• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Another Maggy Thread

Well I am about to the point of tearing this thing apart and starting over, maybe with alittle different layout and using the p/s Keg proposed. I am going to try a different power trans. first just to rule that out. Different opt made no difference in the hum level. Gotta try a couple of other things first too. I wonder if the layout on my individual " circuit boards " is contributing to the hum. I usually have pretty good results building this way although sometimes it makes trouble shooting and mods. kinda difficult. Stan
 
Before you go an tear apart to redo things, can you move the choke to a different
location, as you mentioned the humm did deminish? It may just be in an area that's
to close to the signal with it's open frame design.

Just a thought..
 
Keg, I did move it to another position and that is when the hum decreased somewhat but there is still way too much. There are still a couple of other things I want to try when i get time. Thanks for the ideas... I'll get it straightened out eventually( hopefully!) Stan
 
Do we have a shot of your layout? Sounds like you may need to rotate some stuff 90 degrees maybe. Hum sucks, but it can always be solved.:yes:
 
Jay, Pics are back at post 250. (Choke has been moved, wires to inputs have been changed to shielded wire. I have rotated opt's w/ no change. Made sure input jacks were isolated, speaker jacks are definately isolated, tried different opt with no change, re-soldered ground pts, created center-taps for heaters with 100 ohm res., tried different choke, connected another cap acrosseach cap in p/s, and moved around any wire i could) all with no/minimal change to hum. Gonna try a different power tranny and see what happens. I appreciate all the replies.. Stan
I will post some voltage readings soon I'd like you and/or Kegger to have a look at to give opinions....
 
Last edited:
Here is the way everything is grounded: (looking at keg's schematic and the underside of amp pic for ref.)
On the white circuit boards, the 2 27k res, the 6gk6 cathode res. and the 100pf cap on the 12ax7 share a grnd pt. which then runs back to star ground at power tranny.
on red circuit board, the 330k on the input, the 1000pf cap and the 100ohm and 3.6k res. all share a gnd pt.( one pt. per channel). Both channel gnd pt.s are joined and run back to the star gnd.
All other gnds run to the star gnd.
Do ya'll see anything extremely faulty with this? (except maybe the 100pf gnd should be different.) Thanks.... Stan
 
Dumb question, but do you have the output TX negative secondary grounded? I've forgot to do it before, and the amp will work, but humm like a dickens.:scratch2: I can't see quite low enough on the underneath pic in post 250.
 
Hey Jay, Yes it is grounded and no suggestion for me to look at is dumb...sometimes i overlook the smallest/simplest things. This problem has been a "Hum-dinger". I am gonna try a different power tranny today if i can and if that doesn't change things i am going to let the project sit for awhile and come back to it later. Maybe something will pop out at me then. If you think of anything else to try let me know....Thanks, Stan
 
I just built a frame/base for mine with salvaged pieces of wood from the amp's console. Pictures to come later.
 
stanbp64 said:
Hey Jay, Yes it is grounded and no suggestion for me to look at is dumb...sometimes i overlook the smallest/simplest things. This problem has been a "Hum-dinger". I am gonna try a different power tranny today if i can and if that doesn't change things i am going to let the project sit for awhile and come back to it later. Maybe something will pop out at me then. If you think of anything else to try let me know....Thanks, Stan
Click to expand...

Cool, just for the record, it's a low hum in both channels with the inputs grounded or not.:scratch2:
 
stanbp64 said:
Here is the way everything is grounded: (looking at keg's schematic and the underside of amp pic for ref.)
On the white circuit boards, the 2 27k res, the 6gk6 cathode res. and the 100pf cap on the 12ax7 share a grnd pt. which then runs back to star ground at power tranny.
on red circuit board, the 330k on the input, the 1000pf cap and the 100ohm and 3.6k res. all share a gnd pt.( one pt. per channel). Both channel gnd pt.s are joined and run back to the star gnd.
All other gnds run to the star gnd.
Do ya'll see anything extremely faulty with this? (except maybe the 100pf gnd should be different.) Thanks.... Stan
Click to expand...

Any thoughts on this???
 
Nothing jumps out at me Stan.

The way I usually wire amps, is the entire front end is grounded at one spot, then that
is run back to where the power supply is grounded, seems to keep the amps nice n quiet.
 
Ok, thanks Kegger.... just feeling for what i need to differently if i re-do this amp. A different power tranny did make alittle difference. I think I'll go with your psu on the re-do except work it out with a 5v4g. It'll be awhile before I get to it tho. Thanks!
 
JUst Won't die!

OK, gonna keep this thread alive alittle longer. Never could find the cause of the hum in my Jay-Kegger-ized 9300 so I decided to tear it apart and start over with a new layout and use keg's suggested p/s. Just getting started and it'll take awhile to complete, but I thought I'd post a few pics as I make progress. Wish I would learn not to cut component leads so short so I could re-use more of them! (I'm a cheapo). I've got power-supply hooked up, except lines to the front end, heaters are done, and alittle more. Can't decide if I want inputs on top plate or connected to enclosure. Stan
 

Attachments

  • 9300amp 003.jpg
    9300amp 003.jpg
    115.4 KB · Views: 89
You must log in or register to reply here.
Back
Top Bottom