1272 to 1073 Master Thread

[JessJackson]

There's a load of information on this and I would like to consolidate all info's I could find into this one thread to get others opinions.

I want to get to the bottom of the best conversion techniques. So lets get the drama started and the ball rolling...

I want to get into adding a High Pass Filter board (this will fit without re-racking) and PSU options (sound of passive vs regulated etc..) later but first lets attack the Gain structure...

Eisen Audio

http://www.eisenaudio.com/projects/design-retrofits-1272-sensitivity-switch/

Was Hired by Glide on Fade to create this switch

http://glideonfade.com/electronics.htm

They state the switch is:

LINE
1 = +10 (in other words, a 10dB pad)
2 = +5
3 = 0 (unity)
4 = -5
5 = -10 (10dB of gain)

and 6 positions of mic gain in 5db steps

MIC
6 = -20 (20dB of gain)
7 = -25 (and so on...)
8 = -30
9 = -35
10 = -40
11 = -45
12 = -50

Surely the only TRUE way to get a Line In would be to use a separate 31267 input transformer or create some sort of switch to use the 10468 in reverse and parallel.

No Schematic available on their site but looking at the wiring guide ( http://glideonfade.com/aswiring.htm ) it seems that they use a very similar schematic as Joe at JLM which leads me to...


JLM

Joe published the 1272 Hot Rod Mod ( http://www.jlmaudio.com/JLM1272hotrodmod.pdf )

This is probably the most utilised schematic on the inter web, in fact its the one I used to configure my 1272

Joes design calls for the same 12 position switch but configured with different value resistors to obtain 10-65db of gain.

MIC
1=10db
2=15db
...
...
11=60db
12=65db


Geoff Tanner

I recently came across Geoff Tanners statement on how he doesn't like JLM incorporation of the gain knob ( https://www.gearslutz.com/board/geekslutz-forum/947775-racked-vintage-neve-1272-a.html#post10465269 )

on his FAQ he states to use both the front amp and rear amp sequentially for gain (F & N on rear connectors & T & F on amp card) respectively),  ( http://auroraaudio.net/ask-geoff/faq )

He elaborates on this in this thread in his forums ( http://auroraaudio.net/forums/topic/the-1272-line-amplifier-uses-and-foibles#post-216 )

In Geoff's diagram the attenuation pot is fitted between L and K but thats the same as JLM schematic P & L on the AMP board end up at L & K on the rear terminals.

Summary

So whats everyones thoughts on the gain implementation... Do you like JLM or Eisens approach or do you like Geoff Tanners approach or does this even matter at all at lower <-50db gain settings.. should we re-assess our 1272 modifications.

It would seem that my 1272 was originally fitted with an attenuator utilising the Baxandall trick of a 10K linear pot with a 4.7Kohm resistor from the wiper to the bottom.

In terms of the attenuator, I see people silk screening 0db at centre position and in some cases fitting a pull out attenuator to bypass the pot completely. But isn't true 0db at unity clockwise? or is this just purely subjective?

If you are gaining up the rear amp at the same time as the front amp then I can see the thought behind trim being centred at unity and having the option to either attenuate or overdrive the output transformer but with the output transformer "wide open" as Geoff claims as is JLM approach ( 1.5k and 100uf to -0 ) then I don't see why people would use 0db (unity) centred.

... and just to throw another spanner in the works I found this schematic which is similar to JLM but uses 11position 20db to 70db


Jesse

 

[Biasrocks]

You must balance the gain stages in order to emulate a 1073 mic pre, you need a 3 deck switch.

Also, Glideonfade answer your line input question on his page

This switch additionally allows provisions to use the 1272 as a traditional LINE input with two choices:

The neve 1073 EQ used two different input transformers, a mic input transformer and a dedicated line input transformer. The switch in mic mode would pad and boost the 283AV wired to the 10468 input transformer and in line mode would switch the 283 AV to a 31267 input transformer for line level impedance.

The Neve 1063 EQ used a single 10468 input transformer, in mic mode the switch pads and boosts the 283AV and in line mode, a pad shunts the 10468 for use with line level impedance.

The Glide On Fade Awesome Switch can be configured to switch between two transformers or use one to accomodate a line level input. If you have a 1272 and do not wish to add an additional transformer, order the switch configured in 1063 mode, if you wish to add a line input transformer, order the switch configured in 1073 mode.

Verification is here.

http://www.technicalaudio.com/neve/neve_pdf/1073-fullpak.pdf

Mark

 

[JessJackson]

You must balance the gain stages in order to emulate a 1073 mic pre, you need a 3 deck switch.

Also, Glideonfade answer your line input question on his page

This switch additionally allows provisions to use the 1272 as a traditional LINE input with two choices:

The neve 1073 EQ used two different input transformers, a mic input transformer and a dedicated line input transformer. The switch in mic mode would pad and boost the 283AV wired to the 10468 input transformer and in line mode would switch the 283 AV to a 31267 input transformer for line level impedance.

The Neve 1063 EQ used a single 10468 input transformer, in mic mode the switch pads and boosts the 283AV and in line mode, a pad shunts the 10468 for use with line level impedance.

The Glide On Fade Awesome Switch can be configured to switch between two transformers or use one to accomodate a line level input. If you have a 1272 and do not wish to add an additional transformer, order the switch configured in 1063 mode, if you wish to add a line input transformer, order the switch configured in 1073 mode.

Verification is here.

http://www.technicalaudio.com/neve/neve_pdf/1073-fullpak.pdf

Mark

Cheers mark,

so you would do it Geoff's way then?

 

[Biasrocks]

Yes!

Cheers mark,

so you would do it Geoff's way then?

 

[GabrieleP]

Hi JessJackson and Biasrocks,
Hi anyone willing to contribute,
I own a pair of original Neve 1272s racked (many years ago?) by Brent Averill Enterprises. Own them since 15 yrs and from time to time I have been wandering around the many forums to learn more about the circuit. At some point I decided to implement the Tanner modification (I also "spoke" with him over at GS forum), got a pair of Grayhill rotary switches and all the right resistors to reach 69 dB of gain, simultaneously getting 2 dB from the "preamp section " and 1 dB from the "power amp", 3 dB total for each of the ten steps.
I was also thinking about removing the front panel "D.I." jack and having a LO/HI Z DPDT switch instead...
While researching more, I eventually found schematics for the 1073 and for the 1063.
You know what? I am leaving it like it is, Averill stock.
There is a nice, three deck Elma switch in there wired exactly (realized just a couple days ago) - exactly like in the 1073 schem from 20 to 50 position, same resistor values. So I guess I can say that in those seven positions my 1272s ARE and BEHAVE like any other 1073. Can't I? I don't need more than 50 dB: for condensers they are plenty and for moving coils/ribbons I am doing it with the Cloudlifters (they are awesome, I can utilize my Royer SF-12 as if it was a condenser!)
I have a couple questions: do you happen to know or have suggestions about what I should do with the 5.6k resistor wired in parallel to the secondary of the 10468 transformer? It shows in the Tanner schematic, stock 1272 used as a line buffer amp, but it's not in the drawing EH10023 for the 1073 channel amp. I think I read that the whole gain switch assembly in the 1073 kinda substitutes that 5.6k. The reason why I ask is because many years ago I converted my two 1272s to high input Z, wiring in series the primary of the 10468. It was a very easy mod, closely followed by own Avedis' suggestion to replace the 5.6k resistor with a 10k, "[...]not as necessary but it will help maintain closer to 1200 ohms[...]" (in his own words).
I am still thinking about the HI/LO switch option, fueled by what I see on the EH10023 drawing.
Second question is about the "volume pot": basically that feature was left untouched by Averill, 1272 stock.
Handy if you need to slightly alter the output in those situations when 5 dB more is too much.
But say I am deliberately looking for "too much": crank the gain, lower the volume type of thing.
Doing so at present, I am just bombing the AM section with a lot of signal coming from the NV section and I am NOT overloading the L1066 output transformer, right?
Question: can I get rid of the "volume" pot and have a 600 Ohm T-pad attenuator like the ones featured on the CAPI gear AFTER the L1066? Would it be a nice solution? Can you indicate better ones or counter-indications?
Finally I could redo the gain switch in 1063 style, even have an "OFF" position: that would also be nice and still "original Neve".
Thanks in advance for any comment/suggestion.
Peace.
Gabriele

P.S. @ JessJackson: the last schematic you posted is almost exactly what's on the Averills, just a couple slightly different values: 8.2 instead of 8.7.

 

[ruffrecords]

You cannot make a 1073 out of a 1272. A 1272 has a single BA283AV board. The 1073 has an additional BA283 board which is used in the mic pre and EQ sections of the 1073.

You can make a mic pre from a 1272 but it won't be a 1073.

Cheers

Ian

 

[GabrieleP]

Hi ruffrecords!

I am sorry if I was not clear enough in my post but to be honest I never said I want to make a 1073 out of my 1272.
I am not an electronic expert by any means but I am pretty confident that from position 20 to position 50 of the gain switch, the second BA283 card is NOT involved in the game and there is no difference between a 1272 and a 1073. You confirm that? It's been said here in this forum before, I am not making it up myself.

Thanks, G.

 

[ruffrecords]

Thread topic "1272 to1073 Master Thread" sounds awfully like wanting to make a 1073 out of a 1272 to me. If you are not trying to make a 1073 why even mention it?

So what are you trying to do??

Cheers

Ian

 

[MagnetoSound]

Perhaps you should have put 1290 in the thread title, since 1073 might imply an EQ.

JLM '1073' and others (AML etc)  are usually just mic/line gain stages.

 

[GabrieleP]

I didn't start the thread.

Since it's a clear fact to me that a 1073 cannot be made out of a 1272, I thought I'd contribute to the community reinforcing the not so commonly known fact that a 1272 can be a 1073, only from a certain gain setting up to a certain gain setting and only if you wire it like Brent Averill did years ago. It looked like the right thread to do so.

Cheers, Gabe

 

[MagnetoSound]

I didn't start the thread.

So you didn't. My bad.

 

[ruffrecords]

I didn't start the thread.

Since it's a clear fact to me that a 1073 cannot be made out of a 1272, I thought I'd contribute to the community reinforcing the not so commonly known fact that a 1272 can be a 1073, only from a certain gain setting up to a certain gain setting and only if you wire it like Brent Averill did years ago. It looked like the right thread to do so.

Cheers, Gabe

OK, it is clear we have been talking at cross purposes. I was answering the very first post, not your post. When you replied I thought you were the op.

LOL

Either way, we agree you cannot make a 1073 out of a 1272.

Apologies for the confusion.

Cheers

Ian