Wondering about attenuators, master volume and amp noise/hum

bean7

I have 2 valve amps (same maker fwiw);

a) 50 watt 6L6 with master volume 
b) 30watt el84, non master volume.

Amp (a) is very quiet in terms of background noise & hum at bedroom volume, with master set very low and pre-master volume set pretty low too; just generally a very quiet clean sound. When turned up loud to band practice type levels, either with preamp set for little to maximum drive (there's not alot of it but there's some), there's what I'd consider normal levels of background noise & hum, negligible for the type of volume you're getting.

Amp (b), with simply 1 volume control, has a pretty persistent background hum which is pretty much constant regardless of where the volume is set. There's a little hiss when the volume is increased as expected.

So at bedroom level the amp (b) hum is more noticeable than amp (a), but at louder levels it becomes a non-issue as the signal:noise (hum) ratio equals out, when comparing both amps at high volume.

What I'm wondering now is, would modding amp (b) to have a master volume, or getting an attenuator help with reducing perceivable hum at lower volumes, similar to what I feel like is happening with amp (a) with its master volume?

ICBM

What amps are they? Make? Model?

bean7

Verellen; the 50 watt one is a 'Coop' combo and the 30 watt one is an older custom head, I think fundamentally similar to a Vox AC30 but really simple, just volume, bass, mid, treble controls - both amps are very loud.

ICBM

If it's based on an AC30 then you need an attenuator - the hum will be coming from a combination of the power valves running hot and fairly light filtering in the power supply, so it's after where you would be able fit a master volume.

bean7

ok cool - am curious to try an attenuator

ICBM

bean7 said:

ok cool - am curious to try an attenuator

The Dr.Z Airbrake and other purely resistive attenuators seem to work best with AC30-type amps, for what it's worth. The Jet City Jettenuator (or its Harley Benton equivalent) are probably the cheapest.

bean7

Thanks! I was looking at the Jettenuator which seemed nice and simple for a decent price - didn't realize there were so many options now.

Fenderish

It's "possible" that an MV on amp B could decrease the low volume hum/hiss, but it still depends on the design, not guaranteed at all. There are some MV amplifiers that generate a disturbing amount of hum/hiss even with volume @zero so...

bean7

yeah its an ongoing experiment

ICBM

What's guaranteed is that an attenuator will reduce *all* noise no matter where in the amp it's coming from... it's just that it might not be the cheapest solution to the problem.

paulnb57

@@bean7 ;; I have a Bugera version, brand new in its box unused and unloved, never been opened, looks to be the same as the Jettenuator.....yours if you want it.....
Same as this 

https://www.gear4music.com/Guitar-and-Bass/Bugera-Power-Soak-Passive-100-Watt-Guitar-Amp-Power-Attenuator/223F?origin=product-ads&campaign=PLA+Shop+-+GENERIC&adgroup=GENERIC&medium=vertical_search&network=google&merchant_id=1279443&product_id=96027d1&product_country=GB&product_partition_id=583888973959&gclid=Cj0KCQjwn8_mBRCLARIsAKxi0GI2qjGruK6JSEdK-zOADdYGOB5sH_7Ww9ihIBWyUdxq7nCPn9eLi88aAv1TEALw_wcB

£70 Mailed PPG?

bean7

Thanks for offering - I’m in the US now so probably more hassle than it’s worth 

paulnb57

bean7 said:

Thanks for offering - I’m in the US now so probably more hassle than it’s worth 

Ah!.....

bean7

Someone locally was selling an old THD hotplate in decent condition - I was curious to try that after reading about the light bulb driven noise gating they have. The attenuation really does exactly what I was hoping it would! Nice thick tone with significantly (almost none) less noise / hum. I'm not really driving it hard enough for the bulbs to do anything as I'm not actually trying to get power amp overdrive but rather just lower the noise floor of the cleanish sound, and it does this really well.