Troubleshooting - found trouble...

[ALL212]

A friend of mine purchased a Reduction from the 'bay.  Nice build, well done, however...

After some time horrible noises would come from one channel and in one case the speaker fuse blew.

I found a cold solder joint at 60 on the resistor.  The wire had solder all around it but was not making a solid connection.  If this resistor lost connection would it have done what he described as the symptoms?

I've reflowed the joint, ran all resistance checks and all voltage checks - everything checks fine.

Thanks!

[Paul Birkeland]

Yes, a loose connection there would cause the high DC voltage to be there intermittently, which could make low frequency transients to annoy a solid state amp and blow a speaker fuse.

[ALL212]

Ouch...

I didn't want to test it live until I had confirmation.

As always much appreciated Paul! 

[ALL212]

Follow up:

While "in the shop" I took the liberty of pulling some parts from my stock and I did some updates.  The owner reported he heard an improvement so I thought I'd list what I did here.  To be honest I didn't expect any audible improvement. 

All three power supply caps replaced with Nichicon.  In doing this I discovered the issue with the cold solder joint.  I replaced one diode with a Cree Shotkey and the 3300 uF with another Nichicon.  The last power supply cap got a 2.2uf WIMA attached to it.

[Deke609]

  The last power supply cap got a 2.2uf WIMA attached to it.

There's some interesting points/ideas about bypassing large capacitance electrolytic power supply caps with small capacitance film cap in the recent "Bypassing Capacitors" thread on the Tube DIY Asylum sub-board ... but they are interspersed amongst a lot of totally off the rails bickering.

Lower ESR and ESL, and faster transient response are mentioned as possible benefits.

cheers, Derek