TPA6120A / OPA2134 Headphoneamp
So, here is another project of mine:
A headphone-amp build of a OPA2134 as gainstage and a TPA6120A as output.
Here is the PS-unit: a 15V/16VA CT transformer with Panasonic FC caps, MUR860 bridge and LM7815/7915 voltage regulators.
Here´s the heart of this "machine" (layout by myself):
It´s not ready yet, but it´s the next project to be finished ;p
So... Here´s the first problem:
I feed this amp with a 1 kHz sinus. I´ll get 1 kHz on the left output, but only 30 Hz on the right. I´ve measured some points, and the signal is cut down after the pot, but only on the right side.
Anyone an idea what might have happened?
Thx so far...
did you connect all of the power supply pins? tpa6120 == ths6012 its worth reading both datasheets
"Each amplifier of the THS6012 has its own power supply pins. This was specifically done to solve a problem that
often occurs when multiple devices in the same package share common power pins. This problem is crosstalk
between the individual devices caused by currents flowing in common connections. Whenever the current
required by one device flows through a common connection shared with another device, this current, in
conjunction with the impedance in the shared line, produces an unwanted voltage on the power supply. Proper
power supply decoupling and good device power supply rejection helps to reduce this unwanted signal. What is
left is crosstalk.
However, with independent power supply pins for each device, the effects of crosstalk through common
impedance in the power supplies is more easily managed. This is because it is much easier to achieve low
common impedance on the PCB with copper etch than it is to achieve low impedance within the package with
either bond wires or metal traces on silicon.
Although the THS6012 is specified for operation from power supplies of ±5 V to ±15 V (or singled-ended power
supply operation from 10 V to 30 V), and each amplifier has its own power supply pins, several precautions must
be taken to assure proper operation.
1. The power supplies for each amplifier must be the same value. For example, if the driver 1 uses ±±15
volts, then the driver 2 must also use ±15 volts. Using ±15 volts for one amplifier and ±5 volts for another
amplifier is not allowed.
2. To save power by powering down one of the amplifiers in the package, the following rules must be
– The amplifier designated driver 1 must always receive power. This is because the internal startup circuitry
uses the power from the driver 1 device.
– The -VCC pins from both drivers must always be at the same potential.
– Driver 2 is powered down by simply opening the +VCC connection.
See the schematic and layout here:
Think there´s nothing "wrong" with it...
At a quick look there's nothing wrong with the design and the fact you've also got one channel of this working helps to show that. You're layout seems fine too. Often in situations like this you need to go hunting for bridges of solder, or perhaps any copper that failed to etch off and has connected two parts together that should not be. My first thought when looking at the layout is how little space there is between some traces and the pads of components, this would undoubtedly lead to problems unless handled with extreme care.
As the circuit is rather simple a good plan of attack would be to go at it with a continuity tested on a multimeter to check that everything is indeed connected up as it should be, although mainly checking that parts/traces that are close together aren't touching.
The SMD-parts (resistors) are reflow-soldered. Only the caps and connectors are soldered manually. I think i´ll go with one big phrase in DIY:
"Check everything twice. Once in the morning and once in the evening!" ;-p The "morning" part is absolved, the rest comes within this week.
S... Now everything´s checked twice: it´s dead... there was a small solderbridge on the right channel. So, open up the ashtray and goodbye :-\
But no problem at all... My buffered OPA2134-HeadAmp is already running ;-p
Those 220µF electrolytics will be replaced with some HQ MKPs.
Thinking about Mundorf RXF or something in this direction...
sad to hear about the TPA IC, but congratulations on the succesful build of the buffered 2134 one. :)
As I'm particulately interrested in an application of the TPA, may I casually mention that such an IC from Texas Instruments is delivered extremely quickly and conveniently... :D
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