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i'm on a roll... the kgsshv


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After 5 years from the time I acquired the PCBs and parts, I finally took advantage of the free time created by the pandemic and completed my KGSSHV.  This is the offboard version with +/-500V supply.

Not sure if we have a KGSS thread but I'll just post this here.  So last year it dawned on me that I built my first KGSS amp 15 years ago and something had to be done to celebrate that.  It started of

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It's coming...Just finished drilling some screw holes just now. Steel is much harder than I expected. 

 

Since I bought a RCA to XLR adapter, I am probably not gonna put in the RCA inputs. Amp boards are working, but I have yet adjusted the offsets without the servo on. From what I have done with the servo enabled, it seems that both L and R channel settle to a 0.3V offset.

 

The amp supports 100V, 115V, and 230V mains voltage, which can be switched by the rotary switch at the back. There's also a series overload sensing circuit breaker at the back, which also acts like a switch.

 

I prefer having green ring on the power switch. But for now I will settle with blue. Surprisingly these come with built in resistors. Maybe if I break it I will go buy the green one.

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I need some help. My power board was working fine but after putting it into the chassis, I heard a spark, and then now the -ve rail is -640V. I dare not let it on for more than a few seconds, but the value seems to go higher and higher.

 

I checked the diodes, and they are not shorted. What could have gone bad?

 

Edit: I measure the output from the diode bridge and it's 640V, so it seems something in between has broken and shorting it to output.

 

Ok found out that the 10m90s is fried. 

Edited by kh90123
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D7,8 & 9   (200V, 200V, 100V ZD) ? 

 

I replaced them and found that all of them were working.

 

I suspect it's one of the 5 transistors, either the 2sa1486 or the ksc5026m. Getting help from someone to work on this.

Edited by kh90123
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It's set by the voltage divider between r6 and r5+r29 compared to the 10V reference in the discrete error amplifier. These are for the positive rail, are you just replacing the parts from the positive rail thinking it's going to change the negative rail?

 

Tbh I think the best solution is to get someone else to build you a working power supply from scratch. You could seriously injure yourself at this rate.

Edited by mypasswordis
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It's set by the voltage divider between r6 and r5+r29 compared to the 10V reference in the discrete error amplifier. These are for the positive rail, are you just replacing the parts from the positive rail thinking it's going to change the negative rail?

 

Tbh I think the best solution is to get someone else to build you a working power supply from scratch. You could seriously injure yourself at this rate.

 

No, I didn't mean for the misunderstanding. For the -ve rail I know it's set by the voltage divider between R16, R15, and R30.

 

Since I started replacing parts on the board, the through hole contacts have been damaged, especially on those snap in caps. My current board was working fine until I started putting it into the chassis, where a few parts were damaged because the filtering caps lost proper contact.

 

I will be building a new board. The current board is not safe to continue working on it.

 

Thanks for all the advice.

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Good call to abandon the PSU board. 

 

On a more positive note, look what my spare desk looks like these days:

 

ow35IYth.jpg

 

Soak test plus seeing how the servo behaves.  Finally getting the hang of assembling these though it is still very tricky:

 

J1E1RYVh.jpg

 

These are all reserved but I do have one of these sitting in the US that I really don't want to send back here.  :)

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How come you don't have KGSSHV emblazoned on the front panel?

 

Perhaps 14mA bias version with "KGSSHV - Mini Case - Max Power" would look good above the Volune control...

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Looks good, Birgir. Instead of using 4 3-pin connectors for input and output, wouldn't it be easier (and maybe cleaner) to use 2 4-pin connectors?

Depends if you have sources that use 4-pin connectors, right? :)

Even then, it wouldn't work. You need 5 pin connectors, so Team 5 Pin represent!

Edited by luvdunhill
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