The disadvantage of moving the connection of the trimmer to the V+ output is that C1, C2 and C3 will not discharge through RVB. A drain resistor, RD, has been added to solve the problem.

 

I will take a look if any hum develops once I get everything cased.

 

Just another question: Earlier in this thread someone states that the range of the servo can be increased to -+30v when exchanging the 10k with a 5k resistor. I could use this extra range since I am using the not sooooo stable ixys parts. My offset from cold to warm seems to vary around 30V. 

Are there any drawbacks doing this modification?

 

 

FYI: I can now adjust both boards to 0V offset using the VRs after adding replacing the 2k with a 1.8k resistor. 

 

Furthermore I would like to use this post to again thank all the people involved in making these projects possible and supporting them with their help in the forum. This is really extraordinary!

speaking of extraordinary

http://gilmore.chem.northwestern.edu/dsc_0478.jpg

 

an absolute perfect void free piece of red mallee and a chunk of

absolutely black as can be ebony

The 5K resistor has no penalty or drawback. 

 

speaking of extraordinary

http://gilmore.chem.northwestern.edu/dsc_0478.jpg

 

an absolute perfect void free piece of red mallee and a chunk of

absolutely black as can be ebony

 

Too fucking cool!!! 

Edited October 3, 201312 yr by spritzer

Could the servo be added onto older amp boards (using a small PCB with necessary wires running to it)? I vaguely remember someone doing it but I'm not sure.

yes the servo can be added to the older boards.

... 

 

 

Too fucking cool!!! 

 

Couldn't agree more

Could the servo be added onto older amp boards (using a small PCB with necessary wires running to it)? I vaguely remember someone doing it but I'm not sure.

Yes I have made add-on servo boards, for on-board and off-board. I currently have a number which I have made for my use and some spare. pm me for details

@Remolon

 

I made the bias generator like this to reduce the output voltage variation caused by variations in the mains voltage.

The zeners D21 and D22 are 150V zeners.

Thanks.

I have finished a prototype just to check if everything is correct, before ordering PCBs, and no problema. With a input of 2x300VAC, the output are exactly +350.0, -350.0 and 580.0 volts

Considering that the power supply will be +/-350VDC, do you think that for R26 and RV1 would be adequate to use similar values that the used on the original (HeadWize, 2001) KGSS. That is, 3K48 for R26 and 2K0 for RV1?

I have an other question. For using the amplifier with a unbalanced (just regular RCA) input, and following the recommendation, the +input will be connected to the potentiometer output and -input to ground. The R48 resistor will be in parallel with the potentiometer resistor connected to ground and the resulting value for the +input will be much lower than 500K. In these case, would be recommended to use a lower resistor value for R49? If yes, do you consider appropriate a value of around 7K5 for R49 with a potentiometer of 50K at the input?

The KGSS and KGSSHV are very similar so you might need to use those values.  I don't think anybody has tried the HV at these voltages though. 

 

Don't mess with the input resistors.  You can leave the - one out as the fet is grounded on that side but the + side needs to be 500K to protect the fet should the pot ever float. 

well my KGSSHV just blew a fuse.... sticking another fuse in there and it blew again.

Before it blew, there was some strange physical humming... I couldn't identify from where... In input LEDs were lit along with the humming.... but that's about all the actions I got.... I couldn't identify any burn marks on the PSU board yet..

What transformer do you have? 

SumR... I will take a look at it when I get back from school today.... that was the first thing that crossed my mind as well... but I thought Richard already reinforced it... It has been running for at least 300hours without a hitch.

Mine ran for two years before it crapped out...

oh... forgot to mention... along with everything there was also a strange burnt smell that I can't locate as well.... It took about 20~30 sec before the 4A slowblow blew. Transformer was cool to the touch after the fuse blew.

SumR... I will take a look at it when I get back from school today.... that was the first thing that crossed my mind as well... but I thought Richard already reinforced it... It has been running for at

 

 

 

 

But what were the specs? VA and mA on the hv secondaries?

 

Edit: though I suppose it could be anything at this point until you test the traffo to rule it out.

Edited October 10, 201312 yr by GeorgeP

I'd start with disconnecting the trafo and testing it. 

well my KGSSHV just blew a fuse.... sticking another fuse in there and it blew again.

Before it blew, there was some strange physical humming... I couldn't identify from where... In input LEDs were lit along with the humming.... but that's about all the actions I got.... I couldn't identify any burn marks on the PSU board yet..

 

Sounds familiar.

My SumR lasted about two months - it was rated at 100ma. (a bit on the wimpy side me thinks)

I was running a 3 amp fuse when mine blew, trafo was humming loud.

Upped the fuse to a 5 amp. Electrical stench ensued. Shut it down, SumR was fried.

I believe the trafo was under-rated although it did endure two direct shorts to the psu during initial testing.

FWIW it always had a loud hum during initial start-up due to the initial current draw of the psu / amp.

Some kind of soft start circuit may have helped? Dunno.

So after the SumR debacle, I took Frank Cooter's suggestion and bought a stock Antec trafo.

Off the shelf rated at 400ma it is a monster, some said it was too big. I have an older prototype psu (modded to rev 2)

that uses stacked zeners to down-regulate the voltage. I put some 5 watt buggers in there and my KGSSHV has worked fine since.

Thanks for the advices.

I think it's also worth to note that the first fuse blew during operation. I left it on during night because I was listening to it before I went to sleep and forgot to turn it off (not the first time.) When I woke up, the amp was off and the fuse was blown. I was also using 3A fuse tho with two thermistors in series to get the surge down. I was blowing through 3A fuses with only one thermistor. I used 4A this morning because I couldn't find the 3A fuse...

The trafo was speced using Yun's BOM. 450V @ 125mA IIRC. There was always very faint hum with it, but I had to have my ear within inches of it to hear it. There was not loud hum whatsoever. ( It was humming loud this morning tho... I could hear it clearly standing 2 feet away from it.)

Not going to add more skepticism now.. I'll report back when I have tested it.

Sounds familiar.My SumR lasted about two months - it was rated at 100ma. (a bit on the wimpy side me thinks)I was running a 3 amp fuse when mine blew, trafo was humming loud.Upped the fuse to a 5 amp. Electrical stench ensued. Shut it down, SumR was fried.I believe the trafo was under-rated although it did endure two direct shorts to the psu during initial testing.FWIW it always had a loud hum during initial start-up due to the initial current draw of the psu / amp.Some kind of soft start circuit may have helped? Dunno.

Sounds like hefty current surge putting strain on the windings that deteriorated over time. Thermistors would have helped.

Edited October 10, 201312 yr by johnwmclean

How beefy of an inrush limiter would be recommended? I'm not sure these ones listed in the old BOM are quite up to it.

Sounds like hefty current surge putting strain on the windings that deteriorated over time. Thermistors would have helped.

 

Indeedily........on both counts.