Poor Man's Tube Mixer

Amazing project Ian!! Been hoping for a DIY project like this. Would fit perfect in the hybrid setup we have at the studio to add some tube magic to digital recordings.

Will read through all pages and come back to u with questions and feedback.

But given the choice of  adding EQ on the mic pre or 16 stem passive summing I would go for pre/EQ any day in the week.

If one want passive summing of line outs from the DAW it's easy to just use a DIYRE kit or similar.

Thank you for the encouragement. All input is welcome.

Cheers

Ian

Hello Ian,
I was thinking about how the 500 slot convention was troublesome to make work with your tube pres.  What if we repurposed a 500 series backplane or used the few extra pins to deliver the required voltages? Looking for feedback from others if this is something already discussed or if the idea isn't worth exploring, thanks. For example is it that the xfmrs are just too big?

boji, at the time I'd built my Krässemaschine even the 32 pin DIN connector was very limiting. I had to "misuse" already dedicated pins in a very creative way to get all the signals through the desk.

Straight from the applied source, thanks Holger! 

I can see that as being true if line inserts, aux outs and such other I/O duties were added to its job.
But would you mind being a little bit more specific? 

I guess the big question about making a 100% tube design 500 compatible is why? If you want to be able plug it into a standard 500 series rack then you have a number of issues to deal with - principally how the generate the HT voltage and how to supply enough current. Even the simple two tube 'Classic' design needs 300mA at 12 V and I am not sure how a 500 series power supply would react to the inrush current taken by cold heaters. For HT you need 250V at about 20mA so if you used a switcher to generate this it would draw 200mA from a 24V rail even if it was 100% efficient. I cannot rememeber the 500 series power specs of hand but I suspect you would need to use a double width module to remain compatible with the standard.

Space is the other issue. Tubes take up a lot of room so in a single 500 series module you could probably get two tubes and possibly a tiny input transformer but there is no room for an output transformer. I guess this is another reason a double width module would make more sense.

I have had discussions in the past about an extension of the 51X series connector to include HT and heater voltages but unfortunately nothing came of them.

O the other hand, if 500 series compatibility is nit a requirement but instead you just want to house some tube pres in a 3U rack then the lunchbox project is what you need.

Cheers

Ian

ruffrecords said:

Space is the other issue.

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And so is heat... 10 tubes make a decent space heater enough to keep a bedroom cozy.

The 500 series makes little sense for an all tube design, but the ability to link two of these boxes together may make it more scalable if desired than swappable modules.

This is an amazing and ambitious project, Ian. Best of luck!

tk@halmi said:

And so is heat... 10 tubes make a decent space heater enough to keep a bedroom cozy.

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I think small signal double triodes get a bad press as a result of their bigger brethren in guitar amps and mono blocs. A typical double triode takes 0.3A at 6.3V which is less than 2 watts. My designs typically consume 6mA at 250V HT which is 1.5 watts giving a total of 3.5 watts. So ten tubes is only 35 watts.

Cheers

Ian

tk@halmi said:

The 500 series makes little sense for an all tube design, but the ability to link two of these boxes together may make it more scalable if desired than swappable modules.

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Interesting thought, You could link the outputs of one of them the the lie ins of another which would give you another couple of mic pres and 16 more stem inputs. Or perhaps people would want the seond one to have more mic pres?

Cheers

Ian

I have cut and pasted all the basic blocks need for the poor man's tube mixer onto a single PCB and done a little tidying. Looks like everything will fit. I need to add connectors and mic pre input circuits next.

Cheers

Ian

Thanks for the replies on the 500 series format.

Or perhaps people would want the second one to have more mic pres?

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Flexibility would add value?  In scenarios where desk aca's and such are strictly SS,  having tube pre's switched line-in for mixdown would be a lovely option to have available.

ruffrecords said:

It has long been an ambition of mine to design an affordable tube mixer. I have been working on this recently and I think I have come up with something that people might find interesting. I have tried as far as possible to cut out everything unnecessary and you use standard parts wherever possible. Even so you can pare down the cost even more by omitting some transformers or even whole functional areas. It uses 14 tubes, fits in an off the shelf box and the total parts cost should be about $2200 for the full set of options. For this you get:

4 mic pres with transformer balanced inputs, HPF, echo and foldback sends, pan and rotary fader plus unbalanced insert or direct out
16 input passive mixer (2 x 25way D ) with tube gain make up and rotary fader
2 transformer balanced direct inputs one each to the left and right buses (for expansion)
Echo send master, foldback send master both transformer balanced
Bus master with two channels of REDD PLUS passive EQ, master fader and transformer balanced outputs
2 transformer balanced FX returns
PFL on all mic channels (mono), passive mixer (stereo PFL) and FX returns (mono)
Monitor section with two VU meters, transformer balanced monitor out, monitor level, PFL over ride and 2TK playback input
External power supply

I would make all the PCBs available at cost in the Black Market

What do you think?

Cheers

Ian

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ruffrecords, that is fantastic idea!!....are you going think in sell these units? or is that a dream that can be come true for everyone?

Thanks for share your designs proyects!
Opacheco

opacheco said:

ruffrecords, that is fantastic idea!!....are you going think in sell these units? or is that a dream that can be come true for everyone?

Thanks for share your designs proyects!
Opacheco

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The idea is mainly to make it a flexible, affordable  DIY project. I have not really thought about building them for other people.

Cheers

Ian

ruffrecords said:

The idea is mainly to make it a flexible, affordable  DIY project. I have not really thought about building them for other people.

Cheers

Ian

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Great!!.....

opacheco

I built an 1176 kit into a single space 500 hundred series unit for a guy , worked well for a few years ,but heat and confined space eventually dead'nd it .
I know its common enough to see preamp tubes run without free air over them ,in 1u racks for instance , if there is no air flow what you end up with is a unit whose sound changes over time ,well everything does that to an extent , but if you confine the heat it means everything inside the case including your transformers and inductors will very gradually creep up and up and up in temperature ,settling time will be hours and hours . In a pro studio environment gear is permanently powered ,its worth checking your unit doesnt become hot enough to fry eggs on after prolonged usage .

Boji' why not make a separate 8ch tube rackmount , it doesnt make much sense  cooking the guts of your 'Ground' control unit from the inside out with tubes.

Boji' why not make a separate 8ch tube rackmount , it doesn't make much sense  cooking the guts of your 'Ground' control unit from the inside out with tubes.

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Thanks for the advice TT, I hadn't really considered heat degradation!  Build the 500 frame and now I want some lovely tubeness too, afterwards.  I'm just doing my normal square hole, round peg thing. Did the same darn thing trying to fit the channel cards to the frame.  :

The API-cloner dreams in CTC sidecars.  8)

Just a quick update. I have just got back from half term holidays and I have now nearly finished the main PCB. I took the opportunity to make some simplifications because there is no point including things on this board that some people might not want. So to make wring the HT and heaters simple I have just brought these out to pairs of pads for each main active block. Each one comes out to a pair of pads so it is easy to daisy chain together the sections you are using and equally easy to add stages later if you want to. Originally I had a group of four relays controlling mic/line, pad, phase and phantom switching but I decided this is unnecessarily complex and costly and all sections will not always be needed so I took it out. Whichever of these functions is required can be included on the front panel where the switches for those functions will be.

I have a little bit of tidying up to do, I need to add all the component values to the silk screen so you don't have to refer to a BOM all the time when building just a part of it and then I can order a small number of prototypes. I shall probably order five but build just one. I will make the remainder available to anyone who wants one at cost.

Cheers

Ian

I have now nearly finished the main PCB

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Awesome!  Look forward to seeing your proto take shape.  Thanks for offering your spares to the community!

ruffrecords said:

Just a quick update. I have just got back from half term holidays and I have now nearly finished the main PCB. I took the opportunity to make some simplifications because there is no point including things on this board that some people might not want. So to make wring the HT and heaters simple I have just brought these out to pairs of pads for each main active block. Each one comes out to a pair of pads so it is easy to daisy chain together the sections you are using and equally easy to add stages later if you want to. Originally I had a group of four relays controlling mic/line, pad, phase and phantom switching but I decided this is unnecessarily complex and costly and all sections will not always be needed so I took it out. Whichever of these functions is required can be included on the front panel where the switches for those functions will be.

I have a little bit of tidying up to do, I need to add all the component values to the silk screen so you don't have to refer to a BOM all the time when building just a part of it and then I can order a small number of prototypes. I shall probably order five but build just one. I will make the remainder available to anyone who wants one at cost.

Cheers

Ian

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Fantastic news!!
opacheco

I just saw the PNG image of your layout ,
You have the gain blocks down to a very tidy footprint , that should pay dividends

The idea about the heaters also makes good sense , it allows the heaters to be run in the traditional manner ,twisted pair ,looped up and away from sensitive circuitry and on to the next valve . It also means less chance of any leakages or coupling between heaters and other electrodes .

One thing in the PNG above  is some of the electrolytics are very close to valves , of course on one hand physically adjacent to the components or electrodes your bypassing is good news , life expectancy of electrolytics in very close proximity to valves might be somewhat limited though . One possible way around this is to mount the electrolytics on the backside of the board ,there no further away than right way up but more or less completely sheilded from the direct heat of the valve , that could increase the lifespan by years.

Im also looking into Linux based multitrack recording and processing at the moment , its seems quite feasible to run a distro of linux off a USB stick ,on modern laptop hardware , that can provide both  extremely low latency and automatically pick up your sound interface I/O .

I'm  dreaming of a one box Wunder machine , valve pre's and main bus ,boxed up with a dedicated recording and processing PC that runs Reaper on Linux , it needent be a big horrible hot air blower of a pc either ,just a modest convection cooled mini ITX will do the job nice and quietly , a laptop with the outer casing ,screen and keyboard removed could also make a very handy low profile computer inside a 19 inch rack enclosure

I definately want to try one , you might let me know when you get a costing ,and I'll check and see if the piggybank allows.