Feeler: EZ Tube Lunch Box

[irfrench]

OK,

So it seems like the crux of this as a modular-all-in-one-rack-option is whether the psu can be done on a card?  I suppose this is really dependent on how much the psu will need to, or is able to, provide.

Ian, aside from the noise element (not that this is a small issue), is it feasible to have a PSU card?  What sort of power requirements are typical for your preamp and EQ cards?

Cheers,
Ian

 

[ruffrecords]

OK,
Ian, aside from the noise element (not that this is a small issue), is it feasible to have a PSU card?  What sort of power requirements are typical for your preamp and EQ cards?

Cheers,
Ian

THE EQ cards are completely passive so they have zero power requirements. The mic pre and twin line amp cards have the same active components and there power consumption is identical. Each one needs just under 0.5A at 12V for the heaters and about 15mA from the HT supply. You can fit a maximum of four cards in the proposed space which means we need a 2 amp 12V supply and the HT needs to supply 60mA max. As well as these we should also provide phantom power for up to four mics - say 50mA??

The HT could use my HT350 board but this has space for chunky 470uF caps which may well be overkill. We could probably get away with smaller diameter 200uF types and save a bit of space. The phantom could use my existing phantom PCB layout and the 12V supply probably needs an LM317 in a TO3 package on a chunky heat-sink. Will all that fit on a 100mm by 160mm PCB? Good question. I'll look into it. It might be a handy board to have for building rack based tube projects as well.

Cheers

Ian

 

[michal_k]

Hi Ian,

Tube lunchbox is a great idea, I've given it lots of thought as well. Seeing what you try to achieve here here's my 2 cents:

You've said in the first post you want to make it small = 2 Units (pre and eq). What I'd do would be an enclosure with psu and two slots. I'd avoid backplane as it is one of the most expensive parts in my Lunchbox. Instead I'd use a cable with connectors like this wide ones for hard drives in PCs. There's way less modules working in your standard than in API500 so users won't remove them as often as in regular lunchboxes + this saves lots of money.

If you decide to go for lunchbox with custom width rails though, I may be of some help as I've done all that before.

 

[anjing]

For the sake of brainstorming. Instead of having the preamp and eq side by side @ 28hp and 3u high, why not have the preamp on top and eq on bottom and have 14hp 6u high? This would allow to have 4 modules instead of 2 in one rack. It might as well make it easier  if we want to have to psu on a card. It would also allow more leaway for further development of modules that might need more space. For example 28hp 6u high were you could put a real size meter for let's say a compressor?

Regards,

Pierre

 

[ruffrecords]

We are getting some interesting feedback now. I guess the thing about DIY is that everyone wants something slightly different so the skill comes in trying to decide what the common core should be.

To make it readily applicable to a range of needs I think we do need a 'standard' power supply, whether it is fitted inside or outside the rack/lunchbox. I spent a couple of hours looking at this and my first rough layout seems to indicate that it can be fitted onto a single Eurocard sized PCB. The crucial component is the heatsink for the 12V heater supply. The heaters can consume as much a 2 amps so if we allow a 5V drop across the regulator (LM317 in a T03 package) that's 10 watts to dissipate. I found what looks like a suitable PCB mounting heatsink of 4 degrees C/W which should keep the heatsink below 70 degrees C.

As I said earlier, the mechanics is always the hard bit and an off the shelf 19 inch su-rack is an easy solution that is available to everyone at a reasonable cost. But it is  not a lunch box.

I guess what I am trying to get my head around is what would people use this for? Would it be a permanent addition to a studio or something portable to be used outside the studio?


Cheers

Ian

 

[irfrench]

This is probably a really unhelpful response - but both!

I could see myself wanting to have a rack unit in my room, as well as the option to have it portable in case I need to track in a bigger space.  If the PSU is on a pluggable unit I could simply take the units I want out of the rack and put them in a lunchbox chassis.  8) 8) 8)

In my head the idea of a backplane PCB would work wonderfully if 3 units (PSU+2) in a lunch box would be useful and 6 (PSU+5) in the studio would be suitable.  So if the two backplanes were a standard size (that would fit both a rack and half rack width[lunchbox size?]) and could be linked together there are options for both lunchbox and rack.

I understand this is easy for me to speculate on as I'm not doing the graft - so please understand that whatever your decisions are I, for one, am grateful you are even considering this!

Thanks,

Ian

 

[anjing]

This would work with Ian's 2 module backplane that you can just sidechain if you need more modules....

Regards,

Pierre

 

[ruffrecords]

Well it looks like one issue has been laid to rest. I have struggled for ages and failed to squeeze the necessary power supply onto a PCB the size of a standard Eurocard but it just won't go. There are too may chunky square things to fit in and you need a near square board to get them in. It will go into 130mm by 130mm but not 100 by 160mm and they are almost equal areas. So the bottom line is the power supply is going to have to be external. Which fortunately relieves us of all those potential hum problems. Just need to find a suitable standard box that is readily available throughout the DIY world to put it in. Suggestions?

Cheers

Ian

 

[ramshackles]

Plenty of cheap enclosures by hammond on farnell. You could easily get a suitable one for <20 GBP.

Ideally one with a hole for the IEC connecter already drilled would be great. I dont think you could pick something like that up off farnell though...

 

[ruffrecords]

Plenty of cheap enclosures by hammond on farnell. You could easily get a suitable one for <20 GBP.

Ideally one with a hole for the IEC connecter already drilled would be great. I dont think you could pick something like that up off farnell though...

I had a quick look on Farnell for a Hammond enclosure at least 6in x 6in x 3in. Couldn't find anything for less than 20GBP except in ABS.

Cheers

Ian

 

[anjing]

Hi Ian,
  There are a few ones from hammond that look ok, http://ca.mouser.com/ProductDetail/Hammond-Manufacturing/1401AA/?qs=sGAEpiMZZMsrGrAVj6eTvc4t%252bXlGtxAkw9PfpbRu%252bPg%3d or http://ca.mouser.com/ProductDetail/Hammond-Manufacturing/1454S/?qs=sGAEpiMZZMsrGrAVj6eTvbKui9sLlDKI0vRtCOvcP%2fk%3dWe could find a nice leather handle and a jewel led socket on ebay...Is hammond readily available in europe? Do you have any suggestion for the cable connector? 

Regards,

Pierre

 

[ruffrecords]

Hi Pierre,

That Hammond box is available in the UK:

http://uk.farnell.com/hammond/1401aa/enclosure-instrument-steel-grey/dp/1876465

The supply cable connector is a little more difficult. We need at least 7 ways (2 x heater, 2 x HT, 2 x phantom and 1 x screen). For my mixer I use an 8 way speakon. They are rugged, lockable and have both high current and high voltage ratings. They are just not very pretty or cheap.

http://uk.rs-online.com/web/p/products/385171/?cm_mmc=UK-PPC-0212-_-03_Supplier_M-Z-_-Neutrik_Loudspeaker_Connectors-_-NL8MPR&gclid=CNXy-py7o7oCFWfLtAodk1cAHw

Here is a link to the initial PCB layout for the lunchhbox PSU. There are a few tweaks to do but it is basically there. The phantom and the heater use the same layout, the only differences are the phantom uses a TL783 and the 12V uses an LM338 and a much bigger heatsink.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/power/lunchboxPSUPCB.png


Cheers

Ian

 

[ramshackles]

Could you not use an XLR type connector?
http://uk.farnell.com/neutrik/nc7fdl1/socket-xlr-panel-unified-7pole/dp/261117

http://uk.farnell.com/neutrik/nc7mx/plug-xlr-free-7pole/dp/261014

 

[anjing]

Hi Pierre,

That Hammond box is available in the UK:

http://uk.farnell.com/hammond/1401aa/enclosure-instrument-steel-grey/dp/1876465

The supply cable connector is a little more difficult. We need at least 7 ways (2 x heater, 2 x HT, 2 x phantom and 1 x screen). For my mixer I use an 8 way speakon. They are rugged, lockable and have both high current and high voltage ratings. They are just not very pretty or cheap.

http://uk.rs-online.com/web/p/products/385171/?cm_mmc=UK-PPC-0212-_-03_Supplier_M-Z-_-Neutrik_Loudspeaker_Connectors-_-NL8MPR&gclid=CNXy-py7o7oCFWfLtAodk1cAHw

Here is a link to the initial PCB layout for the lunchhbox PSU. There are a few tweaks to do but it is basically there. The phantom and the heater use the same layout, the only differences are the phantom uses a TL783 and the 12V uses an LM338 and a much bigger heatsink.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/power/lunchboxPSUPCB.png


Cheers

Ian

Hi Ian,

  I'm amazed at the price of some of the things once they cross the ocean! Looks like the 1401a is a good choice as it's widely available. The only downside is it look's like it might be difficult to  have a custom frontplate done because of the way it hook's up to the case... If they could make round IEC connectors it would make life easier!
If this one was higher http://ca.mouser.com/ProductDetail/Hammond-Manufacturing/1455T2201BK/?qs=savM97goi5jNWqogVdbBSQ==, it would be easy to make a faceplate for it but it's only 2" tall.

  The 8way speakeon connector looks very practical, is it easy to solder to the 8core pro power cable?

Amazing work on the power supply it looks like the LM338 can supply up to 5A so it could even supply an eztube mixer!

Regards,

Pierre

 

[anjing]

Could you not use an XLR type connector?
http://uk.farnell.com/neutrik/nc7fdl1/socket-xlr-panel-unified-7pole/dp/261117

http://uk.farnell.com/neutrik/nc7mx/plug-xlr-free-7pole/dp/261014

Looks like the speakeon as a higher voltage and A rating, i don't if it matter as much if we supply only 2 channel.

Regards,

Pierre

 

[ramshackles]

Yes, but I figured if it the idea is to make some kind of small lunch box then it would be adequate?

Either way, I don't think it would be particularly easier to use or prettier than a speakon...

 

[ruffrecords]

Could you not use an XLR type connector?
http://uk.farnell.com/neutrik/nc7fdl1/socket-xlr-panel-unified-7pole/dp/261117

http://uk.farnell.com/neutrik/nc7mx/plug-xlr-free-7pole/dp/261014

They would be nice and neat but unfortunately they are only rated to 150V.

Cheers

Ian

 

[ruffrecords]

Hi Ian,

  I'm amazed at the price of some of the things once they cross the ocean! Looks like the 1401a is a good choice as it's widely available. The only downside is it look's like it might be difficult to  have a custom frontplate done because of the way it hook's up to the case... If they could make round IEC connectors it would make life easier!
If this one was higher http://ca.mouser.com/ProductDetail/Hammond-Manufacturing/1455T2201BK/?qs=savM97goi5jNWqogVdbBSQ==, it would be easy to make a faceplate for it but it's only 2" tall.

  The 8way speakeon connector looks very practical, is it easy to solder to the 8core pro power cable?

Amazing work on the power supply it looks like the LM338 can supply up to 5A so it could even supply an eztube mixer!

Regards,

Pierre

I agree. The speakon is $6.38 in the US and the same in GBP over here. It is a common complaint that we pay in pounds what the Americans pay in dollars for the same product, especially audio and music gear, despite that fact most of it is made in China anyway.

Ragrading the case, I am beginning to think that a 2U rqck mounting box might be simplest for the power supply. Aluminium front and backs are no problem and it would only need to be 150mm  or so deep. Something like this might do:

http://www.modu.it/slimlineeng.html

The LM338 will give more than the 2 amps needed by the lunchbox if you put a big enough heatsink on it.  I did try this basic circuit powering the heaters of the 4 channel demo mixer I am building and it worked OK. That needed about 3 amps. You just need to be careful about the smoothing capacitor. If you use a 14VAC tranformer secondary, and assume worst case the mains is 10% high, then the peak rectified signal could be just under 22 volts. I would not be happy specifying a 25V part for the smoothing capacitor so let's go for 35 volts. The largest vakue 35V capacitor I can find that will fit the given footprint is 22,000uF.

If the load is 5 amps this means the ripple will be 2.27 volts peak to peak (at 50Hz). The LM338 needs at least 3V to regulate which means the average voltage across the LM338 must be at least 3 + 2.27/2 = 4 volts minimum. At 5 amps load that means there's 5 x 4 = 20 watts of heat to dissipate. The TO3 can has a thermal resistance of 1K/W so with the 3.3K/W heatsink in the lunchbox that's a total of 4.4K/W which will lead to a temperature rise of 4.3 x 20 =  86 degrees. With an ambient of 25 degrees the LM338 junction will be at 111 degrees C. What this boils down to is you really need a 1K/W heatsink if you are going to try for 5 amps of current.

Cheers

Ian

 

[ruffrecords]

What about the 170mm by 230mm version if this for an external power supply case?

http://www.modushop.biz/ecommerce/cat154_l2.php?n=1

80mm tall, aluminium front and back panels and only 22.50 Euros.

Cheers

Ian

 

[Dr Gris]

Looks perfect, especially for those that want a slim 2 unit desktop box. I guess for those a
19 inch 2 unit rackmount PSU might be a bit hefty.

Personally I like rackmountable stuff since I move my little home studio around,
and would find it interesting with a "full size 3U rackable lunchbox" enclosure with this
floor box PSU. But I guess that's like building your tube mixer, but without the mix part
and that is not the discussion here...or?

Best
Magnus