Neve 1290 build completed!!

[mitsos]

yes, 1.26A is more than enough for 2 channels.

 

[JoeMorris]

Thanks Mitsos.

 

[Chrome Heart]

Im getting ready to mount the JLM Audio ACDC in the power supply box. Does this get mounted with nylon standoffs?

 

[benlindell]

Yes.

 

[Chrome Heart]

cheers

 

[dribro]

Hi everybody and thanks for this wonderful forum!

I got my first 2 channels up and running and... the 1st is great without any flaws; the second is affected by an audible buzz due to the proximity of the power trafo. I already build an aluminium case, it is much better but still buzzes a little as i rise the gain - specially the last 3 gain stages aren't good.... I also added the jlm gobetween with the oep option - it adds another flavour and i like it.

how can i get off the freaking buzz without building an external box?

best regards,

Adriano

 

[3nity]

I did used a JLM 48V psu as well as the Trex psu..
everything is on the box...the Switching psu as well.

Tell me how you switch input transformers?

 

[Chrome Heart]

The power supply checks out very good. All the voltages are correct (after adjustment) and there is 10ohms resistance between 0v and ground. Ive adjusted to of the 25 turn resistors successfully for 24v and 48v, Im assuming the third 25 turn resistor requires no adjustment?

 

[desol]

No. The third will be your negative rail. Thing is, i think, running the ACDC on the positive rail only, will only give you half-rectification (more ripple). There is a mod to do to it that makes it so you can use the positive rail only at full rectification. There's info on it at the JLM site i think. You should ask Joe, but i'm pretty sure. Also, if i'm not mistaken, you get the full 1.5 amps to the positive rail only, instead of 750ma ea +/-. It's been a while, but i have to do the same thing to the powerstation i'm using to get full amps to just the positive rails at full-rectify.

If you do do the mod's, be careful, don't burn it. Been through that one...a few times.  :

 

[mitsos]

dribro, have you tried removing the toroid, to verify that it is causing the "buzz".. A toroid would normally induce hum, not buzz. Buzz, especially at higher gain, could be oscillation from something else in the circuit. But assuming it's the toroid, try using steel instead of aluminum, it provides a better shield. Silicon steel might be best. Ground it, and make sure it doesn't touch any metal bolt securing the toroid to the case.

 

[geetar_king]

I don't have a board yet. Can anyone tell me which pin on the input 9045 transformer connects to the positive side of C1?  7 or 10? I'm guessing 7.

 

[Chrome Heart]

Geetar, look here at the assembly pdf. It tells you what you need to know.

http://www.groupdiy.com/index.php?topic=22828

 

[Chrome Heart]

Almost finished. All thats left is installing the Carnhills.

 

[desol]

Lookin good man, with the reg's bolted to the wall. Remember, there's alot of DC running through the primary on the 1166, do not short.

 

[madriaanse]

Hi Chrome Heart,

Couple things I noticed on the PSU side.

In the picture it looks like you're running earth to the bottom right hole on the ACDC; it should go to the top right hole. You can verify that you got it right by measuring resistance between case and 0V; it should read 10ohms. Also, if you're going to bolt the regulators to the case, you may want to use nylon screws for the regulators and make sure the drilled holes in the case are burr free.  There should be no continuity between the case and regulators.

You can also remove the negative rail regulator (LM337) since you won't need it.

M.

 

[desol]

That's true. It's actually labelled 'case' above the smiley face.

 

[Chrome Heart]

BTW Martin, good suggestion replacing the screws with nylon, Ill do that. And thanks so much for making this build.

 

[dribro]

thanks mitsos, i'll try what you said. Or maybe i'll leave it on the outside.

 

[penguin]

do i need a choke to use unbalanced out, or is it fine without it ?

 

[haima]

do i need a choke to use unbalanced out, or is it fine without it ?

yes, you need a choke or a output transformer to run this circuit.

an output transformer will be more than happy going into a unbalanced input - and they might be easier to find than the correct value of choke. plus, perhaps "the sounds in the iron" as they say.

if you are running this preamp into a "-10dBV" style unbalanced input you might want to use a 10 or 12db resistive pad on the OUTPUT, after the output transformer to achieve the best signal to noise ratio. but only worry about this if your recordings are sounding overly hissy and you always have to keep the preamp gain switch low to prevent clipping your unbalanced input.