Very quiet bass head

[Peter - Oregon]

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.

 

[Wasnex]

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:

(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

 

[Killing Floor]

Most Class D amps are super quiet when idle. Exception being a fan. But that’s not a big deal.

Also you know it displeases the Lord when you play too softly.

 

[agedhorse]

Sone class D amps have no fans are are basically silent.

 

[Chris Chong]

Did you know Mesa D350 do not have a fan? So there’s no fan noise.

 

[Peter - Oregon]

Did you know Mesa D350 do not have a fan? So there’s no fan noise.

 

[Peter - Oregon]

The D350 is one I am curious about. My local shop is a Mess dealer, so I'll have to check that out. Guessing the 800s do?

 

[Peter - Oregon]

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

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

Thanks for the great info. Unfortunately, I am not technically competent.

 

[agedhorse]

The D350 is one I am curious about. My local shop is a Mess dealer, so I'll have to check that out. Guessing the 800s do?

Yes, the 800’s also support 2 ohm operation so they have a quiet fan.

 

[Marko 1]

Is the OP's problem fan noise, or a hum?

 

[Peter - Oregon]

On my Ampeg amp it's the loud hum. On a future purchase I am looking for overall quiet at very low volume.

 

[bobcruz]

My Genzler Magellan 350 is very quiet at low volume even though it has a fan. The fan is thermal sensing so if you're playing at low volume it barely spins.

 

[gtirard]

All class D amps are noiseless AFAIK.
Most of them have fans, some with variable speed that you hardly hear, but those with fixed speed can become pretty annoying when you practice at very low volume.

There must be a thread somewhere with a full list of fanless amps, but I couldn't find it.
Maybe if there's no pre-existing thread on the topic we can build a list together?
- Mesa Subway 350
- GR Bass Pocket 50
- Quilter Interbass 45
- What else?

(The GR Bass Pocket 50 is interesting for OP, because it's only 50W but it's ok since OP wants to play at bedroom level, and it's super tiny and lightweight, it includes an audio interface, and it has an autonomy of 8 hours with rechargeable batteries, which can be handy in some situations).

 

[Stylee Mousse]

Find something good without a fan. It will probably bug you - why risk it? The mesa probably is great. And yes 350 watts is enough for quiet practice with tv.

 

[gtirard]

Find something good without a fan. It will probably bug you - why risk it? The mesa probably is great. And yes 350 watts is enough for quiet practice with tv.

Yes the Mesa is probably great, yes 350 W is enough, but even 10W is enough, if it's just for quiet practice with tv.

 

[Bodeeni]

I use a older Genz Benz Shuttle 3.0 for quiet no fan operation. I also have a 6.0 I only use for gigs because of the fan noise. Both a great amps. My laptop fan has also gotten .noisy and I have yet to address that.

 

[Chris Chong]

Was using TH350 DI out for recording, when the fan kick in, the power surge resulted in a pop in the track.

 

[themickster]

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.

No noise at all? You'll need one without a fan. They're no worse than a computer fan, but some folk can't handle hearing them between songs - the kind that need everything the same as when they were children.

 

[Vincent Van Low]

On my Ampeg amp it's the loud hum. On a future purchase I am looking for overall quiet at very low volume.

The loud hum is way way common as you now know, just have someone else do the fix for you, this little amp is MADE for low volume work, literally made for it, that and studio work as you dont need to plug it into a speaker cab at all...

 

[Bonecat]

I used an Acoustic Image Coda for many years and it was electrically silent and had no fan. The DI was also perfectly quiet. I used it live for URB for years and for practice and recording with BG. Wasn’t loud enough for the stuff my band played and I stopped playing URB, so I sold it. Within its limits, though, it was the most accurate amplifier I’ve ever used.