Hum/ hiss from older GK 800RB...

sunbeast · #1 10-08-2010, 11:02 PM

I just recieved an 800RB that seems to have an exceptional amount of idling hum through the speakers (present with all controls turned completely down). I have been trying a couple of these lately- one from the same earlier era (late 80s) and one from the late 90s, both of which had some noticeable idling hum but neither seemed nearly as noisy as this one. There is also a pretty strong hiss with the Woofer Volume turned up to half or above, regardless of whether a cord is plugged in or input Volume is turned completely down.

My question- is this to be expected from an 800RB from this era, or is this one in need of some work? (or maybe both...) I have played through a handful of these over the years, but this is the first time I have actually owned one and I want to make sure I'm not just crazy. I love the tone, but for the first time ever with an amp I find the noise nearly unbearable (I guess I've been lucky to have some pretty silent running amps- fan noise excepted- in the last several years). If it needed replacement filter caps, which seem to be the most likely source of the noise issues based on my quick internet research, how much might this job cost me? Are there any other obvious possiblities that might cause this extraneous noise?

Thanks!

WingKL · #2 10-09-2010, 01:45 AM

The hiss may be "normal" but the hum is not. Both can be fixed by a competent tech and I won't try to guess how much that's going to cost. The hiss can be reduced by swapping the old opamps in the amp with higher grade modern replacements like the TLE2072.

sunbeast · #3 10-09-2010, 09:19 AM

Thanks- the "hiss" does seem like something I can work with, as it really only seems an issue with the Master cranked to noon or above. I would imagine a higher input volume would help make that a non-issue.

I have powered it on and let it idle a few times now, and I am definitely convinced that the hum is significantly beyond normal as well- it is loud enough without any signal input to drown out the notoriously loud fan from my Mesa Walkabout. The biggest difference in annoyance is that it is actual noise coming through the speakers (signal noise) vs. ambient noise from a fan mechanism- which will make recording with this amp pretty much impossible unless I get it repaired. I wish I had amp tech friends in Portland- the only guy I've even dealt with doesn't touch solid state amps outside of a select few that he likes!

bassmanbiff · #4 10-09-2010, 09:25 AM

Hum like that can be from aging filter caps in the power supply. It's pretty easy to fix.

Btw .. I'm also in Portland.

sunbeast · #5 10-09-2010, 01:38 PM

Quote:

Originally Posted by bassmanbiff

Hum like that can be from aging filter caps in the power supply. It's pretty easy to fix.

Btw .. I'm also in Portland.

That's what I am guessing based one reading up about these problems- the amp does seem noticeably more muddy to me than the similar older model that I tried, which sounds like it could also be tied to this problem.

Do you happen to know anybody in town that could look at the amp diagnostically and give me an estimate? Service is obviously a bit cost-prohibitive with an amp that sells for so little on the used market!

Thanks,
Karl