Is discrete better than chip op amp

[sumotan]

Hi Guys,

Need to hear from your experiences. There's quite a number of ready made discrete op amp on sale now. I wonder how they compare to chip op amps.
Are they worth the money that they're asking for.

Thanks

 

[TMM]

How long is a piece of string?

edit: just realised you meant op amps as opposed to speaker amps.

IC op amps are on average far better than discrete designs, as components can be matched on the die to much better tolerances.

 

[Keruskerfuerst]

What opamps?
low level <=15V or power level?

Low level: opamps are easier to use.

 

[udok]

They are in general not worth the money, if you do not need the higher possible voltage swing or the higher output power.
see SG-Acoustics · Samuel Groner · IC OpAmps (opamp_distortion.pdf)

 

[abraxalito]

Depends what you're looking for - often the discrete opamps are biassed into classA and hence tend to sound better when normal power supplies are used. But you can simply bias the output of an IC into classA with a current source, generally a much cheaper solution than going fully discrete.

 

[udok]

you will not hear anything from a good opamp if you adhere to its specification.
e.g. a lm4562 has better than 130 dB distortion and 0.4 uV rms Noise in the audio band.

 

[Alan0354]

IC opamp has limitation.

1) low rail voltage except of some high voltage opamps. But those are not necessary low distortion or very expensive like Apex.

2) Low power except power opamp like Apex....$$$

I have designed quite a few discrete opamp mainly because of the reasons above. It's only because I have no choice, not it's better.

Hell, most of the hifi power amp we are talking here are discrete opamp. You can see the reason.

 

[AndrewT]

If one can live with the lower voltages, then a composite of Opamp and Buffer can give exemplary performance.

Some headphone amps are built this way.

 

[sumotan]

Thanks guys for the advice. Actually Im looking into low voltage op amps.
I've recently been fiddling with my UCD 400 AD. Already done many tweaks.
Sound has improved much but I would like to turn my attention to the input
stage now. Thought of going discrete input but could not find any data on how
to implement this. While browsing I came across example Burson Supreme
discrete op amp & the thought just came across of replacing the AD 8620
with something like Burson. Yes the cost of it is already half the cost of
buying the UCD 400 HG. Might not sound logical to many but I've always
like to tweak & learn from it. Would appreciate further suggestions pls.

Many Thanks

 

[TMM]

You can always add a high voltage discrete amplification stage to the output of a low voltage opamp and suitably pad down (voltage divider) the inputs to keep it within it's common mode input range.

 

[abraxalito]

From a quick glance at the Hypex appnote, the input impedance of the two balanced phases is different, so the best way forward will depend on how you're driving the balanced in. If you're feeding it a true balanced signal with the two phases out of phase then the impedance seen on the 'cold' input is going to be really low, around 1k. Whereas on the 'hot' side its about 10k.

If you drive these inputs with opamps they'll definitely benefit from being classA biassed.

 

[sumotan]

Hi
Thanks for the advice. The thing is I do not know much about SS stuff. I've read some papers that Hypex uses some form of instrumentation amp design for the input stage. With my limited knowledge, my impression of an instrumentation amp requires either 2 single input or a dual differential input op amp couple to a single output op amp to make one. The think is when I look at the UCD pcb I only see the AD chip so this is a bit of a head scratching for me.
Unable to find a schematic of how the input for the UCD is configured. Hence . Oh read many threads about mods but it seems there are quite a few versions with different pcb lay out & this makes it even more difficult for me to compare notes & make changes

Many thanks again

 

[sumotan]

Thanks Abraxalito. Right now I'm running only single ended.
I also came across a thread that bypasses the op am completely.
In its place is an SRPP tube stage. In threads that I've read the input
to the power stage of the UCD is 1.8K, with such a low impedance how
can the tube stage drive the output stage well. Certainly the output of
the tube stage can't be that low in impedance right ?

 

[CBS240]

If one can live with the lower voltages, then a composite of Opamp and Buffer can give exemplary performance.

Some headphone amps are built this way.

Full bridge output so as to 'double' the output voltage swing......30Vp

 

[Alan0354]

When you actually design a circuit for particular need, you'll know very quickly whether you can use IC opamp or you have to go to discrete or composite. It's all requirements driven. When you cannot find an IC opamp that is good enough, then you have to start thinking about discrete.

It is very hard to sit here talking about which way is superior. It's all about fitting the requirements. The one that can fit the particular requirements is the best for that particular purpose. Not necessary in the general sense.

 

[sumotan]

totally agree with what you said Allan. That's also why I like to play around with
tubes. Many config can be tested just from 1 or 2 tubes. For SS stuff I have limited
experience just that it seems discrete stuff are usually better hence my curiosity

 

[Alan0354]

totally agree with what you said Allan. That's also why I like to play around with
tubes. Many config can be tested just from 1 or 2 tubes. For SS stuff I have limited
experience just that it seems discrete stuff are usually better hence my curiosity

Discrete stuffs absolutely are not better. We go to discrete ONLY if we have no choice. It is my believe the ONLY reason we DIY audio use discrete is we don't have enough of the market for companies to even do the research to put the circuit into IC. I designed IC before. I can tell you there is no limitation in at least putting the IPS and VAS into IC. You might need to break up the OPS to small pieces only because it's easier for cooling.

It is even advantageous to have IPS and VAS in IC form as you can match the characteristics a WHOLE LOT BETTER than if you do it in discrete form. You can match Vbe and beta very close in IC, you can match CCS closely in IC.

It's all about money and marketing. Unless there is a big market, companies are not going to even touch it. they do have chip amp for lower end audio stuffs long time ago already. It's the low volume of the high end stuff that they cannot justify millions of investment where they have so many other things that they can invest in and make billions.