All things Green Pre

[peterc]

Peter

Sent you an email.

 

[Nadege]

My green pre is slowly dying !!!!  :'(

I build a quad green pre 2 years ago, I didn't used it a lot due to studio changes... But I really like the sound of it .

Some months ago, the first channel died ! The 10r psu decoupling resistor located just under the pads for the gain switch burned (litterraly) as did the the first 10r resistor just above the first IC, and the NE5532 on it's left (the first one) also burned, the IC socket is totally melted!!

I thought I made something wrong and as I didn't had much free time and didn't need 4 preamps, I just disconnected the first preamp PSU and keep the 3 others. But yesterday, the second one burned the exact same way, after 3 weeks of intense use!

I'm betting the other two will die the same way in the next future... :'( :'( :'(

I already checked my voltage (fine), and replaced the two burned resistor, placed a new socket and a new IC, but they burned after a few minutes...

Do you guys have any idea of what's going on ?

Everything was fine for some months, and now... the pre is dying... :'(

 

[Nadege]

Ok

here is a picture of my unit

http://twin-x.com/groupdiy/displayimage.php?pos=-523

and here is where are the burned component located

http://twin-x.com/groupdiy/displayimage.php?pos=-3200

 

[Nadege]

Any idea ?

 

[peterc]

Nadege

For resistors to burn out like that, it sounds almost like there is a dead short from the resistor to ground. Check the coupling caps for shorts, as they go to ground, make sure they are 105 degC rated heat wise. Check the IC socket & preferably use a tulip style socket.

I would also recommend replacing the transistors in the input stage as they can go noisy if the first opamp fails.

Also check the zener diodes, if they have failed, replace with 5w units.

Do you switch your unit off when not in use? The 5532s can run fairly warm, so turning off at night  will help with heat build up

Hope this helps
Peter

 

[Nadege]

Peter,

thanks for the answer, I'll check for short and replace the ic socket with better one.

I always turn off my gear at night . otherwise it's getting way too hot and my electricity bill raise way too much ;-)

 

[Rocket Roll]

Howdy! Started a two-channel Green, and my first conundrum would be: which 22pF capacitors to use? I can choose between ceramic discs (brown and round) or multilayer ceramic (yellow chiclet). In case that I don't find something nicer, would any one of these be OK?

My second conundrum would be: how strong toroidal transformer to use for two channels? I'll have it custom-wound and I was wondering if 500mA would be OK for two channels (I'd like it to work as cool as possible but not be very big).

Thanks in advance!

 

[peterc]

Hi Rocket

Welcome to the forum.

Before answering your questions, I'd like to point you at a couple of threads:

http://www.groupdiy.com/index.php?topic=16013.0
http://www.groupdiy.com/index.php?topic=33355.0

The 22pF di-electric does not seem to make much difference, I personally use COG/NPO ceramics (they seem to have a black spot on the top, in my experience), but I have used other ceramics & polystyrenes with no change in sound.

Allow about 5VA per channel (50mA per rail) when calculating transformer size.

If you were to type in 22pF into the seach box, you will find this thread at the to of your list:

http://www.groupdiy.com/index.php?topic=8080

Please dont feel put out by this post, but realise that there is a LOT of info here, and newbies are encouraged to read as much as possible before asking questions that may have been answered, sometimes many times in the past.

Regards
Peter

 

[michal_k]

Quick question. Just fired up a "new green PSU" for the first time. I've had an electrolityc cap exploded, replaced with another one and I measured voltages. Now what bugs me a bit is that all of them are steadily floating around +-15 and 48 through ~0.1. Thing is I dont know what causes this kind of voltage swing and I don't have a scope at my place and I won't be at my university this week anymore so I figured out I ask here if any of you had similar problem before.

 

[peterc]

Is there a load on the PSU? They need to be supplying current to work properly.

Not quite sure what you mean by "steadily floating around +-15 and 48 through ~0.1", your DC voltage is not 100%stable?

Regards
Peter

 

[michal_k]

I tried it unloaded and with load. Yes, it's unstable in a range of about 0.1V in both cases and a period is about 2-3 seconds. I'll try to replace regulators for +-15V and report if it helps.

 

[slowbass]

Hello !
I've finished one dual green preamp and I have another buzz problem (computer noise ? starting at about 650 Hz) when I plug a microphone into the preamp (both channels act the same way) but the buzz disappear when I connect the input of the preamp to the output of my soundcard or when I leave the input unconnected. I've tried different microphones but the same noise occurs. All the other features seem to work fine.

After connecting the earth and the PSU ground to a single point (star ground), I've tried different things I've found on the forum :
- connect the xlr pin 1 inputs to the chassis with or without the xlr pin 1 output connected to the chassis
- connect the in and out xlr pins 1 to the "star ground" via a cable
- moving the PSu and the transfo out of the box

The buzz quieten when I touch the switches on the front panel...

Do you have any idea where does that could come from ? Thanks !

 

[peterc]

Sounds like a ground problem, is there a ground connection between the preamp & your desk/computer interface?

 

[slowbass]

No, there's no ground connection between the preamp and my computer/audio interface.
In fact, I had the same noise with a compressor I've built before but when I soldered the xlr input pin 1 to the chassis, it vanished... but it wasn't connected to a microphone...

 

[peterc]

No, there's no ground connection between the preamp and my computer/audio interface.

Try making this connection as the preamp might be floating relative to the comp/interface.

Peter

 

[slowbass]

I don't know how to ? I've tried to connect the in and out xlr's 1 and then to the star ground with no effect...
When I touch the chassis, the buzz stops now...

 

[peterc]

Is the mains earth on the Green connected?

 

[slowbass]

Yes, it is.
Thanks for the quick answers, btw.

 

[peterc]

In the cable connecting the pre to the comp, does a wire connect pin 1 in the male XLR to pin 1 in the female XLR?

I am asking these kinds of questions because I have found that in the past, if a buzz disappears when touched by a finger or body, it is because the preamp (in this case) does not have a  ground point in common with the computer (in this case). When you touch it, YOU are providing the ground.....

Peter

 

[slowbass]

In fact I have a firewire interface with balanced inputs so I use a balanced xlr/trs cable.
The buzz doesn't totally stop when I touch the box...

EDIT : I replaced the electric cable and the noise has nearly vanished ! you were right about the main earth, maybe the old wire had a problem or didn't fit with the plug in socket (?) Thanks again !