opamps vs transistors

[burningwater]

I was told that a dual opamp is like 2 transistors with higher gain - but looking at the pinout it seems different. I get there is one shared power lug and one ground but then each gain stage seems to have one output and 2 inputs (neg and pos). Can anyone explain how this is the same / different than a couple of transistors. Id like to try to replace the opamp in a circuit with transitors if thats possible. Thanks

[sfr]

http://sound.westhost.com/dwopa.htm

This article was what helped me understand how op-amps work. 

Why do you want to replace an opamp with transistors?

Here is what's going on inside the 741 op-amp.

[RaceDriver205]

Yeah, an Opamp is nothing like 2 transistors. Opamps are very good, stick with them.

[brett]

Hi
op-amps are good for certain things.  With JFET inpots, such as the TL07X series, they have very high input impedance (thousands of megohms) and give clinical reproduction of signals.
But they are also limited in a few ways.
In discrete circuits we can encourage distortion with mis-biasing and starving and generally mistreating transistors.  There are also transistors with interesting characteristics, such as old germanium ones, that have no equivalent in terms of op-amps.

For me, the usual reasons for choosing an op-amp would be to get a lot of gain in a single stage (say 200+), or wanting two reliable high-gain stages (so I might as well use a dual op-amp).
cheers

[Thomas P.]

aint it all diodes in the end?

No seriously OPAMS where invented as an active device which is only (or mostly) characterized by external components. And as a matter of fact opams are like lots of transistors (look at the picture of the 741).

But maybe you check the Joe Davisson discrete opamp.

[GibsonGM]

Like Brett said, it's about certain characteristics.  That is described in data sheets and device operating curves.  Has been well-discussed in the forum.  For some applications opamps are better (high input impedance etc); discrete transistors sound better in some circuits, though.  They are more "vintage"  and tubey sounding for some things (esp. FETs).  Some think opamps sound cold - they're so accurate they're artificial sounding.  They're both just parts, and each does a very similar job while having different characteristics.   I use both, depending on what I want to do. 

[R.G.]

I was told that a dual opamp is like 2 transistors with higher gain - but looking at the pinout it seems different. I get there is one shared power lug and one ground but then each gain stage seems to have one output and 2 inputs (neg and pos). Can anyone explain how this is the same / different than a couple of transistors. Id like to try to replace the opamp in a circuit with transitors if thats possible. Thanks

It's not possible at your current level of understanding.

Apples ARE very like oranges at some levels of abstraction - they are both round fruits; they both grow on trees; they are about the same range of sizes; there is a lot of red in both colors; they'd both work equally well in place of a baseball for batting practice - the list just goes on and on.

But they are quite different at other levels of abstraction. There's the rub.

Both opamps and transistors are amplifiers (and switches...) and can be used for the same job to a certain degree. Transistors are to opamps as bicycles are to Harleys. There exist certain jobs for which either one will work fine. But they have different support and maintenance needs, and a different degree of training is needed to apply them well.

When you have much more understanding, you will be able to apply transistors where you'd use an opamp, but give it a while.

Like Brett said, it's about certain characteristics.  That is described in data sheets and device operating curves.  Has been well-discussed in the forum.  For some applications opamps are better (high input impedance etc); discrete transistors sound better in some circuits, though.  They are more "vintage"  Wink and tubey sounding for some things (esp. FETs).  Some think opamps sound cold - they're so accurate they're artificial sounding.  They're both just parts, and each does a very similar job while having different characteristics.   I use both, depending on what I want to do.

And this is another extremely good answer.

[Sir H C]

OpAmps are made from transistors, but transistors are not made from OpAmps.

OpAmp = Operational Amplifier, designed to do physics equations with electronic systems acting as an ANALOG for physical systrems.

[PaulC]

An op amp is a CIRCUIT made up of transistors and other stuff.  Like any circuit it's designed to do certain things.  You have many ways to set it up, but it's still that base circuit.  If that circuit is what you're needing then it's the best choice. 

with transistors you can do a whole gaggle of circuits that are not based around an operational amp design, but you can still uses transistors to build an opamps.

PaulC

[sfr]

http://www.forsselltech.com/schematics/VT%20Opamp.PDF

I'm tempted to build a Dist+ using tubes to make an op-amp; just to say that i did, but I've a feeling it's going to sound the same either way.  At least least, the way I run my rig it would.

[RaceDriver205]

It probably would sound the same, or worse. The presense of a tube is not enough for 'magical valve sound' despite what people say.
I think burningwaters gone.

[brett]

I'm tempted to build a Dist+ using tubes to make an op-amp; just to say that i did, but I've a feeling it's going to sound the same either way.  At least least, the way I run my rig it would.

Having built a range of distortions with a typology of: amplifier=>diodes to ground=>output
I can say that the dominant feature of the sound is the diode clipping.  Subtle differences between different amplifiers get overshadowed.

There's an old proverb that says it is unwise to chase a mouse around your kitchen if you are ignoring an elephant that is knocking your house down.

[GibsonGM]

LOL, good analogy, Brett...remembering, of course, that the LM741 in the Dist+ adds some distortion of its own, because it's being driven beyond its linear operating curve. So it does add to the sound.  That aside, diodes sure are gonna be the elephant here and be 95% responsible for the sound!   It's good to explore options, I know I did, and then you know why designers settled on this OA or that transistor. 

[mac]

See Joe Davisson discrete opamp. I tried it on a dist+, red fuzz, rat, ibanez fat cat, etc and it works fine. Basically, Joe has trimmed everything from the differential input to the output, and added an internal clipping diode. Nice, but it may NOT work ok in another circuits.

http://www.diystompboxes.com/smfforum/index.php?topic=44255.0

mac

[petemoore]

  With gain / clipping circuits, there isn't that much variation in waveform while it's getting up and down to the clipping thresholds via Jfet, Bipolar, Oa etc., at least not compared to what invariably happens when it gets there, ie it gets flattened, which is a huge 'event/change' in waveform shape, and quite similar in all disorters which use this method.
  'quite similar' is probably a general overstatement, but in the context of everything else, the clamping events show up in the sound and waveform as distortion most profoundly.
  741's, Ge's
  Bipolar and Jfet
  They all push the waveform to swing a bit differently though, these are a 'big diff' once you've built 'yer basic clipper'. Larger differences become more obvious if any of these different active devices are voltage starved or otherwise pushed to, near, or over an 'edge'

[sfr]

Oh, I was fully aware that the sound would mostly come from the clipping, as others have said here.  (And I sort of said)  Like I mentioned, I was mostly contemplating it for "just because you can" value, and if one built a tube based op-amp, the Dist+ seemed like the easiest thing to tack around it.  I guess I was just thinking out loud. 

[markm]

See Joe Davisson discrete opamp. I tried it on a dist+, red fuzz, rat, ibanez fat cat, etc and it works fine. Basically, Joe has trimmed everything from the differential input to the output, and added an internal clipping diode. Nice, but it may NOT work ok in another circuits.

http://www.diystompboxes.com/smfforum/index.php?topic=44255.0

mac

I, unfortunately, have not had much luck with it myself.....

[mac]

I, unfortunately, have not had much luck with it myself.....

I've just trashed what it was supposed to be my perfect FF...
When I tried JD discrete opamp I was surprised to get 4.5V at the output the first time. I added the dist+ and red fuzz stuff and they sounded ok from the start.

mac

[snap]

took care of the DC blocking?

[burningwater]

Thanks for the info guys. The main reason I want to try to swap in some transistors is to have some more control over the "voice" of the gain. To whoever said "it is not possible with your current level of understanding" all I can say is my level of understanding is changing by the second so that seem like a fairly ridiculous comment. It IS possible for me to do, and I WILL do it! Thanks