8 Channel, 3U NEVE 1073 completed

[indiehouse Recording]

congrats on getting the phantom up!

your ohms for the xfmr look good,

let us say you hve 24 ohms for each pri coil,

with 24 in series you get 48, now when you run the 300 ohm setup, the coils are in parallel,

anytime you have 2 parallel resistors of same value, the calc simplifies to just dividing 24 ohms by 2 = 12 ohms so everything is cool so far.

use the DMM on ohms and connect to pins 2 and 3.

you should get 12 and 48 ohms again.

i bet the 48 ohms was too much for your continuity checker to say yes,

but it liked the 12 ohms ok, so everything looks go for takeoff at 08:00.

that LED across the 48 volts, i figure it is a 48 volt LED or a lightbulb, unless you have a series resistor on a regular LED?

otherwise the LED would have smoked like a chimney, get me?

So, I shouldn't worry that I'm not reading 300 and 1200 ohms? Are you saying that resistors in the signal path are affecting the impedance measurements? If I were to measure impedance with nothing hooked to the input tranny but the toggle switch, should I then measure 300/1200 ohms?

Also, I see what you mean by the LED. If I shorted out 0V/48V with the LED, then the LED would have smoked, right? (Which it didn't).

I wonder then if I shorted out with the trim pot. It's rather big, and I used Martins idea for a trim (post 1399), which uses resistors attached to a stepped (.5 db increments) pot/switch. I don't know, just brainstorming ideas. I'll triple check any potential shorts when stuffing the case.

 

[CJ]

transformers have two kinds of ohms which can be confusing, DC resistance of the windings, and impedance ohms, DCR will always be way lower than the impedance or "Z"  ohms, which is the 300 and 1200 ohms

Z ohms is the resistance to AC due to inductance, which is formed by the turns of wire round the core, DCR is the actual resistance of the copper wire, Q is quality factor, you want a Hi Q, (not poetry)    for audio transformers, that is you want DCR less than Z, usually by a factor of 10 or better, so a Z of 1200 ohms might have a DCR of 1200/10 = 120 ohms, so your Q on the Neve input is better, 1200/48 ohms = a Q of about 24 which is good, you find a Hi Q on transformers with nickel lams since you get more inductance  for the same amount of turns that  you would on lets say a power transformer which uses steel lams,

so when you ohm out the XLR pins 2 and 3, you are ohming out DCR, not Z,

if you wanted to check Z ohms, you would inject AC and measure the current, then divide the AC voltage injected by the ac current, this would give you your Z in ohms,

a little current is used to run the xfmr, so your Z ohms will be off by a small factor due to some of your measured current being used to excite the core. this is called core loss, nickel lams have less core loss than steel, so your Z measurement will be more accurate than if you were to check an output transformer which uses lower perm lams,

so the bottom line is DCR = DC ohms, and impedance (Z) = AC ohms,

your ohm meter uses batteries, or DC, to measure DC ohms, an inductance meter uses AC to measure  Z ohms which then gets computed into Henries, a measure of inductance.

 

[indiehouse Recording]

transformers have two kinds of ohms which can be confusing, DC resistance of the windings, and impedance ohms, DCR will always be way lower than the impedance or "Z"  ohms, which is the 300 and 1200 ohms

Z ohms is the resistance to AC due to inductance, which is formed by the turns of wire round the core, DCR is the actual resistance of the copper wire, Q is quality factor, you want a Hi Q, (not poetry)    for audio transformers, that is you want DCR less than Z, usually by a factor of 10 or better, so a Z of 1200 ohms might have a DCR of 1200/10 = 120 ohms, so your Q on the Neve input is better, 1200/48 ohms = a Q of about 24 which is good, you find a Hi Q on transformers with nickel lams since you get more inductance  for the same amount of turns that  you would on lets say a power transformer which uses steel lams,

so when you ohm out the XLR pins 2 and 3, you are ohming out DCR, not Z,

if you wanted to check Z ohms, you would inject AC and measure the current, then divide the AC voltage injected by the ac current, this would give you your Z in ohms,

a little current is used to run the xfmr, so your Z ohms will be off by a small factor due to some of your measured current being used to excite the core. this is called core loss, nickel lams have less core loss than steel, so your Z measurement will be more accurate than if you were to check an output transformer which uses lower perm lams,

so the bottom line is DCR = DC ohms, and impedance (Z) = AC ohms,

your ohm meter uses batteries, or DC, to measure DC ohms, an inductance meter uses AC to measure  Z ohms which then gets computed into Henries, a measure of inductance.

Ah, I see. So by measuring ohms with my DMM, I'm not actually measuring the impedance ohms of the input tranny, but rather the resistance of DC current through the windings.

In order to measure impedance ohms, I would need AC current flowing through the input tranny. Since the PS is outputting DC current, simply turning on the PS will not suffice. However, it appears that the DCR measurements I am getting are sufficient, and everything is working as it should, right?

Thanks for the great info!

 

[CJ]

you got it wired!

your Z  sw is wired correctly.

 

[dmp]

Finished a second pair, this time with a HPF. Works great.

 

[dmp]

And the front -

 

[CJ]

fantastic!

nice outputs!

 

[indiehouse Recording]

I've got three channels up and running smoothly. Wouldn't you know it, though, the last one is fighting me!

I've got no output on this one. I've swapped out the input tranny, but that did not make a difference. I've checked my wiring, and it's the exact same as the other channels.

Are there any points I can measure with my DMM to trace the problem?

I'm hoping someone can be my hero one last time!

 

[sr1200]

Check the voltage coming into the card then check the voltages on the transistors against the numbers in the documentation.  Best way to find discrepancies.

 

[CJ]

you have a good unit you can use as a side by side voltage comparison,


just start measuring points on both circuits until you get different readings,

set all the controls the same,

 

[indiehouse Recording]

It's definitely the Go-Between. What could be the issue? Is there something common that goes wrong that I should look at?

 

[sr1200]

the only voltage going to the GB is the 48v.  Hopefully theres nothing thats shorting that to ground.  Check over the board thoroughly, and as CJ said, compare against a known working unit.  You have that desolder pump now, if theres anything that looks suspect, clean it up.  Youre almost there

 

[indiehouse Recording]

Figured it out! It was a bad ribbon cable that connects to the DI. Fixed it and now I've got 4 channels of Neve goodness!

I'll post a pic of the finished project tomorrow. I wanted to first thank everyone who helped me make it through this build. This was a challenge for me. Every problem i encountered was a mistake of mine, even though I spent a month reading and re-reading all of the documentation. I have learned much from you guys, and I wanted to express my gratitude.

I owe you all a beer.

 

[desol]

Cool! I was kinda suspecting that it might be that cable, but i wasn't sure if you had installed the DI's?
Regardless, great work! Now the biasing....!?

I think it's great that CJ contributed some good info...he's forgotten more than i'll ever know. 

 

[indiehouse Recording]

Cool! I was kinda suspecting that it might be that cable, but i wasn't sure if you had installed the DI's?
Regardless, great work! Now the biasing....!?

I think it's great that CJ contributed some good info...he's forgotten more than i'll ever know. 

I don't have a scope, though I'm trying to track one down to borrow.

In the meantime, I used my DMM to set the bias to 22.6V, as measures between 0V and the casing of the 2N3055.

 

[desol]

I can't remember exaclty what my bias was, but i think it was between 22.7 and 22.9 volts dc. I think it has to do with the components used. It's been a while.  :

 

[indiehouse Recording]

What a fun challenge! They sound fantastic!!

 

[sr1200]

http://www.audiomaintenance.com/acatalog/Rotary_Switches.html
Its not a pot its a switch.

 

[mikerl]

Hey!

i have a bunch of BC184LC transistors, i was planning on just compensating for the different pinout and using them.  I did a brief search and found a mention of someone else doing this, but i just wanted to double check that these transistors will work.


Thanks,

Mike

 

[mikerl]

So it looks like the BC184LC has a much lower collector current (200ma) than the BC184C (500ma) other parameters seem to be similar

http://alltransistors.com/pdfview.php?doc=bc184lc.pdf&dire=_fairchild_semi

http://alltransistors.com/pdfview.php?doc=bc184c.pdf&dire=_fairchild_semi

what do you all think?