The gain Switch on a 1272?

[Shortgypsy]

Hi there i found a rotary switch eith 2pol 12 pos at mousers now the thing is that at elma and farnell the rotary switch costs about 80$ and up but on mousers it costs 3.80$ so my question is can i use that rotary switch for the gain on a 1272????

here is the link to the spec page
http://www.mouser.com/catalog/specsheets/TW-700031.pdf

 

[wilebee]

for what aplication ?

 

[bradzatitagain]

There is no gain switch on a 1272, read the Neve 1272 schematic, there are switches similar to the channel amp Sensitivity switch on SCA's and JLM's. As a note, Kev has a page called Project 1, I believe it was his first diy project and it all centers around the 1272/BA183 amp. Do yourself a favor and read it.

http://recording.org/users/kev/Project1.htm

 

[Tekay]

To build a proper pre out of a 1272 you'll need a 3x12 switch to make it work like the 1290 but without the 50-80dB gain settings. also need to add a 1k5 in serie with a 100uF cap for the rear stage gain boosting.

 

[Kev]

[quote author="bradzatitagain"]... Kev has a page called Project 1, I believe it was his first diy project and it all centers around the 1272/BA183 amp. [/quote]

... my fist DIY ..... :green: :green: :green:

no,
far from it (I still don't have one yet)
it was the first combined project for Group DIY.
Too hard to explain how Group DIY was born, but it was sprung from a series of threads at Tech Talk. To try to explain things and present pictures a web page associated with the forum seemed a good idea.
blah, blah, blah
It was a much larger plan than people ever realised or I could ever bring to completion by myself ... Mag articles and T-shirts ... the works.

anyway the basic Neve BA283 board through to a complete channel strip of compressor was to be a vehicle to help explain many concepts. This was/is a very popular retro unit and was an obvious choice for Project 1.

NO it is not an easy DIY project (even though a simple 1272 on a new PCB was in the works) and so Project 2 would highlite another popular retro unit that was a relatively easy DIY build.

guess what the other projects might have been. There was even a preliminary sketch for P5 and P6 ... (comps) easy to guess the first two here.

Project 1 was always going to the longest project description of the Group DIY pages and with the most options
and hence the flag ship
... it never quite got there. :sad:

 

[bradzatitagain]

[quote author="Kev"]
(even though a simple 1272 on a new PCB was in the works) [/quote]


sssshhhhhhhhhhhhh!

All I know is what I've swallowed whole in the last 48 hours or so. Never really looked at Neve before, busy with 400V dc. It's fascinating gear, even just a single channel amp. What might not hit people right away is this stuff sounded good pushing signal through HUGE boards to a multitrack and then back again to a stereo master. It's not too hard to amplify one feed signal to recording medium but when there's big huge gobs of lots of signal things tend to turn into toothpaste by the time it gets to the radio. So while these little bits are ingenious in themselves Neve's genius, & API et al, was to get clean signal with out noise & distortion stacking up on itself, and still manage to master 24 or more tracks to two, with all the tape hiss stacking up on itself, & actually make a saleable album (artistry notwithstanding.) Then push the master through a Neumann lathe, press the lp's and start all over again in somebody's livingroom, with this tiny tiny tiny signal at a turntable stylus. Or magnetized waves on the sound track of 35mm motion picture film. Or picking radio waves out of the air. Not to mention television. If we're not quite as busy entertaining ourselves in 200 years or so I wonder what folks will think about this enormous effort we've made to reproduce sound and vision, dontchya?

Anyway, 1073 it is for me, maybe I can get TK to cut loose his secret on adding an HF rolloff switch. Y'know Kev you mention in Project 1 that you didn't think the 1073 was the thing for our digital age, but I don't think you ever got around to explaining why. ???? Why, amigo, why?

 

[rascalseven]

Shortgypsy,

Yes, you can use the Alpha 2x12 switch (make sure to get the 'shorting' type) for a 1272 clone. It would be perfect for this design:

http://www.jlmaudio.com/JLM1272hotrodmod.pdf

Peace,

Joel

 

[soundguy]

if you dont mind pops, the 2 bank greyhills are really nice switches which feel better to me at $18 than the 4 times as expensive elmas do anyday.

I wish someone would stock them shorting...

dave

 

[Kev]

[quote author="bradzatitagain"]Y'know Kev you mention in Project 1 that you didn't think the 1073 was the thing for our digital age, but I don't think you ever got around to explaining why. ???? Why, amigo, why?[/quote]

mmmm
:roll:
did I say that on the web page did I ?
... don't know as I remember what my train of thought was there. :sad:
someone remind me what I was on about !

let me start again from a very general stand point.

Much of what we do now can be about current trends and fashion. Once upon a time the AKG414 was the general purpose ALL rounder but you don't hear much about it these days. It can be a little bright on vocals and hence unforgiving. I think it is still a treat on drums and cymbals ... some styles of acoustic guit and now that electric guits are getting very narly it may be discovered again.

The various Neve channels strips can be a little over the top in the hands of the inexperienced. Dan Kennedy talks about the way this circuit can distort. The GR NV1 is made to take advantage of this and it does require some time to get to know it.

On the other hand the API 312 style of unit is very simple lined and you just dial in some gain. Headroom and drums pack punch.

Both of the above units can drive the current crop of DAW I/O into clipping very easily. This should make life easy but for some reason people still over gain their pre-amps and clip their Digital I/O.
this is bad.

Even so, for those that use the simple mic-pres and don't let see the red lights on the DAW, they usually end up with better recordings. When you add more to the signal chain on the way to the DAW the onus is on your to get your gain structure right.

In the hands of the experienced both of these mic-pres can make the sounds you have all grown up listening too. Sure these are not the only two styles out there ... Telefunken and the Reds just to name another two.

Last point on the 1073.
I may have been thinking about the EQ section and the other send related stuff that you don't need when racked adn tracking to a DAW.
I would prefer to see Mic-pres and EQ's and comps all separate and correctly terminated at the Patch Panel.
Now you can have any combination you want and with ease.

is Kev rambling ???
:shock:
run away ... run away ......

 

[Shortgypsy]

thx guys for all your posts
i forgot to mention what it was i was going to build well,,,
i want to build a 1272 mic pre with only 50db gain
in that case i only need the switch to be 2 pol becouse tha ba283av only has two stages and i don´t intend to use a pre gain stage so the grayhill would fit in just a bout perfect!
I think....

 

[soundguy]

yes, the greyhill will definitely work. Its my favorite switch, very high quality and under $20 per. The only drawback is that most places I know only stock the non-shorting, you get a pop in between the steps.

dave

 

[Family Hoof]

[quote author="Shortgypsy"]i only need the switch to be 2 pol becouse tha ba283av only has two stages and i don´t intend to use a pre gain stage so the grayhill would fit in just a bout perfect!
I think....[/quote]
I know I'm addressing this nearly 3 months late, but I must add this bit of info for future users.

Yes, there are only two stages and if you look at the specs it makes sense to have a 2 deck switch for boosting the two stages. However, if you build it this way you'll be very unhappy. Why? Too much gain! Neve always used a 3 deck switch with their preamps because the first deck is all pads = input attenuation. As a matter of fact, I don't think any boosting happens until the 6th or 7th click. If you look at how much gain initial gain there is before boosting (around 30dB including transformer step up, IIRC) it makes sense to do it this way.

If you look at a 1290 (the preamp only module, like 1073 but no EQ) and most any other 283-based preamp you'll see that Neve always used a 3 deck switch, even though there are 3 stages. The output stage (BA283AM) stays fixed with a 1k5 ohm coupled to a 100uF/25V from pin K to com. You have first the pads, then the boost for one pre stage (BA283NV) up to 50dB, and then from there it starts boost the other pre stage (another 283NV).

So, based on the Neve way of doing things it makes the most sense to wire a 1272 with a 2 deck rotary switch, one for attenuation and one for boosting the pre stage, NOT 2 decks for boosting both stages with no attenuation at all. A pre like that would be TOO HOT and unusable as such. See the schematic labeled Neve Hotrod mod at www.jlmaudio.com for a good example of two deck pad+boost switch.

 

[Family Hoof]

[quote author="soundguy"]The only drawback is that most places I know only stock the non-shorting, you get a pop in between the steps.[/quote]
Dave,

Why not try some 12k anti-click resistors like Neve did? I think the idea is the click gets shunted to ground. I haven't tried it yet but they're going on my next unit which uses the Elma, non-shorting.

 

[Bauman]

I´m using a Grayhill 2x12 switch here:

http://www.thediypill.phx.com.br/forumfiles/1272M_REV1.pdf

I think this Alpha can be use, np.

:guinness:
Fabio

 

[soundguy]

[quote author="Family Hoof"][quote author="soundguy"]The only drawback is that most places I know only stock the non-shorting, you get a pop in between the steps.[/quote]
Dave,

Why not try some 12k anti-click resistors like Neve did? I think the idea is the click gets shunted to ground. I haven't tried it yet but they're going on my next unit which uses the Elma, non-shorting.[/quote]


I dont know anything about that, do tell! Your link didnt show up in the post.

dave

 

[Family Hoof]

[quote author="soundguy"]Your link didnt show up in the post.[/quote]
Sorry about that. I just fixed it. It's a 1063 block diagram from Dan Alexander's site which shows the standard input sens switch but with 12k resistors added around the input transformer secondary. I believe I learned about this at Geoff Tanner's forum.

 

[Mbira]

Do those alphas come in anything other than continuous rotation? I've tried a few times, and that's all I seem to get with them. Is there a "locking" mecanism that you can get seperately?

Joel

 

[soundguy]

wow, I cant at all visualize what those two 12K resistors could do to stop popping? did Geoff go into an explicit explanation of that, I couldnt find anything poking around on his forum. anyone with an insight to how this works?

thanks

dave

 

[JLM Audio]

With a bit of thought you can keep the circuit electrically the same and do all the switching with a 2 gang 12 position switch and one small relay. This is how our Micro1290 works in the photo below. To keep clicks to a minimum with a non-shorting switch all switch positions need a resistive path to ground but most importantly any caps that feed directly to the switching need to have very Low leakage. Tants vary a fair bit in a batch leakage wise. You can buy special Low leakage electro's and tants with only 0.4uA. Where normal caps can vary from 10uA to 100uA leakage or way higher if they are old. Smaller leakage means smaller pops while switching.

Complete 1290,1073,1066,1064 etc Mic Pre in the palm of your hand. These will probabily be a kit down the track but at the moment we are racking them in pairs with the JLM Go between ,DI and JLM in and output transformers to make a 1290 version of our 1272 racks shown below.

Joe
www.jlmaudio.com

 

[soundguy]

[quote author="JLM Audio"]Complete 1290,1073,1066,1064 etc Mic Pre in the palm of your hand. [/quote]


Holy ****!


joe, you completely rule.

dave