*EASY* Relay bypass/fix mod = better sound on 400

In the late 70's, over half of the records in Billboard's Top 200 were recorded and/or mixed using MCI equipment.

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*EASY* Relay bypass/fix mod = better sound on 400

Postby charlesaustin » Sun Dec 30, 2012 2:11 am

Hi, spent some quality time with my mci over the last week. I had one channel that had a bad relay (you can check for this by assigning the channel to it's buss with the direct switch..... now turn up your monitor pot. If you hear signal, your remix relay is the problem.

So now I know the relay is the issue. I have extra...... however I wanted a more permanent fix (trying to make it reliable as possible, taking the relay out of the picture). So looking at the schematic I did this (keep in mind I mostly used the fader in, however it works for the tape machine return as well with an extra step, but let me use the fader in so you can best understand the signal flow.

Remix signal flow

Fader in - eq opamps - buss assign - relay - cue/echo/pan opamp - mix buss

If you turn off the relay power supply the relay sends the buss assign/monitor to the pan circuit.....
so I says to myself....... If we jump from the output of the eq amps, to c38 (after removing the monitor opamp), we will basically be in remix mode (with a couple function changes).

So here is the new signal flow

Fader in - eq opamps -monitor pot (since it is disconnected from the monitor circuit, it acts as a fader only) cue/echo/pan opamp - mix buss

Now to my surprise, it sounded way better.... More punchy lows, extended highs etc etc..... While retaining almost all of the functions. Who wouldn't want that?? Well,..... we will find out in a sec

'''''''What do we lose''''''' - If you do this mod, you will lost the function of your buss sends (which many do not use because it is easily done with the DAW). As well as the monitor amp, essentially you lose the ability to send the cue/echo signal pre fader. You also lose the ability to track with eq (or at least the eq on the same channel).


That being said, we gain (imho) better reliability, better sound, and improved workflow (along with my preamp direct out mod,detailed in another thread). At very least it is a cheap easy fix for a broken relay...... Now, to commence with the science!!!

To do this mod we first remove the acn and monitor opamps. The we have to cut cr3 at the cathode (the line side). This will "turn off" the remix relay. Then install a jumper from the back of the direct buss assign switch to -c38 (this connects the output of the eq amps to the cue/echo/mix buss).... That is it!!! Well, kind of. This works fine for me because I use the fader in to bring the signal into the console.... Now here is when things get interesting. I did that (fader in) because to my ear it sounded much better. I always assumed it was the input transformer killing the fidelity of the signal.... Turns out I was wrong!!!

I installed a jumper from r71 (side facing pins if looking down at the components of the strip) to r12 (side facing knobs). This takes your tape returns (out to the patchbay, preamp out/return) and connects to fader in.

New signal flow

Tape return (transformer in) - patchbay- Fader in (if you want to bypass input transformer, a bit faster/cleaner sound) - eq opamps -monitor pot (since it is disconnected from the monitor circuit, it acts as a fader only) cue/echo/pan opamp - mix buss


Holy crap, this really sounds much better. It turns out it is not the transformer, but a bunch of stuff (relay, resistors, wire, etc) in the signal path that kills the fidelity. We also now have a fader before the eq, and after the eq (the monitor pots new function). I played with it a bit and found that if you put the monitor pot up high and you lower the fader, it gives a "better" sound. I chalked it up to more headroom in the eq circuit. Seriously, the transformer ins really sound great now.

I am either loosing my mind or I stumbled on the holy grail mod (keeping in mind I am already using the bova opamps). I really hope someone else tries this to confirm what I am hearing, which is not subtle btw. It only takes 3 wires (along with the preamp direct out) and 2 snips, it can be removed in 5 minutes...... For the small change in function, we get a much improved sound and reliability.

****** To review the process

1) To do this mod we first remove the acn and monitor opamps. Then you have to cut cr3 at the cathode (the line side). This will "turn off" the remix relay. Install a jumper from the back of the direct buss assign to -c38 (this connects the output of the eq amps to the cue/echo/mix buss).

2) I installed a jumper from r71 (side facing pins if looking down at the components of the strip) to r12 (side facing knobs). This takes your tape returns (out to the patchbay, preamp out/return) and connects to fader in.

3) To complete the mod, I wanted the preamp to be wired directly to the output transformer (check out the other thread for details, cut -c8 attach it to c33+). This way all I have to do is arm a track and the mci preamp signal goes to the tape machine input.


So the complete new signal flow goes like this

Mic - mic input transformer - channel output transformer - tape machine input - Tape return (transformer in) - patchbay- Fader in (if you want to bypass input transformer, a bit faster/cleaner sound) - eq opamps -monitor pot (since it is disconnected from the monitor circuit, it acts as a fader only) cue/echo/pan opamp - mix buss


..... Now please tell me why I should not wire my console like this? Does it not offer increased reliability (no relays to worry about), better sound (less components)..... And if I want it stock, all I have to do is remove 3 jumpers. Am I missing something which electronically I do not understand? Please let me know your opinion. Thanks


Below is mic pre direct out info


Hi, I figured I would share this if anyone runs their setup like mine. Before you do this please read through my relay bypass mod thread (I would advise doing that as well for the best functionality, if not please look over schematic to understand how this changes your signal flow).

First if you use your buss sends alot, this is not for you (we disconnect the buss amps).

The goal was to have the preamp out connect directly to the output transformer. This way all I have to do is arm a track and the preamp is at the tape machine input.

Here is what we do

1) remove acn and monitor opamps

2) cut the negative end of c8- (close to the cap) install a jumper to c33+


The new signal flow goes

mic - input tranformer - output transformer via the channel line output (your mic preamp will show on the vu meters)

That is it. We lose the buss and monitor functions, but if you do not use them anyway (or do the relay bypass)...... The only thing that I miss is not tracking with eq..... which I never did anyway.
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Re: *EASY* Relay bypass/fix mod = better sound

Postby Jim Williams » Sun Dec 30, 2012 12:23 pm

Seems many of the reasons to use an analog console are lost with that mod. MCI's (munchy, crunchy and ittermittant) are known for soft transients and mushy sonics. It's mostly due to those 5534/2 opamps and all those red Roederstein bipolar coupling caps.

The last 636 modules I went through had all those red caps yanked out, fader amp, EQ, ACN, balanced outputs, etc. Only one cap was left in the fet switching to avoid thumps from bias currents. Several of the ceramic high cut caps were also removed or reset to operate above 200k hz. The caps were retained in the mic preamp card. I used National LME49860/70 opamps as they are precision and most el caps can then be removed, permanently. That is like an after your ears pop landing in a jet difference. Then all the console features can be retained and used.
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Re: *EASY* Relay bypass/fix mod = better sound

Postby charlesaustin » Mon Dec 31, 2012 8:27 pm

Jim Williams wrote:Seems many of the reasons to use an analog console are lost with that mod.


I should have written in the original post (copied it from the 400 series forum) that this was for a 400 series console. If you understand the typical workflow of a 400 I really do not see loosing much.

1) Busses are mono. Stereo busses in the daw are easy. I would imagine most are not using these anyway, except to send the mic to the channel output. Which is adding a relay, 5 amplifiers and all their circuitry. Wouldn't you rather have the mic preamp connected right to the output transformer?

2) Really the only thing you lose is the ability to track with eq, and if your mixing through the same console, just add it on the mixdown. If you really want it you can send it out one of the other 6 busses (cue 1/2 and echo1/2) or even the rear master busses. All essentially the same circuitry as the busses themselves. It also looks very simple to add a switch to toggle between mic out and buss output.

So, what else do you lose (ok, pre fader on echo 1)? Is is not worth better sound? I would think you of all people would appreciate less junk in the audio path. Also even if you worked your opamp magic (I already have the bova amps in mine which blow a 5534 out of the water), wouldn't it still sound better this way?

The answer I am really looking for is am I missing something technically that could cause a channel to go into oscillation or another problem I may net be aware of?
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Re: *EASY* Relay bypass/fix mod = better sound on 400

Postby Jim Williams » Tue Jan 01, 2013 12:41 pm

The only way to determine if any harm is done is to compare before/after with a decent analyzer like Audio Precision. Oscillations can be found with a decent scope. Fixing them requires an understanding of feedback circuits and their pitfalls.

The 416/428 modules only have 6 can opamps, 1/2 the count in my little Soundcraft Delta console. Low noise precision opamps fix up any sonic problems if those crappy caps are yanked out. If you don't want to bother with 8 pin can "adaptors" National Semi makes the LME49870HA in a can, plugs right in. Then jack up the power rails to + - 21 volts and enjoy the dynamic range (these are 2.5 nv noise parts with -154 dbu THD).

If you look up the independent analysis of those Bova opamps, you will find they suffer from low open loop gain and excessivly high THD, above most any IC opamp by quite a bit. I would consider them a color device to be used selectivly unless you always want that amount and flavor of dirt with your music.
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Re: *EASY* Relay bypass/fix mod = better sound on 400

Postby AnalogStudio7 » Tue Jan 01, 2013 3:16 pm

Hello Jim,

I was trying to find some indie reviews on those Bova Op Amps but didn't find any real scientific reviews at all.

Could you steer me to the info you're talking about or do you have any web links.

Really appreciate it as I was looking into these Op Amps for an old 416 that we just bought.

Thanks,

Greg
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Re: *EASY* Relay bypass/fix mod = better sound on 400

Postby Jim Williams » Wed Jan 02, 2013 11:05 am

Search the gearslutz site for that info. Someone in the EU did quite an analysis of many common opamps, can't remember the name but just search for it. Most discrete opamps suffer from lack of high open loop gain and slew limitations, THD is not that great either. The 990 variations have the best specs, 85 db OLG at 10k hz with decent THD specs. Most classic discrete opamps reside at 40 db OLG, that adds another 40 db of dirt to your music over those cleaner designs.

Used selectivly they can be a useful tool, but running an entire mix through one would be detrimental in my place.
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Re: *EASY* Relay bypass/fix mod = better sound on 400

Postby Phillip Victor Bova » Mon Jan 14, 2013 4:58 pm

Congratulations Charles!

You are the King of 400 series modders. What a great idea. I suspect many folks are using the same limited number of features on their 400s as you describe - ie: rarely to never using channel assignment buttons, et cetera. I have considered running individual i/o module pre and post fader feeds to a compact line mixer to increase the effects and headphone mix potential of the console. I agree that you can make multiple mixes from within your DAW assuming you have enough spare D/A outs in your system, but I find it is so much quicker to work with real knobs in a busy session.

There are other easy ways to improve the sound of our almost 40 year old babies. One thing we did a few years ago was to polish up 24 bantam patch cables. These were treated with Stabillant 22 [miracle contact enhancer]. Each of the patchbay channel inserts was then exercised with a patch cable initially wetted with 99% isopropyl and then Stabillant 22 [diluted with isopropy]l. All 24 bantams were then plugged into their insert points. Significantly cleaner sound resulted. I found this approach to be much better than merely trying to spray vast quantities of contact enhancer through the patchbay jackfield holes with the faint hope of hosing the normalizing switches.

We have recently designed 24 new buffers to go between the outputs of our DAW line out stages and the 600 ohm transformer line inputs of our MCI 416. This particular buffer amp is a true balanced 14 transistor discrete class A design, conveniently running on +/- 24 Volts. The improvement is not subtle. Low end tightens up and feels like it's extended down half an octave. Top end is more open and very detailed. For the last several years I have been using twin NE5534 balanced buffers for the job, but to me the discrete buffer sonically blows them out of the water. I'll endeavour to post some comparison samples in the next month. Incidentally, these same buffers were employed as output stages for a pair of almost 50 year old HAECO EQs which I recently restored for Studio G producer emeritus Joel Hamilton.

Sadly, very little modern gear can properly drive 600 ohms. Most contemporary line output stages are hoping for the now ubiquitous 10 k ohm bridging destination. A quick way to see if the line output of your DAW [or any other gear] is up to the task is to output a 1 khz tone just below digital clipping. Measure the voltage with a multimeter, and then connect to a line input of your MCI 400. If the level then drops more than 0.5 db Houston has a problem :) I've seen some gear exhibit level drops of several db. This is not good. If you need to be even more alarmed, use a 20 hz to 20 khz sweep tone.

Plugging into the unbalanced fader return at the console patchbay, significantly improves this situation as the channel fader provides a relatively soft landing of 5k ohms if I recall.

I'm going to try your mod soon Charles.

thanks ... Phil
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Re: *EASY* Relay bypass/fix mod = better sound on 400

Postby Phillip Victor Bova » Mon Jan 14, 2013 5:12 pm

Hi Greg
Discrete opamp or other discrete topologies are "the sound" of well known consoles such as API, Neve, Quad Eight, ElectroDyne, MCI, Trident A Range, Sphere, Audio Design and many others. Many years ago I made a list of my top 100 favourite sounding albums. I then attempted to call as many of these studios as I could to find out what consoles, tape recorders, etc had been used on these particular sessions. I was quite overwhelmed by the generous amount of people's valuable time given to a complete stranger. I always keep that spirit close to mind now that I'm the one getting the calls :) Mix Magazine "Classic Tracks" are great research material, but nothing beats connecting with a real
person if you can.
Welcome to the 416 club !
Phil
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and
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AnalogStudio7 wrote:Hello Jim,

I was trying to find some indie reviews on those Bova Op Amps but didn't find any real scientific reviews at all.

Could you steer me to the info you're talking about or do you have any web links.

Really appreciate it as I was looking into these Op Amps for an old 416 that we just bought.

Thanks,

Greg
s a g e
ELECTRONICS®
high-end handcrafted mic preamps, microphones & DI boxes
+ (613) 228-0449
sage@sageelectronics.com
http://www.sageelectronics.com
http://www.myspace.com/sageelectronics
Ottawa, ON, CANADA
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Re: *EASY* Relay bypass/fix mod = better sound on 400

Postby charlesaustin » Tue Jan 15, 2013 8:33 am

A simple solution for the busses if you do that mod is hard wire (on the motherboard) a jumper from buss line 1, to buss line 17..... 2-18, 3-19, etc. This way when you assign channel 1 to buss one, it will appear on Channel line out (buss out) 17.

With or without the mod, when you assign a channel to a buss, it appears on the "buss line" on the motherboard. It would be pretty easy if you know what your doing to wire up those buss lines to do whatever you want, headphone sends, direct outs, whatever.

Remember on a 400, channel 1-16 assign to those busses, channel 9-28 assign to buss 9-24. So..... it is kind of funky anyway (although to be fair at the time, it was pretty useful and ingenious).
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Re: *EASY* Relay bypass/fix mod = better sound on 400

Postby Jim Williams » Tue Jan 15, 2013 1:29 pm

I used Stabiant 22A for several years starting back in the 1980's. I bought a lot of it from DW Electrochemicals in Canada. It is a polymer that becomes conductive in the presense of an electrical current, a "liquid conductor" so to speak.

I no longer use it. It does do as advertized, at first. Then it dries out, gets gummy and makes switches sticky. The residue then picks up more contamination, just like Caig products. Then you are left with attempting to clean out a bunch of goo from your console.

If it is use on any high impedance nodes, you will be in a world of trouble. It lowers impedance and creates leakage paths. Bobby Summerfield used it on the Alps switches in his Soundcraft TS-12. It messed up the automation so any transient waveform would leak into the high impedance solo buss and fire it on beat!

Cleaning it out didn't work. He was left to replace every solo switch on the console before it was restored.

If a quality non-reside contact cleaner doesn't bring back a switch or connector, it's shot and needs replacement. Buy a Hakko 808 and a bag of switches from Mouser and in the time it takes to clean and treat all those switches, you could simply replace them. Then you start again as new.

Most all modern IC audio class opamps are designed to drive 600 ohm loads. Yes, they may loose a db or so, but they can do it. Some I use are specified to drive 150 ohm loads. Those handle 600 ohms loads easily. Most low end audio gear relies on cheap Asian opamps or older designs like TL07x series, those can drive 2000 ohms and up only. Throw a couple of discrete power transistors on them and they can drive 8 ohm loads.
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