Feeler: EZ Tube Lunch Box

[anjing]

Hi Ian,
  I'm away for a few weeks for our yearly pilgrimage to the ring of fire. I'd like to order a few of these backplanes, 4 to be exact.
I will email you when i get a secure connection so i can use paypal.

Hope all is fine for you!

Can't wait to get back to my eztube mixer!

Regards,

Pierre

 

[ruffrecords]

Hi Ian,
  I'm away for a few weeks for our yearly pilgrimage to the ring of fire. I'd like to order a few of these backplanes, 4 to be exact.
I will email you when i get a secure connection so i can use paypal.

Hope all is fine for you!

Can't wait to get back to my eztube mixer!

Regards,

Pierre

OK Pierre, I will put 4 aside for you.

Happy Christmas

Ian

 

[G-Sun]

Sorry if you've mentioned it before
but a 500-module typical is self-equipped regarding balanced in/out.
On the other hand I expect most mixer-mudules to be unbalanced.
So, the EZ tube lunch box, how is each module here?
Is this lunchbox designed to be independent or dependent (channelstrip) module-wise?

And, when we're talking channelstrip. Compressor?
(After all it's 6 slots, making perfect space for a dual full pre/eq/comp)

 

[ruffrecords]

With tubes you need to use input and output transformers for balanced ins and outs. Unfortunately there is not enough room in a single 3U module for both input and output transformers and the three tubes so the output transformer has to be outside the module in the rack itself. As you guessed, EQ modules would be unbalanced in and out and would be connected via the backplane to the active electronics of an adjacent module so they would be dependent on other modules. Any of the current EZTubeMixer modules can be used but at the moment there is no compressor. I have been asked many times when will there be a compressor and I have published some outline designs but as yet I have not found the time to actually build one. If and when I do it will probably be based on the Twin Line Amp card and one group member has already used one of these to build an opto compressor.

Cheers

Ian

 

[G-Sun]

With tubes you need to use input and output transformers for balanced ins and outs. Unfortunately there is not enough room in a single 3U module for both input and output transformers and the three tubes so the output transformer has to be outside the module in the rack itself. As you guessed, EQ modules would be unbalanced in and out and would be connected via the backplane to the active electronics of an adjacent module so they would be dependent on other modules. Any of the current EZTubeMixer modules can be used but at the moment there is no compressor. I have been asked many times when will there be a compressor and I have published some outline designs but as yet I have not found the time to actually build one. If and when I do it will probably be based on the Twin Line Amp card and one group member has already used one of these to build an opto compressor.

Thank you Ian!
So, then the Ez Tube Lunch box is to be considered more like a channelstrip than a variant of the 500-system.
Would suit me fine.

Twin Line Amp card, opto compressor: Sounds good to me. All stepped? Stereo?

Without knowing to much about compressor design, I might prefer some non-tube design if that's gonna prove more useful.

Edit;
I see your comp thread:
http://groupdiy.com/index.php?topic=52847.0
I will read there

 

[Holger]

The first working tube lunchbox. It houses a complete channel strip of my future mixer:
amp card, fader, EQ, VU meter, insert send/return (buffered by Ian's 6922 buffer card with a separate 6.3V heater), channel I/O.

(Edit: exchanged picture)

 

[kante1603]

Wow,that is really great stuff,congrats Holger!
Since there are no writings on some points yet may I ask if the insert point is closed with a switch or a short patchcord?Also where it is located in the signal chain?
And the switches,are these Rafi/Lumotast ,Apem or something else?

Have a nice weekend,

best,

Udo.

 

[Holger]

Udo, exchanged the picture.

Insert point is between gain stage 1 and EQ. Switching is done via relay. The switches are RAFI (IIRC).

 

[G-Sun]

A 19 inch sub-rack is 6 EZtube modules wide. At 3U high, a channel strip with EQ needs two module widths. So, if I felt confident we could get a PSU in 2 module widths that would also not interfere with preamps in the sub-rack I would suggest using a standard 19 inch sub-rack, have 4 module widths for electronics and the PSU in the other two. Mechanics problems are solved because everyone can buy their favourite mass produced sub rack. There's one small problem with this which is that you also need an extra couple of extrusions a the back to mount the rear panel onto and they don't come as standard.

I'm thinking 19"rack width and 3U
2ch pre + eq
a) with compressor, stereo. Ext. psu
b) with psu on board. No comp.

Considerations: I'd like to have some filters before the comp. I have a pair Harrison Ford Filters, but then I would need some kind of insert.
So, the typical solution is to have the comp as a separate unit.
And, for a comp to work well in a channelstrip, it should be very versatile, and that seems a little tricky. Some LA2A behaviour could work, but 3 settings for time-constant and 3 settings for ratio would be prefered. If it's not versatile enough, many would opt out the comp I guess. m2c

 

[ruffrecords]

A 19 inch sub-rack is 6 EZtube modules wide. At 3U high, a channel strip with EQ needs two module widths. So, if I felt confident we could get a PSU in 2 module widths that would also not interfere with preamps in the sub-rack I would suggest using a standard 19 inch sub-rack, have 4 module widths for electronics and the PSU in the other two. Mechanics problems are solved because everyone can buy their favourite mass produced sub rack. There's one small problem with this which is that you also need an extra couple of extrusions a the back to mount the rear panel onto and they don't come as standard.

I'm thinking 19"rack width and 3U
2ch pre + eq
a) with compressor, stereo. Ext. psu
b) with psu on board. No comp.

Considerations: I'd like to have some filters before the comp. I have a pair Harrison Ford Filters, but then I would need some kind of insert.
So, the typical solution is to have the comp as a separate unit.
And, for a comp to work well in a channelstrip, it should be very versatile, and that seems a little tricky. Some LA2A behaviour could work, but 3 settings for time-constant and 3 settings for ratio would be prefered. If it's not versatile enough, many would opt out the comp I guess. m2c

My current thinking is the PSU is best external which would leave room for three modules per channel. 1st slot could be mic pre. This has gain make up for an EQ which could be in the second slot. Compressor could be third slot. I do not have a tube compressor yet. Early ideas have been based on LA2A topology but this has fixed attack/decay and only a primitive adjustment of ratio. I have done some early work on a new side chain which, in conjunction with a relatively fast opto, will allow the several setting for attack/decay. Also there is sufficient gain and drive capability to indicate it might be possible to operate the opto in two or maybe three different regions which would provide three ratio settings. But it is earlydays yet.

Cheers

Ian

 

[G-Sun]

I like the way you're thinking Ian. What do you think regarding filters?
I'm thinking off-3pos and sc/primary path switch would be ideal. But I don't know how difficult that would be to do.

 

[ruffrecords]

I like the way you're thinking Ian. What do you think regarding filters?
I'm thinking off-3pos and sc/primary path switch would be ideal. But I don't know how difficult that would be to do.

There are several ways to approach this. The first is to include an insert point after the mic pre/EQ and before the comp. You can attach a VTB2291 to the mic pre output to provide a balanced insert send. Then add a 10K:10K input transformer to the comp input. This way you can plug in the Harrison Ford for instance or any other filter you like.

The second is to use the Helios EQ. The treble boost/cut control acts as a LP filter in cut mode but the slope is relatively shallow and is at a single fixed frequency. The bass cut is a high pass filter with a modest slope and variable cut off frequency.

And lastly you could design a passive EQ to provide  a high slope HP and LP filter with switched frequency similar the the Pultec HLF3. I have no plans to do this at the moment.

Cheers

Ian

 

[G-Sun]

Cool, thanks!
I think it's pre + ReddEq x2
And optional comp stereo as separate units then for me (or linked).
If/when

 

[Holger]

I found a 4U case and recently finished my portable mixer channel.

 

[kante1603]

Well done Holger!

It even has your "personal signature" (LEMOSAs),I think I would recognize any of the "Holger-Builds" everywhere in the world,hahaha....  ;D

Best regards and have fun,

Udo

 

[Holger]

Udo,
the Lemo's are not connected, they're just spare connectors.

 

[ruffrecords]

I have been doing some more work with the lunch box power supply. The attached picture shows a nearly completed prototype fitted into a 230mm by 170mm  2U Galaxy Maggiorato box made by modushop.biz in Italy. As you can see, you can just about squeeze everything in if you use only one transformer. For this prototype I used a toroidal from Tube-Town:

https://www.tube-town.net/ttstore/product_info.php?products_id=5391&MODsid=sk76ka307jkjj7mpinth1orhv6

It has 220V, 230V and 240V taps on the primary. I used the 12.6V at 1 amp secondary for the 12V supply. Unfortunately,  12.6VAC is not really enough to regulate to 12V after allowing for rectifier diode drops and sufficient voltage across the regulator. To help this, I planned to connect the UK 240V mains input to the 220V tap which would increase the secondary voltage to 13.75. Previous calculations indicated that 14VAC was really necessary and this is very close. However, the HT voltage also goes up and the peak across the first HT reservoir capacitor rises to just over 386V and I an using 400V capacitor. This is too close so instead I used the 230V tapping which gives a peak unloaded HT of 370V which I think is an adequate safety margin. The peak from the 12,6V winding is now 18.6V which is just adequate for a 1 amp supply. The secondary voltage really needs to be 14V rms for guaranteed regulation so a standard 15VAC transformer would be the cheapest option. However, the does significantly increase the dissipation in regulator so to power a full rack of 6 boards an off board heatsink would have to be used. Also, at higher heater currents, the heater supply bridge rectifier gets rather hot. With both of these factors in mind I have tweaked the lunch box PSU PCB layout to make it easier to wire in an off board regulator and rectifier. I am pretty confident there will not need to be any further mods made to this PCB so I will get 20 made and then build a full power version in a full size 2U 19inch rack box. In the meantime the prototype PSU is proving very useful for testing the new 6U channl PCBs for the Mark 3 mixer.

Cheers

Ian

 

[pvision]

I just found this thread and my immediate thought was "Keep the PSU external!"

When I bought my GML 8200 I was amazed that it needed this huge, heavy, non-rackmountable PSU to operate.  Then I bolted it in the bottom of the rack and forgot about it completely. I mounted the light, well-balanced GML kit at the top of the rack.  A while later I conceded it was a great idea.  Daisy-chaining units to one PSU seems sensible

My suggestion would be a 19" rackmount PSU with removable rack ears.  If it's not racked the ears are nasty things with sharp edges

Nick Froome

 

[ruffrecords]

I just found this thread and my immediate thought was "Keep the PSU external!"

My suggestion would be a 19" rackmount PSU with removable rack ears.  If it's not racked the ears are nasty things with sharp edges

Nick Froome

I agree that keeping it external is the safest option. A 19 inch rack size is very convenient for many people. However, I am pretty sure that there will be quite a few who will want to use the lunch box for location recording where a 19 inch unit may or may not be so convenient. With a full size 6 pack of active PCBs you will almost certainly need the space inside a 19 inch enclosure for the heater heatsink. With only three boards and possibly with four, the half size supply above should be sufficient.

Cheers

Ian

 

[ruffrecords]

I know it has been a while but this project is still alive. I finaly got round to tweaking the LunchBox PSU PCB layout and I have ordered a batch. They'll be on sale in the Emporium in a few weeks.

Cheers

Ian