FEA - Dual Band Compressor  [schematic]

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Post by Broadcaster »

Just had a chance to snag this amazing box for a few minutes from the happy owner... guess what happened :wink: .
While designed for bass guitar this is really great on normal guitar as well. From the pics I took without completely disassembling the box I can only say I won't clone this one, but what a nice tight build!

http://www.fealabs.com/products/DBOC-0001.html

Not the cheapest thing around at $345 +S/H but I wouldn't even think about cloning it - looks a little like SMD without SMD parts.

These are all pics I have:

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Post by cpm »

i wonder what are those hardwired components for, over the chips, and on the back side.

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Post by chicago_mike »

I have a schematic of the Trace Elliot SMX compressor pedal, but I'm way to chicken to do a pcb of it. :oops:
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Post by Broadcaster »

Well, this one uses 2 Silonex optocouplers whereas the Trace Elliot SMX uses a SSM VCA chip... even though there is a dual compressor based on the one above but with reduced controls, employing the hardwired timing parameters of the SMX.

I had a chance to test this one a little more and I can only say I'm impressed how transparent is works. My wallet still denies even thinking about getting one for myself :wink: .

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Post by chicago_mike »

I see the silonex's, wich we could always use vactrols or led/photocells for cheaper costs.

We could use the crossover in the smx, and use 2 sorta basic ldr opto style compressors then..

I wonder if we could coax Baja into doing something like this. That would be cool! :hug:

But looking at the board, even though theres a few parts, caps mostly, hanging or glued ontop opamps, it doesnt look too bad. I dont have the time or patience myself, but I would be willing to contribute as much time and effort as I can..

I have a bunch of schematics that if I could find the right people, we could turn out some cool pcb layouts. I could donate pizza's and stuff. 8)



Stupid idea.....its a single sided trace right? why not put that side into photoshop and make the image b&w, make the traces black and what..reverse the image to make a pcb? If the image is angled, I guess we could straighten it out first...

Im talking out of my arse I think... :|
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Post by Broadcaster »

The traces wouldn't be the problem, but one needs a magnifying glass to check all those vertically mounted resistors for their values. I don't know when and if I could borrow that unit again (given the owner would not mind the purpose). Also I guess there's another board with the charge-pump and whatever hidden underneath that white plastic cover (that would not come loose easily when I opened it).
Should massive interest arise I'd give it a go maybe, but... given the knowledge gathered in this forum (with all due respect... there's more than Bajaman - and I'm certainly not talking about me :mrgreen:) I'd figure it would be more fun starting a forum project incorporating our collected wishes and designing our own dual comp?! A question of interest, as usual.

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Post by Broadcaster »

Ok, especially for you... headache country:

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To me, this is not of too great help :wink: . Maybe that's just me.

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Post by chicago_mike »

Ill give it an honest go. :)

What the heck...the worse that can happen is, I find crop circles in this fucker. :o
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Post by pedalgrinder »

I take my hat of to you chicago mike. But without resistor values could be interesting. But as far as i can see this is rated as one of the best bass compressor one can get there grubby little hands on so. Bass players unite this would be a beauty to crack! :thumbsup
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Post by juanro »

Chicago_mike,

I'm interested in the Trace Elliot schematic (in particular the crossover part). Can you upload it here? Thanks.

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Post by lietuvis »

juanro wrote:Chicago_mike,

I'm interested in the Trace Elliot schematic (in particular the crossover part). Can you upload it here? Thanks.

Juanro
Hi I have schematic you looking for, I think its got fixed frequency for crossover and works by blending low and high compressors as it says in manual: Composite crossover point of the overlapping High and Low pass filters = 350Hz
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SMX Dual Compressor.pdf
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Post by stonefreed »

Thanks for those ; are the opamps TL064 ? It's not very legible. But of course you can substitute them with Tl074 or more advanced opamps, I suppose.

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Post by lietuvis »

stonefreed wrote:Thanks for those ; are the opamps TL064 ? It's not very legible. But of course you can substitute them with Tl074 or more advanced opamps, I suppose.
at list to me it looks like it is TL064 and SSM2024, but god knows what diodes are could be germanium or else, as for IC you can swap to TL074 with more current draw if use for pedal. attaching an amp schematic with use of smx compressor in it
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Post by RnFR »

mike hadn't been around in quite a while. there are plenty of crossover schematics on the net. jus attach 2 compw to the output.
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Post by jonasx26 »

Hey guys. I have been tinkering with optical compression a lot lately.
Linearizing the LDR current/resistance-response and getting a useful resistance range out of it is not a trivial task.
Especially not when limited to a single 9v supply and standard components.

Silonex appnotes demonstrate various ways to solve some of these problems. (LDR non-linearities, log-like-response..)
And it seems to me that the FEA Dual Band is a tweaked adaptation of a Silonex appnote.
http://www.silonex.com/audiohm/compressor.html Fig. 6, bottom of the page.

The specs for the FEA even match the Silonex appnote circuit.
Check out the FEA Comp manual, page 2. "About the design" for additional clues..


So instead of tracing the FEA comp, you could use and modify the appnote circuit. Add a charge pump, input buffer, crossover filter etc..

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Post by pedalgrinder »

Are you sure it's that simple. Iam sure fea have put a bit more into than a few buffers and those tech notes and a charge pump they usually tweak the values to get the correct frequency response.
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Post by jonasx26 »

Just thought I would chime in with some thoughts.
For me it's much more fun and interesting to develop my own circuits, I RARELY do clones.
Some time and effort would be required on your part of course. Reverse engineering might be more convenient.
Are you sure it's that simple. Iam sure fea have put a bit more into than a few buffers and those tech notes and a charge pump they usually tweak the values to get the correct frequency response.
Yes, obviously you would have to tweak some values.
That is very easy compared to the difficult part of designing a optical compressor with (truly and independently) adjustable ratio- and threshold- controls.
The appnotes contains the information you will need for the sidechain. Just steal the SMX circuit for the crossover part and tack on buffers of your choice. I don't see the difficulty in that.

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Post by pedalgrinder »

Yeah i totally agree. But optical in some senses just starts to annoy me as you can't seem to get the control you may out of a good vca or jfet or mosfet. I was looking at the different options for designing optical but you just couldn't get the nice crisp attack times i wanted out of it. To much memory in the ldr and getting a good ratio seemed almost impossible. Not that it can't be done. I just never came up with or found a optical design that would meet my needs so i have opted to start playing around with the tda7052a which for price and to use it as it as a good vca you just can't go wrong. This chip has so much diy potential and especially as its cheap and sounds good it only has to be adapted to the voltage range in which is specified in the data sheets. I could be wrong but a good voltage divider will generally adapt this beast to those applications within reason. But yeah something for you to think about.
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