A better sounding 812 monitor module for an API 2488?

[pinebox]

Hello, I have been a repair tech for over a decade but my large active circuit design experience is minimal. One of my friends/clients has been asking me to make better sounding monitor cards for his API for a couple years now. I know a lot of people complain about the audio quality of these, and looking at them there isnt much to the card, just a couple ICs, relays, some routing switches and pots, so I am going out on a limb and assuming that the two dual op amps are mostly what is holding it back from sounding more like its channel side counterparts. The 812 module is half width a normal console channel, so fitting a 2520 to this footprint was limited by the height of the DOA, my solution for this is to face the odd and even modules towards each other and mirror them with a shared face plate just like the 528 module so that the blocks for each side have space between them to live. But perhaps I am putting the horse before the cart by designing the mechanical before getting thoughts on this circuit.

1)Would this circuit benefit greatly from swapping the 4739 IC with two 2520s or is the weak point a bigger picture than that?

2)What values if any should I consider adjusting around the 4739s if replacing with DOAs? Can I essientally swap them 1:1?

3)Could I put a single 2520 after the TAPE/PGM relay switch instead of two of them before the switch? Or is there a good reason for having the op amp previous to the switching?


Thank you anyone who shares their experience with me.

 

[fazer]

Funny my experience is with my 2488 console that was built for a church pa board so it has no monitor modules. I assumed they were simple 2520 circuit. I would assume a replacement socket adapter for a pair of 5534s or even. 5532 would be all you need to help out. My board used 2520 on all the echo and cue modules. With a few chips used in places like meter circuits.

 

[Walrus]

Has it been recapped recentlyish? As according to one of the assistant engineers,
that made a world of difference to the one I used to tech.
The monitor module will always sound different to the main desk as it has less transformers in its audio path.

 

[pinebox]

Funny my experience is with my 2488 console that was built for a church pa board so it has no monitor modules. I assumed they were simple 2520 circuit. I would assume a replacement socket adapter for a pair of 5534s or even. 5532 would be all you need to help out. My board used 2520 on all the echo and cue modules. With a few chips used in places like meter circuits.

Yes, every circuit in the channels and center section use a 2520, the 812 Monitor returns use some 4739 ICs as their op amps. I am going to replace these with a socket for 5532s or a DOA in a 2520 footprint and see what happens. If I didnt live two hours away, I would probably spend some time wiring in some 2520s off board to just test and A/B, but its also a nice project for me to become more KiCAD fluent while at home. I'm about 70% done with the layout, I will get some prototypes made and have him populate it for testing, he likes building kits and stuff. Then if they work well I will design the face plates and make 24 of them.

Has it been recapped recentlyish? As according to one of the assistant engineers,
that made a world of difference to the one I used to tech.
The monitor module will always sound different to the main desk as it has less transformers in its audio path.

Yes, the whole console has been recapped and mostly reswitched in the last 2 years.

I considered building him a board with a ton of transformers in the belly panel just for added tone, this particular client has a parts collecting proclivity and has dozens of Jensens sitting around in boxes, but the 812 modules only ouputs onto a couple unbalanced buses, so TXers are not a necessity.