EZ Tube Mixer

[ruffrecords]

Yes please! What you said 

Totally agree - I prefer the relay method for sure. Much more civilized  8)

Oh, and by the way, there will be an EQ in/out switch.

Cheers

Ian

 

[gemini86]

I'd like to see  an EQ bypass switch if possible.

Also, pushing the boundaries perhaps,

but a HiZ DI connector to grid would be of great benefit.

Just something simple so those who wish to do so can wire in
a switched jack which interrupts the signal to grid and replaces with HiZ DI signal.
Or if really adventurous, with a relay and additional front panel switch position.

Something like this would cry out for at least a few direct injected instruments.

Great stuff

Until the other day it did have a HI-Z input via a relay! I don't like conventional HI-Z inputs that are switched by the jack socket because it means the mic signal from the input transformer secondary has to travel all the way to the front panel jack socket and back again. This part if the circuit it the most sensitive to external interference and I prefer to keep it as short as possible. In the original design I had a relay right by the transformer and the first tube grid so a HI-Z input could be switched in but the transformer to first grid length was kept small. Anyway, because this was turning into a mixer I took out the relay a couple of days ago. Looks like I need to put it back in again!

Cheers

Ian

This was the problem with the original G9, which does have a work around... It's good that you're knocking that potential problem to the curb right off the bat.

 

[anjing]

Very nice project i have been following the poor men's version with great interest!. When this becomes available would it be in the eurocard format? Do you have any plans of making it expandable putting to units toghether making it 16:2?

 

[ruffrecords]

Very nice project i have been following the poor men's version with great interest!. When this becomes available would it be in the eurocard format? Do you have any plans of making it expandable putting to units toghether making it 16:2?

Yes, the whole thing is based on a standard Eurocard size PCB with a standard 32 way connector. The channel electronics will fit into  6U high by 14HP wide front panel which means you can get 6 channels in standard 19inch sub-rack. Three sub racks bolted together will give you space for 16 channels with two spaces left over for the masters and monitoring.

These will be the same Eurocard PCBs I use to build my custom tube mixers for non-DIY clients but I leave the front panel and overall mechanical details up to you so you can customise it to suit your needs.

Cheers

Ian

 

[alexc]

What does '14HP' width refer to?  Is this a 'euro' thing ?

I am guessing the tubes will be mounted in sockets, vertically off the pcb?

And the eq knobs/switches also mounted directly off the channel pcb?

Just trying to visualise the thing  ;D

Cheers

 

[ruffrecords]

What does '14HP' width refer to?  Is this a 'euro' thing ?

I am guessing the tubes will be mounted in sockets, vertically off the pcb?

And the eq knobs/switches also mounted directly off the channel pcb?

Just trying to visualise the thing  ;D

Cheers

HP refers to Horizontal Pitch of 0.2 inches or 5.08mm. It is the horizontal equivalent of the 19inch rack height measurement in U where 1U = 1.75 inches. So my modules will be 14HP = 2.8 inches wide. A 19inch sub rack is 84HP wide so you can get exactly 6 off 14HP modules in it.

The EZ Tube mixer channel is based on the poor man's Tube Mic Pre which is pictured here:

http://www.groupdiy.com/index.php?topic=47424.msg603371#msg603371

The tubes plug directly into the PCB using standard 1mm pin sockets.

The (3U) PCB mounts to the top half of a (6U)  front panel using standard mechanical parts. This leaves a 3U space in the lower half for the EQ. You can build the EQ any way you like. You could build the poor man's EQP1A with or without added mid boost/cut for example and if you want you could use the small PCBs I have already made for this. Since the EQ is passive it needs no power and the gain make up stage is already on the mic pre PCB so the EQ can just be hooked up with screened wire.

Some time ago I built tube based EQ based on the Helios 69 and my plan is to update this and put it on a single PCB that can be mounted to the lower half of the 6U front panel using the pots/switches to attach it but I have not started this design yet.

Attached is a picture of the showing how the PCB attached to the front panel.

Cheers

Ian

 

[alexc]

Thank you kindly Ian. Most edifying 

 

[ruffrecords]

I have completed the first version of the mic pre PCB. This now includes the relay for a HI-Z input, the four ALPS push buttons for phantom, pad, phase and mic/line switches. The rear connector carries HT, heater, phantom and relay supplies, mic and line inputs, chassis and fader connections, four audio buses and the direct out. I have included 4 buses because, although I said before that there could be no AUX sends, I think it would be possible, and more importantly useful, to accommodate two AUX sends (which could each be switched pre/post fader if you wish) without overly straining the amplifiers. Attached is a pic of the PCB layout. I have ordered a few prototype PCBs and while they are being manufactured I am going to look at the EQ section.

Cheers

Ian

 

[bieckmusic]

Awesome Ian, super excited about the aux sends!!  I want to start building up a stock of transformers, so I don't have to buy new sowter transformers, which once you convert the $, are super expensive....  Time to start looking at ebay, etc.  Do you know what type of transformer I should be looking for at this stage, or is it likely to change??  I'd like to get a few nickel, and different metal transformers kind of like the shadow hills pre's.

best, and thank you so much for all of your hard work!

greg

 

[ruffrecords]

Awesome Ian, super excited about the aux sends!!  I want to start building up a stock of transformers, so I don't have to buy new sowter transformers, which once you convert the $, are super expensive....  Time to start looking at ebay, etc.  Do you know what type of transformer I should be looking for at this stage, or is it likely to change??  I'd like to get a few nickel, and different metal transformers kind of like the shadow hills pre's.

best, and thank you so much for all of your hard work!

greg

You need a 1:10 ratio mic transformer designed for a 150 ohm source - something with a primary inductance of 6 Henries or more. There are probably Cinemag (CMM10-PCA) and Jensen (JT-115K-EPC) types that will do the job. I have included space for a secondary RC loading network so almost anyone's 1:10 transformer will do.

Cheers

Ian

 

[letterbeacon]

What an exciting project - looking forward to seeing this progress!

 

[alexc]

Dang! That's just about exactly spot on.

I'm going to have to sell something to get some of this project going 

I'm thinking a few channels in a nice wooden case, desktop style
with large rotary faders and vu's for each.

Can't wait to see the next of your module designs Ian.

Cheers

 

[bieckmusic]

Hope I'm not also pushing the boundaries, but would it be difficult to add a solo feature to the mixing configuration, if one wanted?  I imagine mutes would just be an on-off switch in front of the fader and not difficult to add.  I'm thinking the solo would be difficult and not 'EZ' because it might need an additional buss, a 'solo' buss, that would get activated when a solo button was pushed.  Adding a lot of complexity...  Just thought I'd mention it.    Sorry to be a bother...

I have the Recording the Beatles book, which I love.  This kind of looks partly similar to the Redd series consoles.  I like the quote from Geoff Emerick.  "We used the new transistorized desk for the first time when recording Abby Road, and in no way could I recreate the same bass drum or snare drum or guitar sounds that I got previously (Redd.51)". 

Everything's Looking awesome.....   


greg

 

[ruffrecords]

Hope I'm not also pushing the boundaries, but would it be difficult to add a solo feature to the mixing configuration, if one wanted?  I imagine mutes would just be an on-off switch in front of the fader and not difficult to add.  I'm thinking the solo would be difficult and not 'EZ' because it might need an additional buss, a 'solo' buss, that would get activated when a solo button was pushed.  Adding a lot of complexity...  Just thought I'd mention it.    Sorry to be a bother...
greg

At the moment the PCB layout has provision for four buses. Two would normally be used for L & R and the two others you can use for anything you like but are nominally intended for a couple of AUXes. The trouble with a normal (mono) solo is it really needs two buses. One for the audio and the other a dc bus to switch a relay in the monitor section so the solo'd channel is heard in the monitors. You could use both the AUX buses for this but it seems a bit of a waste. There are two pins on the connector normally used for relay power so if you do not use the channel relay (for an instrument input) then these would be free. To give you an idea of what is provided and how you might tweak it for your own ends, here is a list of the current pin allocations for the 32 way connector:

Pins 1,2 Mic cold&hot
Pins 3,4 Mic screen
Pins 5,6 Line cold&hot
Pins 7,8 Line screen
Pins 9,10 48V phantom power
Pins 11,12  Chassis
Pins 13,14  Sig 0V & preamp 1 output (usually used to drive and external fader and/or pre EQ direct out transformer and/or prefade send to external routing module)
Pins 15,16 Fader 0V & slider
Pins 17,18 Relay power
Pins 19,20 Bus1 & Bus 2
Pins 21,22 Bus3 & Bus4
Pins 23,24 Sig 0V and preamp 2 output (usually used for a post fader/post EQ channel direct out transformer and/or post fader/post EQ send to an external routing module)
Pins 25,26 Heaters +ve
Pins 27,28 Heaters -ve
Pins 29,30 HT+
Pins 31,32 HT/Sig 0V


The mic and line pins are connected to pads near the connector so you can run a screened cable to the front of the module where the input switches are (48V,pad, phase and mic/line). The 48V pin is connected to a pad near the connector so phantom power can be wired in or omitted as required. Similarly, the chassis pin is connect to a pad near the connector so you can wire it to the front panel metalwork any way you choose. The relay pins are connected to pads near the connector because if used they will be wired to your front panel and then back to the relay. The four bus pins are connected to four bus resistors and then to pads for connection to your routing circuit on the front panel.

So as you can see, a lot of the connector pins are routed to pads near the connector and can be used for anything you like.

Hope that helps.

Cheers

Ian

 

[ruffrecords]

Here's a rough first draft of a panel layout for a 6U high channel module with Helios like EQ. Just simple pan on this one, no AUXes.

Cheers

Ian

 

[alexc]

Bravo  :'(

Just wonderful.

 

[spase]

Yes...wonderful!

 

[alexc]

Just wondering,

How easy is it to make a bussing cable for the 32way connector here?

Would it be a ribbon cable with connectors 'press fit'  along the length

or

Would it be a set of separate wires soldered to the back of a connector then onto the next  connector in the string.

Cheers

 

[ruffrecords]

Just wondering,

How easy is it to make a bussing cable for the 32way connector here?

Would it be a ribbon cable with connectors 'press fit'  along the length

or

Would it be a set of separate wires soldered to the back of a connector then onto the next  connector in the string.

Cheers

One issue that has to be dealt with on tube mixers is the currents and voltages involved. The biggest currents are the heaters. You can get 7 x 14HP modules in a sub-rack and each module's heater requirement is about 0.5 amps at 12V dc which makes a total of 3.5 amps which is far too much for ribbon cable. The HT could be as much as 300V which I reckon most ribbon cables should be able to cope with. The other thing to take into account is that there are a lot of pins on the connector that are not bused (e.g. mic and line inputs, amp outputs and fader connections).

So, on balance I think it is best to use connectors with solder bucket tags . Heavy currents and high voltages you will notice I have connected to pairs of pins. This allows you to thread a wire in a straight line right across the back of the sub rack. The heaters, HT, 48V and chassis connections are like this. I use bare wire of an appropriate gauge for this and use slip on insulation between connectors. I laso find that wiring screened lead to IDC connectors is a PITA and I much prefer solder buckets for these connections.

Cheers

Ian

 

[alexc]

Yep. As you said.

What I was thinking, particularly if one wants to use 6.3V heaters,
And not knowing the hv current but it can build up in a hurry.

I only twigged on the pairs of pins just a little before you answered.
Makes it easier to solder.
Thanks for that!

All good.