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Very quiet bass head

#21
Wasnex said:
Most amps do not hum so loudly. Unfortunately this is a common problem with the PF50T. The usual source of the hum is the bias supply filtering is not sufficient. If the PF50T is new, try to get Ampeg to fix the hum under warranty.

The output tubes are connected in push pull, which means they are out of phase which each other. If the tubes are perfectly matched the signal from each tube is pretty much the same size, so the hum cancels in the output transformer. If the tubes are not matched, then one tube produce more noise than the other, so the hum does not cancel. So the matching of the output tubes is highly relevant to the level of hum.


If the amp is not under warranty, there is a relatively easy fix. Here is a long thread: Ampeg PF-50T Humbuster | TalkBass.com

This post shows the Bertr mod: https://www.talkbass.com/threads/ampeg-pf-50t-humbuster.1306043/page-2#post-21127402

This post shows what is believed to be Ampeg's version of the Bertr mod:https://www.talkbass.com/threads/ampeg-pf-50t-humbuster.1306043/page-6#post-21830819

Top image original schematic. Bottom image Bertr mod with C1 and RT added:
View attachment 5227730

(3,300 + 680 = 3,980)


So rather than adding the 3.3k, I replaced R128 with a 3.9K 1/2W metal film resistor and added the the extra 220uF 100V filter capacitor. The capacitor was secured with a bit of electronics grade RTV silicone.

This is suggested in this post: https://www.talkbass.com/threads/ampeg-pf-50t-humbuster.1306043/page-5#post-21338053
Click to expand...

We should probably also mention that there can be dangerous voltages inside a tube amp, even when it's switched off and disconnected from the mains. If the OP doesn't have any experience with electronics he should probably not start here...

Just out of curiosity:

If this problem can be partly caused by poorly matched output tubes (although this specific amp seems to have additional problems), can the hum be fixed, or at least reduced to an acceptable level simply by replacing the output tubes with a properly matched set? The output tubes will need to be re-biased of course but this is a very simple procedure on these amps. Will it also matter if the PI tube is balanced?

Or will these amps still produce an unacceptable level of hum?

Just in case there's a (relatively) easy solution.
 
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#22
Peter - Oregon said:
I often practice at very low volume while watching TV with my wife
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Same here - except for the "low volume" part, and replace "practice" with "noodling". :smug:.
Peter - Oregon said:
the amp has significant loud hum
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https://www.talkbass.com/threads/ampeg-pf-50t-humbuster.1306043/
I just called Ampeg last week; they will cover "the humbuster" through an authorized service center.
OP: This will likely resolve the issue for you.

Killing Floor said:
Most Class D amps are super quiet when idle. Exception being a fan. But that’s not a big deal.
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Agreed in almost every circumstance - but in this exact situation - the fan noise bugs me.
 
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#26
Peter - Oregon said:
I purchased a used Ampeg PF50-T head and PF115 LF cab. This is probably strange, but I often practice at very low volume while watching TV with my wife. Unfortunately, the amp has significant loud hum that is very noticeable at very low volume. Right now I am using my Spark amp for this practice. Unfortunately, it doesn't sound or react much like a bass amp. My question is if you know of a class-D head that makes basically no noise when idle, or played very quietly. Maybe such a thing doesn't exist? My apologies if this is a stupid question.
Click to expand...

GK Legacy 800, on Mute.
 
#27
Chris Chong said:
Did you know Mesa D350 do not have a fan? So there’s no fan noise.
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i absolutely love my mesa D-350. it sounds good at very low volumes (like not waking up my sleeping husband in the next room at 1am quiet), yet it still has lots of yummy tone.

gl1234 said:
The Fender Rumble 40 is a great sounding little combo: amp+1x10 speaker and no fan. It also accepts headphones and aux-in for music source. Very budget-friendly.
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i had a rumble 40, and while i felt it didn't deliver its full tone at middle-of-the-night volume, it did sound good and was very quiet. while i found i no longer used it once i got my mesa, the rumble 40 costs less than a third of the price of the mesa, and is an amp i definitely liked. also for quiet play the hartke HD15 is a good one and tiny, too.
 
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#29
I'm a little confused by this post. I have a PF-20T and it is absolutely dead silent for me noise-wise which is why I chose an all-tube head. Compared with something like an Ampeg Micro VR which is solid state, possibly one of the noisiest heads I have ever played through due to its fan. The hum of the tubes is the issue with your PF-50T? I'd check the tubes if it's really THAT loud.
 
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#30
Deleted member 271037 said:
If this problem can be partly caused by poorly matched output tubes (although this specific amp seems to have additional problems), can the hum be fixed, or at least reduced to an acceptable level simply by replacing the output tubes with a properly matched set?

Just in case there's a (relatively) easy solution.
Click to expand...

Poorly matched tubes definitely contribute to the problem. I don't know if a well matched set would sufficiently mitigate the hum. My guess is no, but that could depend on the cab your are using, how sensitive you are to noise, and other contributing factors in the amp.

I don't have a spare matched set of 6L6GC or I would have tried it. I did try swapping the tubes in the amp. The original position seemed slightly quieter.
 
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#32
OP

Why not use a VOX amPlug 2 bass headphone amp/module? They are small no noise and all You have to do is plug your headphones into them and then plug it into your guitar and you're ready to go. You will hear yourself perfectly and you will not bother anyone else in the room. Some of the models even have rudimentary drum sounds in them in different beats that you can play along with. I have one and I use it frequently.
 
#33
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#34
Lots of good ideas and feedback everyone, thanks for the feedback. I am looking to play any amp I choose at regular volume too. I like the idea of having another amp, like the Mesa, for another sound. Not to start another thread, but I am curious how much of say the Ampeg tone comes from the head vs the cab. I would guess the Mess head and Ampeg can would be a mix of the two.
 
#35
60bass said:
OP

Why not use a VOX amPlug 2 bass headphone amp/module? They are small no noise and all You have to do is plug your headphones into them and then plug it into your guitar and you're ready to go. You will hear yourself perfectly and you will not bother anyone else in the room. Some of the models even have rudimentary drum sounds in them in different beats that you can play along with. I have one and I use it frequently.
Click to expand...

I also have one of these, which I play at times. The use in question is when I want to play and watch TV at the same time without bugging my wife too much. I saw in the Beato interview that Metallica guitarist does similar, so Im not that strange.
 
#36
Peter - Oregon said:
I purchased a used Ampeg PF50-T head and PF115 LF cab. This is probably strange, but I often practice at very low volume while watching TV with my wife. Unfortunately, the amp has significant loud hum that is very noticeable at very low volume. Right now I am using my Spark amp for this practice. Unfortunately, it doesn't sound or react much like a bass amp. My question is if you know of a class-D head that makes basically no noise when idle, or played very quietly. Maybe such a thing doesn't exist? My apologies if this is a stupid question.
Click to expand...
I have two class D bass heads that are dead quiet and some class A/B amps that are reasonably quiet. Reasonably quiet means that besides the fan, there's no other real hum or noise produced by the head.

The two heads I have that are dead quiet are my Eden TN-226 (225-watts rms into 4Ω) and my DNA-800 amp (800 watts rms into either 4Ω or 2Ω). Both of those heads use passive cooling and do not have a fan. Since they don't have a fan, they don't even have any fan noise. I only use the Eden head for small venues and use the DNA-800 head for almost everything else. Eden's class D 500-watt head (TN-501) uses a low rpm fan operating constantly for cooling. That's a much more versatile head, but not sure how much if any noise that fan makes because I don't have one. Neither my DNA nor my Eden TN-226 make any noise at all.

All of my class A/B heads have thermostat-controlled fans which come on when the amp reaches a specific temperature. I don't consider them noisy heads but my class D amps are so quiet I have to look at them to make sure the power lights are on.
 
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#37
Peter - Oregon said:
Lots of good ideas and feedback everyone, thanks for the feedback. I am looking to play any amp I choose at regular volume too. I like the idea of having another amp, like the Mesa, for another sound. Not to start another thread, but I am curious how much of say the Ampeg tone comes from the head vs the cab. I would guess the Mess head and Ampeg can would be a mix of the two.
Click to expand...

The voicing of the head is a significant factor. Mesa makes four 800W Subway heads: D800, D800+, WD800, TT800. They don't all sound exactly alike. The D800 and D800+ cover some common ground, but the + version has some added features such and a variable HPF and bright switch that give you some additional options. The WD and TT are designed for a different basic tone.

I would expect a comparable Ampeg to sound significantly different.

The differences should be way more noticeable if you are playing the amp versus listening to someone else.
 
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