high voltage on speaker terminal

[marcus7601]

Can someone help me with my first gainclone? I am using LM3875-kit from Audiosector. On right channel speaker terminal everything is fine. On left however i have -38V !! this is from my 25V transformer after rectification. How can this be?

I dont use a chassi so speaker ground goes to OG on pcb?

 

[Nuuk]

Make sure that you have both power rails (positive and negative) connected properly.

If you can, measure the voltage on the pins of the chip but be very careful that you don't cause a short!

It is more than likely that one rail is not connected!

 

[marcus7601]

ok, i will recheck my solderings.

 

[marcus7601]

Ok, i have resoldered +V and -V on the rectifier and amp-pcb still same results. I need some help here...

 

[jan.didden]

Ok, i have resoldered +V and -V on the rectifier and amp-pcb still same results. I need some help here...

Is the voltage on the chip output pin the same as on the speaker terminal? What is the voltage on each chip power supply pin? Measured?

Jan Didden

 

[marcus7601]

No on output i have 0V

On -V powerpin on chip i have the same as on terminal -35V

Edit:
I get -35V on output pin

 

[Nico Ras]

Hi, I had a quick look at the data sheet from National. On the faulty amplifier can you measure the voltage between ground and pin 7 as well as the voltage betwen ground and pin 8 of the LM3875.

We will establish if this is input related.