Question about Yamaha 80100 opamp

[JW]

So, I have a problem with these 80100's and 80200's developing crackly popping noises. Probably due to one leg of the bipolar voltage being disconnected for too long (accident)

Anyway, this is the schematic posted in the technical docs. Is there one or two components I can replace and save these or is this a case of I might as well just build all new opamps? (I probably have 10-12 all with the same problem)  Are all transistors subject to failure after the long single power rail exposure? Or can I experiment with replacing one or two components and possibly save these guys?

 

[JW]

This is a lot of bad opamps. Mostly 80200's actually. Worth repairing?

 

[JW]

80200. Don't know if I've seen the schematic for a 80200, but have heard of a 1 transistor difference? 

 

[analogguru]

Looking at the available schematic and the GOOOOOP I would say that it will be easier to assemble self made pcb's than to repiar this stuff.

 

[Matt C]

I replaced some bad DOAs in my PM2000 with the 990 kits that hairball audio sells.  They seem to work well. 

There are also reasonably priced DIY kit options from DIYrecordingequipment.com and CAPI (both have DOAs that will be okay with +-24V).

I find building them to be kind of a pain but probably not as bad as trying to repair the original.

 

[JW]

Well

The goop is not bad at all if I somehow knew what component to go after. It comes off easily. Thankfully like I mentioned they are mostly 80200. So console is functional with some borrowing of 80100's and some kits.

Matt, you should try the new gar quad eightish opamp. That one is rad. I have a couple gar 918's too which are nice and clear.

Just broke right now. Would like to be able to repair these. . . . Oh well. I'm not smart enough to know what a single rail failure would do to this circuit. Don't know it's just a diode or something that is making like 20 of these crackle and pop. Not likely?

 

[scott2000]

You could test the components for obvious failure?? But  I suppose a  transistor may only like to act up when in operation/heat.....

This thread gets into  a bit...if you haven't already looked...

https://groupdiy.com/index.php?topic=44501.0


Maybe someone will have some direction outside of having to test everything... Seems like the hardest part would be cleaning that ectoplasm out of them....

 

[abbey road d enfer]

So, I have a problem with these 80100's and 80200's developing crackly popping noises. Probably due to one leg of the bipolar voltage being disconnected for too long (accident)

Anyway, this is the schematic posted in the technical docs. Is there one or two components I can replace and save these or is this a case of I might as well just build all new opamps? (I probably have 10-12 all with the same problem)  Are all transistors subject to failure after the long single power rail exposure? Or can I experiment with replacing one or two components and possibly save these guys?

I would think the b-e junctions of the input transistors have gone in zener conduction; that's what I would replace first.

 

[JohnRoberts]

I would think the b-e junctions of the input transistors have gone in zener conduction; that's what I would replace first.

The clamp diodes should prevent LTP input devices from zenering (that can make device junctions noisier). Perhaps something else is broken. Of course check all discrete devices, maybe even associated capacitors if allowed to sit with reversed voltage across them over time.. 

JR

 

[abbey road d enfer]

The clamp diodes should prevent LTP input devices from zenering (that can make device junctions noisier).

The clamp diodes, being connected between the bases of the LTP, do not prevent them from zenering.

 

[abbey road d enfer]

The clamp diodes, being connected between the bases of the LTP, do not prevent them from zenering when the positive rail is lost.

 

[JohnRoberts]

The clamp diodes, being connected between the bases of the LTP, do not prevent them from zenering when the positive rail is lost.

I guess it is still possible, IMO unlikely to cause crackly popping noise, but this isn't helping the OP so I'll demur.

JR

 

[JW]

Just bumping this one again to ask. TR1 and TR2. These are the transistors you're referring to, Abbey? They should probably be matched yes? Just hfe, or beyond that?  Should I replace the associated diodes too? Looks like BC560(c) might work for the transistors.

 

[abbey road d enfer]

Just bumping this one again to ask. TR1 and TR2. These are the transistors you're referring to, Abbey?

Yes.

They should probably be matched yes? Just hfe, or beyond that?

Just make sure they're in the same hfe  range.

Should I replace the associated diodes too?

I'm not sure it's necessary.

Looks like BC560(c) might work for the transistors.

I don't see why not.

 

[JW]

Okay,

I'm finding 2SA1084 in the 80200 input positions. These are testing at higher hFe than the BC560C's (though the 2sa1084 pulls don't appear to be hFe matched, at least after they've  been pulled and tested.)

So I guess I'm on a deep dive for the 80200 schematic. I thought it was same as 80100, but with a wimpier output. Just rumors though.

Higher hFe because they're the mic pre opamp input pair?
We're talking average 550hFe with regard to the 2sa1084's and average 450hFe for the BC560c's. From the ones I've pulled anyway.

 

[JW]

I'm finding that 2sa1084(tr1 and 2 in the 80200) have very low Rbb. 2N4403 has been mentioned as replacement, but not quite as good and obsolete as well.

Damn hard to find a current production replacement. Is it BC560c or bust?

 

[abbey road d enfer]

Okay,

I'm finding 2SA1084 in the 80200 input positions. These are testing at higher hFe than the BC560C's (though the 2sa1084 pulls don't appear to be hFe matched, at least after they've  been pulled and tested.)

So I guess I'm on a deep dive for the 80200 schematic. I thought it was same as 80100, but with a wimpier output. Just rumors though.

Higher hFe because they're the mic pre opamp input pair?
We're talking average 550hFe with regard to the 2sa1084's and average 450hFe for the BC560c's. From the ones I've pulled anyway.

20% difference is not significant. Process purity is much more important.

 

[JW]

Process, as in newer silicon, built by some respectable manufacturer (ON Semi?) sourced from Mouser Farnell etc? And then matched?

The gar kits, the many DIY Neve 1290 incarnations use BC550C/560C's so I guess I'm okay if I match then? Though, I've heard of first transistors selected in the Neve circuit specced to above 600hFE for lower noise.

None of these BC560C's seem to be above 500hFe. 

Back to the 80100 whose schematic is posted above, I'm finding 2SA827's for the input transistors. Slightly different from  what that schematic says (2sa627's) but I imagine since the 80100 is a line amp, as apposed to the mic amp, the BC560C's will be fine there.

Just concerned at possible worse noise than the original 2sa1084's that were in these busted 80200's.

Gonna try it with what I got.

 

[JohnRoberts]

Modern semiconductor processes are cleaner (less impurities) to support smaller and smaller device geometries. All parts benefit from these improvements.

JR

 

[brendandwyer]

JW,

Were the pops and crackles intermittent?  I've having the same issue and still can't determine if its an input channel, a buss, or a matrix section issue.

Brendan