What’s the current through the JFET? Should be around 6mA to 8mA. Buzzing on one channel may be a bad JFET or MOSFET.
Please post schematic with all nodes’ DC voltages relative to GND.
Please post schematic with all nodes’ DC voltages relative to GND.
What is voltage below R3 if you went with 910R instead of 1k5? As is, you have only 2mA of bias current through the JFET and this is low and leads to problems with distortion.
Those are the voltage with 910R in both channels, I changed back from 1.5k after it had no effect on the voltage at the mosfet source
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ordered some 10K uF caps off ali express and they just came - gonna swap out the filter caps =D
I think you have either bad JFETs or MOSFETs, did you get a chance to swap them out yet and re-test?
I refer to the circuit in post #47:
xrk971 Desktop Class A (DCA) Headphone Amp
You have used 47R for R113, R114.
Now in the power supply you have used 220R for Gate Stopper resistor.
What is the difference?
And what do you recommend?
For IRF610 and IRF240 and power devices
I have seen several other designers use 220R.
Among them is Nelson Pass.
But can not remember seeing 47R.
xrk971 Desktop Class A (DCA) Headphone Amp
You have used 47R for R113, R114.
Now in the power supply you have used 220R for Gate Stopper resistor.
What is the difference?
And what do you recommend?
For IRF610 and IRF240 and power devices
I have seen several other designers use 220R.
Among them is Nelson Pass.
But can not remember seeing 47R.
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The gate stopper on the cap multiplier is a Juma design from the Juma’s easy Peasy Cap Multiplier thread. I have not modified it. For the ZVN4360 MOSFET, I was trying to use as low of a value as possible and in fact some people suggest not having one at all for maximum music transparency. In truth, one can lower it until there is no oscillation. 220R is a safe bet and most often used. It would probably work fine with 220R there or anywhere in between.
Thanks xrk971
Is as I expected something you have tried out, the 47 Ohm.
I also think gate stopper is for stability in a circuit.
When we have no global feedback, then we do not need such resistans as much.
It is different with a feedack loop. To stop oscillation.
Is as I expected something you have tried out, the 47 Ohm.
I also think gate stopper is for stability in a circuit.
When we have no global feedback, then we do not need such resistans as much.
It is different with a feedack loop. To stop oscillation.
I've managed to break my amp. 😱
I use a jumper for an on-off switch and I plugged it in when the DC was connected and I got a nasty spark.
Now when I listen, I have a booming steady hum at all times (DC?) and some low level distorted music in the background.
Measuring the 24V DC from the step up at the board input connector it's only measuring about 9.8V.
With no electronics knowledge, my basic reasoning says that the caps and resistors should probably take a bit of voltage with no ill effect so maybe I've bust the cap multiplier as that's the first active device in the way?
Any suggestions as to how to diagnose would be appreciated.
I use a jumper for an on-off switch and I plugged it in when the DC was connected and I got a nasty spark.
Now when I listen, I have a booming steady hum at all times (DC?) and some low level distorted music in the background.
Measuring the 24V DC from the step up at the board input connector it's only measuring about 9.8V.
With no electronics knowledge, my basic reasoning says that the caps and resistors should probably take a bit of voltage with no ill effect so maybe I've bust the cap multiplier as that's the first active device in the way?
Any suggestions as to how to diagnose would be appreciated.
What is the voltage of the step up without connecting it to the board? Cap multipliers are pretty tough and immune to turn on transients. The cap multiplier is a slow turn on valve that protects everything downstream. You may have a busted wall wart, or a bad DC step up or a bad (shorted cap in the multiplier). 9v supply will sound terribly distorted.
1. Determine if wall powered DC supply is good still
2. Determine if DC step up is good
3. See if cap Mx works (slow ramp up and output is 4v less than input)
4. What is bias current through MOSFETs? V at pin 3 divided by R in bank (67.5ohm).
1. Determine if wall powered DC supply is good still
2. Determine if DC step up is good
3. See if cap Mx works (slow ramp up and output is 4v less than input)
4. What is bias current through MOSFETs? V at pin 3 divided by R in bank (67.5ohm).
BBG16V,
Any luck debugging where the problem is yet? If it is not the PSU or DC-DC, (and a true 24v is provided upstream of cap Mx), please measure DC voltages relative to GND at all nodes (connections) on circuit, mark up schematic with it and post here. Also, some close up photos so I can see values of all resistors installed, etc - that will let me debug it very quickly. Good luck.
Cheers,
X
Any luck debugging where the problem is yet? If it is not the PSU or DC-DC, (and a true 24v is provided upstream of cap Mx), please measure DC voltages relative to GND at all nodes (connections) on circuit, mark up schematic with it and post here. Also, some close up photos so I can see values of all resistors installed, etc - that will let me debug it very quickly. Good luck.
Cheers,
X
Umm I'm almost done but noob question.. Which is input and output from left to right? Just need to solder input and output jacks.
You just need to refer to the schematic (you can see X101/X102 are teh inputs to the pot):
Then refer to the stuffing guide top view and you see that X101/102 are the two in the middle. So it is Out (L) / In (L) / In (R) / Out (R) from left to right:
Another noob question.. Which is + and - in x132? I think I can figure it out by picture but I'm too scared to experiment without knowing for sure.
Looking at it as shown in diagram with volume pointing down, +ve is the second one so one on right. You can tell because it’s not connected to the ground plane.
Hi X
1. Supply is good. Gets very hot now. Replaced with other 12V supply with indicator and that goes down to 7.75V when attached to amp.
2. DC step up good. 24V. Gets VERY hot when attached to HPA.
3. On attachment see where I have measured the CM voltage at 0.88V.
4. On attachment see where I have measure the MOSFET bias voltage at -9.5V.
It was working perfectly previously.
Does that help or is more info needed?
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You should not be getting negative voltage on a single rail supply amp. If you have negative voltage at output of mosfet pin 3, it means your DC converter is connected to amp in reverse polarity. Can you double check that voltage at pin 2 of cap Mx mosfet is +24v relative to GND?