Cross Fader

[SSLtech]

Got dashpots? -Got an air-line?

Got linear motor?

:green:

Keith

 

[thermionic]

Just to throw more confusion into the mix, I reckon the most sonically-transparent way to do this would be to use logic-controlled relay attenuators. You can drive them via a PIC, giving you multi-mode operation; i.e. one mode for fading, you flick a toggle to give second mode, whereby it jumps from minimum to maximum.

I have a relay attenuator, designed by an associate, that could easily be programmed to perform the above function. The only drawback will be that, by the time you’ve paid for the hardware and the tweaks to the code (unless you can programme PICs yourself), it’ll probably cost nearly as much as Mr Masses’ product. Oh well…I should’ve kept my mouth shut really…

I can ask Mark how much work he thinks it'd be to reprogramme the PIC for you, Paul, if it is of help. I doubt he'd take more than an hour-or-two over it.

BTW – Be careful when mentioning your Willy around Brits, PRR.


Justin

 

[thermionic]

[quote author="SSLtech"]Got dashpots? -Got an air-line?

Got linear motor?

:green:

Keith[/quote]

You could adapt a nail gun. Instead of nails, it pushes a piston connected to a P+G fader.

Job done! Be careful it doesn't come loose and plant a P+G in the belly of one of your clients.

J

 

[thermionic]

BTW - Totally OT: a couple of months back, I thought I'd go 'totally pro' in the workshop and buy a load of air tools... It seemed like a good idea at the time...

I get the tools delivered. The compressor's noisy enough @ 96dBA - I can live with it as it's mounted outside.

The drill attachment is in the high nineties for dB - just about bearable..

The screwdriver...wait for it...


107dBA :shock:

I had to return it... It got a bit much, having to don the defenders every time I wanted to take the screws out of a rack case...


J

 

[Gold]

[quote author="thermionic"]Just to throw more confusion into the mix, I reckon the most sonically-transparent way to do this would be to use logic-controlled relay attenuators.

it’ll probably cost nearly as much as Mr Masses’ product. [/quote]


JLM can do the relay controlled attenuator thing. I may end up having him design something. That was actually the original plan. I'm not sure discrete steps would work though. Do you think they would Justin?

The Maselec is 2 into 2 not 4 into 4. It it designed to tightly integrate into his console. If I could use the maselec I would. I don't expect hiring Joe to design it would be less than the Maselec.

I think I'll give the SSM a shot first. If I don't like the way it sounds I'll go to plan B.

 

[SSLtech]

For a slow crossfade with lots of low 'drone' and no high-frequency content, you CANNOT design a click-free crossfader, no matter HOW much you pay to whom.

Leif is a wonderful designer and a wonderful pragmatist, and I'm certain that he's 'done it right'. I bet there are no relays in his either.

Keith

 

[mikep]

PRR you are the man. that is a great idea. Ive been toying with the idea of making a tunrntable or tape transport with air bearings ever since I got the opportunity to work with oil-based hydrostatic bearings in grad school. I love the idea of having compressed air outlets in the control room. Or you could go with vacuum. dont you have a vacuum system already for lacquer-pube collection? or you could maybe use automotive parts. I drive an old mercedes and lots of things in there are vacuum actuated. you are limited to 14psi, best case, but how much mass does a crossfader have? the piston would not have to be very big to move "fast".

mike p

 

[Gold]

There is a vacuum system for the lathe. I wouldn't want to alter that because it is the weak point of the system. Chip pickup can be a problem in the humid weather. I have mine on a variac because I like to run it at 70v and the built in transformer is 60v.

I just bought a little air compressor for a powder coat system. A lot of the automation on the SMT record press is pnumatic. I have looked at some catalogs that were laying around. A linear actuator would do the trick. I'd have to learn something about control systems.

I like the SSM2402 best so far. For the most part I'm a practical fellow. I also want all connections between system blocks to be balanced. I'm not a purist.

 

[Gold]

To expand, the system will be:

Input amp (JLM dingo with a rotary switch attenuator in the middle), EQ(TBD but probably a big graphic based on the Forsell paper), Pico Compressor, HPF/LPF (Neumann HT75), Elliptical EQ(Neumann EE70), Output Amp(same as input), Crossfader.

For the most part it is short and clean.

 

[PRR]

> use automotive parts. I drive an old mercedes and lots of things in there are vacuum actuated.

'67 Cougar, '79 Thunderbird have vacuum headlight doors. '80s' GM heat/AC systems are full of vacuum motivators. The problem may be that the rubber rots, fresh new parts for these vintages may not exist (maybe at Mercedes prices), and newer (or just Japanese?) cars seem to favor electric motors. (Which will throw hash into the precious audio.)

A wax-cut room is likely to have vacuum, sure. But the race cars use a quite small bottle of compressed gas. Four shifts in 1320 feet, eight tracks on a side, no severe mass restriction... should not require a running compressor. Or a comp with a 1-Gal tank charged at breakfast might slap-fade all day.

> you are limited to 14psi, best case, but how much mass does a crossfader have? the piston would not have to be very big to move "fast".

It starts with mass per unit area. 14psi pressure on a piston with 14 pounds mass per square inch would start moving at 1 Gee acceleration. Someone with a sharper abacus than mine can estimate how fast the first inch can happen. Since most light-duty air motors are far lighter than 14 pounds moving mass per sq.in., it will take off much faster than 1 Gee.

Speed rises until air velocity in some part of the air path approaches speed of sound. The piston speed at this point will be lower, by roughly the ratios of the areas.

(Car engines tend to top-out at 4,000fpm or 800ips mean piston speed, 1/16th speed of sound, because valve open area is about 1/10th of piston area and there's manifold drag too, and if they really maxed-out there's no air to burn.)

Those two concepts give you wild estimates on system speed. Pneumatics Wizards will object that I left out some exponents and other fudges. But the only reason to calculate is to get a clue.

I suspect that many common air pistons from Ford headlights and heaters will need their ports drilled out BIGger and fatter plumbing glued in. This is sweeter in air than in hydraulics because leaks are not messy.

Google "air shifter"

For some reason that turns up a lot of bikes. OK, bike gears are more our size. I know they use this scheme on cars too. Cars may use "CO2 shifters"? Might be a thing about fire in a closed cabin.

http://www.pingelonline.com/ has complete kits for motorcycles.
http://www.pingelonline.com/air_shifter.htm
The stock kits seems to be one-way, since this is for drag racing. But the cylinder seems to have ports on both ends.

http://www.hardracing.com/Misc/MPS%20RACING.htm seems to do road-race, probably shifts both ways.

A movie of an air-shift in action. Not gonna win any cinematography awards, but you can see (or can't see) how fast a really goosed air-piston can jerk. http://www.youtube.com/watch?v=bhFFtFok3DQ

http://www.mpsracing.com/Instructions/MPS/Auto_Sport_Air_Shift.pdf has an installation overview. They seem to aim for 50mS-100mS of engine-kill, which is probably longer than it takes for the shifter to shift, and gears are heavier than fader-knobs.

Part of the gimmick for gear-shifting seems to be the engine-kill system, which is pointless for fast fades, so you don't want to buy the whole kit. I doubt these boys carve their own cylinders, it has to be a standard industrial item. But if you can get one of the race-shops "into" the project, you might get some good tips.


AH! Bimba invented this class of air cylinder and may be the market leader. http://www.bimba.com/


These schemes use electric air valves for remote action. Hands are up high, gears are down low, and long air lines from valve to piston will delay the shift. If you mount fader "at hand", you could skip the electrics. If you want the fader away from the pilot seat, electric gizmos may be convenient (but may shoot big transient fields).

http://www.paradigmmotorsports.com/html/actuator.html

http://www.jegs.com/webapp/wcs/stores/servlet/category_10001_10002_10515_-1_10513

Big trucks also use air shifters, but likely over-built for this use.