Amek Mozart Neve EQ Topology

[GreyboxAudio]

I definitely plan on doing a project with the Mozart RN EQ. I'm not sure yet if it's going to be a 1:1 copy or if I'll have the audacity to touch Rupert Neve's design. Right now I'm in the process of racking up my two Mozart RN channelstrips.

 

[porkyc]

Might be because English is not my native language, but your comment sounds to me like you're telling me how to spend my spare time. I appreciate all the insight about the EQ tho!

I'm very good at telling other people what to do. Delegation!
I think people are seeing the RN bit and decide that this must make it wonderful. The frequency ratios are nearly 28:1 making the top end of each frequency band one shy of useless. This EQ only has merit if you have the 2 paths it was designed to access. As a single mono EQ the M2500/Net EQ is a better EQ to work with.
But I do try to bring the thread back to the original question; I hope my comments help that.
PC

 

[GreyboxAudio]

The RN bit doesn't make it wonderful but it definitely makes it interesting imo. The M2500/Net EQ might be better EQs, but they have already been done. I personally find it more interesting to work on projects that haven't been done, even if that means it's maybe not "competitive".
In case I start working on a clone of this EQ I might actually tweak the frequency ranges, hence why I'm trying to better understand the circuit topology. I'm also thinking about maybe using digipots and a microcontroller for Frequency & Q. This would make it possible to program the bell curves of several Neve EQs, from the Neve 1073 to the RND 551.

 

[GreyboxAudio]

.... also 9098 pre+eq on 500 shape (plate paint, knobs, etc.. included)
would be very good ,
and maybe it would sound better than the Mozart RN ?

let's leave the word about to the experts.

cheers

The preamp in the Mozart RN is actually pretty awesome! It's 66dB of clean gain with low noise, low distortion and a linear frequency response way past 20kHz. It should also be pretty easy to build, as long as you find a suitable replacement for the obsolete 2SD786 transistors (BC550C maybe?).

 

[porkyc]

The preamp in the Mozart RN is actually pretty awesome! It's 66dB of clean gain with low noise, low distortion and a linear frequency response way past 20kHz. It should also be pretty easy to build, as long as you find a suitable replacement for the obsolete 2SD786 transistors (BC550C maybe?).

Yes, I agree. You might look at the ZTX stuff. Although they do not specify as "low noise" they are 1 or 2A devices which means large geometry transistors, which is good as low noise ones.
Look as well at the LM4562/LME49720. Although the 5532/5534 chips are hard to beat.

If you are going to adjust the frequency ranges, then it won't be the MozRN EQ.....................

 

[GreyboxAudio]

Yes, I agree. You might look at the ZTX stuff. Although they do not specify as "low noise" they are 1 or 2A devices which means large geometry transistors, which is good as low noise ones.
Look as well at the LM4562/LME49720. Although the 5532/5534 chips are hard to beat.

If you are going to adjust the frequency ranges, then it won't be the MozRN EQ.....................

The name will be cat-themed anyway =^x^=

 

[Matt Syson]

I just love it when people copy and repeat mistakes! What would you HOPE to achieve by swapping OP amps? It probably won't be lower noise because that is usually (but not always) determined by the transistors ahead of the op amps. but then you need to go back to 'first principles to determine the 'optimumum' operating current for the transistors 9once you have decided on the 'Gain' you EXPECT the preamp to be used at most of the time because of course they were tested and usually specified at MAXIMUM gain because that is what reviewers (not users) would concentrate on rather than the real performance at the probably more common 40 or 50db gain range where modern mics will actually dominate. Signal to noise ratio is not usually consistent over the gain range of any given mic amp, which is partly why the old Neve preamps (the old 'classic stuff) added an extra gain stage to get the highest gain settings because it allowed the overall noise to be reduced (omitting a stage) when mics with high output were used.

 

[porkyc]

"What would you HOPE to achieve by swapping OP amps?"

Hopefully, slightly lower distortion figures, thus making the most of an already excellent design.
I don't believe the micpre should have "character", it should be as transparent as possible.
Also, I'm not a believer in "I can hear the difference between makes of opamps...." as some golden ears do.

Would a 4562 be better than a 5532, probably no difference, but in theory the distortion might be measurably better, although you'll never hear it!

 

[pucho812]

"What would you HOPE to achieve by swapping OP amps?"

Hopefully, slightly lower distortion figures, thus making the most of an already excellent design.
I don't believe the micpre should have "character", it should be as transparent as possible.
Also, I'm not a believer in "I can hear the difference between makes of opamps...." as some golden ears do.

Would a 4562 be better than a 5532, probably no difference, but in theory the distortion might be measurably better, although you'll never hear it!

The 5532 can drive 600ohm while it is long in the tooth it is still quite a good opamp

 

[GreyboxAudio]

"What would you HOPE to achieve by swapping OP amps?"

Hopefully, slightly lower distortion figures, thus making the most of an already excellent design.
I don't believe the micpre should have "character", it should be as transparent as possible.
Also, I'm not a believer in "I can hear the difference between makes of opamps...." as some golden ears do.

Would a 4562 be better than a 5532, probably no difference, but in theory the distortion might be measurably better, although you'll never hear it!

A friend of mine measured the mic pre with a Neutrik A2 and the distortion & linearity are already impressively low. Like you already said it would be mostly a theoretical exercise I also need to mention that I'm running the circuit at +/-15V instead of the original +/-17,5V. The EQ board is dissipating quite a bit of heat and since the circuit performs really well anyway, I thought it best to stay within the recommended supply limits for the NE5532.

 

[GreyboxAudio]

Now that I have the TLA Input/Output working it's time for the main course This EQ will be the Purrtico M and I think I've found a good compromise for the frequency ranges:
LF: 33Hz - 330Hz
LMF: 150Hz - 1.5kHz
HMF: 1.5kHz - 15kHz
HF: 2kHz - 20kHz

 

[GreyboxAudio]

I've ordered some prototype PCBs to test the EQ modifications IRL. Each PCB has a fully parametric mid band and a shelf, which can be populated as low or high shelf. Once I have received and tested the PCB I will publish the files in github

 

[GreyboxAudio]

PCBs have arrived and I've at least got the parametric mid band correct The shelving filter still needs some de-bugging because I've accidentally wired a potentiometer incorrectly. To keep the BoM a bit more flexible I've assigned simple pin headers as footprints for the potentiometers. However this "Hack" does not work for dual potentiometers because KiCad uses a different numbering scheme for double row pin headers and I forgot to manually edit the footprint of RV4 .

 

[abbey road d enfer]

Now that I have the TLA Input/Output working it's time for the main course This EQ will be the Purrtico M and I think I've found a good compromise for the frequency ranges:
LF: 33Hz - 330Hz
LMF: 150Hz - 1.5kHz
HMF: 1.5kHz - 15kHz
HF: 2kHz - 20k

1:10 ratio gives excellent frequency resolution. Doesn't get cramped at the upper limit.

 

[abbey road d enfer]

I definitely plan on doing a project with the Mozart RN EQ. I'm not sure yet if it's going to be a 1:1 copy or if I'll have the audacity to touch Rupert Neve's design.

It should be said, at the risk of being banned for sacrilege, that RN's contribution to the design was something like "let's have a 4 band parametric, make it splittable, make it good, clean and quiet" and give a seal of approval when the design work was finished.

 

[richiyobs]

The preamp in the Mozart RN is actually pretty awesome! It's 66dB of clean gain with low noise, low distortion and a linear frequency response way past 20kHz. It should also be pretty easy to build, as long as you find a suitable replacement for the obsolete 2SD786 transistors (BC550C maybe?).

You can check tech doc section Barry Porter ETI articles... He used same configuration.... Only different values at input impedance and different bjt...It Is well explained....
I'm going to build It with 2n2484, oldies but still available... Simulation went fine...

Best

 

[abbey road d enfer]

uitable replacement for the obsolete 2SD786 transistors (BC550C maybe?).

BC550 is the culmination of the venerable BC109; its best Noise Factor is achieved with source impedance centered at about 5 kohm.
Main reason is its quite high Rbb'.
You need a different family of transistors. Since the VLN transistors (2SB737, LM394 et al) are out of production, the ZTX series mentioned by porky are an excellent choice.
An alternative is the THAT 300 series, but actually more expensive than ZTX.

 

[GreyboxAudio]

It should be said, at the risk of being banned for sacrilege, that RN's contribution to the design was something like "let's have a 4 band parametric, make it splittable, make it good, clean and quiet" and give a seal of approval when the design work was finished.

Unless Graham Langley chimes in we will probably never know the specific involvement of Rupert Neve in designing the MZ-15-RN. But if the EQ was performing to Rupert Neve's standards, that's good enough for me.

 

[abbey road d enfer]

You can check tech doc section Barry Porter ETI articles... He used same configuration....

No. The Barry Porter EQ is a parallel arrangement vs. Amek's cascade arrangement. Results in a minor noise improvement, at the cost of using the infamous center-tapped pots. If not it resulted in interaction between bands.

 

[richiyobs]

No. The Barry Porter EQ is a parallel arrangement vs. Amek's cascade arrangement. Results in a minor noise improvement, at the cost of using the infamous center-tapped pots. If not it resulted in interaction between bands.

I was referring to the preamp... Not the eq... I also studied his net eq config... Nice design but big PCB!
Thanks for your explaining ...