is used on SACD. Be warned you will read

lots of marketing hype about it.

Well technically you could still argue that it has words....the

words just exist in the time domain instead of the voltage domain. []

This discussion should revolve around comparing against SACD, because SACD uses the exact same sigma delta modulation scheme.

At the very input of most of the digital chips on the market, the

signal is going through a sigma delta modulator. This modulator

basically compares the input signal with a triangle wave and outputs a

1 if the input voltage is greater than the triangle voltage and a 0

otherwise. The reason you run the triangle wave at such a high

frequency is to ensure that you don't alias the signal and turn high

frequency information into low frequency information. The "amplitude"

of the signal is stored in how long the bit remains a 1, whereas in PCM

the voltage level captures the amplitude. Digital circuits have more

predictable time behavior than voltage behavior which is why the

digital amps can be so simple and sound so good.

Yes, the input is analog and the output is analog. But in the middle

there is a box that converts to digital, another box that amplifies the

signal, and then a third box that filters it back to analog....though

some of the chips don't even bother filtering the output! They can rely

on the speaker to finish the lowpass filter (since speakers can't play

400kHz...). The ones that don't filter, however, are using negative

feedback to keep the frequency response stable. That's probably

confusing the issue so lets just pretend that they all output an analog

signal.

Anyways, just to stress the point...SACD uses the exact same encoding

scheme. That's why I keep saying that if you claim that digital amps

aren't digital, then you are claiming that SACD isn't digital. I have

no qualms with that other than it makes the term digital meaningless -

but it won't change the fact that SACD sounds better than vinyl []

(ok, though I mean it wholeheartidly I should mention that was intended

as a joke).

[DrWho]

I forgot to mention...

You can achieve the exact same signal as SDM with PCM by varying the clock driving the A/D.

[sfogg]

"Bits are a sub-part of a byte or word - a data carrying and storage unit to be operated on."

Bits are only a sub-part of a byte or word in multi bit systems. In single bit systems that is not the case as there is no concept of a 'word.'

"A bit is not such because it is a pulse, it is such because it is part of a byte."

Nope. Again you are completely ignoring single bit systems.

"I suppose anytime one sees a pulse train one could think of bits and bytes and digital processing, but in these PWM amps there is no such organization of the pulses into bytes, or words that are stored or manipulated."

Again, you are thinking in multi bit systems. In single bit systems there is no organization into words.

"but I would contend that for a circuit to be "digital" it must be manipulating discrete data in words, bytes and bits. "

Again, that completely ignores single bit systems which are digital. Ever do any programming? If so have you ever declared a boolean variable? If so that is a single bit that is not part of a word/byte and it most certainly is digital.

"An ADC is a wholly different electronic process, which creates a different "thing" --namely bytes or words at some sampled rate. "

No, a PCM ADC samples one point of the wave per sample and that point/sample is defined by the bits that make up that word. It is the sampled points that capture the wave, not the words themselves. On playback the PCM DAC simply plots those different points (creating square waves of varying amplitude) and the analog reconstruction filter then turns that back into continuous analog waves. Single bit PWM works totally differently but it still converts analog into a digital state.

Shawn

[DrWho]

If there are words in a PWM amp, please tell me the word length, the start and stop bits, etc? Remember, just quantifiable DATA - no "fancy meaningless hype and chatter." And, what actually does SACD have to do with PWM amplifiers anyway?

Hello? Digital amps are using sigma delta modulation. SACD uses SDM just like digital amps use SDM. You can't use the descriptive terminology for a specific type of digital to describe all types of digital.

[sfogg]

"Hello? Digital amps are using sigma delta modulation. SACD uses SDM just like digital amps use SDM."

Which is why SACD and digital amps have very similar noise characteristics.

Shawn

[pauln]

Trends may be using Intersective rather than Sigma Delta... someone

somewhere must know how these things work, anyone asked the

manufacturer?

[whell]

Well hells bells, all this tech talk is truly fascinating, but I'm listening to the little Trends again tonight, and I'm still thinking it sounds pretty darn great. I've got the Honky Chataeu SACD playing, and it certainly has the RF-7's singing sweetly.

FYI, if any of you are thinking about springing for one of these, the Audiomagus.com site is saying the the manufacturer is raising the prices on these after May 31.

[bhendrix]

I have no expertise in amp design, but enjoy the quality sound this little bugger delivers.

The manufacturers seems to think they are digital amps. From the Tripath website, http://www.tripath.com/tech.htm:

Audio

In Audio, Tripath is enabling personal computers to have home theater quality sound systems. In home and car sound systems, Tripath technology is enabling systems with more power in smaller, lighter configurations. Tripath has used its Digital Power Processing technology to create a new breed of digital audio amplifiers referred to as Class-T® amplifiers.

Class-T® digital amplifiers provide the audio fidelity of traditional linear (Class-A/B) amplifiers with more than twice the power efficiency of these devices. This leads to higher levels of integration and smaller packages at the semiconductor level. At the system level, these advantages reduce the size of power supplies and heat sinks and significantly reduce the heat management challenges of today's dense, complex electronic systems. While pulse width modulated (PWM) switching amplifiers (Class-D) can also achieve similar power advantages, none have been able to do so without a significant compromise in audio fidelity. Hence Tripath?s new designation, the Class-T® digital amplifier the new standard in audio performance and power efficiency. For more details on Tripath's Class-T® technology you can download the white paper below.

Tech paper available here:

http://www.tripath.com/downloads/TLD401.pdf

[sfogg]

Mark,

"Again you are referring to "PCM" and "ADC" which are digital circuits, but there is no PCM or ADC in the PWM amplifiers I was discussing. Not sure why you keep changing apples to oranges, but it's no big thing to me either."

I am not comparing apples to oranges. You keep claiming they aren't digital because their are no words. I'm trying to explain to you why that is. There is an ADC in the amp, just not a PCM one but a PWM ADC. Apples to oranges is trying to fit a 1 bit system into a word.

"But I hardly understand why you insist on talking about "PCM" when all I have ever been mentioning here is PWM in these amplifiers."

Mark, you are the one that keeps insisting digital must have 'Words' in it, not me. Words are a part of a multi bit system such as pulse code modulation, not single bit pulse width modulation.

"The makers of them don't think they are digital, but what do they know?"

Really? Then why is Tripath (the chip in the Trends amp) white paper on their amplifier labeled:

"CLASS-T DIGITAL AUDIO AMPLIFIER TECHNOLOGY OVERVIEW"

with quote like:

"A Watershed in Digital Amplification

Tripath Technology has developed a category of digital audio power amplifiers using a

unique technology. Tripath amplifiers use a completely new proprietary method of Digital

Power ProcessingTM that provides superior performance to conventional methods of

amplification."

or in some of their other papers quotes such as:

"Switching Amplifiers

Alternatively, switching amplifiers produce audio signals by modulating a rapidly alternating digital (or

two-state) voltage so that its averaged (or low-pass filtered) voltage represents the desired audio signal.

The switching frequency is always much higher than the highest frequency of the desired audio output

signal, usually 10 times or more. This rapidly switching output signal is passed through a filter

comprised of capacitors and inductors (which are ideally lossless components) before being passed to

the speakers. The advantage in using this switching output approach is that the power output

transistors, usually MOSFETs as shown in Figure 1, are ideally never operating in mid-conduction and

instead operate much like switches either fully on or fully off. When on and conducting current to

the speaker, each transistor acts like a closed switch, with zero voltage (V = 0) across its terminals and

therefore P = V x I = zero, ideally yielding no wasted power. Of course, when off the switch is open, I

= 0, and the wasted power is also zero.

As a result, the digital amplifiers efficiency is far better than its conventional Class-A, -AB, or -B

counterparts and can reach 80% or 90%. In contrast, linear amplifiers are usually less than 50%

efficient. The high efficiency of digital amplifiers can be a critical advantage in systems where

excessive heat can be a problem, such as in multi-channel surround audio receivers or enclosed

systems such as powered subwoofers. Also, in applications where power is at a premium, such as

battery-operated portable stereos or laptop/notebook PCs.

"

and

"Tripath Class-T Digital Amplifiers

Tripaths Digital Power ProcessingTM technology, which forms the basis of its Class-T amplifiers, uses a

proprietary approach to create a new class of amplifier. Unlike a linear amplifier, Tripath drives the

output transistors with a digital signal, a series of 1s and 0s whose amplitude is fixed, giving Tripath

amplifiers the efficiency advantages of a switching design. Unlike a PWM Class-D amplifier, Tripaths

technique digitally switches the output across a high frequency spread spectrum and contains

predictive and adaptive feedback to constantly adjust and dynamically change its digital switching

characteristics. This technology gives the Tripath Class-T amplifier the audible sound quality as good

as the highest performing linear amplifiers. The amplifier digital adjusts its algorithms based on the

input signals and output load characteristic"

and

"Tripath Class-T Digital Amplifier Advantages

Digital amplification offers distinct advantages over conventional, linear or PWM amps:

Smaller, cheaper power supply (less wasted power)

Smaller, cheaper heat sinks

Greater circuit density, smaller form factors (less need for heat transfer and air circulation)

Lighter-weight products

Higher wattages in single chassis systems (e.g. sound reinforcement)

More channels (e.g. home theatre/surround audio) without the need for a fan

Longer battery life in portable systems

Dramatically higher fidelity compared to Class-D PWM amplifiers"

Tell me again how the makers of the chip that the Trend uses don't consider their chips digital?

But what do they know....

Shawn

[bhendrix]

Apparently, you're both right. According to Tripath, they use both digital and analog technology:

According to Tripath:

Tripath Technology has developed a category of digital audio power
amplifiers using a unique technology. Tripath amplifiers use a
completely new proprietary method of Digital Power Processing that
provides superior performance to conventional methods of amplification.
For the first time, both high signal fidelity AND high power efficiency
can be achieved with the same technology. Tripath refers to this DPP
based amplifier as a Class-T design. The underlying technology of
Class-T does not use PWM and is not a pure analog approach (Classes -A
and -AB). It combines the benefits of both with a completely new approach.

Tripath Class-T technology uses both analog circuitry and Tripaths
Digital Power Processing algorithms that modulate the input signal with
a high-frequency switching pattern. Tripaths proprietary algorithms are
derivatives of adaptive and predictive algorithms used in
telecommunications processors. 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 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 block controls a
power output stage that drives a speaker through an output filter.


Hope this helps!

Mike

Mike Wyatt
www.audiomagus.com
tel: 360.551.6945
fax: 206.238.3130
email: mwyatt@audiomagus.com

[maxg]

I have now heard this argument a dozen times on different forums - as to whether a PWM amp is, or is not, digital and am still none the wiser. I think it is about 6 each in wins - allocating this discussion to a yes PWM is digital.

My question is this.

If a PWM amp is digital why do they always only have analgoue inputs? It seems to me to be totally insane to have an audio chain (starting, for example, from a CD player) where we go from the digital (PCM) data from the CD player - out through its DAC into the analogue connection of a PWM amp to be converted into digital data, to be amplified, to be converted back into analogue data to go out to the speakers.

Wouldnt it make a whole lot more sense to take a digital output from the CD player - straight convert that into PWM and then only convert into analogue at the final stage prior to heading out to the speaker?

Am I missing something vital here?

[DrWho]

Wouldnt it make a whole lot more sense to take a digital output from

the CD player - straight convert that into PWM and then only convert

into analogue at the final stage prior to heading out to the speaker?

Am I missing something vital here?

That is exactly something I will be building this upcomming Fall! Digital fed directly into the digital amplification stage. While you could build an implementation that works with PCM, adapting exhisting digital amp technologies will require that you convert the PCM into the appropriate digital signal. I have no experience with this process, but have read that it's a fairly straightforward transformation.

The timing of this thread is rather wild too...I was just looking up some digital chips with a friend where we ran across descriptions talking about CMOS...it don't get any more digital than CMOS []

[maxg]

Thanks Who,

But there is still something not clear to me. I can see that the PWM amp is digitally controlled - but it is handling digital data? In other words imagine a microprocessor controlled faucet that varies the flow according to some kind of feedback mechanism. There are all sorts of digital things going on - but the flow of water is not, in and of itself, digital - merely the control is. Isnt this what is actually happening to the "music signal" here?

[sfogg]

Max,

"If a PWM amp is digital why do they always only have analgoue inputs?"

They don't always have analog inputs. Check out Tact amps... digital inputs on them. Check out the digital amplifiers in some receivers such as the Panasonics. You feed them a digital signal and it stays digital the whole way through.

As far as why they normally have analog inputs.... 'cause those are the ones they can sell. Not too many people are equipped to hook up S/PDIF connectors to their amplifiers.

Shawn

[sfogg]

Mark,

"Yup, Tripath refers to it as Digital - on that there is no argument."

Good, since you earlier claimed otherwise.

"Again, there is simply no A to D conversion of the signal, but there is a different means of creating the PWM signal,"

The PWM signal is created by an A to D.... a PWM A to D.

"and I think a DSP is used to generate the feedback signal"

Pretty sure the feedback is analog actually.

"but having a DSP doesn't make it a digital amplifier necessarily. But then again, DSP has the word "digital" in it, so if one is glued on the board, I guess it must be digital."

*If* the signal were passing *through* a DSP the signal is digital, no ifs ands or buts about it. But I don't think it actually does pass through a DSP (because it is very hard to process 1 bit systems) but that it uses a DSP to alter the modulation frequency.

"As an aside, you have misunderstood my comments about "bits" and "words" and how either of them relates to "pulses" or a "modulated signal.""

Maybe so, but what you have posted so far appears to try to make the point that a bit is not a bit if it is not part of a word. That is wrong any way you slice it.

In order to have a digital scheme, you have to sample a signal and convert the sample into a binary coded word, or byte or nibble and process those words, bytes and nibbles along a bus, registers and so on.

These are not bits, they are just pulses of varying duration which might look a lot like bits. Bits are a sub-part of a byte or word - a data carrying and storage unit to be operated on. A bit is not such because it is a pulse, it is such because it is part of a byte. I suppose anytime one sees a pulse train one could think of bits and bytes and digital processing, but in these PWM amps there is no such organization of the pulses into bytes, or words that are stored or manipulated.

"And, here there is a huge distinction between a PWM signal (100% analog) and a 1-bit DAC with Delta Sigma (100% digital) . "

And again... a PWM signal is not 100% analog. Look at any PWM signal and show me any sort of linear signal to it. All it is is a 1 bit digital signal that is in one of two states.... on or off.

Shawn

[Daddy Dee]

Max,

Have you ever had the chance to hear one of these little guys?