To be honest, nobody reported the op-amp mod made a real difference. Technically the stock opamp is good enough and I trust the Elektron engineers. Close to zero chance some 5-minutes hack DIY genius beat the Elektron guys who spent months with designing, optimizing, testing Octa circuits.
A much higher chance for a bad result of a chip replacement service. Especially big mess can happen replacing the BJT input opamp for a FET input opamp like it was reported.
Bottom line: I did opamp mod to my own mixer, read a few books, have audio engineering experience. I myself don’t like the Octa sound and really like the Digi sound but it’s not that 5-min opamp swap that makes the difference but a totally redesigned system. Starting from power supply, then digital converter chip selection, even circuit board design and trace routing matter. Opamp selection is just one part and not the most critical.
Sorry to be sceptical but that is how things really work.
Plus in both cases the vast majority of the sound comes from what’s happening at the DSP level rather than the hardware level.
Recently had my mk1 professionally serviced and modded/upgraded to OPA1644. There’s HUGE noticeable gain in sweetness and warmth ; This was only noticeable to me at very loud levels, (sound checking venue). Otherwise, the difference is pretty small. The more I pump through this old mk1, the more I think that it was worth having a professional mod it for me. Most will do it for relatively cheap. Just my 2 cents. regardless of how it sounds; it’s pretty cool to know that I’ve at least extended it’s life by decades 
- what was in there before the opa 1644 ? I heard noticeable difference when i saw a mod with a video capable opamp.
Interesting - you have a bit more info to share? Pricing, etc?
I have no idea. I just had my local shop intro me to an electrical engineer. I showed him this post:
and he said he had everything to make it happen. All I did was pick it up at the shop.
Pretty sure parts were less than $20. The guy charged me $150. (He was going to charge me $200)
This wasn’t something he had ever done before; but he was well regarded among some modular heads here in my town.
so he would pay for the broken machine ?
It’s one dual op-amp per pair of inputs and outputs, right? If so, OPA1644 prices on Mouser right now would make it about $15 for all four for a commercial operation buying quantity, or about $21 for someone who just bought enough to do the mod. For someone with good tools and rework skill it’d probably take 20-30 minutes tops but it’s also risky so a high bench fee seems fair.
Yeah, the Digi sound is unfortunately a class higher than the octatrack. When I put the sound into octa it sounds like decreased mp3 quality
This again! Stop. Extra flattering eq for Digitakt. It doesn’t make it higher class! And it’s mono.
You probably don’t know how to use OT correctly. It has been proven many times that OT is very flat, without noticeable loss.
That was a simple A/B Test. Sound directly from OT and from sample editor in OSX. What could go wrong? My A/D/D/A ? Apogee Rosetta i think its quality is quite good.
Please read this :
so this mod seems to be around for a while, any new conclusions if its worth it?
hooking into the i2s signals from the dsp to the dac should be possible with pogo cables on the cirrus dac. from there ifeed them i2s signal into adat converter chips… might give it a try soon…so then audio out will be digital with no conversion lost at all.
I’m interested in this mod (upgrading conversion at all I/Os or digital out).
Where can I find more info? Is there a clear BOM and guide somewhere? (Stream is not longer linked)
I’m surprised anyone would want to make the OT master clock for your entire audio setup. I was under the impression that the clock source was what determines “jitter” and that sort of thing and that’s why “good” audio interfaces cost so much?
Actually when things are self clocked usually there are 0 issues, the good clocks are not only great reference sources but also amazing at locking to external less accurate clocks without errors. I wouldn’t know how the OT fairs with this, but I can say I’ve used old yamaha receivers, minidisc players etc over spdif on high end interfaces and they all lock as slave to these older devices effortlessly. Alot of the “clocking” issues people experience are from user error and daisy chaining stuff.
Also, clock from a computer is generalyl the least stable. It improves a bit as computers get faster, but it’s still baked in to the way USB works.
The Octatrack’s clock is about as stable as possible with MIDI so it makes a pretty good master clock, but on top of that it’s uniquely picky about external clock, and I’ve personally had issues even when the clock source was MORE stable than the OT’s internal clock. Mostly with pcikup machines (the usual “overdub aborted” error), but it also causes clicks with any looping audio that doesn’t use time stretch (I’ve had a few issues with timestretch on, too, but I usually keep it off so I don’t know how common those are).
Even when I’m not using the OT as the master clock for my setup I don’t sync it to external clock - in that case, I’ll send transport and tempo change messages from another sequencer to keep it in time with the master clock - it’s a bit more cumbersome but works better.
This is still the best techincal explanation of the problem with USB, I think:
The Octatrack is a special case, though, because it’s really just too sensitive to work well with external clock - it wants sample accurate timing and MIDI can’t do that.
do you still have the files? they are no longer online 
Hey… sorry, I couldn’t find the samples on my disk. After three years, I can say modding the OT is not worth it. If you want pure digital outputs, I would suggest going another route, perhaps a Digitakt?