New PassDIY Headphone Amp (now available)

[2 picoDumbs]

Also check you have wired the headphone jack correctly.

It's almost always some dumb mistake.

 

[Tix88]

Photo internal complete

 

[AndrewT]

Yes, if I disconnect the cd player it is always noisy

Hum noise

check you headphone amplifier.
Short the inputs with a dummy zero ohms plug fitted to both inputs.
Remove the headphone load and switch ON.
Measure the output DC offset and the Output Hum+Noise.
If the levels of both are low, then you should get down to the 199.9mV scales on you DMM and you should get readings of <5.0mVdc and <0.1mVac.
Test and report back.

 

[wayne]

Ground the body of the volume control.

 

[Tix88]

Ground the body of the volume control.

Already done but nothing

 

[Tix88]

check you headphone amplifier.
Short the inputs with a dummy zero ohms plug fitted to both inputs.
Remove the headphone load and switch ON.
Measure the output DC offset and the Output Hum+Noise.
If the levels of both are low, then you should get down to the 199.9mV scales on you DMM and you should get readings of <5.0mVdc and <0.1mVac.
Test and report back.

Here is a series of measurements

DC offset 0.6 mV
L out (potentiometer max) 7.4mV
R out (potentiometer max) 7.9mv

L out (poti min) 7.4mV
R out (poti min) 7.9 mV

L out (poti half a turn) 1.6 mV
R out (poti half a turn) 2mV .

 

[2 picoDumbs]

What is AC ripple across each power supply rail ie between positive and 0V and negative and 0V after the regulators?

 

[AndrewT]

Here is a series of measurements

DC offset 0.6 mV
L out (potentiometer max) 7.4mV
R out (potentiometer max) 7.9mv

L out (poti min) 7.4mV
R out (poti min) 7.9 mV

L out (poti half a turn) 1.6 mV
R out (poti half a turn) 2mV .

What is AC volts and what is DC volts?

 

[Tix88]

What is AC volts and what is DC volts?

The measures of the previous post are in DC
These instead in AC

L out 0.017V AC
R out 0.0018V AC

 

[Tix88]

What is AC ripple across each power supply rail ie between positive and 0V and negative and 0V after the regulators?

0.017V on 7915
0.019V on 7815

 

[2 picoDumbs]

17mV seems higher than what I would expect it should be considering the level of filtering there is before it even hits the regulator.

 

[AndrewT]

Here is a series of measurements

DC offset 0.6 mV
L out (potentiometer max) 7.4mV
R out (potentiometer max) 7.9mv

L out (poti min) 7.4mV
R out (poti min) 7.9 mV

L out (poti half a turn) 1.6 mV
R out (poti half a turn) 2mV .

The measures of the previous post are in DC
These instead in AC

L out 0.017V AC
R out 0.0018V AC

An output offset (Vdc) that varies with vol pot setting, points to a DC coupled input.
I consider that a bad thing to do to an amplifier and it's load.

These Vac measurement are enormous.
17.0mVac and 1.8mVac are not acceptable for Hum+Noise measured with a DMM voltmeter.

As I said earlier the H+N should be <0.1mVac with inputs shorted.
Some may measure 0.2mVac and a poor implementation would measure >0.3mVac

 

[6L6]

AndrewT

I suspect the amp is oscillating.

Tix88 -

Remove the 100pF caps in the feedback circuit. Add 2k resistors (Watever you have that's close) in series with the input. Lift your input wires at the PCB and add the resistors in-line.

 

[AndrewT]

If oscillation, then an oscilloscope, or an HF sniffer.

Was it Mooly that posted a simple passive sniffer that gave a reading into a DMM voltmeter?

 

[6L6]

All you need these days is an inexpensive digital oscilloscope - they all have every counter imaginable built-in. That functionality is probably more useful than looking at the waveforms for much of what we do.

The use and power of a new $350 scope is amazing, downright mind-boggling.

 

[Morde]

One cause of hum might be the wiring from input RCA jacks to the pcb input. If I understand the picture in post #982 correctly the wiring is done with three individual cables? These should be at least twisted together and it would be preferrable to use shielded cables.

 

[Tix88]

AndrewT

I suspect the amp is oscillating.

Tix88 -

Remove the 100pF caps in the feedback circuit. Add 2k resistors (Watever you have that's close) in series with the input. Lift your input wires at the PCB and add the resistors in-line.

I added the resistances, but nothing.
I noticed that I now have the Left channel out 7v DC

 

[2 picoDumbs]

There is probably something wrong with your power supply.
Check all soldered joints.

 

[stijn001]

This is the new board with a build ..

Sweet looking build. What value is the brown cap connecting signal ground to chassis ground?

 

[Tix88]

There is probably something wrong with your power supply.
Check all soldered joints.

I reviewed all the points, I removed the potentiometer, now I measured on pins 1 and 7, on pin 1 I have 230mV on pin 7 I have 2.6 V. pin 8 and pin 4 +/- 15V.