simple balanced +6db/-6db gain stage

[dagoose]

I'm in the middle of building a new mastering insert matrix and I was thinking of adding a (relay hard bypassable) active gain stage on the input. I want a boost and cut function, 6db of boost and 6db cut with a stepped attenuator to drive the analog chain.
I want it balanced in to out so I was thinking of using a that 1246 into 1646 stage with something like a 5532 in the middle that takes care of the gain.
But I was thinking if there might be a more simple solution, but I can't figure it out.  :-\
No problem to have a balanced attenuator, but I think i have to bal/unbal/bal anyway.
Anyone?

 

[kante1603]

Hello,


I did something like that with a DingoPup from JLM,formerly as an active fader with some gain in hands.
Basically a bal. to unbal. and a unbal. to bal. stage including a fader booster amp.
I later made it a +/-15dB by boosting +15dB at the booster amp (has a trim pot).
For the -15dB I simply added a trim pot between bottom of fader and gnd.
Works perfect,the circuit is based on OPA2604s running at +/-24vdc.
Has a hard bypass through relays too.
I use it for adjusting the output levels of my recording chains into the interfaces.


Best regards,


Udo.

 

[madswitcher]

Hi Dagoose,

have a look at the line input stage (IC 400 on the left hand side) of the enclosed pdf.  Switchable from -6dB, to 0dB to +6dB.  I think this does what you want.

Cheers

Mike

 

[abbey road d enfer]

have a look at the line input stage (IC 400 on the left hand side) of the enclosed pdf.  Switchable from -6dB, to 0dB to +6dB.  I think this does what you want.

Actually, the gain of this stage is switchable from -12 to -6 to 0dB. By changing the resistor values, it is quite possible to achieve the requested range.

 

[dagoose]

Thanks so far!
What I actually meaned was, +/-6db (5.5 with 23 steps 0.5db per step) gain range, not switcheable, so with a potmeter.

 

[abbey road d enfer]

Thanks so far!
What I actually meaned was, +/-6db (5.5 with 23 steps 0.5db per step) gain range, not switcheable, so with a potmeter.

See attachment

 

[madswitcher]

Actually, the gain of this stage is switchable from -12 to -6 to 0dB. By changing the resistor values, it is quite possible to achieve the requested range.

Hi Abbey road d enfer,

yes of course you are right, it brings down the line level to the working level of the MCI console which is -6dB, but a neat little circuit anyway all done with one op-amp. 

Cheers
Mike

 

[dagoose]

See attachment

Yes, this is basically whay I had in mind with a that/ssm in front and after for unbal/bal.
Thanks, this is useful

 

[dagoose]

I think this should do?
The potmeter will be a stepped switch (10k lin)

Do you guys agree with this?

 

[abbey road d enfer]

I think this should do?
The potmeter will be a stepped switch (10k lin)

Do you guys agree with this?

Don't forget to properly decouple the supply rails  with one pair of 0.1 ceramics at each chip and a pair of 100 uF electrolytics.

 

[dagoose]

Don't forget to properly decouple the supply rails  with one pair of 0.1 ceramics at each chip and a pair of 100 uF electrolytics.

Nope, I won't 
It's not in the schematic right now.

But this should be it then?

 

[abbey road d enfer]

Nope, I won't 
It's not in the schematic right now.

But this should be it then?

Yes.

 

[dagoose]

Yes.

Got it up and running. I only need to make the stepped swithes, but that won't be a problem.
One small mistake, the output phase was inverted because of the  5532 stage but that was an easy fix.  8)