Balanced Line I/O

[mick]

Hi everyone
    long time away from the board, looks like I missed some great projects, I think I now have some time to start looking once again at some electronics projects (in between renovating our house), one of the things I have always wanted to do is an EQ, there are a few that I’ve been looking at, manly from desks, like the MCI vari Q (if someone could enlighten me as to what the laws of the pots are) and some others, anyway I’ve never tried something from scratch like this before. After a lot of musing on the subject I think the best plan of attack would be to start with a good balanced I/O, once I have that I can insert the EQ into it (that’s the theory anyway), many of the EQ’s being from desks are unbalanced plus I’m not trying to clone just be inspired by. Looking at balancing threads I get sense that the THATs chips are probably the easiest ways to go, would that be correct ? if that is the case which one’s ? what I don’t see are any diagrams so if someone could point me in the right direction for those too that would also be much appreciated.

One of the last threads by Igor seems to have exactly what I’ve been thinking about, he put up a schematic but (for me anyway) it’s not clear enough to read.

http://groupdiy.com/index.php?topic=50643.0

Thanks for any help you can give me to get this started.

Mick

 

[abbey road d enfer]

Looking at balancing threads I get sense that the THATs chips are probably the easiest ways to go, would that be correct ? if that is the case which one’s ?

1206/1646

what I don’t see are any diagrams so if someone could point me in the right direction for those too that would also be much appreciated.

Just use the application notes in the datasheets.

 

[bruno2000]

Inputs:  http://www.thatcorp.com/datashts/THAT_1200-Series_Datasheet.pdf
Outputs:  http://www.thatcorp.com/datashts/THAT_1606-1646_Datasheet.pdf
Best,
Bruno2000

 

[mick]

Thank you Abbey road, it was many of your posts on a lot of the threads that lead me to think the THATs chips were the easiest solution

And Thank you Bruno2000 for the links and for making the 1084 dual mids, whilst DIYing our house dry wall jointing (and sanding) and all the other jobs that cover you in crap, my mind is conjuring up ideas, one was was it possible to have a dual mid on a 1084, I was astonished that it was and you had already done it.

Thanks again

    Mick

 

[abbey road d enfer]

Thank you Abbey road, it was many of your posts on a lot of the threads that lead me to think the THATs chips were the easiest solution

Don't believe blindly what pompous old farts write on the internet  ;D

 

[mick]

Please forgive my hack job at putting some examples on a page, I can’t ever get a decent quality drawing out of a PDF file, the resulting bits and bobs are snatch from whatever jpegs I could find for a visual representation to see if I have the right understanding of where the THATs chips are applied to the circuits.
So , I’ve cut and paste some diagrams for the kind of circuits that I’ve been seeing, one input and two types of output, looking at those Data sheets have I correctly interpreted which part the 1206 and 1646 replace in the circuits ? I’m unsure in both the In and Output if the single op amp before (after) the (in) output pair (or transistor pair) remains or is replaced with the THATs chips as well ? (Try saying that lot after a whisky or three).

Thanks

        Mick

 

[abbey road d enfer]

Please forgive my hack job at putting some examples on a page, I can’t ever get a decent quality drawing out of a PDF file, the resulting bits and bobs are snatch from whatever jpegs I could find for a visual representation to see if I have the right understanding of where the THATs chips are applied to the circuits.
So , I’ve cut and paste some diagrams for the kind of circuits that I’ve been seeing, one input and two types of output, looking at those Data sheets have I correctly interpreted which part the 1206 and 1646 replace in the circuits ? I’m unsure in both the In and Output if the single op amp before (after) the (in) output pair (or transistor pair) remains or is replaced with the THATs chips as well ? (Try saying that lot after a whisky or three).

Thanks

        Mick

North: 1206 replaces the 3 opamps, up to (but non-including) the coupling capacitor.
West: 1646 replaces everything including output xfmr, but does not provide variable-gain. Variable gain has to be implemented upstream.
South-East: 1646 replaces the 3 opamps. Output coupling caps are not necessary in most cases.

 

[mick]

Thanks Abbey Road, sorry I haven’t been able to sit down and give this some time till now, so again I’ve hacked some jpegs up, can you tell me please if I’ve got the drift or just a cold.. could be flue, the section after the 1206 is just pasted from another diagram so there maybe odd components which are irrelevant.

Thanks

        Mick

 

[abbey road d enfer]

Thanks Abbey Road, sorry I haven’t been able to sit down and give this some time till now, so again I’ve hacked some jpegs up, can you tell me please if I’ve got the drift or just a cold.. could be flue, the section after the 1206 is just pasted from another diagram so there maybe odd components which are irrelevant.

Thanks

        Mick

Seems ok. Just beware that in order to maintain 90dB CMRR, tolerance on the two 100R at the input must be better than 0.2 ohm.