Hi guys,
The boards I just mentioned were suppose to get here last Friday. The FedEx tracking says I will get them Tuesday. That being said, I figure it’s time to show what I have been working on.
Now, before I continue, this new module was not originally intended to be used for the 500 series modular console. After some thought the last few days, I think I will make a few small changes to it and it will become the “heart/brains” of the console input channel.
The module started with some idea tossing back and forth between myself and my friend Dan Deurloo. I have always wanted to add the “second stage” from my console to one of my preamps. There is something magic about following an API pre with an API eq (even set flat) and the second stage of the console. Dan said he would really like to have a great sounding high pass filter for tracking, mixing and even mastering. Something stepped for recall. I started with a P&G slide fader into a simple, passive, HP filter section with a 2520/2623-1 post fader amp stage. Once we settled on the HP frequency points, Dan also mentioned how nice it would be to have a LP filter for cleaning the hash from digital electric gtr tracks and so on. Since 500 series faceplate real estate is tight already, I knew I would have to ditch the P&G. We thought something stepped would be great for his mastering friends.
So, I went to work on the circuit and PCB. With the original concept, the rotary fader would be the first thing in the circuit. It’s an Elma 24 position rotary. Nice stuff. I’m using a 1K log taper. Unity is 0 as in my console. 12dB of gain “in hand” with the fader. Since most of the steps are 2dB, I’ve added a 56 series Grayhill for a .5dB stepped trimmer.
Next are the passive filters. I have them set up with the same overall concept as they are in my console. I just gave them selectable frequencies. I also added the first order/second order switch to each. I have a 3 transistor discrete follower between the filters. Very much like is used in the old 550a’s. The 2x6 switches are Grayhill 71 series. Since the Panasonic ECQ’s are gone, Wima was the next choice. Plus, they are relatively easy to get in all the values I need.
The following 2520 stage is the same as in my console. BC/Vishay coupling caps and a 2623-1 to balance the output.
During my layout process, I thought it would be pretty easy to add the line input stage from my console. For those who don’t have an API eq to drive the fader, this will serve a similar purpose. Also, if this module is being fed from a transformerless device, there will be less problems as the fader is of course unbalanced. I was not gonna use a 2623-1 after this stage, but it fits no problem. It provides 6dB of gain as well as some API type goo. I have a jumper to skip it if one wants. The feedback C and R would have to be adjusted to make up that 6dB of gain.
Since the boards haven’t shown yet, I have the Gerber screen shots here.
Here is my faceplate artwork. I am pretty certain this is the final revision. Fader knob is a big 3/4" version. The filter knob inserts are a custom olive green very much like that of an original 550 eq.
I have 95% of the parts on hand to build the proto. The rest are being ordered today. I have 10pc of the L-brackets and faceplates being cut next week.
OK. This is a long enough post. More details on how this can/will work for the console.
Cheers, Jeff
Can imagine this not being a huge seller.
