2-mix and other mods on MCI 600 series

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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2-mix and other mods on MCI 600 series

Postby mikethebike » Mon Nov 06, 2017 11:25 am

Hi Folks,

I thought I would drop a note to ask what people have done to bring their 600 series up to date/modify and how it sounded. For example, I am sure there was one mod on the 2-mix replacing the 2-amp single IC ACN with a descret Op-Amp of the 990 variety, but I can't find any further details of it. Has anyone else made a mod in the area and what was the result - I would be intrested to know.

Also, what mods have folks made on the channel in terms of IC swaps and was there any improvement as my understanding is that the 2003/2004 were cherry-picked Signetics 5534/5532, which are not bad chips in anyones book. Is there a register or note book anywhere of any hot-rods?

My console is a 32 channel populated at 26 made in 1971 using standard VU meters. I have replaced the automated faders with P&G 5/10K faders via a small converter board as there were a few faulty and the DBX 202c always sounds grainy to me. I then use the channel switches for Solo and Mute. I also have PPMs strapped in parallel with the VU meters on the main bus, which I do find very useful, and seperated out the 2-mix stereo fader to 2 individual faders.

Any information of the above would be gratefully received,

Thanks
Mike
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Re: 2-mix and other mods on MCI 600 series

Postby porkyc » Fri Dec 15, 2017 2:15 pm

1. Yes, there are details out there of replacing the 5532 2Mix ACN with API style DOAs. There are a couple of modders out there that think DOAs are the cure for everything.
You might try just a small board with separate 5534s as per the Channel ACN to avoid and Xtalk within the dual IC. Somewhere I did a board that replaced all Master dual ACNs with individuals.
2. I've always said that there is very little wrong with the sound of the JH600 until you put the EQ in: then it falls over. Privately, I have had some discussions with another owner about replacing the EQ daughter board with a different EQ sidechain, so it can be done.
The mic pre can do with a couple of tweaks just to improve headroom (3 resistors and a couple of diodes)
3. Did you sell the 202Cs, because they are the best ones. (You should hear/measure the black 202!!)
4. If it were me, I would replace the 5534/5532 with LME 49710/20. Bog all noise, minimal distortion. They are only available now in SMT, so you would have to make SMT to DIP adapters. The point is that the 5534s are slugged for stability. The LMEs are unity gain stable, 20V/μS and cleaner.
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Re: 2-mix and other mods on MCI 600 series

Postby porkyc » Fri Dec 15, 2017 2:21 pm

Incidentally, the 2003/2004 were initially Signetics 5534/2AN, the lower noise version; later they were the Texas versions of these. The general view is that the Philips/Signetics were better.

Also, if you have not recapped the audio path, who cares what IC you put in.
Also, if you've still got the red Aries IC sockets, good luck.

PC
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Re: 2-mix and other mods on MCI 600 series

Postby mikethebike » Sat Dec 16, 2017 10:10 pm

Hi PorcyC,

thanks for the replies and tips.

Yes I have recapped the channels including replacing the infamous red sockets with good quality turned pin types.

I haven't tried replacing the 5532 with LME - I'll try one channel as an experiment.

Making a small board to seperate out the 2Mix ACNs shouldn't be too much so I will try that as well. I assume that you used LMEs in that position too?

As I mentioned in my post, I took the automation out and replaced it with standard P & Gs which made quite a difference.

Thanks again

Happy listening

Mike
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Re: 2-mix and other mods on MCI 600 series

Postby porkyc » Sun Dec 17, 2017 1:14 pm

I don't have a console, I'm a tecchy. BUT, the LMEs are what I would have done if I had one.
Sadly, they are no longer made. Any replacements are going to need DIP adapters these days.
Give me a few days and I'll post some more, but I will move back to my own site.

The DOA in the mix ACN comes from something that someone did on the original JH500 prototype, one of which went to Atlantic in New York. These prototypes were more of a better JH400 running on ±24v, lending itself to the 2520/990 mod. (than the later ±36v of the final JH500). Especially since these prototypes were still running the MCI2001 (Harris 911) opamp throughout. So the DOA was going to be quite noticeable.

I don't think there is a "snap finger" change/fix for the JH600 for reasons that I'll discuss on the other site.

PC
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Re: 2-mix and other mods on MCI 600 series

Postby jensenmann » Mon Dec 18, 2017 8:15 am

The LME497x0 series is available in PDIP. Check here: http://www.ti.com/product/LME49720?keyM ... Everything
RS Components stocks them.
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Re: 2-mix and other mods on MCI 600 series

Postby Tlow » Mon Dec 18, 2017 10:02 am

There is a new DIY Preamp Kit available for the 600 console
from the guys at http://www.elstudiosf.com
Attachments
elpreamp.jpg
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Re: 2-mix and other mods on MCI 600 series

Postby Jim Williams » Mon Dec 18, 2017 11:59 am

I've rebuilt many 600's over the years. When I rebuild that ACN card I strip it down. Everything goes as it's really all 1980's crap. Jeep was a hard bargainer. Those Roederstein bipolar el caps act as a low pass filter.

It is rebuilt with quality resistors, Either Dale PTF or Vishay bulk foil (I perfer the VAT 'naked foil' versions). Those are non-ferous resistors with excellent temp co's. All electrolytic coupling caps are removed. It is a direct coupled audio path, zero hz to about 100k once the feedback caps are applied.

I'll use Analog Devices opamps for general use or BurrBrown for the rockers. The resistor values are also changed, I remove the second opamp stage gain and run it unity. Then the sum opamp feedback resistor is corrected for unity gain summing. Local .1 uf caps are installed on the rear of the sockets to increase the stereo crosstalk specs. Large Panasonic 1000 uf FR caps are also used on the power rails.

Silver wire is used to connect it to the main pcb. All flux is removed, it's a clean looking card when done. The opamps I use have up to 90 db OLG (open loop gain ) at 10k hz, that will lower THD -30 db next to a 5534 that is limited to 60 db OLG at 10k hz. Only one discrete will do that OLG, the 990. However it's not very fast and has much more noise as well. I get better resolution out of the modern IC's.

Similar work is done to the rest of the modules. All the el caps are removed except the mic pre and mute stage. That includes the EQ as well. Once done it's like getting off a jet and then your ears pop.
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Re: 2-mix and other mods on MCI 600 series

Postby mikethebike » Tue Jan 09, 2018 5:40 pm

Thanks guys for all your comments

There is serious food for thought.

Regards

Mike
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