[robertwstephens]

Hello!  I am trying to get the last bit of buzz out of my Clarinet/ DIY ST-35 combo.  I think I I have eliminated any ground loop issues.  I only have a cd player hooked up to the unit right now.  I am getting a low level hum.  It hums a little more in one channel than the other.  The hum stays the same when I turn the volume up through normal listening levels.  When I go past that, the hum I get increases in volume as I turn the knob clockwise.  I have changed tubes and played around with lifting the ground.  I have shielded IEC cables, shielded inteconnects and a Isobar power filter.  I am not sure if this is the Clarinet or if the Clarinet is just amplifying something going on with my DIY St-35.  I did finally figure out that this combo did not drive my multi-driver speakers well.  It sounds really nice on single driver monitors.  Any input would be appreciated.  Peace.  Robert

[hagtech]

Do you still get the hum with the CLARINET turned off?  Sounds like maybe part of the chassis is not grounded.  Or perhaps the RCA jack shields are not insulated from chassis.  Can you post a photo so we can take a look?  Does it hum without any inputs? 

jh

[robertwstephens]

Hello!  When I turn the Clarinet off, the buzzing stops and then comes back in about 20 seconds.  The buzzing/hum does not change when I have no inputs into the Clarinet.  Here are some pics below.  Thanks for the help as always.  Peace.  Robert

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=703&pos=0

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=703&pos=1

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=703&pos=2

[hagtech]

Photos look ok.  Does it buzz with clarinet disconnected? 

jh

[PatOMalley]

there waws a comment previously that said that gouding did not take place for the RCAs untill you remove the paint and get the connector in contact with the bare metal. just a guess.

[ohenry]

I have a similar low-level hum issue with my Cornet2 and I may have inadvertently discovered why.  BTW, I have the Clarinet and Chime as well, and they are quiet.  They all use the Hammond P-T370BX transformer.

After exhausting eliminating hum through shielded cables, external grounding wires, tube swapping, etc., I decided to conduct a little experiment by holding a piece of folded aluminum foil in various postions around the transformer.  It was at that time, I noticed a slightly audible crackle when the foil contacted one of the transformer screw heads and the transformer housing simultaneously.  I tried the same foil action on the Chime (the quiet product) and there was no noise generated from the contact.  Now I'm thinking that maybe the Cornet's transformer is faulty and should be replaced.

Jim, does this seem plausible? 

[robertwstephens]

The ST-35 hums with the inputs shorted.  I was wondering if a grounding mistake I made with the Clarinet was causing the hum.  I did scrape the chassis where the grounding lug attaches to the case.  It sounds like the Clarinet is fine and the ST-35 is my problem.  Is there a way to test transformers for hum?  Peace.  Robert

[analog97]

FWIW, I've always had some level of hum when using a phono pre-amp.  I dunno.  I just dunno what causes it.  I have used all kinds of CD players, from el-cheapo thru expensive SACD and NEVER had hum.  I use a Clarinet and Cornet2 front end.  I have no reason to think they are the culprits.  There may be something to a)lots of wires running all over the place and or b) something about the 100+ fold amplification of a phono pre-amp that somehow picks up a "signal"....I am paying attention to all  "hum-busting" posts.  If I can get my Cornet2/Clarinet as hum-free as the rest of my system, I will rest in peace....

[hagtech]

Hum is not easy to fight, and usually a system-wide issue.  Indeed, with wires and grounds going all over the place, transformers everywhere, it can be a nightmare.  Not supposed to happen, but sometimes it does.

As for the tranny, it can help if the bells connect to chassis.  Scraping a little paint off the corner foot and chassis can help with the connection.  If by touching the tranny and chassis at same time with your hands makes for a quieter signal, than that is the problem.  Sometimes that is the easy way to track down a hum.  Just use the finger test.  Skin conductance from a known ground to a questionable point, like another part of the chassis, or an RCA shield, can point to a loose connection.

If the ST35 is humming wihout an input signal, start there.  Get that machine quiet first.  Then we can start adding more to the mix. 

jh

[robertwstephens]

Thanks for taking the time to reply Jim!  I am definitely excited about building a piccolo.  The hum busting has been a valuable learning exercise for me.  The strange thing is, I can turn on the amp and have hardly any hum and then shut it off and turn it back on and have a moderate amount of hum.  I group tube stereo equipment in the same category as vinyl.  It is definitely quirky, but worth the time expended.  Peace.  Robert

[robertwstephens]

Hello Again!  After lots of emails with a couple of engineer types and lots of playing around, my ST-35 is dead quiet with shorted inputs.  I borrowed a co-workers amplifier and I am getting a decent amount of hum from my Clarinet.  I have lifted the ground with a little bit of improvement.  Is there any harm in reversing the AC mains coming into the Clarinet?  Any other tips would be greatly appreciated.  Peace.  Robert

[hagtech]

No harm reversing ac lines.  I would not recommend lifting ground.  The hum is likely from some other cause.

jh

[robertwstephens]

Hello!  Thanks for taking the time to respond.  I hooked up a volume pot on the ST-35 with excellent results.  I think I am going to convert my Clarinet to a Cornet II and give it to a friend who is in awe of my Cornet II.  I will order the Cornet II board from you in the near future.  I think I can do this with a minimum of new parts needed.  I have really enjoyed the process as always!  Peace.  Robert