Unexpected Hum
 

Hello all,

For the first time since July I was going to play a record. I pulled one out at random to test the new settings on my C2300's MM input to see if I got it right (I'm attempting to increase the gain), and noted the hum coming from the right speaker. I turned everything off, went behind the system and the ground cable seemed a bit out of order. I re-seated it, turned the system back on, put the record on again, still had hum but now no music from the same right channel. I hit the Mono button and got sound from both channels, still with hum from the right channel only. The hum goes up and down with the volume.

I turned everything off again, re-seated the power cord on my C2300, and tried again: only hum from the right speaker (unless I engaged the Mono switch). Finally, I tried playing a CD and had no problem. So it appears to be something specific to the TT setup, which hadn't been touched for months, except to turn on the TT now and then.

I thought I'd run this by the forum before being too quick perhaps to replace the tonearm cable (it's an SME 309 arm). If there's something I haven't tried yet that I've missed, perhaps someone here could point it out. Thanks. BTW, I did just think of cleaning the tonearm cable contacts; I will try that tomorrow.

Aren't the phono tubes dedicated in the C2300? You might swap them and see if the hum moves.

Yes they are. The hum sounds very much like ground hum; that it goes up and down with the volume suggests it's in the signal path.

Re-routing the tonearm cable is another idea. And since the cartridge is low output I can use the 2300's MC input as well, and am planning to try that. If things are fine, then I would try swapping the tubes in the MM input, as you suggest. The cartridge (a Grado Timbre Sonata3) plays with either.

If the MC input works, that should eliminate the tonearm cable/grounding as the culprit, leaving either the MM tubes or the input itself. I'm no tech, but that's how it seems to me. Will report back after more tests.

I'd guess that's the problem - a low output cart should go to the MC input.

There are some Grado carts that are noted for having a hum problem on particular turntable/tonearm/preamps. One of the forums has a list of these interactions.

loose connection on the tone arm/cartridge?. Since the signal disappeared, and mono works, I would start there. I did that when installing the Ortofon Black; same symptoms.

Strong possibility :yes:

Okay, I have just completed another test session, and things are closer to normal. BTW, the TT is a Sota Sapphire VI with a SME 309 arm, if that matters; tonearm cable is Van Den Hul. Here's what happened:

First, I re-oriented the turntable's PC so that it doesn't touch or isn't near any other power cords. It did run perpendicular to a couple and may have been touching them. I relocated the TT's power supply recently, which brought its PC much closer to other PCs. Yesterday was the first time I tried playing any records with it in the new spot.

Second, I switched from the MM to the MC input, turned everything on, then raised the volume without a signal to see what I'd get. With my ear about 3 inches from the speaker, I began to hear hum at about step 39, which increased with volume. Then I went back to zero volume, put on the LP and increased the volume gradually; I didn't hear any hum with the volume up to 36 with my ear right up to the speaker.

Third, I turned everything off, moved the phono cables back to MM input, then repeated the procedure. This time, with no signal I began to hear hum at about step 48. Playing the LP again I was up to step 45 and couldn't discern any hum, even with my ear almost on the speaker. I didn't try the "Mono" setting.

While I'm thinking the power cord adjustment is the main contributor to the improvement I heard, I also changed the settings for the two inputs which has gotten me closer to a volume level comparable to my other sources as well as the Sonata3's specs, as best as I understand them. I'll try dialing that in a bit more now that I have an idea of how to do it. And if the hum problem resurfaces, I'll report it.

This would be something to look at as well. I'm used to hearing hiss or something similar at high volume, not (ground) hum. Even though reduced significantly (it seems), the hum isn't gone.

Follow-up: Turned on the C2300 preamp and MC501 power amps today and ran tests similar to yesterday. With no signal, on the MC input I got up to about step 64 before noise became audible at 2 ft. from the right speaker, and up to 53 on the MM at the same distance. There is no, I repeat NO sound coming from the left channel. That has been the case with every problem of this type that I've ever had. Today, the noise was more like what I've heard before, with the hum underneath a static-like noise. I also re-positioned the TT power supply to its original spot, on the floor between the speakers; that accounts for the additional improvement, I think, as it had been sitting next to my cable box.

For reference, my standard listening volume is 42; I will go lower or higher depending upon the recording. And I would never be listening at the above test volumes normally; it would be much too loud and I would be putting my speakers at risk, not to mention my ears.

The tubes in the MM are Telefunken Black Diamond ECC83TK, made by JJ; in the MC stage are standard JJ ECC83s.

On a lark I switched to the Tuner and DVD inputs and went up to volume step 62. Crickets, both channels. The noise is exclusive to phono, and to the right channel on both inputs. That doesn't seem a coincidence. It may be time to try cpetersen's suggestion and check the tonearm cable; if that doesn't solve things, then I open the C2300 up and mess with the tubes. I may repeat the tests in mono mode, too.