Lowfreq

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« on: September 11, 2005, 09:30:26 PM »
Hi all

Just wondering if anyone can help me with this. I've been putting togther a stereo green pre over the weekend, and seem to have run into a couple of things i'm a little stuck on. It's the older version using the power supply done by kev at this page.
   http://www.diyfactory.com/projects/green/green.htm

Now I've been pretty good with my grounding (all at the same point etc) and for the most part the pre works great (got one going, just doin the rotary switch on the other one).

Anyways, here's the deal. When i use a dynamic mic (sm58), or have no mic and no phantom power, i seem to get a slight buzz (not as strong or deep sounding as and unearthed buzz). But when I plug a condensor in and switch on the phantom the buzz dissapears. If I have the phantom on while the sm58 is plugged in, I get the same buzz as when phantom is off.
Also if i'm using a condensor and switch the phantom off, everything goes dead silent for a few seconds, but then the condensor seems to come alive(well in a half ass kinda way) again, along with the familiar buzz :?

The other question I have (mainly for Kev, but anyone who knows) is to do with the power supply he designed. It's all working great, voltages are good, both of the 15v's and the 48v. There are seven terminals on the PSU, 2 for the LED, 2 for the +&-15v, 1 for ground, 1 for 48v.
The last one on the end next to the 48v, Whats that one for??? After trying to zoom in on some pics on kevs sight and also a couple of other peoples project pics, I can't seem to see clearly enough if anything is connected to it.
When testing with my meter, it seems work like another ground, but if i connect it anything else I get a lovely earth hum(apart from connecting it to the +48v, which i get a very pretty spark)
Is my curcuit not completed or something? I've been racking my brains all weekend over this one(still a newbie, not too smart :wink: ) and not had much luck. Did a search, and looked at the metas, found similar stuff, but not quite the same as my prob.

Anyways, I'm unsure if the phantom prob is to do with that last unused terminal on the PSU, or if i've got issues on the pre itself (i've checked everything with the meter a couple of times, and i'm sure componets are correct.)

If i was just gonna use condensors with the pre (as Matt is) then I prob wouldn't care, but I actually liked the sound of the sm58 on my voice through this thing (sounded clear & gritty at the same time :roll: hard to explain), and would be keen to rid myself of the buzz.

Any ideas or help would be soooooooooo apreciated as my limited knowledge has reached it's peak :oops:

regards

Steve


Kev

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #1 on: September 12, 2005, 03:42:43 AM »
yep just another gnd (0v) connection
you probably will get an earth loop if you use both.
that was for other units that might have an input trafo and so may need the two connections for phantom

0V(48) /  +48V / -15V / 0V / +15 / 0V(LED) / +V(LED)

do you have another dynamic mic to test  ?
it is possible it is a mic to lead to micpre case/gnd/sheild thingo

change mic
change lead

does mic lead join pin 1 and the case of the XL3 ?

just for the record most of my boxes do not have pin 1 and chassis joined.
I tend to rely on the fully floating diff input to common reject for me
So when I say 0 volts I mean it ... not ground.

On my Green I have the earth of the IEC power straight to chassis.
And
the rest of the internals don't connect to earth.
YES
many eyebrows just went up and many are screaming ... what a load of crap.
 :roll:
but you get that

...

and I use alluminuim boxes
people tell me my boxes should HUM like hell.

tell me more about your grounding
Kev
DIY Factory

matta

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #2 on: September 12, 2005, 10:07:36 AM »
Hmmm,

Firstly check your Audio Inputs and that they are wired correctly and not
shorting in anyway way, check for cold joints etc. Also what you describe
can be symptomatic of your dynamic mics being too close to a magnetic field,
i.e a PC CRT monitor, which will can give you hum on dynamic mic, but which
is not prone to happen on condenser mics.

What is confusing is the fact you phantom mic passes audio with no
phantom.... This shouldn?t happen, unless it is a  battery operated mic as
well like a C1000 or Rode NT3 etc.

Report back and let us know what you find. Also check your input/output
molex plugs and that they are properly connected, I had a similar hum on
one of mine and it turned out to be a bad connection on the input molex.

Cheers

Matt
Matt Allison
www.matt-allison.com

Quote
We are not going to start thinking of ways to get an octopus to commit a crime, cause that just has failure written all over it – Earl J Hickey

peterc

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #3 on: September 12, 2005, 03:21:04 PM »
Lost.... :?

As Matt said, try different mic & cable.

Sorry, not much help.

Peter
If opportunity doesn't knock, build a door.

Lowfreq

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #4 on: September 12, 2005, 05:41:00 PM »
Cheers guys,

Yep Kev, I did get a pretty bad earth loop when i connected up that last terminal. Good to know i can stop worrying about that one :grin:

I need to catch up with my mate who has my b*eta57a so I can try a diferent mic too. Cables I have pleanty of.

Only the IEC grounded Kev? I didn't try that one. I did try lots of combonations though, like only the PSU grounded, or only pin 1 on the input xlr etc. I did a search on grounding and the whole "star grounding" thing came up the most.
I ended up pretty much groundin nearly everything, as each time I did the sound got a little cleaner and the buzz got slightly less. So I've got xlr 1 in, xlr 1 out, ground on the psu, and the IEC all going driectly to a point near the IEC inlet, and all connected witht those little round thingy's (mmm, real professional sounding there, steve :wink: ) so they can all be bolted into the same place. I'm using a Jaycar case, and I made sure that I grinded the paint off it at that point to get a good contact there.
(those jaycar cases are pretty fiddly with those extra support pieces and everything :evil: ...is that why you don't use em Kev?)

Matt, the CRT monitor was something I thought about too. I tried turning my monitor off, and that didn't seem to help much. But the preamp is sitting pretty much directly under it. I might try moving the pre to another part of the room to see what happens. I pulled the sm58 away from the monitor too, but i really need to place it another room, with someone else testing it for me. (besides, my noisey fan on my computer can get in the way of listening for noises)

I set up the second pre last night to try and compare (still waiting on some 5532's to arrive from RS, so i've only got enough to get one pre going at a time), but after a busy evening I only had a short time to work with, and when I tested it (at around 1:30am) I found that I had a bad output joint and the whole thing was distorting pretty bad!! :twisted: And i was too tired to go back downstairs and redo it. :musique:  I did test the phantom on the second pre, and it did a similar thing to the first one(phantom going even when switched off), but nowhere as bad as the first pre.

I think I need to do another component check to make sure i've got all my values correct. I've pretty much eliminated the PSU as a prob tho, as that seems all good.

Thanks again guys, for your ideas and advice on this one. One good thing about all these problems is that I've learn't quite a bit more about how things actually work. My JLM99v went together first pop, which was great!! but I still had no idea of how it worked......... :wink:  you live & learn.

I'm determined to get this little bugger working properly :thumb:  :thumb:

regards

Steve

Kev

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #5 on: September 13, 2005, 08:23:06 AM »
Quote
Only the IEC grounded Kev?

yep
imagine it is all on the bench without a box around it
the IEC send AC to the power trafo
+48/+15/0/-15 comes off the power supply board
and then enters the two green mic-pres

shield / hot and cold comes from Mic
shield/ hot and cold goes to destination

the destination may be grounded via the shield.

The rest floats ... most of my stuff is like this when inside an aluminium box.
(The G9 did have a full ground set-up but not much else from me on the various pages)

(those jaycar cases ...is that why you don't use em Kev?)
nope
more about the fact I have been using Elgee cases from the year dot
I even seen the company change hands in the time I've been using and recycling the same cases and parts.
It has been a very stable product supply ... and for me ... cheap.
 
I was with [email protected] today discussing some box ideas and generally saying hello ... so obviously I have a rapport and this is good for me.
but
not for you
:(


Quote
My JLM99v went together first pop, which was great!!

yep
trafo input
and trafo output

but power supply is very similar to the above... except for the off-board toroid.

It is most likely something about the way you have tied and strung the grounds.
Kev
DIY Factory

Lowfreq

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #6 on: September 13, 2005, 08:37:43 PM »
I FOUND IT!!!!!!! :grin:  :grin:  :grin:

After doin another check of all my components (which were all good), I found that due to my cheapo home etching, the 2nd connection point for R10a had been etched a little too much, and whatever the solder was grabbin onto wasn't the copper on the PCB. So I was able to tin it with a bit of extra solder further down, and BINGO!!! :shock: my green pre is now quiet :thumb:

The 58 worked like a charm, and the pesky buzz was gone. Woooohoooo!!!

The Phantom power seems to behave a bit better now too. The mic will still come alive again, but within a second or so, and then die away rather than continuing to work badly. I'm guessing it's just the cap emptying out. It's no prob now, as by the time I switch off the 48v and then turn around to pick up another mic, move a fader or scratch my nuts, everything is back to normal.

The 2nd pre is still distorting tho, so I'll do another check on that one. I'm sure it's gonna be something similar, but prob just in another part if the circuit. But I'm glad the first one is all good. :green: Now I have at least 2 really good quality pre's to play with. A couple of months ago I had none :roll: .

And one thing i've really noticed (apart from the improved quality) is that with both the 99v and the green pre, I can hear the different tones/qualities of each mic I use more. Even between different dynamics, it really shows!! where as with my old cheap stuff there was more of a smearing of the sound that seemed to cover that up (if that makes sense).

I really need to get off my ass now and write some more songs, so I can use this stuff in an actual session. I can tell already that my old demo is gonna pale in comparison.....heck, I might even re-record the whole thing again!! :wink:

So again guys, THANK YOU!!!! HEAPS!!! for all your suggestions. Picking yor brains is a privlege. :thumb:  :thumb:

Kev

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #7 on: September 14, 2005, 03:31:50 AM »
Quote
... and the pesky buzz was gone. Woooohoooo  


woohoo !!
 :thumb:

very good


if I find time ... I'll try to add a couple of pictures and some text to the Green page ... to shiow the wayI wire up the modules and supply and XL3's ... and the ground.
Kev
DIY Factory

matta

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #8 on: September 14, 2005, 06:08:17 AM »
Awesome new!

Glad you got it up and running. The Greens are the bomb, I hope to add a JLM to my collection in the future to  :thumb:

Cheers

Matt
Matt Allison
www.matt-allison.com

Quote
We are not going to start thinking of ways to get an octopus to commit a crime, cause that just has failure written all over it – Earl J Hickey

Kev

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #9 on: September 14, 2005, 04:36:43 PM »
I found time to take a few pictures,
BUT no text yet.
http://www.diyfactory.com/projects/green/green.htm
down the bottom in the ERRATA section

here are a couple of the pictures


0V(48) / +48V / -15V / 0V / +15 / 0V(LED) / +V(LED)
WARNING
I stuffed up the use of the black texta colour.
the screw connector on the left should have been black(0volts) and the second should have been white(48volts).
 :shock:
woops


IEC power connector
NO power switches
Earth straight to chassis
no other chassis connections on this one

that's enough for now
the rest of the pictures are at the site
your unit is now working so this doesn't matter now anyway
 :roll:
I'm too slow
Kev
DIY Factory


Lowfreq

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #10 on: September 14, 2005, 05:11:58 PM »
Cool, cheers for the pics Kev :thumb:

When I get some time, I'll try your way of doing the grounding just to see how it works for me.

Yeah Matt, you'll love the 99v if you do one. What people are saying about it being real silky is very true. I used a Ludahl 1538 in & no tranny out. It's real clean, but not as dry sounding as the green (well to my ears anyway) kinda more polished/smooth......bla blah blah  :wink:
The contrast between to two pre's is defintley good to have.

Next up for me is testing my GSSL while I wait for my vca's to arrive, and then my G1176 and then my, and then my, and then my............................maybe some treatment for this DIY addiction is needed??? :wink:  :green:  :wink:

thanks again for your help guys (i'm slowly becoming an addict)

regards

Steve

Seedysea

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #11 on: September 14, 2005, 09:06:51 PM »
Congrats Lowfreq, your problems, and the responses here are also helping me troubleshoot some noise I have.

Hey Kev,

Thanks for the extra pics, they really help in understanding how the circuits work.  A picture is worth a really big post, or something like that.

Just a quick question.  I took your experience as a guide and used the same IEC connector.  Jaycar also happens to be my local supplier, which is also convenient.  Is that heatshrink insulation?  It looks kind of thick.  My connector didn't come with a boot, which is what this looks like.  Is this something I can buy as a seperate part to insulate the terminals?

Craig

Ptownkid

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #12 on: September 14, 2005, 09:49:10 PM »
So in other words....

the AC filter (where the power comes in) is just hooked to the chassis and that's it?

I added a power switch, so I have a wire going from the ac filter to the switch  as well.

Is that all the grounding i need?

The part i don't get is how the hell is the actual circuit grounded.

I'm having a harder time with understanding grounding than anything else...... :oops:

Lowfreq

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #13 on: September 14, 2005, 10:30:25 PM »
Hi Seedysea,

I found the boot at jaycar. There's two sizes. I think the smaller one from memory is for the IEC without a fuse adaptor built in, and the larger one if you do have the built in fuse.  Jaycar #'s PM4015 & PM4016.

Hope that helps

regards,

Steve

Kev

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #14 on: September 15, 2005, 02:59:49 AM »
I've never used an AC filter in any of my projects  ... yet    :roll:   ?

I only use the Farnell IEC inlet and Boot
not the Jaycar one  just didn't like it

... I've posted the parts numbers on a web page ... somewhere ??
and I'm sure in a thread ... again ... somewhere ?
 :shock:

perhaps I'll do a new Kev's favourite parts at the factory
Kev
DIY Factory

Kev

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #15 on: September 15, 2005, 05:13:31 PM »
Quote from: "Kev"
... perhaps I'll do a new Kev's favourite parts at the factory
stupid Kev
it's already there and has been for ages
 :roll:
http://www.diyfactory.com/data/kevsfavourites.htm
 :oops:
d'oh !
Kev
DIY Factory

Seedysea

Green 48v probs. Kev? Pete? Matt? Anyone??? Problem Solved!!
« Reply #16 on: September 18, 2005, 04:27:45 AM »
Thanks for the info Lowfreq & Kev.

I'll try out both options.


 

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