Author Topic: QRV-08 setup questions  (Read 3541 times)

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Offline mabu0815

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QRV-08 setup questions
« on: September 19, 2014, 02:52:18 PM »
Hi PA,

After being a happy QRV-04 builder/user, I would like to try the QRV-08 now.

I have read the project page and the forum posts regarding the QRV-08, but there are some things I don't understand yet.

- I understood that when I use C1 (which I should as I plan to connect different sources) I have to populate the Pot P1 and set the input bias with it.
Is it correct that I measure it across R1?

- Concerning the Jumpers J4/5: Do I have to connect both or just one?

- If everything is correctly installed, I understand that I only need to set the input bias roughly correct, the servo sets the output DC offset automatically.
To what value should I tune the input bias?


Thanks in advance

Sven

« Last Edit: September 19, 2014, 02:53:50 PM by mabu0815 »

Offline Matthias

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Re: QRV-08 setup questions
« Reply #1 on: November 01, 2014, 03:51:52 PM »
I'm sorry to add another question and not an answer to this topic.
I have recently put together my QRV-08 and I seem to have a technical problem.
WHen measurung the first channel I found that all transistors operate somewhere aroung 0,6V Vbe excxept for T24 which is more than 1,2 V so seems not to work. I receive a DC outpout offset of more than 0,4V which the opamp cannot compensat (it already puts out almost 14V on pin 6 to compensate ...). Another thing I noticed is that I measure no voltage accorss E20 and E22 and measure some accross E21 and E23.

So far I did not calibrate the input bias i.e. the pot has neither positive nor negative current connected. Can I expect that there is a build problem or a transistor problem or is it due to no calibration of input bias?

Regards

Matthias

Offline peranders

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Re: QRV-08 setup questions
« Reply #2 on: November 01, 2014, 04:21:42 PM »
Are the two channel alike when it comes to currents?

First: Adjust the P1 to min (towards ground) Measure the voltage across R1. If it is positive you should put a tin blob at J5 and adjust to zero volts across R1.

Second: Measure all DC currents. Measure across

R4, R5

R8, R9

R12, R13

R16, R17

R20, R21

Since you have 1.2 V across bas-emitter, check that you really have a BC860 there (or other PNP)

/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff

Offline Matthias

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Re: QRV-08 setup questions
« Reply #3 on: November 01, 2014, 05:00:58 PM »
Thanks for such a quick reply.
I managed to calibrate the channel to 0 mV accorss R1.
I did not fire up the other channel yet.

Wenn I measured accross those resistors and only the R4/R5 values seem ok where I have a bit more than mV.
R8 is 270, R9 and R13 are both 80mV and I do not measure a voltage accross R12 ... so I'm afraid i messed something up there ... .
T24 is a BC860 (broken?).

Offline Matthias

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Re: QRV-08 setup questions
« Reply #4 on: November 01, 2014, 05:09:57 PM »
Sorry: R4/R5 show a bit more than 620 mV