Tube DI Box

[Rusan]

Welcome back, Ian! I'm so glad to hear you're doing lots better, and finally back to home sweet home. COVID isn't nice, pneumonia is worse, and hospitals are, well, hospitals. 'Nuff said.

 

[5v333]

Wonderfull to hear that things are going in the right direction!
First time i had Covid was as near death as I've ever been.

 

[nmcgann]

Good to hear you are out of hospital Ian.

 

[CJ]

Glad your out of the hospital
Ian!

Those places will make you sicker than when you went in.

Back to the DI remember that cold tubes draw a lot of heater current til they reach their stable temp.

And I replace a lot of those Max DC to DC chips when fixing stomp boxes. And the new chips seem to fail a year later.

I use 3 vape batts for my pedal board, 4.2 volts each. No memory or self discharge during storage, have a high capacity, but they are expensive, require a charger and are not very eco friendly, but not as bad as a Tesla.

 

[ruffrecords]

One of the most difficult things I found with Covid was that for a couple of weeks, NOTHING was interesting to read, look at, listen to. I massed up all my favorites to try to joy up, But just had to wait it out.
Glad you are safe and out of health jail, take as good care of yourself as you can!

You are right, it really messes with your head. Finding it hard to get motivated. I have been playing favourite tracks all evening but still not getting much mojo. Just got to be patient.

The best bit is just watching the world and those around you and being glad you are alive.

Cheers

Ian

 

[Wavelength]

Ian,
Did you loose taste? My wife did for a month, a friend for six months.
My boards came in last Monday. But stupid me I said I would rebuild the village pool sound system and of course what should have been hours were days. Plus my freaken UPS account got hacked and the idiots can't seem to figure out why, even though it's internal somewhere.
I need to ship a bunch of stuff on Tuesday then I will get on this board using the Hammond power. I have had a bunch of ideas since doing this board, not sure why I didn't just put the TS and XLR connector on board and maybe input level control.
More soon!
gordon

 

[pvision]

Ian, just catching up with this thread. Glad you're out of hospital & on the mend!

We appreciate you

 

[L´Andratté]

The best bit is just watching the world and those around you and being glad you are alive.

The best thing one can make of severe illness is transforming it into personal growth.

 

[Wavelength]

Gang,
Got some free time today and put together the 6922 DI board I designed. I should not have assumed the LR8 regulator would be the same as a LM317L as it's actually reversed. Popped that out and wired it up. I have the regulation at 170V on the SRPP but I think I may lower it a little as the two sides of the tube are not balanced. 90V/80V so probably bring it down a bit. Everything is all over my desk but the regulated supply had really low noise 0.673mV, probably even better if I lower it because it's not dropping the suggested amount of 20V only 16V.
The Jensen 10K:600 is ok it gets a bit weird in the low end and starts ramping up above 10KHz. I don't have a load on the secondary, zobels have always sounded bad to me. I will throw it on the Prism dScope III on Monday when I get back to work. I threw it on my Avertech but that software is getting flaky on the latest macOS. Crashed a few times.
Need to consider some kind of enclosure and get the tube shield on.
More soon, thanks
Gordon

 

[Wavelength]

Ok before changing the B+ from 170V to whatever I figured I better test a few different tubes. Ok so the LED bias was a bad idea as that will always be 2V and the 390ohm bias for the upper tube will change. Since this is a very high transconductance tube the variation in bias will change as well. In the morning I will swap out the LED for a 390 ohm resistor and probably a 47uF cap to bypass it. Another idea would be to replace the 390 ohm with a pot and vary the gain with the wiper connected to a bypass cap. Maybe a 470ohm pot in parallel with a 2.2K resistor will get close to 390 with a 100uF cap on the wiper. More tomorrow.

 

[Wavelength]

All, while I am changing the schematic and board layout I was thinking of adding an output transformer and the connectors dual TS (input & thru) and XLR output. What about output transformer? The Hammond 108N looks ok on paper or the much better OEM CineMag CM-2810. The S217 is super nice, but what's the budget here? Those are going for $250 each. I am going to ask David what the prices are on the CM-2810.
I am also going to put pads in for a Wima MKP10 coupling cap since the ODAMS are pretty pricey.
I am looking at enclosures for this and the Hammond 1455NS1601 looks to fit the bill. Easy to do some Front Panel Express back panels to make it work.

 

[ccaudle]

the Hammond 1455NS1601 looks to fit the bill.

Would you need to cut cooling slots into the enclosure to reduce heat build up from the tube?

 

[Wavelength]

Would you need to cut cooling slots into the enclosure to reduce heat build up from the tube?

Yes but it wouldn't be too bad. I looked around and found a Hammond 1455NS style which is 4x4 inches square and they have them in 6 inch and 8 inch lengths. I am working on the board now.

 

[Wavelength]

FYI, swapped out the LED for a 390 ohm with a BGN 100uF/6.3V bypass and it works great. Frequency response with the Jensen 10K61 is like less than 10Hz -1dB to greater than 50Khz. Phase is real good, but square wave needs some kind of termination. I put a 470 across the secondary and it tammed the overshoot. But I need to play around with values. It was sitting there so I used it. Maybe something like a 6.8K might be fine.
FYI the CM-2810 is ~$60 each in 1-10, 4 weeks out, Hammond 108N is ~$22. Having a bit of a problem getting the CM-2810 on the board because of it's size. More soon!

 

[Wavelength]

First the CM-2810 would not fit the board without practically starting over. So I talked to David and he had a design on a EI21 which he did for PCB. It's a nice size and would work in a 500 series module so I was pretty interested. CM-18401 and he is going to look over the drawing and give me some options for laminations. Previous was all iron, so maybe 49% nickel or some combo or 80% depending on the numbers I sent him. I left the Hammond 108 on the circuit board as well so either can be used. I dumped the ODAM cap, it's nice but also large for a Wima MKP10 type.
So this version has all the connectors on it. The board is 3.925" wide and 4" deep. I added 3 switches to the board in thinking:
SW1 is the ground pin 1 XLR switch.
SW2 is input impedance, basically 100K, center = 1M, 500K of course the 2 resistors could be changed to whatever you want.
SW3 is XLR termination, basically have it a 620 ohms, center no termination, 3K3 as above you could change this too what ever.
Silly me looked at the PDF and never fixed the pinout on the LR8. Ok done.
Thoughts?
Thanks,
Gordon

 

[Wavelength]

Also if anyone is interested in the other 4 boards I had on the first version. You would have to invert the LR8 in the TO92 package and instead of the led put in a 390 ohm resistor in parallel with anything from 49uF->100uF at 6.3V or higher. The PI choke/inductor would have to drop less than 20V at ~6.5ma so less than 3K, Hammond 60H would be killer and it's only 2750 ohms I think. I am sticking with the MEC50 SS choke. It seems to work well and sounds good.

 

[ruffrecords]

I prefer to have the output transformer off the PCB. That way you have some choice of transformer and you can also mount it directly to the enclosure and not place unnecessary strain on the PCB (the Tube DI WILL be dropped )

Cheers

Ian

 

[Wavelength]

I prefer to have the output transformer off the PCB. That way you have some choice of transformer and you can also mount it directly to the enclosure and not place unnecessary strain on the PCB (the Tube DI WILL be dropped )

Cheers

Ian

Ian,
All the pads are there to put it off board like the v#1.01 board.

 

[MidnightArrakis]

The board is 3.925" wide and 4" deep.

Generally.....PCB-fabrication shops can only hold their PCB board-outline dimensions to two (2) places (i.e., 3.93") UNLESS you want to pay extra for a "3-place held tolerance" on your board-outline and -- WHY -- would you even want to do that anyway???

/

 

[ruffrecords]

Generally.....PCB-fabrication shops can only hold their PCB board-outline dimensions to two (2) places (i.e., 3.93") UNLESS you want to pay extra for a "3-place held tolerance" on your board-outline and -- WHY -- would you even want to do that anyway???

/

I suspect it is meant to be 100mm = 3.937 inches
Cheers

Ian