Alice OPA: Adding harmonic coloration?

[Wordsushi]

The Alice OPA circuit is pretty incredible. So clean. Super quiet. Great, great stuff.
And it made me wonder: how difficult would it be to add some level of saturation/harmonic coloration?

I'm thinking about how the Cranborne Audio Camden 500's MOJO circuit works, to add harmonic content to thicken transients and create an almost tube-like saturation.
Could this even be done with some kind of variable saturation control inside the mic, like with a trimmer?

I love the Alice OPA as is, but I just keep going back and asking myself, could it be made to sound more "tubey". Of course, you'll never replicate the exact sound of a tube or transformer, and/or tubes and transformers could be added downstream in the signal chain, but I wanted to ask the group what it would take to add just a little bit of harmonic content into this circuit.

 

[kingkorg]

Add a transformer at the output? Maybe even a tube as the 6418, it can operate properly with phantom voltages. Heater can use a AAA battery. It wouldn't be used as the first stage so the noise and microphonic wouldn't be an issue. Or a carefully tuned back to back diodes with resistors in series, i managed to get amazing gentle soft clipping in my Presonus 1818 pres. By careful tuning you can adjust how they saturate, if the second or third harmonic dominates, tune the ''knee".

 

[capacitor]

I'm interested in this as well. I don't think I could do a tube in my particular application, but would love to get some way of adding 2nd and 3rd harmonic distortion into a circuit.

 

[kingkorg]

You can basically copy the clipping part of the tubescreamer, but obviously not add too much gain, and add pots in series with both clipping diodes. By tuning the pots monitor how the circuit saturates, once you are satisfied, replace the pots with resistors. You need to inject the signal into the input of the op amp, and do this methodically, carefully, you don't want a tubescreamer inside a mic. Of course some diode rolling is necessary. I believe i went for red leds in my pres. This is just a first thing that came to mind, of the top of my head.

 

[Wordsushi]

Jules Ryckebusch alluded to a schematic somewhere in the vault over at the MicBuilders forum, created by a late member named Pat, that supposedly adds "flavor" to the Alice circuit. If I can track it down, I'll post it here.

I think KingKorg is onto something. I'm wondering if the first thing to try would be a transformer on the output. The Tube Screamer idea sounds wonderfully mad scientist and I can imagine how cool it would be to frankenmic it up with a couple of knobs on the mic body, LOL. But transformer... Hmmmm?

So, if transformer, which one? Would you just wire it in off pins 2 and 3?

 

[Wordsushi]

You can basically copy the clipping part of the tubescreamer, but obviously not add too much gain, and add pots in series with both clipping diodes. By tuning the pots monitor how the circuit saturates, once you are satisfied, replace the pots with resistors. You need to inject the signal into the input of the op amp, and do this methodically, carefully, you don't want a tubescreamer inside a mic. Of course some diode rolling is necessary. I believe i went for red leds in my pres. This is just a first thing that came to mind, of the top of my head.

So... do you think the solution could be some kind of daughterboard? Some kind of add on circuit that pinouts 2,3 on the OPA Alice connect to before the XLR? Like a hardware plug in.... That kinda seems like the easiest path to a solution. What's the simplest circuit that would add a little something, something?

 

[kingkorg]

It could be as simple as this. You can just add two red leds without any resistors and see what happens. You can actually see when leds light up, that means they start to clip, but that would happen at higher levels. The trick would be to finely tune the two added resistors to tune the saturation knee. Without the resistors the knee would probably be too hard. It would just suddenly start to clip. Resistors would create a smoother transition. The balance between the two resistors would determine if it's 2nd or 3rd harmonic dominated, so they should not be really equal for tube like sound.

Disclaimer: I just woke up, i'm having my first coffee, so thread carefully

Edit:
Of course it's more complicated than i suggested, forget about the first image, but one might get what i was pointing at. There's the idea, so if anyone wants to experiment... Add a gain resistor?
Read Abbey's first comment.

There are other ways to implement the diodes, place them at different spots, use the other side of the op-amp for clipping, go impedance balanced, or add the transformer for both balancing and color. But all of this needs some heavy experimentation.



The transformer suggestion is still valid.

 

[Khron]

In the second version, you could probably skip the two 47u output capacitors, if the transformer gets driven from both opamps. Or if you really wanna be "paranoid", just one.

 

[rock soderstrom]

How about leaving the mic as is and instead using a micpre that can generate decent distortion (~harmonic coloration)

Hamptone JFet aka Fetboy comes to mind, it can do everything from clean to almost squarewave, depending on the tuning.

 

[kingkorg]

Probably for the same reason people don't just use eq to tame otherwise perfectly usable inexpensive mics, and spend bucks on u87 clones.

 

[abbey road d enfer]

It could be as simple as this. You can just add two red leds without any resistors and see what happens.

It just does nothing because the diodes are shorted. You would need to open one connection for it to do something.

 

[kingkorg]

It just does nothing because the diodes are shorted. You would need to open one connection for it to do something.

I knew i shouldn't have posted that early.

 

[abbey road d enfer]

How about leaving the mic as is and instead using a micpre that can generate decent distortion (~harmonic coloration)

yes, I already suggested that on the micbuilders group. It generated no answer. I think it's the kind of answer that does not satisfy someone with cognitive bias (a.k.a. preconceived ideas).

 

[Wordsushi]

yes, I already suggested that on the micbuilders group. It generated no answer. I think it's the kind of answer that does not satisfy someone with cognitive bias (a.k.a. preconceived ideas).

I was an adult the first time I saw cookies and cream ice cream. And it’s not because Oreo cookies and vanilla ice cream didn’t exist, but because it took decades of these two perfect items existing side by side, before someone thought, “what if…?”

I look at this beautiful mic circuit, that in many regards is pure perfection, and after building a few mics with it, I begin to wonder… “what else can be done with this?”

So, you can imagine my surprise when I ask “how?”, what I get back is “why?” Or the even more disappointing, “why bother?”

So my response is “why not?”

I came with a preconceived idea that this is a forum full of creative people with inquisitive minds and I appreciate Kingkorg and Khron jumping in with ideas. Maybe there is no decent solution and the OPA Alice is just a glorious one trick pony. As I wrote in my original post, I know any harmonic color can be added downstream from the mic in the chain. And I realize that maybe it's a futile pursuit, but I enjoy the journey of the pursuit.

I just thought it would be a fun exercise to attempt, and instead I’m left defending asking a theoretical question about modding a mic circuit in a forum about modding mic circuits.

I mean, it’s not like I’m trying to use the OPA Alice to rip a hole in the space-time continuum to destroy the universe.

Or am I?

 

[Wordsushi]

It could be as simple as this. You can just add two red leds without any resistors and see what happens. You can actually see when leds light up, that means they start to clip, but that would happen at higher levels. The trick would be to finely tune the two added resistors to tune the saturation knee. Without the resistors the knee would probably be too hard. It would just suddenly start to clip. Resistors would create a smoother transition. The balance between the two resistors would determine if it's 2nd or 3rd harmonic dominated, so they should not be really equal for tube like sound.

Disclaimer: I just woke up, i'm having my first coffee, so thread carefully

Edit:
Of course it's more complicated than i suggested, forget about the first image, but one might get what i was pointing at. There's the idea, so if anyone wants to experiment... Add a gain resistor?
Read Abbey's first comment.

There are other ways to implement the diodes, place them at different spots, use the other side of the op-amp for clipping, go impedance balanced, or add the transformer for both balancing and color. But all of this needs some heavy experimentation.



The transformer suggestion is still valid.

Thanks King! I think the transformer idea is pretty cool and probably the easiest thing to try first. Is there a specific transformer you'd recommend for this task?

I have a few of those cheapie 1:1 unbalanced 600:600 transformers sitting in a drawer somewhere. Or, I could maybe go full tilt insanity and I have a UTC A21 wired in a box and I run a 5 pin breakout cable from the mic to use it inside the circuit, maybe with a switch to take it in and out of line just for laughs. I've built so many work tools thanks to this forum. I kinda want to see what kind of crazy misfit toys can be created at this point.

This is all good food for thought. I'm definitely going to try this.

 

[abbey road d enfer]

I look at this beautiful mic circuit, that in many regards is pure perfection, and after building a few mics with it, I begin to wonder… “what else can be done with this?”

As I said earlier, this circuit is the less prone at been modified for dirt.

So, you can imagine my surprise when I ask “how?”, what I get back is “why?” Or the even more disappointing, “why bother?”

Probably because we've down this road (or rabbit hole) before and there is no end to the notion of adding "warmth, "grit", "punch" or whatever. One's "colour" is another's "crap", and vice-versa.

So my response is “why not?”

You are free to do whatever you wish, but shouldn't you listen to warnings?

I just thought it would be a fun exercise to attempt, and instead I’m left defending asking a theoretical question about modding a mic circuit in a forum about modding mic circuits.

OK, I understand you enjoy the journey more than the destination. I don't want to discourage you, but you ought to know that starting with OPA is almost certainly not the best starting point.

 

[Clintcleveland]

Going with the diode clipping idea, maybe something like Ethan Winer’s Mojo Maestro thing, since it’s intended to have a bit of a light touch? You Can DIY! Build the Mojo Maestro

 

[capacitor]

Is there anything other than, say, a triode or transformer, that could add a controllable amount of even-only (or predominantly even) harmonics? In other words if there wasn't enough space, or a large enough power/cooling budget for a proper valve/iron solution?

( @Wordsushi I swear I'm not trying to hijack your thread )

 

[abbey road d enfer]

Is there anything other than, say, a triode or transformer, that could add a controllable amount of even-only harmonics?

Sorry if I sound like a spoilsport, but no analog circuit is capable of producing "a controllable amount of even-only harmonics".

 

[capacitor]

Not at all, I'm at the beginning of this particular learning curve. Thank you.