LM1877N replacement!!!
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Sovkiller

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Any suggestion to replace an LM1877N? Any better compatible option, I have an old headphone amp that uses that one and I was thinking in upgrading it?
 
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rickcr42

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apples and oranges dude.

The LM1877 is an actual power amplifier chip , not an op-amp so no pin for pin or circuit compatable replacement.

But fear not young man ,there IS an upgrade that you can perform.

Connect two amps in the Bridge mode for balanced operation.Eliminates the output cap due to balanced operation , increases the output current drive and reduces distortion.

Check the pdf file overat National Semiconductors website for details.

BTW-built it like that wayback in 1976 or so from an article in Popular Electronics.Be sure to attach some heat sinks to the btop of the ICs

Rickmeister
 
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Sovkiller

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This power chip is on the last path of the amplifier, I think that it is feed by 4 x TL072CN, two per channel (I think) the sound is pretty good, but my question is: do you really think that this will increase the performance or the quality of the audio signal? is that this LM1877N a good or a bad amp? how is it compare with others? sometimes when a thing is not well designed, it doesn't matter how many mods you apply to it, it will still be no good...
 
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rickcr42

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The 1877 is not a GREAT performer but can be enjoyable all the same.I would worry more about the op-amp.That is a notorious bad actor you have there.The worst of "op-amp sound" .
I would attack that first then decide if i wanted to go further.

BTW-if you you could always bypass the output stage entirely.
A-remove the op-amps
B-solder in IC sockets
C-remove any cap or resistor in series with the amp chip (from op out to amp in)
D-let the fun begin !

Take the signal from the op-amp stage directly to the output jack,plug in various op-amps until you settle on one you like the sound of and then , and here is where it gets good , piggy back ANOTHER IDENTICAL op-amp onto the first effectively doubling the output current drive.
Two things-be sure the power supply is up to driving both (should be if it handled the 1877) and do NOT attach the output pins of the two op-amps together.

Instead you need to VERY CAREFULLY (don't want to snap them off) bend the output pins up.
Next solder a 1/4 w 10 -47 ohm resistor to EACH output pin
Then solder the other end of BOTH resistors together
And finally attach this end to the IC socket where the op-amp output pin would normallly go.

Hope this helps

Rick
 
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Sovkiller

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Ok I'm not very used to these terms, I'm not a DIYer in any way, sorry for my ignorance, and even when I have some knowledge I need more details, maybe you think that you are talking to a person who did this every day sorry this is not the case, well they are all mounted on sockets fortunatelly, four sockets and the amp on socket too, is there any way of replacing them by another that works the same way, voltages etc....but just a better performance, which could be those? as for the skipping the output stage, I can just pull the chip out off the socket but how to bypass the pins or legs to let the signal flow....is there any electronic diagram ???
 
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rickcr42

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If I knew the actual circut I could walk youhtrough this step by step.

First-I am not entirely sure about the four dual op-amps.That ends up as eight op-amp stages !
Is there an equalizer or tone control included ?
 
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Ok is an amplifier made by Edcor, the 2020, is a single stage from the original proffessiional amp they produce to drive four cans in studios or so, I just attched a file with a pic, sorry for the quality...I have not a really good camera
 
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rickcr42

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OK

You just happen to be in luck . I just looked at the pin-out of the TL072 op-amp and it follows what is a somewhat standard

link to sheet here (right click and "save as")

http://www-s.ti.com/sc/ds/tl072.pdf

All the specs and the package diagram are there.

A seriously good drop in replacement is the Burr Brown OPA2132 and is readily avilable online from various vendors

Data sheet is here

http://www-s.ti.com/sc/ds/opa2132.pdf

A good size pdf file , almost a meg so again best to save to disk for viewing.

Looking at your op-amps from the top you will see a cutout dot.
This is pin#1.
so on that side are pins one through four.

Obviously the other side is pins five through eight but what is NOT so obvious is the count is continued from the BOTTOM UP now.

In other words-starting at one it counts down one side and up the other.

the output pins are PIN #1 for channel 1 and PIN # 7 for channel 2.

After removing the LM1877 chips you can take a wire directly from these pins to the output jacks though it would be better to add a resistor "inline" for op-amp protection aganst short circuts.

This upgrade is a MAJOR bump up from the TL072 which is dated,though at one time was state of the art (along with the similiar LF357 ) and one of , if not THE first JFET input op-amps

Good luck

Rickeraptor
 
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Hi Rick it seems that I 'm causing you al ot of hassle right? well I was checking the diagrams and they seems to be the same configuration, even very similar voltages, I have another question can I pull the bad guys and just replace them with the OPA2132, in the same place, as they seem to work in a very similar configuration, and later when pull the LM1877N out take the signal from the input of these socket instead of the out of the OPA? Can I leave the LM and try this way first? just to see if the sound improve...
 
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Sovkiller

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Another question I found three different ones the 2132U the 2132P and the 2132UA one is cheaper than the rest which are the diffrences can I use any???
 
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rickcr42

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P version ,you want a DIP (dual in line) package or it will not fit
 
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rickcr42

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OOPS !

Didn't see the previous post (used the last post arrow)

Quote:

Hi Rick it seems that I 'm causing you al ot of hassle right?


Nah ! First of all , being one of the moderators it is my job , second and more importantly I LOVE THIS ***

Nothing brings me more satisfaction than helping out a newbie and encouraging that person down the DIY path .

If the first attempts are totally frustrating that person walks away pissed and we can't have that !




Quote:

can I pull the bad guys and just replace them with the OPA2132, in the same place, as they seem to work in a very similar configuration, and later when pull the LM1877N out take the signal from the input of these socket instead of the out of the OPA? Can I leave the LM and try this way first? just to see if the sound improve...


sure , don't see why not.

But the 1877 WILL degrade the sound of the OPA2132.
But hey ! Go for it man.Nothing to lose right ?

The ultimate ,really killer amp would be to insert buffers into the area now occupied by the amps.

No , they will not drop right in but no doubt could be "jimmied" in there with some thought.

I will check the Edcor site and see if I can come up with some pc board layouts.

Be back soon

Rick
 
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rickcr42

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have the owners manual pdf in front of me and it claims 5 ICs total.

By reading between the lines it sounds like (just says five integrated circuts)

1-line input buffer op-amp
2-buss input buffer op-amp
3-buss output buffer op-amp
4-? op-amp
5-Lm1877 Headphone amp

the "buss" mentioned has to be a mixing buss , hence the op-amps operate in the inverted mode and that is why there are so many stages.

LINE IN=inverted op-amp
BUSS IN=inverted op-amp
MIXING CIRCUIT =inverted op-amp (output is non inverted,adding two negatives = one plus)
BUSS OUT=non inverted op-amp
HEADPHONE OUT= non inverted amp IC

The cool thing about this product is

A-socketed op-amps in a commercial device is VERY rare.For those that enjoy tweeking the sound it is WAY COOL !
Pop one out,one in ,listen,decide,put the cover back on
COOL !

B-the "buss" output means you CAN have your cake and eat it !

You want a comparison between the op-amp?amp combo against the straight op-amp ?
Put a headphone adapter on the buss output !!!!!!!!!!

Simple,classic

 
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Sovkiller

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the last thing before the action where can I get the OPA for a decent price...I found them in newark.com but cost about 10.75 each so 44.00 more or less, just to try, is not a piece of cake, but if there are no other options I will get them anyway...
 
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