Millett "Starving Student" hybrid amp - Page 400

Quote:

Originally Posted by Fred_fred2004 

You will struggle to get a nasty shock from 48 volts :-)

Wikipedia... not exactly the gold standard, but why risk compromising safety to save 3 dollars?

"Voltages over approximately 50 volts can usually cause dangerous amounts of current to flow through a human being touching two points of a circuit, so safety standards, in general, are more restrictive where the chance of contact with such high-voltage circuits exists."

http://en.wikipedia.org/wiki/High_voltage

Approximately - 48V is approximately 50V - you would struggle to measure the difference on the 200V scale of an analog meter. 

dangerous amounts of current - with at least 0.5A on tap there are dangerous ammounts of current in the amp. 

touching 2 points of the circuit - like the grounded headphone jack and the heatsinks while plugging in/pulling out. 

Spend the extra $3

You'd have to be soaking wet in a salt solution to get a shock

I worked for many years for Australian Telstra and its power source was 48 volts derived (believe it or not) from huge lead acid battery banks, and we never took any precautions other than not shorting out the (+) and (-) which fused wires pretty thoroughly :-)

sorry its just not going to hurt you

Quote:

Originally Posted by Fred_fred2004 

You'd have to be soaking wet in a salt solution to get a shock

 

I worked for many years for Australian Telstra and its power source was 48 volts derived (believe it or not) from huge lead acid battery banks, and we never took any precautions other than not shorting out the (+) and (-) which fused wires pretty thoroughly :-)

 

sorry its just not going to hurt you

I have heard stories of people having limbs blown off by 48V battery banks. 

I would not be so casual with voltages outside of an enclosure. People have zapped themselves mighty good on 12V car batteries. Its not even hard - your out working in the sun, your hands get sweaty, you brush the + terminal with your tummy resting on top of the radiator and zap.

I can see an equally plausible scenario playing out where someone with sweaty hands goes to plug in his headphones, grabs the amp by the top, pushes his headphones in (with a metal plug) and zap. 

Agreed, you would need to be somewhat unlucky to zap yourself. The opposite of that is of course that you need to be somewhat lucky so that someone does not zap themself. So the safety of your design decision is conditional on luck, to save $3.

It's actually 62,000VND (vietnamese dong)

so well worth saving

Quote:

Originally Posted by Fred_fred2004 

It's actually 62,000VND (vietnamese dong)

 

so well worth saving

At the current time, not even $3us. 

Creating an electrocution hazard to save less than $3. That sounds pretty irresponsible to me. 

It would be if it was a hazard

its not

Sorry, but I'd have to come down on nikongod's side on this one.  I remember when Dsavitsk was designing the PCB for the Starving Student.  He went to great lengths for added safety - specifically because 48V is high enough to start causing some real pain, under the right circumstances.  The issue as a responsible designer is that you try to limit those "right circumstances" from happening.

While the IRF510 output MOSFET here has internal protection devices built in, it could be possible for the drain to remain "hot" even if the device failed, and the entire circuit were inoperable. A problem with the power supply, be it a Cisco or alternate DIY variety, could pose lethal to even an experienced diy'er. More so with the heatsinks isolated from a safety ground.

And as a responsible DIY builder, one must employ correct electronic assembly methods.

Exposed tube equipment is inherently dangerous as it is, why add exposed voltage on the heatsinks to the equation?

I sure would not want 50 volts at 1/2 amp crossing through my heart.

I've also been shocked by a car battery. Scared the pee out of me.

My left arm went flying into the raised hood of the car.

Might not have killed me, but was still a dangerous wake-up call.

You are all perfectly correct, if there is any chance of danger it should be protected against

and if by any chance you get 1/2 and amp at 50 volts across your heart dont worry you'll be dead already :-)

that was an interesting dirt road... glad we have that issue resolved...

So how does the MSSH compare to other amp? Reading this thread, i only know that it's very good for the price but don't know how well is stack to other commercial products?

Quote:

Originally Posted by capernicus 

 

Ok, so I have this thing mostly complete.  Its Purple Heart and Maple in a 12AU7 build

 

 

Unfortunately, as I mentioned in my previous posts I can't seem to get the Right side working correctly...

 

I took a picture of the internal bird nest below - I'm the first to admit I still have much to learn on how to do clean wiring and am also open for some pointers.

 

I picked up some nice aerospace grade wire scraps from work (silver tinned copper) and used it throughout except for the black wire which is when I ran out of the good stuff and had to dip into my crummy Depot stock.

 

 

Please let me know if you have any suggestions for my sick right channel...

 

OK so I've double checked that R10 is properly connected at both ends and reflowed the solder - no change.  Nothing happens when swapping tubes.  headphone jack is wired properly.  Replaced the MOSFET - till no change.  Both tubes glow nicely and voltages at the tube heaters checkout.  It would appear that I'm not getting a healthy current through the tube as Pin 1 is measuring too high of a voltage ~47 volts.  Any thoughts?

Quote:

Originally Posted by capernicus 

OK so I've double checked that R10 is properly connected at both ends and reflowed the solder - no change.  Nothing happens when swapping tubes.  headphone jack is wired properly.  Replaced the MOSFET - till no change.  Both tubes glow nicely and voltages at the tube heaters checkout.  It would appear that I'm not getting a healthy current through the tube as Pin 1 is measuring too high of a voltage ~47 volts.  Any thoughts?

 

Measure resistance to ground at the cathodes of both tubes with the amp off. Should be the same, probably isn't. 

Its almost certainly not the cause of the problems your having, but the 2Kohm resistors R3/R9 should be soldered directly to the mosfets' gates with the wire going to the middle of the resistor divider. This resistor is a "gate stopper" for the output mosfets. Most of the time these resistors do nothing, but for them to work when necessary they have to be snuggled up close to the mosfets. 

That was it!  Thanks!  The cap and resistor tying the cathode to ground are twisted together and connected to a wire that went over to ground which turned out to be in the correct place but not soldered in...

Now I am enjoying the music - sounds terrific!  I look forward to putting it side by side with my SOHA II...
 

Quote:

Originally Posted by nikongod 

Its almost certainly not the cause of the problems your having, but the 2Kohm resistors R3/R9 should be soldered directly to the mosfets' gates with the wire going to the middle of the resistor divider. This resistor is a "gate stopper" for the output mosfets. Most of the time these resistors do nothing, but for them to work when necessary they have to be snuggled up close to the mosfets. 

So I have my 2k resistor at the other end of the wire from the mosfet - not right on it as you suggest.  How critical is it to put the resistor at the mosfet?  My limited understanding of all this would suggest that either way you have a 2k load on the gate and considering the distance we are talking is very small being right on the gate or 2" away shouldn't matter.  I'd like to understand this better - i haven't worked much with MOSFETs...

Thanks again Nikongod for the troubleshooting assistance!