All things Green Pre

[ivan]

Hi people,

i need BOM for the Green Pre and for the Green Power Supply with Mouser and Digikey numbers of parts.

Please send me via email or pm if you have.

!!! BIG THANKS !!!

 

[peterc]

From the META:

http://www.groupdiy.com/index.php?topic=5150
http://www.mendelt.nl/greenpre_V14/

 

[man-bot]

Hello - I am finishing up a 4 channel green pre and everything has been working great up to this point.

Last night I wired in the 3rd channel, and it passed audio and everything worked fine but the metering - but I remembered the LM339 in that channel had been swapped with another channel's LM339 because it was bad (so the one installed was known to be no good).  Popped a new one in and now I get a lot of noise and the the resistors on the attached PDF (thanks Frank) are burning up (with or without the LM339 installed).

Any ideas?

 

[sunyata]

Hello - I am finishing up a 4 channel green pre and everything has been working great up to this point.

Last night I wired in the 3rd channel, and it passed audio and everything worked fine but the metering - but I remembered the LM339 in that channel had been swapped with another channel's LM339 because it was bad (so the one installed was known to be no good).  Popped a new one in and now I get a lot of noise and the the resistors on the attached PDF (thanks Frank) are burning up (with or without the LM339 installed).

Any ideas?

Hi,
I don't know if this will be helpful. I remember when I was trying out different OP's on my green pre, and by mistake put in one in reverse...Ouch!!! Some resistors were glowing....Luckily these were the only ones I had to replace to make it fine again.

/Lars

 

[peterc]

If the resistors are burning up, then there is a short somewhere.

Measure the resistance from the power rails to ground to find it.

Peter

 

[man-bot]

Well oddly enough I switched out the TL074 and everything worked on all channels... great!  Turned it on later on and burning again!!  So there must be something funny of the underside of the board that is causing a short...  not sure why some physical movement of the board would cause this to happen occasionally.

So basically I just following along the power traces and make sure there are no shorts from those burnt components (and all others) to ground?

I'll get on the hunt tonight.

 

[peterc]

If the resistors were smoking I would replace them & also the coupling caps next to them.

Peter

 

[Janus Audio]

Hey Guys,

I finished a pair of Greens a year ago or so. But now finally having a working scope software, I had to discover that one channel has a lot of distortion (K2, K3, K4....) at about -60dB when I feed a 1k sine into it. It's not the channel close to the PSU and I already check the opamp voltages and tried to replace them, but couldn`t get any improvement.

Any ideas?

--Sebastian

 

[peterc]

How do the DC voltages on the IC pins compare between the 2 channels?

 

[Janus Audio]

How do the DC voltages on the IC pins compare between the 2 channels?

All of the voltages with ICs installed and most of the voltages without ICs were pretty close to the voltage chart from the green meta on both channels, except of:

Pin 7 of IC 1 and pin 1 & 2 of IC 2 are -54mV on the malfunctional and 0V on the working channel (without ICs).

Pin 7 of the TL074 has -50mV on the malfuntional channel and +130mV on the working channel, but as it's only metering...

Thanks for your help.

 

[peterc]

Also compare the voltages on the transistor pins.

Peter

 

[Janus Audio]

Finally found the problem: One of the zeners was blown. After replacing it the channel works fine now. 

 

[SmitH]

Hi everyone,
This is my first post. I've been reading this website for about a year. Thats when I started building a Dual Green Pre.
I just finished it. Almost. Thanks to Peter C for the boards.
It works  . The only thing is I can't set the LED meter level with the 100k trimmer. I've spent 4 hours searching the forum but I still can't figure it out.
All the leds work. But the 100k trimmer has no effect at all. I can turn it either way and it won't change anything.
Distortion happens before the red led comes on.

http://s1012.photobucket.com/albums/af242/DIYSMITH/Green%20Pre/?action=view&current=FRONT1.jpg
http://s1012.photobucket.com/albums/af242/DIYSMITH/Green%20Pre/?action=view&current=TOP1.jpg
http://s1012.photobucket.com/albums/af242/DIYSMITH/Green%20Pre/?action=view&current=Channel1.jpg

I've only put the wire link on one of the channels, but both are behaving the same way.
Does anyone have any ideas?
Thanks
- Brenton.

 

[peterc]

Hi Brenton

Check stage by stage.

First check the output of the audio opamp varies with the turning of the 100k trimmer. [Pin 14 of TL074] AC  Volts

Second check that the DC output of the peak detector varies with the turning of the 100k trimmer. [Pin 7 of TL074] DV volts

Third check this DC voltage is getting into the LM339 [Pins 5, 7, 9 & 11]

I see a small issue. Where you have the blue link connected, it should be either/or. Read the docs for a description of whether you need pre or post metering for this.

Regards
Peter

 

[SmitH]

OK. I've looked at the docs. I'm a bit confused.
I want to monitor before the output trim. So I've soldered a wire from the hole above the 20k trimmer to the hole at the right end of the silkscreened link above and left of the 100k.            Does the small silkscreened link above it need to have a wire in it?

anyway...
The 100k trimmer has no effect on pin 14 or pin 7 of the TL074
And there is 3.2volts coming out of pins 5, 7, 9 & 11 of the LM339

 

[peterc]

The 100k trimmer has no effect on pin 14 or pin 7 of the TL074
And there is 3.2volts coming out of pins 5, 7, 9 & 11 of the LM339

Are you running audio through the preamp?

OK. I've looked at the docs. I'm a bit confused. I want to monitor before the output trim. So I've soldered a wire from the hole above the 20k trimmer to the hole at the right end of the silkscreened link above and left of the 100k. Does the small silkscreened link above it need to have a wire in it?

Then take out the blue link, this is for post fader metering.

Peter

 

[kato]

Your output trim knob is hilariously large; I like it!  :thumb:

 

[SmitH]

Sorry for my stupidness. I've figured it out.
I inadvertently plugged the signal generator into the output of the preamp :-X.
It's all working fine now, Sounds great too.

 

[milkus]

Does ANYONE have a complete schematic for the green pre V14? I have one but the parts are different than what is on the PCB layout and it doesn't seem to have any sign of the LED section from the PCB board. Any help with this information would be GREATLY appreciated. THANKS!

 

[peterc]

There are slight differences from the schem to the board, but they are minor.

The LED section is another schematic.

Everything is correct on the PCB & the overlay.

This has been discussed previously, & in the spirit of DIY, has been left as is.

peter