Barry Porter "Net EQ"

[skipwave]

That said I commend your work and sharing, I hope it helps more people discover the project.

This display of convivial decorum and good ole fashioned hospitality is what brings us all back here. I personally deeply appreciate it. Cheers to you and you.

Apologies for the off topic. Carry on.

 

[MerlynMetal]

Offended is a strong word but I don't think it's cool to come into a longstanding community like this and speculate in that manner.

I'm sorry if it sounded that way but since English is not my mother tongue some misunderstanding is not to be excluded.

An archive update is available (see my original post above).
PCB still to be considered UNTESTED.

 

[FIX]

API did a "constant Q" 550A-1 which they (API) said sounded exactly the same as the "proportional Q" 550A
Sunset Sound Recorders begged to differ with their jaws on the floor. Funnily enough, you can't buy the -1 version anymore.

But since it was me who said, "Don't bother with CT level pots", my work here appears to be done.........

It was actually me that figured it all out. API wanted to lower the cost of the 550A, and the new circuit was designed. It was tested at full boost and matched. The reality was that just about all EQs in those days were inversely proportional to the boost, as you boosted more the EQ was narrower. It never crossed their minds to check that. When Paul Camarata brought it to us at Datatronix (who owned API before me and after they folded), he said “they don’t sound the same”. I listened and agreed, and the normal single frequency test showed that were the same. I dug out an old HO spectrum analyzer and immediately saw the difference. At low boosts, it was wide and at higher boosts it was narrow. The -1 was the same at all points. Saul Walker looked at me with a sinking “oh ****” look and said “we totally missed that”. So basically it was a 3 band 560 eq. Still a good eq, but not an A. We went on to design a new unit exclusively for Sunset, with removable switches and the buffer board. The rest is history. Go to Sunsetsound.com and check out the pod cast we did about it…

And to me, the easiest way to describe it is “constant Q and proportional Q”. It may not be exactly correct, but everyone knows what it means…

 

[Slime_Lord]

Starting on a second Neteq this month and having a difficult time sourcing “nicer” triple (or quad) gang 10KB pots. Trying to avoid using the same ones I had in my last build (link below) but if that’s the best option, so be it.

https://www.mouser.com/ProductDetail/Bourns/PTD904-2020K-B103?qs=Qzws7J6gxqxWUv22rTPYjA==
This EQ will be primarily used for mixing, so no need for stepped switches.

Appreciate the help!

 

[abbey road d enfer]

Starting on a second Neteq this month and having a difficult time sourcing “nicer” triple (or quad) gang 10KB pots. Trying to avoid using the same ones I had in my last build (link below) but if that’s the best option, so be it.

https://www.mouser.com/ProductDetail/Bourns/PTD904-2020K-B103?qs=Qzws7J6gxqxWUv22rTPYjA==

What's wrong with those?

 

[Slime_Lord]

What's wrong with those?

Nothing, they got the job done in my last build. Just wanting to weigh my options.

 

[atavacron]

Thoughts on Barry’s unique Q adjust vs Harpo’s redrawn (and more-commonly-seen-in-other-designs) version?

 

[JohnRoberts]

There are numerous ways to vary the Q of SVF parametric EQs, each with different pros and cons. Over the years I have used several of them.

One tradeoff to manage is noise floor.

-Placing a low impedance to ground at the + or - input of the HP section integrator will increase noise gain. A topology I used for one design was to locate a q pot between the + and - HP inputs with a resistor to ground from the wiper. This delivered very narrow or very wide bandwith with minimal noise build up. As I recall I used end limit resistors because it delivered to wide of a Q at one end.

-The gain of the bandpass section directly affects Q with higher gain delivering narrower Q. I used this in my Parametric kit back in the 80s.

- shifting the BP and LP poles apart will deliver a broader Q. I never used this, but it is a low noise option for say a digitally controlled SVF or using VCA for frequency controls.
===
Besides optimizing noise floor, headroom is another consideration. Not just headroom of the primary path (typically the BP output). Premature clipping of HP or LP sections will ultimately show up in the BP output introducing odd artifacts.


I don't have the equations handy, I think I published them with my kit article. Over the decades I looked at lots of different SVF based parametrics, and there are truly many ways to skin that cat.

JR

 

[abbey road d enfer]

Nothing, they got the job done in my last build. Just wanting to weigh my options.

Have you tried to simulate both versions with identical values except for the "Q" arrangement?
The result is that the response graphs are extremeny similar, as well as the taper of the Q pot. More importantly the noise gain of the 1st opamp in the loop (often called "mixer" is exactly the same.
Choose what rocks your boat...

 

[duende]

Hi,

I'm building a Net eq and i have a Q problem on one channel. The first channel work perfectly and the second have a narrow Q on all bands.

I checked and inverse all the Q switches, measured resistors around filters but i saw nothing...

The first switch position ( widest Q ) works fine ( 10K resistor input directly to + of the first opamp ), and the second step is very narrow ( ~Q 5 ).

Is there a part of this circuit that can define or impact the OVERALL Q setting ?

Thanks.

 

[JohnRoberts]

Hi,

I'm building a Net eq and i have a Q problem on one channel. The first channel work perfectly and the second have a narrow Q on all bands.

I checked and inverse all the Q switches, measured resistors around filters but i saw nothing...

The first switch position ( widest Q ) works fine ( 10K resistor input directly to + of the first opamp ), and the second step is very narrow ( ~Q 5 ).

Is there a part of this circuit that can define or impact the OVERALL Q setting ?

Thanks.

yes, in state variable filter based parametric EQ there are any number of possible interactions that could impact global Q, but not simple to explain or troubleshoot.

When you have one working channel and one identical channel not working properly, the obvious troubleshooting process would be to compare them to each other and look for something(s) different. It will probably be the last thing you checked.

JR

 

[duende]

yes, in state variable filter based parametric EQ there are any number of possible interactions that could impact global Q, but not simple to explain or troubleshoot.

When you have one working channel and one identical channel not working properly, the obvious troubleshooting process would be to compare them to each other and look for something(s) different. It will probably be the last thing you checked.

JR

Thanks,

Yes i certainly forgot to check one thing, and it's maybe just a wrong resistor value.

On the channel working properly i can disconnect a Q switch and the band work properly with a fixed q factor, the widest. On the other channel if i disconnect a Q switch the band are not working, nothing pass or just noise.

So i was suspecting a problem around the first op amp more than around the interrogators, but i think i checked all resistors and a lot of connections...

I will start again tomorrow.

 

[JohnRoberts]

Thanks,

Yes i certainly forgot to check one thing, and it's maybe just a wrong resistor value.

On the channel working properly i can disconnect a Q switch and the band work properly with a fixed q factor, the widest. On the other channel if i disconnect a Q switch the band are not working, nothing pass or just noise.

SVF (state variable filter) topology has multiple feedback paths. If a global feedback path is open the entire SVF will not be stable at DC and peg to one rail or the other.

So i was suspecting a problem around the first op amp more than around the interrogators, but i think i checked all resistors and a lot of connections...

It could be anywhere in the entire chain..

I will start again tomorrow.

Don't overthink it. Pursue a methodical check of the two different channels.

Good luck.

JR

 

[duende]

Don't overthink it. Pursue a methodical check of the two different channels.

Yes, you're right, there is no reason to not find the issue.

Thanks.

 

[Geert Samuel]

So, it's about time to finally dip my toes in the whole DIY scene. I have these boards around for a few years now and really want to start work on them. As I am still in the beginner/intermediate stage, I still will need some help. I have found the Mouser bom a few posts back. That specific cart has a few errors in there. One of them is needing to order a few with a MoQ of 1000 and another one without any replacement.. Is the only way to actually just order a 1000 of them? I have checked other suppliers, without much luck. I'm not too bothered by it, but it will save ~€ 120,-..

And another question is the non replacable part: https://nl.mouser.com/ProductDetail/647-TVX1E101MAD
I tried looking for something similar, but can't find it. As my knowledge is still in the beginner stage..I might need some help on that.

 

[abbey road d enfer]

And another question is the non replacable part: https://nl.mouser.com/ProductDetail/647-TVX1E101MAD

Probably without any direct replacement, but 100uF/25V caps are easily available, probably in radial version. Use your imagination to adapt these to the layout.

 

[j_p_higgins]

This is a redraw of the Porter netEQ PCB to replace the exotic format Gerber files circulating around. I tried those at 2 local PCB shops and 2 major Chinese PCB manufacturers and all of them said files were useless. After spending hours trying to make use of these files I concluded that myself but decided to ask companies that are in the business as well. I assume those were deliberately manipulated so that couple of people can sell their PCBs but that's just an evil conspiracy theory of mine.
Fortunately the archive included PCB tracing and schematic which is plenty enough to redraw the whole thing. Now I offer it as a compete and free Sprint Layout PCB project for everyone interested to use as they would like and to modify it to their needs.

Changes I made:
1/ some PCB traces have been optimized and don't exactly overlap the PDF file tracing
2/ included option to use THAT1246 and THAT1646 for input and output instead of the unnecessarily complicated original stages
3/ included is an option for a LM317/337 regulated onboard power supply section
4/ optimized are positions of the onboard 9mm pots in case one wouldn't use stepped attenuators including a footprint for a 10k center tapped 16mm pot available from Aliexpress
5/ all mounting holes and pots/switches distances are in mm of course

ATTENTION: as of August 10, 2022 this PCB is to be considered UNTESTED!

Check the PCB against the schematic and PDF tracing and layout files before you order these somewhere!
I'll be also doing some more checks and post corrections if any.
If you find any mistakes let me know so I can correct them and post corrected files.
To view the files you can download a free Sprint Layout viewer from here:
https://www.abacom-online.de/updates/Sprint-Layout60_Viewer.exe
or get the full software temporarily for educational purposes from...well, you know how.
Note that ground planes are not visible in the viewer.

Last archive update 13.08.2022

Has anyone tried these pcb files?

 

[CultAudio]

Has anyone tried these pcb files?

I have tried them.They are not ok.As I remember power supply for relays were not properly connected and some other things also and I've decided that it was not worth spending more time with those boards.

 

[richiyobs]

hi folks,
i m trying to redraw Net eq, my question is: how many filters can be added to the cut/boost amplifier section?
i d like to remove relays for switching shelving so to get 6 band in total....shelving always on
simulation looks fine, but don t know if in this way something has to be modified in the cut/boost amp section

thanks for your attention and support

best

 

[abbey road d enfer]

hi folks,
i m trying to redraw Net eq, my question is: how many filters can be added to the cut/boost amplifier section?

The number of bands depends on the output capacity of the opamp that drives the filters. It drives the two shelves, which can result in as low as 500 ohms (if LF is set at 200Hs and HF at 20kHz). Each filter has an impedance of 10k. With 6 bands + the two shelves, the load can be as low as 1.75k. Most opamps are capable of driving that, but often with some penalty regarding distortion.
Then there is the issue of noise. The good noise performance of the BPNEQ relies on the use of center-tapped pots, which make sure the noise created by each filter is limited to the strict minimum.