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Ampeg Portaflex 350 head - Static and Hiss?

Skygoneblue

Skygoneblue

Nov 13, 2007
549
102
Orlando, FL
#1
I recently got a Portaflex head, and it came standard with the typical Ampeg high frequency hiss when I run it through the 2x10 Portaflex cab. I turned the tweeter off, so it's not that big of a deal.

What bothers me though (and that I'm not sure is normal) is that when I plug my headphones into the head, I get the same LOUD staticky hissing sound when I'm not playing. It sounds like I have my ear pressed up against the tweeter with the gain on 10.

Is this normal? I've never had an amp with a headphone jack before, and I was expecting it to be rather quiet considering it's a signal right from the bass.
 
#2
Skygoneblue said:
I recently got a Portaflex head, and it came standard with the typical Ampeg high frequency hiss when I run it through the 2x10 Portaflex cab. I turned the tweeter off, so it's not that big of a deal.

What bothers me though (and that I'm not sure is normal) is that when I plug my headphones into the head, I get the same LOUD staticky hissing sound when I'm not playing. It sounds like I have my ear pressed up against the tweeter with the gain on 10.

Is this normal? I've never had an amp with a headphone jack before, and I was expecting it to be rather quiet considering it's a signal right from the bass.
Click to expand...

Did you ever get a response to this? I picked one of these up today and I am noticing the same thing with the headphones (I am waiting on my cab to show up, but wanted to try the amp)

michael
 
#3
Headphones, like a tweeter, can easily reproduce the high frequencies present in the hiss produced by the first preamp stage.

If the hiss stops (or is greatly reduced) when the instument cable is unplugged from the amp, then it is most certainly input noise in the first stage.

If this is the case, the only way to reduce it is to reduce the impedance at the input. For a passive bass, keep the bass volume at 10. An active bass, or a pedal with a low impedance output will also help.

-
 
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#4
megafiddle said:
Headphones, like a tweeter, can easily reproduce the high frequencies present in the hiss produced by the first preamp stage.

If the hiss stops (or is greatly reduced) when the instument cable is unplugged from the amp, then it is most certainly input noise in the first stage.

If this is the case, the only way to reduce it is to reduce the impedance at the input. For a passive bass, keep the bass volume at 10. An active bass, or a pedal with a low impedance output will also help.

-
Click to expand...
Thanks - interestingly, the noise does not seem to change whether my bass is plugged in or not. It also doesn't seem to matter what the volume and tone on the bass are set to, which is why I was wondering if perhaps it's being caused from the fan. My super cheap Acoustic 15w practice amp is completely silent (but it also has no fan)

Michael
 
#8
B-string said:
I quiet "hiss" maybe acceptable but I am talking very soft and you have the right to a quiet amp. Most amps are rated for -90db of noise at rated power which would be barely detectable with phones. So long as there is gain there will always be some noise in the circuits.
Click to expand...

It's definitely more than just barely detectable - and I found it interesting that it didn't matter if the gain was up or down, or if the bass was plugged in. The only thing that affected it at all was cranking the volume knob up all the way.

I sent a note to Ampeg - I guess I'd be curious if anyone else on here (I've seen one other) has this happen with theirs.

Next time I'm at GC, I'll plug my phones in. I'll also be curious if it will be heard through the cab, or if it's limited to the headphone out

Michael
 
#10
Try connecting a device to the amp's audio in via a stereo ⅛" plug and see if this affects the noise level with the headphones connected.

The signal being sent to the headphone is a mix of the instrument and audio in. If noise is getting in at the audio in, connecting something to this input might eliminate it.
 
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#11
beans-on-toast said:
Try connecting a device to the amp's audio in via a stereo ⅛" plug and see if this affects the noise level with the headphones connected.

The signal being sent to the headphone is a mix of the instrument and audio in. If noise is getting in at the audio in, connecting something to this input might eliminate it.
Click to expand...

Thanks all - I stand corrected a bit - tried a different set of phones...it appears cranking the gain and the treble both increase it somewhat - same with the master. (I also noticed the gain pot was a little scratchy towards the top, but not a big deal)

I"ll see what happens with the audio in. I'll also see what happens with the cab - it's just the straight 15 - no tweeter/horn

update: tried connecting audio to the audio in - no change. It would seem this is par for the course, but I would be curious to know if anyone else has seen/heard this that has a pf head
 
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#12
I don't use tweeters, but I used to have a couple cabs with tweeters and I never had this problem with my PF350 powering them, nor do I have it when I plug it in direct. You are either juicing the treble or you've got a problematic head. Increasing treble also increases the noise floor of the treble.
 
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#13
JimmyM said:
I don't use tweeters, but I used to have a couple cabs with tweeters and I never had this problem with my PF350 powering them, nor do I have it when I plug it in direct. You are either juicing the treble or you've got a problematic head. Increasing treble also increases the noise floor of the treble.
Click to expand...

My cab hasn't arrived yet, so this has all been through the headphone out. I tried it with the treble set at 0, and at 12 o'clock. Same result. I am really curious to try it with the pf-115LF cab, but it's still a couple days out
 
#14
From Ampeg Support:

"
Hi Michael,

This is normal operation for this amps in this series. The more you crank it up, the louder it gets, and the more you can actually hear the fan. Nearly all audio gear has some amount of audible hiss, that’s just the nature of the beast!

All the best,"
 
#15
MBauer said:
From Ampeg Support:

"
Hi Michael,

This is normal operation for this amps in this series. The more you crank it up, the louder it gets, and the more you can actually hear the fan. Nearly all audio gear has some amount of audible hiss, that’s just the nature of the beast!

All the best,"
Click to expand...

Well, THAT sucks. I just looked at the manual: S/N 75db, not as quiet as I would expect.
 
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#19
Well the PF350 seems pretty quiet to me, that's what it has to do with it. Would I use it as a studio reference amp? No. But I'm also not paying less than $300 new for a reference amp, either. A little perspective is required on that front, IMHO.
 
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#20
Thanks all - I'm sure that once I plug the cab in, it will be much less noticeable. I was just honestly surprised to hear it through the phones... my $100 practice amp is almost whisper quiet, but it also doesn't have a fan.

JimmyM - do you still have a 350? What do you hear if you plug a set of headphones in to it?

~m
 

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