Welcome, Guest. Please Login or Register
Decware Audio Forums
10/31/14 at 00:35:46


Pages: 1
Send Topic Print
Hum Question -- not a big deal, though (Read 1958 times)
SMB1968
Verified Member
**




Posts: 21
Hum Question -- not a big deal, though
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
Back to top
 
 
  IP Logged
Rivieraranch
Seasoned Member
****




Posts: 1274
Re: Hum Question -- not a big deal, though
Reply #1 - 08/10/13 at 17:20:37
 
I am only guessing, maybe the pot is bad. It should not do that.
Back to top
 
 

DECWARE CSP2+, TABOO MK III; SE84CKC; HR1; TRAPEZIUM DESKTOP SPEAKERS; TECHNICS SL1200MK5 turntable; Ah! Njoe Tjoeb CD player; MARANTZ 2226B, 2216B receivers; SENNHEISER HD-580 headphones
  IP Logged
SMB1968
Verified Member
**




Posts: 21
Re: Hum Question -- not a big deal, though
Reply #2 - 08/14/13 at 14:58:09
 
Thanks Riv.  It has the stepped attenuator, is it safe to use DeOxit on them?
Back to top
 
 
  IP Logged
hifitubes
Seasoned Member
****




Posts: 201
Re: Hum Question -- not a big deal, though
Reply #3 - 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...


Back to top
 
 
  IP Logged
Lonely Raven
Seasoned Member
****


Jack of all Trades,
Master of None

Posts: 1439
Re: Hum Question -- not a big deal, though
Reply #4 - 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.
Back to top
 
 
WWW Lonely Raven   IP Logged
hifitubes
Seasoned Member
****




Posts: 201
Re: Hum Question -- not a big deal, though
Reply #5 - 12/31/13 at 08:00:55
 
Back to top
 
 
  IP Logged
hifitubes
Seasoned Member
****




Posts: 201
Re: Hum Question -- not a big deal, though
Reply #6 - 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."
Back to top
 
« Last Edit: 12/31/13 at 08:11:52 by hifitubes »  
  IP Logged
hifitubes
Seasoned Member
****




Posts: 201
Re: Hum Question -- not a big deal, though
Reply #7 - 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.
Back to top
 
« Last Edit: 01/01/14 at 05:34:43 by hifitubes »  
  IP Logged
seikosha
Senior Member
***




Posts: 52
Re: Hum Question -- not a big deal, though
Reply #8 - 01/02/14 at 00:39:31
 
Lonely Raven's observation about the different resistors was interesting.  Anyone have any idea about that?
Back to top
 
 

Mini Torii, SE84CKC, Omega Super3XRS, Oppo95 as Transport, Shiit Bifrost UBER Dac, PS Audio P3 Powerplant
  IP Logged
hifitubes
Seasoned Member
****




Posts: 201
Re: Hum Question -- not a big deal, though
Reply #9 - 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.
Back to top
 
 
  IP Logged
hifitubes
Seasoned Member
****




Posts: 201
Re: Hum Question -- not a big deal, though
Reply #10 - 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?
Back to top
 
 
  IP Logged
shold350
Verified Member
**




Posts: 18
Re: Hum Question -- not a big deal, though
Reply #11 - 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.    
Back to top
 
 

Decware SE34I.3 Rachael amp, CSP3, Denon 300F TT with Ortofon 2M red cartridge, Oppo BDP 105,HSU Mid Bass Module 12 MK2, HR1's, Decware ZSTYX speaker cables, Decware silver reference interconnects, LG 60" plasma
  IP Logged
hifitubes
Seasoned Member
****




Posts: 201
Re: Hum Question -- not a big deal, though
Reply #12 - 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.
Back to top
 
« Last Edit: 01/07/14 at 18:36:41 by hifitubes »  
  IP Logged
Pages: 1
Send Topic Print