Feeler: EZ Tube Lunch Box

[ruffrecords]

@Sven,

Will you be making these PCBs yourself?

Cheers

Ian

That was the idea or?

Cheers, Sven

I just guessed because of what you said about making a panel of them. If you had them made by a PCB manufacturer there is not much saving from a panel.

Cheers

Ian

P.S. I use Iteadstudio.com for prototype PCBS. Your 30mm by 50mm PCB would be $9.90 for 10 boards plus about $4 shipping. For that you get green solder resist, silk screening, 100% electrical test  and double sided through hole plating if required.

Cheers

Ian

 

[dipfrik]

I just guessed because of what you said about making a panel of them. If you had them made by a PCB manufacturer there is not much saving from a panel.

I'am a little bit confused. I don't mean etching by myself.
I checked with my pcb agency and i can get boards with a multiple of 6-36 for the same price, if i'am preparing the order for the pcb on a panel.

Your price at http://imall.iteadstudio.com/ is unbeatable!

Cheers, Sven

 

[ruffrecords]

I just guessed because of what you said about making a panel of them. If you had them made by a PCB manufacturer there is not much saving from a panel.

I'am a little bit confused. I don't mean etching by myself.
I checked with my pcb agency and i can get boards with a multiple of 6-36 for the same price, if i'am preparing the order for the pcb on a panel.

Your price at http://imall.iteadstudio.com/ is unbeatable!

Cheers, Sven

Now I understand. For small PCBs, most suppliers will sort out the panelising to fit their production. You get a lower unit price when you order more but the same price for 6 or 36 boards is unusual in my experience.Who is your PCB agency?

Cheers

Ian

 

[dipfrik]

It's https://portal.multi-circuit-boards.eu/

Correct, the "internal" panelising is not my business, but i can decide upfront if i want to use pcb of a specific size, and then tell them what my multiplier is. Anyway, i think they have some kind of "threshold size" multiplier, which defines the next price level...or something like that

My unit price is now around €5 which is ok for me.

Cheers, Sven

 

[ruffrecords]

The three module wide (42HP) mini lunch box enclosure arrived today from SRS.  I ordered a short depth one so there is no room for transformers at the back. You could use one slot for front panel connectors or a VU meter for example and fit transformers on the side panel behind it. This leaves you two slots for active modules. You could have a couple of regular Eurochannel boards in there to make a couple of full blown mic pres or you could use a couple of TLAs or classic boards and squeeze four mic pres in there. You could probably get 4  x Edcor output transformers in the third slot. Here's a pic:

Cheers

Ian

 

[dipfrik]

What a nice little enclosure!

Cheers, Sven

 

[ruffrecords]

Here it is with a two module mother board and one module plugged in.

Cheers

Ian

 

[ruffrecords]

I expect a common use of the lunch box will be to build tube mic pres or simple mixer channels with level and pan controls. The standard 3U high EZTube Mixer Euro card has all you need to make one. It has provision for four push buttons for phantom, phase, 20dB pad and mic/line switching. The PCB also includes provision for a 12 way Grayhill gain switch. You just need to add a pan and fader to make a simple tube mixer channel. SO I have created a couple of front panel layouts for this. The first uses the Grayhill switch on the PCB for gain setting:

Note how the pan and level controls have been offset from the centre to avoid the fixed postition of the Grayhill switch.

You don't have to use the Grayhill switch. You can use a cheap 12 way Lorlin instead (which you can mount anywhere on the front panel) or you can use a 47K REV LOG pot (now you know why I was looking for them). The added flexibility in placing the gain switch/pot means you can create a front panel layout with the three rotary controls in the centre:

Cheers

Ian

 

[dipfrik]

@Ian

You don't have to use the Grayhill switch. You can use a cheap 12 way Lorlin instead (which you can mount anywhere on the front panel) or you can use a 47K REV LOG pot (now you know why I was looking for them).

I'am a little bit surprised how a 47K REV LOG could substitute a stepped resistor based gain range from 430R - 150K that is actual on the amp pcb for the input gain with the Grayhill switch?

Thanks, Sven

 

[ruffrecords]

@Ian

You don't have to use the Grayhill switch. You can use a cheap 12 way Lorlin instead (which you can mount anywhere on the front panel) or you can use a 47K REV LOG pot (now you know why I was looking for them).

I'am a little bit surprised how a 47K REV LOG could substitute a stepped resistor based gain range from 430R - 150K that is actual on the amp pcb for the input gain with the Grayhill switch?

Thanks, Sven

You are right it is not an exact substitute. You add a 430 ohm series resistor so that when the pot is fully clockwise the maximum gain from the amp is the same as the stepped switch (40dB). At the mid point the resistance will be 4K7 which  gives a gain close to 20dB. When fully anti-clockwise  the gain is just under 10dB. So we have about 10dB gain change in the first half of rotation and 20dB in the second. Increasing the pot to 100K only reduces the minimum gain by 2dB but shifts the centre point down to 16dB which makes the second half of the rotation more cramped. Reducing the value of the pot  simply reduces the overall gain range.

Although not perfect, 47K REV LOG seems to me to be a reasonable compromise for a cheap mic pre.

Cheers

Ian

 

[dipfrik]

@Ian

Thanks for the explanation.

btw. the psu transformer arrived today. Looking very good and the size is exactly what we need and fits perfectly inside one half of the 3U module.

Cheers, Sven

 

[ruffrecords]

@Sven,

Excellent. No sign of my transformer yet but he did say it would be 3 weeks. I hope to get the power supply PCBs soon.

I was checking a couple of regular width 3U modules. The gap between the extrusions of modules next to each other is very small. So, if we mount anything to the extrusion in order to heat sink it then we will need to counter sink the screws.

Cheers

Ian

 

[ruffrecords]

I was thinking about what you could squeeze into a module .Given there are a limited number of slots in the lunch box. especially it you use the built-in PSU, then the more you can squeeze into one module the better. For a mic channel with EQ you would normally need two modules - one for the mic pre and another one for the EQ, just as Holger did in his monster mixer. I wondered if you could get a simple bass and top boost/cut in with a mic pre using the second stage amplifier for gain make up. I then recalled the UA 610 NFB EQ I had been working on and came up with a simple EQ with separate boost and cut pots a bit like the EQP1A but with a single fixed frequency. The attached schematic just attaches in place of the gain setting resistor of the second amp so it is much simpler than the UA610 version.

Cheers

Ian

 

[anjing]

Good day Ian,

Could this design be used before  a single amp?For example  between the input transformer and the amp? I am thinking of a single frequency stereo eq for a twin line amp.....

Regards,

Pierre

 

[ruffrecords]

Good day Ian,

Could this design be used before  a single amp?For example  between the input transformer and the amp? I am thinking of a single frequency stereo eq for a twin line amp.....

Regards,

Pierre

It cannot be used before a single amp because it uses the negative feedback of the amp to work. However, it does only need a single amp to work so you could use a Twin Line Amp to make a stereo version. Just connect the EQ network instead of each of the two gain setting trimmers.

The original design had a nominal gain of 16dB with the controls set flat. This was to allow for 10dB in hand on a preceding fader plus the 6dB signal level drop in the output transformer giving an overall gain of 0dB. However, this could only give about 8dB range in the controls. To get a 10dB range I increased the flat gain to 18dB. You can lose this 2dB simply by inserting a 270 ohm resistor in series with the input to the fader. In practice, if the fader is fed by a 10K:10K transformer, there will be about a 1dB loss in the transformer so trimming out the odd extra dB is probably not worth bothering with.

Note that if you are going to make a stereo one with ganged pots you will need to find some two gang 47K or 50K  REV LOG pots.

Cheers

Ian

 

[dipfrik]

@Ian:

Is this EQ design based on the ideas you started on this thread?
http://groupdiy.com/index.php?topic=56384.0

Thanks, Sven

 

[ruffrecords]

@Ian:

Is this EQ design based on the ideas you started on this thread?
http://groupdiy.com/index.php?topic=56384.0

Thanks, Sven

Yes, it is. I have simplified it so that all the EQ elements are in the place where the gain resistor normally goes.

Cheers

Ian

 

[ruffrecords]

The new power supply PCBs and the four module motherboard PCBs arrived this morning (pic attached).

Cheers

Ian

 

[dipfrik]

Nice!

Are they available at the Emproium from now on?

Cheers, Sven

 

[ruffrecords]

Nice!

Are they available at the Emporium from now on?

Cheers, Sven

Not yet. I need to build and test them first to make sure they work. The four module motherboard should be easy to test as I made it simply by cutting and pasting the two module motherboard. I spent the afternoon assembling the sub-rack kit for the large deep lunch box. I soldered connectors to the 4 module motherboard and fitted it to the sub-rack.  (see attached picture). Modules seem to plug in OK so next test it to add some power. Last night I nearly completed the external power supply which uses the V2 regular power supply board so I will probably use that to test it first. I can start building the 3U power supply but I am still waiting for the mains transformer and the enclosure so that will take a bit longer.

Cheers

Ian