C2700 Possible Issue

[dkorbal]

I came back from our short getaway to Maine to find or better yet HEAR a hissing noise coming from my left channel. After investigating I thought I found the problem a partial broken banana plug going into the upper terminal of the speaker. Five minutes later and a new threaded post replacement did not correct the problem. Here are my findings:
1. Swapped speakers left to right and right to left. The hiss remained in the left speaker.
2. Swapped XLR left and right coming out of the mains in the C2700. Hiss moved from left to right.
3. After swapping XLR back and hiss moved back to left I noticed a bump in volume coming from the right speaker. Further investigation revealed the left channel meter was about 8 to 10 db less than the right channel. Balance control was at nul or in the middle.
4. Called my dealer and McIntosh tech and I expect some answers next week but first guess is a tube problem according to my dealer but the McIntosh rep who lives locally near me said the tubes for the mains are NOT left and right but one on the input side and one on the output side.
5. Here is something wired. I run bi-wire on the speaker terminal, when I disconnect one of the plugs going to the terminals that are on the inward side (one red, one black) the hiss goes away. If I disconnect the outer one the hiss remains. Again swapping speaker had no affect.
6. I changed the WW SE 7 Eclipse for a standard cable with jumps and it had no affect. Hiss remained.
7. All inputs on the C2700 exhibits the hiss in one channel only left side.

Any guesses? Question?

[W9TR]

You can swap the phono preamp tubes for the main tubes. That will tell you if it is a tube problem.

[dkorbal]

Thank Tom. I had planned today to do just that when my dealer called and asked me to bring it in. He is going to swap tubes and see if that works. I’ll keep everyone posted.

[W9TR]

Sounds good. Probably a tube. You might want to get a replacement set just to have as a backup. I do this for all my tube gear and it has paid off in uninterrupted musical enjoyment!

[cleeds]

Originally Posted by W9TR

... You might want to get a replacement set just to have as a backup. I do this for all my tube gear and it has paid off in uninterrupted musical enjoyment!

+1.
Having spare tubes on hand is like having money in the bank. Sooner or later, you're going to need 'em.

[UFTE]

This is a bummer Doug, and hopefully an easy fix! Do keep us posted.

-Ryan

[TWInsall]

Now you know why I gave up on tubes is 75. The two 275's went first and then the C-22 and MR 71. I should have kept the 275's longer. I really didn't like the sound of the 2100's. or the 2200's or 2250's. Thats why I went with Crowns till the MC 7200 came along. It was the first Mac SS amp I liked for my speakers. I used the other Macs for commercial installations with no objections at all.

[dkorbal]

Hey everyone. Just wanted to give a quick update. Just got my C2700 back from the dealer after they replaced the tubes which seemed to be the problem. I personal cannot confirm this since I am waiting to hook it back up. I'm waiting on cabinet hardware so I can rearrange my equipment configuration. I want to place the preamp on the top for better air flow. Just in case that was the reason for the tube failure.

One question I do have is if I replace tubes do I need to replace them all? The C2700 has six tubes: (2) R/L MM phono, (2) R/L MC phono, and (1) Input Main, (1) Output Main. Most of my listening (90%) is digital and when I do listen to TT I have a MM cartridge.

[Fbgbill]

I have the C2600 which I bought as a store demo. I have considered buying some replacement tubes as backup. I would think it is best to replace all of them at the same time. There are 5 12AX7 and 1 12AT7. I am getting Genelex Gold Lion as my backup set. I looked around and found the Tube Depot seems to be the best deal. You can get them matched and balanced as well for $4 per tube it that is important to you. FWIW

[W9TR]

Originally Posted by dkorbal

Hey everyone. Just wanted to give a quick update. Just got my C2700 back from the dealer after they replaced the tubes which seemed to be the problem. I personal cannot confirm this since I am waiting to hook it back up. I'm waiting on cabinet hardware so I can rearrange my equipment configuration. I want to place the preamp on the top for better air flow. Just in case that was the reason for the tube failure.

One question I do have is if I replace tubes do I need to replace them all? The C2700 has six tubes: (2) R/L MM phono, (2) R/L MC phono, and (1) Input Main, (1) Output Main. Most of my listening (90%) is digital and when I do listen to TT I have a MM cartridge.

No need to replace all the tubes at the same time. For example I keep the original tubes in the sections I don’t use and replace the tubes in the sections I do use. Ultimately I know I will have to replace the tubes in the sections I don’t use, but I will put that off for as long as possible. I have a C 2300.