All things Green Pre

[peterc]

I still have the previous layout (from my  Tripod account that was deleted behind my back) on my old laptop. I will get it asap & post it on Twin-x

Peter

 

[Teije]

I still have the previous layout (from my  Tripod account that was deleted behind my back) on my old laptop. I will get it asap & post it on Twin-x

Peter

thanks a bunch peter. Btw I've having some trouble with twin-x lately. Could it be that the page is down? thanks

 

[Amazed]

If your 2 green leds stay permanently lit.
The answer my friends might be the 20K multiturn trimmer.
Read the setup doc.

Cheers.
(Home stretch now .....)

 

[peterc]

http://web.archive.org/web/20061214092614/http://1176neve.tripod.com/id10.html

 

[Amazed]

Thrilled to announce the arrival of another green pre today.  Easy delivery.  Congratulations to Amazed and grandparents PeterC & Jaycar.
Thanks to everybody that assisted.

 

[peterc]

Natural or caesarian?

 

[Amazed]

Was a natural birth. Just unusually long gestation. ;D ;D
Don't think we'll be having any more though. At least for a while.

 

[gemini86]

"Get the salad spoons, Man!!!!"

 

[PeteC]

quick question

on the Green pre CMRR trim there is a 150pf bypass cap to ground - will it matter if I use 100pf - I have lots of the buggers !!
and I cant locate any 150pf in my stash right now.
cheers
Pete

 

[peterc]

Should be OK

 

[PeteC]

cool thanks

is there a technical explanation ref the 150pf bypass worth knowing ?

PS - I should have the dual finished this weekend - PSU and 1 board complete - just waiting on some 15v zeners - I only had 12v's. 
Cant wait to use it for dual mic'ing my guitar amps etc !!!!

Rgds
PeteC

 

[PeteC]

Hi All,

first channel of my Green Pre up and running - PSU is spot .  I have sound and everything seems to be working OK based on quick rig-up test just now.

But I have some voltage testing questions before I build the second channel board

NB: THIS IS FOR V1 of green pre - I decided I didnt need the extras on V14

Can anyone help verify if my voltages for the green pre V1 are correct ???

Heres what I have

IC 1
Pin 1 : -3.45v
Pin 2 : 12.20v
Pin 3 : 12.20v
Pin 4 : -15.31v
Pin 5 : 12.20v
Pin 6 : 12.20v
Pin 7 : -3.45v
Pin 8 : +14.89v

IC2
Pin 1 : 92mv
Pin 2 : -1.32v
Pin 3 : -1.32v
Pin 4 : -15.35v
Pin 5 : 0v - nothing at all even measured at mv scale.
Pin 6 : 0.6mv
Pin 7 : 2.8mv
Pin 8 : +14.89v

Any help to verify or otherwise would be verify welcomed - I've searched but cant find a voltages document for V1 of the green.

Thanks in advance
PeteC

 

[PeteC]

OK,
for the last few hours I've studied the schematic and the data sheet for the NE5532 and I think my voltages make sense given the circuit - buty as I'm not that experienced I'd love for someone to help me verify if it looks correct.  I am a little suspect about the quality of my BC550C's as I got a job lot pretty cheap - so not 100% confident everything is working 100% yet. 

Can anyone help me out with a voltage reference check for the original Green pre - is there a schematic with voltage reference data on it anywhere etc ?

Many thanks
PeteC

 

[PeteC]

OK,
so I built the second board and Lorlin/gain switch tonight - but not yet powered up by the PSU , and I still have the phantom and In/Out to wire up - so havent been able to compare the quiescent voltages on both boards.
I guess if board 2 is the same voltage readings then I'm good to go ?

Rgds
PeteC

 

[PeteC]

sorry to bump - but can anyone help me check if my green pre voltages are right ?
Its V1 Green Pre circuit.
I'm fine with tube circuits but have limited knowledge around solid state stuff.

So, apologies but want to get these up and running in a rack asap.

Many thanks
Pete

 

[PeteC]

OK,....

so I finished rigging up the second channel of my Dual Green Pre , and took measurements
but only after I'd managed to short the molex pins when testing the PSU - result = 1 fried LM317 - so other newbies - be careful not to short the pins when you do ! If you get a high Phantom voltage ( I got 66v ) then replace the LM317 Reg at the Phantom section as you have just shorted it and its useless.  lesson learned !

I replaced the LM317 and tested voltages on the second channel and everything is within a few millivolts of the first channel so I feel this is spot !!!

now to get hold of some high tolerance 0.1% 100Ohm resistors to set up the CMMR settings.

Then get it in a box and get on with recording my stuff !!!

Cheers
Pete

PS - If anyone wants to chip in on voltages I'd still be grateful

Meanwhile thanks to peterc for a brilliant project,  and Kev's info for inspiring me to have a go at this one. 

 

[Phrazemaster]

Hi gang! I'm still plugging away at my "rainbow" pre - the green of course. I had some great successes; finally got all my relay boards up and running and working, and the power supply seems very stable. I will post more pix of the build later, but really I have a couple pressing questions.

1) Is it OK to have the output from the PSU voltages be: 15.09, 15.40? The combined output of the torroid is 30.5, and I notice these values add to that number. However, just curious if it's ok that the two rails aren't exactly the same voltage?

2) A more pressing concern, I was testing the PSU for stability and accidentally bumped one of the heat sinks with my hand - a light bump. There was a "popping" sound - rather loud actually, and perhaps a flash but I couldn't tell exactly. No smoke, no smell, no blown fuse, and everything was still working. See the inserted image in this post.

I disassembled everthing and performed a visual inspection for damage, melted components, etc - nothing visually wrong whatsoever. And no visible shorts or build problems that I could detect. That kind of "pop" seems like a cap discharge, but there's nothing shorting anywhere that I can see, and "moving" the heatsink slightly back/forth does not put it in contact with any wires or short anything. To MY eye anyway! Do caps ever just discharge if they're bad? Or bumped? There is one big cap that might have been slightly bumped when I bumped the heatsink; should be able to see it in the photo. The heatsink is around it.

I tried powering up again, and...no problem - at all! Strangest thing...the voltages are stable, no smoke, no heat...

Needless to say I'm nervous now. I'm really wondering if I have a spotty component, or if there's something I'm missing.

Can anyone weigh in here - what steps would you take to troubleshoot this? I'm tempted to leave well enough alone because it all seems to be working fine - but I don't want to have a meltdown later or something!

Comments welcome, thanks.

Mike

 

[Phrazemaster]

A couple more photos of the psu, in case it helps...

Note I circled a set of 3 caps that have a triangular formation - I couldn't fit all 3 so the middle one I raised up very high...perhaps stupid? Although you can't tell in the photo, none of the caps are actually touching - there is a few mm between the tops of the 2 lower ones and the bottom of the topmost one...if that makes sense. Is that a no-no? Just didn't have more room for the caps and didn't know how else to put them in...could they arc over and spark if they are in close proximity like this?

I tested the PSU again today, again, no problems, no smoke, no heat...it is "working perfectly" except for the previous incident.

Thx for your insights.

Mike

 

[Harpo]

1) Is it OK to have the output from the PSU voltages be: 15.09, 15.40? The combined output of the torroid is 30.5, and I notice these values add to that number. However, just curious if it's ok that the two rails aren't exactly the same voltage?

No problem, but the numbers don't add up. A transformer is AC voltage. This gets rectified and smoothed to (AC voltage * SQR(2) - 2 diode drops), giving about 42V raw DC between both extremes or + and -21V raw DC when measuring with your meters reference voltage at 0V. This raw DC voltage gets regulated down to +15 and -15 VDC  (+/- parts tolerances) by your voltage regulators.

2) A more pressing concern, I was testing the PSU for stability and accidentally bumped one of the heat sinks with my hand - a light bump. There was a "popping" sound - rather loud actually, and perhaps a flash but I couldn't tell exactly. No smoke, no smell, no blown fuse, and everything was still working. See the inserted image in this post.

The heatsink, applied to the 7815 got in touch with its neighbouring heatsink, applied to the 7915. You seem to have left out the isolation kit for each regulator/heatsink, so the 0V potential at the center pin of the 7815 is conducting to its heatsink and the neg.raw.DC input voltage at the center pin of the 7915 is conducting to the other heatsink. When these heatsinks touch each other, the -21V raw DC rail is shorted out to 0V/the transformers center tap with only a rectifying diode in between. Bang. With a little luck your bridge rectifier survived.
This might happen again when moving your case or it rattles lose on a truck, so get some TO220 isolation kits, mica discs and a little (less is more) heat conducting grease in between.

 

[Phrazemaster]

Thank-you harpo! I will look into the isolation kits; geez there's no end to what one learns! I really appreciate it!

It was a head scratcher for sure, since there was no smell and no visible damage or anything, and it seems to still be working...

The voltages of 15.09 and 15.40 apparently are OK then?

Again, thanks!

Mike