Forums https://www.decware.com/cgi-bin/yabb22/YaBB.pl EQUIPMENT FORUMS >> SE34I.5 >> Hum Question -- not a big deal, though https://www.decware.com/cgi-bin/yabb22/YaBB.pl?num=1376095653 Message started by SMB1968 on 08/10/13 at 01:47:33

Title: Hum Question -- not a big deal, though Post by SMB1968 on 08/10/13 at 01:47:33 I have my Rachael hooked up to a CSP2+ and run the Rachael's volume wide open.  Tonight I noticed a hum from speakers, which went away as soon as I dropped the attenuator on the Rachael down 2 notches.  Again, this is no big deal -- and remedied by this slight adjustment -- but does anyone have a guess as to why it would only/what causes hum when wide open? Scott

Title: Re: Hum Question -- not a big deal, though Post by Rivieraranch on 08/10/13 at 17:20:37 I am only guessing, maybe the pot is bad. It should not do that.

Title: Re: Hum Question -- not a big deal, though Post by SMB1968 on 08/14/13 at 14:58:09 Thanks Riv.  It has the stepped attenuator, is it safe to use DeOxit on them?

Title: Re: Hum Question -- not a big deal, though Post by hifitubes on 12/30/13 at 04:56:26 I have a straight Rachel, and after months of tweaking power in my house, I have quite a bit of hum. I can't hear it from the sweet spot, but it's more than I ever remember any Decware amp having. It might be a design trade-off, the grounding scheme on these amps is unique, to me at least...

Title: Re: Hum Question -- not a big deal, though Post by Lonely Raven on 12/30/13 at 17:07:17 What a beautifully simple amp! Great photo by the way, I could practically build it from that photo! The floating ground is pretty common in point to point amps. I'm wondering why the left and right filter sections have different resistors in there... Also, it's been mentioned to me recently that DC on your 120v outlet will cause the transformers and even the tubes to resonate. Some power line filters deal with DC, and some don't.

Title: Re: Hum Question -- not a big deal, though Post by hifitubes on 12/31/13 at 08:00:55

Title: Re: Hum Question -- not a big deal, though Post by hifitubes on 12/31/13 at 08:08:40 OP, can you check that your amp: all (4) +/-speaker terminals and the - RCA short to the IEC ground and each other? steve pinged me that "The resistance of the output transformer secondaries is less than 1 ohm, so many meters would read that as a short when in reality it is not.  I don't think there is anything wrong with your amp or safety issues that should prevent you from continuing to use it and trace down the noise problem."

Title: Re: Hum Question -- not a big deal, though Post by hifitubes on 01/01/14 at 05:30:38 I have come to the conclusion that this amp is relatively quiet after testing with a Bel Canto SS amp last night using both balanced and SE. Bel Canto XLR = low-level hiss with oscillating harmonics (power supply noise?) Bel Canto SE = low-level hiss with oscillating harmonics + buzz  (power supply noise?) Decware EL34 = low-level hum The amplitude of all of these on 98db/w speakers is very similar with the Bel Canto possibly being louder especially in SE mode. Overall, the low-level hum is quieter and isolated to 60hz and some harmonics, and would seem to have less affect on the speaker's performance imo,  because there is no power supply noise whatsoever. I tried grounding the chassis of my DAC to the transformer mounting on the Decware with no improvement, and measured 0 mvDC on either component anyway.

Title: Re: Hum Question -- not a big deal, though Post by seikosha on 01/02/14 at 00:39:31 Lonely Raven's observation about the different resistors was interesting.  Anyone have any idea about that?

Title: Re: Hum Question -- not a big deal, though Post by hifitubes on 01/05/14 at 01:45:59 With shorting plugs the low-level hum is still there. It's not too bad on my 98db/w speakers but I wish I could eliminate it. I measure it at 40dba within a foot whereas the acoustically treat room is 33dba.

Title: Re: Hum Question -- not a big deal, though Post by hifitubes on 01/05/14 at 03:03:08 Would some kind of drain wire work from the transformer to ground? Can anyone else test theirs with shorting plugs?

Title: Re: Hum Question -- not a big deal, though Post by shold350 on 01/07/14 at 16:16:05 I have run into what seems to be somewhat of a common problem. I am getting some pretty noticeable hum.  I only have two sources coming from my Decware input selector box into the amp. One is a Denon turntable and the other is an Oppo 105 BDP. When I remove the interconnects from the Oppo the hum is eliminated. All of my components are run through a low dollar surge protector which is going into a standard wall socket. I have tried switching plugs around. Moving the Oppo/Amp off of the surge protector individually and plugging them directly into the wall with no change in the hum (didn't really expect to make a difference). I don't have the budget to have a special circuit created just for this room or the buy any exotic type of power conditioner. Any suggestions as to a reasonable remedy would be welcomed. I have a Rachel amp and have read in the forum that their may be a difference in the grounding on these compared to other Decware amps. I am no engineer and don't know if this actually accurate just trying to get it quiet. I have also noticed that dvd soundtracks do not play as loud as music cd's. Having to turn up the volume to play some concert dvd's just makes the humming a larger problem. I spoke to Steve about this issue and he has sent me some 6N2P input tubes to bump up the gain.

Title: Re: Hum Question -- not a big deal, though Post by hifitubes on 01/07/14 at 18:34:48 I'm wondering if you have more of a ground loop issue. You are using 94db/w speakers? I've told Steve that while I'd like to get rid of the remaining hum, it is very quiet, and comparing to a SS Bel Canto amp...MUCH quieter! There is no PSU hash or tweeter hiss, nothing spurious, just very low-level hum. I'm close to forgetting about it until I test out my Mini-Torii which should be here soon. I'm troubleshooting some other electrical issues in the house regarding DC current.

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