Alice OPA: Adding harmonic coloration?

[Wordsushi]

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 )

LOL. No worries. I'm just trying to have an open brainstorming session to see what I can learn so hijack away!

I'm definitely leaning toward a transformer as the first thing to try and then upscale the concept from there, if necessary.

 

[Wordsushi]

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

That's really interesting. Hmmmmm... I'll have to take a deep dive into that article. Thanks!

 

[abbey road d enfer]

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

If you read the article, you know that predictable operation of this gizmo requires good control of the signal level, which is seldom the case with a microphone.

 

[Wordsushi]

If you read the article, you know that predictable operation of this gizmo requires good control of the signal level, which is seldom the case with a microphone.

Well, I guess I don't have to read it now after all.

 

[Purplenoise]

Maybe there is a way to add a sub-mini tube starved plate design ( like cheap preamps and pedals) and blend some of the signal to the clean signal?

 

[kingkorg]

Maybe there is a way to add a sub-mini tube starved plate design ( like cheap preamps and pedals) and blend some of the signal to the clean signal?

No need for starved plate, the 6418 i mentioned works at full potential with phantom voltage.

 

[Purplenoise]

No need for starved plate, the 6418 i mentioned works at full potential with phantom voltage.

Oh nice, that’s good to know. I meant a separate circuit to be able to blend the clean signal of the Alice with the low headroom grit of the starved plate tube.

 

[Wordsushi]

No need for starved plate, the 6418 i mentioned works at full potential with phantom voltage.

The 6418 seems really affordable. How difficult would this be to implement into the circuit?

 

[Fastunov]

For a very short time, the Alice opa board with a 6418 lamp was sold on aliexpress. I managed to buy two boards, then the sale was stopped.

If you're interested, I can take a close-up photo of everything

 

[Videon]

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

That’s not true.

The original Aphex Aural Exciter did precisely that, albeit the control was a little iffy.

A later, licensed, “Aphex Exciter” product was developed by a third-party which took a very specific, active, approach to generating controlled even-order harmonics. That said, a tuneable low-pass filter limited the bandwidth of the generated even harmonics.

The company was “Novasystems” (a subsidiary of Orange County Electronics) and the product was the NSA-1 Stereo Aphex Exciter.

 

[abbey road d enfer]

That’s not true.

The original Aphex Aural Exciter did precisely that, albeit the control was a little iffy.

A later, licensed, “Aphex Exciter” product was developed by a third-party which took a very specific, active, approach to generating controlled even-order harmonics.

All marketing blurb. They fail to mention that is also an uncontrolled amount of odd harmonics.
And anyway even harmonics are not necessarily euphonic, 6th and 10th in particular. hnece the necessity of a low-pass filter.

 

[Videon]

All marketing blurb. They fail to mention that is also an uncontrolled amount of odd harmonics.
And anyway even harmonics are not necessarily euphonic, 6th and 10th in particular. hnece the necessity of a low-pass filter.

I was involved in the design. It created asymmetrical sine wave output from the LPF side chain and mixed it with the pure passthrough signal. There wasn’t significant, nor “uncontrolled” odd harmonics.

I’ve got one here. I’d be happy to run some demo test material for you and provide the results.

PS. I see other chatter on this forum. We used 1537 chips in the side chain to generate the even order harmonics.

It was all very proprietary at the time so we potted the side chain but I can have a look for some schematics if that is useful for anyone.

I think I even have a spare side chain module.

 

[Wordsushi]

For a very short time, the Alice opa board with a 6418 lamp was sold on aliexpress. I managed to buy two boards, then the sale was stopped.

If you're interested, I can take a close-up photo of everything

The plot thickens! Yes, please.
Have you tried it out?

 

[Wordsushi]

I was involved in the design. It created asymmetrical sine wave output from the LPF side chain and mixed it with the pure passthrough signal. There wasn’t significant, nor “uncontrolled” odd harmonics.

I’ve got one here. I’d be happy to run some demo test material for you and provide the results.

PS. I see other chatter on this forum. We used 1537 chips in the side chain to generate the even order harmonics.

It was all very proprietary at the time so we potted the side chain but I can have a look for some schematics if that is useful for anyone.

I think I even have a spare side chain module.

You, sir, have piqued my interest for certain.

 

[abbey road d enfer]

I was involved in the design. It created asymmetrical sine wave output from the LPF side chain and mixed it with the pure passthrough signal. There wasn’t significant, nor “uncontrolled” odd harmonics.

I’ve got one here. I’d be happy to run some demo test material for you and provide the results.

PS. I see other chatter on this forum. We used 1537 chips in the side chain to generate the even order harmonics.

It was all very proprietary at the time so we potted the side chain but I can have a look for some schematics if that is useful for anyone.

I think I even have a spare side chain module.

OK, so it's the proverbial exception that confirms the rule.
The overwhelming majority of circuits that are supposed to restore/enhance/recreate harmonic content are just dirtifiers. I must say that the amount of mystery/BS/misinformation about the original Aural Exciter has not really helped clearing the mud.
But homage must be paid to those who have designed a clever solution.
It doesn't seem this has been rewarded with much popular success, though.
And yes, a look at the schemos is always an interesting prospect.

 

[rogs]

It was all very proprietary at the time so we potted the side chain but I can have a look for some schematics if that is useful for anyone.

Another vote for a look at the schematics here..... 'Urban legend' has it that the effect created by the original Aphex Exciter was discovered 'by accident'?
I think I recall it was only available to be leased in the early days?
The simplified schematics included in the original patents show diodes used to create the effect, as I recall.
Such limited later schematics as have been 'leaked' onto the internet seem to show 13700 transconductance amps instead?
Love to know more.....

 

[Videon]

Another vote for a look at the schematics here..... 'Urban legend' has it that the effect created by the original Aphex Exciter was discovered 'by accident'?
I think I recall it was only available to be leased in the early days?
The simplified schematics included in the original patents show diodes used to create the effect, as I recall.
Such limited later schematics as have been 'leaked' onto the internet seem to show 13700 transconductance amps instead?
Love to know more.....

This was all 42-ish years ago,

Our unit was a standalone, stereo, unbalanced device intended for what, at the time, we referred to as the emerging “semi pro” market. It was a passthrough device, not requiring a mixing desk. It used RCA/DIN connectors to be connected to the “tape loop” of a stereo system. I think it sold for a couple hundred bucks.

It was very effective.

I didn’t know that there was any remaining “mystery” about the original Aphex device! Kurt Knoppel miswired a consumer vacuum tube preamplifier kit amplifier (Dynaco?). One channel had an “Eerie effect”. He had no idea what it was. If you look up the patent, you will find a schematic of a mis-wired audio kit!

[It was kinda like the children’s story about people burning down barns so that they could taste that wonderful well-cooked pork! ]

AKG distributed the Novasystems product. I designed it under contract and was not much involved beyond that,

There was a write up in Billboard magazine.

 

[capacitor]

Gyraf has the Aphex Exciter II service manual https://gyraf.dk/schematics/Aphex_Exiter_II.PDF but I would love to see how it was implemented in the NovaSystems version!

 

[Script]

Take some low level audio, filtered to taste, fed to control port of VCA, and audio filtered again to tasted after VCA -- maybe ?

 

[Fastunov]

close-up photo of the board with a lamp

In the board I bought on Aliexpress, when magnified, it is clearly visible that a single-channel opa134 amplifier is used.

Jules Ryckebusch in its version, Alice uses opa1642 and achieves gain by inverting the second channel and thereby increasing the level of the useful signal. The boards assembled according to his scheme have a very high signal level.

https://www.instructables.com/OPA-Based-Alice-Microphones-a-Cardioid-and-a-Figur/