An API Compressor Project

[gemini86]

Do we know what output pair they use on the original 2510? The original package seems too small for to220 size parts.

 

[etheory]

Do we know what output pair they use on the original 2510? The original package seems too small for to220 size parts.

As far as I can gather the original is completely surface-mount, and the output transistors aren't much beefier than any of the other transistors within the main circuit itself (the original isn't designed to drive any type of scary load whatsoever).
I over-sized my variant on purpose, due to reading that the 2510's tend to consistently fail due to a lack of output protection and drive capacity, and also to increase it's applicability - i.e. in mine I can, and have, literally, to see what it sounds like, swapped the 2510 and 2520 over for a different sound, without any issues.

I can't pretend this version will sound the same as "the real-deal", but I can guarantee it'll last a LOT longer.

Unfortunately though, as you hint, in the form I have it in here, it's unlikely to be able to be made as small as the original package.
However as "yet another flavor" for your 2520 sockets, it's an interesting option.

 

[etheory]

Seems to be a lucky good few days.... (touch wood....)  I just tested the VCA by devising a simple voltage divider across the supply and using that to drive the VCA side-chain input with a potentiometer.
With lovely and boring linearity and precision, it does it - you turn the pot, and as the CV voltage changes, so too does the VCA output volume.

One small step for compressors, one giant leap for me.  Unfortunately, it's a sour victory.  Due to a misread of a couple of different things, I've inverted the Ec- and Ec+ inputs to the 2180, so the CV is being inverted before application.  But, it's a test board, so I'll just do a snip and cross some wires underneath to fix it.  The board for revision 2 has already been fixed in Eagle.

I will have to park this project for a while now as I have just found some full-time employment again, but, very soon, I'll pick it back up and start working on the control voltage and side-chain board.

Thanks for the help to those who contributed it - it's been a lot of fun, catch you soon.

 

[bruno2000]

Just checked the DC Offset on the output of the 2510 and my little scope has difficulty measuring it, so I will call it negligible and also call it a day.  Awesome.
Would anyone be interested in 2510 boards in 2520 format?  Or would there be only interest for the original footprint?

Me!  I'd like some!
Best,
Bruno2000

 

[etheory]

Me!  I'd like some!
Best,
Bruno2000

Sweet, in which format, the 2520 format?  Cool, well, I am pretty close to submitting the order, so, I'll PM you about details cause it would be great to have someone help test it more thoroughly as well.  It all seems good on my end but I don't have enough gear to put it through its paces like a more seasoned prodigy-pro'er probably could.

 

[bruno2000]

Yep, 2520  I think it's great to be importing other devices to this format, much like the Sphere project.
Best,
Bruno2000

 

[desol]

Great thread. Can't wait to see what happens next!  ;D

 

[etheory]

Great thread. Can't wait to see what happens next!  ;D

Thanks desol, it's been quite the journey that's for sure!  But there is still a lot to do.

For instance one thing I've been doing also is seeing how many different type of op-amps can be safely substituted into the circuit exactly as it is, with no other changes.
Thus far, with almost total generality, the following seem, at least on the simulator (which so far has proved 100% reliable due to my careful and detailed simulations), to give acceptable results:
"My" 2510, "My" 2520, any standard 2520, the NTP M-100, The Neumann OA10, and, with some minor modifications, Tamas' BigFetBloak, FetBloak and GainBloak and the Neve BA440 and BA340.  So basically any truly differential opamp and, with modifications, some others too.

This is really quite exciting, as the possibilities for "tone" are therefore almost endless, which is excellent, and another huge goal for this project (I don't want to have to make another entire compressor just to change some of the tone of the unit, I'm trying to make it much more flexible than that).
I am also, as a part of this, attempting to squeeze all the previously mentioned opamps to 2520 format, which is also very challenging, interesting and exciting.  The Neve's in particular I have never seen in 2520 format, and would be a great addition to anyone's kit for sure.  More to come soon....  I'm also simultaneously making headway on a Calrec PQ1061 clone here: http://www.groupdiy.com/index.php?topic=5295.msg597036#msg597036, which I'm potentially going to build a prototype of on the weekend also.  So there is a lot going on in the etheory studio ;-)

 

[etheory]

OK a small update....

I FINALLY have the LTSpice simulation for the side chain kinda-sorta-but-not-really working perfectly.
I'm just messing with my updates to it (more attack and release settings, and control over more of the internal parameters, including being able to overdrive the output, and the stereo linking/side-chain options for filtering etc.)

I also almost have the funds (after some freelance work I'm about to finish) to be able to buy the rest of the parts for the main compressor prototype (i.e. a side-chain test board to plug in to the existing audio-board) - I can't wait to test this thing - I've been patiently waiting for far too long now!!!!

Sorry also to bruno2000 who has been patiently waiting for a small eternity for my test 2510 boards - sorry mate, I promise I'll finally get around to it soon (although my one-and-only prototype one has been working perfectly for some time now) - work has been fun, but still a PITA recently, and the contract I am on is soon coming to a close = more free time for me!

more soon....

In other news, for no apparent reason, I also managed to design a modern Neumann U473 comp/limiter derivative that works in the simulator also, from entirely modern parts - and also transformerless so it should be cheap-as-chips to make - it'll be a totally awesome comp too - more soon as well, but first I godda finish this 225L and the Calrec pres....

 

[etheory]

Finally, an update!
The amplifier boards finally came back from the fabrication plant, and they look VERY nice.
I don't have them in my hot little hands yet, but, for my first ever print, I could not be happier that the design I did came out so close to what I'd hoped for.

On the left is my interpretation of the 2520, and on the right, a severely bastardized 2510 in 2520 format.

These are both generic amps, and can be used in place of any DOA from any voltage from +-15 to +-24.

More news soon.  Thanks so much to bruno2000 for you patience, your boards will be sent very shortly.  I will PM you soon for details:

 

[etheory]

Another pic of the front and back.
2520 on the right, and 2510 on the left:

 

[etheory]

Looking good!

 

[gemini86]

indeed!

 

[etheory]

I've updated my website with a large post about where I am up to at the moment.
More to come:

http://www.evolutionarytheory.com/2012/04/custom-audio-compressor-%E2%80%93-part-3/

 

[etheory]

I finally have some more progress on this crazy project that I have no time for at the moment....

The PCBs I had fabricated returned to me a week or so ago, and I've only just managed over the weekend to solder a couple together and test that they work properly - so I have some pimp shots of the 2510 and 2520 I've developed for the project.

Note the original prototype CNC boards behind the final ones.  It was chalk and cheese working with each one.  The silk-screening and solder-masking, unsurprisingly, was SO SO nice to work with.  Being the first boards that I have EVER had professionally made, I am extremely happy with the way they perform and the way they look too:

 

[etheory]

Another one:

 

[etheory]

And another:

 

[etheory]

8)

 

[imloggedin]

very cool project! nice job

 

[etheory]

Cheers!  It's currently on hold for a little bit as other life stuff has come up, however, I'll be back onto it as soon as I can!