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rules for a quiet amp

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12/31/1999 3:49 AM
Ricky	rules for a quiet amp could someone give me a quick rundown of things to pay attention to for making a tube amp as quiet as possible? I want to make sure not to overlook anything I may not know about.

12/31/1999 4:54 AM

a) good filtering of DC power supply rails. This means essentially attempting to elminate all AC whatsoever.

b) addressing the AC heaters if so equipped. If AC, they must be as tightly twisted as possible, perhaps even shielded. They must be kept either as far away from other leads as possible, or pushed flat against the chassis.

c) good star/heavy buss grounding scheme. In my experience, if you must connect signal ground to the chassis, do it RIGHT AT the input jack sleeve. Ground wires should be as thick as possible. I use 18awg to the buss, which is 12awg copper.

d) in the realm of noise, the metal film resistor is far far better than the carbon comp. Use the biggest values of power rating for the resistors as your wallet and chassis space allow.

e) good layout is absolutely critical. Keep sensitive stages as far away from large signals/noise as you can. Stages should flow naturally from one to the next, with a minimum of interconnection path. I try to get by with JUST the component leads. Transformer cores should be in different axis of orientation--especially chokes--and well away from everything.

f) low resistances everywhere will minimise the thermal noise of the resistances themselves. This includes pots.

g) running tubes at high current will produce less shot noise from the electrons hitting the plate.

h) DC heaters can be the final step towards deathly silence. Use at least 10,000 microfarads for every amp of heater draw, or perhaps switch to a regulated circuit, or both.

That's the big stuff...

KG

12/31/1999 6:18 AM
Ricky	Great! thanks for the excellent info, a couple more questions that I forgot, does the shield in shielded wire have to be connected to the ground? if so, does it have to be at both ends? also, can the heater supply be totally isolated from the chassis? (its DC) thanks again, Ricky

12/31/1999 1:03 PM

Ricky,

I think of the shielding as part of the chassis myself, which itself is one large shield. From my perspective, I connect all shielding to the chassis (one end only) and run a separate buss or star grounding for the circuit ground, which is isolated from the chassis.

Finally, at one big central bolt, the mains ground, signal ground buss and chassis all meet.

Yes, a DC filament supply can float happily, although some folks like to reference it to ground, either thru a resistor or a cap.

Hope that helps...

... Whit

12/31/1999 8:28 PM
Ricky	how bout chokes? should they be a certian distance from the PT? the one I'm going to use is a hammond open frame. can I have the choke on the same axis as the OT, or would it be better to tilt it diagonally? one last thing, is there any websites up that have some really good photos of chassis layout? thanks, Ricky

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