[mbd2884]

Hello Head-Fiers,

Allow me to pick your brains and help me understand some terminology and how they work. I tried googling some stuff, but I don't understand as I have no engineering or electrical background.

So if you have patient can you explain some terminology for me?

As I went through Audio-dg's website and the Compass thread, these are the questions I have.

Is HDAM and Opamp being used interchangeably? I read from Marantz that HDAM is their proprietary technology, so confused me that Audio-dg would sell proprietary Marantz technology.

What is an HDAM?

What is an Opamp? I gather Opamp can be used to increase gain? And try to balance input and output, but I don't really know what that means. I also don't understand how it can affect sound.

If an amp is discrete means there is no Opamp? So what is the difference between discrete and having an Opamp.

Kingwa said the Compass has a discrete amp so no Opamp. But he is selling the Compass with an Opamp. I don't quite understand why or how it will affect the sound. It seems its just another point where sound is processed, and I see a Head-Fi thread saying people prefer the sound to be processed last by the DAC and that is it. Quite confused.

I noticed on Audio-dg's website, it doesn't seem any of their DACs or Amps use their Sun, Moon or Earth Opamps, so why do they sell them?

If you can answer my questions, I would very much appreciate it, and well I will have learned a lot of new stuff today.

Thanks.

 

[Sherwood]

I'll see how well I can do, hopefully without causing too much confusion,

An HDAM is a kind of opamp. It can be used in place of an opamp, but it is designed to sound better. Marantz first developed the technology, and the units that Audio-dg sells are adaptations of Marantz' designs. They are also called HDAMs just for clarity -- they are not exactly the same thing.

An opamp is a kind of integrated circuit. It performs numerous functions in an amplifier, none of which are terrible simple to explain without a knowledge of electronics.

"Discrete" refers to an output stage of an amplifier that is designed with common parts -- resistors, diodes, capacitos, etc. -- instead of an integrated circuit (opamp). an HDAM is a plug-n-play discrete output that can be plugged into an opamp slot, making it a kind of opamp/discrete hybrid.

 

[mbd2884]

Alright, so it seems from just browsing amps, I see a lot of the high priced ones are discrete.

So if it makes sense to use common parts without an integrated circuit, why do some of the lower quality amps use Opamps? Is it just an easier way to mimick the sound of high priced discrete amps?

And just a brief description like the english above, what exactly do opamps do?

But the most confusing part is, Kingwa says the Compass is a discrete amp, but on one of the diagrams it shows a socket for his Opamp and that the moon Opamp will come as default with the Compass. I don't understand what the Opamp is doing in the Compass.

Thanks for the explanation above, helped me to understand a bit more.

 

[Sherwood]

An opamp serves a lot of functions, none of them so simple as "gain" or "balance". It compresses an entire circuit, comprised of many separate components, into a small, prebuilt package. I don't have the skill to sum it up, but wiki does.

Discrete amps are more expensive because they require much more engineering. The output stage needs to be designed and assembled. An opamp can substitute an entire output stage, or can serve specific functions within an output stage. The compass looks to be usnig its HDAM in the latter capacity -- as a component of a discrete output. Since the HDAM is itself a discrete component (since it is not an integrated circuit, but a small circuit board usnig premium parts) the output stage can still be described as "discrete", even if some parts of it are based on the HDAM.

In general, discrete refers to a design built using more expensive parts, and necessarily demanding more expertise in engineering. The best products are discrete, though discrete in itself is not a mark of quality necessarily.

 

[nikongod]

Quote:

And just a brief description like the english above, what exactly do opamps do?

By rough definition an opamp is a device which has these characteristics:
infinite input impedance
infinite open-loop gain (gain is purely defined by external feedback)
infinitly low input capacatance
and zero offset voltage as the "input" passes to the output.
Infinte frequency bandwidth (from DC to light)

In practicality they dont meet the ideals, but they are easy to use and design because any flaws in your design are ultimately corrected by the huge ammounts of feedback.

The term "amplifier" can be applied to an op-amp (which is a specific type of amplifier) BUT has some interesting things. By not imposing the "restrictions" on the various input, and gain parameters, the design can be made to have lower distortion BEFORE the application of feedback.

When you look critically at the many things feedback does, you quickly see that it dosnt ELIMINATE distortions, but rather moves them around. The general trend is to use lots of feedback to move a LARGE lower order distortion (which would be obviously audible and BAD) into the higher orders where its smaller and less obvious. Tests have shown that these distortions at high order are discernable.

OOH, you can make opamps with tubes as well as transistors. They existed before transistors, but nobody used them in audio because its less expensive to build a tube AMPLIFIER than a tube op-amp. Some newer tube designs have approached op-amp levels of feedback but thats different.
Quote:

Originally Posted by mbd2884 /img/forum/go_quote.gif So if it makes sense to use common parts without an integrated circuit, why do some of the lower quality amps use Opamps? Is it just an easier way to mimick the sound of high priced discrete amps?

A discrete amp can be a discrete amplifier OR a discrete op-amp.

The only thing you are gauranteed of with a discrete amp is that there are a bunch of separate transistors as opposed to one "chip". This allows the designer greater flexibility in how "hot" to run the individual transistors but beyond that you can make either with discrete parts.

 

[Sherwood]

Quote:

Originally Posted by mbd2884 /img/forum/go_quote.gif Yeah I got the basic gist of what he said, and understand the difference between the HDAM and Opamp now. But the questions I have now are: When does one choose to use an Opamp, and when to go with a discrete design? The other is related to Audio-gd. Kingwa stated that the Compass amp is discrete with no Opamp in the Amp section, but the Compass will arrive by default with his Moon Opamp. I don't understand what the Moon Opamp is doing or where it is. Link to the Compass with schematics and pictures of the board. н¨ÍøÒ³ 1 I personally think it would be really great if one of the Head-Fiers here could volunteer to write up two Stickied threads to explain Solid State Amplifier with my questions included and one for Vacuum Tubes. So it will really help anyone interested in headphone amps to understand what it is they are looking for, and what it is they are reading about. It would strengthen the community around headphone amplifiers and make for smarter, more knowledgeable lurkers, better conversations.

(continued)

 

[Sherwood]

The choice to use an opamp is always to save money or space. An opamp is a compromise.

To clarify -- the Audio-gd Moon, Sun and Earth are NOT opamps in the traditional sense. They are discrete circuits. They serve the same function as opamps, but they use discrete components. An output stage using Audio-gd HDAM units would still be discrete.

I doubt the sticky will materialize, as your questions aren't about amplifier design, so much as about the Audio-gd compass. Useful information, sure, but only to people who care about the compass, and other audio-gd products.

 

[mbd2884]

Yeah I meant if someone could volunteer by creating 2 new threads, one about tubes, one about solid state as a general FAQ about them. Stickied.

Thanks for your input Sherwood and nikongod. Made everything a lot easier to understand.

And it appears he placed the OPA as he calls them on the DAC unit. I'm guessing its DAC to OPA to AMP.