Simple unbalancing and balancing line amp

[thomasdf]

As I specified before posting (you quoted that part too) the 1/2/3 pins are totally random, I just took whatever connector was handy in terms of footprint in Eagle's librairy and used it to quickly submit the schematics here. In real life I'll do a clean and appropriate wiring, no worries.

Regarding the NE5532s : there are TWO ICs per channel in the schematics. In each channel, the first IC is called U1and both "halves" of this 5532 are used . Second IC is U2 and I'm only using half of it.

Anyways, in the newer and last design I removed the second IC. The 2nd half of the first IC is now driving the output transformer, as discussed here with Abbey

I'll post updated schematics if you want, as well as PCB pictures and will keep you guys updated with the build.. if you want to

 

[JohnRoberts]

Hello everyone,

I've done some homework, and here is what I came up with. This is pretty simple, I use the THAT 1250 for unbalacing, then go to the DBX118, then out of it into Douglas Self's baxandall active volume control "Precision Preamplifier 96", and then into his transformer output module. Max gain would be 17dB, which is perfect for me. My question is : can I skip the 2nd 5532 and directly use the inverting amp (half of U1) to drive the output transformer (Edcor 1:1) ?
I am drawing this in Eagle, working on the PCB and then out to Fusion 360 to cut if with a milling machine.

Thanks

Thomas

ps:
1) sorry for the DIP8 view in the schematic instead of two halves of the 5532, I could find a decent 5532 in the librairy so I had to use a generic DIP8 socket
2) didn't pay much attention to phase when hooking up to the in & out connectors, it's more about the circuit concept and component values here (straight out of Self's book)

from a quick glance it looks like the power pins are reversed ... pin 8 should be +Vcc, and pin4 -Vcc

JR

 

[thomasdf]

Oops you are right ... ! I guess I'll have to cut and rewire some traces on my PCB ... oh well Good thing I finally have a single 5532 per channel instead of two... That will save me some time !!

 

[MidnightArrakis]

As I specified before posting (you quoted that part too) the 1/2/3 pins are totally random, I just took whatever connector was handy in terms of footprint in Eagle's librairy and used it to quickly submit the schematics here. In real life I'll do a clean and appropriate wiring, no worries.

Regarding the NE5532s : there are TWO ICs per channel in the schematics. In each channel, the first IC is called U1and both "halves" of this 5532 are used . Second IC is U2 and I'm only using half of it.

Anyways, in the newer and last design I removed the second IC. The 2nd half of the first IC is now driving the output transformer, as discussed here with Abbey

I'll post updated schematics if you want, as well as PCB pictures and will keep you guys updated with the build.. if you want to

[I'll post updated schematics] -- ALL READY AND "STANDING BY.....!!!

[I guess I'll have to cut and rewire some traces on my PCB] -- Based upon what little I was able to understand about your circuit and its various changes and updates.....I myself thought that you were having the PCB's fabricated a little too early in your project design and development and that it was going to be a mistake. But, people on this forum do what they want to do as they want to do it!!!

And.....because I happen to have some extra time on my hands at this point in my life, I decided to replicate your schematic using my CAD-design software. While I am not saying that what I have done is all that great or anything but, there may be a miniscule chance that you -- may -- wish to model your schematic to be similar to how I have drawn things out. Now.....I don't know anything about the EAGLE software, so of course, I have no idea what is or isn't within their libraries. In any case, you will see that my schematic symbols more accurately reflect what would be actually used within an audio environment. This makes it just a teensy-bit easier for someone reviewing the schematic to more easily understand what exactly is going on. And.....YES!!!.....there are going to be errors within my schematic because I am merely following your lead and the errors within your own schematic.

I am also attaching some other files for your "enjoyment" and use within your EAGLE program. Because this forum only allows files with certain extensions to be uploaded, I have renamed the file titled, "NE5532AP - EAGLE.pdf" from its -- ORIGINAL -- filename of "NE5532AP - EAGLE.lbr". Simply rename the - .pdf - file to be as - .lbr - and you should be "GOOD TO GO"!!! There is another PDF file attached here which will easily explain to you how to import this library file into your EAGLE program. You should also make note.....that since the THAT-1250 and the NE5532 both use the same -- PCB Footprint -- decal, you can use this library file for both of the PCB footprints, but -- NOT -- the schematic symbols!!! Those are totally different types of symbols. (NOTE: I am assuming that you will be using the "DIP-8" IC-package for these devices. If not, I can also get various SMD footprints as well.

[the 1/2/3 pins are totally random] -- That's fine and it is your prerogative to do things this way. I just find it to be somewhat easier with trying to do things as correctly as possible as I am creating a schematic so there are less things to have to think and worry about correcting later on. In addition, by using the type of "audio connector" symbols from within my program's standard library, I am able to fairly well rest assured that the correct pin numbers and names have already been assigned to all of the pins. That's one of the reasons of why they even exist to begin with!!!

[as well as PCB pictures] -- NICE!!! I am interested in seeing what type of configuration you have this PCB designed as.

HAVE FUN!!!

/

 

[paolomunarini]

I made the same modification to a DBX118 a few months ago. It's based on THAT receivers and drivers, with the DIYre building blocks PCBs.

The owner wanted it modded with XLRs on the side.

Only down side is that I had to rebuild the PSU in order to keep up with current draw.

 

[thomasdf]

I made the same modification to a DBX118 a few months ago. It's based on THAT receivers and drivers, with the DIYre building blocks PCBs.

The owner wanted it modded with XLRs on the side.

Only down side is that I had to rebuild the PSU in order to keep up with current draw.

View attachment 100355

Very interesting ! Did you notice a change regarding the noise of the unit, when upgrading the PSU ?
I am upgrading it on mine too, and also adding a makeup gain and true bypass.
I plan to bend rack ears / front plate and fix them on both side of the unit, and then add the new electronics in an enclosure attached to the front plate. I’ll post pictures

 

[paolomunarini]

Very interesting ! Did you notice a change regarding the noise of the unit, when upgrading the PSU ?
I am upgrading it on mine too, and also adding a makeup gain and true bypass.
I plan to bend rack ears / front plate and fix them on both side of the unit, and then adding the new electronics in an enclosure attached to the front plate. I’ll post pictures

Actually it got a little better in noise floor (btw the unit hisses like a snake, even more with high compression settings). I don't have measurements but my ears told me that

Maybe this is thanks also to the gain in SNR due to adding balanced IOs.

FYI the PSU is switching. It's a brick from RS. RECOM RAC10-12DK/277.

The owner of the unit I modded suggested using a pre-emphasis - de-emphasis tilt EQ in order to attenuate a little bit of the hiss.

 

[thomasdf]

I'll post updated schematics -- ALL READY AND "STANDING BY.....!!!

Here's the updated version of the schematics with the power supply pins fixed, 1 is ground now if that makes you feel more at ease

Thanks for chiming in but I'm happy with the footprints I am using in Eagle as well as my overall workflow, and as I specified this was more a work in in progress / doodling in order to get comments on the basic blocks and overall design.

FYI the PSU is switching. It's a brick from RS. RECOM RAC10-12DK/277.

That's great ! I was planning on using 2 meanwell SMPS. With the added chips I want the power rails to be strong, it can't be a bad thing

 

[paolomunarini]

That's great ! I was planning on using 2 meanwell SMPS. With the added chips I want the power rails to be strong, it can't be a bad thing

I see you are using two LM7X12 on the power rails.

I went straight from the SMPS brick to the ±12V rail, without linear regulators. No particular problems.

 

[MidnightArrakis]

Here's the updated version of the schematics with the power supply pins fixed, 1 is ground now if that makes you feel more at ease

Thanks for chiming in but I'm happy with the footprints I am using in Eagle as well as my overall workflow, and as I specified this was more a work in in progress / doodling in order to get comments on the basic blocks and overall design.



That's great ! I was planning on using 2 meanwell SMPS. With the added chips I want the power rails to be strong, it can't be a bad thing

[I'm happy with the footprints I am using in Eagle] -- I was merely trying to help you out, but apparently you don't need any assistance in either your schematic drawing or PCB-designs.

https://mega.nz/folder/6uRS0bqZ#6OoLf3qKN2F474FcSM2JdQ
The above link goes to a folder that I have on an online web-storage site and it contains about 500MB of PDF files that are ALL related to PCB design, documentation, tips, techniques, routing, etc., for you (and anyone else who is also interested) to download, read, learn, digest and understand so you may become better at the design/layout/documentation of your PCB's. These PDF files are all from leading companies and sources within the specific domain of PCB design and documentation. So, you cannot go wrong with reading and following what is contained within all of these PDF files. But, then again.....perhaps you are already well-versed in knowing all about all of this and you don't really need any of this industry-leading PCB design information.

I would recommend making a "PCB Design Reference Material" folder on your hard-drive somewhere and then download either the entire folder that I have or the selected PDF files that are about the subjects and topics that are of interest to you. Then, instead of lurking and prowling the streets late at night and stealing hubcaps off of old vintage cars, you can be hunched over your computer monitor reading about how to best place components and route an analog or digital PCB. Reading about PCB design techniques is a whole lot safer, too!!!

And.....while I am certain that your EAGLE program already has its own library of CAD-models, here is a 3D file of a DIP-8 package attached as a "STEP" file. (NOTE: This forum does not allow the uploading of CAD-data files, so I have renamed the original file to be a "PDF" file. After downloading this file to your computer, simply rename it to being -- NE5532PE4.STEP -- and then you will be able to import this file into a CAD-program "as is").

HAPPY PCB DESIGNS!!!

/

 

[thomasdf]

So this is where I am now
I need to gather the last bits and start soldering. The +/-12V PSU will also replace the original DBX PSU

 

[thomasdf]

Hello everyone ! I wanted to thank you ! Operation is a success and I am very pleased with the result. This little thingie is dead silent, and has just the right amount of gain on tap to compensate for even the most abusive compressions My only concern is that the THAT1250 line receiver seems to add a bit of gain to the signal so on a master buss the unit is already compressing with the threshold all the way up. I'll add a simple 3dB pad or maybe I'll switch to a -3dB chip, I'll see.
I'm using Edcors 1:1 on the output, had them laying around.

Now I need to finish this all up with rack ears... and report back

Cheers

 

[thomasdf]

Well ... if it's not broken don't fix it, right ? Previous tests were done with the original onboard DBX psu powering the comp, and my SMPS powering the I/O board.

I totally removed the PSU of the DBX to feed it a +/-12 VDC from my outboard PSU (meanwell SMPS into chokes into regulators, as per the schematics) but now the DBX doesn't compress anymore. It passes clean audio, the LEDs are lighting on / off so I guess the sidechain / detector is working ... but no compression / expansion is happening.
Could it be that my power supply is not powerful enough ?
Here's the orignal schematics. My PSU is 7812 and 7912 (so approx 1A out) powering two THAT1250 and two NE5532, plus the DBX.

 

[paolomunarini]

Well ... if it's not broken don't fix it, right ? Previous tests were done with the original onboard DBX psu powering the comp, and my SMPS powering the I/O board.

I totally removed the PSU of the DBX to feed it a +/-12 VDC from my outboard PSU (meanwell SMPS into chokes into regulators, as per the schematics) but now the DBX doesn't compress anymore. It passes clean audio, the LEDs are lighting on / off so I guess the sidechain / detector is working ... but no compression / expansion is happening.
Could it be that my power supply is not powerful enough ?
Here's the orignal schematics. My PSU is 7812 and 7912 (so approx 1A out) powering two THAT1250 and two NE5532, plus the DBX.

What did you remove in order to remove the internal PSU?

 

[thomasdf]

I feed my +/- 12VDC at each side of C4, which I removed. I also removed the main transformer, and every resistors / trimmer that connected to + / - legs, in order to feed my PSU to the rest of the circuit and not mess with the PSU components being fed any juice.
Here's an updated crappy drawing of the PSU now, not much left of it...

 

[thomasdf]

Ok, I realised OA2 is used in the compression circuit .. I had removed it ! (one half of the IC is in the PSU section, the other one in the dynamic circuit). So I put it back, along with R5 and R37 and now it's working perfectly ! Happy ! Now to the racking

 

[TwentyTrees]

It's great to see this all coming together! One question, do you know how tall the PCB assembly is in the 118, would it squeeze into a 1U chassis by any chance?

Thanks!

 

[thomasdf]

No, because of the VCA cards that are sitting perpendicular to the main PCB. But they are fitted into slots, so I can't see why you could not mount them horizontally next to the main PCB. Worst case scenario you use shielded wire.

I took a pic for you, the tape measure is in centimeters

 

[TwentyTrees]

Brilliant, that's very helpful - thanks for taking the time.

 

[thomasdf]

I am nearly finished with the final assembly. the proto sounded very good and promising, now everything is in a tight box, bypass switches and all ... and for some reason one channel is super quiet. When I swap the That 1250 from each channels, I can clearly state that one of the two THAT1250 is faulty, or at least responsible for the huge volume drop... It's weird since it was socketed from day 1 and received no PSU overload, short or anything... If a 8€ IC dies after 2 months for no apparent reason I am a bit bummed.