Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: serpent68 on May 13, 2014, 01:14:02 AM

Title: Buzz + ringing sound on left channel [solved]
Post by: serpent68 on May 13, 2014, 01:14:02 AM

I was attempting to add bypass capacitors to the 1st and 2nd power supply cap, and also changed out the bypass cap to the main output caps. 

After installation, there is a loud buzzing sound with a high pitch ringing sound on the left channel.  The buzzing sound does not change with volume change.  There is no music coming from the left channel, but the right channel is perfectly fine.  The high pitch ringing sound seems to come and go.  When the amp is switched off, there is a very loud pop sound, and the buzzing sound remains in the left channel for about 1 second before dying off.

I have removed the bypass caps for the power supply caps but the problem remains.  Also re-soldered all the joints that I touched, but the problem is still there.

Any suggestion for quick troubleshooting?  Thanks in advance.

Title: Re: Buzz + ringing sound on left channel (after trying to install bypass caps)
Post by: Paul Birkeland on May 13, 2014, 04:26:51 AM

I'd start by measuring the voltages and reporting any that aren't in spec.

Title: Re: Buzz + ringing sound on left channel (after trying to install bypass caps)
Post by: Doc B. on May 13, 2014, 05:00:40 AM

Bad signal ground connection

Title: Re: Buzz + ringing sound on left channel (after trying to install bypass caps)
Post by: serpent68 on May 13, 2014, 05:26:43 AM

Both the LEDs on the small PCB B are not lighted up.

Terminal 5 reads 0V instead of 90V
Terminal A1 reads 0V instead of 90V
Terminal B4 reads 0V instead of 90V
Terminal 9 reads 28V instead of 100V

What's wrong?

Thanks PB and Doc.

Title: Re: Buzz + ringing sound on left channel (after trying to install bypass caps)
Post by: serpent68 on May 13, 2014, 01:18:46 PM

I've checked all other voltages are within specs.  The LEDs on the big PCB and the small "A" PCB are all lighted up.  Seems to me like a one sided problem.  I've checked all ground connections resistance and they appear fine.

Appreciate any guidance on what to do next.  Should I re-solder everything on the small PCB?  Thanks.

Title: Re: Buzz + ringing sound on left channel (after trying to install bypass caps)
Post by: Paul Birkeland on May 13, 2014, 01:40:38 PM

Resolder the center leg of the MJE350 on the small PC board by the volume pot.

Title: Re: Buzz + ringing sound on left channel (SOLVED)
Post by: serpent68 on May 13, 2014, 06:41:51 PM

Problem is resolved.  Bad solder joint from terminal 4 to the small PCB.

Thanks PB for your advice.