<how does it work> calculating cutoff Frequency for 1073 12K cut / boost

[wells2p]

Happy Friday,

in the picture shown below I am trying figure out the calculations for how 12K is allowed to pass through B then C for the high frequency boost cut. I am assuming it is the frequency dependent impedance of Section B plus the impedance of whatever resistance is present at section C based on the wiper position and the 15nf cap. also assuming the 6K8 resistors on each side of the entrance to the LF section have something to do with it? Lastly I drew in RA1 and RA2 whose purpose I am unsure of. In any case I believe I understand how the LF section works I that I was able to come up with the cutoff frequencies but confused by the HF section.

Can anyone help me understand how this works along with the formulas?

thank You.

Paul

 

[metalockpick]

The two 22nF caps set the 12k point here. .033uF/33nF would be ~10k, .01/10nF is ~16kHz, as per the Neve 1084 tone controls. M is the output of the tone controls, connection to the 3rd gain stage input. H is the feedback connection to the output of the 3rd stage of the circuit. The 15nF cap sets the low freq cutoff of the HF control. You may want to draw the complete circuit, as there are missing components in this drawing.

 

[wells2p]

The two 22nF caps set the 12k point here. .033uF/33nF would be ~10k, .01/10nF is ~16kHz, as per the Neve 1084 tone controls. M is the output of the tone controls, connection to the 3rd gain stage input. H is the feedback connection to the output of the 3rd stage of the circuit. The 15nF cap sets the low freq cutoff of the HF control. You may want to draw the complete circuit, as there are missing components in this drawing.

Thank you very much. I have the all of the original schematics- i just grabbed a section to illustrate my question. I actually cloned the entire thing from the manual and it is working. I just didn’t understand how the hf boost cut works because i am still learning thanks for taking the time to answer- much appreciated!!

 

[wells2p]

The two 22nF caps set the 12k point here. .033uF/33nF would be ~10k, .01/10nF is ~16kHz, as per the Neve 1084 tone controls. M is the output of the tone controls, connection to the 3rd gain stage input. H is the feedback connection to the output of the 3rd stage of the circuit. The 15nF cap sets the low freq cutoff of the HF control. You may want to draw the complete circuit, as there are missing components in this drawing.

Reading this again and realizing still have questions about the low shelving section. Here is a correct composite of the board and connections - if you would be so kind as to offer some explanation - specifically which direction the signal travels for this one as well.

 

[metalockpick]

The first switch position components that set The level/load of "off"; a straight wire would be more output than any of the capacitors, so this way it's unity gain from off to bass boost (or cut).
The next positions of the switch are capacitors which set the center frequency of the bass control.

 

[metalockpick]

I should note that the letter circuit designators I quoted in my post refer to the original Neve schematic.
You should use those reference designators, as they reflect the original work. The treble in / out is the same as the bass in / out, The feedback connection is shared as well.

 

[wells2p]

I wasn't clear with my question, my apologies. I can't figure out if

A> the signal comes in through A or V relative to the potentiometer position and enters the filter section through the switch center tap then goes through the 10nf cap and back up through the 12k resistor and finally to pin M amp (Red Line shown below)
the idea being the filters are the cut off point that WILL be cut or boosted by the amp

OR

B> the signal comes in through A or V relative to the pot position and enters pin L through the center tap of the potentiometer and some of the signal (to be cut or boosted) goes through the 12k resistor to pin M and the other part (the orange line) goes through the filter and back down through the center pin of the switch and this part will NOT be cut or boosted.
The idea being the filters are the cut off point that WILL NOT be cut or boosted by the amp e.g. bypassed

 

[metalockpick]

1) You need to get the document "1073-fullpak.pdf". I got it by searching google for Neve 1073 schematic; You can probably find it in the documents section of this site under "Neve".

It has correct schematics for MOST of the circuitry, you'll need to find a 1973 or later schematic for BA182 HPF board, as the 1970 circuit is wrong. Your drawing doesn't use the same references, and I don't want to get confused.

2) On the B 205 circuit page, the signal comes in "F", goes out "M", with "H" being the feedback connection to make the Boost/Cut work for Bass + Treble.
Midrange is a separate circuit.

3) You need to look at the "1073 channel amp" drawing, and then look at the BA 205 circuit to get an idea of what the full Bass & Treble circuit is. I don't think any of the stuff you are pointing out are gemaine to what you are trying to do.

4) The bypass is S7 "EQU", which is visible on the 1073 channel amp schematic. That bypasses all EQ, including HPF.

5) If you are bypassing the EQ, you don't need 2 of the 284 circuits. If you use a mic with a decent output, you can use just the 283 AM and 283AV boards and make an excellent preamp. Personally, I don't like the sound of the 1073 with two preamps operating (higher gain than -50 dB on the switch).

6) The Neve EQ sounds pretty good with the correct frequency points. Personally, i like the 1084 EQ points (damn nearly the same as 1073, with a few different values for dif EQ points on Treble). With this circuit, I prefer 16kHz on Treble.

7) To me, clipping these preamps sounds ugly (API's clip lovely, even with everything dimed).

8) Other than the simple and effective EQ, the real secret to the Neve 1073 sound is the single ended output and output transformer (get a quality unit).
That circuit delivers Hysteresis distortion. Basically, this delays the attack, without delaying the rest of the wave, and adds a sort of punch to the sound passing through, regardless of level (works the same at low level as it does loud).

 

[wells2p]

I have read fullpack and it is the same, actually a subset of the pdf below which i have read in its entirety so many times that I’ve memorized it…and my circuit is an absolute mirror of it. The ba205 board was taken from it. Currently it is working beautifully with the eq lifted and im almost done the eq harness . Ive had many people on this board verify its correct and i only showed a small prt of the circuit (which again is the EXACT same as fullpack) because i wanted to know exactly how it works - I personally like 1073s more than 1084s . I’ve owned several original units s and prefer them to anything including apis. Just my preference. Itll be done in a week - thx for your input

http://www.hausverwaltung-heger.de/al_leck_trick/Neve1073_Manual.pdf

 

[metalockpick]

You're absolutely right about clipping drums with these having a lot to do with great recorded drum sounds. I wasn't thinking properly.
Clipping everything else on these isn't my jam.

 

[wells2p]

I finally understand it. the selected frequency allows that which will NOT be boost or cut to go up through one switch and out through the other (second order). All frequencies that do NOT go through the switch go up the pot center tap to pin L and on to the amp via pin M and then returned to pin H. After that the negative feedback works the same as the midrange filter or any other Baxandall type filter. BTW. I built it EXACTLY like shown in the schematic above and it works perfectly