heaters ac or dc

[blaise]

any opinions,
considering a bass preamp, simple 12ax7 design
i'm not sure on which route to heat with.

[TD_Madden]

think DC will be quieter.

[defaced]

There has been significant discussion in the past regarding heating schemes. A search should turn them up.

I a high gain amp I am working on, DC heaters exacerbates the noise problem while simply grounding and elevating the AC heaters results in lowest noise floor. Others report that DC is the best way to go. Others yet use high current switching supplies for their heaters. YMMV. I'd advise get it put together and see where you're at before adding more parts to the amp.

[txstrat]

I believe there'll almost NEVER be any tube amp with NO hum. You can hear it when you go close to the speaker or the PT.
I'd say if you have to almost warp your body to make yourself hear it, it's quiet enough.
Even if you play an amp at living room at midnight volumes the hum should disappear for your ears. If not the hum's too loud.
I assume with a single 12AX7 bass preamp you're not gonna hear it.
Like defaced said, it's more of a problem in high gain amps, since they pick up more hum due to the gain factor of the stages.

[Enzo]

Hum comes from a variety of sources. The ONLY thing DC heaters does is prevent the AC in the heater from influencing the signal. It will have zero effect on any other source of hum.

[loudthud]

IMHO DC heaters are a waste unless you are trying to build a preamp on a printed circuit board. Even if done right, DC heaters only get rid of the 60Hz hum, and do nothing for the 120Hz buzz. That all comes from grounding.

[blaise]

well that sure cleared the air, (NOT)
i might have known asking that question would yield
several varying results.
actually i think i will go "ac" for the ease of less components
i planned on p to p with turret lugs, so it's ez enuff to add
parts later on.

[GibsonLover]

DC heater is another way to worry too much. Even my Hi-Fi amps use AC, and they're quiet as all get-out. It's a little like grounding methods- many ways to do it, some better than others on paper, but if it's quiet- you're done.

[tedmich]

Gerald Weber (Trainwreck /Kendrick Amps) describes 6 ways to run heater supplies:
1)series
2)daisy chain
3)hum canceling/center tap ground
4)hum canceling/artificial ground
5)positive bias
(all AC)

and
6) DC

he states he started thinking DC was the best but implementing it was a real problem and (4) is better, especially if a "hum balance" pot is included. Positive bias (5) is supposed to help de-hum SE amps which don't symmetrically cancel noise like PPs.

Oh an the cool experiment is the 6v lantern battery to see if REAL DC gets you anything on a heater (not too many tubes though), once you sweat a DC supply and gut your amp you'd swear it sounds like an angel singing (classic experimental bias)

[Enzo]

You always have to take Gerald with a grain of salt. Push pull output stages cancel ONLY the hum introduced in the power amp stage itself. They do nothing to remove hum coming to them from the preamp. SE output stages by definition cannot cancel anything. So they are more prone to B+ ripple creating hum. Elevating the heaters will have zero effect on B+ ripple. The only hum elevating heaters reduces is that caused by free electrons causing currents from heater to cathode within a tube.

[dai h.]

Gerald Weber is a former meat salesman and really shouldn't be confused with those with more solid technical understanding. It would be smart not to unquestioningly accept the advice given in his books without checking it first(though it's not all wrong of course). Also, it's my understanding that Ken Fischer (of Trainwreck) was not on good terms with GW after some dealings went sour and would (probably) roll over in his grave having GW described as part of "Trainwreck"(Amps).

[blaise]

ok, my design thus far is a se output.
i haven't finished my design yet (well more of a compilation of other designs)
but what i gather is:
1) pay close attention to psud. (good filtering)
2) quality components.
3) shielding.
4) grounding.( try to stick with a single location)
what about induction in the tranny itself. is their issues with
crosstalk between the windings
what about dedicated tranny's ?
to much weight ,clutter, hassle, not to mention more wires.?
also i was going to go hybrid, and have an opamp tone section and compressor.
but after studying rectifiers, learned that i could get some compression out
of a slower laggy'er tube. 5y3gt @ 44 miiliseconds response.
can anyone testify to sound of this, is their a mild to fair amount of squeeze.
if so, i will scratch the whole opamp section, eliminate split supply.
and use a more traditional tone stack. (simplify) i like that.