Channel Strip Project (API+Pultec+1176)

[Dyonight]

Hi!

I want to put togheter a channel strip for tracking drums.

Since I aim for 16 of them, I want to reduce cost and put as few transformers as possible, ideally one at the input and one at the output of each channel.

I don't care for "mojo" or any of this nonsense, all I'm interested in is low noise and the specific functionnalities of each device.

The more simplified the design is, the better.

Here is the signal chain:

API312 clone -> Harrison High/Low pass filter clone -> Solid State Pultec -> 1176

In short, I want to eliminate the transformers of:

Api 312 Output
Pultec Input and Output

What's the simplest way of connecting all those directly and cleanly? What options are available? What should I be looking for?

The goal is to mount each pcb side by side, or even fit all the traces on the same pcb, so interconnection distance will be as short as possible so I don't think balanced in/out between each modules would make any sense, would it?

I'm aware there's a lot I need to learn before attemping anything but I guess I'll start here!

I have quite a lot of DIY experience putting things togheter but I'm basically a puzzle maker, I've never designed anything so don't hesitate to point me to things you think I need to know.

I joined a block diagram to visualise the signal flow, the blue lozenges are the parts that concern me for now... I'm aware there's a lot to talk about...

Thanks!

 

[iampoor1]

If you don't want mojo then why are you building a channel strip with a ton of mojo?  ???

 

[Dyonight]

Thanks all!

Well I have nothing against circuits designs that add harmonics, distorsion, compression or mess with the frequency content (in a way that help of course). I won't go out of my way (and budget) to have those if I can get the same control over the sound with a simpler design.

I'm just used to interact with these designs.

Why I choosed those specific parts:

API 312 = I have 16 of them already built from kits and would like to intergrate them

Harrison filters = The schematics are easy to find and the board easy to clone and are renowned to work well. Any other suggestions are more than welcome!

Pultec Eq = For rough tonal shaping, I always use those first. The way each band interact with it's "cut" counterpart always get me in the ballpark without having too many options to get lost or screw things up too much. I get the initial results that I want way faster than with a parametric Eq and are easy to recall. If I can get that effect with a chip based design I'm all ears!

1176 = The way it grab transients and keep things under control while maintaining snap. I have a favorite setting that "always work" on drums so I'm gonna hardwire the release, attack and ratio controls and only leave a knob for the input and output to drive it as I see fit. Also if there is a chip based design that can work here thanks to let me know!

I just want to do basic clean up and pre-shape the sound for mixing later.

 

[Dyonight]

If you really want low noise, low running costs, lower build cost, function only, etc do something with IC chips (i.e. THAT Corp), cheaper, faster, more efficient, more neutral.  Clean, low noise, low distortion.  They have a bunch of design papers to help you.  And, the good folks of GDIY, especially the moderators will be pleased you don't care about mojo.

If you do go with ICs, I suggest using sockets for them, especially if you don't have a desolder station or solder sucker.  No need to get gold sockets in my opinion.  Sockets make it easier to replace an IC in the future, if and when you need to.  You'll need to build a dual rail power supply and filter well throughout.  I'd suggest you look at SSL 4000 schematics but they are pretty complicated too, but you can learn from it.  Primarily runs on the NE5534 integrated circuit, which has a distinct THD of its own, but a little less apparent than what you have in your list.

All the best with it.

Adam

That was extremely helpful, I'm indeed looking for functions first. I already have the 16x API built, so I guess I need to find a good Hi/Low pass design, a circuit that can emulate the interaction of the bands of the Pultec and something that would behave similar to a 1176 in term of attack/release/ratio.

Also, I'd like to have a transformer on the input and one on the output. I think it is a good thing regarding isolation and the way it handle peaks compared to a solid state output stage. Also, I already have them with the 312 so why not use them. Correct me if I'm wrong.

To do so, I'd take the API output transformer, find a way to connect its tranformer-less output to the next module and fit the 2503 Tx after the compressor. Not sure what this imply or if it even make sense.

Thanks a lot for your time!

 

[john12ax7]

If it's all going in one box you can just connect all the interstages unbalanced.  Removing the 2503 after the pre will give you 6 dB less gain there,  but shouldn't be an issue with drums. If you put the 2503 at the end in 1:2 configuration make sure the output stage can handle it.

The 1176 character is due to the response and also the sound of the gain stages.  You seem to care more about the former,  so could simplify things by making the gain stages opamps , this would change the tone but you would still get the response of the fet compression.

 

[Dyonight]

Hmmm.

Since you are familiar with the gear you mentioned, and you've use them, and like them, and have some stock already, then I personally feel it's a good plan to move forward with the things you already know you like.. if you indeed want to go forward*.

But, before you do that, maybe rent a more economical mixer with some of the eq and a 'one knob squeezer' type compressor built in to each channel, and just see if it gets you in the ballpark of were you want to be.  It may be all you need, and that'd be great.  On the other hand, after that test you may realize, afterall, that the inherit harmonic distortions, natural compression and imperfections of the gear you like already, is helping in getting things in the ballpark easier.  This is my design/artistic belief, not a set in stone reality for all.  I would use your 312 and transformers.

If you're definitely going to do something yourself, and if you've determined a small mixer with IC based designs is getting you where you want to be, you could try to integrate your 312 kit into your own design with other opamps (mainly IC based) and go mostly transformerless, if you like that thing.  Cross that bridge when you get to it though.

ps. I like Pultec more than parametric too but they're both good for different reasons.  You already know you like Pultec though.  There's not much that grabs like an 1176 either, and lots of people like API for drums.  They call it aggressive. 

Adam

* You are already aware it's a big project to take on, but please realize these projects take even more time than one would think.. it can distract from music making in a big way.

Hi again!

Yes small mixers do the trick quite well but my quest is to integrate what I already own and add the fonctions that will save me steps later. Low power low noise  transformerless versions of a pultec and 1176 are definitely what I'm aiming for.

I'm completely aware this is quite the undertaking, I am at a level of experience that allow me to understand how much I'm currently clueless ahah!

I'm looking at this as something I'll tackle when the important things are done, so it may move slowly. I still need to have a clearer idea of what will go where and why.

Once this is clear, maybe I'd like to hire someone knowledgeable to put togheter a schematic for me, I'm sure there's plenty of people around here who could handle this. We'll see once I'm closer to a clear design.

 

[Dyonight]

If it's all going in one box you can just connect all the interstages unbalanced.  Removing the 2503 after the pre will give you 6 dB less gain there,  but shouldn't be an issue with drums. If you put the 2503 at the end in 1:2 configuration make sure the output stage can handle it.

The 1176 character is due to the response and also the sound of the gain stages.  You seem to care more about the former,  so could simplify things by making the gain stages opamps , this would change the tone but you would still get the response of the fet compression.

Oh yes happy to hear that can be done! Indeed 6db is nothing on drums since the pad is active on every channels when I use them...

You got it, a FET compressor with opamp gain stages. I guess I'm looking for a Pultec with opamps gain stages as well.

Awesome! Thanks!

 

[TwentyTrees]

A Pultec with an op amp  makeup stage is very doable, that's pretty much what the later solid state ones are (using an API 2520, from what I've read). You could crib this wholesale for more API colour, or use an appropriate IC for a cleaner version. Main thing will be getting your impedances right into and out of the filter section, as passive EQs are particular in that respect, but it's totally doable.

Sounds like a fun (big) project, I like the ambition. Please keep us posted!

 

[Dyonight]

A Pultec with an op amp  makeup stage is very doable, that's pretty much what the later solid state ones are (using an API 2520, from what I've read). You could crib this wholesale for more API colour, or use an appropriate IC for a cleaner version. Main thing will be getting your impedances right into and out of the filter section, as passive EQs are particular in that respect, but it's totally doable.

Sounds like a fun (big) project, I like the ambition. Please keep us posted!

Using discrete opamps could be fun! They are easy to find and DIY versions are relatively cheap. I like how they react and shave peaks when the drummer get carried away and plays louder than he did in the soundchecks! (which is all the time)

That could be nice to use them everywhere possible... that's an option I won't rule out yet!

Thanks!

 

[Dyonight]

Thanks for the insight again!

I own a cnc that I plan to use for prototyping pcb, but that's something I'll have to master first, so I guess I'll have to destroy a couple of copper plates before I can even talk of getting a circuit prototype testable.

I will also take care of the metal work on the cnc with laser engraving on anodysed alluminum.

All of this is quite the undertaking but it's not my first time undergoing something stupidly out of my reach. It will take time but that will be quite a ride!

Thanks all for your inputs, I'll post my findings here so anyone who wish to add something will be more than welcome!

 

[ruffrecords]

I would recommend you get your PCBs made outside, It saves a huge a mount of work, you get a much better quality result and all the component idents are silk screened  on the surface so you know exactly what goes where - you would not believe the amount of time you can spend chasing a wrong component value on an unmarked PCB. And these days they are not expensive.

Cheers

Ian

 

[Dyonight]

I would recommend you get your PCBs made outside, It saves a huge a mount of work, you get a much better quality result and all the component idents are silk screened  on the surface so you know exactly what goes where - you would not believe the amount of time you can spend chasing a wrong component value on an unmarked PCB. And these days they are not expensive.

Cheers

Ian

Hi! Thanks for your input!

Once I have a working prototype, I'll definitely have the final pcbs professionnaly made, they simply achieve a quality that I won't ever be able to match. I have a long way before getting there but that's indeed part of the plan!

While having them manufactured, maybe SMD could be an option for certain parts but I'm way ahead of myself here...

Cheers!

 

[Dyonight]

I had another think on this morning and to me it seems counterproductive to aim for an 1176 and Pultec functionality, without following the original designs.  It really is a sum of the parts and I am willing to bet once you start hacking those designs with modern IC chips it'll not only function/sound/react different, it'll be overkill.  I.e. Using an IC where only one transistor could do the job.  OR worse, using a discrete opamp where a single transistor might do.  So, why not take the exact schematics, build them as they were intended when and as you can afford each channel?  The functionality, great usability/application of them goes hand in hand with the original design.  For a Pultec, sure, use a opamp as the makeup gain.

Slew rates of ICs won't match, THD profiles might not match well, and the current gain .. so while we can try to ignore these things and say the mojo doesn't matter, you do in fact like what those classic circuits do.  You've made reference a couple times to the gear handling peaks well, and it's going to be very hard to do that in chips.  The attack and release will feel different, that's my guess.  Total Harmonic Distortion profile will also be pretty different than what you're used to ...

I don't know, I'm skeptical now about the design goal/intention.  You like the mojo of the circuits as originally designed but don't realize the mojo goes hand in hand with the functionality of those classics.

You'd probably be better off tracking flat with an instrumentation amp chip (applied as mic preamp) of some kind, or with your 312 preamps which you already built, and then using digital plugins.  I say that because if you go hacking the circuits with ICs you may just end up with something quite similar to a Behringer, or a Yamaha.  I'm not knocking those products at all, but why go through the immense work load only to end up with something much more neutral, that is already on the market for a cheaper price.

Is it really worth redoing an 1176 or a Pultec?  I pose this to all.

Adam

Hi!

Those are legitimate questions, I'll try to be more clear on the points you underlined.

--------------

First I guess: gear character or "mojo" (damn I hate that term ahah)

Let's say it determine the way a piece of gear alter the original signal in a unique way.

I indeed can, to a certain extend, identify the effect it have on some audio signals. If I have a choice, since the design phase leave some freedom, I'll consider both options and see if it make sense to incorporate the "old school" one or not.

But the main goal is to move fast while setting up. I want the preamp to increase volume, the filters to approximately cut a bit of rumble, clear the mud, tame harsness and add presence that I can't improve with mic placement. The compressor should have some snap going and help getting a consistent signal. I say help, all of this will get mixed later using plugins.

I'm not looking for pinpoint identical. The goal is to have minimal knobs where it matter and access them as soon as I think of something. I want to get closer to the final result in the tracking step and do all I know I'll do later immediately.

I've narrowed the core elements on which I want immediate control while things are happening. Volume, low end, top end, consistency.

-------------

Next, why not going direct from the preamp to the daw and use plugins?

It's less interactive. I want to act on things while they are happening, I don't want to take notes and figure stuff later. I'm tired of that. I don't want to search and click in a project and ajust some pixel knobs later, when I hear something now. The toms get boomy when played togheter? Reach the knobs, clean that crap out, add a bit of resonnance back, done. When you press play, it already sound great and balanced. Recording have to be fun and intuitive, computers softwares, for me, are not. I don't have the feeling that I'm doing things. Well I guess you get the point!

-------------

Why not use already made mixers that offer similar feature set?

Well, none does!

I don't need extra buttons. I don't need a monitoring section. I don't need headphones output. I don't need aux sends. I don't need parametric midrange. I don't need tons of leads flying all over the top of my desk. I don't need all those knobs gatering dust and confusing me.

I want to access some parameters only and leave the rest for later:

Gain - High Pass - Low boost - Low Notch - High Boost - High Notch - Low Pass - Basic dynamic control - Output

Gain - The 312 is doing great on drums and I already have them

Low/High pass - The Harrison circuit is easy to find, hit the right frequencies and is known to achieve great results.

High/Low boost notch - Nothing does these curves like the Pultec design as easily. Gets in the ballpark fast.

Dynamic control - A Fet compressor will perfectly do this on drums. A 4:1 ratio, slow attack, fast release will tame the transients while letting the snap through. Nothing gets screwed but take a desirable direction. More intense processing will happen with plugins, while mixing, if necessary.

Anything else is distraction.

-----------

And of course: Is it worth it!

The pultec design.

It seems only the original make up gain stage cause problems. Seems like the option to use a chip IC or DOA can be fitted on the same pcb. I'll join a picture of a design made by the guys at DIYRecording equipement. I'm sure it can be shrunk quite a bit if we ommit the space to fit the transformer. I'm sure it's absolutely awesome even in it's bare bones configuration. It will be more than good enough.

1176/Fet compressor:

I believe what matter most for initial drum takes taming is the FET behavior, the gain stages may have an impact when digging in like a madman but for basic transients handling, getting in the ballpark will still get punchy drums and if some DOA can be added as an option that may help round the sound when the headroom limit is reached. I'm not sure how the 1176 design can be adapted but I think it's a good starting point.

Those simplified version will definitely be cheaper, so yes for me it's worth it.

-------------

Well that was quite a lot of rambling... but I hope it give a better picture of my vision and motivations. I've been thinking about this for the last couple of years and now I think it's time to start talking about it.

Thanks!

 

[Dyonight]

Are you familiar with the expression "you're preaching to the choir?"  I mean no offense with that, I'm trying to help as much as I can, but your goals are contradictory in my opinion.  You started by saying you don't care about mojo and all that nonsense.  Let's replace that term with characteristic profile, if you prefer.  You clearly do like a characteristic profile imparted on the sound though, so I'm trying to save you building something you don't like.  If you really don't care about characteristic profile imparted on the sound then you really should sell your 312 preamps, and use instrumentation amps in a DIP8 package.  Check out THAT Corp for IC based compressors, and setup basic tone shaping controls.  BUT, this is not really what you want, is it?    You actually want the transformer juice/excitement/magic/mojo, all the exciting current gain, noise, smearing, and all that stuff that makes tracking drums more fun and more "functional" for you.  I put quotes there not to be saucy but to emphasize that functional is also a vague term here.

I am all about committing to sounds you like, on the way in.. and not waiting.  I really don't like plugins much either.  I'm not a big fan of ICs for audio either.

My question that I posed about is it worth it, is IF you decide to redesign these things, the 1176 in particular.  It most likely will take significant effort whilst the original schematic is already available to you, and you know you like that design.

A 312, pultec and 1176 are quite simply a mojo factory.  Put 16 together, that's a lot of juice.  If it could have been done economically, it'd most like be out there en masse already.

I think I've helped as much as I can..  sincerely hope you do well with it, whatever road you go on.  Seems like you know more than I thought you did, and don't need much input.

Adam

Hey!

I may have misinterpreted your previous post, one thing sure I don't want you to think I'm arguing or whatever, if anything this exercice help me pinpoint what I'm really after!

Regarding mojo, what I mean is I won't go out of my way, complicate things or exponentially increase cost to achieve that little extra something. Cost-effectiveness and workflow are the priority but of course we're all some kind of nerds and like to push things as far as they will go ahah!

I will most likely have to tone down my expectations as I progressively realise how this electronic reality really work but for now I'll keep going and with what you guys all suggested it's that much more interesting!

SO far I know that doing a full blown 1176 is just too pricey, I'm curious how simple this circuit can get.

Thanks for your time and feel free to add anything!

 

[john12ax7]

Take an 1176, convert it to ICs and you get a distressor.  It definitely changes the sound,  but wouldn't say it's not worth doing. The fet smack is still similar.

 

[Dyonight]

Take an 1176, convert it to ICs and you get a distressor.  It definitely changes the sound,  but wouldn't say it's not worth doing. The fet smack is still similar.

Really?? Oh damn.... now that's interesting... I need to find out more about that...

 

[TwentyTrees]

And if you're interested in how tiny an 1176-type circuit can get...

https://store.louderthanliftoff.com/products/implode-colour-module

(Caveats: they describe it as the full preamp and detector circuitry of the Rev F, though I've not compared schematics; assembled only, no kits; and I expect there's a ton of SMD parts on the bottom of the board. Still pretty good though, for smaller than a credit card!)

 

[Dyonight]

And if you're interested in how tiny an 1176-type circuit can get...

https://store.louderthanliftoff.com/products/implode-colour-module

(Caveats: they describe it as the full preamp and detector circuitry of the Rev F, though I've not compared schematics; assembled only, no kits; and I expect there's a ton of SMD parts on the bottom of the board. Still pretty good though, for smaller than a credit card!)

Holy damn! That quite the achievement ahah! In fact this point in the right direction....

And yes you're right the bottom is pretty filled!

That's great to get a sense of what's possible though...

 

[Bo Deadly]

API312 clone -> Harrison High/Low pass filter clone -> Solid State Pultec -> 1176

In short, I want to eliminate the transformers of:

Api 312 Output
Pultec Input and Output

You mean like this?

  https://groupdiy.com/index.php?topic=65032.0

Are you located in the US lower 48? If yes, here is a PCB for the Pultec:

  https://groupdiy.com/index.php?topic=74351.0

But I I'm only giving out 5 / person (and I don't have 16 of any one board anyway). But it might be worthwhile to play around with them just to help you figure out things. I also have similar boards for the API and 1176 but I didn't include them in the post because I believe there are errors and I don't recall what they are. They're probably minor. Something that is easily fixed by cutting a trace and jumping something with a little piece of bus wire. But it might not be fun to debug.

Otherwise, what you describe is perfectly doable (obviously). There are a few concerns however:

One is that if you make one giant board and there's a problem (and there always is - I don't think I've ever made a PCB that didn't have an error the first time around), it could be very disappointing and expensive to fix. That's why I made lot's of little boards so that if (when) there's a problem I can just swap out the one board. Many early console designs where the same way. There was a frame with edge connectors that cards would mount to. A little different from my "stac" of PCBs separated by standoffs but the same conceptually. If you just don't like the whole prototype-ish vibe, the next step up would be to make a backplane with several daughter boards.

The second concern is matching levels. The API gain is only 40dB. If I'm not mistaken, in a real API console, the "output" transformer is actually for interfacing with the mix bus. Then there would be an output that amplifies more. Also, the 1176 cannot handle a lot of signal on the input. So you could use the 40dB, run through the pultec and 1176 and then add another fixed 20dB on the output stage. But that might not be the best for noise performance. Generally, for the best noise performance, you want to make all of the gain up-front. So the alternative would be to put an extra fixed 20dB right after the API pre, put a trimmer in front of the 1176 followed by a makeup stage just for the 1176. That's what I did in my "Channel Strip 1".

The final concern would be scaling up to 16. The thought of building 16 channel strips like that makes me twitch a little. That I don't have a solution for but I would imagine the procedure for building 16 efficiently and correctly is not that different from building 1,600 so I assume you have some serious time and money to burn.

 

[Dyonight]

You mean like this?

  https://groupdiy.com/index.php?topic=65032.0

Are you located in the US lower 48? If yes, here is a PCB for the Pultec:

  https://groupdiy.com/index.php?topic=74351.0

But I I'm only giving out 5 / person (and I don't have 16 of any one board anyway). But it might be worthwhile to play around with them just to help you figure out things. I also have similar boards for the API and 1176 but I didn't include them in the post because I believe there are errors and I don't recall what they are. They're probably minor. Something that is easily fixed by cutting a trace and jumping something with a little piece of bus wire. But it might not be fun to debug.

Otherwise, what you describe is perfectly doable (obviously). There are a few concerns however:

One is that if you make one giant board and there's a problem (and there always is - I don't think I've ever made a PCB that didn't have an error the first time around), it could be very disappointing and expensive to fix. That's why I made lot's of little boards so that if (when) there's a problem I can just swap out the one board. Many early console designs where the same way. There was a frame with edge connectors that cards would mount to. A little different from my "stac" of PCBs separated by standoffs but the same conceptually. If you just don't like the whole prototype-ish vibe, the next step up would be to make a backplane with several daughter boards.

The second concern is matching levels. The API gain is only 40dB. If I'm not mistaken, in a real API console, the "output" transformer is actually for interfacing with the mix bus. Then there would be an output that amplifies more. Also, the 1176 cannot handle a lot of signal on the input. So you could use the 40dB, run through the pultec and 1176 and then add another fixed 20dB on the output stage. But that might not be the best for noise performance. Generally, for the best noise performance, you want to make all of the gain up-front. So the alternative would be to put an extra fixed 20dB right after the API pre, put a trimmer in front of the 1176 followed by a makeup stage just for the 1176. That's what I did in my "Channel Strip 1".

The final concern would be scaling up to 16. The thought of building 16 channel strips like that makes me twitch a little. That I don't have a solution for but I would imagine the procedure for building 16 efficiently and correctly is not that different from building 1,600 so I assume you have some serious time and money to burn.

I mean like this indeed!

I live in Quebec, Canada so unfortunately no I'm not it the US.

I plan to build each piece on its own, test them individually, test them togheter and then see if it make sense to integrate everything on a single board or not. The answer will probably be no but I'll see at that time what make sense to be grouped and what does not.

Indeed, the way to interface each board togheter while maintaining the best noise ratio will be a major concern. Thanks for your input on that!

Fitting 16 channels in one enclosure and using one common psu is indeed the ultimate goal. I don't have infinite money and I need to spend my time where it count. I'll see where that whole thing takes me. There's a lot I need to figure out before scaling that chimera to 16!

Cheers!