Poor Man's Tube Mixer

[ruffrecords]

@Tim

For a line level mixer this is an excellent approach. Additional screening around the tubes themselves is always a good idea. Signal cables should always be shielded as well but ground connections should not need it. Make sure all the sign writer's aluminium sheeting is electrically connected together and that there is a single connection from it to analog 0V (HT -ve) right where the power inlet socket is located.

47K bus feed resistors are fine in all cases. Make sure the LCR switch grounds any unused 47K to minimise crosstalk. If you use 100K pots for FX sends you can use LOG or LIN parts. LOG pots will typically give you 20dB down at 50% rotation. To make them more like slider faders which are  normally 10dB down at 50% travel you can use a LIN pot. The 47K bus resistor then acts also as a slugging resistor to give 10dB down at 50% rotation.

The only thing I am not sure about are the input transformers you have chosen. Which mixer did you pull them from. Could be useful to see a schematic of how they were used originally.

All in all an excellent project.

Cheers

Ian

 

[Tom snich]

Hello Ian

I bought this cable https://www.thomann.de/se/concab_lastkabel_8x15qmm.htm for the power to the mixer, the extra wires will come in handy for the analog 0V HT-ve, good!

Glad 47k bus works I have wired the the LCR using your concept, and I used 100k LIN for sends.

Been reading tons here on the forum trying to apply it to this mixer.

 

[Tom snich]

The Transformers come from 80's broadcast mixer AMIX CSL AV 20 French.
I contacted AMIX but they would not help me with schematics :/ Gears-Lutz gave nothing either. I am a bit doubtful that they will work, just would be nice to save some money on the transformers. Here's a pic of the PCB  the transformers go in to 39k resistors and then surrounding the NE5532's are  39k 10k 100k  22k, I know this does not help much. They look about the same size as an OEP transformer.

Cheers
Ben     

 

[ruffrecords]

Your block diagram looks fine!!

Hard to say about the transformers. The AMIX CSL AV 20  definitely appears to be a line in only mixer so the transformers should be good enough. I think it is worth trying them.

That Concab cable is good. I recently bought some myself to try out.

Cheers

ian

 

[scott2000]

Just happened across this site looking for some extrusion profiles..... didn't look too closely at the dimensions of these enclosures but still neat..

https://www.prioline.de/en/enclosure-types/sloped-enclosure/sloped-enclosure-type-3/#c155

 

[ruffrecords]

Just happened across this site looking for some extrusion profiles..... didn't look too closely at the dimensions of these enclosures but still neat..

https://www.prioline.de/en/enclosure-types/sloped-enclosure/sloped-enclosure-type-3/#c155

Interesting. I have not come across this company before. Definitely worth looking at in more detail. Thanks for the link.

Cheers

IAn

 

[ruffrecords]

Quite some time since the last post. Things have moved on quite a bit since then so I have started documenting the evolution pf the PMTM in a new blog. The first post is here: https://pmtubemixer.blogspot.com/

More to follow.

Cheers

Ian

 

[scott2000]

Oh yeah. I remember the original plan. Forgot what exactly would work..Need to look back...Just saw these for the first time..some big ones in there ..

https://www.tequipment.net/Hammond1488EH7.html

 

[ruffrecords]

Oh yeah. I remember the original plan. Forgot what exactly would work..Need to look back...Just saw these for the first time..some big ones in there ..

https://www.tequipment.net/Hammond1488EH7.html

Definitely some big ones but unfortunately all made of steel. I have looked through Hammond's entire range without success.

Cheers

Ian

 

[radiance]

What a great project Ian! ......respect....

 

[Tubetec]

So whats the new approach going to be ?

I like the way in old RCA mixers the channels are modular , the same units, input or line driver are replicated on their own small sub chassis . The German approach is more or less the same ,but the mic amps tend to have their own self contained power supply which is very costly in terms of engineering and screening .

The benefits of a modular approach is acessibility , the ease of understanding of the basic principles and the construction is matter of replication , the user can start up with a pair of mic amps, perfectly usable in their own right and subsequently build the mixer and output sections or extra input channels as required .


Die cast enclosures dont come cheap , but it doesnt need to be very large , alternatively steel could be used ,
preferably simple hand tools would be all thats required to do the sub chassis tooling . There is also places now that will supply machined enclosures at a small extra cost . A module would need xlr in/out , power connector , transformer /tube socket cut outs along with the various screw holes involved .



The form factor of the RCA style module minus any of exposed live wires or components would be nice ,
A simple two tier sloped wooden rack with metal mesh shelves would suffice for the modules , A small rack mount enclosure could house faders eq and mixer circuits lower down .

Seems to be some good options for tube transformers coming our way from UTM industries lately , just over 30 euros for a fully enclosed tube output either single ended or balanced drive , in the UT3580 or UT3590 . Input iron/mumetal might only cost 25-40 euros depending on which option you want . A small enclosure might cost 20 , your still sub 100 euros for the main costs , excluding components and valves and power supply ,which most of us have already .

As the most basic example of the modular approach here is a line driver I made from an EL84 triode connected ,
its pure and simple no feedback or gain control , in conjunction with a step up transformer to the grid it takes high level dynamic or tube mic input , direct its 1meg DI type impedence .

PSU is obviously external and remotely located .

 

[ruffrecords]

So whats the new approach going to be ?

I like the way in old RCA mixers the channels are modular , the same units, input or line driver are replicated on their own small sub chassis . The German approach is more or less the same ,but the mic amps tend to have their own self contained power supply which is very costly in terms of engineering and screening .

The benefits of a modular approach is acessibility , the ease of understanding of the basic principles and the construction is matter of replication , the user can start up with a pair of mic amps, perfectly usable in their own right and subsequently build the mixer and output sections or extra input channels as required .

The blog lags this thread somewhat. Check out posts 148 through 170 and you will see I basically agree with you.

Cheers

Ian

 

[Tahoebrian5]

The blog lags this thread somewhat. Check out posts 148 through 170 and you will see I basically agree with you.

Cheers

Ian

Hi Ian, I have been reading through a few of your threads and website. I’m very interested in building or purchasing possibly, or combination thereof, a tube mixer. The info seems pretty scattered so having a hard time getting a handle on what options are available. Is there an over all description of what is available?

I’m looking for something to use for tracking live rock band performances in a purpose built live room, and pipe the recording tracks upstairs to the control room, and have the mixer in the main room to control what is coming out the PA speakers. Possibly incorporate a splitter snake as not everything will likely need to go to the PA.

Anyway please give me a point in the right direction.

would also love to hear some feedback on some of this stuff If any is available.

thx a bunch, Brian!

 

[ruffrecords]

Hi Brian,

The Poor Man's tube mixer (PMTM)has moved on quite a bit since the last blog post. I now have two customers who each want a different version. One has four mic pres with 2 band EQ and two AUX sends per channel. The other has eight line ins, again with 2 band EQ per channel so currently these are the only options. As I am retired I do not work on these full time and I have the Mark 3 mixer to finish, and a mastering EQ and a tube tone box upgrade to do for customers. I reckon that is at least two years work so in terms of options, DIY is the way to go. In many ways this opens up options. For example you could use longer extrusions to allow more channels (Holger Classen built a 12 channel version of my EZTubeMixer design which is one metre wide). At the moment, none of the PCBs for the PMTM are available since the design is not yet frozen, but when it is I will make them available to DIYers.

The big question is how many channels do you think you need and what features should they have?

Cheers

Ian

 

[Tahoebrian5]

Hi Ian, DIY is great as I will surely have a lot of fun and learn a bunch as well.

12 channels should be plenty, although 16 line in would probably be more useful to me as I could just use a 500 series rack of pre’s, or build a second box of some of your tube pres. Ideally I think 8 pres and 8 line ins would be ideal For my use but I can work around other configurations as long as there are line ins on the pres so I can bypass if needed. im definitely leaning towards the Helios style eqs

also i think I would definitely need an out/in insert per channel ideally after the eq so I can run outboard 500 gear for gates / compressor for drum mics. Maybe prefader so I can change the output level without messing up compression?

definitely would want selectable hi pass available on all channels.

is there a mute/solo function currently planned?

two Aux sends per channel should be fine

last thing I can think of is a splitter per channel. I could just use a splitter snake but would be cool to have it built in

this sounds amazing!

is there any audio from any of the pieces available?

thx a bunch!

 

[ruffrecords]

Hi Brian,

if you are thinking in terms of 12 channels you should take a look at Holgers mixer which has 6 channel each side and a middle monitor section;

Krässemaschine

But that is based on the EZTubeMixer design rather than the PMTM so it is a lot more expensive to build. But you can have 3 band Helios, or Pultec or REDD EQ options. In the PMTM the EQ is based on the REDD but has only two bands (each with two or three selectable frequencies). Note, I think the Helios is largely derived from the REDD.

Note that space is very limited in the PMTM so there is not room for extensive features like switchable inserts, Solo/Mute/Pfl and HPF. It has a limited amount of front panel space and there is only so much you can fit in. I have attached preliminary layouts of the two versions I am building at the moment. You can see how limited the space is. If you need more controls then you probably need to move to the EZTubeMixer design.

The main amplifier circuits in the PMTM, the EZTubeMixer and the Mark 3 are electrically identical - they differ only in physical layout and construction. I do not have many sound samples because most users cannot supply them for copyright reasons but if you PM I will be able to send you a couple.

 

[Tahoebrian5]

The Holgers looks to be pretty amazing.

any idea what kind of cost I’m looking at in parts to DIY this baby?

is there a specific build thread somewhere?

 

[ruffrecords]

The Holgers looks to be pretty amazing.

It certainly is. There is a video somewhere showing it in a side by side comparison with an SSL. Apparently everyone there preferred Holger's mixer to the SSL (maybe Holger can chime in with a link?)

any idea what kind of cost I’m looking at in parts to DIY this baby?

Certainly a lot more expensive than it was pre-pandemic. Transformer and inductor prices and lead times have shot up as have those of rotary switches, but for the kind of features and number of channels you have in mind I would budget £1000 per channel.

is there a specific build thread somewhere?

Everyone wants something different in their mixer so there is no one set of build instructions. However, there is a lot of basic information under the DIY tab of my website:

Custom Tube Consoles - DIY

Just scroll down and click on the EZTubeMixer folder.

There is an EZTubeMixer support thread here: EZ Tube Mixer Support Thread which started back in 2013 so next year the design will be 10 years old. Some of the links in that thread are to my old web site. I have started going through and updating them but all the documents referenced are available on my current website.

Cheers

Ian

 

[Holger]

It certainly is. There is a video somewhere showing it in a side by side comparison with an SSL. Apparently everyone there preferred Holger's mixer to the SSL (maybe Holger can chime in with a link?)

Actually I only have a screen shot at hand. We've had a live performing jazz combo and a couple of signal splitters and mixed the signals both to the SSL and the Krässemaschine and switched back and forth. It was fun to compare.

 

[rjuly]

... I use 1mm cross section wire for the Mark 3 mixer and just double up conductors for the heaters. With you modest heater requirements a single pair should be OK...

Do you need to double up on the heater gnd wire as well?
- Richard