Eros 2 - Right channel suddenly very quiet after a year of great sound

[charleskeough]

Hi, I completed the setup of the amp last January and it has been working perfectly. But a few days ago I went to power it on and the right channel is barely audible. First thing I did was confirm that the problem was within the Eros and not my turntable or Stereomour. Second thing was to swap tubes but the right channel stayed quiet. Then I broke out the meter and did the resistance and voltage checks. They all checked out and nothing seemed out of whack there so I'm not sure what the problem could be. Any tips on to how to move forward would be greatly appreciated.

Thanks,
Charlie Weber

[Paul Birkeland]

I would triple check your cables and measure the DC resistance of each channel of your phono cartridge (just measure at the cable ends that plug into your Eros).  If your phone has a headphone jack, you can turn the volume all the way down, then up just one click and feed some music into your Eros with an 1/8" TRS to RCA cable to eliminate the TT entirely from the debugging process.

I recently had a similar issue and it turned out that one side of my phono cartridge was dead.

If all the voltages are OK in the Eros, that leaves solder joints on the inputs/outputs, cables, and the phono cartridge as the primary possibilities. 

[charleskeough]

I just fed some music into the Eros with my phone via the 1/8" TRS to RCA cable and the problem still persists. Just to be sure I broke out a cheap little phono preamp I have and hooked my turntable and Stereomour up to that and the problem is gone, so I definitely think the problem is in the Eros somewhere.

I was wondering if there's a longer list for the resistance and voltage checks because I purchased a Reduction a while back and looking at that manual theres a reading for every terminal. Where as my Eros manual has resistance and voltage checks for just a few of them. I'm guessing that its not necessary but I wonder if with a longer list that maybe a problem could be diagnosed in there?

[Paul Birkeland]

A Reduction will have more consistent resistances in the stock form because it does not have active loads and it doesn't have the big bypass caps that an Eros does.  These parts in the Eros make a lot of resistance readings pretty meaningless, and the resistance readings are really only intended to give the go ahead for voltage checks. 

You very likely have a loose connection or a solder bridge somewhere that is causing the issue.  What resistance to ground do you get on the center pin of each RCA jack?

[charleskeough]

Ok yes that makes sense to me in regard to the resistance checks.

Here's the resistance to ground readings I'm getting from the center pin of each RCA jack.

Right output center pin 469K
Right input center pin 47.1K
Left input center pin 47.1K
Left output center pin 470K

Thanks for all your help so far with this.

[Paul Birkeland]

Nothing wrong there. 

Still, look for loose connections and debris in the amp. 

[charleskeough]

Sounds good, I'll check look for loose connections and debris this weekend and let you know what happens.

[charleskeough]

I figured it out with your help and from a phone call with Doc today. The 6922 tube was the problem. I suppose it was half dead. I replaced the tube and both channels are working as they should.

[Doc B.]

Well done!

[Thermioniclife]

It seems odd to me that replaing the tube helped when you swapped the tubes and the problem did not follow the tube. I would tend to think there is a poor connection on the right tube socket that made connection when wiggled. Or a dirty socket cleaned itself with the tube swaps. I think I would reflow the connections on that socket. Just my 2 cents.
Bet you if you put the old tube back in it will work.

[Doc B.]

The problem was the 6922. There's only one so you can't swap it from left to right like you can the EF86s, you have to replace it with another to test. You may be right that there was a dirty contact.  The direct coupled 6922 is a sensitive spot in this circuit and is always worth checking when there is an issue in only one channel. I have seen replacing a 6922 solve problems a few times over the years.

[Thermioniclife]

I stand corrected, not owning an Eros I am unfamiliar with it's topology.