Bay Area Studio Engineering

Servicing Analog Equipment since 1981...


the MCI 400 series consoles - replacing the MCI 2001 Opamp...

Bit of history first !!
The very original David Harrison/Jeep Harned 400 consoles actually used their own DOA,
but these potted amps got hot, as they usually do, but instead of just dying, They caught fire!.
What the Heck do we do now?
Then in walks the Harris Semiconductor rep   "We've got a +/-25v chip!" he says.
The HA-911...
The channel board was re-done to use these (branded as the MCI 2001) and those original first 400 series consoles
had their modules exchanged for these new boards with the Harris Chip labeled as the "MCI 2001" IC in the TO-99 metal can.

So now, you've got a JH400/A/B, that's full of MCI 2001/Harris HA-911 ICs
that alas you can't get any more.

  There are a number of replacement options available,
none of which are straightforward or simple,
as you will have gathered as you plod through Internet searches and forums.

As you may have read, the main jump from the 400/A to the 400B
is the SE5534AH/(MCI 2003) in the main and mix buss summing amps.
MCI put a 680 ohm resistor in each supply feed to the IC and kept the overall high 24v rails for the MCI 2001's,
and because of the resistors, the actual power at the MCI 2003 IC pins dropped down to 20 volts,
which the SE5534AH could take without damage or failures... though the IC will be a bit warm.

You can do a lot worse than to expedite this mod in a few places and gain yourself some HA-911/MCI2001 chips
from the positions you change over to another IC to use as future spares -
BUT as 5534s in the TO-99 can were originally cheap and plentiful... the SE5534AH and NE5534AH
alas are now are near impossible to find.

And there are circuit mods/compensation issues that require a 22pf capacitor
across pins 5 & 8 for unity gain stability with the 5534, AND Pin 1 on the MCI 2001 / HA911
is used as a ground for the case...while the 5534 uses Pin 1 as a compensation input.
So you have to issolate Pin 1 to use a 5534AH TO-99.

But we are not just talking about just replacing 1 or 2 chips on the module;
we are looking for a practical solution to an on-going problem as the original MCI ICs fail over time.

The real problem is the +/-24v IC Power supply which severly limits the possible replacements,
because you do NOT want to drop the power supply down to +/-18v because you loose a bit of headroom.
BUT You CAN drop the Audio Power Supply voltage down to say +/- 20 volts without to much headroom loss.  
Even dropping down to +/- 18 volts (normal voltage for the 5534 and 5532 IC's in use)   does
NOT cause many problems at all...as this is what almost all modern console use.
But the best thing to keep the MCI 400 'Vintage' is to keep everything working at the higher voltages.

Since there is no one-size-fits-all easy solution to this,
let's look at some possible choices:-

The industry standard NE5534 20v chip, used to be available in TO-99 cans - as the SE5534AH and NE5534AH
but is now available only as an 8 pin DIP or Surface mount chip.
From time to time some of these old TO-99 style ICs do come up for sale though, mainly overseas.
And it would be worth it to buy them and do the easy mod of adding in the unity gain stability cap,
and changing resistors in the IC power feeds from the existing 10 ohm to 680 ohms or so...
you may need to experiment to find the right value.
and then cutting off Pin 1.   No adapter needed if you can find them in the TO-99 can.
Do this only in some of the less important circuits - cue/echo sends and so on.
Note the 5534 is NOT unity-gain stable, so you will have to install a 22pf cap between pins 5 and 8
And you have to remove the 12pF cap the old MCI 2001 used from pin 8 to ground or the positive voltage rail.

The Texas Instruments LF156H is STILL being made in the TO-99 can... but costs slightly over 20 dollars each as of 2020.
As is normal, Pin 1 is used for DC conpensation (which is not normally needed)
so it may be possible to just cut pin 1 off to issolate it from the socket's Pin 1 ground as needed for the MCI 2001.
You would need to make sure the pin 1 stub can never touch the socket though - or you could cut the trace to pin 1
on the module... but then you would have to jumper the cut if you wanted to use the original MCI 2001 again.
What is nice about this option is literally little board modification is needed and the drop in overall power voltage is
only going to cause a slight drop in headroom.   You would need to change the power resistors in the power feeds
10 ohm to around 390 ohms or so - you will have to test to get the right value -
you want no more than 22 volts MAX at the pins to the IC - better is +/- 20 volts.
And you have to remove the 12pF cap the old MCI 2001 used from pin 8 to ground or the positive voltage rail.

The OPA 445 is a Burr Brown IC that is still available in the TO-99 can.... and can work with up to a +/- 50 volt power !!!
Priced at $25.00 per IC this can be a very good choice.... good slew rate, low noise, low distortion.
Since it comes in the TO-99 can, it is an easy replacement with little modification needed.... just cut off Pin 1,
remove the 12pF cap from pin 8 to ground or the positive rail (needed with the original MCI 2001), and you're done.
Costly yes.... but it is the best simple replacement I've seen.
Note I have not had any experience with this IC myself.... and so far I've not heard any comments on it in use
in a JH 400 series console... so if you try it out please let me know how it works and sounds !!!

OPA 604 is one VERY good solution that does NOT necessitate dropping the supply rails or changing the voltage feed resistors.
it's cheap ($2.88 in 2016), has low noise and a good Slew rate.   It is also unity-gain stable.  BUT..it needs an adapter board,
and it is certainly better than the original 2001 spec wise... and it works with a +/- 25 volt power supply !!!
Comes in the standard 8 pin DIP.   Like the 5534 it uses Pin 1 as DC compensation
so Pin 1 must be issolated - remember the MCI 2001 uses Pin 1 as case ground.
This is Possibly the BEST REPLACEMENT that will use an adapter board as no power voltage drop or mod is needed.
Just cut Pin 1 on the IC, put it in the adapter (8 pin DIP to TO-99 adapter) and put the adapter into the TO-99 socket.
And you have to remove the 12pF cap the old MCI 2001 used from pin 8 to ground or the Positive Voltage Rail.
Total cost should be about $10 each replacment.
OPA 604 data is here:     http://www.ti.com/lit/ds/symlink/opa604.pdf

BUT you'd have to have adapter boards made...
or use Brown Dog's nice TO-99 adapter boards...
    Link to the Brown Dog DIP 8 to TO-99 adapter    
Note I have NOT used this adapter board myself, but it looks as if it will work fine.

NOTE: If you use the Brown Dog adapter you MUST still mod the adapter or your console
at any IC replacment you do !!! Pin 1 on the MCI 2001 is connected to the metal case
and ground - while pin 1 on most ICs now is used for DC compensation...
so you MUST make all the approiate changes as needed !   usually you can just cut Pin 1 of the IC.
Also note that the MCI 2001 may have a 12 pF compensation cap from Pin 8 to ground or the Positive Rail
and this will have to be removed in any place you install a replacement IC.

The key point is that since NONE of these chips are perfect drop-in replacements,
all requiring some degree of board and component modification
so the question becomes how much you want to spend in tech time and money.

Yes there are better ICs out there... some costing about $ 50 bucks each.
but at best they are +/-22 volt units, and the cost of the IC just is not worth it.
And you can NOT hear the difference !!!

To mod an entire JH 400 series console over to regular DIP 8 pin IC's would
be a bit costly... with custom made adapter circuit boards and so on.
And you would have to drop the power supply voltage down to 22 or 20 volts at the ICs by changing the voltage resistors
feeding each IC... lowering your headroom a bit if you use the very standard 5534 or the TO-99 LF156H (but not with the OPA 604)

BUT REMEMBER... in changing the ICs you will also CHANGE THE SOUND OF THE CONSOLE !

And what you want is the somewhat gritty but FAT Vintage sound of the JH400 series consoles.
It's kinda stupid to go changing the sound of a Vintage Console such as the MCI consoles...
It's like buying a Vintage Fender guitar, then changing the pick ups, the neck,
putting a preamp inside the guitar.... maybe nice, but it ain't no Vintage guitar anymore!!!
And it won't sound like a nice old Vintage guitar, which is why you bought it in the first place !!!

So by far the BEST option is to purchase Any original MCI 2001 or HA911 ICs (TO-99 case) that you find
YES - they will be expensive if you can find them
But you will not have to mod your console....

What I'd suggest is just changing some of the less important IC's
in the Echo Sends and Echo returns, and the Studio Monitor sends.
I would Use the Brown Dog adapters with the OPA 604 as no supply voltage mod needs to be done,
and you keep the main power supply at +/-24 volts - as the console was designed.
This gets you - assuming you're lucky - a few original MCI 2001's you pull out of those circuits
as spares to use in the future in more critical positions such as Mic preamps - and you won't affect the sound of your console.

Sage Electronics also makes replacement IC modules - but they admit on their website they don't
sound like the original MCI 2001's do..... which you may like or dislike...and they cost $ 59.00 per unit !!!
But these are slip-in replacements, no mods needed, no adapter cards.
If you have a JH400 series console I recommend getting a couple to have on hand as spares...

Finally - I've just sold off all my remaining stock of original MCI 2001 ICs - for $30.00 each
In changing around my parts shelves I found a small box with 20 MCI 2001's and a few other MCI IC's
that had fallen under a bottom shelf - and sat unseen for 20 years !
So keep looking around - the original MCI 2001 ICs can show up unexpectedly from time to time !

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