Problem with QRV07

[Bertel]

Hi!

I have bought a QRV07 kit some time ago. Unfortunately I hadn't had time to build it, but today I managed to do so. It looked like everything went fine, but to my surprise I hear music on both channels only at a veeeery low volume, barely recognizeable. I feed the signal from my DAC (TPA Buffalo32S, 2Vpp) into my ALPS 10k stereo poti and then to the QRV07, but even when I turn the poti all the way up the volume level is so very low.

Just an idea: Would it be possible to get that effect if I have accidentally fitted the two ICs IC1 and IC2 the wrong way round, i.e. rotated by 180 degrees? I couldn't find any clue to the pin layout, i.e. couldn't identify pin 1 (my AD8610 don't have the dent or mark the datasheet shows...), so I mounted both ICs so that you can read the print on them when looking from the transistor side. Is that correct?

Any other hints or recommendations where to look?

Many thanks
Robert

[peranders]

The opamp has some marking. Consult the datasheet for the brand you've got but I have never seen anything else than readable text and the pin 1 at the bottom left.

You could have fried the opamps but one way to find out is:

Do you have +- 12 V at the supply pins 4 and 8?

Is the output voltage at 0.0 mV? The opamp has extremely low output offset voltage.

[Bertel]

I have the standard Analog Devices AD8610 from Farnell. No marking. Datasheet shows which pin does what, but it doesn't help me identify if I have the chip in correct orientation or have accidentally rotated it 180 degrees.

You mention readable text on the chip - can you read it when looking from the transformer side (I wrote 'transistor' below but meant transformers, i.e. when looking from the end of the board where the transformers are located) or from the side of the input connector?

Abd yes, you're right - I have -12.6V for V- on pin 4 on both IC1 and IC2, but only 7.3V for V+ on pin 8 of IC1 and 7.5V on IC2!! Where did I go wrong? Which voltages should the regs IC4 - IC7 measure?

I would look that up myself in the schematic but i can't find the login anymore for the download page...?

Thanks
Robert

[peranders]

The log in is only when you are at the frontpage of my website.

Sorry, the supply pins are of course 7 and 4. See the datasheet.

Pin 1 in the pcb is located towards the input terminal and if you can read the text, pin 1 is at the bottom and to the left.

Check also the datasheet figure 72 and the profile of the package. The pin 1 side is a bit different as you can see. You'll have a 45 degree slope there.

Anyway, you should have +- 12 V supply voltage. Do you have that?

[Bertel]

Ah, thanks, found the login and downloaded the PDFs.

Yes, right, I was also looking at the picture for AD8620 ;-) Pins 4 and 7 is correct, and yes, I have +/-12V there as it should be.

Aaah yes, found the 45 degree slope of pin 1 side - and indeed, I fitted both IC1 and IC2 incorrectly, i.e. rotated by 180 degrees! Thanks for helping to identify this - now I have the great pleasure of trying to unsolder them...  :x  :wink:

[peranders]

You may have fried them but harm in trying to use them. One way to unsolder them is to use a hot air gun or two soldering irons.

[Bertel]

Have rotated the AD8610 by 180 degrees, and now it works  :-) Thanks P-A for helping me with this!

Sound is ok so far, probably needs some burn-in time. Will also experiment with different cap models and direct battery power supply.

[peranders]

Nice that you didn't fry those expensive opamps.

When I comes to burn in, my point of view is that this is nothing to be concerned about. Just use the amp.

Please report back after a while write what you think.