Nyan 1073 EQ =^x^= (formerly Cheap's73 / Poor Man's 1073)

Help Support GroupDIY:

Joined
Sep 4, 2020
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In case anyone is interested, a simulation of the high/low shelving section of the EQ is available at the web version of the tone stack calculator. It defaults to 220Hz for the lows and 10k for the highs. But you can change that by entering in different cap values.
 

krabbencutter

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Jul 11, 2018
Messages
104
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Germany
Thanks for the info, that's really useful and in some ways even much more convenient than LTSpice!
Speaking of the shelving circuit: how could I reduce the maximum gain to +/- 12dB while keeping the original frequency response? If it was a standard tone control, I would just increase the 620R & 6.8K resistors. But because of the added low frequency bump/dip it's not that simple. And while I could try all sorts of component values until it kinda looks right, I wouldn't say no if there was some method to the madness :D
 
Joined
Sep 4, 2020
Messages
7
Thanks for the info, that's really useful and in some ways even much more convenient than LTSpice!
Speaking of the shelving circuit: how could I reduce the maximum gain to +/- 12dB while keeping the original frequency response? If it was a standard tone control, I would just increase the 620R & 6.8K resistors. But because of the added low frequency bump/dip it's not that simple. And while I could try all sorts of component values until it kinda looks right, I wouldn't say no if there was some method to the madness :D
Not quite sure I understand the goal. Would the desired effect be the same as limiting the potentiometer's range of motion, so that the user could not turn it to the extreme ends? If so, and if you plan to use a digital potentiometer to get recall on the eq settings, you could limit the effective range of motion programmatically while leaving the circuit unchanged.
 
Joined
Sep 4, 2020
Messages
7
By the way, I am curious whether 6.8K or 6.2K is the original value of the resistors on the low side of the shelving high/low. I have seen schematics both ways and photos of B205 boards both ways. It makes only a tiny difference to the curves but... Maybe the value got changed at some point during its production?
 

krabbencutter

Well-known member
Joined
Jul 11, 2018
Messages
104
Location
Germany
By the way, I am curious whether 6.8K or 6.2K is the original value of the resistors on the low side of the shelving high/low. I have seen schematics both ways and photos of B205 boards both ways. It makes only a tiny difference to the curves but... Maybe the value got changed at some point during its production?
I was able to find three different revisions of the schematics.
1073-fullpak.pdf has the first B205 revision from Feb. 71 with 6k8 resistors. The B211 schematic seems to be the original revision from Dec. 70 and has incorrect pinouts on the T530 inductor.
This schematic has the second B205 revision from May 72. The resistors haven't changed but pins A&V have been swapped. The B211 schematic is from Nov 71 and has correct pinouts on the T1530 inductor.
Neve_1073_1084_User_Manual_Issue5.pdf has the latest B205 revision from Mar. 79 and includes the handwritten 6k2 resistor values. The B211 revision is from Jun. 75 and has an additional 220k resistor across the 450mH inductor tap.

The B182C schematic is identical in all three files and dates back to Jul. 71.
 

krabbencutter

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Joined
Jul 11, 2018
Messages
104
Location
Germany
Built a prototype today and it was a success. I initially planned to use the LM4562 as buffer & EQ amp while the GIC circuit would be built around a TL072. The LM4562 however created lots of interference and distortion, so I ended up using TL072s only, which worked much better.

(Because I was too lazy to build everything from scratch, I modified another circuit I had lying around. The blurred out part is just some leftover components I didn't remove)
 

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