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Audio Developments direct out mod


Wyatt Tuzo

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Hello all,

I just picked up a used 8 channel AD-146. Unfortunately, the previous owner had not opted to perform the factory  direct-out mod. I have priced out the boards from AD (at £85 ea.). I am entirely willing to go that route, but first wanted to check to see if anyone here had personal experience taping an unbuffered, high Z output from the channel strips as they are.

One thing that I am apprehensive about with the AD mod boards, is that Ill be sacrificing my line ins, which I would prefer to keep for interfacing with a Lectro venue.

Anyway, I'm just putting out feelers. I havent seen a schematic yet and dont know how the internal/panel real estate looks. Thanks in advance for any tips.

Wyatt

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Thanks Philip,

I went ahead and submitted an email request for the schematics. I'm pretty comfortable that I'll be able to find an unbalanced, high impedance point from which to draw a direct out. I suppose I just thought to check if anyone had any specific experience with a similar modification. Has anyone found a benefit in going with AD's balanced/low Z/buffered outs when interfacing these boards with modern recorders?

I mean... Input impedances are are so high on most modern equipment that I doubt I would load down the outputs too considerably. The buffering from the main outs is my greater concern.

I also plan to replace the stepped attenuators on the input trims (with 10k rev log continuous pots), and potentially reroute the slate mike to hit the direct outs as well as the masters.

Thoughts and experiences are always welcome.

--Wyatt

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Thanks Richard,

Unfortunately, AD only has the block diagrams listed on their site. I have emailed them for the schematics. They have been pretty good about corresponding to emails, so I expect to have them in a day or two.

Ill try to document my processes in the event someone finds this thread helpful down the road.

--Wyatt

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  • 3 weeks later...

Hello all,

I just picked up a used 8 channel AD-146. Unfortunately, the previous owner had not opted to perform the factory  direct-out mod. I have priced out the boards from AD (at £85 ea.). I am entirely willing to go that route, but first wanted to check to see if anyone here had personal experience taping an unbuffered, high Z output from the channel strips as they are.

One thing that I am apprehensive about with the AD mod boards, is that Ill be sacrificing my line ins, which I would prefer to keep for interfacing with a Lectro venue.

Hi Wyatt,

Alex at Gotham did a nice job on an AD-147 board of mine.  I don't remember exactly what it cost, but my guess is it would be cheaper than 85 quid a channel.  If you want to DIY he might be able to help with questions you may have.

Good luck!

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Thanks to everyone for the replies.

Just as an update... I have been in touch with AD and they have scanned and emailed me the schematics (I have found everyone at that company to extremely personable and helpful). I have run a few tests, and have decided that I'm going to draw my direct outs unbalanced. After tracing the schematic, I found that I'm going to be able to use a single jumper cable on the channel strip to one of five available pins that channels din connector to carry the direct + audio to the motherboard. The benefit in this is that system will remain completely modular. Ill take a common audio gnd from another point on the motherboard. I'm going to use a 9pin D-sub for my direct outs.

Im making a trip home to Baltimore on labor day weekend. I decided that instead of ordering all of my cables, connectors, and components online, that this would make for a perfect excuse to go to my favorite, family-run, electronics store in the world (baynesville electronics).

The continually variable gain pot is already taken care of. All I have to do now is the direct out mod, and to replace two trimpots so I can re-calibrate my meters to 0VU=0dBu (.775Vrms). Its factory calibrated to +4dBu.

I will be sure to document my process once there is something more visual to share. As my wedding day is quickly approaching, I'm finding myself with less and less free time for these sorts of projects.

Best,

Wyatt

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  • 5 weeks later...

Hello all,

So, I finally got around to doing the work I promised on this board. Everything is tested, and working fine. The one thing that I'm a bit bummed about is that on my direct out channels, I'm coming up short about 10dB. I was expecting this since Im connecting an unbalanced source to a balanced input circuit, I guess I was just hoping that since I wasnt unbalancing an already balanced signal, that it may not bean issue. Anyway, I guess its not. I still have plenty of glean gain on both my 788 and 744 to make up for the lower input on those channels. Here is a brief description of what I did:

4997244334_35610eddc1.jpg

First, I bought some 9 conductor cable. Here is the connector end, stripped and ready for duty.

4996637091_f50b47eb6b.jpg

I found a few expansion points on the motherboard that were available, allowing me to keep the board entirely modular (see channel jumpers below. I basically drew the direct out post pre-amp, pre EQ down to the bus connector, then up from the receiving end of the connector to my D-sub. The ninth wire flies over to an audio ground point just out of frame.

4996638181_d03f74a123.jpg

Here is one of the channel strips out of the chassis. There is a protective side-panel that you cant see. It is sitting just out of frame. This is as they cam from the factory.

4997244534_d7c2b9d9d5.jpg

Here is the same channel after I installed  the direct out jumper from the pre-amp to the bus connector.

4997244172_ee8830282d.jpg

Getting ready to machine out a hole for my connector. I built a protective catch out of junk mail and gaf tape to catch any nasty metal bits. Wouldn't want metal filings floating around the inside of the board when powered up.

4996637287_266453b6aa.jpg

I realize that I didn't achieve the cleanest cut on this, but it works. I have some specialty tools lying around, but apparently not the ones I needed for this task :-)

4996637447_cf03429fe3.jpg

Here it is from the inside. If I ever had to do this again, I would have made the connections at the D-sub end prior to soldering to the motherboard. There were 9 fairly tight solder points to be made, and not a whole lot of room to work nor slack to work with.

4996682131_de8bd07619.jpg

... And, here she is all put back together. Sorry I didn't document the exciting testing stages or the making of the snake. I had to keep reminding myself to stop to take a photo from time to time.

As you see, I decided to go with a 9 pin D-sub connector for my direct outs. This was mostly based out of necessity and rear panel real estate. I have the 8 channel outputs on 1-8, and a common audio ground on pin 9 (isolated from chassis and power gnds).

For the time being, Im going to leave the limiters as they are. I don't really plan on needing them in the immediate future anyway. to be used practically, they WILL need to have the threshold and recover times adjusted.

I was able to replace a few resistors on the VU driver board to get 0VU to equal 0dBu, which is where I like the board set up.

It took me a decent amount of time pouring over schematics to figure out just how to tackle this project, but I'm quite happy with the results.

All-in-all, mission accomplished. Lessons learned.

Cheers,

Wyatt

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Wow! Thanks for all the compliments guys (and gal). I'm really happy with the way everything turned out.

Greg, I'll make sure to let you know once I get around to resetting my limiters. Ill try to make a note of the output voltages and resistance ratings at the trim-pots. The settings may be applicable to your board as well.

I plan to, at least, raise the threshold and speed up the recovery time. God, they just pump so nastily as they are now. I can't promise I'll get to it any time in the next month, but I'll get to it. Probably after the honeymoon.

Best,

Wyatt

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How do you find the levels with the loom in use? I had to change the opamps

for this in my 145 mod -different, yes

Any chance you could be a bit more specific, Matti? Do you mean the internal levels to the mix bus? Can the power supply of your 145 handle the upgraded opamps without sacrificing headroom? I would worry about starving them with anything more than the circuit was designed without upgrading the PSU.

The direct outs are about 10dB lower, but that has to do with the unbalancing, and I have plenty of clean make-up on the 788 that I'll accept it.

-Wyatt

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  • 1 year later...

Trim pots and direct outs on a Audio Developments AD 145.

I just finished two AD 145's, a 4 channel long throw and a 6 channel short throw. Channels 1 and two now have trim pots, and each channel has a unbalanced mono out. Here's what you do;

The tap-off point for the direct out from the input channel is under the PFL switch and PFL board. For pre-fader the point under the PFL circuit board marked 202. IC1 will need to be changed to a TL071 to increase the drive capability. The post-fader tap-off point on the circuit board is marked 203. IC2 will need to be changed to a TL071 to increase the drive capability.

 

Adding a trim pot in addition to the gain selector switch; This can be added after capacitor C11 and before the Eq circuit. The value is 10kR Log.(audio taper) I just cut the trace between C11 and the EQ circuit and soldered into both sides.

Here's how I did the mechanics of the changes;

For the trims I removed the PFL switches and boards, and mounted pots in the empty holes. For the mono outs I put in a micro mini mono jacks the same size as the Comtek IFB transmitter input. I mounted them just to the left of the gain selector switch above the "line" lettering, basically you drill through the -10 red lettering. I also countersunk them into the panel using an ex Boing tapered drill for airline flush rivets. Tight fit so measure many times before drilling into the panels.

Be aware these are long in the tooth mixing panels and you should really go through them and replace all the electrolytics. Yes I have too much time on my hands. Not a bad back up mixer with a fairly "warm" sound.

BTW I am looking for an attenuation switch, the grease had crystallized on one and when I took it apart, it flew apart and I never did find half the spring loaded parts. Duuuuhh.

Jeff kindly put the photos in for me because most things past a Nagra confuse me. In the top picture the grey and black wires are for the trim pot. You can see where I cut the trace. 2nd picture shows connection 202 with the PFL circuitry pulled the green pot is the added trim pot. Third picture shows where you can pick up the mono out it's the red wire and I just added it to the PFL switch position that connects to 202. Bottom one shows the mini plug.

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