I think most people are using the ON Semi parts. They released an EOL notice last fall that apparently their Korean packaging subcontractor would no longer do TO92s . Mouser still has some in stock, so I'd buy what you think you will need now.

^^ like he said....

I use these: http://www.mouser.com/ProductDetail/ON-Semiconductor/MPSA56RLRMG/?qs=sGAEpiMZZMshyDBzk1%2fWi%2fPUgtclNldl2ZkToUCMhk0%3d

Edited March 25, 201511 yr by GrindingThud

On the KGST, dumb question but the schematic is out of date and it should be documented here, it's either the A1486 or the STN9360, correct? Not both. I soldered the 9360 already so it's hard to see the traces, but it looks like they're both connected so it should be one or the other. 

Best to go by the PCB, as that is further developed from the schematic.

And yes, it is either A1486 or STN9360. Not both.

Best to go by the PCB, as that is further developed from the schematic.

And yes, it is either A1486 or STN9360. Not both.

 

Any advantage to either? Other than having to solder surface mount STN9360, which is easy as long as you have paste.

/

Edited November 11, 201510 yr by JoaMat

The advantage is that the 2SA1486 is out of production and the 9360 isn't... 

 

At 350V rails the A1156 works perfectly.  At 400V I'd use the 600V parts just in case.  

Passed power supply smoke test. B+ and other supplies come up fine, except "Bias" has nothing on it. I see a reference here on this thread to a trimpot but it's not clear if that's on the PS or the ones on the amp boards. I don't have a trimpot on my power supply, but there is a mystery "1M three terminal spot near the output jack - is that for a 1M trim? It has a null symbol next to it (zero with a cross through it) which I took to mean no-op.

This is a 1M Trimpot which needs to be populated. The crossed zero is the screw of the trimpot ;-)

This is a 1M Trimpot which needs to be populated. The crossed zero is the screw of the trimpot ;-)

 

Burp. Thanks. 

 

Speaking of which, what is the test point for, the bias?

Edited March 29, 201511 yr by Earspeakers

yes, because the output is taken after 4.7M

Fortunately I have a workplace with a big lab stock that is supportive of home electronics projects (as long as you're learning something). Quick trip into work ... fixed. We have bias!

Smoke test with amp sections, servo jumpers out. 

 

LED's no comma on, not good. Turned down variac, scratched head and found one channel had chassis wired +-15 backwards. Well, it's like a stage play,  something has to go wrong. Easy fix and now it comes up with LED's. 

 

So today I'll adjust bias and such, double check me. 

 

• Bias - test point on PSU, adjust 1M until 580V approximately
• Amp DC offset - Plug in jumper, use the two trim pots, fine and coarse, put DVM between + and - output pins on channel and adjust until approximately 0VDC between them (also - what is the jumper there for?)

Then if all good, should be ready for test with headphones. 

/

Edited November 11, 201510 yr by JoaMat

Are there fine and coarse trimmers for offset? Isn't one trimmer for offset and one for balance?

 

Doh - my mistake. The way the chassis is, it's difficult to read the legend. Handy to have spare boards to compare to, yes one is balance and the other offset. 

 

So what is balance then (did a search but it's not clear)? From the mask looks like it is a resistor between two FET's, maybe source resistor. I'll take a guess, updated version for adjustment

 

• Adjust PS test point to 580V DC headphone bias
• Adjust each amp board Offset pot to give 0VDC between + and -
• Adjust each amp board Balance pot to give 0VDC from either + (or -) to ground

 

Correct?

Edited March 31, 201511 yr by Earspeakers

With the jumper pulled deactivating the servo, power up the amp.

First adjusting the Balance trimmer for close to 0VDC between + and - outputs.

Then adjusting the Offset trimmer for close to 0VDC between either output to ground.

Repeat in order several times. Let the amp run for a half hour or more. Remeasure and readjust as needed. Turn the amp off and replace the jumper after a few minutes.

The circuit is so stable once set, I don't bother with the servo. YMMV.

Edited March 31, 201511 yr by Laowei

Great thanks Laowei!

 

Even with the stability, why not use the servo? Seems like it can't hurt. 

Some people claim they can hear servos. I'm not one of them. Since they normally operate well below 1Hz, and having the servo can protect you from bad things happening, I see no downside to using it, even if the circuit is stable without it.

Does anyone have any tips of desoldering board mounted Teflon tube sockets. Would like to use them somewhere else at the moment.

a metcal soldering iron with the big tip.

 

still its not going to be easy.

Desoldering anything sucks, don't do it unless you have to. 

Does anyone have any tips of desoldering board mounted Teflon tube sockets. Would like to use them somewhere else at the moment.

Tried to do something similar for a botched Megatron board I picked up, almost impossible with a normal tip.

 

JoaMat said he had some sort of gun which he referenced when he was making the bootleg KGSiC. 

Fired up! Sounds good, reeeeeeeeeel good. 

 

• I get a hum at the top of the volume range, but I'm using a Hosa RCA to XLR converter plug and it's only with that plugged in. Pulled it's dead silent. Pulled out a cheap DAC with XLR output and it's dead silent, except near full bore there's a oddball slight noise that comes in at one channel and then travels to the other, then disappears at full volume. Odd, need to look into that. 
• The gain seems a little low, compared to the 323. I've got just enough, maybe that was the intent to have the amp playing at the low end of the volume control.

 

Wow, quite a delicious little amp. Compared to the Stax offerings there's far greater separation between instruments, each is more distinctly themselves. Presumably better separation between channels compared to the 323S. 

Edited April 1, 201511 yr by Earspeakers

Does the Hosa RCA/XLR adapter short the L/R - signals to ground? On a differential input, those need to be grounded when going SE. I know Kevin recommended the Neutrik adapters for the multiamp, which do this.

Does the Hosa RCA/XLR adapter short the L/R - signals to ground? On a differential input, those need to be grounded when going SE. I know Kevin recommended the Neutrik adapters for the multiamp, which do this.

 

 

Good question, probably not. Pieces of crap I just bought for this. I'll get the Neutrik. Edit: This one I guess

 

http://www.mouser.com/ProductDetail/Neutrik/NA2MPMF/?qs=sGAEpiMZZMv0W4pxf2HiV9y0EyfHsAgRVcOPr0CUs0o%3d

 

 

Damn this amp has a lot of bass control. Scary. Just listening with my test headphones (207) for a few days at least. I'll try a 404 next, my go-to headphone at the moment. It's a warmer amp than the 323S too I believe, but it might be the 207's that I haven't heard in a while. There's some muddy too which is the 207's, need to try some better headphones soon. 

Edited April 1, 201511 yr by Earspeakers