All things Green Pre

[Freq Band]

[quote author="Freq Band"]
3 QUESTIONS while I'm here....

1) Regarding the Voltage Check doc.....it says to check IC#1 with no NE5532, then with it installed.....but do I leave #1 installed when going on to IC#2, leave #2 in, and go to #3 ?....in order?.....or is there no real order, and each IC voltage check is not dependant on there being other IC's installed?

2) I have built a seperate +48v PSU.
http://members.aol.com/ecc81/ps48.html
Should there be any ground connected to that. If so, where to where ? (transformer has no ground leg on the Primary)

3) (nevermind, found answer)
----------------
=FB=[/quote]

I still wonder about the above Q's ?

Also new Q:

My first voltage check (no IC's, all empty) resulted in skewed #s...here they are :

IC#1:
SHOULD BE NEAR:............WHAT I HAVE:
1) 0v...................................2.09v
2) 14.8................................12.9
3) 12.2................................11.87
4) -15.2.............................. -14.5
5) 12.2................................11.9
6) 14.8................................13.8
7) 0.07................................5.7
8) 14.8................................14.5

IC#2:
1) 0.07................................5.7
2) 0.07................................5.7
3) the rest are ok.

IC#3
all ok.

Meters' led's are all lit.

Same results for both boards.


Could it be I have the (bc550/560) transistors backwards? I'm using the NTE123AP cross ref. part here. The data sheet for these is VERY unclear as to pin assignments. I cannot tell if the NTE diagram is a front/top view or....See here:
http://www.nteinc.com/graphics/diag9a.gif


I could not locate the bc550/560 parts....but I do have some 2N3904/3906 parts laying about..???

help greatly appreciated !!! Thx

=FB=

 

[enthalpystudios]

So.... I don't have a scope, so i'm using my fluke to setup. I've got a 100hz tone coming into the 2 100r resistors to set the CMRR, and the DMM is measuring 1.04v ac rms.

I get to pin 1 of the middle 5532 and ground (using that handy jumper ;] and the 1k trimpot is only getting me between 180 and 190 mv RMS.

voltages with IC's out are very close to the voltages Document.

Also, as I feel like handling the op amps may have caused me problems, is there a good way to determine whether or not an opamp is fried???

I definitely had the lm339 and the tl074 backwards on the first powerup

(which may be your problem, freq band, as it caused all of my LED's to light up.


Thanks, if anyone has any ideas.

billy

 

[enthalpystudios]

Well, all voltages with IC's in are all 0v.

BUT... I have the gain switch connected.

Still, I have a feeling they're fried, aren't they?


Well, gotta go see a movie, maybe somebody'll have popped when I get back.

Thanks,

billy

 

[peterc]

Are both of you guys getting any audio through?

Peter

 

[enthalpystudios]

before I posted 0v with IC's in, I had very distorted audio

all out clipped I would say.

I'm just about to try new IC's, as my voltages without IC's are very very close to those in your voltages text file.

thanks

billy

 

[jeroddumas]

I want to bypass the hpf on my pre. do I put the jumper between the first two pins or the last 2?

 

[enthalpystudios]

LIft off!

First, I had all clipping audio and crap noise due to the backwards tl074..... when I went back to check and found 0v on everything, I realized that alligator clip on the 0v jumper had shorted with the 48v switch. blown fuse.


duh.


so, I'm passing some very clean, beautiful audio at this point. Thanks so much peter, and everyone whos had problems I didnt have to repeat.

One thing bugging me... I'm definitely getting around 72 volts of phantom. coming out of the PSU. Any ideas?


thanks again!

billy

 

[peterc]

I realized that alligator clip on the 0v jumper had shorted with the 48v switch.

Sounds like the 48v LM317 is blown. It does so when shorted......

Peter

 

[enthalpystudios]

had a feeling that was it. it wasn't warm either... that kind of gave it away for me


billy

 

[enthalpystudios]

what, btw, will happen to mic with ~72 volts on phantom? i was testing with a 421 (which sounded awfully nice, btw) so it wasn't an issue, but out of curiosity i'm wondering what the tolerance of microphones is (generally)

billy

 

[Freq Band]

Yes, my substitute transistors were in backwards....turns out the euro type t's (BCxxx) most often have Collector and Emitter positions switched from the american type (2Nxxxx, NTE, & others).
Add to that, my lack of experience in reading a line drawing on the NTE datasheet...e.g. - I was supposed to "already know" that those NTE drawings are depicting the "front (flat)" view of the part. Most other datasheets I read all have a 3-d view of their parts. Oh well.

As I needed to pull and reverse these parts, I instead used two new 2N5809 (for the BC550)...lower voltage parts, but still 100ma. All voltage checks came out perfect. I'll hook up a signal tomorrow, to be sure.

Pay no attention to my other questions (all worked out)......
.......except my diy phantom 48v PSU - grounding......

http://members.aol.com/ecc81/ps48.html (48v PSU)
Does this wiring seem right ?:

Two 115v ac wires to tranny (with 1.5a fuse),,,,
+ 48v wire to greens, 0v (ground) to the star ground.

??

-=FB=-

 

[Flatpicker]

Well, my anal self finally reached a limit dealing with the discrepancies between the Green Pre schematic and the V14 printed circuit board, so I drew up a new schematic based on the V14 board. Since the board silk screen shows no referenced designators, I decided it was useless to include them on the schematic, so I left then off of there as well. Only the part values remain. I am also putting together a Mouser/ Digikey BOM (hopefully forthcoming in the not-to-distant future) for those that want to brave the waters of ordering their own parts.

Beware that even though I?ve double checked this, there could still be errors, so I?d appreciated it if others would take a look and let me know if you find any. Here?s the link:
http://mywebpages.comcast.net/tamron1958/Green_Schematic_V14.pdf

 

[BladeSG]

I haven't finished my greens yet, but I think it's supposed to have +/-15V. You have it down as +/-18V....?

 

[Flatpicker]

Thanks. It'll run on +/-18V, but I meant to put +/- 15V since that's where most folks are running them. I'll add it to the "fix" list.

A schematic for the meter section is coming soon. I found a few discrepancies there as well.

Haven't looked at the PSU yet...

 

[Flatpicker]

Ok, here's the schematic for the meter section. Looks like the V14 board uses extra filtering for the TL074 and LM339, hence the "+/-15V" to "+/-V" conversion. Don't know if this was accidental or on purpose, but it's there.

http://mywebpages.comcast.net/tamron1958/Green_Schematic_Meter_V14.pdf

Again, I've triple checked this but please let me know if you see anything I overlooked.

Edit: I found and corrected an error where the LM339 power supply pins were incorrect. The original schematic had pin 3 connected to "-V" and pin 12 connected to "+V". In reality, pin 3 connects to "+V" and pin 12 connects to ground.

 

[peterc]

Tim

Check the resistor attached to the 20k trimmer, shown as 10R on your drawing, should be 10k.

Peter

 

[Flatpicker]

Got it. Thanks!

 

[BladeSG]

[quote author="Flatpicker"]Thanks. It'll run on +/-18V, but I meant to put +/- 15V since that's where most folks are running them. [/quote]

Is there an advantage to run it at +/-18V?

 

[Flatpicker]

[quote author="BladeSG"]Is there an advantage to run it at +/-18V?[/quote]More head room.

 

[BladeSG]

Thanks Flatpicker.