Ampeg PF-50T Humbuster

[Jim C]

Hello,

I'm a newbee on TB. I bought a PF50 last week. It's came at home; I was so excited to hear the Sound...
But there is the hum, too big for me!
(sorry for my poor english words, I am a little french, more bad in translation then bass playing)
I call the seller, a great webshop in Europe. They tell me they are not allowed to do the modification...
I can do the mod myself but the warranty will blow up... I dont understand why this "old" problem is still on new equipement... Maybe it's coming from an old stock...
I 've just the possibility to ask for an exchange... but I'm not sure to have a good one in return...
Thanks for this thread, I thought that mine was "alone"...

Has the remaining inventory of PF50's been pulled from sale and modified to correct this problem?
Sounds like if one were to buy a brand new amp in the box, it might come with a known defect that can be easily repaired, for free, at a factory authorized service center?

I just can't believe that any major manufacturer would do this.
Perhaps only limited to overseas stock?

 

[scotch]

I have a PF50t that definitely has the hum. Honestly, its pretty insignificant. I've had amps with fans that were just as loud if not louder. I'm not sure if I personally would characterize this noise as a manufacturer defect. It's pretty minor!

That said, I'll probably have the mod done "just because". There's no practical live or studio situation where the noise I'm hearing would be an issue.

 

[jnewmark]

Maybe this question has been asked already, ( too lazy to look ), but, does the hum/buzz come through when using the DI ?

 

[JimmyM]

Maybe this question has been asked already, ( too lazy to look ), but, does the hum/buzz come through when using the DI ?

Yes. But the humbuster mod fixes it.

 

[MarcVador]

Hello,

Just some really good new for me!
I've make it done last week. Less than an hour of cool job in an Ampeg authorized repairer ( and great talk about valves amps!)
Simply great!!! No more hum and the sound is... THE SOUND!
Special thanks to @mnats and @Bertr for the time and sharing!

It's really a pleasure for me to play with it now...

 

[onestone]

Hello,

Just some really good new for me!
I've make it done last week. Less than an hour of cool job in an Ampeg authorized repairer ( and great talk about valves amps!)
Simply great!!! No more hum and the sound is... THE SOUND!
Special thanks to @mnats and @Bertr for the time and sharing!

It's really a pleasure for me to play with it now...

That's great news! It's a wonderful amp indeed. Did you get the job done as a warranty service (in other words you did not pay for it yourself)?

 

[MarcVador]

I've paid the technician who have done the work. It was more simple and quick for me.
I bought it on a great webshop. I 've called them but they "can't" do the modification... They only offers me to bring me back my money... I thought it would be easier for me to do it, even at my own expense, rather than send it back and wait for a hypothetical update. In addition, because the country is confined, it is not easy to ship a package right now. I was only charged one hour’s work (and offered the parts!)
It was a B stock; the price of amp and the price of "mod" is lower than a new one... and full warranty!

 

[onestone]

I've paid the technician who have done the work. It was more simple and quick for me.
I bought it on a great webshop. I 've called them but they "can't" do the modification... They only offers me to bring me back my money... I thought it would be easier for me to do it, even at my own expense, rather than send it back and wait for a hypothetical update. In addition, because the country is confined, it is not easy to ship a package right now. I was only charged one hour’s work (and offered the parts!)
It was a B stock; the price of amp and the price of "mod" is lower than a new one... and full warranty!

Yeah, i totally understand why you chose to go that route. Every amp that is covered by warranty should have had this fixed at no expense though IMHO.


Now go get those tubes glowing!

 

[Doner Designs]

The fix is so easy I can't help but wonder if there is some negative impact that kept it out of the original design.

I guess noise is in the ears of the beholder because there have been plenty of satisfied customers who have probably never heard of this fix.

In my case I probably would have eventually sold the amp. Now it's definitely a keeper. The ability to run without a load makes it pure gold for anyone who wants to do recording or add character to their tone in a silent stage situation. Just a little bigger and heavier than a REDDI and it does so much more.

Another cool thing I discovered one day when goofing around is that you can come out of the transformer balanced DI output and run that into a separate power amp. Two situations when that could make sense. The obvious one is when you need more power. The other is when you need LESS power. The DI output is at a low level but after the power tubes. So you can go into a separate amp (even a headphone amp) and crank the crap out of the Ampeg gain and volume. Just keep the volume low on the second amp and you get full tube character at the speaker at low volume. Same result as if using a power soak.

Transformer balanced DI output>>>to the micro amp of your choice. You can go into the main input or the power amp (effects return) on the secondary amp. First time I tried this I went from the Ampeg into a Phil Jones BigHead headphone amp.

Besides the humbuster, this is one of the best tricks to know about how to use the PF50 or PF20 in my opinion.

 

[JimmyM]

The fix is so easy I can't help but wonder if there is some negative impact that kept it out of the original design.

Hodgy reviewed the fix and did it to a couple. He would have definitely said if there was a problem with doing it.

I can't state with any certainty why LOUD released it that way, but I have a feeling it had to do with not wanting to compete sonically with the B-15.

I guess noise is in the ears of the beholder because there have been plenty of satisfied customers who have probably never heard of this fix.

I was one of them till this thread came along

 

[beans-on-toast]

Hodgy reviewed the fix and did it to a couple. He would have definitely said if there was a problem with doing it.

I can't state with any certainty why LOUD released it that way, but I have a feeling it had to do with not wanting to compete sonically with the B-15.


I was one of them till this thread came along

The original bias circuit has a design flaw that nobody caught. Maybe my memory is out to lunch but it’s my understanding that the 20T and 50T were designed by the same person when the V4BR was done and they were put on the shelf. Designs held back until needed is not unusual in the industry. The engineer/designer that did tube equipment left before they came out. Someone else (from another division???) would have taken over the project.

 

[JimmyM]

The original bias circuit has a design flaw that nobody caught. Maybe my memory is out to lunch but it’s my understanding that the 20T and 50T were designed by the same person when the V4BR was done and they were put on the shelf. Designs held back until needed is not unusual in the industry. The engineer/designer that did tube equipment left before they came out. Someone else (from another division???) would have taken over the project.

Yep, she's very talented, and the V4B reissue was a great design, and while LOUD was a fine company IMHO, they seemed to treat the engineering staff as disposable.

 

[agedhorse]

IMHO, they seemed to treat the engineering staff as disposable.

We're not???

 

[starjag]

This is a crazy trick! I have a little mixer with instrument and line level inputs. Just missing the proper DI cable to make it happen.

The fix is so easy I can't help but wonder if there is some negative impact that kept it out of the original design.

I guess noise is in the ears of the beholder because there have been plenty of satisfied customers who have probably never heard of this fix.

In my case I probably would have eventually sold the amp. Now it's definitely a keeper. The ability to run without a load makes it pure gold for anyone who wants to do recording or add character to their tone in a silent stage situation. Just a little bigger and heavier than a REDDI and it does so much more.

Another cool thing I discovered one day when goofing around is that you can come out of the transformer balanced DI output and run that into a separate power amp. Two situations when that could make sense. The obvious one is when you need more power. The other is when you need LESS power. The DI output is at a low level but after the power tubes. So you can go into a separate amp (even a headphone amp) and crank the crap out of the Ampeg gain and volume. Just keep the volume low on the second amp and you get full tube character at the speaker at low volume. Same result as if using a power soak.

Transformer balanced DI output>>>to the micro amp of your choice. You can go into the main input or the power amp (effects return) on the secondary amp. First time I tried this I went from the Ampeg into a Phil Jones BigHead headphone amp.

Besides the humbuster, this is one of the best tricks to know about how to use the PF50 or PF20 in my opinion.

 

[Doner Designs]

This is a crazy trick! I have a little mixer with instrument and line level inputs. Just missing the proper DI cable to make it happen.

Jimmy said something like that when I first discovered this sorcery.

Ability to run without a load is super useful when you think about the possibilities like this.

Instead of a fancy tube preamp, get a PF50 and get more tube character than you could ever want.

 

[JimmyM]

Jimmy said something like that when I first discovered this sorcery.

Ability to run without a load is super useful when you think about the possibilities like this.

Instead of a fancy tube preamp, get a PF50 and get more tube character than you could ever want.

While it does put some very sweet tubery into a SS device, I greatly prefer to go bareback.

 

[Bertr]

We're not???

No. But it usually takes stuff like a big disaster for people to realize that farmers, engineers and doctors are cool people to have around.

 

[jwt1305]

Is anyone aware of a service centre or electrical engineer in the UK who can perform this mod?

 

[Rogulus]

is there a way of knowing if my stock pf50t has been shipped with this fix already? is there certain revisions that's had this done?

Not that I can hear anything from my amp, maybe I should leave well enough alone.

 

[starjag]

The stock hum is perfectly acceptable, even for recording. The hum reduction with this mod is measurable of course, but most owners are perfectly happy with the stock amp.

is there a way of knowing if my stock pf50t has been shipped with this fix already? is there certain revisions that's had this done?

Not that I can hear anything from my amp, maybe I should leave well enough alone.