Anybody else prefer discrete semiconductors over opamps?

DrNomis · Post by **DrNomis** » 21 Dec 2011, 02:49

In the end, it really depends on what you're trying to achieve with the design, and what your design budget is, discrete and integrated designs can work equally well if designed right....

culturejam · Post by **culturejam** » 21 Dec 2011, 05:17

RnFR wrote: as far as the 4049 goes, i wouldn't know. i haven't really messed with them much. i should!

Yes, you should! It's a surprisingly great sounding gain source. Here's one of my favorite applications of it:
http://www.runoffgroove.com/22-7.html

And here's (one of) my own take on the chip:
http://circuitworkshop.com/forum/index.php?topic=828.0

^^ My schematic needs to be updated to include a current limiting resistor in series with the inverter's VCC pin. Without it, the chip runs hot and wastes power. Or you can go all out and use Escobedo's clever little JFET setup to radically reduce current draw. Hmmm, I think I'll revisit that project now and make some updates.

You guys inspire me.

juanro · Post by **juanro** » 21 Dec 2011, 11:35

JakeAC5253 wrote:
bhill wrote:Is this going to turn into one of those "Poly vs Nitro" holy wars?
Preamp tube covers vs. no covers

Covers r 4 pussies.
I like my woman busty and my tubes glowing freely.

bhill · Post by **bhill** » 21 Dec 2011, 16:50

No covers - gotta let them tubes breathe

Seiche · Post by **Seiche** » 21 Dec 2011, 17:30

i love how covers keep the tubes from rattling, but they themselves rattle just as bad

Pruttelherrie · Post by **Pruttelherrie** » 21 Dec 2011, 18:34

Covers are for sissies, except when they look like this: (scored at a flea market last year)

DrNomis · Post by **DrNomis** » 21 Dec 2011, 18:51

There's a certain hands-on coolness that you get when working with big components and easy to read labelling, don't you agree?....

I love watching glowing tubes, I'll have to admit, there's something eternally cool about that dull orange glow, those power tubes with their cobalt-blue glow ....

earthtonesaudio · Post by **earthtonesaudio** » 22 Dec 2011, 01:03

I must say I tend to prefer ICs, except when it comes to PCB layout. Then discretes rule.

culturejam · Post by **culturejam** » 22 Dec 2011, 01:35

earthtonesaudio wrote:I must say I tend to prefer ICs, except when it comes to PCB layout. Then discretes rule.

Ugh, agree so much on this.

JiM · Post by **JiM** » 22 Dec 2011, 01:36

I assume that you guys all know the Mother of All Opamps :
http://www.philbrickarchive.org/k2-w_op ... lifier.htm

culturejam · Post by **culturejam** » 22 Dec 2011, 01:45

Yeah, but does it come in sub-mini format that can run at low voltage?

briggs · Post by **briggs** » 22 Dec 2011, 01:59

JakeAC5253 wrote:
DrNomis wrote:J-Fets can produce similar distortion harmonics to the harmonics generated by Valves/Tubes, you can think of a J-Fet as being the solid-state equivalent to Valves/Tubes, both types of devices are Voltage-Controlled, whereas a Bi-Polar Transistor is Current-Controlled, a single J-Fet stage on it's own doesn't really produce alot of gain, and what gain it does produce tends to vary a bit depending on how much current flows from the Source to the Drain (I'm using electron-flow here, negative to positive), as the Source-to-Drain current goes down the gain goes up, so a Fet tends to exhibit similar non-linearities to Valves/Tubes (predominantly Even-Order Harmonics due to asymmetrical waveform clipping).

Because the internal circuitry of Op-Amps tends to be symmetrical in design, the non-linearities are different, add to that the usual amounts of negative-feedback and you'll find that although the distortion figures are lower, the distortion harmonics are different (predominantly Odd Order Harmonics due to symmetrical waveform clipping).

I tend not to have any preference for Discrete Semiconductors or Op-Amps, I'm happy using either.....
Cool summary. The JFET's being voltage biased as opposed to current biased may be the reason I have not yet fully grasped them yet.

juanro wrote:Have you seen this: https://www.diystompboxes.com/analogalc ... opamp.html ?

Sort of a discrete op-amp. While limited in it's posibilities, I have used it in the past and it worked and sounded fine.

Juanro
Now that is cool. Sort of like a modified long tailed pair with a single ended output amp? Seems like it would make for a neat little project. Thanks for sharing.

Here's a little design I came up with a while ago using a discrete opamp: https://www.freestompboxes.org/viewtopic ... 1&p=174264 I loved the sound of it, especially using a PNP Germanium transistor in there! It's the best of both worlds, by tweaking different components you really could come up with any sound profile you wanted - the only draw back is that this circuit isn't 10mm by 6mm and can't clip into a nice little socket on your pcb

diagrammatiks · Post by **diagrammatiks** » 22 Dec 2011, 02:52

the schematic for the 741 is on wikipedia I just noticed...

might make for a fun project.

RnFR · Post by **RnFR** » 22 Dec 2011, 07:36

Briggs!! WTF?? he's back from the dead!!!

briggs · Post by **briggs** » 22 Dec 2011, 10:03

RnFR wrote:Briggs!! WTF?? he's back from the dead!!!

heh, yep - I'm back building again, I suppose it's one of those things that I can't stay away from!

Boy has it changed round here, I seem to have missed some interesting stories too (Freakish Blues?!? ha).

JiM · Post by **JiM** » 22 Dec 2011, 10:51

culturejam wrote:Yeah, but does it come in sub-mini format that can run at low voltage?

Hey, great idea !
Let's get FrequencyCentral started on that

And welcome back, Briggs !

RnFR · Post by **RnFR** » 22 Dec 2011, 12:45

briggs wrote:
RnFR wrote:Briggs!! WTF?? he's back from the dead!!!
heh, yep - I'm back building again, I suppose it's one of those things that I can't stay away from!

Boy has it changed round here, I seem to have missed some interesting stories too (Freakish Blues?!? ha).

well, right the f on! look glad to have you back, brother!

Hides-His-Eyes · Post by **Hides-His-Eyes** » 22 Dec 2011, 12:53

diagrammatiks wrote:all semiconductors sound the same.

harumph.

"It's all silicon, rite?"

JakeAC5253 · Post by **JakeAC5253** » 14 Feb 2012, 21:23

Little bit of a different angle than the initial post. What do you prefer for pre-post gain buffering, JFETs, BJT Opamps, or JFET opamps? I am ruling out discrete BJTs because they are so common, and furthermore, I just don't like them as buffers. I almost think that from a design standpoint, you could more easily tweak the output impedance on the discrete JFET buffers than you could using an Opamp buffer, though strictly mathematically I think the JFET opamp would make the most efficient buffer because the output impedances are usually measured in hundreds of ohms. Of course efficiency doesn't always sound good...

Discrete JFET buffers can be used at 9v, but with a JFET opamp like the TLO72 (a JFET input opamp that I like) the specs say that it needs to be powered closer or exceeding a single supply rated between 18v-24v. BJT opamp buffers are lower input impedance, so it wouldn't really be the ideal part for an electric guitar to see first in the chain, although they have a lower output impedance than even a JFET opamp, which may be better for the gain part of the circuit to see... I read a post from RG that said that using discrete JFET input/output buffers would increase the amount of noise and parasitic crosstalk between traces due to the high input impedances... how bad is this typically, and do JFET input opamps exhibit this as well?

Talking about discrete JFET buffers, does the buffer become closer to unity gain as the voltage is raised higher? What is the relationship there, because I know a 9v supply is not ideal in most, if not all, instances of the circuitry we often play with.

marshmellow · Post by **marshmellow** » 14 Feb 2012, 22:43

JakeAC5253 wrote:Little bit of a different angle than the initial post. What do you prefer for pre-post gain buffering, JFETs, BJT Opamps, or JFET opamps? I am ruling out discrete BJTs because they are so common, and furthermore, I just don't like them as buffers. I almost think that from a design standpoint, you could more easily tweak the output impedance on the discrete JFET buffers than you could using an Opamp buffer, though strictly mathematically I think the JFET opamp would make the most efficient buffer because the output impedances are usually measured in hundreds of ohms. Of course efficiency doesn't always sound good...

For output buffering a BJT would be in most cases be preferable, because you will more easily achieve a lower output impedance than with a JFET, if this is what you aim for. Of course the preceding stage has to be taken into account as well for what might be the better choice. For any opamp the output impedance will be a fraction of an Ohm, so typically a resistor is used to isolate the output from a possibly capacitive load. Still, I don't see much merit for guitar circuits to optimize a circuit in that respect, an output impedance of a few kOhms is perfectly fine in that environment.

JakeAC5253 wrote:Discrete JFET buffers can be used at 9v, but with a JFET opamp like the TLO72 (a JFET input opamp that I like) the specs say that it needs to be powered closer or exceeding a single supply rated between 18v-24v. BJT opamp buffers are lower input impedance, so it wouldn't really be the ideal part for an electric guitar to see first in the chain, although they have a lower output impedance than even a JFET opamp, which may be better for the gain part of the circuit to see... I read a post from RG that said that using discrete JFET input/output buffers would increase the amount of noise and parasitic crosstalk between traces due to the high input impedances... how bad is this typically, and do JFET input opamps exhibit this as well?

Too many, not necessarily true, generalizations for my taste. You just can't look at one specific part without taking the closed loop that is surrounding it into account. As for noise, the specific circuit has to be analyzed to see which part will perform better.

JakeAC5253 wrote:Talking about discrete JFET buffers, does the buffer become closer to unity gain as the voltage is raised higher? What is the relationship there, because I know a 9v supply is not ideal in most, if not all, instances of the circuitry we often play with.

No, the supply voltage doesn't matter for output impedance (assuming it is reasonably high for the circuit to work at all). Simplified, the amplification of the source follower will be A = gs, so in order to minimize the loss a JFET with higher transconductance would be the better choice. But I don't really see the point for most circuits where you almost always have a preceding stage with gain that will easily compensate the small loss. So it won't really matter that much if your output buffer has an amplification of 1 or 0,9 or 0,8.