Slight hum with C500T

[jbaudio68]

Hey everyone.

I'm demoing a C500t against my 2500 and 2301 amps. I noticed a slight hum when the volume is up past 45. It is not discernible from my sitting position but I do hear it if my ear is close to the speaker(s). I checked the ground and the connections-- they are tight. The hum does not occur with other sources. Any suggestions on what it could be and/or how to fix? Perhaps adjust gain or something?

Thx for your input.

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[jdandy]

Jeremy.......I am assuming you mean your source is your turntable, right?

[jbaudio68]

Originally Posted by jdandy

Jeremy.......I am assuming you mean your source is your turntable, right?

Dan, you are correct. To clarify, the hum only occurs when I have Phono MC selected (VPI Classic 3 with Denon DL103-R cart.

AMR DP-777, VPI Classic 3, McIntosh C2500, 2301 (2), PMC IB2S (2), JL Audio f112 (2)

[jdandy]

Jeremy.......Lets try a little process of elimination. Try disconnecting the turntable interconnects and the ground from the C500. Is the hum still there when the volume is raised? If yes, then it may be an issue with the phono stage tubes. Try swapping the MM phono stage tubes with the MC phono stage tubes.

If the hum is not present with the turntable interconnects disconnected try connecting only the interconnects from the turntable without the ground wire connected. Is hum present? Louder than with the ground wire connected? Land the ground wire to the ground terminal on the C500. Does the hum drop in volume or grow louder?

Do these things and let me know what happens.

[jbaudio68]

Hi Dan. Here's what I have so far:
- hum is still present but less without interconnects.
-the ground attached seems to lessen the hum a bit
- the cables (ww silver 7) seem to add/lower level of hum as I adjust connection-- swapped out with diff set of cables-- less hum but hum still present

Pre is located in cabinet --tight fit-- so cables may flex a bit. However, not an issue with the 2500 -- to my knowledge

Constant seems to be buzz -- regardless of cables/ground

Makes sense to swap tubes next, right?

On other note, even with slight hum-- which again cannot be heard from sitting position-- c500 is really nice sound-- even with only two hours on it. I'm definitely getting a little more out of my system in terms of control, space, separation and dynamics. Jury is out on C500 and 2500 for me still.

Again, Thx for your insights.

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[o0OBillO0o]

[Golucid]

Yikes! Holding off on that C500 order. Very curious as to how this all sorts out.

[jdandy]

Jeremy.......Thanks for going through those steps. I am wondering if it is actually a hum you are experiencing or the rushing type sound often referred to as tube grid noise. The reason I mention this is because I experienced tube grid noise in the MC phono stage on my C1000C/T preamp at a volume level of about 35 with the stock McIntosh tubes. It would get progressively louder as I raised the volume and was objectionable at 45 on the volume. I swapped the factory 12AX7's for Telefunken ECC83 smooth plate tubes and was able to raise the volume level to 48 without a signal before I began to hear the rushing sound in the background. With a moving coil signal playing I could not hear the grid noise except between tracks. I moved the C1000C/T to the living room system and the C1000C/P solid state preamp to the studio system. The phono stages in the C1000P, both moving magnet and moving coil, are dead silent at all volume settings. Eventually I sold the C1000C/T and replaced it with the single box C2300 tube preamp. The tube phono stage performance is on par with the C1000T and grid noise was improved with the Telefunken tubes versus the factory tubes.

Something else you might consider, try adding an additional ground wire from the C500 ground terminal to your amplifier. For testing purposes you don't have to attach the ground wire to the amp, just touch it to the chassis to see if that reduces the hum.

What are your power sources for the turntable, preamp, and power amplifier(s)?

[Golucid]

Originally Posted by jbaudio68

"...I'm demoing a C500t against my 2500 and 2301 amps."

I can not wait to read your review, jbaudio68. I have 4 and soon to be 6 MC2301s and a C2500 and considering the C500 + T. You are in the dream position. Again, I can no not wait to read your thoughts. This shall be so helpful in determining if I buy or not-buy.

[jbaudio68]

Originally Posted by jdandy

Jeremy.......Thanks for going through those steps. I am wondering if it is actually a hum you are experiencing or the rushing type sound often referred to as tube grid noise. The reason I mention this is because I experienced tube grid noise in the MC phono stage on my C1000C/T preamp at a volume level of about 35 with the stock McIntosh tubes. It would get progressively louder as I raised the volume and was objectionable at 45 on the volume. I swapped the factory 12AX7's for Telefunken ECC83 smooth plate tubes and was able to raise the volume level to 48 without a signal before I began to hear the rushing sound in the background. With a moving coil signal playing I could not hear the grid noise except between tracks. I moved the C1000C/T to the living room system and the C1000C/P solid state preamp to the studio system. The phono stages in the C1000P, both moving magnet and moving coil, are dead silent at all volume settings. Eventually I sold the C1000C/T and replaced it with the single box C2300 tube preamp. The tube phono stage performance is on par with the C1000T and grid noise was improved with the Telefunken tubes versus the factory tubes. Something else you might consider, try adding an additional ground wire from the C500 ground terminal to your amplifier. For testing purposes you don't have to attach the ground wire to the amp, just touch it to the chassis to see if that reduces the hum. What are your power sources for the turntable, preamp, and power amplifier(s)?

Dan, this is really helpful... It sounds like the same issue as I only hear the hum as the volume is turned up past 30-- readily distinguishable around 55. I'm using GL tubes which helps diminish the hum a bit I'm sure.

I'm having my reseller look into grid noise and will try the extra ground. As for my power sources, I'm using RGPC 400 x 2 with ww 7 PC for everything but TT. It is worthy to note that I do not remember hearing hum with 2500. 500 SS may be next step but am curious to resolve this for my system and perhaps for others who may benefit.

Last note-- I agree that I do not hear him during playback or even between songs. This is me wanting the unit to meet performance/cost requirements. One thing is clear-- as we attempt to climb the ladder the complexity of our units seems to increase as well.

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