2254C build/support thread

[matta]

Hey Kam,

I thought about that too, but it still doesn't make sense... you see, I'm using plastic stand offs, BUT I took this into account and on the PSU board I have a separate ground wire running from the provided solder pad that is LINKED to the PSU mounting holes i.e CHASSIS GROUND and I took that to my ground point as the IEC inlet, and have continuity between all the chassis grounds... the AUDIO GROUNDS and CHASSIS GROUNDS are not connected at the PSU that I can see, we have done it ourseleves by taking the AUDIO GROUND of PIN2 of the O/T Meter to the CHASSIS GROUND at the Output Transformer... Igor? Any thoughts?

Cheers

Matt

EDIT: Found it, the MIDDLE stand off hole on the PSU is AUDIO GROUND, the other 4 are CHASSIS GROUND, very sneaky... ok folks, be warned, you will need at least 2 conductive standoffs, one for the center post and one for one of the corner holes, by doing it at the PSU you tie the AUDIO & CHASSIS grounds together!

this is freaky  :

EDIT : Matt, i think its from PSU board... that pin 2 i told you to connect on main board is actually on same ground_plane as on main PCB, which is
also connected to PWR molex ground.... so when PSU board is not grounded properly to chases then there is a missing grounding link to output trx etc too...
i think that solves the mystery...

 

[kambo]

very sneaky...

;D ;D ;D ;D ;D

 

[juniorhifikit]

Hi all.  I'm finally getting around to stuffing my boards, and had a couple questions so far that I couldn't find answers to in this thread.

- On the switch boards there are a few extra holes: Makeup next to the 27 Ohm; threshold next to the 680 Ohm; attack next to the 5K6 Ohm.  Anyone know what these are for?  Since the boards are black, it's hard to trace where these go.

- Makeup gain resistors 51 & 33 Ohm seem to touch (solder bridge) as well as 310 Ohm & 180 Ohm.  Is this intentional?  My eyes are bad

- Also R'11 & R'12 connect also, as does R'12 & R'13 - is this right or am I a slob?  They don't seem to share a pad, but they're REALLY close.

Thanks!

 

[kambo]

  My eyes are bad

how about a magnifying glass to start with 

 

[matta]

Hey Guys,

I've wired up the 2nd unit and looking to start calibrating, will set RV1 first for the DC level/Headroom for the BA183/283 first... then onto this:

Ok I admit it....I'm an idiot 

Of course what I was doing wrong was that I failed to remember that the output is balanced and was only measuring pin-2 to ground.
When I measured across Pin2 & 3 of XLR, all was well

I got to the point of calibrating as per 33609 instructions, not sure if that is correct or Pot numbers (ie RVn) are equiv.
- I set Pot on PSU to give 3v at +CV and -CV on PSU
- Adjust gain pot to get unity gain with unit Bypass In
- I croc clipped +CV from PSU to Link on main board
- Adjust RV2 to get -8db at output XLR
- Adjust Pot on PSU for -20db at output
- Adjust RV3 for 20db on meter
- Put threshold to -2db (1st click)
- Adjust RV5 for -1db at output
- Put Threshold to -20db and measure -16db (ish - slightly less in fact on my unit)

Onto the RHS now

Thanks all

I've got to admit I'm a little confused though... the input signal comes from the CV from the PSU correct? Measured at 3V croc clipped to the LINK on the PCB, but then I'm confused, how are you measuring -8dB at the XLR and -20dB on the Output? From the VU/DC meter or on your multimeter? And is so what are those values in real world terms?

Sorry for the seemingly stupid question, level always just freak the heck out of me and I STILL, 5 years in, can't seem to get them right.

I also assume all these tests are done WITH the control boards attached to the main board?

Thanks in advance!

Matt

 

[kambo]

control boards are attached, as you need to set some atack, release, thrshold levels...
CV from PSU yes, small chip on side for test DC, with trimpot...
reading -8db, -20db are from DMM...
set DC on PSU, connect to link..  reading -8db on output XLR pin 2-3....make adjustment....
connect DMM to XLR pin 2-3 and adjust trimpot on PSU to read -20db on your DMM...  make adjustment...

it seems confusing, i admit, read 33609 full calibration sheet, it will give you clear idea ...

EDIT :
http://www.sengpielaudio.com/calculator-db-volt.htm

0.775V ( RMS ) = 0 dbu

 

[matta]

Thanks Kam,

Yes that calculator is most useful! That was the missing link for me... converting dB's to a DMM reading. Reading Jplum's calibration procedure it make sno mention of setting on the control panel, hmm... need to hunt down the 33609 cal procedure then. Thanks again!

Matt

 

[kambo]

attack 8'clock
release CCV
ratio 1:2

 

[jplum]

attack 8'clock
release CCV
ratio 1:2

Dont forget to read the DC Bias post (2 pages back i think)

I think I had the attach Full Clockwise (Fast)
ratio 1:2
Recovery CCV
Threshold CV
Gain CCV
HPF & +10 both in Off position

Yes, all the db measurements were done on Fluke Meter using calculator as reference info!

 

[kambo]

fast attack is CCV

 

[substitute]

cool thanks!  Now I can go back and re-calibrate mine.  I did it with meter plugins in logic and the results were a little screwy, I've never understood the vdc/db relationship either. 

Kambo, I believe some where in this thread you mention something to the effect of being a beginner, yet I would say "you've been dropping science like Cosby droppin babies"!

 

[matta]

Hey jplum,

Yup read that, and also think yours may be a little high... just spoke to PeterC who has worked on a bunch of Neve modules and feels that a safer bet it 100mA of current, which across the 47R resistor would be 4.7VDC.

Also like you I tried it with my scope and saw little to no difference when using my scope... interestingly enough my Pro Tools 002R output can't put out a CLEAN +20dBu signal, it will only do about +18dBu and by then it is bordering on a square wave... interesting...

Cheers

Matt

attack 8'clock
release CCV
ratio 1:2

Dont forget to read the DC Bias post (2 pages back i think)

I think I had the attach Full Clockwise (Fast)
ratio 1:2
Recovery CCV
Threshold CV
Gain CCV
HPF & +10 both in Off position

Yes, all the db measurements were done on Fluke Meter using calculator as reference info!

 

[kambo]

Kambo, I believe some where in this thread you mention something to the effect of being a beginner, yet I would say "you've been dropping science like Cosby droppin babies"!

;D
i am seriously a beginner, just a quick learner, and math/ engineering background...

Also like you I tried it with my scope and saw little to no difference when using my scope... interestingly enough my Pro Tools 002R output can't put out a CLEAN +20dBu signal, it will only do about +18dBu and by then it is bordering on a square wave... interesting...

add a ba283 or something...

 

[matta]

Adjust gain pot to get unity gain with unit Bypass In

Also, I'm WAY confused on the using the onboard GAIN trimmer to get unity gain in 'bypass', surely in bypass the audio goes straight from the IN to OUT without passing through the circuit, in which case you won't know if you are adding gain or now, and in bypass the controls are bypassed? To set the GAIN trimmer should you not set the Make-up Gain knob to 0, Threshold to zero and then toggle between 'bypass' and 'compression' and then match the levels there?

Cheers

Matt

 

[kambo]

Adjust gain pot to get unity gain with unit Bypass In

Also, I'm WAY confused on the using the onboard GAIN trimmer to get unity gain in 'bypass', surely in bypass the audio goes straight from the IN to OUT without passing through the circuit, in which case you won't know if you are adding gain or now, and in bypass the controls are bypassed? To set the GAIN trimmer should you not set the Make-up Gain knob to 0, Threshold to zero and then toggle between 'bypass' and 'compression' and then match the levels there?

Cheers

Matt

attack 8o'clock,
release CCV
ratio 1:2
makeup 0
thrshold CV, +10 switch at 0 position...
red bypass led  on, unit passes audio through comp circuit

feed 1khz 0.775v 0dbu

adjust gain trimpot until you read 0.775 v 0dbu at output

 

[matta]

Thanks Kam,

That is what I thought, the confusing part is 'Bypass In', it sounds counterproductive and confusing, an oxymoron... either the unit is 'bypassed' or 'compressing', so it makes more sense to say 'switch the compresser in', rather than 'switch the bypass out', though both have the same results  ;D

Cheers

Matt

 

[kambo]

i totally agree 

 

[juniorhifikit]

  My eyes are bad

how about a magnifying glass to start with 

That was helpful - thanks for that.

Does anyone have anything useful to add that might address my other questions having nothing to do with my eyesight?  Are these solder pads supposed to touch, and what are the extra little holes for?

- On the switch boards there are a few extra holes: Makeup next to the 27 Ohm; threshold next to the 680 Ohm; attack next to the 5K6 Ohm.  Anyone know what these are for?  Since the boards are black, it's hard to trace where these go.

- Makeup gain resistors 51 & 33 Ohm seem to touch (solder bridge) as well as 310 Ohm & 180 Ohm.  Is this intentional?

- Also R'11 & R'12 seem to connect also, as does R'12 & R'13 - is this right?  They don't seem to share a pad, but they're REALLY close.

Thanks

 

[kambo]

yes they share pads, if you look at the other side of the pcb you will see...

if you send a jpeg etc with marks, where 5k6 etc wholes are, then i can help,
my eye sight is worst than urs  ;D

 

[jplum]

Hey jplum,

Yup read that, and also think yours may be a little high... just spoke to PeterC who has worked on a bunch of Neve modules and feels that a safer bet it 100mA of current, which across the 47R resistor would be 4.7VDC.

Also like you I tried it with my scope and saw little to no difference when using my scope... interestingly enough my Pro Tools 002R output can't put out a CLEAN +20dBu signal, it will only do about +18dBu and by then it is bordering on a square wave... interesting...

Cheers

Matt

attack 8'clock
release CCV
ratio 1:2

Dont forget to read the DC Bias post (2 pages back i think)

I think I had the attach Full Clockwise (Fast)
ratio 1:2
Recovery CCV
Threshold CV
Gain CCV
HPF & +10 both in Off position

Yes, all the db measurements were done on Fluke Meter using calculator as reference info!

Thanks for the tip on DC Bias. Right now i've not seen anything bad so i'll carry on for now but i'll maybe back off bias next time i'm inside.

fwiw, I used a ferranti signal generator @ 1khz as my signal source