Recreating the Harris HA909/911 into a discrete op amp

[Aniol1349]

Hello guys,

I would like to recreate the (in)famous MCI 2001 chip otherwise known as the Harris HA909/911 chip.
I would like to build it into a discrete op amp which I can use for a project I'm working on.

I found a data sheet for this particular op amp with the internal schematics, however they are missing all the values and I'm not sure how to approach it.

has anyone got any info which could help me?

Thanks!

 

[Samuel Groner]

Basically you'll ned to determine the collector currents of Q3, Q7, Q14 and Q15. I think Q7 should have half the collector current of Q3 for correct DC balance of Q5/Q6, so R6 = 2*R5. To determine the collector current of Q3 the following considerations will help:

* input bias current = collector current of Q3/2/beta (assuming there is no input bias current cancellation omitted on the schematic)
* slew rate = collector current of Q3/C1
* estimations with respect to voltage/current noise as a function of Q3 collector current

There are far less hints to guess the collector current of Q14 and Q15. As a starting point, I'd allocate one quarter of the total supply current to each of them.

Keep in mind that this schematic is probably simplified.

Samuel

 

[Bill Wilson]

Hi I ran console checkout at MCI, when we were shipping the 416 consoles. The 911 was not that great a chip; if memory is correct they slewed about 7uv per second. A TL0 series chip would be better or NE5534; which has lower output & greater drive capability.

In order to find 911's quiet enough for the preamp circuit I had to plug them into an input strip one at a time & look for the lowest noise ic's.

 

[Aniol1349]

@Samuel

Thanks for that, it seems a lot more tricky than I expected, however your information is a good starting point.

@Bill

Basically I wanted to recreate the sound of the MCI JH500 pre amp series into a stand alone unit and I wanted to keep the circuit as close the the original MCI as possible. I wanted to go for the Harris 911 because despite it's poor specs it has a nice character for rock. Do you think I can omit the original op amp and still retain the original sound characteristics of the board?

 

[JohnRoberts]

@Samuel

Thanks for that, it seems a lot more tricky than I expected, however your information is a good starting point.

@Bill

Basically I wanted to recreate the sound of the MCI JH500 pre amp series into a stand alone unit and I wanted to keep the circuit as close the the original MCI as possible. I wanted to go for the Harris 911 because despite it's poor specs it has a nice character for rock. Do you think I can omit the original op amp and still retain the original sound characteristics of the board?

Inside ICs they have access to active components that you can not source as discrete parts (like transistors with 2 collectors, or other hybrid variations). The published schematic may be schematic and not literal. IIRC Harris, may have had an esoteric IC process (Dielectric isolation?) back then that may be difficult to mimic in discrete.

Good luck and have fun.

JR

 

[moamps]

Basically I wanted to recreate the sound of the MCI JH500 pre amp series into a stand alone unit and I wanted to keep the circuit as close the the original MCI as possible. I wanted to go for the Harris 911 because despite it's poor specs it has a nice character for rock.

How many 911 opamps do you really need?

 

[Bill Wilson]

The 500 console did not use the 911 chips. it used NE5534's & a higher voltage chip, sorry I do not recall its number.

 

[mjrippe]

The 600 series used 2003P chips, which were very similar to 5534.  I have a tube of them around here somewhere...

 

[Aniol1349]

ok, so the bottom line is that I 5534 would be a good replacement for the chip, right?

Well basically my idea is to design a pre which would be based on the MCI 500 D series using the Jensen 115KE input transformer.
I want to retain the character of this pre amplifier and my first thought went into trying to recreate the original op amp into a discrete opamp.

This will be my first ever attempt at something like that so there is a lot of uncertainties.

Any help is welcome,

Thanks