FEELER: API style console (Toft ATB complete rebuild)

[Floti]

Update 04/21/2019 - Added finished schematic/layout


Update 10/29/2018 - Please read last post!

Hi everyone!

I am planning and starting my little crazy “Rebuild my TOFT ATB” project.
Most of you would advise me against it, since the TOFT is not a great console and not the easiest platform to plan any modifications, but the truth is that I like its features (8 Bus, 6 Aux, Tridents style eqs) and the size seems perfect to me.
Well, I did the mods suggested by Jim Williams for the master module and they worked great and made the board more fun to use, but I know I want something more, and buying a vintage API or Neve is completely out of question. I started with the idea of adding the CAPI 2-ACA/Booster to my master module, but there is no place for additional features in the frame, so I thought, why don´t I just redo the master module to accomodate the changes? That led me to going completely crazy and thinking about redoing the whole mixer, little by littlle. I can really use the frame and the way things are layered would work fine for me, so that´s where I´m now. The plan is to design pcbs that I can replace the stock modules with.

INPUT MODULES:
The stock module signal flow is:

Mic/line preamp - EQ - Insert (unbalanced) - Insert return buffer - Fader - Pan - Mix bus buffer
After the fader there´s also another buffer that feeds the auxes
There´s also a Tape return which goes: Buffer - Fader/Pot - Pan - Mon/Mix bus buffer

My idea is to convert this into an API input module with the Trident style EQ. It would go:

Mic/line preamp - (EQ) - Insert (Balanced?) - (EQ?) - Fader - Booster - Pan - Assign

I´ve been looking at the 528 input modules and would like to replicate that. Signal comes in to a 2622 input transformer, goes to a 2520, and from that I would add a switch where I could bring the unbalanced signal to the EQ or straight to an 2623 output transformer. This output would be half normaled in the patchbay and would return as a balanced signal. The other switch position would put the EQ after the signal has come back from the insert point. In this point, the 528 goes unbalanced. Jeff Steiger suggests the use of an INA134 to unbalance a balanced return. I would use that and then go either to the EQ or directly to the fader. After that, I´d copy the 528 (2520 - (2623 for direct output) / Pan - Assign to Buses and Auxes).
That would use all the jack inputs in the back of the console, since the unbalanced Insert has become two. I would love to have the Tape return enabled to double the Inputs by mixdown. My idea here is to build a DB25 output where the unused faceplate for the digital card is, and that would be my preamp out. Then the insert would work as insert in and the tape returns would still be there. For the tape return I was thinking about just doing a 325 booster style circuit where it goes to a Pot/Fader - 2520 - Pan and then unbalanced to the Mix bus. I guess I would also use an INA134 to unbalance the signal here.

If I did all the pcbs exactly the same, they wouldn´t fit into the frame, so I´m thinking of designing two layouts so that even and uneven channels hace their transformers in different locations. That way everything would fit into the frame and I wouldn´t need to use an outside box with transformers.

EDIT: The new pcb modules with transformers and 2520 opamps would fit in the TOFT easily.

I don´t know about the power consumption, maybe the PSU won´t be able to power such a console. I have the ATB16 and it´s supposed to have the same PSU as the ATB32, but I wouldn´t have anything against upgrading the PSU too. Any suggestions here?

I will come back next week with my Input modules schematics and my ideas for the submaster and master modules.

Do you guys see any big problems I´m not taking into account?

Thanks!!

EDIT: SCHEMATIC AND LAYOUT ATTACHED.

 

[Floti]

I'm working on my schematic, mixing what the user Boji drew in his Console Project with the original schematics and some of the features I'd like to have on my boards. It's my first time doing a Schematic/PCB on Eagle, so it's coming up a bit messy, but until now I haven't run into big problems.

As I wrote in my last post, I'd like to have the possibility of choosing if the EQ comes before or after the insert point. The faceplate of the Toft won't be modified, but I never use the Mon to Auxes 5-6 switch, since I can make easier and more customizable Headphone mixes using Pro Tools. I'm using this spot in the faceplate to put the EQ Pre/Post switch.

Here's my schematic so far. I only got the Mic/Line amp until the preamp out and the EQ. I redid the Toft EQ, and I wanted to ask some things about it. I see a lot of coupling capacitors after and before every OPAMP, do I really need them? Should I replace the with higher value ones? The power inputs of the OPAMPS aren't shown in the schematic, but should I add .1uf ceramic caps at each input to ground? I saw that in Jim Williams mod for the master module..

Also, I'd like to use a Balanced to Unbalanced driver in the return of the insert point so I don't have to rethink my cabling. Jeff Steiger suggests using an INA134 but I can't find anywhere a circuit to do that same thing with this opamp. I've seen it being named as interchangeable with others, but I thought the INA134 required less additional components and I don't see that anywhere. Could you guys help me with that?

Thanks!!

I noticed I forgot to draw the ground sign in the preamp Audio com, but I'm aware of that!  ;D Also the diode values are false, I just used them as placeholders.

 

[pucho812]

The atb is transformerless and the input for mic and line on the channel is based around an ina217/that 1510 depending when it was made. there is little room to menuver or add transformers.  It won't be able to happen because of space.  If your slick you would bypass the ic's that sum in the master module and go to the capi board.  You can wire from those ic dip sockets.  I have notes on what and where.  You then could come back in and have the fader control.  Use the plate for the digital cars that never got made to make it all workable.  Other things to consider the pots and switches are soldered in.  The pots mount the channels to the frame, the switches are just soldered in.  So you remove them and might not be able  to get something else in that would fit. 

Yes there are coupling caps everywhere, they are necessary unless you doing things like d.c. servos  to remove caps in the audio path.

If you look at the toft, think of it as an 80B with a different front end and more noisy. 
We can help you out with it.

 

[Floti]

Thanks pucho812! That's actually clear to me, but my goal is to create new pcbs and replace the existing modules with the ones I create. I've been making some calculations and I'd say it looks like it would fit. It's a lot of work but might be fun to try!

 

[Floti]

And with the coupling caps, for example if you look at c25 and c28 in my schematic, they are there in the Toft Eq, but I don´t see them in the Trident EQ. Also it´s the same cap two times, shouldn´t one cap alone take care of DC filtering? And as I said, I got rid of all the electrolytics that were following an opamp in the master module when I did the Jim Williams mod to it, so I thought this might be another improvement area, getting rid of all those 22uf/16v caps in the EQ section and adding the ceramic caps from the power inputs to ground on each opamp. Am I wrong here?

 

[Floti]

Today I spent some time working on the schematic. I still need to add the Auxes and check for mistakes, but so far I haven't noticed anything that could possibly be completely wrong or spots where I can't come any further.

Is this the way I'm supposed to use the INA134s for the balanced to unbalanced inputs? I might as well use an INA2134 if I'm having two inputs, right? I supposed that since the 134s got already their internal resistors, all I have to do is what I did plus the capacitors from power inputs to ground. Does it sound right?

Well, I'd really appreciate if any of you who know so much could have a look at my schematic so far. I'll try to tidy it a bit more in coming revisions.

Thanks again!!

EDIT: I already spoted some mistakes on the schematic, I´ll post a revision later today

 

[Floti]

Hi again!

So I think I got my input module schematic finished. Just hoping some of you will chime in and tell me if the balanced to unbalanced is actually THAT easy with the INA134s  and if you guys are able to spot some mistake I haven't seen yet.

Next step is fixing this all into a pcb that needs to have all the pots and switches in the exact same spot as the original TOFT ATB modules. 

 

[iampoor1]

Im having some issues reading the schematic, but a few notes.

Are you planning on using tl072's for the mic preamp? There are many better opamps for this.

All of the opamps appear to not have bypass capacitors, I would add local bypass capacitors to each opamp.

The bulk decoupling at the input of the module is too small (marked as 1uf in the schematic), but should probably be somewhere between 100-470uf

I think adding some input and rfi protection to each INA134 would be a good idea, also a capacitor on the output if they have a dc  offset. I usually use the THAT 1246 as a line receiver, and the data sheet has a good input protection circuit explained.

Good luck, I dont understand the purpose of this project but Im excited to see it.  ;D

 

[Floti]

Hi iampoor1! Thanks for the reply, I really appreciate it.

Well, the schematic is surely difficult to read. I´ve tried to tidy things up a little as I´ve come further, but it´s my first schematic on eagle and I need some time to learn. Maybe I should´ve done the different sections on their own, so that it´s easier to follow.

The opamps look all the same in the schematic since I used the same symbol on eagle, but if you look close enough the Mic/Line preamp, insert return and tape return use a 2520 as opamp. It´s a copy of the 528 circuit without the filter and with a switchable Trident 80 style EQ before or after the preamp out. The way the buses and auxes are wired if taken from the original Toft ATB modules. Also the signal LEDs and meter feed are copied from that.

About the capacitors in the opamps, I wrote that in a previous post, I plan on using  .1uf ceramic caps from each opamp´s power input to ground.

I see what you say about the input capacitor. I actually copied that from the 528 schematic (added as atachment in this post). It would be c18 there. But I just checked and saw that Jeff Steiger uses a 10 uF/25v cap on the input of his 325 boosters, so I guess that would be a better choice.

Here the CAPI ACA/Booster: http://www.capi-gear.com/catalog/images/gallery/PCBs/2-ACA-Bo/CAPI-2-ACA-Bo-Rev-B.1-schematic.pdf

I´ll look at the THAT1246 documents and maybe change the INAs to those, since it seems to be more information on those everywere.

But let me help you understand this project. I want to have a really nice sounding console. I enjoy doing DIY stuff. I´m not a fan of metalwork. I got this TOFT ATB console which I think has really nice features but doesn´t give me anything soundwise. So my thought was, at first, I´ll mod the Toft. I opened it up and there was no place for that, so I thought that if I build the pcbs for the input modules and replace the original modules with the ones I built, then the mods would fit and I´d be able to have a really nice, pocket size console. So I´m planning to do 16 Input modules, 8 Submaster modules and a Master Module. That means, I´m building and API style console with Trident EQs using the metalwork from the TOFT. Is that clear now?

Thank you very much, I´ll try to update my schematic later today.

 

[Floti]

I added some rf and bypass caps and changed the value of the input capacitors.

Also added the updated version of the schematic to the first post, so that it's easier to follow.

Any help would be appreciated!

 

[Floti]

Simple question, I guess.

The Toft Modules use 10K bus resistors. The API 528 Modules use 47K bus resistors. If I want to try one prototype module with the rest of the Toft Modules in place, should I match the bus resistors? Should I use 10K on my prototype when I´m testing it with the stock modules in place?

 

[boji]

Hey glad to see you're chugging away on your console build. I'm also trying to finish what I started years ago.  Post picts as you progress!!! ;D

 

[Floti]

Hey glad to see you're chugging away on your console build. I'm also trying to finish what I started years ago.  Post picts as you progress!!! ;D

Thanks boji!! Your posts have been a great source of information! Sure, I will post more pics as I go. I'm a couple of days out of town but I managed to work a bit on the plane. I fixed some mistakes on the input module schematic and started drawing the submaster modules. I'll post everything when I got the time.

Show also your progress too! I'd love to see how far you've come.

 

[pucho812]

sorry I was not completely understanding of what you were undertaking.

don't mind me.

 

[Floti]

Hi guys!

I stopped working on this for a couple of months and just recently came back to this project. I finished the PCB design and ordered a prototype from PCB cart which I´m planing to try this week, hope it works! Had some problems with the measurements of some of the switches/pots, but that will be taken care of in the next revision. I´ll post more details in the next days.

 

[qmp audio]

and this one

i can't seem to view  IMG_0599.jpg attachment.

btw,  this is great.  i want to implement into my Toft also.

 

[Floti]

I couldn´t either. Hope it works now!

 

[nielsk]

It should use less current with the DOAs if they are accurate 2520 types.
you may want to change the mix resistors if they are going to the API ACA amps, leave as is if going to Toft mix amps.
If you get this working I may know folks who would want PCBs to replace some channels in their consoles...

 

[Floti]

Cool! I won´t be able to do much next week but after that I´ll finish testing the module and I´ll order the new ones with the correct layout for the toft. I don´t have any problems ordering a few more if someone wants to test them out too. Just let me know how many you´d like to have and I´ll see what I can do.

 

[warpie]

Look great! So, are you keeping only the frame and the PSU from the ATB?