Handsome Audio Zulu/Passive Distortion Theory

[living sounds]

I have no idea how Zulu works. All I can say is that my ears tell me there is a big difference between the effect I get from my Telefunken (and other tape machines I have used in the past) and the Zulu examples I have listened to online.

It's a good idea to use your own ears and ignore internet chatter. Opinions about sound vary drastically, and it's a difficult thing to measure objectively. And there's so much wishfull thinking and motivated reasoning involved.

I would love to be able to get rid of the tape machine and have a 19" unit that does with no delay what the M15 does. So far, I haven't found anything close to a replacement.

 

[living sounds]

do you know the specs of these transformers?

Apparently Neve changed to a much bigger transformer in their more recent unit. Still doesn't sound like tape IMHO.

 

[SWAN808]

I have no idea how Zulu works. All I can say is that my ears tell me there is a big difference between the effect I get from my Telefunken (and other tape machines I have used in the past) and the Zulu examples I have listened to online.

It's a good idea to use your own ears and ignore internet chatter. Opinions about sound vary drastically, and it's a difficult thing to measure objectively. And there's so much wishfull thinking and motivated reasoning involved.

I would love to be able to get rid of the tape machine and have a 19" unit that does with no delay what the M15 does. So far, I haven't found anything close to a replacement.

Im a rookie in these forums but I feel compelled to say the obvious, that there is so much going on in tape that I assume it will be very difficult to emulate the whole thing. I assume differences of opinion on this matter vary depending on how much emphasis different people put on, and desire specific aspects of tape. For me personally - it is the tape saturation and dynamic aspects I like. I assume that is doable with some saturation circuits and perhaps also a limiter/compressor. I wasnt crazy about the original Portico 5042 but I hear the 500 is better...The Zulu to me sounded good and had the ability to enhance the sound at lower levels which often seems difficult for processors. Certainly a useful production circuit which I frequently recommend.
Perhaps because I am working on a piece of hardware myself that makes me a frenemy to illacov but I hope that the sort of device I am working on can  draw attention to a production approach relevant to others like Louder Than Liftoff where the DAW is coupled with a specific hardware processor made for the modern era.

 

[ruffrecords]

Im a rookie in these forums but I feel compelled to say the obvious, that there is so much going on in tape that I assume it will be very difficult to emulate the whole thing.

Indeed, it is obvious, which begs the question why is the Zulu advertised as "The world's first passive analog tape simulator" or is that just marketing?

Cheers

Ian

 

[abbey road d enfer]

Now someone is adding fuel to the fire... 8)

 

[gyraf]

I'm pretty sure it's significantly later than our G21  :

 

[abbey road d enfer]

I'm pretty sure it's significantly later than our G21  :

Is the G21 designed to specifically emulate the "sound" of tape?

 

[gyraf]

No, it's clearly a side effect, you're right, but nonetheless...

Jakob E.

 

[Liutmod]

Is it possible Gyraf want help us with a basic version of his machine ? 

 

[weiss]

Regarding the passive clipping/distortion, how do i need to imagine a circuit like this one

(https://www.audioxpress.com/article/you-can-diy-build-the-mojo-maestro)

to sound compared to the schematic attached?

Is it about the amounts of diodes which makes it sound "softer" or less aggressive?

 

[abbey road d enfer]

The second circuit (with 5 diode-strings) is made to operate with larger signals than the first one, but there is no difference in character. However, differences may exist, caused by a different type of diode, a different ratio between the series resistance and the dynamic resistance of the diodes, and also how the signal is shaped after. In the first schemo, the 47nF capacitor cuts some treble. And the source impedance must be accounted for; a typical passive guitar has a much higher impedance than 1k.
Many distortion pedals rely on this simple type of diode clipper; the diiferences in sound signature can be chalked mostly on how the signal is low-passed after clipping.

 

[weiss]

The second circuit (with 5 diode-strings) is made to operate with larger signals than the first one, but there is no difference in character. However, differences may exist, caused by a different type of diode, a different ratio between the series resistance and the dynamic resistance of the diodes, and also how the signal is shaped after. In the first schemo, the 47nF capacitor cuts some treble. And the source impedance must be accounted for; a typical passive guitar has a much higher impedance than 1k.
Many distortion pedals rely on this simple type of diode clipper; the diiferences in sound signature can be chalked mostly on how the signal is low-passed after clipping.

Thank you for that explanation!

 

[RSRecords]

What about diodes in the feedback path of an opamp? wonder how they would simulate.

 

[JohnRoberts]

What about diodes in the feedback path of an opamp? wonder how they would simulate.

That will look like a typical gain stage until the voltage across the diodes causes them to conduct. This is also known as a diode clipper and pretty common. More advanced networks known as diode break amps can combine multiple diodes and dividers to create non-linear transfer functions.

Back last century for my kit business, my last/best tape noise reduction compander used a simple back to back diode clamp across the compressor section to clamp transient overshoot events until the side chain could catch up. Briefly clipping a transient sounds much better than saturating the inexpensive gain cells that could throw out ugly artifacts when overloaded and persist longer and more audibly. 

You will see in my circuit I feed the diodes through a resistor divider scaling up the effective clamp voltage by the divider ratio, and somewhat softening the hard clip. There is a lot going on in that compressor side chain so don't hurt yourself trying to follow everything. I mainly shared it to show a practical use of diode clamps in an otherwise clean audio path.

JR

 

[abbey road d enfer]

What about diodes in the feedback path of an opamp?

It's a very common alternative to the passive diode clipper in distortion pedals; as far as I can tell, there is no significant difference sonically speaking, once the levels are aligned similarly.

 

[PRR]

The non-inverting NFB diode clipper will only attenuate to unity gain. If the un-clipped gain is very high, this may not be noticed. But when input exceeds 0.6V the output is no longer clipped. This is un-natural.

 

[JohnRoberts]

The non-inverting NFB diode clipper will only attenuate to unity gain. If the un-clipped gain is very high, this may not be noticed. But when input exceeds 0.6V the output is no longer clipped. This is un-natural.

Diode clipping is not exactly natural, but the best sounding diode clipper I ever designed was patented.
========
US05509080 Roberts

04/16/1996 Bass clipping circuit. This circuit combines a simple clamp diode with a Baxandall tone control circuit to provide frequency selective (bass only) clipping. The benefit is allowing relatively large amounts of bass boost at low level but simultaneous clamping of the bass at high amplitude. Further the clamping of bass frequencies only, allows the high frequencies to mask the clamping. Limiting high amplitude bass frequencies prevents saturation of transformers commonly used in constant voltage distribution systems. This invention was used in several Architectural Acoustics mixer/amp products. Patent assigned to Peavey Electronics.
====
AFAIK this is probably still in use but patent has expired by now. The unclipped HF portion of signals masked the LF clipping and didn't suck, allowing the customers to use tons of bass boost while protecting the output transformers from LF saturation at higher output levels.

JR

 

[john12ax7]

It's a very common alternative to the passive diode clipper in distortion pedals

Arguably the most popular pedal of all time,  the tubescreamer.

 

[abbey road d enfer]

The non-inverting NFB diode clipper will only attenuate to unity gain. If the un-clipped gain is very high, this may not be noticed. But when input exceeds 0.6V the output is no longer clipped. This is un-natural.

Please note that the original schematic includes a resistor in series with the two back-to-back diodes, which results in a similar effect once the leveis are matched.

 

[user 37518]

For those interested here a video:

https://www.youtube.com/watch?v=gV0Af6ai2-s

I must be deaf because I only really hear a difference with the knob all the way up, and it sounds like crap, I dont really like distortion on most instruments, I strive to get the lowest THD from my equipment, just to get it all mud up later doesnt make sense to me. I sure went through the "color " and "warmth" phase of using transformers and tape just for the sake of coloration, gladly it was only a phase...