"fisss" on the 6C33C-pp

[felixx]

I finish my project ...an pp with 6c33c....this is the schematic:
http://translate.google.com/translat...schreibung.htm
But...I have a problem....the noise...is not "humm"....is "fissss".
I replace some C's.....more close to 470uf/450V and the little "hummm" was disappeared.....but I still have that "fisss".All the ground wires was strictly the same like in the original project.From each plate is only one single ground wire,exactly like is in the pictures,and all connected in only one point,to the chasis.
That "fisss" is hear by some 7...10cm from the speaker(an 85db/m speaker).....and it's fine ........but when I connect an 96db/m speaker,the situation is not so good.The noise is detectable from about 1,8 meters.It's only "fisss" but it is and is not depend from volume level.
So ....do you have any ideeas how can I remove that ?
Many thanks.

[Giaime]

Are you sure you are using metal film resistors all the way? Standard carbon film resistors (or worse, carbon composition) DO have higher hiss (by the way, "hiss" has some deeper technical explanation, maybe this is interesting for you).

[felixx]

I removed all the "humm"...simply by replace some values of filters and "pi" filters but that not reduce the "fisss".That noise is not a problem for the 85-87db speakers......but for the 95-100 db is a pain in the a**.
Tomorow I want to work a little on the 400V power supply ...to replace regulator with fast switching diodes with parallel 4,7nf.....and see what happens.
If you have any experience in that issue please explaine.
I know .....the problems with noise rezistors.....but maybe that power supply was not sufficient filter....
Any ideeas.......?

[SY]

Put a wide-bandwidth oscilloscope on the output with the speakers connected. You might have ultrasonic oscillation.

[felixx]

So what do you think was that cause?.........the output trafo?

[wfmali]

Did you run it without the pre-tubes? Did it still "fisss"? The power supply for the final stage looks fine to me-quite some effort here for PP - but maybe you hear some "switching" noise from the rec diodes?
Anyway - would also eMail Ernst directly and ask him, if nothing else,
cheers,
Marcus

[felixx]

I run it without the pre-tubes.....the "fisss" is gone.So....the pre-tubes plate may be the cause.
I write to Ernst Roessler ....the owner .....but nothing.

[felixx]

What do you think about this filter?
Do you think that make some good results for tube amps?

[kevinkr]

In regards to the input noise you are experiencing, are you using high efficiency loudspeakers?

Is it just a simple hiss (more or less white noise) or does it include lower frequency rumbling, burbling, popping and the like?

If you are using carbon resistors as plate loads you may want to reconsider.. MF and non-inductive wirewound are much quieter.

Also some 6SL7 are quieter than others, so you may want to try some different brands.

I have rarely used a commercial rfi filter that did not seem to have a negative impact on the sound, (And I'll admit I don't know why) yet by the same token similar devices I've built or borrowed using air core inductors and low esr/esl film caps seemed helpful in electrically noisy environments.

[felixx]

Yes...I have 97db speakers.The noise is clean ...no pups or everything.
I replace some rezistors but not all from the tubes plate and the noise(that fiss and a little 50hz from the mains) is detectable only from 25cm between ear and speaker.Is a poor noise but is.From 30cm distance the noise disappeared.I tryed with 86db speakers and is hard to hear that noise...only 1 or 2cm from tweeter.
Also I replace 6sl7 with other brands and yes.....some of them are quieter then others.
I think ...to every tube amp is that noise...more or little but is.
Put your ear close to the speaker and tell me from what distance is the noise detectable.

Do you think that noise from mentioned distance is normal?
Thanks.