Crash Sync (chip stuff)

[jmusser]

I have had a note out to John Hollis, but have had no reply, so I ask it of the forum. I have a whole fist full of NE5532s, and no TL072s. could I sub the 5532s for the TL072s in this design? I know they have the same pinouts and all that, but it doesn't mean that they are a direct substitute. I had saved back a chip all this time for this project, and it turns out it was a TL082. This is kind of a weird dual op amp with the two positive legs and the two outputs tied together. It's a bifet (whatever that is). Is there an effect that this could be used in? Last chip question (honest). I have several LM386Ns, which are single op amps. they have identicle input pins when compared to the TL061,70,71 & LM741s, etc , but the output is on a different pin. Could they be used in the place of these chips, as long as I observe the proper pinouts?

[Torchy]

crp

[jmusser]

Thanks a lot. My package with the TL082 has a very blurred internal schematic on the back. I can see what's going on in there. I'll probably just wait until I get the proper chip, and build an Octave Up Sick Box with the 5532. I would like the Crash Sync to sound as close to the sample as possible. I will have to read up on the difference between an operational and audio amp. I thought the were the same thing, since they must both be able to amplify audio signal, so I never looked into the differences.

[toneman]

Torchy wrote:
"BIFET relates to the way the offset voltage is trimmed internally. "

Sorry dude, bifet means "2 fets", as in the input differential pair of the opamp.  
the 5532 is a bipolar input; the TL072/82/62 are fet input.
the 5532 have more current drive capabilities as PAIA(model 9605K)
uses them in their supersmall headphone amplifier/buffer.
The BiFET opamps have a much higher input resistance due to the differential input FETs.
Look at the datasheet that gives the internal structure of the opamp.
But, pin 4 pin and circuit wise they are interchangable.
Got that part right.
JM,
google for the part number plus "datasheet" and U can usually find
all the info U need on the pinouts and other characteristics of almost any opamp.  
They are usually in PDF format so U need the latest version
of Adobe Acrobat Reader(its free)
stayinformed
tone

[Paul Perry (Frostwave)]

Sorry dude, bifet means "2 fets", as in the input differential pair of the opamp.  

According to Bogart's "Electronic Devices and Circuits" 3ed. , BIFET means a combination of bipolar (ie normal transistor) and fet, usually arranged so you get the high input impedance of the fet & the high voltage gain of the bipolar junction transistor.

http://perso.wanadoo.es/chyryes/glosario/ampopfet.htm
Yeah, there are 2 fets in this diagram, but that isn't why it is called a BIFET!

[Eric H]

Jeff, while we await the higher significance of "bifet" the tlo82 is nearly indistinguishable from the 072 in every way and would work fine in this circuit. The 5532 is a --very-- different design and may, or may not work --I'd use it somewhere else where its characteristics are more beneficial (a clean preamp, for example).


-Eric

[Torchy]

crp

[Paul Perry (Frostwave)]

Texas Instruments ...
"These devices are low cost, high speed, dual JFET input operational amplifiers with an internally trimmed input offset voltage (BI-FET II™ technology).  Internally trimmed offset voltage: 15 mV,  Low input bias current: 50 pA. On-chip Zener trimming of offset voltage through BI-FET II™ optimisation yields precision grades as low as 1.5 mV for greater accuracy in dc-coupled applications. Texas Instruments improved BI-FET II™ process and optimized designs also yield improved bandwidth and slew rate without increased power consumption."

Sunderland University ...
"BIFET is an acronym for 'BIpolar Field Effect Transistor'"

Stay informed ... I thought I had, but if TI are wrong then so am I.

the confusion is this: the TI chips (and other "bIFET" chips) have fets at the inputs, to get the high impedance.
And as the acronym implies, there are BOTH fets and (normal) bipolar transistors there (the BI comes from the bipolar transistor).
The fact that there are TWO fets is a coincidence.

The "bifet breakthrough" was finding a way to make fets & bipolar transistors on teh same substrate, cheaply. And automatically trimming them with a laser to get the voltage offset down (you know how hard it is matching fets.. !!!)

We take the modern cheap op amp for granted, but my goodness it didn't come easy to the pioneers..

[jmusser]

Well, this will all work out great, because as luck would have it, I'm also bipolar! Since I can't wait to build the Crash Sync, I'll go ahead and use the TL082, and just pay attention to how the pinouts are different from the 72. If the 82 ends up working out OK, then I'll have a chip I can get locally at Rat Shack. They don't sell the 72, and they're about the only electronics place I have close out here in the boonies. Thanks for the info. I have to leave now. I'm having a bipolar field effect!

[Torchy]

crp

[toneman]

no problemo Torchy.
i was letting thread sort itself out.
PP is most correct!!
Don't know what i was thinkin'??
BIpolar + FET front end....yep!!
Absitively!!
My "explanation" *sounded* reasonable  
As with all 8pin dual opamps, U usually lose the offset null pins.
But, as depicted in all opamp datasheets, U can add offset
nulling by additional summing resistor.
U null for zeroV in(on both inputs) equals zeroV out.
If things are capacitavely coupled, makes little difference.
staycorrected
tone

[Torchy]

crp

[Eric H]

I'll go ahead and use the TL082, and just pay attention to how the pinouts are different from the 72. If the 82 ends up working out OK, then I'll have a chip I can get locally at Rat Shack.

Jeff --the pinouts are identical (as they are on all dual opamps I'm aware of).


-Eric

[Eric H]

We take the modern cheap op amp for granted, but my goodness it didn't come easy to the pioneers..

That's the truth --it really wasn't that long ago, either.

-Eric

[jmusser]

Well after looking at the TL082 as compared to the other common dual op amps, Eric was right, that the pinouts are the same. I believe the only thing that's different about the little internal schematic, is that it actually shows how the fets are getting their power and ground from by a physical connection, as opposed to a implied connection of the other chip schematics. I built the Crash Sync last night, and it'deader than a door nail, so I have some looking around to do. One thing I was wondering about, was pin 5 of the 555 timer chip. It doesn't show a connection on the schematic, and it's supposed to be for control voltage. Does this need hooked up for this circuit to work, or was it intentionally left off?

[Torchy]

crp

[jmusser]

Thanks for the info. It looks like it's not required for this circuit to do what it does. What is a good book to get that is like effect circuitry 101? I only understood about half of what you just wrote there, and I would like to get more of a handle on what is being accomplished in these effects circuits. I have read RGs Distortion 101 which makes a lot of sense, but I get lost on what happens to signals as they make their ways through a circuit. First of all, I need a little clarification what the sinewave is. Is it a microvoltage from the pickup that is getting rectified, or audio signals? When I'm used to seeing audio, it is usually modulated on a carrier wave, and then stripped off the carrier, as in radio. I'm familiar with AC getting rectified to DC, and the reference changing so that you could get an octave up effect. On power supplies you have filtering after rectification, is that what we're doing with high pass and low pass filters? I mean there is a lot of stuff I'm cloudy on, and the terminology is too advance for me to grasp, until I get a good basic audio teory under my belt.

[jmusser]

I was able to go through my build last night with a fresh schematic last, and found 4 wiring errors! Hopefully tomorrow, I'll have it whipped into shape and give a review on it. Basically all those wiring errors could have been avoided, if I hadn't been in such a hurry and would have labeled all the components on my perf board to start with. There were several with the same value that I thought were one resistor, when they were actually another one. Maybe everybody else already does this, but it will do you a world of good to go ahead and asign all your components a designation on the schematic to start with. Then stick a a small piece of tape by the component with that designation on it. Then go underneath and at least mark pin one on the chip and it's designation. On this particular circuit, it has two 8 pin chips on it. It is very easy for the left hand chip to become the right hand chip once you turn it over to solder it. It's also just as easy for pin 1 to become pin 8 too. Now, all I have to do, is not get in such a hurry and follow my own advice from now on!