8 Channel, 3U NEVE 1073 completed

[madriaanse]

Cool; you're very welcome! 

M.

 

[snipsnip]

Hey guys,

Im a little confused about what the voltages im getting at the input XLR.

I measure around 33v at pins 1 & 2.

Whats the purpose of the 6k81's? We have 48v at the toggle switch, so why are the resistors required?

Im also a bit spun out as the 3k9 take the 48v line down to 5v for the LED, so wouldnt the 6k81's theorectically do more than this?

Im sure Im missing something very simple here 

Any ideas?

Thanks a lot
jake

 

[johnR]

I measure around 33v at pins 1 & 2.

Is that with a mic plugged in? The voltage will drop when loaded by a mic.

Whats the purpose of the 6k81's? We have 48v at the toggle switch, so why are the resistors required?

Without them the 48V supply would short out the ac mic output signal. With them in circuit, they give a 13k6 (2 x 6k8 in series) load in parallel with the input transformer primary, which most mics will be OK with.

Im also a bit spun out as the 3k9 take the 48v line down to 5v for the LED, so wouldnt the 6k81's theorectically do more than this?

Yes, if the mic draws more current than the LED. The resistors limit how much current can be supplied to the mic. Most phantom powered mics draw a low enough current not to cause a problem.

http://en.wikipedia.org/wiki/Phantom_power

 

[snipsnip]

Thanks John.

Thanks for the info. What you said made me look at voltages with different loads. Seems its actually the line to mic level pad I had hooked to my second set of input XLR's that was doing funny things.

So in case anyone else was thinking of doing this (4 conductor mic cable> 1 pair to XLR with +48, 1 pair to XLR with no +48)... dont! 

Well having the input split over 2 XLR's doesnt do anything, but having the pad in the second set of XLR's creates some kind of load... maybe the resistor network? Its all a bit over my head really.

Thanks for the tip john.

 

[snipsnip]

Right - seems most of my problems are gone.

No crackle, no oscillation, working with and without phantom.

Perfect except one small thing.

The pre's sound distorted when turned up highis (45db+), but not clipping according to any digital metering. Could this be the result of not biasing properly?

I have attempted to bias but had issues getting a clear result on my scope.

Thanks a lot
Jake

 

[snipsnip]

Sorry to bump this.

Any ideas regarding how possible incorrect BIAS will effect the sound?

Thanks again
Jake

 

[mitsos]

I have attempted to bias but had issues getting a clear result on my scope.

What do you mean? Are you unable to see both sides of the wave simultaneously?  If so, are you feeding a steady signal and then turning up the gain on the 1290 until it clips? Try keeping the gain on the low side and then turning up the signal you are feeding it.  Play with both until you can see both sides of the wave on your scope and the uneven clipping.

 

[desol]

As far as i understood it, your supposed to turn your pre to full, then input a 1k sine until you see clipping, then adjust for even clipping on both sides with the trimmer. Martin was correct in that, 22.6vdc was about right; i think i fine adjusted to 22.65 or something. Still working on them..

Why your getting distortion +50 could be a number of reasons. These pre's will distort something after it pretty easily? What are going out-into? Are you sure the thing your going into isn't distorting?

 

[snipsnip]

thanks for the tips guys. I know this shouldnt be so hard, but im a bit of a novice with a scope so please bear that in mind.

Delsol.. where are you measuring your 22.5v? At the power terminal on the board?

Maybe mines running a bit hot @ 24v? Although I thought that was standard requirement for neve?

Im going straight from my mic (or SSL alphlink converters depending on source for test) and straight back to converters, so no chance of distortion coming from anywhere else.

The SSL has nominal operation level of +4dBu.

 

[mitsos]

As far as i understood it, your supposed to turn your pre to full, then input a 1k sine until you see clipping,

yes, that is on martin's pdf, I tried it and it did not work for me. I could not get both sides of the wave on my scope. Maybe my sig gen gain is jumpy, I don't know.  I was a bit lost until someone told me to try turning the preamp gain down, which turned out to work just fine.

where are you measuring your 22.5v?

Check the first post of the thread. Take your measurement from the case of the 2n3055 w/respect to ground.

 

[desol]

Weird? I'm assuming you tried all the vert divisions...hmph.

My sig gen rig isn't great either...lol. Using the output of a computer soundcard half hazardly into the input...with a small resistor network inline.

 

[mitsos]

yeah, I did play with the scope quite a bit.  I think the sig gen level knob is jumpy. I should check that out I guess, but it works for most things.  Anyway, this was a long time ago and my memory cells are not what they used to be... but as far as I remember, I lowered the preamp gain a few notches, fiddled with the signal generator level a bit and then could finally get both sides of the wave on the scope at a decent enough resolution where I could see what was going on when adjusting the trimmer. weird for sure.

 

[desol]

I just wanted to post these shots for anyone interested. This is my new JLM powerstation with the mod's done for full rectification, + rails only (neg's disabled/parts left off ) with 1.5 amps going to each positive rail. This will do up to eight channels, 375 mA per channel.

 

[snipsnip]

Neve gurus... sorry to constantly pester you with my troublesome build... but Im still straching my head over this distortion Im hearing.

If I run a line signal into the pre (using a fearne lp-1 to make it mic level) this thing sounds awsome. Really big and controls the bottom end into a lovely tight bundle.

When I run mic signals into it, either condensor or dynamic, the pre sounds pretty distorted and closed. Someone has suggested input transformer saturation. But how come it saturate from mics only? It sound like it clips way before I reach FSD on my SSL alphalink converters.

The biasing may not be 100% accurate but its definitely close.

Can anyone help me? The fact it happens on both channels if making me think its human erro somewhere, rather than a faulty part.

Are any parts I should swap out just incase they got damaged or are prone to failure?

Thanks so much... been working on these babies for a long time now

Cheers
jake

 

[snipsnip]

in fact, any of you UK builders want to take a look at it for some money?

I just want to use them now. Have to let go of my pride

 

[desol]

Do you have some up close shots of the board? You should be able to use a scope along the way to see where the clipping is occuring, 1st stage, 2nd stage, etc..

 

[snipsnip]

thats a really good idea..... but I cant hear the clipping when im feeding a tone into the pre, which might make this difficult huh? Or do you think I'll still maybe see something?

 

[Biasrocks]

thats a really good idea..... but I cant hear the clipping when im feeding a tone into the pre, which might make this difficult huh? Or do you think I'll still maybe see something?

Depending on how much gain you're applying (very little with a line input) there's two extra gain stages that kick in, three in total for a 1073. I suspect that either the second or third gain stage is the culprit.

Mark

 

[snipsnip]

good thinking. although Im actually padding my line signals to mic level with a fearne LP1 and applying similar gain. I will try tomorrow without the pad.

Thanks for all your input so far.

jake

 

[Dazazone]

Hey Martin,
Just wondering if you or anyone else has tried out the EA-1166 on an EZ1290 yet?  They are a lot cheaper than the Carnhills and I suspect a lot better. 
Also I have a funny story about my calibration procedure.  I hooked up my nord lead into EZ1290 into Lynx Aurora into PTHD.  I could see the waveform in Pro tools and stuck down a pure sine wave note on the nord, turning it up to the clipping point.  I had my speakers off and thought I was going crazy but the Carnhill output transformer was audible. Like a mosquito, but I could definitely hear it.  I even played a song on the Nord and the output transformer was singing along in tune! Quite amazing.
A side story to my calibration procedure, I accidently dropped my screw driver whilst calibrating channel 1.  It landed on Carnhill output transformer of channel 2 and joined a couple of the terminals for a couple of seconds, then there was a burning electronics kind of smell, oh no!  Anyway that channel still works totally fine, I'm hoping I haven't damaged anything but there is one problem in the sound and I'm not sure if it was there before calibration or not.  With a mic I get the same output and tone as channel one but there is a 50Hz hum going on very quietly, I could prob hpf it out but I know it's not right.  I haven't done any more testing since then and it is in my rack.  I'm suspecting either I rooted the output tx with the screw driver short circuit or another machine in my rack is too close with its toroidial power tx. My JLM ACDC PS for the EZ1290 is external.  I'll test more and report.  One thing I noticed is when a 57 is plugged into it the 50Hz is actually a bit louder than a bald mic lead.
Hmmmmmm.......