Neve 1272 and impedence question

[rascalseven]

I suggest you try the gain structure I posted earlier. Most of the time you won't be requiring higher gains, and so the sound will be pretty much what one would get from any class-A Neve at 50dB or below. As for the higher settings, the second stage does get kicked up a bit, so it shares the burden some rather than placing all the extra gain on the front end. Also a 2x6 Lorlin (or an Alpha from Mouser) is much cheaper than a 3-pole switch, and the input 'pad' eliminates the need for a separate fader.

It's simple, cheap, and sounds great.

Another option would be to build a combination of the SimpleMod and HotRodMod by using the input pad pot from the SimpleMod, and then just use a 1x12 Lorlin (set to six positions) for the six gain settings on the preamp stage. This dumps all the gain on 1st stage, but if you not gonna be using higher gains much, then perhaps that's cool overall. The input pot again eliminates the need for a separate fader, and then you can use the 1-pole switch (in fact, you could calculate resistors to create 2.5dB steps instead of 5dB steps and go ahead an use all 12 positions of Lorlin switch for finer control....?)

I built the SimpleMod first, and it was great (that's my quote on Joe's schematics page). After that I altered the design to the one in my previous post to make it more flexible and to get more gain while still sounding good. The SimpleMod, however, does sound fantastic, and is the simplest Neve-type design I've seen, so I highly recommend it as a first Neve project.

I think you would find any of these options would result in excellent-sounding, useful preamps. Just make sure you check the threads about proper grounding and shielding of old Neve's to help you get the best results with whichever design you choose.

JC

 

[mich]

No resistor, you need a big inductor. N*eve T1310 or something equivalent. se here

so, there is no other way for "checking the circuit" without the LO1166 or T1310? if i just put a jumper in place of the transformer?

i understand that this inductor is about 700mH ,where could i get one?or something "equivalent"?

 

[chrissugar]

[quote author="mich"]
if i just put a jumper in place of the transformer?
[/quote]

That would be a very bad idea. :grin:

chrissugar

 

[clintrubber]

so, there is no other way for "checking the circuit" without the LO1166 or T1310?

I've seen a (small) resistor being mentioned (just to see if all is well while you're waiting for your TXs to arrive).

 

[mich]

...sorry to insist...but:
what happens if i conect a non gapped transformer primaries with the same impedance as the LO1166 (600ohm) ,and then take the output from pin F?
what will the 24 VDC do to the transformer?
thanks

 

[Family Hoof]

It will drive it into saturation, maybe magnetize it, maybe burn it up and cuase some windings to split or short. There's usually around 80mA. Depends on the transformer, but it's bound to do some damage.

Honestly, there are at least 3 companies making a suitable transformer right now. Get the right part and be done with it.

 

[Aryuserius?]

After many sheilding issues, I am left with one question:

For the gain up to 40db using Joe's hot rod method, does Pin T from the ba283 have to go to ground? In other words until that gain stage kicks in from pin T through resistors to ground, should T be grounded with no resistor?

I have seen it shown as "open"???? Any clarification would be great!!

BTW thanks for everyone's help to get to this point!! I litterally couldn't have done this without members from this site sharing their knowledge!!

-Mike

 

[Tekay]

Without any extra gainboosting "T" shall be open!
Think you have 18dB of gain in the first 283 stage, the rest of the gain is from the transformers and the output stage.