Help with parallel & summing with THAT IC's

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Sine Star Audio
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Joined: Mon Dec 29, 2008 11:17 am

Help with parallel & summing with THAT IC's

Post by Sine Star Audio »

HI ALL,

I am building a box with various bits in, (M&S boards when available, Stereo Width control)

But also i would like to provide 2 Parallel O/P's and then SUM back in with Level and Mute controls. Here is a rough diagram i drew up,

I appreciate this is a bit simple for you guys so try not to laugh too much.. :D

but would this work?

1. in the parallel section can a 1246 drive 2x 1646's?

2 in the summing section, can i add a mute switch and attenuator where indicated?

3. and can i use the 1240 in summing mode as the data sheets specifies using the ref input so you have two matched 9k input resistors?

Image

any help would be really appreciated.

best

Pete
Sine Star Audio
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Re: Help with parallel & summing with THAT IC's

Post by Sine Star Audio »

Hi Roger,

thank you very much for your reply.

is there a better more elegant way to provide multiple outs then in this case?

i'm trying to achieve the cleanest most transparent circuit possible, perhaps my way is not good enough.

thanks

Pete
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mediatechnology
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Re: Help with parallel & summing with THAT IC's

Post by mediatechnology »

1. in the parallel section can a 1246 drive 2x 1646's?
Yes, but what Roger said.
2 in the summing section, can i add a mute switch and attenuator where indicated?
What Roger said.
3. and can i use the 1240 in summing mode as the data sheets specifies using the ref input so you have two matched 9k input resistors?
Yes. Just make sure at least one of them returns to a DC ground such as an op amp output to provide bias current for the 1240.

For a voltage follower consider the bipolar AD797. The OPA604 may have CM issues. When I used a bifet as a follower I compared the AD823 to the 604 and the 823 outperformed it.
Sine Star Audio
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Joined: Mon Dec 29, 2008 11:17 am

Re: Help with parallel & summing with THAT IC's

Post by Sine Star Audio »

thank you both,

ill prototype it up and see how it performs.

in the parallel section could i add another buffer to help drive the 1646's? im wondering how it would be done in a mixing console...

best

pete
Sine Star Audio
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Re: Help with parallel & summing with THAT IC's

Post by Sine Star Audio »

Ha ha yes my memory is bad too...even forget mt own name.

Excellent info chaps, It is for my mastering chain so AD797 it is.

Paul.....no, Pete!! :mrgreen:
Sine Star Audio
Posts: 14
Joined: Mon Dec 29, 2008 11:17 am

Re: Help with parallel & summing with THAT IC's

Post by Sine Star Audio »

3. can i use the 1240 in summing mode as the data sheets specifies using the ref input so you have two matched 9k input resistors?
Yes. Just make sure at least one of them returns to a DC ground such as an op amp output to provide bias current for the 1240.
OK, not quite sure i understand you, here is the drawing from the data sheet

Image

Do i need to add some thing to this circuit? or is it enough that Pin2 is to Ground?

All the best

Pete
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mediatechnology
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Re: Help with parallel & summing with THAT IC's

Post by mediatechnology »

I didn't exactly say the right thing.

One of the inputs has to have a DC path, not necessarily to ground. If you tie one of the 9Ks to an op amp output (as you intend to do) the bias current will have a DC path. Both inputs (pins 1 and 3) cannot be AC-coupled since there's no DC path for Ibias. If you look at the matrix stuff you'll see how I used both inputs for summation.
Sine Star Audio
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Re: Help with parallel & summing with THAT IC's

Post by Sine Star Audio »

Hi Wayne.


1. If I understand you correctly, i can go ahead as per the drawing in the data sheet?

2. learning here so bear with me, what is lBias?

3. looking at your M&S Matrix you summed via pins 2&3, grounded pin1 and Pin 6(out) to pin5(sense) at least to the drawing i have here..

4..sorry about this, if i have still have not understood maybe a little drawing if i maybe so cheeky.

I'm all good to go on the AD797, looking fwd to trying these out.

Best

Pete
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mediatechnology
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Re: Help with parallel & summing with THAT IC's

Post by mediatechnology »

1. If I understand you correctly, i can go ahead as per the drawing in the data sheet?
Yes, correct.
2. learning here so bear with me, what is lBias?
There has to be some path for the bias current at the input of the 1240 op amp to flow. That's true of all op amps. That current flows through one or more of the 9k resistors.
3. looking at your M&S Matrix you summed via pins 2&3, grounded pin1 and Pin 6(out) to pin5(sense) at least to the drawing i have here..
That's the bottom 1240 and the "difference" circuit.

The top 1240 in the drawing shown in the first post http://www.picocompressorforum.com/foru ... 12&start=0 has Mid into pin 3 and Side into pin 1 to produce "L."
syn
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Re: Help with parallel & summing with THAT IC's

Post by syn »

Hi
a bit off topic, but it seems that 1240 could be used to summ stereo signal to mono?(fig.10) 1240data

Thanks
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