Feeler: EZ Tube Lunch Box

[dipfrik]

I spent the afternoon assembling the sub-rack kit for the large deep lunch box.

"large deep" means for modules with deeper pcb's eurocard sizes?

Cheers, Sven

 

[ruffrecords]

I spent the afternoon assembling the sub-rack kit for the large deep lunch box.

"large deep" means for modules with deeper pcb's eurocard sizes?

Cheers, Sven

It means with room to fit output transformer to the rear panel as shown in this sketch I drew a couple of years ago:

Cheers

Ian

 

[dipfrik]

Got it!

Thanks, Sven

 

[ruffrecords]

I have just updated the schematic of the mini EQP1A to improve it. I did not like the way the boost controls were never 100% off so I have made a small alteration so that they go fully off when the control is fully anti-clockwise. it also means the two compensating 1K resistors in the cut section are no longer needed. Simulations indicate it works as expected, you even get close to half the attenuation and the half way point of the pot which is nice. Updated schematic attached.

Cheers

Ian

 

[dipfrik]

@Ian

I'am scratching my head around this new miniEQP1A.

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.

If it's in place of the 2nd gain resistor, which is actually a trimmer, how could we trim the second gain stage finally?
Maybe it's because i have problems in understanding the whole NFB topologies topic. Could you make a short note, how this schematic of yours should be connected to the amp card?

Thanks, Sven

 

[ruffrecords]

If it's in place of the 2nd gain resistor, which is actually a trimmer, how could we trim the second gain stage finally?
Maybe it's because i have problems in understanding the whole NFB topologies topic. Could you make a short note, how this schematic of yours should be connected to the amp card?

Thanks, Sven

Hopefully the attached diagram makes it clearer how it would work. The thing to remember is that the EQ works by changing the gain of the second amplifier by altering its negative feedback. It is arranged such that, with all the controls set to flat, the second amplifier has a gain of about 18dB, To cut, it reduces the gain and to boost it increases the gain. In the diagram the signal first goes to the channel fader via a 4K7 trimmer pot. It is this trimmer that is used to trim the overall gain. It usually drops the input level by about 2dB. Then the fader has 10dB in hand so at its 0dB position it attenuates a further 10dB making a total loss of 12dB. The amplifier then adds 18dB of gain so its output level is +6dBu.. The VTB2291 then drops the level by 6dB because it is a 2:1 transformer and the output ends up at 0dBu .

Cheers

Ian

 

[dipfrik]

Short update on the Sowter 2K4/600 custom output transformer.
I got these two babies in my hand this morning. Couldn't find the time so far to go for a test run, but Sowter is really confident that these are good ones! Because of that, they are now officially available from there webshop as 1380.

1380 2400/600 2:1 ratio Input/Output Transformer
High level. Similar to 5069. May be used as 1:2 or 2:1 ratio . +25 dBu on 600 Ohm side

Price: £58.35

Link: http://www.sowter.co.uk/acatalog/SOWTER_TRANSFORMERS_ISOLATOR_BALANCERS_2.html

Cheers, Sven

 

[ruffrecords]

Well done Sven. It is good to have a choice of output transformers,#

Cheers

Ian

 

[ruffrecords]

While waiting for the power supply transformer and enclosure to arrive, I have started assembling the 3U PSU board. I soldered in all the big electrolytic caps, the chunky resistors in the HT and the snubbing capacitors across the rectifier bridges. Out of curiosity I thought I would see if it would fit into a 3U 14HP Fischer type HB cassette. A couple of interesting things happened. First, some of the big cap leads fouled the enclosure when the PCB was slid in. I had imagined there would be a lot more spacing between the bottom of the PCB and the wall of the enclosure. In most places there is, but along the top and bottom where the PCB is supported, the extrusion is much thicker. This is where the capacitor leads foul the enclosure. I had not trimmed the capacitor leads after soldering them in, because I thought there would be plenty of room, so I trimmed them and the board then slid in easily. The only thing that stopped it going all the way in was the smoothing capacitor for the 12V supply  which, at 53mm high, hits the other side of the cassette. This is not a problem in the final power supply which is 28HP wide.

The interesting thing is that even with the capacitor leads trimmed, there is not  a lot of clearance between  the ones at the top and bottom of the PCB and the cassette. At the bottom of the PCB is the HT supply and the capacitor pins with the least clearance are fortunately the 0V ones. At the top of the PCB it is snubbing caps for the 12V and phantom supplies.

I can think of several ways of improving the situation:

1. Add an insulating layer of thin plastic between the PCB and the cassette.
2. The HB cassette has PCB slots at 5.08mm intervals so we could just move the PCB 5mm further away from the bottom, provided it and the toroid will still fit in the 28HP cassette
3. Change the PCB layout so that the edges of the board are left free. The board is already squeezed so this may be difficult. However, the successful experiments with the TO220 low drop out regulator for the 12V supply mean we no longer need to heatsink a TO3 regulator. The TO220 LDO regulator can be bolted to any convenient lump of metal so there is no reason in principle why this could not be the cassette itself. I plan to try this when the cassette eventually arrives. If this works then we no longer need the space for the heatsink on the PCB and can use this space to re-arrange components so they avoid the top and bottom edges.

Cheers

ian

 

[ruffrecords]

I have nearly completed the external power supply prototype using the new PSU board (not the 3U one). All the outputs produce the right voltages and I have connected the heaters to my test rack containing six modules. I am pleased to report that with the large heatsink you can see in the attached picture and using the TO220 LDO adjustable regulator we can use regular 12V transformers and the heatsink barely rose by 10 degrees when loaded with six modules. The custom transformer for the lunch box has not yet arrived so the prototype external power supply uses three different transformers I happened to have lying around.

Cheers

Ian

 

[ruffrecords]

The custom mains transformer arrived yesterday morning. It is a heavy beast. I just chased Buerklin about the 28HP cassette so hopefully I will have all the parts together by Christmas.

Cheers

Ian

 

[dipfrik]

Too heavy/big? Will it fit?

So you chased the last available 28HP cassette from Buerklin!
Damn, it's really hard to get cassettes right nown.

Cheers, Sven

 

[dipfrik]

Hey,

i want to give you all a 1st and short insight of something that has been evolved on my desk over the last weeks. Suprise, let's talk about a compressor module again

The idea was in my mind since i finished two D-AOC's (http://groupdiy.com/index.php?topic=26585.0) a few month before. So i started to think of an adaption that fits in a Fischer module and can be easily used in the whole EZ-Tube mixer context. Basically a S-AOC

Based on the available schematics and experiences, i was able to develop two eurocard pcb's in a 1st iteration for prototyping. The AOC parts including input and output transformers plus an additional psu board for the specific power requirements of the the AOC.

I have tested my 1st ideas with these boards over the last days and can definitively say, that everything works like charm. It behaves exactly like D-AOC but only as one channel.

Here an actual photo of my two prototype pcb's and the progress of work.
Left - one AOC channel and right - the necessary psu board.

What do you think?

Thanks, Sven

 

[ruffrecords]

Too heavy/big? Will it fit?

So you chased the last available 28HP cassette from Buerklin!
Damn, it's really hard to get cassettes right nown.

Cheers, Sven

I just had a couple of emails from Alexa at Buerklin. The 28HP cassettes were supposed to be in stock from 18th November because the supplier said they had been despatched.  However, they had not reached Buerklin. When Alexa asked the supplier again  it turned out they had not left the supplier. They are on their way to Buerklin now and Alexa says she hopes to ship  to me on Friday.

Cheers

Ian

 

[dipfrik]

Good news, which means that the i can order two at the minimum before christmas.

Cheers, Sven

 

[ruffrecords]

Hey,

i want to give you all a 1st and short insight of something that has been evolved on my desk over the last weeks. Suprise, let's talk about a compressor module again

The idea was in my mind since i finished two D-AOC's (http://groupdiy.com/index.php?topic=26585.0) a few month before. So i started to think of an adaption that fits in a Fischer module and can be easily used in the whole EZ-Tube mixer context. Basically a S-AOC

Based on the available schematics and experiences, i was able to develop two eurocard pcb's in a 1st iteration for prototyping. The AOC parts including input and output transformers plus an additional psu board for the specific power requirements of the the AOC.

I have tested my 1st ideas with these boards over the last days and can definitively say, that everything works like charm. It behaves exactly like D-AOC but only as one channel.
What do you think?

Thanks, Sven

Well done Sven! A very worthwhile project. My only reservation about the D-AOC design is the way it drives the opto. As originally designed it is a peak detector because there is path to ground for the capacitor on -ve half cycles. It really needs a similar opto connected across it in anti phase in order to work properly. Have you included this?

Cheers

Ian

 

[dipfrik]

If you mean the double vactrol, known as one of the kubi mods, than yes it's build right my pcb design.
On the photo i only used for testing a simple blue led.
Or are we talking about something else?

Cheers, Sven

 

[ruffrecords]

If you mean the double vactrol, known as one of the kubi mods, than yes it's build right my pcb design.
On the photo i only used for testing a simple blue led.
Or are we talking about something else?

Cheers, Sven

Yes, I  it is included in the kubi mods so you are OK.

Cheers

Ian

 

[dipfrik]

Puhhh

There are a few mods i will integrate into the next revision.
Especially i need to clear some (a lot) space at panel side of the pcb.
The big solen fast caps are blocking a lot of space and we need this for a proper vu meter to show the gain reduction.

Cheers, Sven

 

[ruffrecords]

Puhhh

There are a few mods i will integrate into the next revision.
Especially i need to clear some (a lot) space at panel side of the pcb.
The big solen fast caps are blocking a lot of space and we need this for a proper vu meter to show the gain reduction.

Cheers, Sven

Where in the schematic do you use the Solen capacitors? I think it is not necessary to use a film capacitor to couple to the optos. You can use an electrolytic.

Cheers

Ian