Rat Box

[Phend]

Hello:
Just finished a ProCo Rat using the GGG schematic.
Got a LM301 from SB (used in place of LM308)
It works, all 3 pots work. (Never heard an original Rat so hard telling not knowing)

Any Comments on these IC voltage readings...
This is my first build using an IC. (I have more 301's)
Comp is out of wack, Don't know what comp does.

Battery out of circuit = 9.5
Battery in circuit across rails = 8.5

(First is GGG Second is Mine)

Pin 1 Comp  8.4   1.4
Pin 2 IN 2    4.5   4.2
Pin 3 IN 3    4.1   3.9
Pin 4 V -      0      0
Pin 5 Bal      0      1.3
Pin 6 OUT    4.5   4.3
Pin 7 V +     9.0   8.5
Pin 8 Comp  4.6   3.7

Thanks in advance, have a great weekend !

[PRR]

> Comp is out of wack, Don't know what comp does.

Don't even look at that pin! Some opamps, the COMP pin (or BAL) is super fragile. You can burn-out the first stage load.

301 is NOT same-as 308 so you are not looking for same readings on the funny-pins.

You want to know V+, V-, In+, In-, and OUT.

In most single-9V systems, these should be near +9V, -9V, and 4.5V 4.5V 4.5V.

When an input is fed from a big 1Meg resistor you expect some meter loading. Another guy here today is observing 0.3V "difference", as expected.

Your "9V" seems to be weak, 8.5V, so I'd expect the "4.5V" point to be a bit low too.

[Kevin Mitchell]

Since you're using a 301 you may want to tweek the compensation cap to taste.
Electrosmash has some good info on this circuit.

[PRR]

> Battery out of circuit = 9.5
> Battery in circuit across rails = 8.5

The difference is the 47 Ohm R14? 1V/47r is almost 20mA. This is a 4mA chip, and less than a mA in the JFET. Is there an LED you have not mentioned?

[Phend]

^ PRR , I have not included the led or resistor,  but could add it. R14 is on the GGG schematic.

[PRR]

So why is it sucking about 4 times more current than it should? Rounding error? Or misconnection?

[Phend]

I shall verify values and connections.
Upon looking at a few variations I see 100ks in place of the 10ks in the voltage divider. Plus 100 in place of the 47 ohm r14.
And other comps off the 1m before the gate of 5458. Others have the 1m just going to gnd.

[Phend]

Got it sounding pretty good.
After reviewing numerous Rat circuits, none of which have a LM301 ...
Changed R15 R14 from 10K to 100K .
Removed the added GGG 2N5458 Bias circuit and just went with R9 1M to ground. (ie unbiased)
Now getting half the voltage at the divider.
However....these Pins are out of wack (does it matter with this different chip)
Nothing is connected to them other than the 30pF cap on 1 and 8.
Pin 1 Comp 1.38 (should be 8.4)
Pin 5 Bal     1.30 (should be 0.0)
Pin 8 Comp 4.10 (should be 4.6)
Other Pins are within 0.2 v of GGG spec.
Battery = 9.5

Thanks for the help

[PRR]

The 100/47 change accounts for the difference I asked about.

Why are you still poking the funny-pins BAL and COMP? They do not tell you anything.

[Phend]

^ Thanks for the pin advice, learning curve for me, my first IC !
Except for the RS flasher I made 30 years ago.
Thanks PRR