Discrete or not Discrete, that is the question

[Seth=L]

I have a question that has been bothering me for sometime, so here it goes.

What is the difference between discrete output and....well.....non discrete output transistor configurations.

The non-discrete has one large transistor for the front two channels, and the discrete ones have one or more smaller transistors for just one channel. Why?

 

[JoeE SP9]

Non discrete really means integrated circuit. For power amps it usually means an integrated module that has most if not all of the power amp circuitry on one large chip. Discrete means just that. Discrete separate transistors and assorted components mounted to a printed circuit board.

Non discrete usually has more than one transistor per channel you just can't see them because they are all integrated into one chip along with the necessary resistors and capacitors.

 

[Seth=L]

Any sonic differences? I observed that the Pioneer VSX-815 for example has a two large transistor chips attached to a heatsink, they are in turn cooled by a fan. This seems like a bad configuration to me.

I also have a Sony receiver, a really cheap one, from a couple years back. It has a discrete output stage and has two transitors for each channel. Now people rave about these pioneer receivers and everyone downs the Sony ones, but it seems to me the Sony receiver is more thoughtfully designed.

 

[JoeE SP9]

All competently designed and manufactured amplifiers should sound pretty much the same when used within their power limitations.

The fan may be there for loads less than 8 Ohms.

In today's world most receivers are built to a price point not a quality point.

It's more economical to use amplifier modules than discrete transistors.

 

[Ampdog]

Some further remarks (I design amplifiers).

Seth, what you see in an IC as a "power transistor" is actually the heatsink for 4 power transistors, apart from the rest. These transistor elements can be some 5 x 10mm in size for a fair output IC. The circuits for both topologies can be quite the same basically; the advantage of an IC is that temperature drift can be well-controlled because everything is on the same substrate. Those designs are "transistor-rich", because transistors are smaller than resistors and thus easier to accomodate. Capacitors are rather difficult to put in, they are comparatively large in size. Also transistor elements can be matched quite closely because all is made in the same process.

On the other hand discrete components in a very high quality power amplifier can be rather better proportioned to meet certain requirements e.g. a wide open-loop bandwidth. (That translates into maintained negative feedback over a wider frequency range than ICs are capable of - not to go into further details.)

One can thus say that very good sound quality can be obtained from power ICs and at quite an economy (a very strong point in favour of mass production). But a properly designed discrete power amplifier could sound "cleaner". But that is also very much a factor of the design; I am afraid one gets some horror shows on the market either way. One can always make something a little worse for a little cheaper, scoring on mass marketing expense in the end.

 

[Seth=L]

So cheap receivers like my Magnavox probably don't sound good next to most discrete output stage designed amplifiers. Do any high end amplifiers use the non-discrete configuration?

 

[Ampdog]

Seth,

I must apologise for sounding like a cheap lawyer, back-door open. "Can be, properly designed" etc. Not all amplifiers are properly designed (not intending to be arrogant). Thus your Magnavox might well sound better than some more expensive discreet component designs. I am unfortunately not familiar with most commercial designs. I have seen the circuit diagrams of some, and some could be improved. How to put it: I would say that it is easier to get I.C. products sounding good - they "come" with much of the circuit finished at the I.C. factory. But as mentioned, if I need a "blameless" amplifier I would use discrete components because I can design the (smaller) imperfections of I.C.s out of the circuit.

That leaves you without a simple reply, but I hope you understand what I am stating. I rather think most high-end circuits use discreet designs, no ICs that I have encountered. But I am not familiar with enough of them to say. Hopefully someone else can shed light here. The things to look for (which most do not give!) are phase and loop gain graphs.

 

[Seth=L]

I wasn't thinking of it the way you did, I figured my Magnavox wasn't as good as many discrete amps. I also understand that there aren't many truly discrete amplifiers, and that discrete in most cases only discribes the output stage.

So I.C. configurations are cheaper, and more efficient, correct? But in higher end amplifiers more discrete applications are capable of having higher quality?

 

[JoeE SP9]

As far as I know there are no high end or higher end amplifiers that use any kind of construction but discrete. It would seem that IC amplifier modules are pretty much restricted to receivers which as I already said are designed and built to a price point not a quality/power point.
This goes back to one of the main reasons I have never owned a receiver. For ultimate power/quality only separates can qualify. Also the added flexibility and resale/trade value can't be ignored. A used Adcom GFA-545 amp (for example) will cost $200 today, put out 100WPC into 8 ohms and you can sell it next year for $200. No receiver ever made will give that kind of return on investment. I should also point out, that same amplifier will happily drive loads that will cause a lot of receivers to emit large amounts of smoke and funny smells.

 

[Seth=L]

I agree, and I don't want anymore I.C. powered receivers. The only one I considered lately was the Pioneer VSX-815 or 816, can't remember the exact model, but the only thing keeping me from getting it was that is wasn't discrete.

 

[JoeE SP9]

The only way to really get away from IC power modules is to get away from receivers. I use an ARC preamp for all 2 channel listening. When it's time for MC sources the front channels go from my Lexicon to a bypass on my preamp this way I can use my front speakers and amps for stereo or MC with out re-wiring anything. The rears/surrounds are powered by their own power amps running directly from my Lexicon processor.