AD797 Preamp based on stolen trademark

As for AD797; that has to be one of the best monolithic amplifying devices made by man. The thing to remember about it is that it has superbly low voltage noise. Current noise is not as good, so use low value resistors around it, since resistors turn current noise into voltage noise which then get happily amplified by the op amp. The resistors also add their own Johnson noise as well. You can get away with doing that because AD797 has excellent current driving capability. I built a phono stage using 3 of them per channel, and it's dead silent.
 
The 5534 nulls to V+ on pins 1 and 8. The 797 to V- on pins 1 and 5. There will be equal resistors if measured at the pins (make sure the voltage burden of your meter is <.5V or you might see an ESD diode).

To verify a genuine AD797 what is the approximate resistance that I should measure between pins 1 & 4 and between pins 4 & 5?

Is 1000 Ohms what we are looking for? (That was quoted above for AliExpress sourced parts in #134.)
 
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The 5534 nulls to V+ on pins 1 and 8. The 797 to V- on pins 1 and 5. There will be equal resistors if measured at the pins (make sure the voltage burden of your meter is <.5V or you might see an ESD diode). Jan, the fakers can't do anything about the pin out.

A real LT1028 would have 130 Ohms rather than 12K on pins 1 and 8 if it was a rebranded 5534.

It would be helpful if you could mention the resistor values that should be measured on a genuine AD797. This is because the attached schematic shows that the LM741 null circuitry has 1k Ohm resistors from Pin 1 and Pin 5 to V-.

And I have pretty good reason to believe that there are fake AD797 that measure 1k Ohm from Pin 1 and Pin 5 to V-... ...and around 1mA quiescent current.

Thus probing with an ohm meter is not going to detect fakes if we don't know what resistance to look for.

Does anyone have a real AD797 that they can probe (between Pin 1 and V- and between Pin 5 and V-) and then post the result?
 

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Thank you for quick tip. I just measured SOIC AD797BRZ's that I bought from Aliexpress couple years back then.

The nulling pins, Pin1 and Pin5 measure exactly 1000 Ohms each to the V- pin as you described. I don't know the original value of the resistance.

They were arrived in sealed reel sheet. But pressed numbers at bottom varies like 48D04, 48C50, 48C62 which looks fishy. Probably numbers must be same if they were really on same reel. I never used them to judge their performances btw.

1000 Ohms is the value shown on the LM741 schematic between those pins.

Can you measure your AD797BRZ and post the quiescent current? (Depending on your meter you use could possibly use something like a 1 Ohm sense resistor in between pin 7 and your positive supply.) I wonder if those AD797BRZ are fake.
 
1000 Ohms is the value shown on the LM741 schematic between those pins.

Can you measure your AD797BRZ and post the quiescent current? (Depending on your meter you use could possibly use something like a 1 Ohm sense resistor in between pin 7 and your positive supply.) I wonder if those AD797BRZ are fake.

Did you sort this out? I have some around here I think that arent already on a board. might take some digging to find them, but will do so in the next few days if this is still of interest to you.
 
I haven't made partial replacements. I have changed everything, altogether: with components purchased from Farnell (reputable UK supplier from Leeds). Just the bare board was from China (Aliexpress).
Dear @Berlusconi

Thanks for your posts on this project, helped me a lot.

I have a question though... Where did you take the parts values from? You used the PCB and values from there or from the schematics? I'm particularly interested in resistors - If I see correctly on your pictures, you used 470R instead of 220R in one place... Any reason for this change? Have you made also other changes?

Thanks!
 

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Dear @Berlusconi

Thanks for your posts on this project, helped me a lot.

I have a question though... Where did you take the parts values from? You used the PCB and values from there or from the schematics? I'm particularly interested in resistors - If I see correctly on your pictures, you used 470R instead of 220R in one place... Any reason for this change? Have you made also other changes?

Thanks!
Hello Pawlok,
I have strictly used the values from the PCB. It is difficult to read from the photos at Aliexpress. Also, it is difficult to read color bands from photos because reproduction of colors on photos isn't accurate. Even if you read from the actual resistor directly, it is impossible to know with certainty which values they have.
Just look at the snapshot below. Values are on the silkscreen.
Please let us know about your experiences with this project.
Good luck
 

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@Guiness
I have two preamps and intend to build the third:
in one I have ALPS926G 20K X2 logarithmic
in another I have ALPS 832G 50KA X2
Look at the snapshot below, where I use one in combination with 2 way Linkwitz-Rilley active crossover for my 4 chanel chipamp based on SANYO STK 4042Xi. It is modest, design in plastic industrial cabinet for time being while tested, but performs great, producing crystal clear sound. Low distortion and low noise, far below audible.
 

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