I just took care of that myself and swapped the opamps for inputs and outputs on my OT for some quality OPA opamps. That’s really where it was lacking, the DAC itself is a pretty decent Cirrus Logic chip. To my ear it makes quite a difference, and I bet upgrading the opamps is exactly what they did on the DT too.
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Hi @alfred,
Thanks for letting me split this out as a separate topic. I’m very interested in what you did. Could you share any more details with us?
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I would love to know the exact specification of the op-amps you used and any challenges / considerations to note before doing the same 
need to get my first step key and main encoder replaced on my OT. might let me local synth techs deal with it if they can do the op-amp upgrade as well.
cheers for breaking this post out into its own thread @PeterHanes
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Ok, first I have to say I am not a professional in the field, I’m a self taught DIY person. Do this at your own risk.
The opamps I used are type OPA1644. They are among the cream of the crop for audio. They are the same SO-14 package as the original opamps in the OT. The OPA1644 costs around 6,50€ a piece and you’ll need 2 of them to have inputs and outputs covered. The OT has 3 in total but one of them is only for the headphones.
The original opamps are all LM837. They are around 1,50€ and they have BJT input stages as opposed to the OPA1644 which has a FET input stage. I don’t know the details about the circuitry, since the OT is not open source. Since it is a simple audio amplification stage I don’t think it requires the opamp to have a BJT input stage. It is hard to tell without the specifics of the circuit but I gave it a try and it worked out perfectly well.
Mind you, these are small surface mount packages that are surrounded by even smaller, very delicate smd parts. You need some experience with smd soldering and you need to work very carefully. To get the old opamps out I used a Dremel with a cutting blade and I carefully cut through the legs, desoldered the legs and removed the solder with desoldering braid. Then I placed the new parts and soldered them.
To my ear the top end is less harsh and it sounds more transparent and “3D” now. Especially running audio through it won’t degrade the sound anymore as much. I still have to do more testing. I also made a before/after recording that I can dig out and post when I find the time.
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Smd soldering doesn’t seem very easy. 
That sounds some surgeon level ninja soldering action to me.
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chips ordered, looking forward to testing it out!
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Ha, that’s really tempting mod. Not sure if I would manage so delicate soldering myself but my mother in law does SMD soldering for living so it seems I have a little project for her 
Thanks for sharing any details!
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SMD soldering is not bad with a little practice. The hardest part of this mod will be desoldering the existing SMD components.
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Desoldering the parts is a lot easier and cleaner if you do the brute force method and just cut through the legs. You can also do the “solder bridge” method to heat and loosen up all legs simultaneuosly but it’s a lot messier and there’s not much space around the ICs.
The two chips for inputs and outputs are the two parallel ones that are placed further towards the edge of the pcb, close to the corresponding inputs/outputs. I can post a picture in 2 weeks when I am back home, but they are hard to miss really.
Soldering smd takes a bit of practise so if you’ve never done it I would recommend practicing with some old, broken electronic devices first. You will definitely need solder flux to get a good connection and to make the solder settle in nicely, you should get some desoldering braid to use after removing the old ICs and you should use a soldering station so you can regulate the temperature to make sure you don’t fry your chips. Mine was like 30€ and all the things I listed can be had for cheap in any hardware or electronics store.
For cutting the legs I used a Dremel tool with cutting blades but there’s also wire cutters with very fine tips especially for tasks like this.
SO-14 packages are pretty small but there’s also much tinier ones than these, so I would say it’s totally doable for anyone with a bit of soldering experience.
I’m curious about your results!
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This seems like such a brute force approach! You are brave, friend.
I have a hot air gun for SMD stuff, but I have no clue if these are multi-layer boards and don’t want to mess anything up. I’ll probably just cut the chip legs with side cutters (though this risks ripping up the pads via shear force)
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I guess you can find a smaller version of something like this for cutting.
Or just dremel the heck out of it to create thinner bottom and sides.
Yes, there are special smd cutters like these. Good stuff but hard to find and probably very expensive. But on the other hand ruining the motherboard is also very expensive.
Place thin rubber at the bottom of the cutter legs.
I have a DYI tool like this that I use when I tinker with my old Amiga computers. I’m not worried it will scratch the board or any components. Not very elegant lol but pretty dumb proof 
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Any chance one of you masters can post some pictures of this mod?
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Yes, pics or even a video would be much appreciated!
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I definitely would love to have this mod and am definitely not skilled enough to try it myself.
Chip-quick, a low-melting point solder, is really good for this kind of manual smd rework. You apply it like normal solder to existing joints and the solder remains molten for much longer than usual, allowing you to flow the other pins and remove the part before any of the joints solidify again.
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+1 to Chip Quik. I’ve performed some minor SMD rework using it, and it made it relatively trivial to complete component removal without hot-air equipment.
http://www.chipquik.com/store/product_info.php?products_id=220001 or the like.
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Could one of you guys offer some advice to which one of OPA1644 chips from the models available is the correct one to order?
http://www.mouser.co.uk/search/refine.aspx?N=4294759686&Keyword=595-OPA1644
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