khstudio

NEVE 1272 - CLIPPING
« on: January 14, 2007, 03:55:30 AM »
My 1272 Pre is finished & sounds pretty good but I NEED some help so I can put the lid on and go.  :green:

OK,
When adjusting the trimmer for Symmetrical Clipping my waves on the scope don't look right. I asked JC (Joel) & he also agreed it doesn't sound right. He said the TOP & BOTTOM halves SHOULD stay Symmetrical when pushed!

Test tone .5v PP. Everything looks OK, I can set both halves of the wave to clip evenly (Just at the point of clipping) but when I push the volume to see what happens when clipping it harder the bottom half stays put & continues to flatten but the top continues to rise (about 1v more than the bottom) with about half or less of the flattening of the bottom. :roll:

 - I replaced ALL the active components.
 - Both channels do the same thing.
 - To my ears & JC's (I sent him samples) it sounds pretty good.

If any of you guys could PLEASE post some pics of your Neve pres at subtle to extreme clipping would REALLY help me out here.

I'm using On Semi - 2N3055G - 60v, 15A, NPN
(Digi-Key PN# 2N3055GOS-ND)

Gain & PAD Settings - onset of clipping (Looks OK)
Looks to be clipping at around 2 volts - input voltage is aprox .5v



Scope - onset of clipping


Gain & PAD Settings - MAX Clipping with GAIN=40


Scope - MAX Clipping with GAIN=40
Top Half is almost 3v & the bottom has droppped a little now to 1.5v



Does this look right?

Thanks,
Kevin
Kevin ~ KHStudio


AnalogPackrat

NEVE 1272 - CLIPPING
« Reply #1 on: January 14, 2007, 11:59:07 AM »
Is your vertical amp on the scope set for DC coupled?  If it's AC coupled and you've got big asymmetry the wave will shift like this.  It still doesn't look quite right, though.  Can you turn down the input until it just starts to clip?  I can post pics of mine later if you need them.  I'm heading out in a few minutes and won't be able to do it any time soon.

A P
If it is to be, it is up to me.

khstudio

NEVE 1272 - CLIPPING
« Reply #2 on: January 14, 2007, 05:44:46 PM »
Quote from: "AnalogPackrat"
Is your vertical amp on the scope set for DC coupled?  If it's AC coupled and you've got big asymmetry the wave will shift like this.  It still doesn't look quite right, though.  Can you turn down the input until it just starts to clip?  I can post pics of mine later if you need them.  I'm heading out in a few minutes and won't be able to do it any time soon.

A P


Damn, I tried to take a big enough pic so you guys could see ALL the scope settings... but YES, it's set to AC.


Posting pics of your NEVE at CLIPPING & beyond would definitly help show me if something is wrong or not. :thumb:

Thanks, A P

Kevin
Kevin ~ KHStudio

Steffen

NEVE 1272 - CLIPPING
« Reply #3 on: January 14, 2007, 08:43:14 PM »
here´s mine (f=1kHz):



steff

khstudio

NEVE 1272 - CLIPPING
« Reply #4 on: January 14, 2007, 08:58:38 PM »
Hey THANKs man  :thumb:

That looks a LOT more uniform than mine.

Are you set to 1v DIV on the scope?

Also, what 3055 are you using? Motorola, etc...


Thanks,
Kevin
Kevin ~ KHStudio

khstudio

NEVE 1272 - CLIPPING
« Reply #5 on: January 14, 2007, 09:02:56 PM »
I'm sorry,

What were your gain setting set to on the NEVE?

Kevin
Kevin ~ KHStudio

AnalogPackrat

NEVE 1272 - CLIPPING
« Reply #6 on: January 14, 2007, 09:21:29 PM »
Kevin,

OK, here's a somewhat useful shot of my 1272 starting to clip at 1kHz:

My 1272 with approximately adjusted clipping

Adjust your input sinusoid to really low level and then set your gain to a point where it clips.  You don't want to smack the input iron so hard that it starts to muck with your waveform.  Now reduce the "pad" setting (the control right after the input iron in JC's setup) until the wave is just clipped.  Adjust your scope's horizontal time scale to show only 1-1.5 cycles so you get an easier to see wave on the screen.  Now waht does it look like?

<edit>  You should be able to get about 40Vp-p out of that thing, BTW.

A P
If it is to be, it is up to me.

Steffen

NEVE 1272 - CLIPPING
« Reply #7 on: January 14, 2007, 09:24:12 PM »
Quote from: "khstudio"
Hey THANKs man  :thumb:

That looks a LOT more uniform than mine.

Are you set to 1v DIV on the scope?

Also, what 3055 are you using? Motorola, etc...


Thanks,
Kevin



10V/div, NOS Tesla

Quote
What were your gain setting set to on the NEVE?


dunno, measured my 1176 w/1272 makeup which I just had on the bench
when I read this post.

steff

Steffen

NEVE 1272 - CLIPPING
« Reply #8 on: January 14, 2007, 09:27:20 PM »
Quote from: "AnalogPackrat"
Kevin,
.....
<edit>  You should be able to get about 40Vp-p out of that thing, BTW.

A P


yepp, that´s right...as seen on the pic mine spits out 53.6Vpp (into 600ohm)

khstudio

NEVE 1272 - CLIPPING
« Reply #9 on: January 14, 2007, 09:36:57 PM »
Quote from: "Steffen"
Quote from: "AnalogPackrat"
Kevin,
.....
<edit>  You should be able to get about 40Vp-p out of that thing, BTW.

A P


yepp, that´s right...as seen on the pic mine spits out 53.6Vpp (into 600ohm)


I had mine set at 1v DIV  :?

I'm swapping out one of my 3055's right now... maybe I fried them both when I was searching for the hum a few days ago.

I will then Re-DO the test like Anlalog PR said :thumb:

I'll be back & Thanks for helping,
Kevin
Kevin ~ KHStudio


AnalogPackrat

NEVE 1272 - CLIPPING
« Reply #10 on: January 14, 2007, 10:08:37 PM »
You should try probing between amp stages to make sure it's not happening before the 3055.  BTW, I used new ON Semi 3055s on my pair.

<edit> Were you using a 10x probe?  If so, I believe you are seeing just over 40Vpp on your trace.  Can you verify output voltage using an AC volt meter of some description (one which is accurate at 1kHz--most DMMs are OK).

A P
If it is to be, it is up to me.

khstudio

NEVE 1272 - CLIPPING
« Reply #11 on: January 14, 2007, 10:32:48 PM »
Quote
ON Semi 3055s


I'm using a 3055GOS, not sure if it matters or what differences to even look for that would matter.

Where did you find the "S"? I couldn't find it at Digi-Key or Mouser :sad:
Just the "G" and a few other of the On Semi's.

BTW, I just rechecked ALL the resistors on both boards
& replaced one of the 3055's with a brand new one ( I ordered 1 spare)

I'll post back in about 20 minuts with the results... I hope it work.

I'll also check with a DVM :wink:

Thanks,
Kevin
Kevin ~ KHStudio

khstudio

NEVE 1272 - CLIPPING
« Reply #12 on: January 14, 2007, 10:35:55 PM »
Quote from: "AnalogPackrat"
You should try probing between amp stages to make sure it's not happening before the 3055.

A P


O... Do I just attatch the GND of the probe to any ground on the board then probe around (carfully)

I think I'm good enough to use the schematic & find what's going where but if you can recommend some "specific spots" before the output stage would be helpfull :green:

K
Kevin ~ KHStudio

khstudio

NEVE 1272 - CLIPPING
« Reply #13 on: January 14, 2007, 11:23:15 PM »
OK,

The NEW 3055 did not change anything :mad:

Measuring AC Voltage acrossed Pins 2 & 3 = 20v @ clipping (like 1st pics I posted = onset of clipping)
(this is with my gain on 40, output fader MAX, & input PAD about 70%)
About 12v or less from GND/pin 1 to (2 or 3) Half

When I crank the input pad (like the 2nd image I posted) I get about 25v acrossed pins 2-3 but the clipping looks the same... not good.

What the hell :?: HELP ME.

Kevin
Kevin ~ KHStudio

CJ

NEVE 1272 - CLIPPING
« Reply #14 on: January 14, 2007, 11:41:46 PM »
I like to pull up the sig gen on one screen and the other on the clipping in order to be able to figure out where the trouble statrs
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

khstudio

NEVE 1272 - CLIPPING
« Reply #15 on: January 15, 2007, 01:52:01 AM »
I think I need a lesson in how volts PP = Volts on a DC/RMS volt-meter.

My input signal (1k tone) was reading .5v on my DVM... I'm thinking this is too much :?:  :oops:

Also, my scope set to 1v DIV looks like the ones you guys posted (scale wise) 10x so like my 1st picture (just clipping) I read about 20v on my DVM - & this fills around 2 square blocks on the scope view.

Am I right in thinking I should multiply the voltage I'm reading on my DVM X2 to get the Push-Pull voltage? This would make more sense. 20 x 2 = 40

Kevin
Kevin ~ KHStudio

khstudio

NEVE 1272 - CLIPPING
« Reply #16 on: January 15, 2007, 07:09:04 AM »
I still think I need a lesson (above PP to DVM volts) :sad:

BUT

I put the lid on this thing & it sounds great :green:

#1 I think my input level was too hot.

#2 I think it's working as it should up to & slightly over clipping.

It's when I push the thing to max levels (something I will probably never do) it reacts like my second pic & the top half of the wave rises like I explaned 1 mil times. So it MAY just be a dumb test to begin with & I'm not sure any of you guys actually did that (slam it to see what happens)

I tracked a KICK & SNARE with it last night & compared it with my API/YAM pre I made & my PM2000 (these have been the BEST performers in my studio up until now)

This 1272 just sounded great... much more realistic, up front, clearer & WAY Tighter
The headroom was also better.
The 1272 is faster sounding & punchier to me.

I AM HAPPY... THANKS JC :thumb:
And everyone else for helping.
This pre definitly filled a HUGE gap in my mic pre needs... I want more.


BTW, if any of you guys want to slam your 1272's & post the results I'd love to see if it responds the same... until then, I could care less. Lid Closed!

Kevin
Kevin ~ KHStudio


 

Related Topics

  Subject / Started by Replies Last post
0 Replies
1171 Views
Last post January 30, 2006, 06:13:20 PM
by Mbira
12 Replies
2205 Views
Last post April 29, 2008, 01:27:51 AM
by gyraf
2 Replies
1714 Views
Last post December 22, 2009, 11:52:36 PM
by glazer56
4 Replies
1615 Views
Last post September 19, 2011, 08:48:49 PM
by rafafredd