Simple FET Compressor

Consul was asking about a simple FET compressor. Never built it, but I am thiking about it.
http://freespace.virgin.net/ljmayes.mal/comp/comp.htm

Tamas

Hey, thanks!

I actually managed to find that one. It looks like it would make for a good starting point.

I was hoping that someone might know some resources that explain the theory behind FET compressors, though.

Thank you all for the help!

Dang!
You guys don't waste any time , do ya!
:lol: :lol:

nice to see the first tech post...

Well, we may as well get started, right?

Ah, I think I see...

FETs can act like a voltage-controlled resistor if biased a certain way. Cool!

It shouldn't be hard then to make an FET compressor at the complexity level of the What Compressor, then.

Say, do you think you could replace the What Compressor's LED with an EL panel and make it work?

To replace the led with a el-panel, I think you have to look at the LA-3
with the 100v step up transformer

Hmm, I think the idea behind the What Compressor was to do something similar to what the LA2 did, but with less esoteric components.

I am working on a fully adjustable opto-compressor based on the Fred Forssell schematics using an NSL-32R3.

Also, I am wondering if David would get mad if I started offering What Compressor PCBs here for DIY purposes.

Tamas

Well, I suppose you could always ask him.

As you can see, I'm interested in unique variations and new designs more than cloning. That's why the What Compressor fascinates me, as well as this FET compressor at the top of this thread. Neither would be hard to build.

...

http://www.youtube.com/watch?v=R_PKmkv64dc

Just to let everyone know, I need to go home now, where I have no Internet connectivity for now. I also have laundry to do.

I'll be back tomorrow morning, hopefully to much merrymaking and good tech talk. And also hopefully to some more people finding their way back home.

See you all later!

Hey, Winston! I didn't see you post that for some odd reason last night.

That looks like a worthwhile circuit to study. Thanks for alerting me to it.

SSL 82E33 talkback compressor:

http://www.gyraf.dk/schematics/SSL_82E33_Talkback.GIF

..also simple and FET-based. May have been the basis for Smart's "crush" circuit on his version of the clone..

Jakob E.

...

Thanks for the schematics Jakob!
Have you come across a Vishay part called VCR2? It is supposed to be made especially for attenuators. I am trying to find a place that carries them.

Tamas

Yes, I think it's a JFET device:

http://www.vishay.com/docs/70293/70293.pdf

For FET attenuator circuits, you may also try the H11F1 type optocoupler. I think I have an application note somewhere for a compressor with this.


Jakob E.

btw: this is an excellent semiconductor search database:
http://www.datasheetcatalog.com/catalog/p117420.shtml

Jakob,

I was just reading the specs for this H11F1 device. It says it is an LED controlled FET with over 99.9% linearity. Sound too good to be true.
Can you please find the application note for it? I would like to offer sending you a few pieces to make up for your time.

Thanks,
Tamas

I just went through my papers, but didn't find the schemo. I'll think of you when I find it.

Jakob E.

Hey, I remember some time ago (it was before even the switch to the new software on RO) that I posted some questions about using an H11F1 as a gain reduction element in a compressor.

I never did pursue that experiment, but it's worth pursuing, I think.

[quote author="Consul"]Hey, I remember some time ago (it was before even the switch to the new software on RO) that I posted some questions about using an H11F1 as a gain reduction element in a compressor.
[/quote]

IMHO, you should be able to use them as you would use an LDR. In fact I will plug one into my LA2-Light once these buggers make it here. They are almost a couple of magnitues faster than the fastest photoresistors (NSL-32R3) and may make excellent limiters. I think they take somewhat less voltage than photoresistors. The resistance versus input current looks similar though not identical to the above mentioned optocell.

Tamas