Feeler: EZ Tube Lunch Box

[G-Sun]

For the mic pre stage the options are:

1. First half of Eurocard with built in  gain switch and mic/line/pad/phase/phantom switches
2. Half a Twin Line Amp (TLA). Add your own gain control and input switching
3.  Half a Classic, with your own input swiching

Thanks!
I wasn't previous aware there were three preamp-options. What a a tube heaven

Are there any sound-differencies between the TLA and the Eurocard?

mic/line/pad/phase/phantom switches are what I need, so I guess going for the Eurocard is the obvious option.
Does it fit right into the 3U form-factor?

For the passive EQ gain make up, the corresponding choices are:

1. Second stage of Eurocard
2. Second half of TLA
3. Second half of Classic or half of a separate TLA

The compressor always needs both halves of a TLA.

Bottom line is for a mic pre, passive EQ and comp together you always need four amps. There are no spares that I can see.

I have looked at including gain make up with the EQ. I have a design that uses a single tube that was developed for a different aspect of a mixer. For adequate performance this tube needs to be equivalent to  a 6922 but with a 12V heater. Such a tube does exist but it is very rare and expensive so it is not really a viable alternative. The only other alternative is to use a 6922 and provide a separate 6.3V supply just for it - again not really a viable alternative.

Ok, many thing I'm not aware of as you understand.
Thanks for the clarification!

 

[G-Sun]

Documentation:

I am conscious the documentation is disparate and incomplete but so is the development! I will try to collect all the Lunch Box data together under a single heading even if it does mean duplicating data (I don't want to alter the organisation of the present data as a lot of it is linked to in pages of threads at groupdiy)

You've done a tremendos work allready. Thanks a lot!

 

[ruffrecords]

I wasn't previous aware there were three preamp-options. What a a tube heaven

Are there any sound-differencies between the TLA and the Eurocard?

mic/line/pad/phase/phantom switches are what I need, so I guess going for the Eurocard is the obvious option.
Does it fit right into the 3U form-factor?

There's really only two choices because the Eurochannel and the TLA contain identical amplifiers; it is just the support circuitry that is different. The Eurochannel has provision on the PCB for a mic transformer,  the stepped gain switch and phantom, pad, phase and mic/line push buttons. It fits into a 3u 14HP slot - its a standard 160mm by 100mm Eurocard. The TLA has provision for two input transformers but nothing else. It is the same size.

Cheers

Ian

 

[ruffrecords]

Just received the 'Classic' front panel from Frank Rollen this morning,. Fitted it to the prototype PCB and added the HPF:

Tested the HPF to make sure it performs as as expected. The following three graphs are the flat, 40Hz HPF and 80Hz HPF curves:

Cheers

Ian

 

[G-Sun]

I'd like to better undersnad the difference between the Eurocard preamp and the Classic.
Gain is 50db +20db from the input transformer for both?

Classic Mic Pre:
Does the Classic plug right into the 3 U motherboard?
It has fourtogglesPCB for +48/pad/Ø/line right? How does it connect to the main pcb? Molex?
You show a HPF above. Is that on the pcb?

The Classic you said has a little more distortion when pushed.
Are there any soundsamples anywhere, where I could compare the two?

 

[ruffrecords]

Eurochannel:

Designed to be part of a 'modern' mixer so it has very good drive capability for buses, includes mic transformer, stepped gain control and mic/line, phase, pad and 48V switches and an EQ gain make up amplifier on the PCB. Mic pre gain variable from 27dB to 60dB (including 20dB from input transformer). Second amp has a trim pot that allows the gain make up for the EQ to be set.

Classic:

Harks back to the good old days when things were a lot simpler. The PCB contains two identical fixed gain amplifiers (just under 30dB)and space for up to  two uncommitted input transformer - and nothing else. It is intended to allow you to configure it as you wish.

For example, in its simplest form you could just include a mic transformer at the input and a pot between the two stages and you have a 70dB ribbon mic pre. If you want, you can add a simple HPF before the pot using a couple of caps wired on the back of a toggle switch (which is what I did in the prototype). If you want more control at the input you can add four toggles for 48V, pad, mic/line and phase - I designed a little PCB for this which I used in the prototype which connects by flying leads to Molex connectors. You could include other passive EQ between the stages but you need to bear in mind its insertion loss will be subtracted from the overall gain.

There are lots of other possibilities. I designed the four toggles PCB to be as small as possible so you can actually fit two side by side on a 3U front panel. This would allow you to make  two simple mic pres in a single 3U module. Gain would only be 50dB each but for many uses that is fine.


Note, both the Eurochannel and the Classic are standard 160 by 100mmmm Eurocards with identical connectors that plug into the back plane; ditto the TLA.

Edit: I should have mentioned that the TLA is much like the Classic in terms of configuration  - it is just two uncommitted amps and two uncommitted transformers on a PCB. However, the gain is variable and can be set by an on board trimmer or by an external resistance (variable, fixed or stepped) and the maximum gain is 40dB per amplifier. In addition, the TLA can be configured to operate as a virtual earth mix amplifier.
The Sound:
Here's a link to a test recording made by Pierre using the Eurochannel:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/sounds/Eurochannel/directouttest.mp3

Here's a link to a track mixed on my first all tube mixer which was the first version of the classic design. This is now earning its keep in a studio in Switzerland.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/sounds/6into2/mix_d_inst.mp3

Although this uses 6CG7 tubes rather the the 6922 that I use today, the sonic signature should be the sme.

Cheers

Ian

 

[G-Sun]

Thanks!

So, as I need the a second gain stage for 3band pulteq gain,
then the classic will only give me 20 + 30 = 50db gain. A little low I'd say.

The Eurochannel will give me 60db, a more suitable value.
When configuring the second stage for eq makeup, should it be as an insert in the preamp,
or can I treat it as a separate module wired from eq out?
transf. mic> Preamp1st > transformer out
transf2in > Eq > Gain2nd > transformer out
(Guess that's ok)

Soundwise I really liked the Eurocard-sample,
but there are so many factors contributing

 

[ruffrecords]

Thanks!

So, as I need the a second gain stage for 3band pulteq gain,
then the classic will only give me 20 + 30 = 50db gain. A little low I'd say.

The EQ will need 20 something dB make up gain so there may be some left over but then you lose 6dB in the 2K4:600 output transformer so overall the gain will be in the region of 50dB.

The Eurochannel will give me 60db, a more suitable value.
When configuring the second stage for eq makeup, should it be as an insert in the preamp,
or can I treat it as a separate module wired from eq out?
transf. mic> Preamp1st > transformer out
transf2in > Eq > Gain2nd > transformer out
(Guess that's ok)

If you  have an insert after the first amp then the 60dB gain is reduced by 6dB due to the output transformer. Do you really need a pre EQ insert. In the EZTubeMixer I go:

trans.mic?Preamp1> fader>EQ>Gain2nd>transformer out

There is enough gain in the second amp to make up for the EQ and the output transformer for 60dB overall gain.

Cheers

Ian

 

[G-Sun]

Thanks Ian!

If you  have an insert after the first amp then the 60dB gain is reduced by 6dB due to the output transformer. Do you really need a pre EQ insert. In the EZTubeMixer I go:

trans.mic?Preamp1> fader>EQ>Gain2nd>transformer out

There is enough gain in the second amp to make up for the EQ and the output transformer for 60dB overall gain.

That's a good question. And it could save me 2 transformers per channel.
So, I'll only get 54db gain with the insert, and 60 without? 54 is a bit low again.

The insert is a work-flow-question for me. As I work much alone i studio, I'll just use the pre first for a rehearsal-take, then loop it back through eq and comp, adjust settings. Then I'll patch in the preamp again for recording.
If I had a line in on the preamp with some sort of fixed setting for 0db, then I could leave out the insert.
Or I could just write down the gain-setting mic vs. line-loop.

 

[G-Sun]

Is the pcb for the psu ready?
For 6 units, 2x (pre, eq, comp)
It's in the Eurocard-format as well, right? 100x160mm
Any BOM?

I'll mount this in an external box.
Any recommendations? Size, hammond.
Hole for out power dc, in pwr ac, fuse, switch, on led

How many rails/cores?
What do you recommend for dc-cable and in/out mounting for it?
Something like this:
http://classicapi.com/catalog/product_info.php?cPath=176_178&products_id=325
?

Transformer
How many VA do I need for 230V?

 

[ruffrecords]

Is the pcb for the psu ready?
For 6 units, 2x (pre, eq, comp)
It's in the Eurocard-format as well, right? 100x160mm
Any BOM?

There is a PSU PCB available for external power supplies. There is a BOM but it needs updating in the light of recent discoveries concerning heater regulator oscillation. It is larger than  100mm by 160mm

I'll mount this in an external box.
Any recommendations? Size, hammond.
Hole for out power dc, in pwr ac, fuse, switch, on led

I mount mine in standard 19 inch rack mounting boxes for which there are many suppliers. Getting front panels done is always an issue. Frank Rollen has a new series of 19 inch cases and of course he can do custom front and rear panels for you. I just got one into which I plan to build a lunch box PSU so this can act as a reference design.

How many rails/cores?
What do you recommend for dc-cable and in/out mounting for it?
Something like this:
http://classicapi.com/catalog/product_info.php?cPath=176_178&products_id=325
?

I like to use cores that are at least 20AWG so the classic API cable will be good. However, it is important that the power supply cable is screened (the screen connects the chassis of the lunch box to the chassis of the the power supply). You can either use a cable that is already screened:

http://www.rapidonline.com/cables-connectors/unistrand-screened-signal-multicore-cable-defence-standard-82987

or add a separate braided screen:

http://www.rapidonline.com/cables-connectors/sleeving-braid-mbs-95-7-5mm-10m-reel-03-1913

Transformer
How many VA do I need for 230V?

I created a spec for a suitable transformer. Sven got a quote from Don Audio for it and I got one made by Canturbury windingc in the UK. The spec for it is here:

http://groupdiy.com/index.php?topic=53765.msg735001#msg735001

Cheers

Ian

 

[G-Sun]

Thanks!

There is a PSU PCB available for external power supplies. There is a BOM but it needs updating in the light of recent discoveries concerning heater regulator oscillation. It is larger than  100mm by 160mm

I mount mine in standard 19 inch rack mounting boxes for which there are many suppliers. Getting front panels done is always an issue. Frank Rollen has a new series of 19 inch cases and of course he can do custom front and rear panels for you. I just got one into which I plan to build a lunch box PSU so this can act as a reference design.

Thanks! How big is the psu pcb?
What's the name for ordering?

I'll mount mine in a sort of hammond-box I think. But I need to know approx size pcb, and hight.
Edit: I see here
http://eztubelunchbox.blogspot.no/2014/12/power-supply-and-enclosure-update.html

Is that a 2U 19"?

 

[ruffrecords]

Thanks! How big is the psu pcb?
What's the name for ordering?

I'll mount mine in a sort of hammond-box I think. But I need to know approx size pcb, and hight.
Edit: I see here
http://eztubelunchbox.blogspot.no/2014/12/power-supply-and-enclosure-update.html

Is that a 2U 19"?

The original external lunch box PSU PCB is 150mm by 110mm. It will fit in a 2U high enclosure. The one I used is by Schroff from Farnel I think. It is 150mm deep and the PCB only just fits in it.

For ordering purposes we will call this PCB LBPSUV2.

Cheers

Ian

 

[G-Sun]

Thanks!

The regulator heatsink(s): Does it fit on the pcb (for 6 modules) as it is now?
Or, do I need to mount it of board?
The SCHAFFNER  FN2010:  What's the benefit of using such filter?

I'm thinking something like this:
http://no.farnell.com/bernstein/ca-270-ukf/box-diecast-ip65/dp/1016380
for psu box.

Some 1,5m of this
http://no.farnell.com/alpha-wire/b956044/cable-18awg-4-core-per-m/dp/1924036
for psu cable.
Now, need to find suitable connectors for it.

 

[ruffrecords]

Thanks!

The regulator heatsink(s): Does it fit on the pcb (for 6 modules) as it is now?
Or, do I need to mount it of board?
The SCHAFFNER  FN2010:  What's the benefit of using such filter?

I am not entirely sure. In the past I have had problems with noise from laptop power supplies getting in via the mains input. I started fitting filters like these in an attempt to keep it out even though they are intended to stop interference getting out.

I'm thinking something like this:
http://no.farnell.com/bernstein/ca-270-ukf/box-diecast-ip65/dp/1016380
for psu box.

That looks a little on the small side to me.

Some 1,5m of this
http://no.farnell.com/alpha-wire/b956044/cable-18awg-4-core-per-m/dp/1924036
for psu cable.

That looks good to me.

Now, need to find suitable connectors for it.

I am leaning towards these types:

http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryId=700000005038&st=connector&pageSize=25&showResults=true&pf=110179367,110181653

There are loads to choose from, there are all sorts of pins and sockets they can take and wading through the data to find a compatible set is a nightmare.

Cheers

Ian

 

[G-Sun]

Thanks!

The regulator heatsink(s): Does it fit on the pcb (for 6 modules) as it is now?
Or, do I need to mount it of board?

Do you have a comment on this one?

That looks a little on the small side to me.

..

http://uk.farnell.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=44&storeId=10151&categoryId=700000005038&st=connector&pageSize=25&showResults=true&pf=110179367,110181653

There are loads to choose from, there are all sorts of pins and sockets they can take and wading through the data to find a compatible set is a nightmare.

Thanks! Very helpful!

Contact: I don't need more then 5pin, do I?

Something like this maybe?
http://www.farnell.com/datasheets/1084905.pdf
(yes, so many to choose from  )

 

[ruffrecords]

Thanks!

The regulator heatsink(s): Does it fit on the pcb (for 6 modules) as it is now?
Or, do I need to mount it of board?

Do you have a comment on this one?

Sorry, missed that one. As designed, the heatsink on the PCB should have been big enough to support 6 slots in the lunch box but in tests it got too hot. I therefore recommend using a larger external one.

Contact: I don't need more then 5pin, do I?

Something like this maybe?
http://www.farnell.com/datasheets/1084905.pdf
(yes, so many to choose from  )

You need two for the heaters, two for the HT and one for the screen. If you want phantom power then you need two more.

Cheers

Ian

 

[buildafriend]

Hi Ian,

I'm curious what voltages your tube lunch box modules will require. I ask because I have a power supply in the works that I was hoping might be usable for your tube lunch box.

My power supply will have 24VDC, 48VDC, 12VDC and ~300VDC.

Thanks again, I always appreciate your input.

-JP

 

[ruffrecords]

Hi Ian,

I'm curious what voltages your tube lunch box modules will require. I ask because I have a power supply in the works that I was hoping might be usable for your tube lunch box.

My power supply will have 24VDC, 48VDC, 12VDC and ~300VDC.

Thanks again, I always appreciate your input.

-JP

It needs:

300V at about 60mA for the HT
12V at about 3 amps for the heaters
and 48V  if you need phantom power.

Cheers

Ian

 

[G-Sun]

Ian,

I've made this overview for my EZTubeLunshBox
https://docs.google.com/spreadsheets/d/1h9Vu5I3k-HZLL5n_xHm78kBiX8PYbSDd33haBqSYbiM/edit?usp=sharing

Is it approximately right?
Any boms available? Where?

There's a boom for the pultec
http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/PultecHeliosBOMs.ods
But it might be a few changes for a eurcardversion, right?