Bass Master XM100 Type:100B

[redkurn]

I’ve proved around the board and the voltages where I was able to get a reading seem fine, Q10 is about 1.5v lower than the schematic shows, but that shouldn’t be the problem.

If it is the fet, do I just jump it or leave the drain or source detached?

When I turn the volume up it does distort, so I’m kind of thinking it’s not the new parts, but could it be something else?

[g1]

Side note, the J111 is reverse of the original 2N5638, I did make sure to check all of my parts against the originals datasheet and should be fine as they all tested good. (Flat face of J111 is GSD, the 2N5638 is DSG)

The datasheets I have show both to be DSG (looking at flat face with legs pointing down). See attached. (The J111 is GSD when looking at the back.)
If it's in there backwards you will have volume problems.

[redkurn]

Hmm, that is possible I put it in backwards even though I did the opposite since these sheets show they are flipped.

https://www.mouser.com/datasheet/2/3...-D-1801440.pdf
https://www.mouser.com/datasheet/2/3..._D-1811481.pdf

I'm not getting a positive voltage on the base of Q10, it's supposed to be + 38v, but I am getting a little over - 36v.
My common lead is on the chassis ground when probing.

Is it possible they intended the fet to be orientated in the same manner as the original? they specifications do seem opposite of the original part, this one I chose because they listed at the part to use on yorkville...

[The Dude]

Collector of Q10 is 38V, not the base.

[g1]

That is bizarre that ON semiconductor would flip the pinout like that, the J111 is an established part. If that is the exact part that you got, then I would trust the datasheet.

Q10 leg at +38 volts is the collector. Emitter should be around 0V and base around +1V.

[The Dude]

Check R57. If it's good, what are the voltages on Q4?

[redkurn]

Collector of Q10 is 38V, not the base.

Yes that is showing 38.98v, I measured the wrong leg. XD
R57 was replaced and juimped, it has -35.82v and Q4 1: -35.89v 2: -37.68v 3: -38.32v

That is bizarre that ON semiconductor would flip the pinout like that, the J111 is an established part. If that is the exact part that you got, then I would trust the datasheet.

Q10 leg at +38 volts is the collector. Emitter should be around 0V and base around +1V.

Not sure if ON did, but yorkville suggested this part as a replacement and the specs are opposite as far as I can see unless whoever made one of the datasheets made a mistake it looks like the J11 is a -35mv to active??
Also the legs are reversed, what I wonder is if yorkville intended it to be installed in the same orientation as the original, maybe that's why volume is low.

[redkurn]

Can’t seem to edit my post from my phone, J111 not J11.

[g1]

The J111 pinout depends on the brand. When yorkville made that sub chart they probably had the fairchild part or equivalent, so the pinout was the same. The new ON-semi part has changed the pinout. So if you got the ON version from mouser, you need to flip it like you did.
Here's another thread elsewhere about ON changing the pinout: https://www.diystompboxes.com/smffor...=126803.0;wap2

Like I said earlier, you can just disconnect the fet for testing and the amp should work normally. It's just a mute to prevent the turn on thump.
I think it is fine the way you have it though. Your problem is that Q10 is not running.

What is the voltage at Q10 emitter?

[redkurn]

The J111 pinout depends on the brand. When yorkville made that sub chart they probably had the fairchild part or equivalent, so the pinout was the same. The new ON-semi part has changed the pinout. So if you got the ON version from mouser, you need to flip it like you did.
Here's another thread elsewhere about ON changing the pinout: https://www.diystompboxes.com/smffor...=126803.0;wap2

Like I said earlier, you can just disconnect the fet for testing and the amp should work normally. It's just a mute to prevent the turn on thump.
I think it is fine the way you have it though. Your problem is that Q10 is not running.

What is the voltage at Q10 emitter?

I'll take a look, per ON website it matches the original pinout...
https://www.onsemi.com/pdf/datasheet/mmbfj113-d.pdf

Maybe I should desolder and flip it?

[Helmholtz]

Use your Ohmmeter to find the gate: https://www.allaboutcircuits.com/tex...ansistor-jfet/

Drain and source can generally be interchanged without difference as Jfets are symmetrical.

[redkurn]

The J111 pinout depends on the brand. When yorkville made that sub chart they probably had the fairchild part or equivalent, so the pinout was the same. The new ON-semi part has changed the pinout. So if you got the ON version from mouser, you need to flip it like you did.
Here's another thread elsewhere about ON changing the pinout: https://www.diystompboxes.com/smffor...=126803.0;wap2

Like I said earlier, you can just disconnect the fet for testing and the amp should work normally. It's just a mute to prevent the turn on thump.
I think it is fine the way you have it though. Your problem is that Q10 is not running.

What is the voltage at Q10 emitter?

-35.98v

I'm going to take it back a part and see if it changes with the fet out, check and see as Helmholtz suggested.
Maybe the datasheet is wrong for the part or something.

Use your Ohmmeter to find the gate: https://www.allaboutcircuits.com/tex...ansistor-jfet/

Drain and source can be exchanged without difference as Jfets are symmetrical.

I was considering doing that as well, while I had it out and think I should have checked that from the beginning as I was testing to see if it was good.

Tested it in place, the datasheet on mouser is wrong, it is the same orientation as the original part.
Guess I should let them know.

[g1]

You can forget about the Fet for now, your DC voltages are completely wrong. I had assumed you determined there was no DC on the output, yet you have -38V at the emitter of Q10 which is basically at the output. Unless the emitter resistor is blown. (R58 & R60)
Approx.DC voltages you should be seeing:
0VDC at speaker output.
Q10 emitter 0V
Q10 base, around 1VDC
Q10 collector 38V

Q9 emitter 0V
Q9 base, around -1VDC
Q9 collector -39V

[redkurn]

You can forget about the Fet for now, your DC voltages are completely wrong. I had assumed you determined there was no DC on the output, yet you have -38V at the emitter of Q10 which is basically at the output. Unless the emitter resistor is blown. (R58 & R60)
Approx.DC voltages you should be seeing:
0VDC at speaker output.
Q10 emitter 0V
Q10 base, around 1VDC
Q10 collector 38V

Q9 emitter 0V
Q9 base, around -1VDC
Q9 collector -39V

I think you are right, the voltages are off and I can't get a resistance from those two, but I do get voltage and can get a reading of resistance and voltage from R61.

Is that 27R or .27R?? Pretty sure that's .27R... 5W00 0R27 5% BLK RES

These should be fine?
https://www.mouser.com/Passive-Compo...7+ohms&FS=True

[g1]

edit: corrected typo (.27 not .027)

Yes, they are .27 ohms. 'R' is used to designate the decimal place. Or 'K' or 'M'. 4K7 is 4700, 3M3 is 3.3Meg. 27R is 27 ohms, 0R27 is .27 ohms.
Those ones from Mouser should work fine.
When measuring (good) resistors less than 1 ohm like these, your meter will probably give you a zero reading on resistance range. Or whatever the resistance of your probes is when shorted together.