Headphone opamp recommendation

[sweetbeats]

The headphone opamp in my prototype Tascam mixer may be dying so I'm thinking about replacing them. Not looking for super fancy or anything and I wouldn't even think about upgrading were their functionality not suspect. Good middle-of-the-road recommendation?

They are presently 386's.

 

[mshilarious]

LM386 is not a standard opamp, it's designed specifically as a small power amp. I don't know of anything that follows the same pinout. It would be a significant hack to use a different chip.

That's not to say there isn't a hi-fi version somewhere, but no luck at my usual sources.

 

[Dr ZEE]

You can get LM386N at radioshack for buck and a half a piece
I am not sure if you'd need to play around a bit with the circuit though.
Or maybe you can just swap the chips just as is. I don't think you can hurt anything by trying, however I would double check the schematics and pinouts first.
Do you have exact schematics of the headphone amp in your unit?

I've used those LM386N that I've got from rShack for headphoneamp and they work fine and it sounds pretty good (for simple monitoring purpose, that is.)
I have exact schematics of the circuit that I have around these opamps, see headphone amp section on this diargam: http://www.mzentertainment.com/pics/vu_meter_unit/dr_zee_workshop_vu_meter_monitor_schematics.gif

I aslo used old JRC 386D in a diffrent unit, that I happen to have around (those actually were parts from old parted-out tascam portastudio), and the circuit was similar, but a bit diffrent, also those sounded pretty damn crappy. I never had energy to investigate the details though, maybe I did something wrong there. See this schematics (headphone amp section): http://www.mzentertainment.com/pics/silicon_driver_overdrive_distortion_spring_reverb/dr_zee_silicon_driver_guitar_preamplifier_overdrive_spring_reverb_schematics.gif

But again, as far as I know those modern LM386N(s) work fine, sound good and the pins are the same as JRC386...

 

[sweetbeats]

Thank you both.

Very interesting.

Upon closer inspection they are indeed 386D chips...hm...so...no direct upgrade available for those either?

I am indeed just using the headphone amp for monitoring purposes. Not expecting it to be a critical listening source.

Not schematics whatsoever except for those I've dredged up from the depths of my pea-brain out of necessity to troubleshoot and repair. This is the M-___ prototype mixer.

I'll have a look at how the two chips are hooked up and maybe that will help determine if something else might wok in there. It sounds fine for what I need at present, just LOTS of crackle and hiss when powered up. The caps are new and there was no problem after recapping. This came up spontaneously recently. Haven't looked for bad solder joints or anything yet. Every component is suspect as of yet until I get deeper into it so that's why I'm inquiring about the opamps.

 

[Minion]

The LM386 is a pretty crappy sounding chip and unfortunately there are no direct drop in replacements .... I would suggest you maybe buy or build a Headphone amp and the Line output from your Mixer to plug into the headphone amp and monitor that way .....


Cheers

 

[evm1024]

Many options

There are many options. The first is to replace the chip with another 386 (D, N who cares?)

You could bypass the 386 and install your own headphone amp. THe Rane headphone amp circuit is an option or one of the single chip stereo amps.

Are pins 1 and 8 of the 386 connected? THese set the gain. What are the supply voltages?

Regards, Ethan

 

[sweetbeats]

Pins 1, 7 & 8 are not connected. Looks like the supply voltage is +6VDC. There are, naturally, two 386D chips, one for each headphone channel, both configured the same:

Pin 1: not connected
Pin 2: input (from headphone level pot [which is on a different PCB] via 1Kohm resistor and then a 3.3uF/50V cap)
Pin 3: 0V
Pin 4: 0V
Pin 5: to pins 3 & 4 via 10,000pF ceramic disc cap and a 4.7ohm resistor; to headphone jack via 1000uF/10V and a 1ohm resistor (this trace is also again at this point, coupled to pins 3 & 4 via a 10Kohm resistor)
Pin 6: +6VDC
Pin 7: not connected
Pin 8: not connected

There are some suspicious looking solder joints in all this, and I'm curious as to why the shield for the R channel is not connected to the level pot ground (it is floating), while the left channel is...both connect to ground at the other end on the PCB with the 386D chips...wondering what might happen if I duplicated the L channel's ground connections in the R channel...hmmm...though it looks like the L channel is linked to a couple transistors that make their way to the talkback mic and the R channel does not...maybe I shouldn't mess with that...