Forssell Opto Compressor

[Svart]

bad cap?

 

[hitchhiker]

that's a different circuit than I built. I'll update mine now.

Lance

 

[Gus]

Instead of the JFET try a bootstrapped EF. A BJT circuit can be made to bias up right with almost any Si transistor that you might want to use. Try a MPSA18 or 2N4401?

Pick the current you want make the bias resistors(in ||) 10 times the emitter resistor, Use a cap from the emitter to the junction of the two bias resistors and say a 4.7K from that junction to the base. You can use a good small input cap becauce of the high input R.

I like Jfets but they are a pain because you need to select them or change the circuit values for simple circuits that sound good.

 

[hitchhiker]

buttachunk,

This circuit works and sounds good. The noise I'm getting is my parts layout with long leads etc. I got it almost dead quiet by twisting the leads
away from each other.

One thing, when I turn the gain control right down it turns off the FET.

Could be a matter of selecting FETs.

Lance

 

[tk@halmi]

Butta, nice buffer. Have you guys tried to hook up a constant current source to Q1 instead of a resistor (R5)? You can really minimize distortion that way. You need a FET with just a little lower Idss than Q1 with a 22 to 33 ohm resistor between source and -V, connect gate to -V. There are good examples in the Borbely FET revolutions documents.

 

[hitchhiker]

I should have said that with the gain control all the way down then I
get no sound. Maybe that's what should be? I don't think I was right to assume the FET was turning off.

 

[hitchhiker]

Don't need more gain. This is perfection.Great Job!

thanks Butta

Lance

 

[hitchhiker]

Are we ready to get back to the layout for the boards?

Lance

 

[soundguy]

are yoou guys going to stay with the 5534 for the layout, or incorporate a discrete opamp as well?

dave

 

[Svart]

excellent guys! BRAVO! i'm in for a bunch already! :green:

 

[hitchhiker]

yes Buttachunk , I also am excited to get 4 of these boards.

I just did an A B test between the tl071 version and your new FET/5534 make-up amps.

No contest. The FET/5534 is much cleaner, especially in the treble.7k & up.

cheers,
Lance

 

[soundguy]

definitely looking forward to get this project going.

thanks so much to the two of you guys for developing this one!

Hopefully this will be a popular project here and can steer the group in a new direction towards developing original designs as a team effort.

dave

 

[StephenGiles]

Absolutely great stuff chaps. When I get back from South America, I'll be making this compressor. Will somebody be able to come up with a final circuit for this at some point?
Stephen

 

[tommytones]

And Tommy is jumping back into this one :green:

I'll bang this out over the week-end (along with some other stuff I have to do). Good work everyone!

:guinness: :sam: :thumb:

 

[tommytones]

I just saw that this thread has had near 10,000 :shock: views :!: :!: :shock:

 

[StephenGiles]

buttachunk - I think I'll have to build this one on the official pcb in honour of flat chested ladies who drop out of marathons and 10km races, in honour of ex prime ministers' sons who fall foul of South African governments, and last but not least in honour of all you fine folks who have put in a great deal of effort on this compressor.
Stephen

 

[bluebird]

:green: :green: :green: :green:

 

[hitchhiker]

hey Buttachunk,

I really like this new make-up amp of yours, it's a keeper!

Since we were talking about caps , I tried some different things.

C2 & C6 the BC axial from digikey (that Dave mentioned) &

C3 SU series bipolar by Panasonic,

(edit) oh yeah and transformerless out.

This combo rocks on my system.

cheers,
Lance

 

[hitchhiker]

hi Buttachunk,

I've gone cold on the bi-polar on C3. The colored quality of the amp is better with a crisp hi end. Back to the 10u FC series I started with.

cheers,
Lance

 

[ChuckD]

Hey Tommy

Did you bang out one of these opto's last weekend as you said? How is the progess coming on this, when do you think a project will be releaseed to the masses... if at all?

Thanks for your great work guys. I am looking forward to trying a stereo opto comp very soon.


-ChuckD