Feeler: EZ Tube Lunch Box

[G-Sun]

I like a challenge so I had a go at squeezing 5 pots and two switches onto a PCB to sit vertically to the right of a 3U Pultec board. Like the EQ board, the pots board cannot be more than 100mm tall and you need to leave 2.5mm unpopulated at top and bottom which gives you 95mm to play with. I decided to use ALPS RK09L pots which are 12.1mm wide. The three frequency selelction swotches are 25.4mm apart (1 inch) and for the hi and lo switches there is both a boost and a cut pot. So I placed one pot level with the switch and the other above it, in the case of the hi band, or below it in the case of the lo band. Then, between the lower pot on the hi band and the higher pot on the lo band, there is just enough room to squeeze two ALPS push button switches, one for the mid boost/cut switch and the other for the EQ in out. I laid this out in front panel designer and the resultant .fpd file is here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/PMP/3Upassivepultec.fpd

I printed it out full size and laid the smallest knobs I could find on it. They are 13mm in diameter. They fit fine for the three frequency select switches. They are a bit tight but workable for the five pots. The only thing I am not 1005 happy about is the two switches which seem a little too close to the pot knobs. A reasonable compromise might be to have just the boost/cut switch for the mid section of the PCB and have the EQ in/out as a toggle on flying leads. It could probably go next to the lo cut pot. A picture of the layout with the knobs in place is attached:

Cheers

Ian

Wow, that looks very good.

Maybe the the eq in/out would fit on the first pcb, under fq-switches?
Flying it is of course not bad, but it seems it would do fine under there.
I understand 13mm pots is not ideal, but it's of course a natural compromise.

Impressed.

 

[ruffrecords]

Wow, that looks very good.

Maybe the the eq in/out would fit on the first pcb, under fq-switches?
Flying it is of course not bad, but it seems it would do fine under there.
I understand 13mm pots is not ideal, but it's of course a natural compromise.

Impressed.

Many thanks for the vote of confidence.

Fitting the EQ in/out switch under the freq-switches may or may not be possible. It depends on the mechanical configuration you choose of which there are two:

1. The original EZTubeMixer module mechanics is designed for low cost so it is little more than a PCB with a front panel attached. There are standard parts for fitting front panels to eurocards and they go just above and just below the top and bottom freq-switches - exactly where you want to put the EQ in/out switch.  This link shows the PCB layout for the 3U Helios baord. You can see the three switches with the square areas above and below them where the front panel fixings go.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/Helios69EQ/3UHelios69PCB.png

2. The Mark3 module mechanics which are designed for maximum performance (and corresponding higher cost). They use Fischer extruded modules to completely enclose and screen the boards. There is no need for front panel fixings as the board simply slots into grooves in the extrusion. In this case the space below the Lo freq-switch IS available for an EQ in/out switch. This  pic shows how this would look:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/PMP/3UMK3passivepultec.svg

So as usual you pays your money and takes your choice.

Cheers

Ian

 

[G-Sun]

Many thanks for the vote of confidence.

Fitting the EQ in/out switch under the freq-switches may or may not be possible. It depends on the mechanical configuration you choose of which there are two:

1. The original EZTubeMixer module mechanics is designed for low cost so it is little more than a PCB with a front panel attached. There are standard parts for fitting front panels to eurocards and they go just above and just below the top and bottom freq-switches - exactly where you want to put the EQ in/out switch.  This link shows the PCB layout for the 3U Helios baord. You can see the three switches with the square areas above and below them where the front panel fixings go.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/Helios69EQ/3UHelios69PCB.png

2. The Mark3 module mechanics which are designed for maximum performance (and corresponding higher cost). They use Fischer extruded modules to completely enclose and screen the boards. There is no need for front panel fixings as the board simply slots into grooves in the extrusion. In this case the space below the Lo freq-switch IS available for an EQ in/out switch. This  pic shows how this would look:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/PMP/3UMK3passivepultec.svg

So as usual you pays your money and takes your choice.

I see.

Well, I'm not into the details of the mechanical and cost here, but in this case it seems like yes
either
- flying the eq in/out
or
- Mark3 on first board

Personally I'd need to see the cost-difference, but last option seems better.

This one looks sexy:
http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/PMP/3UMK3passivepultec.svg
Design-wise, ideally first board should be better vertical centered.

 

[G-Sun]

Just so I understand the inner workings of e.g a EzTubepreamp and the 3band pultec.

The preamp
-vertical mounted (1 module width)
pultec
-vertical mounted (1 module width)

Transformer in/out (anything on pcb?)
with optional insert/in/out transformers

Gain-board for the pultec?
Mounted in case horizontal?

Psu, pcb + pwrXformer
Mounted free/ in case horizontal

6 Module Backplane

Right?

 

[G-Sun]

And,

a 4 module lunchbox can have psu on board

while

a 6 module box needs external psu

right?

Edit:
saw this: http://eztubelunchbox.blogspot.no/2014/12/power-supply-and-enclosure-update.html

 

[G-Sun]

/PMP/3UMK3passivepultec.svg]http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/lunchbox/PMP/3UMK3passivepultec.svg[/url]

BTW: Now it's singel-side-mounted on the second pcb.

Could it be dual-side mounted, to make room for bigger knobs?
Maybe with smaller text-circle for the fq-knobs, and aligning the HiCut between the mid and hi fq
and the LoCut or LoBoost in similar fashion?

Personal disclaimer: I'm just about to order parts for an dual pq1549. This would take my time and money for some1-2 years.
But, if seeing the option for a EZTubeLunshBox with pre, 3 band pulteq and a la2a/comp, I might jump on board here first.

 

[ruffrecords]

Just so I understand the inner workings of e.g a EzTubepreamp and the 3band pultec.

The preamp
-vertical mounted (1 module width)
pultec
-vertical mounted (1 module width)

Correct.

Transformer in/out (anything on pcb?)
with optional insert/in/out transformers

Input transformer is on the mic preamp board. Output transformer mounts on rear panel of sub-rack and wires to the motherboard. There are no specific arrangements for inserts. You can add them after the mic pre or at the output.

Gain-board for the pultec?
Mounted in case horizontal?

The standard mic pre board  contains two amps. The first is configured as the mic pre itself with an input transformer plus phantom, phase, 20dB pad and mi/line switches. The second is intended as gain make up for passive EQ. It includes a preset pot to set the gain

Psu, pcb + pwrXformer
Mounted free/ in case horizontal

PSU can be internal or external. I have nearly completed testing a double width PSU module that will go in the lunch box sub-rack. You can mount the PSU board in a 19 inch case. Both Sven and I have sourced custom mains transformers that you could use.

6 Module Backplane

The 6 module backplane (motherboard) s no more. I now have 2 module and 4 module motherboards.

Cheers

Ian

 

[ruffrecords]

And,

a 4 module lunchbox can have psu on board

while

a 6 module box needs external psu

right?

Edit:
saw this: http://eztubelunchbox.blogspot.no/2014/12/power-supply-and-enclosure-update.html

Correct on both counts.

To address your earlier question about the cost differential, the original EZTubeMixer board front panel mounting schem used a couple of these:

http://uk.farnell.com/schroff/60807-181/bracket-to-fix-pcb-to-panel/dp/2292872

A pair will cost about $3

The mark 3 uses this enclosure (third one down at 20 Euros inc tax):

https://www.buerklin.com/default.asp?event=ShowArtikel(71H432)&context=ArtikelSubsetId:0;SE:fischer;PHNode:SE,vt,5711;ALArtikelProSeite:100&l=e&jump=ArtNr_71H432&ch=69472

which is about $20 so the cost differential is around $17 per module.

Cheers

Ian

 

[G-Sun]

Thanks a lot Ian!

3 band pultec
-vertical mounted (1 module width)

Edit: That's 2 module width now, right

Input transformer is on the mic preamp board. Output transformer mounts on rear panel of sub-rack and wires to the motherboard. There are no specific arrangements for inserts. You can add them after the mic pre or at the output.

Thanks! Ok, can the insert/extra in/out transformers be mounted the same way as the output transformer?

The standard mic pre board  contains two amps. The first is configured as the mic pre itself with an input transformer plus phantom, phase, 20dB pad and mi/line switches. The second is intended as gain make up for passive EQ. It includes a preset pot to set the gain

Ah.. nice

PSU can be internal or external. I have nearly completed testing a double width PSU module that will go in the lunch box sub-rack. You can mount the PSU board in a 19 inch case. Both Sven and I have sourced custom mains transformers that you could use.

Thanks!

The 6 module backplane (motherboard) s no more. I now have 2 module and 4 module motherboards.

Ok, good to know

 

[G-Sun]

To address your earlier question about the cost differential, the original EZTubeMixer board front panel mounting schem used a couple of these:

http://uk.farnell.com/schroff/60807-181/bracket-to-fix-pcb-to-panel/dp/2292872

A pair will cost about $3

The mark 3 uses this enclosure (third one down at 20 Euros inc tax):

https://www.buerklin.com/default.asp?event=ShowArtikel(71H432)&context=ArtikelSubsetId:0;SE:fischer;PHNode:SE,vt,5711;ALArtikelProSeite:100&l=e&jump=ArtNr_71H432&ch=69472

which is about $20 so the cost differential is around $17 per module.

Thanks! Ok, $17 for not flying the eq in/out switch. Will have to depend on other factors then I guess.

 

[G-Sun]

Ian: What's your thought regarding ezComp?
Just an abandoned module?

la2a in one slot? two?
Threshold-knob, makup-knob, eq in/out, vu-meter, (comp/lim)

or singel or dual channel DAOC.
Does the pwr-requirements match?
Easier/cheaper than the la2a? One slot? Two?

 

[ruffrecords]

Thanks a lot Ian!

3 band pultec
-vertical mounted (1 module width)

Edit: That's 2 module width now, right

One mic pre plus one EQ equals two 3U modules.

Input transformer is on the mic preamp board. Output transformer mounts on rear panel of sub-rack and wires to the motherboard. There are no specific arrangements for inserts. You can add them after the mic pre or at the output.

Thanks! Ok, can the insert/extra in/out transformers be mounted the same way as the output transformer?

They can, limited only by the available real estate at the rear of the sub-rack.

Cheers

Ian

 

[ruffrecords]

Ian: What's your thought regarding ezComp?
Just an abandoned module?

la2a in one slot? two?
Threshold-knob, makup-knob, eq in/out, vu-meter, (comp/lim)

or single or dual channel DAOC.
Does the pwr-requirements match?
Easier/cheaper than the la2a? One slot? Two?

To be honest I am as yet undecided. It is certainly possible to make something close to an LA2A in one slot using the current twin line amp and that's what the EZcomp prototype is. Power requirements are therefore no problem.

The meter is a bit of a pain as it eats up half the front panel space but I think there's still room to squeeze in threshold and gain make up pots plus a comp/lim switch. Is there an eq in/out on the LA2A?

If you have the meter then you need a dual opto. Thing is I am not 100% happy about using just one opto for gain reduction as it will only respond to one half the waveform. There are ways round this but they raise the threshold. Then there's the question of stereo linking. I think this is an essential feature but it has to be done properly. There was quite a bit of discussion on this in another thread recently.

On top of that, at the end of the day it will be just another LA2A look alike. I would really like to design a new tube compressor with attack and decay controls and possibly a ratio control but that is a much bigger project. I suppose one way forward would be to do a simple LA2A look alike as a first step and leave the improved comp for a later date.

As I think I mentioned, there was not a lot of reaction when I first posted the EZcomp prototype. I am happy to take it further if there is a reasonable level of interest.

Cheers

Ian

 

[G-Sun]

One mic pre plus one EQ equals two 3U modules.

Ok, I thought we needed two modules width for the 3band Pulteq, but you managed to get it into one slot. Nice.

To be honest I am as yet undecided. It is certainly possible to make something close to an LA2A in one slot using the current twin line amp and that's what the EZcomp prototype is. Power requirements are therefore no problem.

The meter is a bit of a pain as it eats up half the front panel space but I think there's still room to squeeze in threshold and gain make up pots plus a comp/lim switch. Is there an eq in/out on the LA2A?

If you have the meter then you need a dual opto. Thing is I am not 100% happy about using just one opto for gain reduction as it will only respond to one half the waveform. There are ways round this but they raise the threshold. Then there's the question of stereo linking. I think this is an essential feature but it has to be done properly. There was quite a bit of discussion on this in another thread recently.

On top of that, at the end of the day it will be just another LA2A look alike. I would really like to design a new tube compressor with attack and decay controls and possibly a ratio control but that is a much bigger project. I suppose one way forward would be to do a simple LA2A look alike as a first step and leave the improved comp for a later date.

As I think I mentioned, there was not a lot of reaction when I first posted the EZcomp prototype. I am happy to take it further if there is a reasonable level of interest.

Yes, you mentioned there was not that much interest. Could be different reasons.

Without being an expert there are several designs to either clone or use as inspiration.
La2a, D-La2a, DAOC, PM660/670 and I'm sure more.

Personally I'd left the idea of stereo channelstrip, as I thought the pulteq would be 2 modules width,
and the mono la2a would be no joke in a mono EzTubeLunshbox strip. But with 5 slots left, stereo is still an option.

Yes, of course attack, decay and ratio and stereo-link is tempting. Yet, a new design with all those features could be a long way from ideas to final good working design.

Is the original la2a using two optos?? The gain-reduction of it has no issues with not responding to half of waveform I belive?
Eq bypass-switch is a design-choice. I'd find it very useful for level-matching.

I guess something in the direction of Tube Tech  CL 1B/CL2A / Gyraf Gyratec X is the ideal goal

 

[dipfrik]

On top of that, at the end of the day it will be just another LA2A look alike. I would really like to design a new tube compressor with attack and decay controls and possibly a ratio control but that is a much bigger project. I suppose one way forward would be to do a simple LA2A look alike as a first step and leave the improved comp for a later date.

You are absolutely correct, that a  comp with dedicated attack/release/ratio controls would be the ultimate goal.
For now i have only proven, that you can build an "S-AOC" fitting into a 3U module. I posted an initial prototype here.

http://groupdiy.com/index.php?topic=53765.msg739238#msg739238

Sounds great as expected but needs a few iterations/mods. Two main topics here:

1) Solen Fast Cap substitution for more front panel space
2) actually you need a separate 3U/24HP psu module. Maybe it is possible to use the HT/HTR from the lunchbox psu, but this is something i can't do alone.

So bottom line. Easy adadption of the AOC is possible and is working here on my workbench.
Unfortunately i have not enough knowledge to design a new one with all the extra controls. But i i'am happy to do the schematics and pcb layouts.

Cheers, Sven

 

[G-Sun]

You are absolutely correct, that a  comp with dedicated attack/release/ratio controls would be the ultimate goal.
For now i have only proven, that you can build an "S-AOC" fitting into a 3U module. I posted an initial prototype here.

http://groupdiy.com/index.php?topic=53765.msg739238#msg739238

Yes, that's a nice build Sven

My main consern/question is the need for a separate psu-board.

Yet, if thinking stereo-strip, that would be 6 modules width, with external psu,
so then a modified psu would maybe not be so much extra work.

 

[ruffrecords]

Without being an expert there are several designs to either clone or use as inspiration.
La2a, D-La2a, DAOC, PM660/670 and I'm sure more.

To be honest, I have no interest in making a clone - there are more than enough of those already. As regards inspiration, there are two basic methods of gain reduction to consider - vari-mu and opto. Opto is by far the easier of the two so that's what I started with. The LA2A is basically two amplifiers and an opto. One amp does gain make up and the other drives the opto. The EZcomp prototype I built uses the two amps in my twin line amp card to fulfil these functions. A few tweaks, add a meter and a switch an you have an LA2A look alike. I think this is about as far as you can go without a major development.

Personally I'd left the idea of stereo channelstrip, as I thought the pulteq would be 2 modules width,
and the mono la2a would be no joke in a mono EzTubeLunshbox strip. But with 5 slots left, stereo is still an option.

Yes, a 6 slot sub-rack could hold two sets of mic pre, EQ and compressor. Handy little box.

Yes, of course attack, decay and ratio and stereo-link is tempting. Yet, a new design with all those features could be a long way from ideas to final good working design.

Agreed!!

Is the original la2a using two optos?? The gain-reduction of it has no issues with not responding to half of waveform I believe?

The original uses a different light source that does respond to both halves of the waveform. Modern optos (Vactrols) use an LED that responds only to one half of the waveform. You can use two Vactrols to overcome this or add a full wave rectifier but this raises the threshold.

Eq bypass-switch is a design-choice. I'd find it very useful for level-matching.

I think we were talking at cross purposes. I agree an EQ bypass switch is necessary. I thought you were talking about EQ  in the LA2A  ;D

Cheers

Ian

 

[G-Sun]

To be honest, I have no interest in making a clone - there are more than enough of those already.

Well, that's fair enouh. I was personally thinking that if you offered a EZla2a board for a T4-opto-cell I'd go for a mono EZstrip.

As regards inspiration, there are two basic methods of gain reduction to consider - vari-mu and opto. Opto is by far the easier of the two so that's what I started with. The LA2A is basically two amplifiers and an opto. One amp does gain make up and the other drives the opto. The EZcomp prototype I built uses the two amps in my twin line amp card to fulfil these functions. A few tweaks, add a meter and a switch an you have an LA2A look alike. I think this is about as far as you can go without a major development.
[..]
The original uses a different light source that does respond to both halves of the waveform. Modern optos (Vactrols) use an LED that responds only to one half of the waveform. You can use two Vactrols to overcome this or add a full wave rectifier but this raises the threshold.

Ok, if price and performance are decent for the vactrols, that would be fine for me.
But if we're talking stereo, then HiPass-filter is maybe needed for 2-bus duties?

The issue for me here is: I don't think I have time, money and skills to prototyping with unsure results. That's both for internal and visual design.
So, I guess I'll make a poor contribution for you here

I think we were talking at cross purposes. I agree an EQ bypass switch is necessary. I thought you were talking about EQ  in the LA2A

Yes. I was personally thinking in/out-transformer post-preamp, pre-eq. But not between eq and comp.
So, then on/off for both eq and comp would be rather mandatory.

 

[ruffrecords]

To be honest, I have no interest in making a clone - there are more than enough of those already.

Well, that's fair enouh. I was personally thinking that if you offered a EZla2a board for a T4-opto-cell I'd go for a mono EZstrip.

OK, now I see where you are coming from.  Just to be clear, I have no plans for a compressor using s T4 cell - too close to cloning for my liking

Ok, if price and performance are decent for the vactrols, that would be fine for me.
But if we're talking stereo, then HiPass-filter is maybe needed for 2-bus duties?

The DAOC you mentioned uses Vactrols as do a lot of other tube  and semiconductor based optical compressors so I guess the performance aspect is likely OK. Vactrols are a lot cheaper than the T4 cell so on cost it is a no brainer.

Not sure if HPF necessary for 2 bus duties. HPF is usually only necessary where you have separate attack and decay controls. When both fast attack and decay are set , the compressor can 'follow' low frequency bass notes which is when an HPF is handy.  Simple opto compressors tend to have longish attack and decay times so this is not usually a problem.

The issue for me here is: I don't think I have time, money and skills to prototyping with unsure results. That's both for internal and visual design.
So, I guess I'll make a poor contribution for you here

No problem. I am a qualified EE, retired and love designing tube audio circuits. You're an end user able to articulate specific needs. I think that is nicely complimentary.

Cheers

Ian

 

[G-Sun]

OK, now I see where you are coming from.  Just to be clear, I have no plans for a compressor using s T4 cell - too close to cloning for my liking

Well, that's clear enough.

The DAOC you mentioned uses Vactrols as do a lot of other tube  and semiconductor based optical compressors so I guess the performance aspect is likely OK. Vactrols are a lot cheaper than the T4 cell so on cost it is a no brainer.

Not sure if HPF necessary for 2 bus duties. HPF is usually only necessary where you have separate attack and decay controls. When both fast attack and decay are set , the compressor can 'follow' low frequency bass notes which is when an HPF is handy.  Simple opto compressors tend to have longish attack and decay times so this is not usually a problem.

Well personally, I've reconsidered my wanted workflow and tasks, and a mono compressor for tracking is the main thing for me . Typical in the 1176 and la2a-territory. No HPF really needed. Stereo is a possible bonus.
Others will have to chime in if 2bus-duties for program-material is to be handled (that's when HPF gets more essential I guess)

No problem. I am a qualified EE, retired and love designing tube audio circuits. You're an end user able to articulate specific needs. I think that is nicely complimentary.

I'm glad you can view it this way. You're very generous!

Now, the questions remains:
- If I'm in, will you develop the EZComp further?
and
- What directions would you/we go for?

Personally the combination of fast with slow would maybe the most optimal.
Could there be a two stage comp?
Some (in the territory of) 2-4:1 fast and 2-20 slow (if knee), with two controls for threshold, and one for makeup?