green pre, not quite right

edjohnwhite

Member
Joined
Oct 14, 2005
Messages
13
Location
London
Hello, i put this in the all things green thread the other week, and didn't get any response....i thought i might get more luck if i put it hear...or maybe my etiquette is off..fingers crossed.


Hi anyone

A first post here, i hope people are still hovering around this thread.

Firstly Matta (and everyone thats contributed), thanks for looking after this Green metta. It's helped me through my first big DIY, a 4ch green. Also PeterC thanks for starting this whole thing up and Ptown thank for the kit.

Ok, so the problem..4 channels and psu done and all racked up. All channels are passing some nice audio, with a little white noise, a bit of hum of the channel nearest the toroid, but there isn't much i can do about this.

When it came to setting up, i noticed i'm not getting much output and and the output starts to distort at quite low gain. When setting the led meter levels and measuring the output from the + of the pre, I can't get any more than 3v ac. At around 2.5v ac it starts to distort.

This is the same on all channels which are otherwise ok. So i'm guessing this could be a PSU thing, or something i've not noticed and done the same on all channels. After searching the forum and reading around i have a hunch this could be related to the transistors being in the wrong way round (?).

Does anyone have any ideas or kind words of wisdom? I wouldn't be surprised if i've just totally missed the point of something, and am happy to be told this.

thanks
ed
 

lofi

Well-known member
Joined
Aug 27, 2006
Messages
852
Location
Bolton, UK,
sorry i cant help!! just laid all my green bits out on the kitchen table, much to the wifes displeasure (especially as i just ruined a saucepan boiling the transformer out of one of my SM57's :grin: ) so will be hoping for a decent answer to this aswell.

Iain
 

SonsOfThunder

Well-known member
Joined
Jun 11, 2004
Messages
1,144
Location
Mid Coast (Oklahoma)
So what have you checked? Are the transistors in the wrong orientation? We can't see your unit so you have to give us more details about what you have tried.

HTH!
 

peterc

Well-known member
Joined
Jun 4, 2004
Messages
2,229
Location
Johannesburg, South Africa
If it is happening on all the channels, then it is probably something common to all the channels, i.e. power supply or grounding.

Have you checked all the DC voltages, with & without chips in? First thing to do.

Check stage by stage using a scope. There is quite a bit of info on this in the Green threads, it should be fairly easy to find.

Ptownkid, any ideas here?

Regards
Peter

EDIT: All the docs you need are here:
http://www.mendelt.nl/greenpre_V14/
 

matta

Well-known member
Joined
Jan 11, 2005
Messages
1,640
Location
Cape Town, South Africa
Hi Ed,

Thanks for the kind words on the META.

I'm with Peter on this, check your grounds and that all the parts are in correctly.

Also list the voltages on your IC sockets with and without the IC's, normally a dead giveaway as to where the problem lies.

If they are all the same and off it means you either stuck in a part wrong on all 4 units or there is an issue with your PSU.

What are your PSU voltages looking like? All up to par?

Shoot some pics of the boards and link them here, I'll take a quick look over for you just to have a 2nd set of eyes.

Cheers

Matt
 

edjohnwhite

Member
Joined
Oct 14, 2005
Messages
13
Location
London
thanks for all the replies.

It's not the transistors, I've tried turning them round.

the state of things at the moment:

PSU appears to be fine, putting out a nice +15.3, 0.0, -15.3, 48.5 V.

Grounding: I have all xlr pin 1 inputs and all xlr pin 1 outs going to a star ground. I have the 0v out on the PSU going to the star ground and a mains earth also connected to the chassis going to the star ground. XLR pin 1s nor connected to board. Shielding on input from XLR to board also connected to pin 1 on XLR.

The IC voltages are all pretty close to those stated.

When i stick a scope on it the distortion occurs from the first ne5532 out.

I think your right Matta and Peter. maybe i've got something grounded that shouldn't be and its sapping some of my in or out. I can't find where though,and its driving me nuts. I'm going to take the big bits apart and put things together again. with a bit of luck that might do it...
 

SonsOfThunder

Well-known member
Joined
Jun 11, 2004
Messages
1,144
Location
Mid Coast (Oklahoma)
Silly question, but are you sure you've hit pin 1 on the inputs and outputs correctly? Recently, I opened up something that I built a while back and discovered that I had reversed the wires to pins 1 and 2...that explained why it worked somewhat but hummed. :oops:

HTH!
 

Ptownkid

Well-known member
Joined
Jan 31, 2005
Messages
4,256
Location
Ajax, Ontario, Canada
Do i read correctly when you say that the xlrs are ALL grounded via the star and you have NOT attached the third wire from the input XLR to the pcb?
 

edjohnwhite

Member
Joined
Oct 14, 2005
Messages
13
Location
London
oh dear what a balls up. dismantled and reassembled and things are working fine now. My XLR pins were muddled, i'm such a bell.

I was so sure there must have been some component it put in wrong on all the boards. I was about to start testing things piece by piece, which i didn't have much hope for.

Thanks all so much for the point in the direction. You saved weeks of tears.

Time for a deep breath now. Take in lessons, and i'll try something else next week.


ed

sounds awesome by the way!
 

SonsOfThunder

Well-known member
Joined
Jun 11, 2004
Messages
1,144
Location
Mid Coast (Oklahoma)
Good going Ed! Don't know why the XLR pin thing came to mind. I could not tell you how many XLRs I have wired correctly. That's why I was so alarmed to find that I had wired that one in my DI wrong!! Arrrrg!

You will probably never make that particular mistake again. On to a new mistake!! :grin:

I have used "HTH" around here for quite a while and I wondered how long it would take before someone asked. I forget how I learned that but I don't think it was actually on this board.



Have I mentioned lately how much I LOVE this board and the DIY community? :thumb: :thumb: :thumb:

To quote our DIY "grandfather" Kev Ross: Happy, Happy, DIY, DIY!

Peace!
Charlie
 

lofi

Well-known member
Joined
Aug 27, 2006
Messages
852
Location
Bolton, UK,
[quote author="SonsOfThunder"]

Have I mentioned lately how much I LOVE this board and the DIY community? :thumb: :thumb: :thumb:

Charlie[/quote]

i agree, but as i know so little about this lark i just lurk in the back ground waiting for the day i can post pics of my finished green pres, just got to wait for the panic attacks to stop every time i open the box of parts.

Iain
 
Top