All things Green Pre

[peterc]

Apologies, been a while.

Use a link to bridge the 2 terminals of the pot closest to the switches.

100Hz, 6dB slope

Peter

 

[tomas1808]

Awesome, thanks!

 

[Phrazemaster]

Apparent microphonic effects...

Hi gang, I had microphones plugged into a couple channels of my quad green "Rainbow" pre, and the other unused channels happened to have gain up fairly high. I noticed that the LED's on the channels without the microphones were lighting up in time with the music too!

In fact I can clap my hands with no microphone plugged in, and all channels of the pre seems to hear it...they call this "microphonic" right?

Is this normal, or is there a way to eliminate this? I'm not sure it will really be a problem, but it shouldn't be happening, right? Did I do something wrong?

Thanks,

Mike

 

[Phrazemaster]

Update...ok it's not microphonic; I read up on it and that's only for mechanical vibrations. I realized that with no microhones plugged in, the issue went away.

So obviously we have cross-talk or poor isolation of channels of my 4 boards. Can this be through the DC power lines; they are close to or touching some of the inputs...was kind of tight inside the case despite having a large case...

Any thoughts on how to eliminate this problem?

Thank-you,

Mike

 

[Phrazemaster]

Just wanted to report back...my quad green passes nice, full, clean, quiet audio! Thank-you Peter!!!

About halfway through the session, one of the channels suddenly started a very low hum that increased with increasing gain. It still passes audio, but the hum was loud!

I swapped some of the op-amps and the humming went *mostly* away...any thoughts what could cause something like that? It had been working, and quiet, before that.

Thanks gang; great project!!

Mike

 

[tomas1808]

Another question:

Building a 2 channel green pre with external PSU.

I have been reading about grounding this pre but due to English not being my native language I think Im not getting it completely.

The PSU connector will supply the ground to the individual channel boards. The PSU ground will go to the mains star ground.

Do the circuit and chasis share the same ground? Or are they independent?

Is the "PSU ground" the same ground that "goes" to the preamps?

I feel like an idiot  :-[

 

[peterc]

Tomas

Ground your chassis and PSU ground as close to the PSU connector as you can.

Then use this as a star ground point. Then I would run ground wires from each of the preamp PCBs to this point. I would also connect all the XLR pin 1s to a busbar (if possible) and connect this to the star ground as well.

Peter

 

[tomas1808]

What confuses me is that I am building  a green with an external PSU.

Specifically when it comes to the cable between the Pre and the PSU.

I know I need wires for +15v, -15v and +48v... but I am not sure if I need another two wires for chassis and circuit ground separately or just one wire for both.

In other words, do I need a 4 or a 5 wire cable to connect Pre with PSU?

Thanks for bearing with me 

 

[peterc]

I would think just one wire for the ground.

I have never seen 2 ground wires on gear with  an external supply.

Regards Peter

 

[tomas1808]

Thanks 8)

 

[mdmedia]

I would like to build a two channel version of the Green pre. Since I don not want to self-etch my PCBs,  I am searching for two pieces of the V14. If anyone has some PCBs  left, please let me know.

 

[Shanej]

I second the post above.me. On another note,  about how mich does it cosJt to build one of these? Just curious, ive looked through the forums and cant seem the find a price haha.

 

[amaurythewarrior]

attention fellow DIY-er (is that even proper english ?), i need your help for some ... troubleshooting, what a surprize.

my green was working fine, for one year, but it still didn't have his enclosure. so i had to unsolder the xlr connectors wires (because i didn't have appropriate molex or similar connectors). I took the precaution to take off the ICs ... which, looking back seems kind of excessive. what had to happen, happened, when i put them back on, one of the NE5532 was put the wrong way and instantly fried. it was immediately replaced. i believed it is since that moment that the pre stopped working. all the other ICs are cold to the touch. for some reason i thought something might be wrong with the PSU also that doesn't really make any sense ... the problem is that i ****ed up when trying to measure the tension, and now my multimeter's fuse is done for.

there are more details which i don't think are worth mentioning, but for now my question is simple. is it possible that nearby components have been damaged too ? this was the NE5532 to the right.

i'm kinda stuck without a fuse, i'll have to get a replacement asap anyway ...

 

[amaurythewarrior]

okay so ... someone told me that the psu regulators might have suffered ? and that next i should check the transistors ... only problem is my multimeter doesn't allow that ...

 

[amaurythewarrior]

it seems it might be either the voltage regulators which have suffered, or the input transistors. i'll find out in a few days when i receive my mouser order !

 

[amaurythewarrior]

the PSU voltages seem fine ... but i'm a real catastrophy when measuring tensions, i keep causing shortcircuits ... i don't shake but that's still a big problem.

i've swapped all the transistors and IC ... nothing's changed. what could be next ?

 

[amaurythewarrior]

this must DIY holidays right now ! ^^
i've been through the entire topic, seen a few things i might have to try or examine more closely. but since i have all the parts for a second green, maybe doing it, and getting it to work, and then comparing the working one with the other would be more efficient !

a good thing is that now it's possible to get free shipping from radiospares if ordered on week ends. and quick delivery too, so that i don't feel compelled to order the minimum of 65€ on mouser ...

but i also come to regret not having a more complete multimeter. seems it would make troubleshooting much easier !

 

[amaurythewarrior]

i don't know if anyone is still following this thread these days, but never mind, i'll post !
i've measured the tensions for the ICs, but i forgot that i had to disconnect the lorlin. however it was at max gain.
i can't have precise readings with my analog meter, but everything seemed in order. pretty damn close.

can i deduce that the problem lies after the NE5532 ? by the way, is there a schematic for v14 ? or is the only difference the metering section ?

 

[amaurythewarrior]

oops, there's been something wrong with my last message ...

so, i meant to say that it's finally working again. the culprit were my poor wiring and a xlr cable i should have replaced long ago. but it's not working "well" yet.
i have some pretty random distortion which occurs ...

http://soundcloud.com/amaurythewarrior/green-mic-pre-distortion

distortion and rather low volume ... in the example, both the gain and output trim are cranked all the way up !

previously in this topic, i found that somebody had at least a similar problem and traced its origin to one of the BC550. couldn't find the final word on the matter though ...
anyway all transistor have been swapped, no improvement
i am using a jack connector to go directly into my soundcard's line in, could this have anything to do with my problem ?

 

[Enchilada]

I've been searching for a few days now and I can't find anyone who is doing V14 Green Pre PCBs. So is self etch the only option? I have no real issue with self etching and only ever etch my own PCBs when I build microphones but for preamps I much prefer working on professionally manufactured preamps. Also, I'll be building at least 8 channels of Green Preamps and self etching gets a little cumbersome after a while.

Does anyone have a gerber handy for the V14 PCB? I might get a run of them made and surely I could offload what I don't use here.