i'm on a roll... the kgsshv

[johnwmclean]

P.S. A word of caution for safety - the bias voltage sustained much longer than the +/- outputs after powering down the PSU. When the output voltage dropped to below 1V after a couple of minutes the bias voltage still measured well over 100V!!!

Indeed. A killer of an amp, and another good reason to test under load and fully drain the caps.

Edit: If you want to test the psu under load you need two resistors over each output to ground. I've used 2 x 4K 50W bolted to a large chunk of al, leave it on for 4 hrs or longer, use a fan over the whole set-up to keep things cool, the idea is to push/stress the components to maximum operating limits to expose any potential weakness.

Edited April 10, 2015 by johnwmclean

[JoaMat]

/

Edited November 11, 2015 by JoaMat

[spritzer]

I agree, the PSU either works or it doesn't. 

[mwl168]

Now that I have a variac, should I use it to test the amp board (kkgsshvampv16mini) as well?

Since there are two voltage sources for the amp and I use separate transformer for the +/- 15V supply, which is the correct ( or better ) procedure?

1. Hook up both transformers to the variac and test the entire circuit (PSU and amp) through the variac.

2. Only hook up the high voltage transformer to the variac. Power up the +/- 15V part fully upon turn on and use the variac to gradually bring up the high voltage part.

Thanks!

[JoaMat]

/

Edited November 11, 2015 by JoaMat

[spritzer]

I never use one either, just have a hand on the power switch and quick reactions. 

[kevin gilmore]

and a face mask

[mwl168]

Thanks JoaMat and Birgir and Kevin.

Edited April 12, 2015 by mwl168

[eggil]

I usually hide behind a wall. Safer that way. I have had a couple of nice explosions, more like firecrackers if you ask me, and the occasional green smoke, but I have never had a major fire.

Seriously, I do wear goggles if I am a little concerned

I know it is scary at first, but if you triple check your build and check as JoaMat said it should (usually) be OK.

Powering up is actually the highlight, the rush of your build. Have fun!

Edited April 12, 2015 by eggil

[justin]

ive had transistors hit a wall 20 feet away almost instantly, so i do like the goggles idea

[llamallama]

Does anyone know the max or typical power consumption (e.g. watts) of a full sized KGSSHV? I was thinking of running it off a PS power plant.

[mwl168]

Before I test the amp boards, I thought I give the PSU one more test and I ran into a weird problem on the -15V part which previously tested fine. The +15V tested fine.

The power transformer is a Triad FS36-350 that I know Birgir has used. I wired the secondaries to provide a center tap. It tested fine without load (21v - 0 - 21v). I used a variac to test the regulator and here is the scenario:

With the variac turned up to around 75v, the - output showed -14.96V and stayed there till the variac output past around 85v, from this point on, turning the variac up continues to raise the, supposedly regulated, output till it hits over -18V when I quit. Meanwhile the + out hits +15.17V at 75v and remains there since.

Another weird thing, when I turn down the variac and keep monitoring the -out, it would gradually and continuously decrease and hit -14.96V and then stay there for a few seconds and then continue to decrease afterwards.

So what gives? Any one has a logical explanation? I am guessing the 7915 regulator is probably bad but I cannot think of a logical explanation of the "magic" -14.96V phenomenon.

[GeorgeP]

Are they ST parts? Had read that their negative regulators could be hit and miss.

[mwl168]

Yes, it is a ST Micro 7915 negative regulator that I believe is causing the problem.

Pars has previously posted that he had issues with ST Micro regulators as well. This does not inspire confidence at all - what is to guarantee that a working part may someday fail which is basically what happened in my case.

What's the consequence of the +/- 15V supply goes out of balance by a few volts? Maybe those with running KGSSHV amps should double check?

Is there a pin-compatible replacement part we can use?

 

 

Edit: Just to set the record straight, the ST part L7915 is working as designed - it needs a minimum 5ma load to function. 

Edited April 14, 2015 by mwl168

[Kerry]

Some regulators require a load in order to regulate properly.  Try adding a 2K or so resistor across the output before you power it up.

Edited April 14, 2015 by Kerry

[mwl168]

Thanks Kerry.

You beat me to it and you are exactly right. The 7915 requires a minimum 5ma load to function. I found a thread on DIYAUDIO that explains it.

It's a bit confusing since the 7815 positive regulator behaves differently. As it was explained at DIYAUDIO, even though the 7815 and 7915 appear to be complementary parts their internal constructions are very different.

I put a 1K resistor across the output and I am getting -15.5V regulated output now.

Edited April 14, 2015 by mwl168

[spritzer]

Don't use ST parts is a good way to work. 

 

Does anyone know the max or typical power consumption (e.g. watts) of a full sized KGSSHV? I was thinking of running it off a PS power plant.

 

To many variables but something around 50-60W should be the norm. 

[mwl168]

Powering up is actually the highlight, the rush of your build. Have fun!

Oh yes, I did have the rush all right - the rush of my heart beat! )

Well, I powered up both amp boards (kgsshvampv16mini) one by one tonight. Both boards seem to power up fine - all three LEDs light up and after about 25 minutes from cold start, I was able to adjust both balance and offset to 0V and from that point on they drift back and forth within a few volts (one of the boards I pretty much exhausted the last bit of the offset VR adjustment, I think the other one was close too). This test is done without the servo ICs installed. The power supply was very stable during the test, giving +15.15V, -14.97V, -405V, +408V and 558V bias.

Not to say everything is rosy yet - I have not powered up both amp boards at the same time and still need to rig up all the wires and connectors so I can try to play some music through it.

Thanks all for your help in getting me this far. Hopefully music is not too far away )

Edited April 15, 2015 by mwl168

[eggil]

You are making good progress. Keep it up!

If both rails work in the pSU and both amps worked fine, it's just a matter of wiring everything together. Just be very carful and triple check all your wires.

I usually check outlaid the components and wiring agains each end, and do it more than once. And never do it when you are tired.

[JoaMat]

Good work!

[mwl168]

Thanks for your encouragement!

 

Another question: what kind of wire do you all recommend using between the amp and the headphone socket?

 

I’ve always preferred using 24 AWG solid core, pure copper wire for signal path based on things I read. In fact, I often use wires I harvest from the Cat5e cable. But this is the first time I build an amp to drive capacitive load.  

[kingofsnake]

 And never do it when you are tired.

SOOOOO true. Was 2am when i finally fired up my first KGSS build and Boom! a couple of resistors (RN60D) coatings was blown clean off along with a nasty smell. Realised i had connected the HV wires on one side of the amp board the wrong way round....Twat!   Never got round to repairing the damage i just use the board to practice de-soldering.

[spritzer]

I use Belden mil spec 600V wire for everything, stranded naturally.  Don't use the crappy cat 5 wire for high voltage, that insulation is easy to damage. 

[eggil]

http://www.bulkwire.com/wire-cable/stranded-hookup-wire-600v-ul-1015.html

[kevin gilmore]

that is the company I buy from, but I go for the Teflon.

its more expensive, but I have the right stripper and always

liked Teflon.