Chip and Diode ? for the Ross Compressor

[rosssurf]

1) I am building the Ross Compressor seen here http://aronnelson.com/gallery/Toneys-Album/Rossv4 I was wondering if a TL072 would work instead of a CA3080e ?  I have some TL's and 4558DD's but do not have any CA3080e's.

2) Also Is a 1n4148 diode the same as a 1N914. Different#'s so I would assume not, but I have some conflicting info.

[pbrommer]

1. Nope. A TL072 will NOT work in the place of a CA3080. A TL072 is a dual operational amplifier. A CA3080 is a operational transconductance (?) amplifier. A suitable replacement would be a LM3080. They currently do not make these chips anymore. Good luck finding them -- they're expensive (unless you know where to look  )

2. They're perfectly fine. In fact, I hay a 1n270 germ diode and everything seems to work just fine. Keep asking questions. We'll be here to help.

Patrick

[markm]

A great source for parts is Small Bear.
Steve is very friendly and helpful.
Here's the link to the CA3080e;

http://www.smallbearelec.com/Detail.bok?no=219

Happy Trails!

[rosssurf]

Thanks Mark! I have bought almost all of my stuff from him. He does a good job. I will order the chip from him as well as many other parts I need for the Ross Compressor.

[Mark Hammer]

One of the keys to optimal functioning of that unit will be matching of the two halves of the rectified signal.  If you've ever driven a vehicle with a tachometer that shows how high the motor is revving, think of this as the difference between a jittery and smooth tach.

Using http://www.tonepad.com/getFile.asp?id=9 as our reference, you can see that Q2 has two outputs, one from the emitter and one from the collector.  Each side goes to a .01uf cap, with a 1M resistor and diode to ground, then to either Q3 or Q4.  The outputs of Q3 and 4 are combined at Q5 and that is what ends up feeding the 3080 chip with the control signal to change the gain.  Matching those two combined halves is what moves us from jittery to smooth.

If you have a meter with transistor and diode testing, you can help to achieve that smoothness, by:

1) Selecting a pair of diodes, whether 1N914 or 1N4148, that have equivalent or near equivalent voltage drops.  So if one out of a trio measures a 527mv drop, another measures 534mv, and a third measures 523mv, then use the first and third because they are more closely matched.

2) Select a pair of 5% 1M resistors that are very close or simply use 1% resistors.

3) If you have capacitance measurement, pick a pair of caps closely matched (though this part is less critical)

4) Select transistors out of the pile that have fairly close hfe.  These transistors are used in a way that does not involve how they sound.  All that really matters here is that the positive half wave doesn't receive more favourable treatment than the negative halfwave (or vice versa).

Keep in mind that NONE of this has any impact on the frerquency response or distortion or hiss of the unit.  However, when the control signal that adjusts gain is less than optimally smooth, it is sometimes heard by people AS distortion, simply because they don't know what else to call it.

[rosssurf]

Thanks ! Great stuff!! I need to get a better DMM so I can check caps and transistors.