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Old 27th November 2009, 05:58 PM   #1
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Default What makes me believe that discrete is better

My belief is based into observation about "what others do".

Many factories decided to discrete into some critical functions... you see this function generator, not so old to use discrete because old..in the same circuit you see TL022 and some other chips, and those are not that bad.

Why they decided to use discrete into the main amplifier, the one amplifies the tones generated, sending them to the output connector...in other words, a very important stage and using discrete when they could use operational amplifiers.

Not only this application, where you need low distortion into the waveform, but some others you can see industries, professionals, selecting discrete components to produce critical, important circuits.

Observe the simple three stages, a differential, a very standard circuit, a voltage amplifier and the simetrical output, all them class AB ... it is very interesting, as crossover distortions are not good to appear into a waveform generator output.

If professionals, using the same voltage to the supply, having nice operational amplifiers, if they prefere discrete.... of course this is a clue that reinforce my belief that discrete is better.

There are technicall reasons that makes discrete better, bigger physical distance (space) between input to output, not needing too much neutralization against oscilations.... less interactions between parts because heat and magnetic fields..and some others too.

Do you think the opposite?... can you please explain your ideas to uncle Charlie..i will be very happy to read you and to learn some new things...please, destroy my belief!, this will turn myself more wise..each belief dell down to ground will drive me more wise.... increasing my distance from the disgusting ignorance.

regards,

Carlos
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File Type: pdf Simpson 420 - Function Generator.pdf (65.2 KB, 58 views)
File Type: pdf tl022.pdf (91.9 KB, 36 views)

Last edited by destroyer X; 27th November 2009 at 06:28 PM. Reason: include image, pdf schematic
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Old 27th November 2009, 06:25 PM   #2
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Default The output stage circuit

attached.

regards,

Carlos
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Old 27th November 2009, 06:45 PM   #3
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Hello Carlos

I agree with you.

I've listen to chip amps like the TDA7294 and LM3886, they sound good but wen I compared them with any DIY or commercial well design and well made discrete amps, those discrete amps allways have better resolution and soundstage.

Bye

Gaetan

Last edited by gaetan8888; 27th November 2009 at 06:54 PM.
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Old 27th November 2009, 07:30 PM   #4
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The likes of AD797, OPA827 and OPA627 are really hard to beat. At the moment I'm enjoying the combination of OPA827 and OPA627 in a headphone amp. It leaves very little to wish for.

I think one of the problems with opamps is that they sound a bit thin, lacking some fullness. This could be perceived as being detailed and give the impression of a grander sound stage. When measured, most opamps seem to be dominated by 3rd harmonics, and there's very little 2nd. My discrete amps are dominated by 2nd and have some 3rd. Maybe this could explain some of the differences.

On the positive side, it's very easy to upgrade an opamp based amp or DAC when newer and better devices arrive, or when you think it's worth spending some money on those higher grade opamps.

Last edited by nelsonvandal; 27th November 2009 at 07:37 PM.
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Old 27th November 2009, 07:39 PM   #5
Suricat is offline Suricat  Canada
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Carlos,

Good thread you are starting here. I think you will have as many opinions as they are members of this forum.

My take is that it depends what you define as being 'better'. One thing for sure, do not trust these so called professional to make the 'better' choice because they are not necesseraly looking for the same goals. And I am an EE so I know what I am talking about! Who knows, they might simply have chosen a discrete design to simplify legal issues, or because they already have the design so it is cheaper to reuse it. Or the procurement office has a beef with Sanken! You'd be surprise!

For me, using discrete designs allow me to play with the sound. For example, I can change local feedback caps, I can change polarization, I can implement dual supplies, etc. If I'd use an amp IC, simply attaching a supply to it wouldn't be enough to sustain my 'pleasure' and get me the feeling that 'I've done something'.

After, alls we want is to get the same adrenaline rush of exquisite sound as when we heard our first crappy sound project way back when !! :-)

Ciao,

Patrick
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Old 27th November 2009, 07:59 PM   #6
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by destroyer X View Post
.in other words, a very important stage and using discrete when they could use operational amplifiers.
No.
The output must be capable of withstanding a short-circuit at the max amplitude, and at 2MHz. In this case, the output impedance is a mere 600ohm, unlike the usual 50ohm, but even that would have been too much for "normal" op amps of the time

Quote:
Not only this application, where you need low distortion into the waveform, but some others you can see industries, professionals, selecting discrete components to produce critical, important circuits.

Observe the simple three stages, a differential, a very standard circuit, a voltage amplifier and the simetrical output, all them class AB ... it is very interesting, as crossover distortions are not good to appear into a waveform generator output.
A function generator has a pretty high distortion figure anyway, typically 1%, 0.3% for very good ones (I'm not talking about "modern", synthetised F.G's, or AWG's).
An AD797 would easily outclass this output stage on every aspect, and even an humble NE5534 could do a good job too... but not a TL022, or a A741, LM301, etc.

Note that I am not myself an IC "pusher": if you look into the circuits I have proposed, you will see little or no opamps: I am perfectly capable of designing without them, but can also recognize their true value.

One last point: function generators are not designed to be listened to. Or maybe I am missing a point in some new audiophile trend...
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Old 27th November 2009, 08:04 PM   #7
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Default Hello Gaetan, Nelsonvandal and Elvee

Thank you by the contribution..

I see Elvee, op amps cannot withstand with so low impedance for long time...but, if they want op amps because superiority they could use it with a simetrical output transistor pair to support the low impedance job.

regards,

Carlos
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Old 27th November 2009, 08:09 PM   #8
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Hello

Op-amp, because their high gain, need quite a lot of NFB, so the THD harmonics are spreaded to a wide spectrum and with a lot of odd harmonics.

Some op-amps do a better job but most of the times discrete op-amps do a better job, especially for a DAC I/V output.

Bye

Gaetan
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Old 27th November 2009, 08:15 PM   #9
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Quote:
Originally Posted by nelsonvandal View Post
The likes of AD797, OPA827 and OPA627 are really hard to beat. At the moment I'm enjoying the combination of OPA827 and OPA627 in a headphone amp. It leaves very little to wish for.
Hello

There is also the THS4031 and LM4562, but the LM4562 are less good for the soundstage.

I use myself a OPA637 for a phono preamp, the sound of this op-amp are quite close to a discrete circuit amp.

Have you try biasing an op-amp into class A ?

Bye

Gaetan

Last edited by gaetan8888; 27th November 2009 at 08:21 PM.
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Old 27th November 2009, 08:21 PM   #10
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Default Thank you Patrick, i think we wrote same time and i could see your message

latter.... just now.

about definition...better option to engineers decide to put a chip in place of discrete or the opposite...in the reality there's a question hidden into my afirmative, and the question is:

Why they have used discrete instead of chips, as they are using chips in other subcircuits in the same generator, why this option, why not a chip into the output if chips are good enougth to output (having some discrete stage to help face low impedance and shorts of course)

In my belief discrete is much better, and all i want is someone to change my mind about..or to confirm, as i am sure, but not 100 percent sure, maybe 95 percent sure.

One reason is the low impedance, but a simetrical output can fix that and the Generator designer could use a chip instead of discrete amplifier, so, the decision was not because of that... i would like to enter the designer head to understand his reasons, in my mind is because discrete is much better, but may exist other reasons and this thread will clarify the issue.

Those chips Nelson is talking about can hold a headphone and may work into 600 ohms short too, observe the generator output, even shorting the connector, the amplifier will see minimum of 600 ohms, because the two resistance in series.....so, chips that can work with 600 ohms loads can withstand the short into the generator output.

The main reason makes me suspect the chip performance is the fact that we cannot have small distance, small gap from output to input, and chip has this small gap because the size, so, if the hell thing is not oscilating is because has circuits to avoid, and these circuits (or parts), for sure kill sonics.

thank you,

regards,

Carlos
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Last edited by destroyer X; 27th November 2009 at 08:32 PM.
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