how to remedy a noisy transformer?

[km-r]

I constructed this stereo amplifier with two EL84 in SE triode mode fed by a SRPP 12ax7 gain stage. When the amplifier is turned on, a high frequency motorboating noise and an underlying 60hz hum is heard from the headphones. I used a rather large main filter capacitor 330uf. I traced the root of the problem from the preamp to the power amp then the filter caps then rectifiers then transformer. When the amp is turned off the capacitors let the amp operate for about 5 seconds before emptying the filter caps this turn off phase makes the amp run very quiet [no hum/motorboating].

Now about the power transformer, I rewound the transformer myself from recycled low voltage transformers. Secondaries are 220vac/100mA and 6.3v/3A. I have installed bell caps which were grounded and now I don't know what to do. Below is the uhhh flowchart/details of the powersupply section.

Transformer HT – 1n4007 bridge rectifier each bypassed with a 4n7ceramic  cap – 150ohm WW resistor – 330uf/400v + 100n/630v capacitor – 100ohm WW resistor – 250V MOSFET regulator – 100uf/400v capacitor – power amps

How do I remedy a noisy transformer?

[geertjacobs]

Hum can have lots of causes:

- Is the power transformer placed as far away as possible from the output transformer?
- have you rotated your output transformer 90 degrees from the power transformer to reduce magnetic coupling between the two?
- have you referenced your 6.3V heaters to ground using the center tap or 2 x 100Ohm resistors?
- did you use a starground?
- did you use insulated input/output connectors?

A picture of your chassis could help.

edit: added more questions

[geertjacobs]

When a push-pull amp squeals it can also be caused by reversed primaries of the OT causing the negative feedback loop to become a positive feedback loop.
You can try reversing the primaries of the OT.
Also, did you ground your output transformer secondary?

[km-r]

thank you for your reply, kind sir.

sorry i left a lot of info out.

its a stereo headphone amplifier with EL84s wired as output transformerless cathode follower triodes.

yes i did a starground on the main filtercap's ground lug.

the filament is dc filtered.

im so stumped on this... im thinking my transformer is the culprit 

[amptramp]

Do you run any of your input or high-impedance wiring anywhere near the transformer?  Is is a true 60 Hz or is it the buzz of a rectified 60 Hz?

[km-r]

there is 60hz hum though no as loud as the motorboating, like a tzzzzzzz sound. its like the raspy fuzz you hear when you click on your dr.boogey or similar highgain distortion. even when i ground the input and other input grids the noise is there. 

of course thats a bit okay for guitar but for a music amplifier its very stressful to listen to.

[R.G.]

(1) does the transformer hum/buzz all by itself when not in the amp?
(2) is the transformer potted or impregnated with varnish?
(3) is there any chance the transformer is arcing internally?
(4) does the transformer high voltage CT go to the first filter cap (-) terminal ONLY? Nowhere else?
edit:
Forgot: Power transformers do not cause motorboating. That's something else.

[km-r]

thank you for your reply mr R.G.,

(1) no buzz
(2) no varnish, i wound the transformer myself
(3) i dont think arcing would cause a continuous noise. theres a thick cardboard insulation between the primary and secondary winding
(4) theres no CT, i used a bridge rectifier.

any other point where i should look into mr RG? bad tube?

and uhh, do you get the idea of the noise im referring to? like a tzzzzzzzzz-ish sound. its a 120hz sawtoothish sound.

here are some pictures of my newbie build and the schematic.

the wires are to be cable-tied when the issue has been resolved. i think i still have lots of cutting to do before it will be tied down.

outside. the chassis is from an old-school modem


schematic [i forgot to label the 12ax7 and el84]

[Minion]

I actually find it better to referance the heaters to about 25v  ,you can use the Cathode of the output tube to referance the heaters or use a Voltage divider from B+ ........