the 20ch *all tube* line mixing/sum/mixdown console

[themagicmanmdt]

hey everyone -

yes, well, it's been a design i've had on the books for quite a while, and after some good R&D, i'm at least going to build one for myself, and, from there, maybe more in the future.

in short:

20 transformer inputs (using high-NI custom ones by Edcor)

6 aux sends/buss (1/2, 3/4, 5/6 grouped stereo, with pan pot for each send); master volume on each send

100mm P&G faders, mute and solo on each channel as well as a stereo master fader.

The summing amps are going to be triode based 6SN7, with the final stage being transformer-loaded (ala Fairchild 666, V72, the original Neve tube mixer, et al) direct to balanced line to drive 10k very easily. The aux send sum amps and the master L/R amps are identical, which allow for a modular troubleshooting design and uniform mega-fidelity.

I'm going to skip a 'solo' feature off the get-go for both 1) I mostly never use it, 2) classic simplicity, and 3) bigger fish to fry first. I wouldn't have a problem letting the solo section and switching go through op amps before the main L/R for buffering if need be. Not sure.

I've also decided to forgo the quest to have EQ on each channel. Why? Well, for my sake, I've got a couple of outboard EQ's that I use particularly on certain sources. EQ addition would mean a makeup amplifier addition - for each EQ channel added - and since if I was to make an EQ to match the fidelity an amazingness of the summing section, I'd do it right with a 3 or 4 band inductor EQ, and that just shoots up cost considerably. Plus, most people are either using outboard EQ's or, if they're a DAW person, use their plugin EQ's and flexibility anyways, and just need to get their hands on some faders and a better outboard summing mixdown. Perhaps with a MASSIVE budget I'd do EQ's on each channel, but I don't have THAT much at the current time. Not to mention, if I do 'extend' the board with EQ, the design would just patch the EQ into the line input transformer anyways (which would be needed for correct impedance matching), so it's another modular add on.



So, that's the goal. A line input, fader touchin', all tube hi-fi analog mixdown and even tracking summing amp. 20 channels to me means 16 during mixdown + 4 for effects returns. 6 aux sends for effects, cue send while monitoring/tracking scenarios. No VU meters or anything - metering to me is best done on the tape machine/DAW you're recording to. No need for redundant needles bouncing.



I'm finalizing a parts list and triple checking schematics and theory. I'll post more as I go along. Any thoughts, concerns, functionalities, comments etc are MORE than welcome from everyone. We can get techy specific, too, and I'll eventually post as-built schematics from these designs of mine.


Groovy.

mt

[honkyjonk]

Awesome dude.

The design philosophy is close to what I'd like to do some day as well. I'd sort of want to base mine around an analog 8 track though, maybe with the option for future expandability.

I regards to eq, first thing that comes to mind would be inserts for some ss pultec type eq's w/ say, 2520 style DOA's for makeup gain. If you did the DOA's yourself for $15 a pop or whatever the classicapi guy over at prodigy pro charges for his kits, it could be fairly cost effective & w/out the need for output transformer on the eq. But then again, that's messing with your topology. Have you checked out the Poor Man's Pultec design going on as Prodigy Pro right now?

I similarly would find the solo function to be more hassle than it would be worth, especially when dealing with small track counts. With 8 tracks, soloing is simply a two handed affair, as opposed to a one fingered affair.

But that's my world.

Does this design have anything to do with the NYD one bottle circuit?

Would be nice to have like 4 channels of mic level amps too. But that's another can of worms.
Gotta have mutes of course, but that's easy.

I assume the "D" for development means you've built up one of these line amps and tested? I don't know enough about tube circuits yet, but would this be Single Ended, Push Pull, low/high feedback?

I bet the tough part is going to be the chassis.

[themagicmanmdt]

I'm basing mine around my Scully 280 8 track. Phssssaw to DAW's.

Why inserts? Since each channel doesn't have an individual channel gain, what is there to insert in the middle of? My thoughts were that if the line input of each channel goes pretty much straight to the aux send network, then that L/R pan/fader/sum, then if anything (EQ, comp, etc) needed to be inserted, it's simply patched in before it hits the board. Did I miss an idea for the insert?

This way, ANYTHING can be built and used before hitting the console, and allows for there to be, say, a Lunchbox of EQ to be patched in with ease...or a poor man's pultec (I have!) -

The bigger thing is that I don't want to 'overbuild', and especially with things like mic pre's and EQ's, where we're at the point now of realizing that all of that is a color - although a nice inductor based I could use on most anything....but NOT really a pultec style. I figured that would be an option, and also keeps the price down for anyone who might be interested in one purely for tube analog summing with faders (unlike these 'set and forget' summing boxes with trim pots and rackmounts.)

NYD one bottle circuit? Well, mine is a one tube per summing amp, but I haven't seen NYD's. *EDIT* Found it. No, very different. Both tube, topology and output stage.*

Mic pres are mic pres. I've got three different tube mic pres already designed and in the bag. This is the final frontier in 'tubeland studios' for me. That is, other than redesigning the tape machine....bah!


For the line amps...I've got a few variations that I'm going to see how they sound. Some were built, some weren't. My first instinct is SE, no NFB. I want the ability to get a little dirty push out of the board, and I'm going for big bass, clean transients - good enough for jazz - but with that 'hightened realism' that tubes do so well. I'll tune in NFB to taste in a few ways - post OT, pre OT, and see what sounds good.

I'm hesitant for PP for the sake of loosing what I'm engineering to be a good operating level to start getting some THD when the mix gets loud. I'd rather have the sound of the mix buss getting grit when getting up there in the +18 dbu atmosphere than accomplishing ultra clean transients up to +28 or so and having tape saturate when I'm pumping a loud mix for the sound of the mix buss. That way, there's a nice blend of tape saturation happening on transients along with ZZINGG, especially on snare. That's the theory on 'why SE, why not a nice PP'. Cause 6SN7 is linear and pretty enough at sensible levels, and we're going for fun, here. Hi-fi fun. Not harmonic cancellations!


The chassis is the 'spensive-ish part. Budget for transformers, faders, pots, jacks - great! How to mount it all..... much less where are the machine shops who would do such a thing?

[The Scum]

Wow. Ambitious project!

A few thoughts:

I get the no-inserts thing, and agree with your reasoning...there's really nothing to insert in between.

Some things to consider:
-Are the auxes sourced pre or post fader?
-I tend to find having subgroups to be very useful, with an insert point before they meet the main stereo bus...for parallel compression.
-Similarly, inserts on the 2 bus, before the master fader and output amp might be useful.
-I assume they'll be passive mix busses with makeup gain, rather than virtual earth? They differ a bit in how you can do the mute and buss switching.
-I find that the control room section is something that can set a good console apart from a mediocre one...multiple inputs and outputs, and a volume control so you can turn the control room down without attenuating the signal at the mix outputs. The Dangerous ST is probably the one with the best feature set to study.
-I understand simplifying by removing the solo on the channels, but I like being able to hear what's going to the auxes & groups, so I set up FX and cue sends without flying blind.
-Since you'll be making 20 channels to start, and possibly more later, consider having good PCBs made. They take some of the variability out of repeating the same circuit time and again.
-Similarly, some SPICE sims can be useful to get to know the circuit before building it.

Scott Hampton built a mixer that's somewhat similar...I think the stereo summing was with tube amps, and the auxes were JFET. Heck, building a JFET summing module that fits in the place of the tube summer could be an interesting color option.

The frame might vary depending on how big you want it to be...you could cram 20 channels into a rack chassis, and use commonly available rack furniture to house it...Mackie squeeze 21 faders into a 19" wide package.

If you turn 19" panels vertically, you get a nicely sized single channel strip.

If you want something larger, maybe a wood outer housing with braces to hold aluminum panels.

Or t-slot pieces for a skeleton...frame-world.com.

where are the machine shops who would do such a thing?

Yellow pages. Or http://www.100kgarages.com/.

Many machinists will want really good drawings to work from...brush up on your CAD chops.

[Snarl 12/8]

What about phase flip?

What about a simple high pass filter?

Those are things that to my mind need to be easily accessible on almost any track. I wouldn't want to patch every time for those.

I keep thinking the coolest thing about going completely custom DIY would be to have different channels optimized for different things. Like, I always record kick on track 1, always have. So having the things I generally like on kick (distortion, often a really low freq high-pass filter) would be nice there. I can think of things that I'd love to see wired in to my mixer that suit the various sources that I generally bring up on each channel. But I almost always record only myself. That might not work if you have to be able to quickly service anyone that walks through the door, much less let freelancers use the console. But I bet a little [defeatable] section at the top of each strip that was clearly labeled and "made sense" musically would be grokkable by almost anyone with half a brain and a little experience.

If it was me, and I had the electronics chops to make different circuits that actually worked, I'd want different topologies on different channels. Maybe just 8 and 8, like a Sytek with the Burr Brown mod on channels 3 and 4 on steroids. I'd also overbuild like crazy the master section. Headroom and features.

I just had a thought. What about a 500 series slot at the top of each channel and in the master section? Then you could have something standardized and recognizable in there.

[themagicmanmdt]

good thoughts!!!!

scum:

-i'm thinking auxes 1-4 are pre; 5/6 post. i thought about making 3/4 switchable pre/post fader, it's not too hard to do. it's on the idea block.

-i've not used paralell compression except once, and it wasn't what i ended up keeping. but, hmm.... to me it sounds like that a stereo aux buss would work fine for the paralell comp send... yes? is there something funtionally i'm not considering by using aux sends as the comp send and the faders as the uncompressed drum feeds?

-inserts on 2 bus - one of the things 'bout tube design is that things are buku impedence, and if I was to get a 2 bus insert to line level, it would have to still have it's own output amp for not only gain but impedance matching, which would, really, look and be exactly what the 2 mix amp would be like. i've got the mixing amp designed to only have ONE CAPACITOR in the output path for mega-fidelity aspirations, so an insert wouldn't work as easy as it would on SS consoles. does that make sense?

a thought I had would be to simply have an additional line input passive stereo 10k fader to be patchable after whatever 2 bus inserts are used. maybe that might do the trick.

-well, all mix busses are 'passive', but in short, yes, all line-transformer buffered (non-active) to makeup gain using lowest values possible for a good noise floor. the 'mute' is going to be post input transformer. i'll experiment with noise factors on muted channels and mute location.

-yes, yes, solo logic DOES help a lot. i suppose the idea is 1) i'm initially building this console for just me, right now, and that 2) there's no rule that a solo logic CAN'T be implemented. mainly, i'm holding off for the sake of cost, as I've got enough saved up and coming it to make the rest happen, but not solo as well. the future awaits -

-all components (transformers, faders, pan, level, etc) are all mounted on the chassis. the only thing that would warrant a PCB would be the active amp sections, and since there's only one per channel (6 busses plus 2 mix = 8 channels!), it's not enough to warrant a PCB run. plus, I love the servicability of tube gear that's not PCB due to the heat involved, so first build will be purdy and point to point, but exacting. if i'm lucky that i may make a few of these boards, or offer a DIY kit, then PCB's are in my future.

-i'll peer into SPICE a bit, especially for noise floor and distortion analysis, if SPICE does that stuff.



Hampton built one? The only one I've seen around that's somewhat close is the Manley one, but that's not a proper 'console', more like a portable extended tube mixer...

I'll leave the JFET module for down the road rainy days. There's enough amazing legendary SS gear being made. I'm just filling in the niche of what's missing, methinks.

I've been really thinking 'bout making the whole console fit to rackmount sizes and modularity. I think it would work fine - doing something about the case is the only step. I'm aiming for this console to be portable, too. i like having my faders close together, so I'm going to try for 19" wide... i'm doing space planning about the whole thing and having one or two schematic changes due to these considerations....

Sadly, I have NO CAD chops. Might have to team up with someone to help me on this.



Snarl -

Phase - possible, yes. I've almost never grabbed for phase during mixdown, but it does come up.... might have to add them pre-input transformer, for sure.

HPF - Another thing that I personally never use, so haven't considered it. If I do use it, it's set up during tracking anyways. It's one of those things that, personally, if I was to do it, I'd make it selectable at a few different freq's. How steep? Would -6/oct be ok? If so, I could use a simple R-C cap coupling and a multi-pole switch. I think it's a consideration that I might consider adding. I'm planning on leaving some extra space on the front panel should I find I need to add these things (phase, HPF, etc)


The 500 series idea is what I'm going for - and the idea that this is just a very basic, super clean and hi-fi tube mixer with aux sends and a kick ass master section. Anyone can 500 series up top with a lunchbox or be as modular as they like. I can't say that I would want to 'sign up' for ONE console config. I wouldn't buy a full Neve mix desk even if I could afford it. API...maybe! I'd rather have sprinkled EQ when I need it that I can patch in on a whim.

Further inspiration was reading on the new "Trust Me, I'm a Scientist" interview was that Wilco bypassed their entire Sony/MCI board on mixdown and just used the faders, aux send and master section, opting for outboard gear for whatever they needed. They just patching into the 'insert return' for line mixing. This is the same principle, only with tube makeup amps for aux and 2 buss.

The one thing that I am thinking about is doing JFET for the Aux sends if the tube fidelity or sound isn't jiving with me or others. However, personally, tube amps, tube preamps, tube mics - they're my preference - and the era of music and the recordings I enjoy the most, so I'm 'all systems go' for this stripped down REDD, of sorts...




Great ideas. Will add to the 'considerations' list I've got going with my schematics. I'll probably throw the phase switches on for sure, since they're easy enough and are needed in a pinch.

[Snarl 12/8]

To my mind having a any slope isn't HPF anymore, that's a shelf, but actually that's what I've been doing more and more and -6db has been working about right for stuff. Just enough to tame the rumble. I've been gravitating towards a slight shelf down at 40, 80 or 100 Hz (ish) when I want to tame some rumble or just be more confident that I don't have a lot of subsonic stuff (that I can't hear in my monitor situation) effing up my mix.

Is this board going to be strictly for your own use? If not, I'd say HPF and phase become a bit more important. What about one JFET aux and one tube aux (or different numbers of each). I kinda missed the aux thing in your post, that's not something I think I've ever seen on a "summing box". That would be really cool and open up lots of options, obviously.

I just had a thought. I only tend to want distortion, phase, hpf, etc. on a few channels, if any. What if you made a sortof sidecar (maybe that's not the right term) for this thing that had like 4 channels of each that was practically built in, but basically patchable to any channel, but somehow with better fidelity wiring, shorter wiring and great matching impedences and all that for your board. So you could hardwire bypass it (by default) or have it there and sounding great very, very easily, without having to decide which 500 module or other piece of outboard to patch in to do the job. Once you got the patching thing figured out you'd have less circuits to build onto every channel too.

[Artifex]

Hey Marshall,

Glad to hear that your up to something new! Did you ever come back to the Chicago area?

[themagicmanmdt]

nope - still in WNC for a few more months, then off - maybe portland?

don't think i'll move back to chi-town. :/

[GussyLoveridge]

hey folks -

I just thought I'd mention this company. They are situated in my tiny hometown of Sydney, Nova Scotia and make custom electronics enclosures, specializing in one offs and prototypes. Have done work for Apple, Microsoft, NASA, Intel, GE, GM to name a few. I'm not affiliated with the company in any way, other than I do know some of the kind folks that work there.

Check them out. The can help you design and build a custom enclosure and can turn around projects in as little as 2-3 days.

Anyway, I hope this helps. Good luck with the build, this is super exciting.

http://www.protocase.com/

[themagicmanmdt]

nice link - thanks!

currently i'm working on building and testing a few variants of the summing electronics. they're easily adaptable as a line amp, so i'll be able to pass signal through them to hear sound quality.

basically, i've got three possible configs, and two of them are calling for a costly output transformer for each channel. it'll be one of the crucial parts of the tone, and easily a good 1/4 to 1/3 of the cost of the summing amp in it's entirety, so i'm saving at the moment to order them...

good things cost $ to build!


i have decided that the prototype i'm building will have 4 aux sends along with the 2 mix, for a total of 6 channels of 'summing amp'. i can build the 6 channels, which are going to be based around a 6SN7 or 6FQ7 tube (8-pin big bottle/9-pin small bottle variants of the same design) on one 3-RU chassis, power supply shielded internally, transformer mounted outside. connections to and from the 'mixing plate' (faders, pots, etc) for each channel will be similar to what a tube mic PSU connection would be: 5-pin XLR connectors to and from; which will allow for channel swapping to a different amp for both prototyping different summing amp sounds/builds A/B as well as for intermittent summing amp channels during a session.

i'm skipping having any type of meter, not that i'm opposed to it, but rather A) I ALWAYS meter off of my recorder/tape machine's meters, and B) would rather put the money into better transformers, interconnects, etc...

i think, eventually, when i get these three different summing/line amp builds built (simultaneously), i'll be able to run audio through them and get some feedback of what everyone likes the best. of course, these are going to have to be 24/96 files to download....

i'll probably have more progress after the holidays and new year to post.

[jhharvest]

I think this project is awesome. Thanks for posting these updates. I'm really interested in how you are doing with it.