All things Green Pre

[sunyata]

Lars

Sounds like it might be an earth loop.

Keep the mains earth connected and do not connect the signal earth between the pre and sound card.

Also, try isolating the pre signal earth from the mains earth with a 10R resistor.

Peter

Thanks Peter!
Would that be cutting the ground shield on the balanced TRS cable at the sound card end? My Fireface400 has no ground.
Should I replace the signal groundlift with the resistor or in series with the lift switch?

/Lars

 

[peterc]

Lars

Sounds a bit odd that the 400 has no ground, according to this page

http://www.rme-audio.de/en_products_fireface_400.php

the line ins are fully balanced.

I would cut the cable shield at the source end. The resistor would replace the ground lift switch. You could even put the resistor across the switch and have it switchable.

Peter

Lars

Sounds like it might be an earth loop.

Keep the mains earth connected and do not connect the signal earth between the pre and sound card.

Also, try isolating the pre signal earth from the mains earth with a 10R resistor.

Peter

Thanks Peter!
Would that be cutting the ground shield on the balanced TRS cable at the sound card end? My Fireface400 has no ground.
Should I replace the signal groundlift with the resistor or in series with the lift switch?

/Lars

 

[sunyata]

Lars

Sounds a bit odd that the 400 has no ground, according to this page

http://www.rme-audio.de/en_products_fireface_400.php

the line ins are fully balanced.

Yes - but the PSU has no ground.

/Lars

 

[peterc]

Probably grounded via the Firewire cable to the PC which then be grounded via mains earth

Peter

 

[sunyata]

Probably grounded via the Firewire cable to the PC which then be grounded via mains earth

Peter

That is sorted out now. I have another problem. I connected the Green PSU V6a 1-3-7. +/-15 Volts were OK, but the Phantom was close to 80 Volts first, slowly going down, then C15 exploded. How can I solve this?

Best regards
lars

 

[peterc]

Lars

You probably put in an extra stage on the Voltage doubler/tripler. I added an extra stage to the design as some folks were using 15-0-15 transformers and some using 18-0-18v transformers and mains voltage can vary quite wildly.

Take out the third stage and measure the voltage, it should be around 60v and put in a jumper across the missing diode.

Sorry for the hassle.

Peter

 

[Majestic12]

I've drawn the layout again to make pcbs for me, but I don't know how peterc thinks about making some extra boards for you guys.

 

[sunyata]

Lars

You probably put in an extra stage on the Voltage doubler/tripler. I added an extra stage to the design as some folks were using 15-0-15 transformers and some using 18-0-18v transformers and mains voltage can vary quite wildly.

Take out the third stage and measure the voltage, it should be around 60v and put in a jumper across the missing diode.

Sorry for the hassle.

Peter

Thanks!
Would that be D4?

/Lars

 

[peterc]

Yas, check the voltage at the junction of D3 & D4

 

[sunyata]

Yas, check the voltage at the junction of D3 & D4

should I keep C13?
and replace C15 with a 10uF/100V?

And how does LM317 figure out what voltage to put out? (curious)
/Lars

 

[peterc]

Correct, take out C13 and replace C15.

Datasheet gives  VO = 1.25V (1+ R 2/ R1)+IadjR2 

so in our case 1.25(1+(8200/220)=47.84.

Iadj is really tiny so can be ignored

 

[sunyata]

Correct, take out C13 and replace C15.

Datasheet gives  VO = 1.25V (1+ R 2/ R1)+IadjR2 

so in our case 1.25(1+(8200/220)=47.84.

Iadj is really tiny so can be ignored

Thanks! I'll try that.

/Lars

 

[Hammond]

Hi Peter
It has been 5 years since I built my 2 channel green pre, and it worked very well, i love it.
But now it started make a noise on ch 1 only.
Here is the audio file http://www.datafilehost.com/d/6b27e39d
Please can you direct me where start to look for troubles?
Thnaks in advance.

 

[Rockitdog]

I know this is an old thread.

But, does anyone still have the green pre setup files laying around somewhere? (Voltages, setting the LED meter etc...) All the links seem to be broken or old.

Thanks.

 

[wolan42]

Hope this helps.

 

[Rockitdog]

Fantastic!

Thank you! That's exactly what I was looking for.

;D

 

[bigshum]

Hello all,

I have been working my way towards an 8-channel 1U green pre unit.

I’ve started work on the PSU requirements for the project, and have been initially working off the Green Pre design found here;

http://www.lorcan.me/projects/green-mic-preamp/

I have obtained a toroidal transformer, the data sheet for which is here;

http://docs-europe.electrocomponents.com/webdocs/0da0/0900766b80da0cc3.pdf

My questions are as follows;

[list type=decimal]
[*]I see that the PCB layout for this PSU has connections allowing for four channels of preamps. Will this design allow for 8 channels, with the addition of additional connectors?

[*]The transformer I have obtained is 230 input, 2x 15V output at 30VA. Is this sufficient to power 8 channels?

[*]According to the data sheet, I notice that each of the 15V secondary windings has its own 0V wire. The PSU power input connector has 3 connections, two for 15V and one for 0V. Am I correct in saying that I should connect the 0V wires of both secondary windings to the same 0V input on the PSU board?

[*]I will be adding a fuse for additional safety, inside a fuse holder. At which point in the circuit should this fuse come?

[*]What type of fuse is most suitable? Am I right in saying it should be a fast-blow type?
[/list]

Thanks in advance for any help. I rarely post, but scouring the pages for information pertaining to these questions has left me with more questions! And seeming as it’s a matter of mains voltage and potentially safety, I thought it best to ask.

Regards

Alex

 

[peterc]

Hi all

PCBs are available again for a limited period.

http://groupdiy.com/index.php?topic=62900.0

Regards, Peter

 

[Precocyous]

Hi! in the schematics it shows that the circuit needs a little ferrite bead, but I've been days looking for it and defintely I couldn't find it out. But I was wondering, can I use a little 1000uH inductor as used in the Aphex Exiter II instead of that ferrite bead?

http://www.gyraf.dk/schematics/Aphex_Exiter_II.PDF

 

[peterc]

Literally any small ferrite will work in there. They work in the 100kHz and above area.

Peter