pucho812

does a neve 2254 really work this way
« on: September 08, 2010, 09:11:16 PM »
I have never seen a 2254 schematic or ever used a 2254. But one of my co-workers was insisting that a 2254 takes the line level signal knocks it down to mic level. does the compression stuff and then boosts it back up to line level at about 70db and that the make up up gain is really an an attenuator....  Never used one but the idea just sounds wrong to me....

 what's really going on in there?
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.


shabtek

Re: does a neve 2254 really work this way
« Reply #1 on: September 08, 2010, 10:13:40 PM »
fwiw:
i'm looking at an uncle fester schematic not the original--don't know the 'trunny' [slang is bugging me (transformer)] ratios but after the input xfmr I see about a 10 or 20:1 signal knock down b-fore the fets that feeds another trans and some boosters sidechain etc...don't about the attenuator but it don't sound too wrong to me--shunt-fet agc don't allow for big signal at the active portion afaict.
"really fine players do not use stomp boxes or master volume, they match the amp to the room and turn it up to 11.  Stevie Ray, BB King, Albert King, Duane Allman, Dicky Betts, Louis Armstrong"
   -CJ

pucho812

Re: does a neve 2254 really work this way
« Reply #2 on: September 09, 2010, 12:43:13 AM »
fwiw:
i'm looking at an uncle fester schematic not the original--don't know the 'trunny' [slang is bugging me (transformer)] ratios but after the input xfmr I see about a 10 or 20:1 signal knock down b-fore the fets that feeds another trans and some boosters sidechain etc...don't about the attenuator but it don't sound too wrong to me--shunt-fet agc don't allow for big signal at the active portion afaict.

I never seen a schematic.... so thanks for that...
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

PRR

Re: does a neve 2254 really work this way
« Reply #3 on: September 09, 2010, 10:44:00 PM »
> what's really going on in there?

I don't have a clue what you are talking about.

However most variable-gain schemes have a narrow dynamic range. Often, the noise is not so high, but the maximum level is quite low.

Diode-bridge is clean to 20mV, distorts bad past 60mV.

OTA-like gain-cells the same.

JFETs go wonkers somewhere above 50mV-200mV.

Opto-resistors are not so abrupt. 200mV is pretty darn clean. I could hear the change when I built with 3V limiting level, noticable IM.

The DBX et al VCAs would be nasty above 20mV and servo-away their input so the actual emitter level is a teeny fraction of a mV (ideally zero).

Tube limiters may reach several Volts on the grids, but distortion is rising. Start-of-limiting is usually 100mV-200mV.

Potentiometers can handle line level but have trouble with speed.

Any of these lower levels "might" look like "mike level". And some of these would naturally use something like a "mike preamp" after the gain-cell.

QUEEF BAG

Re: does a neve 2254 really work this way
« Reply #4 on: September 09, 2010, 11:02:46 PM »
pucho-

i put a schemo in out gmail acct. i'll add block with levels too.

Tekay

Re: does a neve 2254 really work this way
« Reply #5 on: September 10, 2010, 03:00:31 AM »
The level coming out from the diode bridge is -40dBm, see below signal flow diagram.
http://danalexanderaudio.com/neveinfo/neve2254aSchem.jpg
Thomas "TK" Kristiansson
----------------------------------
"The Sound Is In The Iron"
www.vintagedesign.se  www.tkaudio.se

pucho812

Re: does a neve 2254 really work this way
« Reply #6 on: September 10, 2010, 03:36:54 AM »
once again ask a little question and get a wealth of knowledge from people around here. thanks guys.. I will digest the info....
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

tv

Re: does a neve 2254 really work this way
« Reply #7 on: September 10, 2010, 07:18:51 AM »
.. I will digest the info....
BEWARE!
It will give you some BAAD gas!
If you sprinkle when you tinkle, please be neat and wipe the seat.

jensenmann

Re: does a neve 2254 really work this way
« Reply #8 on: September 10, 2010, 07:39:33 AM »

Potentiometers can handle line level but have trouble with speed.


What does that mean, PRR? Could you pleasse elaborate this?
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

Kingston

Re: does a neve 2254 really work this way
« Reply #9 on: September 10, 2010, 07:47:54 AM »

Potentiometers can handle line level but have trouble with speed.


What does that mean, PRR? Could you pleasse elaborate this?



Sredna

Re: does a neve 2254 really work this way
« Reply #10 on: September 10, 2010, 09:25:45 AM »
 ;D
Hmm... in which direction do the electrons actually go?

jensenmann

Re: does a neve 2254 really work this way
« Reply #11 on: September 10, 2010, 09:27:52 AM »
 :-\ I have to work on my humor skills
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

PRR

Re: does a neve 2254 really work this way
« Reply #12 on: September 10, 2010, 12:07:09 PM »
Panasonic used to make affordable motorized pots. I'm not seeing the low-price ones at DigiKey today. They do have a $50 motorized slide-pot. You can also salvage motorized volume knobs from 1980s stereos.

If sound is too loud, apply a negative voltage to the motor to turn the knob and volume "down".

When sound is not excessive, but was, apply a positive voltage to the motor to restore the original gain.

If motor speed is proportional to voltage, then attack/release slew rates may be set with voltage stops.

An advantage: this limiter pot may also be your main gain pot, keeping the audio system simple.

Speed: IIRC the slew was OTOO 20dB per second. A smooth manual fade. This might be OK for a slow leveler. It is far too slow to limit transients. The motor voltage could be raised above specs and speed would increase. Motor would not overheat because the over-volt period is short. But 10X voltage is still only 200dB/Sec or 0.2dB/milliSecond or 2dB in 10mS. And 10X voltage might cause arcing in the brushes and rapid pitting and early failure.

There are fastor motors, and Mechano or robotics hardware to couple motor to pot. But electric motors rarely hit the millisecond speed we need for rapid audio limiting.

We could try voice-coils. Lower mass. However a long-travel voice coil's self-mass gives about a millsecond max response, slower with pot mass, and probably leverage to convert to wide rotary swing (or long linear swing) from short linear motion.

Air pistons and valves are a bit quicker.

All fast mechanical contraptions are prone to be clunky so may have to be isolated from the monitor room.

Re: does a neve 2254 really work this way
« Reply #13 on: September 10, 2010, 12:33:06 PM »
What about a flywheel and a clutch?

Or maybe compressed air? You'd need a compressor to power your compressor.


Justin
Prepare yourself. You are about to become the voice of Interplanetary Parliament.


 

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