Krell KSA 50 PCB

[Mark A. Gulbrandsen]

I used the stock value pots as on Jan's schematic and the amp is super stable. Offset can easily be trimmed to zero and bias doesn't drift even a tiny bit after the amp has thermally equalized.

Mark

 

[mpmarino]

Al,
Thanks so much for the suggestion 🙄 . Not shorting the inputs was indeed my problem. The behavoir of the pots is now seemingly linear and predictable. Now I need a little time to prep it to actually make music.

Mark,
I see what you mean, just as you say.

Thanks Guys.

 

[kvholio]

Mpmarino, i'm glad you got it sorted out.
I still think its strange however. With unshorted input i measure +4 mv offset, perfectly adjustable and 0.3 mv wandering.
With shorted input i measure - 8 mv. 0.3 mv wandering.
btw, "safety ground" is optional here in Holland

with kind regards,

Klaas

 

[mpmarino]

kvholio,

what are your rail voltages? I'm a bit high at ~41v, I wonder if that somehow changes anything... or... that noisy ballast in the shop lights is acting up again, or 😕

 

[bikehorn]

hey mark, can i buy some PCBs?

 

[kvholio]

I'm running it on +/- 34 Vdc rails.kinda low.
While tinkering with my just-acquired oscilloscope (still need a waveform-generator) i noticed my plasma-tv is throwing its noise "all over the place".(btw, imo this has nothing to do with your previous problem).
Also, i'm not a great fault-seeker.I dont fire up amps, i slowly start them and check...
This doesn't mean i'm not willing to help, i'm just not very good at it 🙁

with kind regards,

Klaas

 

[Mark A. Gulbrandsen]

hey mark, can i buy some PCBs?

Sure! Just fire me an instant message though the site with your regular e-mail address and I'll send you back all the details.

Mark

 

[kvholio]

Mpmarino, do you have your secondary(=amplifier-electronics) ground connected to your primary(=safety) ground ?

Klaas

 

[mpmarino]

Mpmarino, do you have your secondary(=amplifier-electronics) ground connected to your primary(=safety) ground ?

Klaas

If you mean: Is your secondary 0v connected to earth

the answer is yes

 

[kvholio]

Thanks Mpmarino. I mean a connection between your secondary ps-ground and "a copper pole in the ground/earth". I don't ever use that. As i said earlier grounding is optional here


With kind regards,

Klaas

 

[AndrewT]

Hi Kv,
Netherlands is part of the EC. Or isn't it?

I am surprised that in a country aligned to our treaties that 220Vac is allowed in metal cabinets without a compulsory safety ground.

 

[AndrewT]

Hi Mp,
if the DC output offset is stable and near zero with the input shorted and then changes when a source is connected, that indictates there is something being fed from source to the DC coupled KSA that is causing the enforced output offset.

The DC gain of KSA is 1 so the output offset must, near enough, equal the source offset.

Either the source needs a DC blocker or the KSA needs it.

Find and eliminate.

 

[kvholio]

Andrew, actually the connection of the chassis to safety-ground is compulsory, but its only the piece of euipment where the connection is made. In practice, most older houses dont have ac outlets in f.i. hall, living-room, bedrooms with a connection to safety-ground. I hope this makes clear what i mean.

with kind regards,

Klaas

 

[AndrewT]

Hi Kv,
seems a bit like the US, but they (used to?) omit the safety ground on 110Vac.

 

[kvholio]

Andrew, i actually only have safety-ground in my kitchen.
Also, i (perhaps falsely) assumed Mpmarino was measuring with open inputs, nothing connected, as he mentioned having to wire up his xlr's. Lesson one in troubleshooting:assume nothing 😉

with kind regards,

Klaas

 

[konst]

Mark, I just sent you a PM

PLz check spamfilter as some messages appear to have not reached you

 

[jacco vermeulen]

Here's how it is done overhere.

There are three combined 40 Amps automatic fuses/earthleak switches after the main switch.
Each 40 Amps automatic fuse feeds a group of 16 Amps automatic fuses.
The earthleak switches trip at leak currents in excess of 0.03 Amps.

Earthleak switches are mandatory in wet areas, such as kitchens and bathrooms. Bathrooms in new constructions even need to have a safety earth net installed in the floor besides the automatic earthleak switch.

I believe the only EC country way ahead of its time has been France,...as usual.

 

[jacco vermeulen]

And a bonus, toroid separation transformers with 8 Amps primary fuses.
Ex-army transformers, adapted to run balanced(see posts by P-D and WuffWaff on the balanced transformer thread)
Using 4 of these hunks with 20 Amps Shaffner filters for the audiogear.(each one weighs 48lbs)

 

[Mark A. Gulbrandsen]

Andrew is right, ther used to be no dedicated earth grounds over here... I think too many people were electrocuted in the bathroom so earth polorized pligs, dedicated ground and ground fault breakers came into being. I believe the new National Electric wiring code came about in the mid to late 1960's. First came polorized two prong plugs and then later on the third dedicated gound pin was added! Ground fault breakers are the ultimate in protection and include a built in test button.

Mark

 

[jacco vermeulen]

Ground fault breakers are the ultimate in protection and include a built in test button.

Hear, hear.
Earth-ground by itself means very little. Touch both the phase and earth wire and you're fried chicken without the earthleak breaker.