Cornet Channels, Mismatched

Doc Jr 8156 · « **on:** 2 Apr 2004, 04:08 pm »

Hello,
Can anyone help me regarding how to fix my Cornet. The left channel is weaker than the right. I tried changing tubes, changing interconnects, to no avail. I narrowed it down to the left channel because when I switch ICs (output) my right speaker will then be the one weaker. However, if I switched ICs in the input, no change. I measured the voltage parameters according to the manual and both channels are fine. Measured all continuity from RCA in to RCA out and they are all fine. I even tried on removing my step-up transformer from the path but still the left channel of my Cornet is weaker than the right. I also aligned my cartridge on my Teres 3x. I swiched R and L tonearm RCAs, same problem. Any ideas? Thank you very much.

Grover · « **Reply #1 on:** 3 Apr 2004, 12:21 am »

I'm a relative newbie, and I always find this sort of thing difficult to figure out. What I would do first is check to make sure that all the resistor values are proper. The second thing I would do is to reheat all the solder joints going to each of the capacitors on the left side, and add a bit more solder to each. Then try again and see if this made a difference.

hagtech · « **Reply #2 on:** 3 Apr 2004, 05:03 am »

A good trick here is to short together the inputs. Cart will still work and both channels have same signal for sure. Maybe you can trace gain of signal through each stage? Then you'll narrow down which section that is different.

My guess is resistor or capacitor value. Maybe in the EQ, because tube bias is ok. Shifting the 3180us corner can have a large affect of gain.

jh

Doc Jr 8156 · « **Reply #3 on:** 5 Apr 2004, 01:42 am »

Grover,
Thanks for the suggestion. I did it. Still the same. When I was upgrading the parts, I was very careful in sustituting one set of resistor or capacitor so the value problem may not exist. This Cornet was fine before, Jim, seriously, I did not understand the last sentence in your comment. I'm not that technically inclined.

I did an experiment though. How come when I used the left channel as the right and the right channel as the left it improved? I have no idea what happened. One day I will get the Trumpet if this thing will not behave itself.

GRD · « **Reply #4 on:** 5 Apr 2004, 04:21 pm »

Doc,

All good suggestions above. Your last comment makes me wonder if the problem is not the Cornet board but something about the connections to and from the Cornet (inputs, outputs, RCA chassis connectors, and interconnects themselves). Your initial description had the left channel consistently weaker but your last post said that the channel strength changed when you swapped connections. I like the idea of shorting the inputs to have a uniform signal to compare channels. I would try the easiest thing first and just swap out interconnects and see if there was a change. Then on to the rest of the chain.

C7 is the first part of the equilization circuit and is responsible for the initial (in this case 3180us) signal shaping. Some of the signal coming from V1 is removed (sent to ground) via R9 and R13 through C7. If the R9, R13, and/or C7 values are off, the signal sent to ground through C7 can begin to occur earlier (or later) than we want so less (or more) signal makes it to V2 for the next stage in amplification. Small changes here can make for bigger changes in signal later.

Regards,

Grant

Doc Jr 8156 · « **Reply #5 on:** 5 Apr 2004, 04:53 pm »

Grant,
Thanks for the reply. I'll check them out later and report on the progress. By the way, I used 4 different interconnects and swap L to R and vice versa. Same result. Last night I re-solder every single connection including all caps and resistors and re-checked the values of each. I hope it will improve, for I finished so late last night that I never had the chance to listen. Will report back. Thanks again. Godspeed.

hagtech · « **Reply #6 on:** 5 Apr 2004, 07:00 pm »

My confusing comment on the 3180us corner - is that this is the low 50Hz turn and basically can have a large affect on overall gain if positioned incorrectly. The entire frequency response curve shifts up or down in gain. A bad EQ value in one channel might recreate your problem.

So is your low gain channel consistent? Or can you sometimes get it balanced?

jh

Doc Jr 8156 · « **Reply #7 on:** 6 Apr 2004, 03:10 pm »

Jim, GRD thanks a lot. problem solved. It was a grounding problem. basically I removed all ground leads from the PCB except the center one and star-ground all (-) from the RCAs to the central ground. My Cornet is now singing beautifully. Quieter than ever and channel balance returned. I think this qualifies as a tweak because I never heard this Cornet as quiet as this, ever. Thanks. Godspeed.