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FH9HVX - Budget Conscious 100w Class AB for Lean Times

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#422
I am referring to the All C's PSU. When I looked up the LED on the Mouser website it directed me to the Wurth Elektronic part which was the 12V. It is a new product, so that is why I asked if it was the one to use.

So thanks for the replies, I will order the 2V led.

X, I thought you were on holidays.
 
#425
Be wary that some SMPS don't like the turn-on surge current that charges a bulk rail cap and they go into auto shutdown. For example, the Connexelectronic SMPS800RE powers a pair of 4700uF bulk rail caps on my TPA3255 amp just fine but the SMPS300RE goes into auto shutdown unless there is a soft start between the SMPS and the amp. In general, a larger one is more tolerant to turn on transients. The FGH9HVX has only a 470uF bulk rail cap, so probably is not an issue. However, if you wanted to add some CRC smoothing caps in between the SMPS and the amp, the the max value needs to be considered.
 
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#427
xrk971 said:
Be wary that some SMPS don't like the turn-on surge current that charges a bulk rail cap and they go into auto shutdown. For example, the Connexelectronic SMPS800RE powers a pair of 4700uF bulk rail caps on my TPA3255 amp just fine but the SMPS300RE goes into auto shutdown unless there is a soft start between the SMPS and the amp. In general, a larger one is more tolerant to turn on transients. The FGH9HVX has only a 470uF bulk rail cap, so probably is not an issue. However, if you wanted to add some CRC smoothing caps in between the SMPS and the amp, the the max value needs to be considered.
Click to expand...

Sounds like your experience doesn't match up with the brochure:
To prevent harmful effects which this high value inrush current might have to the Power Supply components, a thermistor was used to limit the inrush current to a lower value than the mains fuse will trip or might damage any components from the Amplifier Power Supply. This thermistor is a passive component which has the property to decrease its resistance when the temperature increases. It has higher electrical resistance at low temperature, thus reducing the inrush current, and when the current which passes through, will heat-up the thermistor, the resistance will decrease, and the dissipated power will be reduces. One drawback might be the increased operating temperature, especially when the SMPS300R delivers high output power. The thermistor is placed on the edge of the board close to the Mains input connector, this avoiding heating-up other temperature sensitive components. Note that there is no need to use any other external power soft-start circuit when the SMPS300R is powered from standard mains supply voltage of 110 or 220V AC.

The SMPS300R features a soft-start characteristic, which allows progressive charge of the output filter capacitors, with a controlled charging current, without tripping over-current protection. The value and the working voltage of the output capacitors depend on the type of the SMPS, single or dual voltage, and the value of the output voltage. These capacitors have enough capacitance for most stringent applications, adding extra capacitors are not necessary or recommended, because if the capacitance is too high, the over-current protection might trip during power ON.
Click to expand...
Aspirational vendor advice? Must be a first .. :rofl:

Boards received about a month after dispatch - the joys of Covid-era shipping.. 😱

xrk971, I sent you a PM via Etsy. Please take a look when you're back from your time away. Enjoy your break.. :up:
 
#428
They are talking about thermistor between mains and SMPS. I am talking about in rush current from SMPS to the amp proper. Adding a hefty 47ohm (cold) thermistor between the SMPS and the amp will fix it - but the voltage drop across that is huge. A better alternative would be a SSR soft start between the SMPS and the amp. Or get a bigger SMPS.
 
#429
Hi X, Vunce , others,

I need to order some Molex 22-27-2031 headers for the FH9HVX from a different outlet due to Mouser/Digikey having no product. So I want to order some of the headers, fastons, etc for the Nirvana project to make shipping worthwhile.

So is the Mouser BOM for the Nirvana (Dec 14th, 2019), as listed on the 1st page of thread OK to use?

Will be building Nirvana after the FH9.

Thanks for the help,

MM
 
#430
Well, finally got time to sort out all the power supplies, a steady 53V on both the positive and negative rail. Brought the amp up with a variac and...... Nudda, no bias across the output devices. Output offset is about 80mV

Both channels do the exact same thing, so I have masterfully botched the same thing on both amps - this is what comes from overconfidence 😉

Back to the drawing board and reviewing part by part

.. dB
 
#431
Not so fast. Did you try adjusting the bias trim pots? The default position may be set so low that there is no current. Try slowly turning it while monitoring voltage drop across the source resistors. I recall zero bias current when I turned mine on for first time. It takes about 4 turns in the right(correct) direction. Try CCW ?
 
#433
842132d1588999708-fh9hvx-budget-conscious-100w-class-ab-lean-times-fh9hvx-v001a-schematic-jpg


Hi Dbel,
Sorry this is giving you a hard time. It is really a simple amp to get working and there must be a part value or part orientation error. The MOSFETs and bias circuit should function even without the input stage working properly. So the problem is somewhere in the bias setting circuit. The BD139, pot, and resistors around the BD139 all control this. Make sure that the value of the resistors are correct. Being off by 100x or 1000x will prevent a correct voltage on the VBE multiplier from allowing the bias from forming.

So please check values on R123/125. Check orientation of the BD139. Check orientation and position of the drivers KSA1381 and KSC3503. Check orientation of the protection diodes between the MOSFETs.

Also, I noticed you have a yellow LED on the LTP CCS. Is it glowing?

If you can get a voltmeter and probe the voltages (relative to 0v ground) at all the transistor pins, potentiometer pins, and redline the schematic and post it here, we can get to the bottom of it quickly.
 
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#434
You won't believe this. I just installed the led blind and assumed cathode to ground. Looking at the circuit, I realized my error, flipped it and the amp comes up perfectly. 7mV of DC offset and easily biased correctly.


Edit. Just saw your post. Does the color matter? I initially assumed just an indicator but it clearly sets voltage across the transistor.

.. dB
 
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#435
Great news! Yes, that was actually a tricky spot. When I drew schematic I showed it Anode to ground but in layout, JPS64 put K to ground under same assumption and we had to flip the LED i. The schematic. Awesome news!

We need to reinforce this point then in Post 1.

Thanks for sticking it out and checking things!

Have you listened to it yet?
 
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#436
Not listened yet, inputs still floating and haven't hooked up the output to the binding posts.

Going for the retro styling and adding little VU meters, so still lots to do before I can take it up to listen properly

Thanks X. Very well put together and (as long as you follow the circuit and layout) it is a very easy/ clean board to build.

Sadly I have to put some slides together for a talk, so that's all my fun for the day.

.. dB
 
#437
LED H111, green or red?

xrk971 said:
On the FH9HVX amp board, there is a red LED that is an indicator on the input stage CCS. That one is less than 2v drop.
Click to expand...

I assume this is H111 on the schematic, which is shown as a green LED. Are red and green LEDs interchangeable in this application?

Vunce used a red LED so we know it works, but would green be better? dBel84 used yellow! What should current builders use?
 
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