All things Green Pre

[Phrazemaster]

Hi Peter and Harpo, thanks for the hints.

So IC 5 voltages look fine without the IC's; what about the other voltages that look off? I'm reattaching the voltage chart here. The ones in red are out from your specs Peter.

For example in IC's 1 & 2: in 2 of my boards the voltages drop, drop, drop over time; in the other 2 they don't. And in IC 2 those voltages are significantly different than yours - 3.5v vs .07v for pins 1 and 2. Later when I measured the same pins they were around 4.4v and dropping...shouldn't I be concerned about that and the other voltages that are way out in IC 4 as well? Doesn't the dropping indicate a bad cap or something?

I am going to test the caps with my cap meter when it comes (supposedly in a day or 2).

I know it's a PITA to look over others' work, so thanks in advance. I'm willing to do the work myself too, and I am! But any hints from the gods are most welcome.

Thanks a lot,

Mike

 

[Phrazemaster]

Hi gang, wanted to report back...I'm still having problems with my 4 channel greens. I followed the advice to go ahead and stuff in the IC's even though my voltages were off in some places, but I'm not able to set CMRR on one board at all (turning the trim pot has no effect at all on the scope waveform)- and all the boards have voltages off when the IC's are inserted as well! The funny thing is, all 4 boards have pretty much the SAME wrong voltages - can't figure that one out!

Here's my voltages on one channel (first number is the reference from Peter). Asterisks to make it easy to see wrong voltages.

Note that I've already replaced all transistors and zeners, which had basically no effect on voltage levels. Anyone point me in the right direction? I hate to replace things part by part, but if I must, I will...


IC 1 (No NE5532)
Pin Ref    My Values
1 0   0
2 14.8   15.08
3 12.2   12.35
4 -15.2  -15.26
5 12.2   12.35
6 14.8   15.08
7 0.07   3.6v and dropping ***What would cause the falling voltages? Bad cap or two?
8 14.8   15.09

With NE5532
1 -3.34 14.05 *** Whoa! That's a 17v difference!
2 12.08 13.58
3 12.08 12.85
4 -15.1 -15.17
5 12.08 12.84
6 12.08 12.9
7 -3.34 2.234 *** 5v difference!
8 14.7       14.97

IC 2 (No NE5532)
Pin
1 0.07       3.5 and dropping***
2 0.07       3.45 and dropping***
3 0       0
4 -15.2    -15.26
5 0       0
6 0.01     -0.005
7 0.01     -0.005
8 14.8       15.1

With NE5532
1 -0.11 7.57 *** Yikes!
2 -1.4       5.44 *** hmm
3 -1.4       5.44 *** "
4 -15.1    -15.18
5 -0.01    -0.006
6 -0.01    -0.007
7 0     -0.006
8 14.7       15.01

IC 3 (No NE5532)
Pin
1 0.11       0
2 0.11       0
3 0       0
4 -15.2    -15.26
5 0       0
6 0.05       0
7 0.05       0
8 14.8     15.1

With NE5532
1 0.004 0.003
2 0.001 0
3 0         0
4 -15       -15.17
5 0         0
6 0         0
7 0.001 0.002
8 14.8       15.02

IC 4 (No TL074)
Pin
1 0.4       -0.004 *** .4v diff
2 0.5       -0.007 *** .5v diff
3 0       0
4 15       15.02
5 0       0
6 0.5     -0.007 *** .5v diff
7 0.4     -0.005 *** .4v diff
8 0       0
9 0       0
10 0.5     -0.007 *** .5v diff
11 -15     -15.2
12 0       0
13 0       0
14 0       0

IC 5 (No LM339)
Pin
1 -13.1 -13.3
2 -11.2 -11.43
3 15         15.01
4 1.2         1.051 *** .15v diff
5 0         0
6 12       10.47 *** 1.5v diff
7 0         0
8 0.012 0.011
9 0         0
10 0.12         0.105
11 0         0
12 -15     -15.2
13 -9.5     -9.53
14 -7.5     -7.64


So, O Knowledgeable Ones, short of this newbie randomly replacing the capacitors (what's left to replace that would create dropping voltages?), where should I look next?

Thanks,

Mike

 

[Phrazemaster]

OK, in the interest of proactivity and DIY I have replaced also the 22uF caps, the three 47uF 63v caps, and one other in the section near the first IC with the crazy dropping voltages on Pin 7 which then propagate to pins 1-2 of IC2. This because I could only imagine a bad cap might give rise to falling voltages if the dialectric was leaky/bad.

Still no joy! Voltages drop starting around 4v or 3.5v, then continuously fall on IC 1 Pin 7, which then affects pins 1-2 of IC2. This without the NE5532 installed.

I really don't want to replace all the caps on the board, and it seems to be some issue that starts near IC1 and then propagates (that's my theory at this point).

Can anyone suggest the next place to look? Remember, I also replaced all 4 zeners and all the transistors as well. My boards are fairly clean; my soldering is fairly good. I'm just working with 1 board to begin with (all 4 boards have the same strange behavior).

Thanks for any help,

Mike

 

[Phrazemaster]

Well I spoke too quickly...for once a positive note to that phrase!

Even though I still have the dropping voltages with no IC's installed, I just thought what the heck let me put in the NE5532's and check the voltages after replacing all the caps and transistors and zeners I mentioned in my previous post.

Voila! All voltages are basically in range! Hmm, the caps I took out were the expensive Elma Silmic II's, and I replaced them all with Nichicon HE's, 47uF 100v - even the 22uF caps! I figured more capacitance and voltage can't hurt, and apparently, I was right! Wow...

So have others had bad experiences with the Elma Silmic's? Since I don't have a proper cap tester yet, no way to know which one was bad...I used the Nichicon HE's from a thread where Jim Williams recommended them, and I had some extras from building the PSU...hope it sounds good!

I still need to try to set CMRR and the other setups; I'll post back here again with results.

Again, though I have to say - the other THREE boards all have the "bad" voltages using the Elma Silmic's, which I will also replace  soon (have an order coming in from Digikey).

Thanks gang,

Mike

 

[Phrazemaster]

Well ladies and germs...I'm the happy proud father of a working channel of Green! I was able to callibrate everything correctly; have not yet done the acid test of using a microphone with it yet but I will soon. Using my eBay oscilloscope man!!

I still have the other 3 boards that I need to replace the caps on - I'm assuming that's what was wrong with the first board, since changing the caps resulted in the board working. (again, all expensive Elma Silmic II's...tsk tsk tsk!!)

I'll post back on my progress when I get the new caps in, but this will be in a week or so (on order from digikey).

It's been 5 freakin' years you guys! I know that's a helluva snail pace, but I want to thank-you guys for the incredible support!

PeterC - you're awesome dude! Genius; great project!

Matta - the best; your posts have kept me goin' man!

PRR and Harpo...and Tin Man and Auntie Em...lol thanks everyone for the help and encouragement!

GREAT project!!

And by the way, any newbies reading this - it IS a gift when the board is silent - it puts the Y back in DIY!!!

Cheers,

Mike!

 

[Phrazemaster]

Hey gang, I realize I'm the last comic standing as far as building these greens (really is ANYONE reading this thread anymore?)...

But, I ran into an issue while checking phantom voltages...

Even with the phantom switch OFF I still get 48 v on the mic input (either pin to ground). The voltage drops VERY slowly (47.9, 47.8,...) over time, and with phantom turned on, it stays rock solid at 48.3v.

So...is this normal? I checked 2 of my boards and they both do this...I would have expected to read no DC volts with phantom disengaged.

Also while testing the phantom I accidentally touched pin 3 to ground pin and sparked on both boards! I'm going to replace the zeners just to be sure there's no problem just in case - anything else I should replace while I'm at it?

Thank-you.

Mike

 

[peterc]

So...is this normal?

Yes. With no mic plugged in, the 48v takes quite a while to discharge, plug in a mic, and it discharges a lot quicker.

Check for noise after replacing the zeners.

Peter

 

[Phrazemaster]

Thank-you Peter!

Check for noise aurally...as in try it out and see how it is, or is there a test bench method? Sorry to be lame!

 

[peterc]

The Green design is VERY quiet, so if there is any extraneous noise it should be easily apparent.

Peter

 

[Phrazemaster]

Thank-you kind sir.

 

[Phrazemaster]

After much ado, I'm happy to report 4 working channels of Green! I will be testing them in my studio over the next couple weeks and will report back. All respond as expected to mic input, and I'll know more after actual recording.

Thanks to everyone who contributed, especially you Peter! What a great project...HUGE learning curve for a total newbie but...awesome!

Mike

 

[peterc]

Good one! Hanging pays off....

Now for some fun. Get to know the sound of the pre, and in a couple of weeks time, try some 2604s in the IC positions.

Peter

 

[Phrazemaster]

Thanks Peter!

Actually as it is 4 channels, I first used NE5532's to calibrate all the channels and make sure they were all able to pass your 3 settings.

Then I took channels 2-4 and changed the 5532 IC's. So this is what I currently have:

Channel 1: NE5532's

Channel 2: OPA2134's

Channel 3: AD825's (had to use a Brown Dog adapter and solder 2 of those suckers onto each one to make dual op amps...)

Channel 4: OPA2604's

So...I know it would have been better to wait and test all 4 channels with the 5532's to begin with...but...I couldn't wait! I want to compare the flavors and then settle on which chips I like best...I'll be glad to report back my opinions here...

Funnily enough, I went to recalibrate each channel after changing the IC's but the calibrations held from the original 5532's...guess changing them didn't affect the calibrations at all!

I did plug in a mic and check each channel and all lights vary as expected but...heh heh, a real test is needed asap!

Thanks again Peter!

Mike

 

[Phrazemaster]

Hi Peter and gang,

I thought I would post some thoughts about what I learned doing the Green. I'm sure many of you could add your own ideas to this! Let me start it, and please chime in.

Peter, maybe this should be a separate thread? I think it's a great idea!

What I Learned Doing the Green...

1. Connectors can be the most expensive part of a project. By far eclipsing even premium components!

2. There is no need to solder AND crimp connectors. Really. They make the project several orders of magnitude more frustrating and time-consuming, and a good crimp is a good connection. Or just solder everything if you must

3. When the board answers a direct question, it’s a gift. When the board doesn’t answer a direct question, it’s also a gift. There’s this thing called Google, and books, and the person you become by solving problems on your own is of by far more worth than whatever cool project you managed to build. Even if it doesn’t work

4. The person you become as a result of doing your DIY is way cooler than whatever project you may happen to come up with or build. I said this in 3, but it deserves another mention.

5. Have the courage to do things over if you’re not totally happy with it. Doing it right is worth it, and you’ll be a lot prouder of it in the end. After all, that’s why you bought “10” of all components anyway!

6. Listen to PRR. Lol!

7. You can do any project you set your mind to. Really.

 

[isophase]

Well done Prazemaster !
so whats your next project ;-)

 

[Phrazemaster]

Thanks isophase!

I have some kits from Seventh Circle Audio and Sound Skulptor...these should be cake compared to the Green! Paint by numbers lol!

What about you; what are you working on?

 

[isophase]

just finished studer 169EQ, havn't had a chance to try out my quad green preamp properly yet.. i have recording session programmed soon so will try it in real conditions.
all the best

 

[tomas1808]

Hello GroupDIY,

Just finished my first Green Pre. I skipped the "output trim" and the meter section.

Should I replace it with a wire or should I put a fixed resistor? I think I hear a slight distortion when replacing in with a wire, but maybe I'm just going crazy.

Also, does anyone know what the cutoff frequency is for the HPF?


Thanks!

 

[peterc]

Can you be more specific? There is no output trim on the preamp.....

Pics of the PCB, maybe?

Peter

 

[tomas1808]

Hmm, maybe I am using the wrong terminology?

I am talking about this:

http://i.imgur.com/5Xhqk.jpg


BTW thanks for this awesome project Peter