Feeler: EZ Tube Lunch Box

[ruffrecords]

Just finished most of the metalwork for the 28HP power supply:

The IEC is to the left on the rear panel  with the 12V rectifier below it mounted to the extrusion for heat sinking. The toroid is in the middle and the mains fuse and on/off switch you can see on the right mounted to the front panel.

I have not yet decided what to use for the dc output connector. Any suggestions?

Next step is to wire it up.

Cheers

Ian

 

[dipfrik]

Happy new year,

i'am back and hardly trying to catch up here

Let me give a short overview from my workbench:

1) S-AOC Prototype needs a next revision. Both for PSU and the module itself.
Sounds great, but the available space is very small, especially for fitting pots and meter on the frontpanel. The solutions lies in the big solen cap. So i will come back in a later post with a 1st approach. As Ian mentioned a 10uF electrolytic will be just as good.

2) Lunchbox - "squeezed" PSU need also a next iteration.
Let me collect all the input from Ian and Dan.

- avoid vias and increase the track with (main heater 0V, 12V heater supply to smoothing cap etc.)
- heat sink reorientation for better air flow
- general rule: 0V and +ve tracks a.fat.a.p
- wire links or zero ohm resistors rather than vias
- 1st resitor in the HT smoothing chain should be rated 5W
- high voltage trace to the 220R/7W resistor in between the pins of the high voltage connector are ambitious
- need to check the idea of Dan for high power resistor after the diode bridge instead of seeing the large filter caps
traces to electrolytic caps on the bottom side of the pcb

Design idea from Ian

One thing that might help is if you put the 12V heater supply on the right hand side so it is near the output connectors, then have the HT supply to the left of that and then the 12V utility and lastly the phantom power on the far left.

Currently the 28HP modules from Bürklin are finally on the way and i can make a 1st test and go from there.

3) "two pot NFB EQ" from Ian

I definitely need a few extra post for this!
Awesome idea and great addition for the (pair of) mic pre!

4) 'four toggles' PCB from Ian for the Classic with the two knob EQ

Again, need an extra post for this.

I did a 1st step towards a 6U test-pcb design with a lot of extra stuff on it.
Because i want more freedom in the choice of switches (e.g. wide range of illumated switches), i build everything on relays which can be controlled by a small "logic control voltage" from 1V-12V.
At the end it should be an optional board too. The top switcher logic area is responsible for 48V-Line/Mic-Pad-Polarity.

So now i need to study the "The Classic" schematic!

Cheers, Sven

PS: i got my hands dirty with a prototype pcb i made for a PM660/M660 "attempt", which combines all the informations, mods and available schematics here on GDIY. Well, yes it sounds awesome but unfortunately nothing you can fit nearly into a 3U module last but not least another psu module. Maybe 6U or as "master compressor module". Anyway, this thing get's so hot i couldn't imagine.

 

[ruffrecords]

Looks like you have been very busy Sven I like the 6U board with the XLRs at the back. Is it deeper than the regular 160mm boards I make?

Cheers

Ian

 

[dipfrik]

Cheers Sven,

yeah, very busy with a few other construction sites too

So the board is actually 220mm depth, but only for testing. I think it "shouldn't" be a problem to fit everything on a 160mm deep pcb. The XLR's at the back was also only for testing, but in the meantime i like it. Solves a few problems with additional wiring of all the needed I/O.

I had a long chat with Holger about the whole 3U vs. 6U topic, and  at the moment, i think 6U is the way i should go.
At least for the next days

Cheers, Sven

 

[ruffrecords]

I had a long chat with Holger about the whole 3U vs. 6U topic, and  at the moment, i think 6U is the way i should go.
At least for the next days

Cheers, Sven

Both the 3U and 6U have their own advantages.

The advantage of using 3U modules is you can have the mic pre and EQ in separate modules which makes it easy to have different EQs on a channel in a mixer. Originally when Holger first proposed this I was concerned about running the unbalanced signal to and from the EQ module but this has not been a problem in practice (I recently learned that Ward Beck did exactly the same thing in their consoles back in the 70s).

The disadvantage of 3U modules is their limited front panel area. You loose nearly 15mm at the top and bottom of the panel due to rack fixings and the modules case which leaves only about 100mm of vertical panel space to play with. This becomes a problem for an EQ that has lots of controls like the Pultec three band EQ. There is simply not enough room on a 3U front panel to squeeze in all the required controls and still be able to operate them.

A 6U module still loses about 15mm at the top and bottom but because it is nearly 270mm tall there is nearly 240mm of  front panel height to play with. This allows you to fit the controls for a mic pre and a Pultec EQ. You also gain a strip of PCB 160mm deep and nearly 40mm wide.

It is a pity that 4U modules are not more common because you could get any EQ into one of them and another could have the mic pre and the routing.

Cheers

Ian

 

[dipfrik]

Hey Ian,

maybe a good mix of 3U & 6U to pick only the advantages would be the best!
What drives me actually more to 6U is exactly this additional strip at the front panel plus extended pcb space to not squeeze anything to limits on a standard 160x100mm eurocard.

This is why i find your divided 6U/3U testrig absolutely perfect. Unfortunately i need to talk to Fischer directly to see if can get one in this specific configuration. Based on there catalog the "prebuilt" divisions in there are not usable.

Cheers, Sven

 

[dipfrik]

Hey Ian,

let me jump into your last posts regarding "The Classic" with a few questions:

1) what was the reason for this different design? I never heard about this before. Is it "better", "cheaper" or "easier"?
2) are they sonically differences between EZ-Tube Amp Card and "The Classic"?
3) are HT & HTR voltages the same? Which means -> can we use our 3U lunchbox psu? I see only 6922 and no 12AX7.
4) two "simple" mic pres in one 3U module are possible? From my understanding the same can be archived with a EZ-Tube Amp Card or a Twin Line Amp card right?
5) can i put an EQ between OUT1 and IN2? If so, where should i adjust the gain make up in the 2nd amp stage. I couldn't see any trimmer?
6) can the new "Easy-EQ" integrated/used in this architecture?
7) i saw on the emporium a frontpanel (3Uclassictoggle.fpd) file which shows a space for a HPF? (Flat-80-40). Is this an idea? I really love to see something this simple on the mic pre.

Sorry, a lot of questions

Thanks, Sven

 

[ruffrecords]

This is why i find your divided 6U/3U testrig absolutely perfect. Unfortunately i need to talk to Fischer directly to see if can get one in this specific configuration. Based on there catalog the "prebuilt" divisions in there are not usable.

Cheers, Sven

I would also recommend you talk to Schroff. They may be more flexible.

Cheers

Ian

 

[ruffrecords]

Hey Ian,

let me jump into your last posts regarding "The Classic" with a few questions:

1) what was the reason for this different design? I never heard about this before. Is it "better", "cheaper" or "easier"?

It is simply the one I designed before the Eurochannel. It was my second mic pre design and the first one I built into a mixer. The big problem for tube mic pres is negative feedback (NFB) so my early designs avoided NFB altogether. They were inspired by the RCA broadcast consoles of the 1940s which had descrete amplifying stages interspersed with attenuators to set overall gain. I spent a lot of time testing different topologies and tubes trying to minimise distortion at pro audio levels without using NFB. I eventuality settled on the mu follower topology and the 6CG7 tube. My first tube mixer was a 6 into 2 based on this design. This mixer is now in daily use in a studio in Switzerland.  The poor man's tube gain make up stage is the same design. However, the 6CG7 tube is rather tall, too tall to fit into a 14HP module and also has limited drive capability due to its relatively high anode resistance. That is when I designed what I called at the time the 'power mu' follower using a 6922. This runs at a  higher current and has a better output drive capability than the 6CG7 version but with virtually identical distortion performance. That is the design that forms the basis of the Classic.

2) are they sonically differences between EZ-Tube Amp Card and "The Classic"?

Probably, but my ears are not good enough to detect them.

3) are HT & HTR voltages the same? Which means -> can we use our 3U lunchbox psu? I see only 6922 and no 12AX7.

The connector and power supplies are identical to the Eurochannel. The heaters of the two 6922s are wired in series to make 12V just as in the Eurochannel.

4) two "simple" mic pres in one 3U module are possible? From my understanding the same can be archived with a EZ-Tube Amp Card or a Twin Line Amp card right?

Correct

5) can i put an EQ between OUT1 and IN2? If so, where should i adjust the gain make up in the 2nd amp stage. I couldn't see any trimmer?

Yes you can. To trim the gain make up you need to add the input circuit used on the poor man's tube gain make up.

6) can the new "Easy-EQ" integrated/used in this architecture?

Unfortunately the answer is no. The Easy-EQ fits into the NFB loop of the Eurochannel  so, as there is no NFB in the classic, the Easy-EQ cannot be used.

7) i saw on the emporium a frontpanel (3Uclassictoggle.fpd) file which shows a space for a HPF? (Flat-80-40). Is this an idea? I really love to see something this simple on the mic pre.

Yes, it is a simplified version of the HPF I included in my first 6 into 2 mixer. This used a 2 pole 6 way switch to give three frequencies with 6dB/octave cut and two frequencies with 12dB/octave cut. This mixer was intended for live orchestral recording to the HPF was essential for removing rumble in such situations. Unfortunately there is not enough room to fit this into a 3U module so I decided to include a simpler version which happens to be very much like the one included in the old Helios 69 mic pres.

Cheers

Ian

 

[G-Sun]

maybe a good mix of 3U & 6U to pick only the advantages would be the best!

I can't see myself doing a 6U-version. A 3 U stereo channel-strip on the other hand would be tempting.

 

[ruffrecords]

maybe a good mix of 3U & 6U to pick only the advantages would be the best!

I can't see myself doing a 6U-version. A 3 U stereo channel-strip on the other hand would be tempting.

I guess that depends on what you want to include in a stereo channel strip.

Cheers

Ian

 

[G-Sun]

I guess that depends on what you want to include in a stereo channel strip.

Yes, for me it would be the standard preamp-section, eq hi/lo-shelf and comp, either with sidechain hipassfilter or insert. Much like the UA LA-610, stereo I guess.
But, you know more about the space needed for that than me

 

[ruffrecords]

I guess that depends on what you want to include in a stereo channel strip.

Yes, for me it would be the standard preamp-section, eq hi/lo-shelf and comp, either with sidechain hipassfilter or insert. Much like the UA LA-610, stereo I guess.
But, you know more about the space needed for that than me

I think it would be very difficult to squeeze that lot into a 3U module. It night even be difficult to get it all into a 6U module.

Cheers

Ian

 

[G-Sun]

I think it would be very difficult to squeeze that lot into a 3U module. It night even be difficult to get it all into a 6U module.

Ok.
I was thinking 11 slots can be done in 500/3U, so I thought 6 in the EZ tube-mixer lunsh-box would go

Thanks for all you good work, help and info!

 

[ruffrecords]

I think it would be very difficult to squeeze that lot into a 3U module. It night even be difficult to get it all into a 6U module.

Ok.
I was thinking 11 slots can be done in 500/3U, so I thought 6 in the EZ tube-mixer lunch-box would go

Thanks for all you good work, help and info!

You are right, exactly 6 EZTubeMixer modules will fit in a 19 inch sub-rack. You might squeeze what you want in such a module if you used semiconductors but not with tubes I am afraid.

Cheers

Ian

 

[ruffrecords]

I have been building the lunch box 28HP power supply PCB and found some discrepancies between the PCB and the original schematic. So I have updated it to correct the mistakes, reflect the change in regulator to a low drop out version, the change in the 48V reservoir capacitor to 2200uF and added voltage ratings for the capacitors. I have renamed the schematic specifically for the 28HP version. You can find it here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/PSU/lunchboxpsu-28HP-version.png

Cheers

Ian

 

[dipfrik]

Hey Ian, great!

 

[ruffrecords]

I have just added a 9 pin circular output connector to the 28HP module. I had to locate is just below the IEC mains connector otherwise it would have fouled the 12V heater reservoir capacitor. This in turn meant I hade to move the 25A heater bridge rectifier out of the way:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/PSU/mechsoutputconn.png

The 9 pin output connector is at the bottom left with the relocated 25A bridge just above it.

At some point I will do a FPD of this panel. If you want to do one yourself, this file shows the rear panel of a Fischer 14HP module. It should be easy to tweak it for 28HP:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/PSU/Fischer14HPmodulerearpanel.pdf

Cheers

Ian

 

[dipfrik]

Hey Ian,

you pointed me to a question/issue i had over the last days, about how to transfer the power rails from the psu module safely to the modules or motherboard.

I have just added a 9 pin circular output connector to the 28HP module.

If i'am compare this solution with the one from Holgers initial lunchbox, there is a huge difference in the required size to be capable of providing the power rails to the motherboard or modules directly. What kind of connector and more important cable/wire size you think are save in our use case? Which size (AWG) of cable can the output connector pins carrying?

Cheers, Sven

 

[G-Sun]

You are right, exactly 6 EZTubeMixer modules will fit in a 19 inch sub-rack. You might squeeze what you want in such a module if you used semiconductors but not with tubes I am afraid.

Ok, wouldn't be a tubemixer then I guess