Nyan 1073 EQ =^x^= (formerly Cheap's73 / Poor Man's 1073)

[krabbencutter]

THAT 1646 is a dedicated output driver and is not compatible with a regular opamp.  If you want simple and inexpensive the question becomes do you "need" a dedicated driver? If your circuit overall output is from an opamp, using an impedance balanced output is simple and effective.

Since you mentioned TL071, I would avoid using that for an output, as it doesn't have much drive capability.

The last stage of the EQ is the passive HPF and is loaded with 5,1k. So I guess an output stage with a lower impedance makes sense? But I got to admit, that I jumped head first into this project and my understanding of impedance/loading/driving is still lacking. I found an interesting overview of the different driving characteristics of different opamps in one of the apllication notes from Rane: https://www.rane.com/note126.html
I guess an NE553x would be more suited?

 

[john12ax7]

Yes,  NE5532/4 would make a better choice.

 

[krabbencutter]

update: my small caps arrived today (150pf, 220pf, 470pf) and I gained some really great insight over at gearslutz https://www.gearslutz.com/board/geekslutz-forum/1235388-diy-poor-mans-1073-eq.html

I'll try to bring my github repo up to date over the weekend.

 

[Whoops]

Great work, this looks quite interesting.

Congrats, will enjoy following your developments

 

[krabbencutter]

Thanks! I've just pushed a whole lot of changes to my gihub, to reflect the latest developements. The EQ circuit is now finished, including an input buffer and gain makeup stage. SNR, Headroom, as well as filter accuracy have been vastly improved! SNR will be 75dB in the worst case (aka in my chaotic perfboards + breadboard circuits), but with proper layout, grounding and shielding 80dB and more should be easily achievable. I've included measurements for frequency & phase response, as well as THD+N (got a bit of a ground loop  ) and a reference measurement of my audio interface. An updated BoM should be available later today.

update: new BoM has been pushed

 

[cromwell]

Are you going to create a pcb as well?

Cheers

Eric

 

[krabbencutter]

Are you going to create a pcb as well?

Cheers

Eric

I'd love to at some point, but at least for me it feels much too early for that. Mainly because I'm still pretty new to the DIY game and just don't feel confident enough to call this EQ 'ready for production'. I also don't have any real life outside feedback on the sound & performance of the unit yet, which I plan to change tho. Here's what's also on my mind:

• I want to keep the circuit as open as possible, to easily enable modifcations. So whether somebody wants to just add the HPF to an existing preamp, build the EQ but with different input/output stages or wants to build a stereo version, my 'ideal' pcb should mostly fit
• I also want to keep the 'build target' flexible. Eurorack, Lunchbox, Standalone unit would be ideally based around the same PCB
• I'm also thinking/dreaming about adding a modern twist to this EQ by making all controls digital and pairing it with an arduino for some sort of recall. The unit could then additionally function as a midi controller for your favorite 1073 plugin. Encoders & digital potentiometer ICs aren't that expensive. But I'm a bit clueless what ICs could replace the lorlin switches. I was thinking about analog multiplexers, but am not sure if that would work?
• I also want to take the time to compile some sort of documentation about the 1073 EQ with all the bits and pieces I gathered around the internet

Anyway, I'm first going to build a front panel this week,  so I can actually start to properly operate the EQ. Once that's done, I'll try to take my prototype to some music-making friends, to get some hands-on feedback.

But that's just me and my neurotic perfectionism.

If you or anybody wants to go ahead and make a pcb of the current state of the EQ tho, I'll happily try to assist you

 

[krabbencutter]

I hope you're in for a treat: I'm happy to announce that the basic circuit, including the input & output stage, should be final now  *fingers crossed*
Rev:06d has just been pushed to my GitHub, including an updated BoM. The only change that's expected to happen now, will concern U1A/B. Cabirio over at gearslutz (again, massive thanks!) suggested to replace the NE5532 in that spot with an LM4562. My delivery should arrive next week and once that's tested, I'll add them to the schematic. Fortunately they should work as a drop-in replacement, so no further modifications to the circuit should be neccessary.

 

[krabbencutter]

The last kinks have been ironed out and Rev: 07 is now up. I'm happy to announce, that I now have achieved my initial goals. The Cheap's 73 EQ is as true to the original 1073 EQ, as possible; both in design and in frequency response.  And all while only using standard electrical components. Pots & Switches aside, that one LM4562 was the only electrical component, that cost me more than 1$. And given the scope of this project, performance is surprisingly good! The basic frequency response is flat within +/-0,5dB from 20Hz-20kHz and SNR will be at least around -80dB.

I've already begun writing a build documentation and a first draft will hopefully be available in the coming weeks. I also might start with a PCB layout, but don't nail me on that  ;D In the meantime I'll be happy to answer any questions you might have!

 

[krabbencutter]

So it's been a bit over a year and I started revisiting this project. I actually just wanted to design a cleaner perfboard-layout and accidentally made some new discoveries about the gyrator implementation:

- all capacitors should be 10nF (63v, 10%, film)
- the feedback resistors should match the resistances of the original inductor. In cases where the inductor resistance is <100R the feeback resistor should stay at 100R
- the 2k7 resistor in the mid-band should be omitted and instead each (simulated) inductor tap should have a 5k trim-pot in front. That way the maximum gain & q can be calibrated, to compensate for the higher series resistances in the gyrator circuits

The simulation results so far show much higher accuracy, in reference to the (simulated) inductor-circuitry. However this all seems too easy and I'll need to poke around a bit more, to be sure I'm not running into any unforeseen limitations  ;D

About the overall circuit layout: ordering custom pcbs is currently not an option for me, neither is etching them myself. So I thought about having the whole EQ circuitry on a single pad-per-hole board with as little cables as possible. If I put all opamps in a single line, I'll be able to run the power supply rails in a straight line underneath. And if I set the bypass-capacitors up like on the attached image (ignoring the cap that's currently in the way ), I can have a single ground lane while still having access to all IC-pins.
What do you think?

 

[Spencerleehorton]

This is great, you say it’s the same as original, is it +/- 18db?

 

[krabbencutter]

Yes, but the headroom & THD+N will depend on your supply voltage and the opamps. With a +/-12V PSU und NE5532 it can handle input signals up to 3Vpp before it starts clipping (The Sound is in the Silicon  ;D)

 

[ruffrecords]

Note that Neve typical internal operating level is around -8dBu.

Cheers

Ian

 

[krabbencutter]

Thanks, that's good to know! I was always wondering, why I'm exceeding the available headroom, when the 1073 is basically running in the same voltage range (although in Class A). But I could think of so many reasons, why my circuit would perform worse, that I never dared to ask  ;D

 

[krabbencutter]

Just started putting together finished the mid EQ section and so far it's going to be much cleaner & efficient than the first version

 

[krabbencutter]

aaand it's done 8) You can find Rev08 of the schematic here https://github.com/ravettel/cheaps73/blob/master/cheaps73.pdf

 

[shabtek]

beautyful!

 

[krabbencutter]

thanks  I'm probably going to clean it up a bit more (at some point). Next up is balanced I/O. To follow my own "no iron" paradigm, I'll give this one a try https://sound-au.com/project87.htm

I've also attached an image of the supply layout, in case someone's curious.

 

[Whoops]

thanks  I'm probably going to clean it up a bit more (at some point). Next up is balanced I/O. To follow my own "no iron" paradigm, I'll give this one a try https://sound-au.com/project87.htm

Yes it seems a good circuit to study and implement.

Congrats for your work, really good idea

 

[krabbencutter]

Inductors are cool and such, but here's some digital re-call instead