My chip looks.... too new - help a guy out - LM301AN

[Kevin Mitchell]

Thanks for digging in, Rob! I really do appreciate the breakdown, references and your opinion - all of which are valuable to myself and future visitors.

I've just purchased an LM301 (AH, the metal can variety) to compare. Should be legit, it's smallbear stock. I'll side-by-side these with the feed-forward comp circuit and share the plots. Will post that some time next week.

Calibrating the beast tonight, been busy playing with my 3d printer after hours.
After sifting through the schematic of said beast, most of these opamps are using the compensation cap. Considering it's current functioning status being untuned & uncalibrated, I think is good sign. But we'll see!

The absolute prof will be in the plots. I'll throw whatever other BJT input opamps I have in the mix as well.

[Rob Strand]

Thanks for digging in, Rob! I really do appreciate the breakdown, references and your opinion - all of which are valuable to myself and future visitors.

No problem.  I had a few attempts at doing stuff like this in the past (ie. building a valid marking library) and to be honest it ends up being an overwhelming task.

I've just purchased an LM301 (AH, the metal can variety) to compare. Should be legit, it's smallbear stock. I'll side-by-side these with the feed-forward comp circuit and share the plots. Will post that some time next week.

Good idea to have some trusty reference devices.

Calibrating the beast tonight, been busy playing with my 3d printer after hours.
After sifting through the schematic of said beast, most of these opamps are using the compensation cap. Considering it's current functioning status being untuned & uncalibrated, I think is good sign. But we'll see!

The absolute prof will be in the plots. I'll throw whatever other BJT input opamps I have in the mix as well

Good luck with it.    Many circuits which used the LM301A and the basic 30pF compensation cap will work fine with an LM741 or even a TL071.  All you need to do is pull the compensation cap.   
The tricky ones are:
- The compensation cap isn't 30pF.  Usually a faster (or slower) circuit, here try a TL071.
- when the circuit uses feedforward compensation to speed up the response.  Not a lot of options here
  without considering the design details.  Pulling the compensation network and using a TL071 can sometimes work.
- input DC levels close to the +V rail.   This was unique feature of the LM301A.   You would need to
  use a modern opamp with common mode to +V rail.

- I knew I forgot one, it just wouldn't come back in my head.
  Offset/balance adjustments.   The connection is specific to the LM301A you would need
  to rejig those for any replacement opamps.

I've been running on negative sleep the last few days and I forgot to post these.   I found the 1989 Raytheon schematic has the 5k resistor.   A lot of variations on the schematics (I've found this to be the case for LM741's as well, so no surprise).

Raytheon 1989, 5k



RCA early 70's, 7k5,



editted

[Kevin Mitchell]

Good luck with it.    Many circuits which used the LM301A and the basic 30pF compensation cap will work fine with an LM741 or even a TL071.  All you need to do is pull the compensation cap.   

You know Rob, I figured if there was going to be any trouble it would be where the comp cap value differs the most and go figure, there's trouble afoot.

I won't drag you into the nitty-gritty of the project's circuit, but here's what's I'm seeing so far.
I've gone through 5 sections of calibration and decided that I should stop.

I have 3 sawtooth sources that are provided from circuits with no LM301. They look correct.
-Sine wave shaping, set up a nice sine wave at the proper peak-peak voltage (2 LM301, each have a 30pF comp cap)
-Clock (the flashing LED of optimism), set frequency & duty cycle no problem (1 LM301, no comp cap)
-Preamp,  This has high gain at minimum actuation of the gain control and clips far too soon making it very difficult to set properly - if you breath on the knob it'll probably move a couple of volts. (1 LM301, 5pF comp cap)
-Envelope Follower - peak-peak voltage is a few volts above what it should be.  (3 LM301, 2 30pF comp caps and one 330pF)
-Ring Modulator - output is not at all what is expected, should resemble a modulated mix of previously verified sine and saw-tooth, shows only a quick spike. Also, Audio mode should be half of the peak-peak voltage than DC mode, which it isn't - it's a few volts above DC mode (2 LM301, 1 10pF comp cap and 1 220pF from comp (pin1) to inverted input)

Of course, I'm no pick n' place soldering robot. There could be builder errors though being this far into the game I know that my suspicions are justifiable.

I'm going to put an order in for AS301AN chips today to get ahead of the impending doom - been itching on it too much. I'll take a hit for peace of mind. But I must know what the deal is with these chips.

Edited: forgot about the verified sawtooths and sine calibration

[Rob Strand]

Of course, I'm no pick n' place soldering robot. There could be builder errors though being this far into the game I know that my suspicions are justifiable.

I'm going to put an order in for AS301AN chips today to get ahead of the impending doom - been itching on it too much. I'll take a hit for peace of mind. But I must know what the deal is with these chips.

I'm on the same page, looks suspicious.  The good thing is you are onto it!   A bit of circuit weeding and I'm sure you will push it over the line.

[Kevin Mitchell]

No plots yet, have to rethink my 200KHz pulse source to simulate the Feedforward comp inverter for it to be 1:1 to the datasheet circuit.
While I wait for my LM301AH to come in, I had received the AS301AN chips today. I immediately installed them into the big project and right away I'm hearing improvements.

First off, the basic stuff we've been doing.
Diode test shows 797mv - to be expected from what we know.
Resistance test shows ~6.7K

Scoping the feedforward circuit with a 0-5v 200KHz pulse there are some very obvious differences. While not a perfect representation of the pulse wave shows on the output, the difference between the two chips is far from negligible. My immediate observation is that the output signal of the Nat-semi chips show 1.5v p-p and the Alfas show ~3.8v p-p. That's a hell of a difference.

Edit: trying the test again tonight just to have the plots drawn out. Would be nice to actually use the record function on my scope for once lol. Was having trouble level shifting a 5v clock pulse for ±5v. My workaround will be a transistor switch into a cmos buffer.

[Rob Strand]

No plots yet, have to rethink my 200KHz pulse source to simulate the Feedforward comp inverter for it to be 1:1 to the datasheet circuit.

When you check the slew-rate it's good idea to stick to the same supply and input voltages as the datasheet, also the same load if one is shown or implied.   Otherwise you can get quite different looking waveforms.

Scoping the feedforward circuit with a 0-5v 200KHz pulse there are some very obvious differences. While not a perfect representation of the pulse wave shows on the output, the difference between the two chips is far from negligible. My immediate observation is that the output signal of the Nat-semi chips show 1.5v p-p and the Alfas show ~3.8v p-p. That's a hell of a difference.

The original NatSemi devices are looking at bit fishy aren't they.   Maybe confirms you original suspicions.

[Kevin Mitchell]

Well really, this absolutely confirms my suspicions;
±5v 200KHz pulse signal, opamp is powered by ±15v

AS301AN


"LM301AN"




Ignore noise from input signal (noisy probe)

[Rob Strand]

Well really, this absolutely confirms my suspicions;

That LM301AN waveform is totally whacked.

What's really weird is there's no negative swing.   

You might perceive it as a signal inversion.   You might be able to confirm that with a low frequency sine wave overdriving a non-inverting buffer stage.

An other alternative is the device is very slow and cannot recover at the 200kHz rate, you would have to drop it to 20kHz and see what happens.

Another effect is the output stage cannot pull down much current and it's kind of rectifying some capacitive load.   Try the probes on x10.

Bottom line though: AN301AN looks respectable and LM301A looks whacked!

I wonder if there's any YT videos of someone busting fake LM301A's with an oscilloscope?