Feeler: EZ Tube Lunch Box

[dipfrik]

Hey Ian,

Hopefully this will make a useful compressor  in its own right but also answer basic questions that will help a later full blown comp development with attack/decay etc etc.

Yes, absolutely!

I don't now where i grabbed this (maybe it's total nonsense) but i thought that getting VTL5C4/2 like in the D-AOC in the future could be more and more difficult?

Thanks for the explanation as always.

Cheers, Sven

 

[ruffrecords]

Some Vactrols will become more difficult to get hold of becuase they contain cadmium which is now banned in the EU. There are others that use different materials but of course thay have different characteristics.

Cheers

Ian

 

[ruffrecords]

An update on the oscillation problem reported a few posts ago. I have now carried out a lot of tests and I hope I am homing in on the problem,. I know other builders have had this problem and Holger came up with a solution some time ago which seemed to work. However, he recently told me he had a reoccurrence of it but was able to kill it with small value capacitors across the HT in the modules. He also mentioned that the oscillation was at about 1.6MHz which is the same frequency I am getting right now.

At the moment I can reliable get oscillation with a single board.either the Eurochannel, the Classic or the twin line amp boards irrespective of gain setting. It occurs on both OUT1 and OUT2  even with inputs shorted. I have been using the 28HP power supply.

I have tried small caps on the HT, 33pF from anode to grid on the 12AX7, 33pF across the 47K NFB resistor, 1K grid stoppers, extra RC decoupling of the HT on the board, PCC88s instead of the 6922, different 12AX7s, without the 12AX7 and I even tried a pair of 6CG7 tubes instead of 6922.

Although the level varied a little between these tests, in all cases the 1.6MHz was there. However, in all cases, after a period of time, the oscillation began to dwindle and eventually stopped altogether. If you turn off and then turn on within a couple of minutes, there is no oscillation. If you leave it for about 10 minutes and then turn on again, the oscillation is back but again dies after a few minutes.

One night I left the unit powered on over night. I then plugged in various cold boards and none of them oscillated. I left the unit off for a couple of hours, tried again and sure enough back came the oscillation. Yesterday we had the log burner on in the front room so we turned down the heating. This meant it got quite cold in my workshop on the top floor of the house. Last night I powered up with a single Eurocard connected, the oscillation was bigger than before and took over 45 minutes before it died.

From this I conclude that a cold power supply will cause the oscillation but a warm one does not. I am not sure if the power supply itself is the source of the oscillation but that's is the next step.

This morning I warmed up the power supply with one card until its oscillation died. I then swapped it for several different cards but all cold ones. None of them oscillated. From this I conclude it is not the cards warming up that makes the oscillation die but the power supply being warm.

I still do not know what is going on and it is puzzling that all cards oscillate at the same frequency, even Holger's and he has a different power supply.

I'll keep you posted. Any tips, suggestions, cries of "I've seen that before!" are welcome

Cheers

Ian

 

[ruffrecords]

At last I feel I am making some progress. I could not understand why the oscillation happened on all card layouts and at the same frequency. So I tried a card with just the heaters wired up and the tubes fitted - no active electronics and no HT draw. Not surprisingly there's no oscillation output from OUT1 or OUT2 as they have no active electronics connected to them. So then I tried monitoring  ac on the HT supply via a capacitor to my scope. To my surprise there was a small amount of the 1.6MHz oscillation on the HT line itself - but there's no active electronics on the HT line! Then I tried the same test with a regular active card, and the 1.6MHz is there on the HT line but it is still very small, much smaller than seen at OUT1 and OUT2.  Maybe it is getting into the HT from somewhere else. So I just now re-connected the scope capacitor to the heater +ve and, using the card that draws no HT but just heater current, I get a big 1.6MHz sine wave on the heater - 4 times bigger than I get at OUT1 or OUT2.

So it looks like the oscillation is on the heater supply itself - nothing to do with instability in the amp cards at all.

Tomorrow I investigate the heater supply.

Cheers

Ian

 

[dipfrik]

Hey Ian,

that are quite impressive test scenarios!
I love the "keep it cold" one the most!

So it looks like the oscillation is on the heater supply itself - nothing to do with instability in the amp cards at all.

But so far still related to the temperature of the power supply?

Cheers, Sven

 

[ruffrecords]

But so far still related to the temperature of the power supply?

Cheers, Sven

It looks that way. It certainly takes longer to disappear if the supply is cold. I am going to do a little web research first on oscillating regulator chips.

Cheers

Ian

 

[G-Sun]

Ok,
I need to read up on  the rack, mounting and such.

The project is now for a 19" 3U Fisher rack, right?
Is the final format decided yet?
Is Mark3 for 3U as well?

I need to understand the motherboard (2+4 pcbs for my 6 modules?),
the space/ wiring,
and what transformers will go on pcb or how they best should be mounted and wired on the back.
How much depth is it behind the motherboard, and how is it mounted to the rack?

Likewise I need to know wiring.
I'm thinking Pre1 Pre2 PulteqEq1 PEQ2 Comp1 Comp 2.
Then preamp second amp will be gain-stage for the PulteqEq, right?
Does the motherboard/pcbs have connectors for that wiring?
Same with comp stereo link?

And frontpanel metal work. How do you currently do that? Any blank panels around?

 

[ruffrecords]

Ok,
I need to read up on  the rack, mounting and such.

The project is now for a 19" 3U Fisher rack, right?
Is the final format decided yet?

The project will fit in any standard 19 inch DIN compliant sub-rack. Lot's of people make these including Fischer and Schroff in Germany, SRS and Vero  in England,  and many others.

All the manufacturers products are subtly different but they all meet the spec so the modules will fit in any of them. The basic principle is each sub-rack has metal sides held together with aluminium extrusions. SIdes are typically 3U, 6U or 9U high. Depths range from 180mm to over 260mm. All manufacturers provide front horizontal rails for mounting modules. A tapped strip in the extrusion is used to secure modules to the rack. Manufacturers also provide special back plane mounting extrusions which also include a tapped strip. The motherboard/backplane PCB simply bolts to the extrusions.  In simple cases the backplane mounting extrusions  are the only rear rails but you can use deeper side plates and fit another set of front panel rails at the back for mounting a rear panel - this provides the space necessary to mount output transformers.

In addition, each manufacturer has different types of sub-rack for different applications - some for example are ruggedised for use in railway applications, others have special rfi provisions. There are low cost, unscreened versions which are ideal for experimentation but they do leave high voltages exposed. Most manufacturers have models with top and bottom screens available, usually vented or solid.

Verotec has an excellent introduction to sub-racks here:

http://www.verotec.co.uk/documents/brochures/Section%201%20-%20Introduction.pdf

Here is a sketch I drew a long time ago showing the basic construction of a sub-rack:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/Mechanics/MIcPreMechAssyShortscaled.jpeg

The good thing about the DIN sub-rack system is there are suppliers throughout the world and in the end they are all compatible at a module level. You will just have to find a local one that will give you the necessary support.

Is Mark3 for 3U as well?

The Mark 3 can use any of the 3U EZTubeMixer cards . However, the  newMark 3 channel modules are all 6U and include provision for built in EQ, so they are not physically compatible with a 3U lunch box. Most manufacturers provide special kits that allow you to split a 6U rack into a 6U space and a couple of 3U spaces so it is possible to make a 6U sub-rack containing both Mark 3 and EZTubeMixer modules. The Mark 3 modules are100% plug compatible with the EZTubeMixer modules.

I need to understand the motherboard (2+4 pcbs for my 6 modules?),
the space/ wiring,
and what transformers will go on pcb or how they best should be mounted and wired on the back.
How much depth is it behind the motherboard, and how is it mounted to the rack?

Likewise I need to know wiring.
I'm thinking Pre1 Pre2 PulteqEq1 PEQ2 Comp1 Comp 2.
Then preamp second amp will be gain-stage for the PulteqEq, right?
Does the motherboard/pcbs have connectors for that wiring?
Same with comp stereo link?

There is already a lot of documentation for the EZTube Mixer that applies equally to the Lunch Box. However, the lunch box is meant to be an 'easier' build so I will create more documentation as and when necessary, but it is not meant to be a beginner's project. I suggest you begin by becoming familiar with the EZTubeMixer documentation, most of which you can find here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/

And frontpanel metal work. How do you currently do that? Any blank panels around?

Like many other I use the free FrontPanelDesigner progam and get my panels made by Frank Rollen:

http://www.schaeffer-ag.de/en/front_panel_designer/the_idea/


Cheers

Ian

 

[ruffrecords]

I managed to cure the power supply oscillation problem. As much as anything this is my own stupidity for changing the regulator device and assuming its stability components did not need changing. The data sheet for the LT1084V, which is the new LDO regulator I am using, recommends an output capacitor of at least 150uF for stability, especially if a cap is used across the feedback network to reduce ripple (which I do). At present I had just a 10uF electrolytic in there which is fine for the old LM338. So I removed the 10uF and replaced it with a 220uF 63V just to be certain it was big enough.

Held, my breath, turned on....  and no oscillation at all - in fact the output is cleaner than ever before.

I tried the new classic PCB, which had burst into oscillation at max gain, and it was fine at all gain settings. I measured the maximum gain at almost exactly 70dB (which includes the 6dB loss in the output transformer) and the noise measured -53dBu which gives an EIN of -123dBu - perfectly respectable. Encouraged by this I did some further tests:

Distortion : set to line input, +4dBu in, gain set for +4dBu out into 600 ohm load- 1KHz distortion 0.19%

Turn gain up for +20dBu output into 600 ohm load - 1KHz distortion 1.08% which is not bad for a mu follower.

Frequency response was -1.63dB at 20Hz, -0.13dB at 20KHz and -1.26dB at 40KHz

Overall a very satisfactory result.

Cheers

Ian

 

[G-Sun]

The project will fit in any standard 19 inch DIN compliant sub-rack. Lot's of people make these including Fischer and Schroff in Germany, SRS and Vero  in England,  and many others.

All the manufacturers products are subtly different but they all meet the spec so the modules will fit in any of them. The basic principle is each sub-rack has metal sides held together with aluminium extrusions. SIdes are typically 3U, 6U or 9U high. Depths range from 180mm to over 260mm. All manufacturers provide front horizontal rails for mounting modules. A tapped strip in the extrusion is used to secure modules to the rack. Manufacturers also provide special back plane mounting extrusions which also include a tapped strip. The motherboard/backplane PCB simply bolts to the extrusions.  In simple cases the backplane mounting extrusions  are the only rear rails but you can use deeper side plates and fit another set of front panel rails at the back for mounting a rear panel - this provides the space necessary to mount output transformers.

In addition, each manufacturer has different types of sub-rack for different applications - some for example are ruggedised for use in railway applications, others have special rfi provisions. There are low cost, unscreened versions which are ideal for experimentation but they do leave high voltages exposed. Most manufacturers have models with top and bottom screens available, usually vented or solid.

Verotec has an excellent introduction to sub-racks here:

http://www.verotec.co.uk/documents/brochures/Section%201%20-%20Introduction.pdf

Here is a sketch I drew a long time ago showing the basic construction of a sub-rack:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/Mechanics/MIcPreMechAssyShortscaled.jpeg

The good thing about the DIN sub-rack system is there are suppliers throughout the world and in the end they are all compatible at a module level. You will just have to find a local one that will give you the necessary support.

Thanks a lot!
Looking at it now.
There's a lot of documentation. Thanks!
Yet, I sometimes have a hard time finding what I'm looking for. Maybe it goes better when I'm more into the details and variations.

So, I need a 3U 19" din rack depth typical card size + 75mm.
Or is the drawing for 275mm total?
Card size depth is..  160mm?
No mark3 for me I guess if that's only for 6U.

Checked Farnell, but couldn't find the din racks there.
Vero has no price/shipping-info.
Edit: Farnell has this one: VERO CASE, 3U, 422MM
http://no.farnell.com/vero/760-236563b/case-3u-422mm/dp/1277417?ost=VERO+CASE%2C+3U%2C+422MM&categoryId=700000005086
Not cheap, but could have been worse I guess.

SRS:
http://www.srs-products.co.uk/eurorack.htm

Didn't find any supplier in Norway (except Farnel)

Will have to decide on specific dimensions and elements.

 

[G-Sun]

There is already a lot of documentation for the EZTube Mixer that applies equally to the Lunch Box. However, the lunch box is meant to be an 'easier' build so I will create more documentation as and when necessary, but it is not meant to be a beginner's project. I suggest you begin by becoming familiar with the EZTubeMixer documentation, most of which you can find here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/

Yes, tubes and mechanical, I don't expect it to be plug and play. But, hope I'll manage with some basic metal and electronic skills.

 

[G-Sun]

[quote author=ruffrecords ]

Like many other I use the free FrontPanelDesigner progam and get my panels made by Frank Rollen:

http://www.schaeffer-ag.de/en/front_panel_designer/the_idea/[/quote]
Ok, no blank panels that fit from the rack-vendors?

..I'd really like to make a beautiful looking build. Yet, I should maybe take into account early stages modifications and so on.

 

[G-Sun]

I managed to cure the power supply oscillation problem. As much as anything this is my own stupidity for changing the regulator device and assuming its stability components did not need changing. The data sheet for the LT1084V, which is the new LDO regulator I am using, recommends an output capacitor of at least 150uF for stability, especially if a cap is used across the feedback network to reduce ripple (which I do). At present I had just a 10uF electrolytic in there which is fine for the old LM338. So I removed the 10uF and replaced it with a 220uF 63V just to be certain it was big enough.

Held, my breath, turned on....  and no oscillation at all - in fact the output is cleaner than ever before.

I tried the new classic PCB, which had burst into oscillation at max gain, and it was fine at all gain settings. I measured the maximum gain at almost exactly 70dB (which includes the 6dB loss in the output transformer) and the noise measured -53dBu which gives an EIN of -123dBu - perfectly respectable. Encouraged by this I did some further tests:

Distortion : set to line input, +4dBu in, gain set for +4dBu out into 600 ohm load- 1KHz distortion 0.19%

Turn gain up for +20dBu output into 600 ohm load - 1KHz distortion 1.08% which is not bad for a mu follower.

Frequency response was -1.63dB at 20Hz, -0.13dB at 20KHz and -1.26dB at 40KHz

Overall a very satisfactory result.

Thanks for you doing all this essential work!

btw: This is a clean tube design, right? What if we wanted to go in the RudeTube/UA-thick direction?
Is that another design, or could there be a button/pot adding some pleasant distortion?

 

[G-Sun]

The Mark 3 can use any of the 3U EZTubeMixer cards . However, the  newMark 3 channel modules are all 6U and include provision for built in EQ, so they are not physically compatible with a 3U lunch box. Most manufacturers provide special kits that allow you to split a 6U rack into a 6U space and a couple of 3U spaces so it is possible to make a 6U sub-rack containing both Mark 3 and EZTubeMixer modules. The Mark 3 modules are100% plug compatible with the EZTubeMixer modules.

So, for me, 3U rack, that means flying that 3band pulteq in/out switch, right.

btw. Those 3band pulteq pots: Should we consider 2 deck pots or switches?
Or is that just making things difficult/costly?

btw2: I'll be away for a month. Can read on my phone. But not write/do so much

 

[ruffrecords]

Enclosure:

Here is a basic Schroff 3U sub-rack that is 295mm deep:

http://uk.farnell.com/schroff/24563-133/subrack-3u-295mm-84hp/dp/1455788

It is a type designed to hold a back plane.  As I say it is very basic. You need to add rear rails for the back panel and you will need to get top and bottom covers. However, as a base line it is very cheap.

The reason I use SRS is because they are very flexible and will happily put together the exact package I need. I will email my contact there and ask if they can ship to Norway. Here is the complete 3U sub rack with top and bottom covers they supplied to me:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/boxnochannels.jpg

Front Panels:

Most manufacturers include front panels  and complete plug in modules in their range. The blank panels are reasonably cheap but not many distributors seem to do the 14HP width we need. Plug in modules tend to be quite expensive apart from the Fischer 3U 14HP ones available from Buerklin in Germany. RS do have a 3U 14HP blank panel:

http://uk.rs-online.com/web/p/rack-panels/0172518/

The Sound:

What I have been trying to do is design tube based circuits that can be built into a 'modern' console design. That means they need to do things like drive several buses and AUX sends as well as a direct out, have stepped gain,  include provision for EQ , have a large headroom, be plug in modules and so on. In effect they are small power amps (they can output about 200mW). Creating power inevitably means creating distortion so I use NFB to tame it and to allow the gain to be varied with ease. Bottom line is this leads to a certain kind of 'sound' which several people have said they rather like, even though it is relatively 'clean'.

If you want a 'ruder' sound then the 'Classic' is probably the way to go. It is a much simpler design with no NFB so it does produce a 'natural tube' sound and the harder you hit it the dirtier it will sound. The Classic PCB contains two classic amps and has room for two input transformers.  The amps can be built either as mu followers (for a high gain fairly clean sound) or as SRPPs (for a lower gain rather dirtier sound).

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)

Cheers

Ian

 

[G-Sun]

Thanks a lot Ian!
Most companies will ship here.
It's just what the final cost will be. I often have to pay for shipping, handling, Vat-handling fees and vat. All depending on various factors 

 

[ruffrecords]

Thanks a lot Ian!
Most companies will ship here.
It's just what the final cost will be. I often have to pay for shipping, handling, Vat-handling fees and vat. All depending on various factors 

It might be worth checking out your local Schroff franchised dealer. I did this in the UK when I wanted to build the chassis for the monster mixer. I needed to by some one metre extrusions and a whole bunch of side plates most of which are not available through RS or Farnell so I used the franchised dealer. They were able to get all the parts I needed and deliver them direct.

Cheers

Ian                                                     

 

[G-Sun]

The Sound:

What I have been trying to do is design tube based circuits that can be built into a 'modern' console design. That means they need to do things like drive several buses and AUX sends as well as a direct out, have stepped gain,  include provision for EQ , have a large headroom, be plug in modules and so on. In effect they are small power amps (they can output about 200mW). Creating power inevitably means creating distortion so I use NFB to tame it and to allow the gain to be varied with ease. Bottom line is this leads to a certain kind of 'sound' which several people have said they rather like, even though it is relatively 'clean'.

If you want a 'ruder' sound then the 'Classic' is probably the way to go. It is a much simpler design with no NFB so it does produce a 'natural tube' sound and the harder you hit it the dirtier it will sound. The Classic PCB contains two classic amps and has room for two input transformers.  The amps can be built either as mu followers (for a high gain fairly clean sound) or as SRPPs (for a lower gain rather dirtier sound).

Ok, so it's basically 3 preamp-options?

I'm thinking.. I'm building a strip Preamp 3bPEQ and Comp.
The TwinLineamp premp has 2 gain-modules, the same has the comp.
And 3 are needed, one for each module. So, it's one spare, right?
Could this be utilized as a SRPP-gain, with possible blend-control with the clean sound?

Or, are my presumption about 4 gain-stages wrong?

Then, the 3band pultec Eq pcb is not made yet, right. Could the gain-stage for this be implemented on the pcb?
It would make a cleaner build I guess.
The extra pot-pcb could maybe have a hole for the tube, or something?

 

[G-Sun]

It might be worth checking out your local Schroff franchised dealer. I did this in the UK when I wanted to build the chassis for the monster mixer. I needed to by some one metre extrusions and a whole bunch of side plates most of which are not available through RS or Farnell so I used the franchised dealer. They were able to get all the parts I needed and deliver them direct.

Thanks!

I found Scroff on Farnell
http://no.farnell.com/Search?st=schroff&CMP=KNC-GNO-FNO-GEN-SUP-OSP&mckv=sI90caDJQ
(Farnell is in this sense a Norwegian store)

 

[ruffrecords]

Ok, so it's basically 3 preamp-options?

I'm thinking.. I'm building a strip Preamp 3bPEQ and Comp.
The TwinLineamp premp has 2 gain-modules, the same has the comp.
And 3 are needed, one for each module. So, it's one spare, right?
Could this be utilized as a SRPP-gain, with possible blend-control with the clean sound?

Or, are my presumption about 4 gain-stages wrong?

Then, the 3band pultec Eq pcb is not made yet, right. Could the gain-stage for this be implemented on the pcb?
It would make a cleaner build I guess.
The extra pot-pcb could maybe have a hole for the tube, or something?

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

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.

Cheers

Ian