NJM 4560S Mackie 1202 mixer Chip

[fazer]

I have an old Mackie 1202 - 1st gen. I have a problem with headphone amp being out of phase left right and suspect a NJM4560S  SIP Chip is bad. 

The chips are marked NJM4560S which is a 9pin chip.  When looking online , The NJM4560L is shown as the only SIP version  and its an 8 pin chip with different pins used from the Mackie 1202 schematic.  Small bear has a 9pin chip but no info and so far I have not found a 9 pin version with data sheet.   

Any info would help.  I have a schematic for the output side showing the headphone circuit

 

[JohnRoberts]

the 4560 is a very common GP (jelly bean) opamp widely used in the industry. 
https://groupdiy.com/index.php?topic=31731.0  discussed here before

As a typical dual op amp it only has 8 active pins...  1,5 are power, 234 is one op amp 678 the other.  It appears pin 1 may be common to pin 9 so if you pop in a 8 pin device you may need to jumper power over to pin 9.  I do not see any mention of a pin 9 on the Mackie schematic so they probably used the more common 8 pin parts. (you can check by looking at the PCB for pin 9 connections).

I hate looking at other company's schematics. The 1202 is supposed to be a value product (cheap) but they used one more op amp than needed to perform that headphone amp... Instead of two 4560s buffering each side they could have used the opamp driving them for one of the two 120 ohm resistor outputs. Or you could add a third 120 resistor from U14A/B for a 50% increase in drive current capability.  :-[

JR

 

[scott2000]

Data sheet here

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwjw1cvkzOzbAhUa24MKHTr3DKcQFggsMAE&url=http%3A%2F%2Fdatasheet.octopart.com%2FNJM4560S-NJR-datasheet-108729.pdf&usg=AOvVaw2nM5SFkLIyaPWJq1XimQxi

 

[fazer]

Thats it Scott 2k.  hope the small bear chips work.  Don't want to adapt chip so I'll order some.  This is a simple mixer I use for a few solo gigs a year.  Have a wedding coming up.

Thanks John for the info as well.

 

[scott2000]

Hopefully it's not mis-numbered or something on Small Bear....There is that ROHM BA546 which is 9-pin but I haven't looked at what it is....????

I can't find a 9-pin data for ROHM4560 either....... But there is an 8-pin sip data..... ,,,if that's what you're looking at

 

[abbey road d enfer]

-pin versions of

I have an old Mackie 1202 - 1st gen. I have a problem with headphone amp being out of phase left right and suspect a NJM4560S  SIP Chip is bad. 

The chips are marked NJM4560S which is a 9pin chip.  When looking online , The NJM4560L is shown as the only SIP version  and its an 8 pin chip with different pins used from the Mackie 1202 schematic.  Small bear has a 9pin chip but no info and so far I have not found a 9 pin version with data sheet.   

Any info would help.  I have a schematic for the output side showing the headphone circuit

Woah! Woah! How could a defective chip result in polarity inversion? If one section of U14 was completely gone, it would not invert the signal coming from the pot, but also the level would be significantly lower. Is that the case?
9-pin versions of SIL dual opamps generally have a direct connection between extreme pins 1-9. It's vert simple to use an 8-pin and add a jumper.

 

[fazer]

Woah! Woah! How could a defective chip result in polarity inversion? If one section of U14 was completely gone, it would not invert the signal coming from the pot, but also the level would be significantly lower. Is that the case?
9-pin versions of SIL dual opamps generally have a direct connection between extreme pins 1-9. It's vert simple to use an 8-pin and add a jumper.

Your Right Abby after looking at the to chips pinouts ,  I can just offset the Sip by one pin. 

John brought this up earlier as well. 

Also I have not checked the actual condition of the chip U14 in question just thought if one of those inverting chips was out , it could cause the problem and when phones are plugged in, it cancels the signal with noise and such poking thru.  So I'll check that amp today.  The signal out from the main mix is good. its just the headphone out that has the problem.  I thought about the ground on the headphone jack being lifted but the phones would just sound the S part of the Signal with out the M and thats not what is happening its just cancelled out and if you pan the signal to L or R on a channel , you hear it fine in the headphones side you panned to.

 

[fazer]

So while I had the mixer apart , the headphone jack grounds off of the face plate and when not connected to the face plate it only gives the Side signal across L R outputs of the TRS.  The problem when it was in the mixer assembled , there was no lock washer to ground and so it behave that way.  I cleaned some pots and tested and its working well.  I think I might go ahead and replace some caps later on this thing. they show higher ESR and this has to have been bought in the 90's so getting old.  I'm going to order a couple of the 9pin chips as well to have but Good to know you can use the 8pin SIPS with a wire jumper for 1 and 9 V+. 

I think I got my moneys worth from this thing but for the purpose it works well enough and is repairable.  On to building some pedals for the gig.  This is more fun than fixing old mixers.

Thanks for all the help everyone. 

 

[JohnRoberts]

Your Right Abby after looking at the to chips pinouts ,  I can just offset the Sip by one pin. 

John brought this up earlier as well. 

Also I have not checked the actual condition of the chip U14 in question just thought if one of those inverting chips was out , it could cause the problem and when phones are plugged in, it cancels the signal with noise and such poking thru.  So I'll check that amp today.  The signal out from the main mix is good. its just the headphone out that has the problem.  I thought about the ground on the headphone jack being lifted but the phones would just sound the S part of the Signal with out the M and thats not what is happening its just cancelled out and if you pan the signal to L or R on a channel , you hear it fine in the headphones side you panned to.

The buffers are non-inverting, so no likely scenario for them to ever cause an inversion.

JR

 

[Audio1Man]

Many MFG used the 9 pin version as it can be inserted either way and still works as designed. Pin 1 & 9 are the V+ and typically don’t pass current through the chip to power other circuits.

As for the headphone polarity / phase / LR ?  Look for a bad headphone cable.
Duke

 

[fazer]

Not a cable problem 2 sets of studio phones had same issue.  Inversion was the Mackie headphone jack not grounded on PCB .  It is grounded from the metal face plate ground references .  Weird but once I used a lock washer it grounded jack and it’s working .  I thought it might be u 14 which is an inverting Gain amp that drives the buffers.  But checked phase and output with dual trace scope and signals were in phase so it had to be the headphone jack ground.  I ground the jack and that put the headphones back in phase so it worked after that .  Used a lock washer under the top panel and it worked great after that . 

 

[living sounds]

I once replaced all of the SIP op amps in a Mackie 1202 with DIP8 NE 5532.  I think I used three short pieces of wire per op amp, the rest would fit the pinout. Measured and sounded really good afterwards.

 

[JohnRoberts]

I once replaced all of the SIP op amps in a Mackie 1202 with DIP8 NE 5532.  I think I used three short pieces of wire per op amp, the rest would fit the pinout. Measured and sounded really good afterwards.

The 4560 is popular for value mixers because it has decent drive capability, is fast enough for audio, and has benign turn on/off characteristic, and did I mention it was really cheap? 

I suspect 5532 will not turn on/off as gracefully. Maybe pop 5532 in bus sum amps and more difficult (high gain) sockets.

JR

 

[RuudNL]

At little off topic: a series resistor in a headphone output is a bad idea.
I understand why they did it(!): the 4560 can't drive a low impedance and the two 120 ohm resistors level out any minor differences in output voltage of the two OpAmps. But: this gives an effective output impedance of 60 ohms.
Most headphones are dynamic and behave like an inductor.
This means that the impedance of a headphone isn't constant over the whole frequency spectrum.
With a relative high source inpedance (the output impedance of the headphone amplifier), you will get a frequency dependent attenuation. (The headphone has a higher impedance at high frequencies.)
This gives a certain coloration, especially with 32 ohm headphones, very common nowadays.
I have heard a good quality headphone sounding very different on several output stages!

 

[JohnRoberts]

At little off topic: a series resistor in a headphone output is a bad idea.
I understand why they did it(!): the 4560 can't drive a low impedance and the two 120 ohm resistors level out any minor differences in output voltage of the two OpAmps. But: this gives an effective output impedance of 60 ohms.
Most headphones are dynamic and behave like an inductor.
This means that the impedance of a headphone isn't constant over the whole frequency spectrum.
With a relative high source inpedance (the output impedance of the headphone amplifier), you will get a frequency dependent attenuation. (The headphone has a higher impedance at high frequencies.)
This gives a certain coloration, especially with 32 ohm headphones, very common nowadays.
I have heard a good quality headphone sounding very different on several output stages!

It is unfortunately common practice in such circuits because they may have to work with headphones ranging from 8 ohms to 600 ohms. You can reduce the value of the 120 ohm but may risk damaging the ICs. (you could also add a third resistor like I suggested , dropping the source impedance and increasing drive capability.)

More serious outboard headphone amps can have stronger outputs and lower output Z (I did one that could drive loud speakers).

JR

 

[abbey road d enfer]

At little off topic: a series resistor in a headphone output is a bad idea.
I understand why they did it(!): the 4560 can't drive a low impedance and the two 120 ohm resistors level out any minor differences in output voltage of the two OpAmps. But: this gives an effective output impedance of 60 ohms.
Most headphones are dynamic and behave like an inductor.
This means that the impedance of a headphone isn't constant over the whole frequency spectrum.
With a relative high source inpedance (the output impedance of the headphone amplifier), you will get a frequency dependent attenuation. (The headphone has a higher impedance at high frequencies.)
This gives a certain coloration, especially with 32 ohm headphones, very common nowadays.
I have heard a good quality headphone sounding very different on several output stages!

Ther would be an easy fix for that with the Mackie circuit; putting the actual output under NFB control. The opamps would be equally protected and the output impedance would be much lower.
However there is an advantage to having such a high impedance; it tends to equalize power between low-Z (8 ohms) and high-Z (600r). I agree that it's at the cost of deteriorating teh frequency response.

 

[living sounds]

The 4560 is popular for value mixers because it has decent drive capability, is fast enough for audio, and has benign turn on/off characteristic, and did I mention it was really cheap? 

I suspect 5532 will not turn on/off as gracefully. Maybe pop 5532 in bus sum amps and more difficult (high gain) sockets.

JR

I never noticed the pop. It gets quite hot due to the 5532's much higher current draw. But I used 105 degree rated caps in the PSU and the mixer is still going strong.  I also put polystyrene caps in the high frequency filter sections -  it is one of the nicest sounding EQs I've heard.  8)

 

[JohnRoberts]

I never noticed the pop. It gets quite hot due to the 5532's much higher current draw. But I used 105 degree rated caps in the PSU and the mixer is still going strong.

heat (and PS output current) is more of an issue for larger mixers

I also put polystyrene caps in the high frequency filter sections -  it is one of the nicest sounding EQs I've heard.  8)

I absolutely loved polystyrene... They were great sounding caps and cheaper than dirt, my idea of a win-win. 8) But unfortunately they were not very tolerant of manufacturing stresses. Not an issue for my old hand soldered kit business back in the 70s, but even my small company commercial manufacturing processes in the 80s could damage the fragile polystyrenes. My former business partner killed a bunch with a high pressure air hose blowing water off PCBs (he blew water inside the caps). 

Thankfully we now have cog/npo smd caps that are robust and linear, but I had some bad experience with early SMD film caps that couldn't survive the reflow ovens temps. It kind of doesn't matter if the CM screwed up or the caps were bad, when the whole production run is trashed, and doing it over would likely have the same result (I changed the cap dielectric to something more robust). 

====

Ironic perhaps but Peavey customers were hyper critical of cosmetic issues like switch clicks and turn on/off transients, while far from golden ears about audio path performance. Peavey sound quality was far better than the market perception, but I know better than to spit into the wind against the overwhelmingly negative market opinion. (saying good for the money is like kissing your sister, not much fun).

JR