Aengus graphic EQ (thumbwheel) information sought--any leads?

[dmp]

Could put in a 2520 footprint for a DOA output. Could make the Aengus into a DOA if wanted.

 

[dmp]

These are unbalanced in, I believe—so maybe adding an input Tx is advisable? Would love some thoughts.

If there is space, or could use the input stage of the 560B

 

[dmp]

There is the RC741 over by the edge connector used as an input buffer, but it indeed looks to be unbalanced in as pin 8 is grounded and 9&10 are summed into the RC741 input. From there, it looks really similar to the API 560B. The MC1741S opamps are in place of U2 and U3 with the bands being summed every other one into the two stages. I guess this is to maintain good separation as the bands overlap.

 

[soapfoot]

So maybe 560B input would be the way to go?

Obviously at that point it's not a straight "clone," but it does seem like an improvement over unbalanced in

 

[soapfoot]

Output amp card schematic. Someone check my work, seems strange (edit, fixed a mistake)

I'm far from the most qualified to check this work, but I just had a quick look and nothing jumped out at me.

I've also got a text message out to a friend to see if they might know anyone with documentation. A longshot, but worth a try.

 

[dmp]

I tried simulating this - the 1.5k around the U2/U3 opamps are important. With the 560B values the response was way off
But looks good!

 

[dmp]

So maybe 560B input would be the way to go?

Obviously at that point it's not a straight "clone," but it does seem like an improvement over unbalanced in

A straight clone would be really hard with the switches. I don't really care about trying to do a straight clone. Especially when it requires difficult to source or expensive parts.
I guess decide how important it is to you to fit it in 500 series and be authentic. The differential input opamp would be transparent, just a little more resistant to hum/noise issues.
Would be a lot easier to put it in a 1U and use 1x12 grayhill switches. And could add the option for a 100k S taper pot, to do continuous vs stepped switch, aka the 560B. Could build with the Aengus frequencies or the 560B frequencies - just a few different R/C values. Would be pretty cool EQ project.

 

[soapfoot]

500-series is appealing just because in both of my studios, rack space is at a premium (but 500-series slots are not).

Having the authentic look would be cool, but I've made my peace with that being highly unlikely due to those thumbwheel switches.

Having authentic/original functionality would be great, but I'd probably be okay with a balanced input stage (whether via a small transformer or a differential op amp)

 

[Bobby Baird]

Custom, 30-channel Aengus/API mixing console installed by an eccentric audio guru named Deane Jensen.
This eq was a huge part of the sound of the recordings that came out of Indigo Ranch. "The sound of my youth." Substituting thumb-wheels with grayhill rotary switches would be very expensive. Probably just go with S-curve sliders to keep in 500 format add 2 more bands low and high. Say 25Hz & 20kHz.

 

[wlinart]

Maybe use the same principle as the CAPI LC40? NKK MRK112 switches, 10 fit in a 500 series module

 

[dmp]

Good ideas. Something like the LC10 with stepped switches OR like the G.TEN with faders (560 clone).
I wonder how close you would get adapting just the gyrators in one of these two builds to the Aengus values

 

[pvision]

Decent thumbwheel switches are expensive but there are cheaper alternatives, sadly without the levers. Watch out as some thumbwheels are binary-coded and I think they won't work in this application

https://www.amazon.co.uk/Single-Unit-Pushwheel-Thumbwheel-Switch/dp/B005FO42K0/
I have a bag full of metal-can 741s if anyone wants to go retro

I looked into thumbwheels as a way of making a 16-step sequencer, like the ARP sequencer but using thumbwheels rather than slide pots

 

[NOON]

The thumbwheels aren't part of the sound, if it's difficult and expensive then pots, sliders or some kind of more economical modern switch is fine by me.

 

[soapfoot]

yeah, unless I could get the same exact parts with the +2, +4 etc. indices on them, I think I'd rather go for accessible modern switches!

I assume there would be no audible difference between a metal can 741 and a standard 8 pin DIP package?

 

[Walrus]

I don't know about audible, but there must be some difference about the RC741T and the MC741's or they would have used the same ones.

 

[Slenderchap]

We made one a few years ago (managed to get hold of a real one to look at) .... works fine... it is over at a friends studio.... I'll go get it back.

It is our usual full PCB implementation... in a 1U format. We actually made 2 in a 2U box.
[If I remember correctly, we did one channel with 741's and the other channel with something modern to see if anyone could tell the difference].

The only reason it was not released as a kit was because I did it with Grayhill switches.... so I decided that it was too costly for the DIY market and intended to re-lay it out for Lorlins...

I don't have a photo on hand but it looked like this:
https://www.audiomaintenance.com/downloads/ez404.jpg
We probably have a couple of PCB's left over... but it isn't cheap to make.

If there is enough demand I could make them as DIY kits.... but to be realistic cost it does need changing to Lorlins.

Colin
www.audiomaintenance.com

 

[Slenderchap]

The schematic is here;
http://www.audiomaintenance.com/downloads/ez404_Schematic.pdf
This was the PCB:
http://www.audiomaintenance.com/downloads/ez404_PCB.pdf
[The edge connector was only so that we could easily test it using our 500 series jig... just me being lazy].

 

[Walrus]

The big question Colin is, did it sound like the original?

 

[soapfoot]

Wow, fantastic!

Thanks so much for this info

The little NKK switches and squeezing it into 500 series would probably make it cheaper, and be doable

 

[Slenderchap]

I will have a look at the NKK switches... do you have a part number for them ?