Neve 1290 output transformer question

I have just finished stuffing the Neve 1290 boards from Thomas Kristiansson site (www.vintagedesign.tk) and the three gain stages seems to work as they should. Thank you very much Thomas for the layout.
I'm planning to use Lundahl transformers, because they are easy to get in Denmark and because I already got some lying around. I will use the LL1538 for input but don't know which one to use for output. Have anyone tried LL5402 and what should the ratio be (1:1) ?

Best regards, Klaus

N.B. This morning I thought that the output stage didn't work and it took me some time to realize that two of the transistors are bias through the output transformer, which I initially didn't have connected.

Thank you for this extremely nice forum.

Yes, that´s why you need a gapped transformer.

or a neve 1310 t inductors

Wilebee

IN a less than gracious attempt to hijack this thread, where, if anybody has done this before, would you pick off the insert for the eq if you were to build a 1073 w/Kristiansonn's board as a base for the project? BONUS: I'll even attempt to answer my own question in the next couple of days.

rgrds,
Brad

[quote author="bradzatitagain"]IN a less than gracious attempt to hijack this thread, where, if anybody has done this before, would you pick off the insert for the eq if you were to build a 1073 w/Kristiansonn's board as a base for the project? BONUS: I'll even attempt to answer my own question in the next couple of days.

rgrds,
Brad[/quote]

quickest version of my own answer:

http://www.wagrecords.net/neve.htm

EQ is inserted between gainstage 2 output and the output amp! When the EQ is bypassed a 2k7 resistor shall be connected instead of the EQ circuit.
The level control ot fadee is connected right before the outputstage.

Klaus,

You will need a "gapped" output transformer because there is DC flowing in the primary winding.

These are special transformer types - and I don't think that Lundahl makes any that are suitable for Neve output stages.

Sowther or some of the other british companies are the only ones making these.

Jakob E.

Hi Jacob

Thank you very much for the clear answer. I was not aware of the difference in the types of output transformers. I will buy the Neve replacement from Sowter. I was however able to power the amp through the LL5402 trafo, but I haven't listened to it.

Brad,
your work looks extremely professional, at least compared to mine, which is already a mess even though I only have wired a part of one channel. I would like to try some of your eq boards at some point in the future, when I get more experienced.

Here are some pics:

http://medlem.jubii.dk/klausdiy/hobbies.html

I included some comments on the gain switch for first-time builders.

Best regards, Klaus

[quote author="Klaus Mogensen"]Hi Jacob
Brad,
your work looks extremely professional, at least compared to mine, which is already a mess even though I only have wired a part of one channel. I would like to try some of your eq boards at some point in the future, when I get more experienced.

Best regards, Klaus[/quote]

Doh! Those are bona-fide Neve 1073's on Chris Vallejo's diy page you're lookin' at. The only work I've done so far is open the box the transformers came in and stayed up all night reading Neve schtuff.

You could burn your LL5402 up if you power the pre with it in the circuit, I'd leave the whole thing alone until you get the right transformer. There's direct current running through the output transformer, the windings have to be gapped or you might open one up, or in the best case saturate it, and then it'll be garbage. Might as well wait.

[quote author="Klaus Mogensen"]Hi Jacob

I was however able to power the amp through the LL5402 trafo, but I haven't listened to it.
[/quote]

:shock: Lots of DC there...

Thanks for the comments

I will skip the LL5402 (maybe I burned it. I hate burning transformers, when they are so expensive).

Untill I get the correct transformer, I'll use the unbalanced output and power the ouput stage with some small ohmic power resistor (I guess).

There's a lot Neve talk at the moment. I haven't got much time to read though. Now I'll go and play some music with my friends :grin: .

Klaus

You could always wire the output stage in class A/B aka Neve 340 which uses a cap to feed the output metal.

To use the output of a B183/283 without an appropriate transformer you will need to hang a T1310 inductor (or equivalent) between the card's pins M and B to get output swing from the card to drive the unbalanced out (pin F). You can hang any decent 1:1 output transformer (api works great!) once you've got the inductor hooked up.

BTW, the T1310 inductor reads 650mH on my meter, though it is VERY large (like a medium-sized output transformer). I don't know what an equivalent would be for an inductor of this size, as much smaller (physically) inductors can often have much higher values. My guess is the size of the T1310 has to do with it seeing 70mA DC between these connections and maintaining it's inductance under the charge?????

Don't use the card without an appropriate transformer or inductor between pins M and B.

If you do mount and inductor and then hang a transformer off the unbalanced out, you should change C7 from 80uF or 100uF (depending on the schematic you happen to be looking at) to 220uF/25v to maintain excellent LF response.

That's a lot of iron that card will be driving!

JC

BTW... Neve Class-A cloners who wish to add flexibility to their units can hang an api output transformer (or other 1:1 output trafo) off the 283's pin F and install a toggle switch to allow you to select which output trafo feeds the line output connector at a given time. I've done this, and it gives really useful tonal variation... both of which sound fabulous (I switch between a Marinair LO1166 and an api 2503). The Marinair is chunky and full while the api is smooth and silky. Again, change C7 to 220uF if you do this.

[quote author="rascalseven"]

If you do mount and inductor and then hang a transformer off the unbalanced out, you should change C7 from 80uF or 100uF (depending on the schematic you happen to be looking at) to 220uF/25v to maintain excellent LF response.

JC

BTW... Neve Class-A cloners who wish to add flexibility to their units can hang an api output transformer (or other 1:1 output trafo) off the 283's pin F and install a toggle switch to allow you to select which output trafo feeds the line output connector at a given time. I've done this, and it gives really useful tonal variation... both of which sound fabulous (I switch between a Marinair LO1166 and an api 2503). The Marinair is chunky and full while the api is smooth and silky. Again, change C7 to 220uF if you do this.[/quote]

Hey, JC, that's nice, thanks. Brown wire on API to E? Or D? Do you have to terminate the outputs on the LO1166 when using the output from F? (See? I'm a doofus too!)

rgrds,
Brad

Hi, Brad,

I'm assuming you are talking about the api 2503 (Profile 4804) output transformer. Unfortunately, "brown wire" doesn't tell me enough. I don't know if you mean the positive or negative of the primary (brown is both, depending on which api schematic you look at). For clarification sake let's just assume that brown will be the positive lead of the primary:

Brown wire to B283 pin F (or 1290 module output pin P)
Red wire to 'B-' (audio ground) which is pin E on the 1290 module output
Connect Yellow and Green wires together
Orange wire to XLR pin 2 (positive)
Blue wire to XLR pin 3 (negative)
XLR pin 1 to chassis

Note that this wires the 2503 in a 1:2 ratio, which gives about 6dB passive gain compared to the LO1166's 4dB, so it'll be a touch louder.

For the switchable output I mentioned above, use a DPDT toggle switch (on-on), connecting XLR pins 2 and 3 to the two poles of the switch. Then wire the positive leads from the LO1166 (pin 5) and 2503 (orange wire) to the positions for pin 2 and the negative leads of each (pin 8 on LO1166 and blue wire on 2503) to the positions for pin 3. This will give you a choice of output transformer at the flick of the switch.

And no, you don't have to terminate the outputs from the LO1166 or the 2503. Just so long as the primaries of the LO1166 are always connected to B283 pins M and B, you'll be in good shape.

And don't forget to change C7 to 220uF.

Peace,

JC

[quote author="rascalseven"]Hi, Brad,

I'm assuming you are talking about the api 2503 (Profile 4804) output transformer. Unfortunately, "brown wire" doesn't tell me enough. I don't know if you mean the positive or negative of the primary (brown is both, depending on which api schematic you look at). For clarification sake let's just assume that brown will be the positive lead of the primary:[/quote]

si, brown wire in the 312 schematic, which shows red and brown, in the 312 signal hot to red signal ground to brown, so I'll just switcheroo what you said below. The rest of your wiring scheme is as the 1:2 output on the 312, could probably use the left over winding as 1:1 for three (count them, three) outputs.

Brown wire to B283 pin F (or 1290 module output pin P)
Red wire to 'B-' (audio ground) which is pin E on the 1290 module output
Connect Yellow and Green wires together
Orange wire to XLR pin 2 (positive)
Blue wire to XLR pin 3 (negative)
XLR pin 1 to chassis

Note that this wires the 2503 in a 1:2 ratio, which gives about 6dB passive gain compared to the LO1166's 4dB, so it'll be a touch louder.

For the switchable output I mentioned above, use a DPDT toggle switch (on-on), connecting XLR pins 2 and 3 to the two poles of the switch. Then wire the positive leads from the LO1166 (pin 5) and 2503 (orange wire) to the positions for pin 2 and the negative leads of each (pin 8 on LO1166 and blue wire on 2503) to the positions for pin 3. This will give you a choice of output transformer at the flick of the switch.

Click to expand...

One from scratch could have four pushbuttons, like the four at the bottom of Tommytones 1081 w/the fourth one on/on: eq, phase, phantom, and API, ha!

And no, you don't have to terminate the outputs from the LO1166 or the 2503. Just so long as the primaries of the LO1166 are always connected to B283 pins M and B, you'll be in good shape.

And don't forget to change C7 to 220uF.

Peace,

JC

Click to expand...

Right, and don't forget to change out the phase switch so you can switch phase on both outputs with the same switch. Okay, so not knowing toooo much about API either, is this the transformer that's been described as "not much" as far as transformers go? Iron core, four windings, 75ohm each, originally a crappy $8 piece? Not to say it doesn't sound good, but it was a cheapo. I think this is the one. Any 1:1 or 1:2 with the right impedance should do fine, I'd think.

Unbalanced, what's the impedance of pin F? <10K? <1000? <100?

Here's Tim Ryan's schematics of the various doo-dads discussed for folks who can't find them--
SCA A12:
http://www.barryrudolph.com/greg/seventhcircle/a12/a12pdfs/io.pdf

N72:
http://www.barryrudolph.com/greg/seventhcircle/n72/n72pdfs/io.pdf

BA283:
http://www.barryrudolph.com/greg/seventhcircle/n72/n72pdfs/ba283-1.pdf

BA283 again:
http://www.barryrudolph.com/greg/seventhcircle/n72/n72pdfs/ba283-2.pdf[/quote]

Quad winding goes up to mega hertz with no phase shift=clean.
cj

[quote author="CJ"]Quad winding goes up to mega hertz with no phase shift=clean.
cj[/quote]

Okay, so Cinemag CMMS-4, 1:1+1+1, mic splitter at 150ohm nominal; Lundahl has 1555 1+1:1+1+1+1, but dats six. And Jensen is three digits $ so, why? (I heard it used to be JE-123 but I don't know if they even make it anymore.) Used API: Do we really want to pay Dan Alexander's electric bill this month for what was once an $8 transformer? SCA's BOM calls their's a Profile 4804. But you've already been there!:

http://vacuumbrain.com/docs/Sub_Docs/api.html

Where'd you guys get those? I started to read the 312 threads but I fouled a sparkplug. Nap for lunch!

K! Nap worked, found it:

http://www.profileelectronics.com/index-2.html

I'd be a lousy research librarian, man.