Feeler: EZ Tube Lunch Box

I have just updated the lunch box blog with all that has happened in the last seven months:

http://eztubelunchbox.blogspot.co.uk/

As usual, I am happy to hear questions and comments.

Cheers

ian

Back in this post:

http://groupdiy.com/index.php?topic=53765.msg751719#msg751719

I referred to a 12V heater, single tube, gain make up stage attached to my standard 3U passive EQs. The other day I sent off the first of these EQ with built in gain make up PCBs for prototypes to be made. I am sure many of you will be pleased to know I did the Pultec 3 band EQ first. I even included the bypass pad and connections for the DPDT bypass switch. Unfortunately I forgot to include the overall gain trim control. However, as the make up amp has only just a little over 20dB gain the EQ will only have about 3dB gain overall. I'll let you know when the boards arrive.

Cheers

Ian

Pultec EQ boards with built in gain make up amp arrived a few days ago. Just started to build one.

Cheers

Ian

ruffrecords said:

Pultec EQ boards with built in gain make up amp arrived a few days ago. Just started to build one.

Click to expand...

Good news. Will be looking forward to see/hear one of the units

It seems much better to be able to have preamp and eq separate, independent out/in or not.

Now, there's a free gain-stage in the classic, right?
Do you have any ideas for utilizing that?
I was thinking about it. A 1-2 more bands mid eq would be nice, but.. would clutter things up.

Could there be a second gain/drive-knob? With a different sound-character than the first stage?
I believe that would be a nice addon to the concept, and be attractive to many.

G-Sun said:

ruffrecords said:

Pultec EQ boards with built in gain make up amp arrived a few days ago. Just started to build one.

Click to expand...

Good news. Will be looking forward to see/hear one of the units

It seems much better to be able to have preamp and eq separate, independent out/in or not.

Click to expand...

The inductors arrived the other day. I need to fit the hi boost caps, the two inductors and an input transformer and it will be ready to test. I am planning to try the OEP Z3003E  transformer as the 10K:10K input transformer as they are very good value for money.

Now, there's a free gain-stage in the classic, right?
Do you have any ideas for utilizing that?
I was thinking about it. A 1-2 more bands mid eq would be nice, but.. would clutter things up.

Could there be a second gain/drive-knob? With a different sound-character than the first stage?
I believe that would be a nice addon to the concept, and be attractive to many.

Click to expand...

As you know, I try to make my designs flexible as this allows DIYers to configure them  exactly as they need. The Classic PCB contains two identical amplifiers (basically 6992 based poor man's tube gain make amps) and space for two input transformers. This means you can configure it in many different ways some of which are described in the  Classic Construction Guide on my web site. On the DIY tab, click the Lunchbox folder and then the Classic folder to find it. One of the options described is connecting a passive EQ between the two stages. Another describes how to make two separate mic pre by moving the gain control to sit between the output of the mic input transformer and the input of the tube. There is no reason why you cannot apply this technique to the standard two stage design by adding an extra pot after the first transformer. This would allow you to vary the drive to the first stage and compensate for the gain change with the regular gain control. And of course you can add a gain control on the output of the ouptut transformer as described in the guide to allow you to drive the second stage guide.

As I said,  it's flexible. The only limitation is what you can sensibly accommodate on a 3U high front panel.

Cheers

ian

ruffrecords said:

As you know, I try to make my designs flexible as this allows DIYers to configure them  exactly as they need. The Classic PCB contains two identical amplifiers (basically 6992 based poor man's tube gain make amps) and space for two input transformers. This means you can configure it in many different ways some of which are described in the  Classic Construction Guide on my web site. On the DIY tab, click the Lunchbox folder and then the Classic folder to find it. One of the options described is connecting a passive EQ between the two stages. Another describes how to make two separate mic pre by moving the gain control to sit between the output of the mic input transformer and the input of the tube. There is no reason why you cannot apply this technique to the standard two stage design by adding an extra pot after the first transformer. This would allow you to vary the drive to the first stage and compensate for the gain change with the regular gain control. And of course you can add a gain control on the output of the ouptut transformer as described in the guide to allow you to drive the second stage guide.

As I said,  it's flexible. The only limitation is what you can sensibly accommodate on a 3U high front panel.

Click to expand...

Yes, it's really flexibel. Thanks!

I have been working on rationalising the power supply PCBs for the Lunch Box. Originally there were just two - the external one and the 3U one and both had dc heaters. Things got a little more complicated when it appeared that AC heaters would work fine for an internal supply and also when it became apparent that a 5 slot 500 series style Lunch Box could be built using Frank Rollen's new enclosures. The result is there are now four power supply PCBs to choose from. However for conventional Eurorack based Lunch boxes I would recommend using just two of them - the external one with dc heaters if you want to use all 6 slots in a sub-rack or the 3UPSU V3 with ac heaters for an internal power supply and up to 5 audio slots.

For Frank's enclosure you can again use the external power supply if you want to retain dc heaters, or the new internal 500 AC board for an internal power supply. In both cases you get 5 audio slots to play with.

I have summarised all the schematics, build info and BOMs into a single document which you can find in the Lunchbox/PSU folder under the DIY tab of my web site. Direct link here:

https://drive.google.com/open?id=0B_n67A1hN3qtODdWaXNlaU1zLXc

Cheers

Ian

Thanks for your work Ian!
I've rethought my needs and Franks  5-space module with internal psu, seems fine,
for 2x pre + eq.

G-Sun said:

Thanks for your work Ian!
I've rethought my needs and Franks  5-space module with internal psu, seems fine,
for 2x pre + eq.

Click to expand...

That should be fine. The main limitation with Frank's enclosure  is that both the mains transformer and the power supply PCB is at the back. This leaves less room for output transformers and input/output XLRs but that should not be an issue for two pres with EQ.

Cheers

Ian

Would the DB25 x 2 fit as 5th slot with the twin line amp
and a couple of  VU-meters?

G-Sun said:

Would the DB25 x 2 fit as 5th slot with the twin line amp
and a couple of  VU-meters?

Click to expand...

I think you should be able to squeeze in a couple of DB25 boards side by side but I suspect the remaining  room would be insufficient for a couple of mechanical VU meters. A couple of small :LED bar graph ones should fit. I am not sure what two DB25 holes right next to each other would do to the strength of the front panel.

Cheers

Ian

ruffrecords said:

I think you should be able to squeeze in a couple of DB25 boards side by side but I suspect the remaining  room would be insufficient for a couple of mechanical VU meters. A couple of small :LED bar graph ones should fit. I am not sure what two DB25 holes right next to each other would do to the strength of the front panel.

Cheers

Ian

Click to expand...

Thanks!
I was thinking db25 on back.
Would require transformers in/out x2 as well I guss.

Or combined with 2ch Ezcomp,
Ext. Pwr.

G-Sun said:

ruffrecords said:

I think you should be able to squeeze in a couple of DB25 boards side by side but I suspect the remaining  room would be insufficient for a couple of mechanical VU meters. A couple of small :LED bar graph ones should fit. I am not sure what two DB25 holes right next to each other would do to the strength of the front panel.

Cheers

Ian

Click to expand...

Thanks!
I was thinking db25 on back.
Would require transformers in/out x2 as well I guss.

Or combined with 2ch Ezcomp,
Ext. Pwr.

Click to expand...

DB25 on the back is much better. There is room on the twin line amp for the two input transformers so you just need to find room on the rear panel for the output transformers.

Cheers

Ian

Further to my post a few weeks ago on power supply options for the Lunch Box, I have just received the latest version of the 3U power supply with DC heaters PCB. This is very similar to the AC heaters 3U power supply board except it has dc heaters!. It plugs into a 6 slot motherboard just like the AC version and allows you to use five slots in a standard Eurorack.  Unlike the AC version I have used terminal blocks (or 0.2 inch pitch Molex conns if you wish) for the AC inputs. I id this mainly because of the high current spikes in the 12.6V supply  AC input. It does use the low cost DIL bridge rectifiers for the HT and phantom power just lie its AC brother. I have updated the power supply build and BOM document to reflect these changes.

https://drive.google.com/file/d/0B_n67A1hN3qtVnphbzJRc0FVQkE/view?usp=sharing

Cheers

Ian

I am now at the point where I think the design of the EZTube Lunch Box is pretty much complete and I am now busy creating all the necessary documentation for it. In doing this I realised there are some holes in the original EZTube Mixer project documentation which I am hoping to plug. I plan soon to start an EZTube Lunch Box support thread in the Mixers/Monitors section where links to all the documentation will be included in the first post.  I will update the first post as new documentation is created. All the documentation will be available on my web site.

Cheers

Ian

How compatible is the Poor Mans 660/670 with the EZ Tube Lunch Box?
http://groupdiy.com/index.php?topic=28274.0

Would it fit the general idea for the EZ Tube Lunch Box?

I guess the design here is more updated:
http://groupdiy.com/index.php?topic=51478.0
(But I'm not the expert )

G-Sun said:

How compatible is the Poor Mans 660/670 with the EZ Tube Lunch Box?

Click to expand...

Looking at its documentation I would say it would be hard to integrate this into the Lunch Box. The most series drawback it is power supply requirements. Its HT needs between 60 and 100mA which is more than an entire Lunch Box consumes . Also, its heaters are 6.3V rather than 12V as used in the Lunch Box .  It also needs a 17V rail for some of the silicon circuits. So you would need to do something extra to provide these three.

Phyically the PCB is 120mm by 80mm which is smaller than the Eurocard size used in the Lunch Box . Obviously it will not plug in but you should be able to mount it from a front panel.

Cheers

ian

ruffrecords said:

Looking at its documentation I would say it would be hard to integrate this into the Lunch Box. The most series drawback it is power supply requirements. Its HT needs between 60 and 100mA which is more than an entire Lunch Box consumes . Also, its heaters are 6.3V rather than 12V as used in the Lunch Box .  It also needs a 17V rail for some of the silicon circuits. So you would need to do something extra to provide these three.

Phyically the PCB is 120mm by 80mm which is smaller than the Eurocard size used in the Lunch Box . Obviously it will not plug in but you should be able to mount it from a front panel.

Click to expand...

Thanks for you answer Ian!
Kingston has -12,6VDC for the heaters etc.  it seems (here)
but the has a B2+ of 100-190VDC
(I'm not sure of if the B2+ is for supersoft knee only, or if there's some other need for it)

Amp-size would not be that hard for an external psu would it?

G-Sun said:

ruffrecords said:

Looking at its documentation I would say it would be hard to integrate this into the Lunch Box. The most series drawback it is power supply requirements. Its HT needs between 60 and 100mA which is more than an entire Lunch Box consumes . Also, its heaters are 6.3V rather than 12V as used in the Lunch Box .  It also needs a 17V rail for some of the silicon circuits. So you would need to do something extra to provide these three.

Phyically the PCB is 120mm by 80mm which is smaller than the Eurocard size used in the Lunch Box . Obviously it will not plug in but you should be able to mount it from a front panel.

Click to expand...

Thanks for you answer Ian!
Kingston has -12,6VDC for the heaters etc.  it seems (here)
but the has a B2+ of 100-190VDC
(I'm not sure of if the B2+ is for supersoft knee only, or if there's some other need for it)

Amp-size would not be that hard for an external psu would it?

Click to expand...

I think if you are prepared to go with an external power supply you should be OK. I don't know enough about the actual circuit to be able to comment on the HT voltages.

Cheers

Ian

I think if you are prepared to go with an external power supply you should be OK. I don't know enough about the actual circuit to be able to comment on the HT voltages.[/quote]
Cool.
But, it's not something you see yourself incorporating into the EZ Tube Lunsh Box project?

btw: What does EZ stand for?