EZ Tube Mixer Support Thread

[Holger]

Pierre, wonderful.
I have some questions:
- Do you have five or six pre amps running?
- What output transformers do you have?
- Do you have direct outs per channel?

 

[ruffrecords]

I am really pleased you are making progress again Pierre. As you have found, hum problems can be hard to track down but often turn out to be quite simple in the end.  Any chance of a sample or two of mixed tracks?

Cheers

Ian

 

[anjing]

@Holger For now i have 5 preamp going to 1 summing card. I have four direct outs using the VTB2291 and  the main output sowters 5069c.
 
@ Ian I will try to  record something.

 

[ruffrecords]

I am going to order some more backplanes in the next few days. Anyone want one? Price will be the same as last time (can't remember the number).

Cheers

Ian

 

[KMB-AUDIO]

I think I will need two more.

 

[ruffrecords]

I think I will need two more.

OK, I will order five. I will put two aside for you.

Cheers

Ian

 

[anjing]

@ Holger were did you buy you 240v torroidal?

 

[anjing]

Hi Guys,

  I'd like to ask for some advice. I need to upgrade my HTR power supply to a higher Amp rating in order to accomodate the spike of inrush current when powering the modules.
  I was discussing this problem with Holger and he was suggesting looking for some kind of power limiting device.
  While browsing online i found this from Power One. It that has an inrush limiting device. I was wondering if someone would care to have a look at it and tell me if they think it could be a suitable candidate.

Thanks,

http://www.power-one.com/sites/power-one.com/files/abc200-10xxg_ds_final_070511.pdf

 

[ruffrecords]

Hi Pierre,

That power supply does have inrush current limitation but it limits the inrush current on the mains input not on the dc output so unfortunately it will not solve your problem.

I have been giving this problem some thought as it will affect anyone who builds this project. The mixer I designed prior to this one had a low drop out 12V regulator on each preamp PCB. All you had to do was supply roughly smoothed 14V dc to the boards. Inrush current was not a problem because the transformer just sagged a bit and it was easy to over rate it.

For the EZTubeMixer there was not enough room on the PCB to fit a regulator so the PCBs are fed with 12V dc. This means a single power supply supplies all baords and the inrush current becomes a problem. I see three possible solutions to this problem.

1. I suspect the International Power linear supplies we are using have foldback current limiting - if over current is detected the supply voltage is dropped until the current reaches a very low value. There is no recovery from this with tube heaters as the very low current is not enough to warm the heaters and and raise there resistance. So one answer would be to modify these power supplies so they limit the current to their full capacity rather than a very low value. The tubes would then warm up and the current would reduce. Looking at the power supply I have, it seems to use the LM723 regulator chip with external series pass transistors. I will look at whether these have foldback limiting as I suspect. The downside of course is that this will void the warranty.

2. Use a roughly smoothed dc supply and have some form of local heater regulation. For example, the LM338 will supply up to 5 amps in its TO3 package so we could use one of these per sub-rack. I have ordered some of these and a couple of different sized heat sinks to try out on the demonstrator mixer I am building.

3. Go back to the regulator per Eurocard. There is not enough room for this on the Eurocard but there might be room on the back of the backplane PCB. I need to do a new version of this PCB to correct some outstanding minor errors so this would be a good time to include a regulator per card. I used the LM2940 type in the other mixer and I think this would be a good choice here.

Cheers

Ian

 

[anjing]

Hi Pierre,

That power supply does have inrush current limitation but it limits the inrush current on the mains input not on the dc output so unfortunately it will not solve your problem.

I have been giving this problem some thought as it will affect anyone who builds this project. The mixer I designed prior to this one had a low drop out 12V regulator on each preamp PCB. All you had to do was supply roughly smoothed 14V dc to the boards. Inrush current was not a problem because the transformer just sagged a bit and it was easy to over rate it.

For the EZTubeMixer there was not enough room on the PCB to fit a regulator so the PCBs are fed with 12V dc. This means a single power supply supplies all baords and the inrush current becomes a problem. I see three possible solutions to this problem.

1. I suspect the International Power linear supplies we are using have foldback current limiting - if over current is detected the supply voltage is dropped until the current reaches a very low value. There is no recovery from this with tube heaters as the very low current is not enough to warm the heaters and and raise there resistance. So one answer would be to modify these power supplies so they limit the current to their full capacity rather than a very low value. The tubes would then warm up and the current would reduce. Looking at the power supply I have, it seems to use the LM723 regulator chip with external series pass transistors. I will look at whether these have foldback limiting as I suspect. The downside of course is that this will void the warranty.

2. Use a roughly smoothed dc supply and have some form of local heater regulation. For example, the LM338 will supply up to 5 amps in its TO3 package so we could use one of these per sub-rack. I have ordered some of these and a couple of different sized heat sinks to try out on the demonstrator mixer I am building.

3. Go back to the regulator per Eurocard. There is not enough room for this on the Eurocard but there might be room on the back of the backplane PCB. I need to do a new version of this PCB to correct some outstanding minor errors so this would be a good time to include a regulator per card. I used the LM2940 type in the other mixer and I think this would be a good choice here.

Cheers

Ian

Hi Ian,
  I personally would not mind solution 1.
Solution 2 would be benificial to most people being the most flexible.
Solution 3 is probably the most elegant, good too for new adopters.
  They have quiet a few circuit examples in the application hints for the LM338 i'm gonna order a few as well and also experiment. Could be a good learning experience!

Regards!

Pierre

 

[ruffrecords]

Hi Ian,
  I personally would not mind solution 1.
Solution 2 would be benificial to most people being the most flexible.
Solution 3 is probably the most elegant, good too for new adopters.
  They have quiet a few circuit examples in the application hints for the LM338 i'm gonna order a few as well and also experiment. Could be a good learning experience!

Regards!

Pierre

OK, I'll have a look at #1.

When you buy your LM338s, don't forget to buy a big heatsink (about 2.5 degrees C /W) and a TO3 insulating kit.

Cheers

Ian

 

[ramshackles]

Hiya,
I've been lurking/watching the eztube mixer threads for a while...you guys are doing a great job

It's very interesting and even helpful for my EQ build (using 2 of the universal eq cards and the twin line amp card).

The mechanics of how everything fits together is interesting and these eurocards systems look great.

I was wondering about the pinout of the DIN connector you are using; 2 pins are always for ground/screen connections and power...is this for extra security or is there some bigger reason why you should use 2 pins? Or, rather, is there a reason why you should not use just 1 pin for these connections?

 

[ruffrecords]

Hiya,
I've been lurking/watching the eztube mixer threads for a while...you guys are doing a great job

It's very interesting and even helpful for my EQ build (using 2 of the universal eq cards and the twin line amp card).

The mechanics of how everything fits together is interesting and these eurocards systems look great.

I was wondering about the pinout of the DIN connector you are using; 2 pins are always for ground/screen connections and power...is this for extra security or is there some bigger reason why you should use 2 pins? Or, rather, is there a reason why you should not use just 1 pin for these connections?

When the pinout was originally designed I was hand wiring the racks. The two pins for screens was put in because it makes it real easy to wire in the screen of a screened twisted pair to the two pins on the connector and the cable is nicely supported while you wire in the other two signal wires and they are pointing in the right direction. The cables then exit horizontally from the connector and can be easily grouped and routed to the input XLRs for example.

The two pins for power are primarily from the point of view of ease of hand bus wiring. You can literally push a bare copper wire from connector to connector and make a bus across the back of the rack without having to do leg around any adjacent pins. it ruens out to be rather convenient from the point of view of laying out the backplane PCB.

 

[ruffrecords]

@Pierre

I have taken my International Power 12V 5.1A supply apart and traced the current limit part of the PCB. It looks like they have included a pot, R8 labelled I.LIM which sets the foldback current. I think if this is turned fully anti-clockwise, the foldback current limit is disabled and regular current limit operates. So I suggest you note the position of the pot R8, then turn it fully anti-clockwise and see it it will then power up 6 cold modules. If you don't want to do this then wait a couple of days and I will try it myself.

Cheers

Ian

 

[anjing]

Hi Ian,
  I think i identified that pot. On mine they fix it in position with some kind of gooey material. I will reassemble my console and try it tomorow.
Thanks for the tip Ian!

Regards,

Pierre

 

[ruffrecords]

Hi Ian,
  I think i identified that pot. On mine they fix it in position with some kind of gooey material. I will reassemble my console and try it tomorow.
Thanks for the tip Ian!

Regards,

Pierre

That's interesting. Mine has no gooey stuff at all. The pot is a small black preset pot. There is also another one, a small blue one, that is used for adjusting the output voltage. Do you have that one too?

Cheers

Ian

 

[anjing]

Hi Ian
  I also have a voltage pot. I'll take a picture of it later.

Pierre

 

[ruffrecords]

Holger is a genius!!

On his recommendation I just purchased some of these connectors:

http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1656165

From the picture they look too short for the EZTubeMixer. From the description they appear to be 2.54mm spacing but they are 32 ways and they cost less than 1GBP each. Holger said he is using them instead of these:

http://uk.farnell.com/harting/0904-232-6831/socket-din41612-d-32way/dp/1106773

which I have been using for the backplane 32 way connectors and which cost over 8GBP each.

When the cheap ones arrived I was very disappointed. From the front you can see they are 2.54mm pitch and all three rows have holes so there are 96 of them. But then I turned one over and looked at the connecting pins and there are only 32 pins fitted and they are on 5.08mm spacing exactly as required for the EXTubeMixer backplane PCB!!! I tried plugging in a Twin Line AMp PCB and it fits perfectly.

So many, many thanks to Holger for saving us all a bunch of money.

Cheers

Ian

 

[Holger]

Holger is a genius!!
...

I wished that would be true.

I was a bit irritated that you've mentioned in a mail that you've spent 50 quid for a couple of 32 pin connectors.
The Harting BTW link points to a D-type connector.
I use the DIN 41612 32-pin C type for the project. The male-female combo should't be more than ~2.50€.

 

[anjing]

Looks like  i can get them at newark as well with a two week leed....i spent 120$ for 12 female connectors!
Thanks Holger!
That's worth a lot of microbrewery beers if you even pass by Montréal....