Intersil CA3080 and CA3094

[Mike L.]

Hello all,

There was an article a couple of months ago in AudioXpress written by Nelson Pass concerning his Kleinhorn enclosure, various fullrange speakers and transconductance amplifiers. Mr. Pass is also now marketing a transconductance amplifier called the First Watt. I have recently constructed a backloaded horn using a small, inexpensive Fostex speaker connected to a homemade single ended tube amp. The talk in the Pass article about transconductance amplifiers got me thinking that I might like to try that. Unfortunately, I do not have $2500 for a First Watt.

I did, however, find an application note published by Intersil describing a preamp and an amplifer built with their CA3080 and CA3094 Operational Transconductance Amplifiers. Across the top of the application note it states that the referenced parts are obsolete without recommended replacements. So far, I have found a few of CA3080's still for sale, but none of the CA3094 device.

Does anybody have a suggestion as to how I should proceed? Is there a currently produced equivalent? Maybe an alternative design published by another manufacturer. Any suggestions will be welcomed.

Thanks.
Mike L.

[janneman]

Mike,

I don't know the details of what you want to do, but chips like the MAX435/436 and the AD844 (at pin 5) provide an output current in personse to an input voltage (with some proper implementation). Could you use those?

Alternatively, any normal voltage output amp can be made a current output amp by feeding back a voltage related to the output current (like across a load series resistor)


Jan Didden

[leadbelly]

The one application I have come across where the CA3080 is uniquely suited to the job is a guitar volume pedal, since it can run from +/- 2V it is perfect for 9V battery supplies. It is the only major difference of the CA3080 from the LM3080 that I saw when scanning the datasheets.

Is the design you are looking to build using this feature? If not, you can probably substitute easily as janneman says.

[Mike L.]

Hello all,

Thanks very much for replying. To tell you the truth, I reallly do not feel qualified to extend or modify the designs I found on the application note. If you are interested, here is the link http://www.intersil.com/data/an/an6077.pdf

I generally build designs I come across either in application notes, on websites like Elliot Sound Products and Angela Instuments, or in books and magazine articles. The only independent electrical designing I've done is the occasional power supply or single ended tube circuit.

What I am looking to do is build a reasonably high fidelity audio transconductance amplifier (inexpensively) to see if I personally perceive a difference in the sound from what I am accustomed to.

Mike L.

[leadbelly]

Oh, it sounds like you got hung up on the word transconductance and went astray. There was nothing special in that app note, no shortcut to First Watt nirvana

If you are interested in a First-Watt-flavoured gainclone there are threads on various ideas you can maybe try or follow up with the authors.