CMMI-2C in a 1272?

[3nity]

Its bassicaly a 1290 but some changes..

 

[3nity]

Please correct me if i'm wrong if this wont work!

:thumb:

 

[rascalseven]

[quote author="3nity"]Please correct me if i'm wrong if this wont work!

:thumb:[/quote]

I'd have to see the schematic to know, but in generally people don't use pots for setting the gain on Neve's. It can be done, but I don't see how a dual 10k pot could be substituted for a rotary switch.

The gain switch on a Neve mic amp uses 3 poles and accomplishes three purposes: 1) to control the gain of one preamp stage, 2) to route signals among the three gain stages, and 3) to manipulate a pad network within the signal routing to help achieve specific overall gains.

On some 1272 variations (like the HotRodMod from JLM) the gain switch is a 2-deck affair that 1) manipulates the input pad, and 2) alters the gain of the preamp stage.

I don't see how a dual gang 10k of any taper would be a suitable substitute for either gain switch.

I use a pot as a continuously variable pad on my JC1272, but that's a 5k audio, and usually an output fader (between last preamp stage and output stage) would be a 5k audio as well, not 10k, though 10k could work. If you want pots for the gain stages then I'd suggest a rev. log 2k for the output stage in series with a 300R-ish so you don't blow it up on max gain (don't forget the 100uF cap!) and a 500R rev. log for the preamp stage with a 10R-20R in series.

I don't see how a 10k dual gang would work in a Neve.

Are you building your own design or something someone else has already done?

If you can provide more info on the circuit I can probably be more helpful to you.

Peace,

JC

 

[3nity]

http://www.soundskulptor.com/pdf/mp73-schematic.pdf

this is the link to schematic.

 

[rascalseven]

That is an interesting adaptation of the class-A Neve topology. Neither of the 10k pots are adjusting any gain, they’re trimming signals instead. And I don’t know why it uses dual-gang pots, because it appears only half of each is even connected, so a pair of single-gang 10k audios will do the same thing.

There are three levels of actual gain in this thing, 15dB apart each. At the lowest setting (about 40dB) there are only two stages engaged, and the first 10k pot is acting as a variable pad fed straight from the secondary of the input transformer. At the next level it is the same with the preamp stage adding approximately 15dB additional gain. At the highest level the first stage drops back 15dB and the third stage (a second preamp stage) comes into the picture cranking out about 30dB of gain. At this loudest setting the first pot becomes trims the level between the first and second preamp stages.

At all gains the second pot trims the level between the earlier stages and the output stage.

15dB is a huge step between settings – so big I would think this design awkward in actual use. When using this circuit you will definitely want to develop the habit of trimming back the input pot significantly before advancing to a higher gain setting. A 15dB jump in level can actually blow things up (like speakers and ears) depending on what you’ve got running through it, so trim that input knob back quite a bit before stepping up the gain.

This design is probably a compromise in the interest of space limitations and desire for low parts cost.

Yes, it’ll work, and true you don’t have to buy a 3-pole rotary switch for the gain. I don't really agree with their claim that "from an electronic point of view, the circuit remains identical to the original." This is most definitely not like an original, but perhaps I'm splitting hairs.

Despite the potential awkwardness of the gain arrangement this will probably sound nice.

If you build it please report back your thoughts on it.

Much peace,

JC

 

[3nity]

Screw it i cant experiment at this moment.
My studio has been shut for a while, DIY reason.
I need to bring finish those and experiment later.

I received my Grayhills just waiting for my Cinemags.

Cheers.

 

[3nity]

digging on this old thread to report back on using the cinemags on a ez1290.
the dual channel unit has had great reviews from people who used it on a loan.
they said its sounds like silk an kind of it has a little compression going on!??
Well im very happy of my neve.

Cinemag transformers are just awesome and the most beautiful sounding transformers.
you loose some dbs but in a 1290 it doesnt really bothers me!

good luck.