dbx 160vu clone

[David Kulka]

David,

Thank you for sharing your expertise.  I love old dbx compression - there's nothing like it.  The more I learn about these old VCAs/RMSs, the greater appreciate I have for the complexity of the design considering they are built from only a handful of common components.  It's brilliant engineering, no question about it.

Yep, handful of components. If you put a dbx 303 card and a Dolby A card side by side, the contrast is remarkable -- the Dolby card uses about ten times as many components, provides less noise reduction, and in a way, is actually more error prone, because it has 4 separate compression bands and requires alignment.

Maybe the downfall of dbx NR was that it worked too well. It doubled dynamic range of tape recorders, but also doubled frequency response and other tape deck errors, which I think was its main weakness. (Dolby magnified recorder errors too but to a lesser degree, because it did less compression and expansion.) Maybe, if dbx had settled for 1.5 to 1 compression instead of 2:1, it would have found more acceptance in the pro audio world.

 

[arska]

Have we forgotten the sound of iron, there is output transformer out there. Jensen Sowter Lundahl Cinemag OEP, anyone........

 

[Biasrocks]

Have we forgotten the sound of iron, there is output transformer out there. Jensen Sowter Lundahl Cinemag OEP, anyone........

Ah, no output transformer in any of the dbx 160's I've seen.

The schematic seems to confirm that.

Mark

 

[abechap024]

David very interesting info. Amazing how Dolby got so widespread.

I would be happy to host your high res files if you find you still need someone to. abe(at)acsoundstudio(dot)com

Arska: thanks for confirming the transistor choices. I'm going with your recommendation and use BC550/560s for the VCA.

DY: Keep in mind that with the transistor choices that are being made now, we can't easily change later because of all the different transistor footprints. You stated that your making yours as original as possible, but just wanted to be sure your aware that the BC550 footprint is whats going to be on the board. I am not sure what the bc109 footprint is - with any luck they are the same - but possible they could be different.

Besides the transistors in the vca, the other transistors are all exact NTE replacements for the parts. They NTE are nice and big so they can handle a lot of current!
But I've tried to keep everything  as original as possible. It seems to be a balance between what products are still availible

And to confirm what Mark said: the 160 doesn't have an output transformer. It does use some heavy lifting output transistors, it probably wouldn't flinch if you chose to hang one on the end, but that is out of the scope of this clone.

Also NTE929 is a good replacement for ca3083

 

[damnyankee]

AC,

The BC550 is fine - no problem.  I was referring to building the original VCA instead of using the THAT chip (I changed my mind).  I apologize for the confusion.

Now that you have the boards nearly completed and will be putting them together to test, should we start discussing which LEDs (PICA?) to replace the VU meter?  What's the configuration in the rack (1 unit per rack? 2 units per single rack?)?  Is purusha willing to do one of his miracle creations for the front panel?  Do we have a source for switches, knobs, etc?

DY

 

[Biasrocks]

Is purusha willing to do one of his miracle creations for the front panel?  Do we have a source for switches, knobs, etc?
DY

May I suggest getting someone who contributes to this board to make the panels and/or cases.

Pete or Dan would be ideal candidates.

http://www.groupdiy.com/index.php?topic=38500.0

http://www.groupdiy.com/index.php?topic=35422.0

Mark

 

[abechap024]

Hmm, those are all great questions.  The PCBs measure about 8 by 3.5 inches without the power supply and 8 x 4.5 with the power supply. We could fit two in a 1 ru case.

I'm going to be ordering prototype boards soon. If someone would be interested on purchasing/paying for any that would really help to get the ball rolling. I'm almost 99% sure there are no mistakes in the circuit and PCB, and will check it all at least one more time before I send out the gerber files.  I want to order prototypes because  I know there will be SOMETHING we will want to change in the final version. It might be component spacing or foot print or maybe just the color! Anyway
There is a one time $50 dollar tooling fee and then the boards are 20$ a piece .The more people to prototype it the less the tooling fee for each because we could split it. Then 5$ dollars a piece to ship it out.
I would send out an order for prototypes right now but I have no extra money (college!) :-(. hence the fund-raising lol! And if no one is interested, then I'll be able to send out for prototypes in about a month or so.
thanks!
AC

 

[Rybow]

Hey Abechap. Great work on those PCB's! I would certainly be able to help out getting the prototypes rolling.

 

[damnyankee]

AC,

are the VCA & RMS boards included in that $20/board fee?  Or is the plan to etch/drill them ourselves?

Secondly, I'll be going to be in for (4) boards with power supplies...but I want to be 100% sure the boards are correct (I don't want to be re-tooling all those boards).  Can you consult with arska, David, or one of the other pros to double check your work?  I've learned in my business (Medicine) that an extra pair of eyes or two is ALWAYS a good thing!

Thanks!

DY

 

[damnyankee]

Pete or Dan is fine.  It's obvious they both do top quality work and since Abe & I are in the States, I'm worried freight is going to cost a small fortune.

But before we consult with them, we need to agree on LED arrangement/size so the holes on the face plate can be punched (Pico?  Velleman? http://www.arcade-electronics.com/detail.aspx?ID=17696).  Do we want to keep a dbx'ish font look?  Are we going to use the push buttons for the meters (if that feature is being built in to the circuit)?  If so, those holes need to be punched in the face plate.  What about sourcing dbx-style knobs?  (size of knob is critical for face plate labelling). 

Abe, et al:  I need your input here...!!!  I've only done 9V geetar pedals.

Thanks!

DY

 

[abechap024]

Hi there DY,
Yes the $20 includes one board, and on the board is the original power supply. also you can build an RMS unit right on the board or plug a DBX RMS unit in. Then the VCA: the option to build a vca is on the board or plug in a that 2180 or DBX vca is there.  I've tried to make it so we don't have to buy all sorts of extra PCBs.
But we still have options.

I would hold off buying 4 boards all at once. While I'm going to do everything in my power so we don't have any mistakes on the PCB these are in no way a final version of the board. While It wouldn't hurt to start stocking up on parts. I would love to have someone with the time look over my schematic. Though it is very confusing at some points because in my constant adding/deleting parts and everything (i'm still learning mind you lol) some of the traces overlap others (parallel) on the schematic. While I can drag my mouse over and see which is which, It will take some work so it looks good on an export. But I agree It should be done before boards are sent out.

And about all the meters and diodes and holes and punches. all that stuff is always an after thought for me! lol Me personally I am going to wait till I have circuit in hand before I commit to a LED meter or VU meter. I think its really up to your taste. I've left the meter circuit stock so someone can tweak it to however they want. I don't feel the need to see the input or output level. I can get a good idea about that through my console and other tools. That solves the push button switches for me. But the option is there is someone wants to wire up the original VU/ push buttons.

If no one beats me to it, I'll write out some steps to get the meter circuit into just GR mode (it should be a few jumpers)

As for cases, I haven't given it any thought and don't plan to tilll the pcbs are running like champs!

I am eager to get these prototypes sent off! So I'll work on pinning up the schematic to double check
AC

 

[damnyankee]

OK Abe-inator,

I'll start stocking up on parts but I'll need a parts list.  And another question: the LM723 DIP-14 voltage regulator is interchangeable with the 10-pinned TO-canned version.  Obviously the pinouts are different - including number of pins.  Which DIP-14 LM723 version should I be getting?

Thank you for your mentoring...this has been a wonderful learning experience and it sure beats building another geetar pedal.

DY

 

[abechap024]

Hi DY,
Thanks for all your help and motivation! any verison of the LM723 should be fine. They seem to sub classify the different chips based on different specs (some that are lead free, some that are roHS complaint  some that have slightly better/different specs than others, etc) If your really curious you can usually check the spec sheet or manufactures website. But when In down just get the cheapest one! Orrrrr get the most expensive one lol. Least thats how i do it - for now.
Thanks again DY and all who have helped , This is hopefully going to be a fun project and a definite learning experience for us all.

 

[damnyankee]

AC,

Check your PM...

DY

 

[damnyankee]

Hi matthias,

As I read more and more about those early VCAs, I think you are right about the early ones were potted to hide the ingenious VCA design.  It's stunning that technology was created with just a handful of ordinary components.

But I've also read there those match transistors required thermal stability (as I understand it, a constant temperature range) - so maybe that's why they are encased in that white block with the holes drilled in it to accomodate the transistors.

As far as schematic, this is the best one I could find (from the original owners manual):

http://www.dbxpro.com/product_downloads/Owner_Manuals/160-161%20Owners%20Manual.pdf

Ensure the page says 160 or 161...as they are found in the same area of the manual.  I hope that helps.

DY

 

[abechap024]

Hi All,
Here's the schematic. Granted its not for the weak of heart - its not the most organized mess of wires I've ever seen, It got kinda screwy beyond repair when I converted it from Eagle to DipTrace. But, Hopefully it will be legible enough for some people with keen eyes to mull over. I've gone over it a couple times and will go over it again, I can only look at it till my eyes go cross eyed from the big CRT monitor.
I color coded the schematic for (hopefully) easier viewing:

Ground = Green
Red = 15+
Blue = 15-

Thank You All! I figure once a few people give the Ok, we'll be that much more safe on sending out the Prototypes (which who ever wants to sign up for one Is still more than welcome).

www.acsoundstudio.com/DIY/160vu/Final160schem.jpg

edit: www.acsoundstudio.com/DIY/160vu/schematic.jpg

edit: updated to reflect input FET changes on VCA. +1 arska

DY: Yes, your exactly right on the thermal issues with the VCA, and on the PCB layout I've made the 4 transistors that are thermally coupled very close together, that way we can thermally couple them with some thermal silicone or something, heck even a good old penny super-glued to the top of them all would probably work! Also, I've read that is good to keep them away form other electronics that might get hot, so I've tried to design the PCB to reflect that. (Power supply with hot transistors down by the RMS unit away from thermally sensitive VCA)

 

[damnyankee]

Thanks for putting an idea onto Eagle, AC!

I'm in for a board.  I'll be in for a total of 4 (maybe 6) of the final product.  I'm eyeballing my dbx 118s and 119s right now and they could be sacrificial lambs for this project...*heh heh heh*

DY

 

[arska]

Hi All,
Here's the schematic. Granted its not for the weak of heart - its not the most organized mess of wires I've ever seen, It got kinda screwy beyond repair when I converted it from Eagle to DipTrace. But, Hopefully it will be legible enough for some people with keen eyes to mull over. I've gone over it a couple times and will go over it again, I can only look at it till my eyes go cross eyed from the big CRT monitor.
I color coded the schematic for (hopefully) easier viewing:

Ground = Green
Red = 15+
Blue = 15-

Thank You All! I figure once a few people give the Ok, we'll be that much more safe on sending out the Prototypes (which who ever wants to sign up for one Is still more than welcome).

www.acsoundstudio.com/DIY/160vu/Final160schem.jpg

DY: Yes, your exactly right on the thermal issues with the VCA, and on the PCB layout I've made the 4 transistors that are thermally coupled very close together, that way we can thermally couple them with some thermal silicone or something, heck even a good old penny super-glued to the top of them all would probably work! Also, I've read that is good to keep them away form other electronics that might get hot, so I've tried to design the PCB to reflect that. (Power supply with hot transistors down by the RMS unit away from thermally sensitive VCA)

Still error in the VCA part of schematic. missing connection from Jfet Q9 pin1/Q8 base  to connection point R89,R90;C34. !!!

 

[abechap024]

Bless you Arska!!

Matthais - your documents of the 200 VCA needs to be updated with a trace from drain for the input FET Q3 to the junction of R1 and C1.
Also if you multiply the size of your picture for the VCA PCB by 1.0496 (on the same document) you should have the exact right size of the standard modules (I believe, someone please correct me if I'm wrong)

Thanks again Arska, you saved us at least one prototype error. I fixed it on the Schematic and will post the update.
Keep it coming guys! :-D

oh and DY today I was browsing the bay for possible dbx units to cannibalize for their modules! hehe

 

[abechap024]

Compliments of David here is some information on the 303 modules that can be modded/tweaked to be used as compressor counterparts.


www.acsoundstudio.com/DIY/303modules/dbx_4vert_trimmers.pdf
www.acsoundstudio.com/DIY/303modules/RMS_block.pdf

Thanks David!
AC