[Laslen]

Well, that's pretty much it.

I'm wondering if the Pan Am is output transformerless.

For some reason, I cannot find this information anywhere, including and especially on ALO Audio's website. 

 

[TontonJoK]

I,
Why do you want to know That ?

 

[Laslen]

Why wouldn't you? It's helpful information about a product I own.

I've been warming up the tubes with no headphones plugged in.

 

[TontonJoK]

I tried to find out the real output power of the pan am and i'm still waiting for the answer
I saw some posts on HF with somebody saying it's an otl amp but I've no idea if it's true

 

[Bill-P]

No, Pan Am uses a hybrid topology, so it isn't OTL. OTL means you take the output directly from the tube amplifying stage. Hybrid means you put another solid-state buffering/amplifying stage between the output of the tube and the headphone.
 
But hybrid can theoretically be good enough if the hybrid buffering stage is transparent enough, so you shouldn't be concerned about it.
 
This whole OTL/non-OTL thing started because people thought the less components you have in your audio path, the better... but then... more sophisticated amps actually have a lot of components because they have better filters for suppressing distortions, power ripple, non-linearities, and etc...

 

[Laslen]

So, to clarify, you are saying it is safe to turn it on with no headphones plugged in?

That's the only reason why I'm worried about it, since doing so is harmful to OT amps.

 

[Bill-P]

I'm not sure what you are trying to say there...
 
It is not safe to leave your headphone plugged in to any amplifier as it's being turned on because during the process of power-up, the amp may send a DC signal through the amplification stage that may exceed the power handling capability of a headphone and cause bad things to happen. Read: you'll damage your headphone.
 
Same reason why some people reduce volume to 0 before plugging in a headphone, because if the gain is too high, the voltage being fed to the amplifier may well kill off the headphone.
 
Having no headphone plugged in would not do anything to well-designed amps where the amplification stage would just block the signal that's coming in.

 

[Laslen]

That's actually not true.

Many amps have a muting relay on powerup, which prevents the issue you described.

Having an "open circuit" (powered on with no headphones) on OT tube amps will actually damage the amp. On OTL, it is generally not an issue.

From WooAudio:
"Just to clarify, the problem of open circuit in an OTL tube amp is not as serious as output transformer (OT) coupled tube amp. In an OTL amp as the WA2, there is a pseudo load on the headphone output, which means you can switch on the amp without the headphone plugged in."

 

[Bill-P]

The "many amps" part may be misleading. Just a few years ago, that problem was plaguing one of Schiit Audio's products, and one guy made such a big fuss out of it...
 
Some portable amps, such as the Cmoy or AMB Mini3, don't have such a thing (AFAIK), for instance. And it can still potentially be a problem with these portable amps. That's why certain implementations use a volume knob that also doubles as a power-on switch. It's both a safety mechanism and a convenience.
 
But anyway... I think I misread your question.
 
A hybrid amp should not have a problem with no headphone plugged in while being turned on.
 
An OT tube amp can potentially be problematic because if there is no load while it's turned on, the output transformer may be fed stray DC that then gets multiplied to some dangerous level that can potentially cause damage.
 
But then a good design will have a short right at the output when no load is plugged in, which should be fine.
 
I guess it's only a matter of whether you want to damage your headphone or your amp, and seriously... not a lot of headphone can take the sort of voltage spike that may result from a tube amp going bad, so precautions should be taken.
 
That's why most tube amps now are hybrids rather than OT.

 

[zazex]

  I'm not sure what you are trying to say there...
 
It is not safe to leave your headphone plugged in to any amplifier as it's being turned on because during the process of power-up, the amp may send a DC signal through the amplification stage that may exceed the power handling capability of a headphone and cause bad things to happen. Read: you'll damage your headphone.
 
Same reason why some people reduce volume to 0 before plugging in a headphone, because if the gain is too high, the voltage being fed to the amplifier may well kill off the headphone.
 
Having no headphone plugged in would not do anything to well-designed amps where the amplification stage would just block the signal that's coming in.

 
I used to work up the street from the 'famed' Electric Lady Studios on
West 8th Street in NYC; I was a 'kid', it was my first job out of college.
 
I worked in high end home audio and professional audio and often had
occasion to be at EL.  Sold them a lot of big McIntosh amps, and Revox
tape recorders, for example. 
 
It was a pretty cool place at the time mostly because it drew a lot of cool
and knowledgeable people. (And the musicians, of course.)
 
One day, during an install, an Englishman with a
beard and beer in hand yelled loudly (to get my attention)
(Turned out he was a highly respected and well known
studio engineer in the UK)..
 
"Turn DOWWNN the volume."
 
I looked at him; he smiled briefly.
 
"Always turn down the volume.  Always, always.
When you're connecting or disconnecting any gear,
don't do it until --- you've turned DOWN the volume.
And if you're at all unsure, and you're digging around
in the wiring back there - turn  DOWN the volume first."
 
Following that advice has not hurt me through the years.
And it just may have saved my hearing, large amounts
of money in damaged equipment, and otherwise.
 
I've made it a habit to turn down the volume first.
 
Cheers.
 
 
TL;dr: Turn DOWN the volume when you're messing
with your hi-fi gear

 

[TontonJoK]

+1 following the different advices on HF I always turn the volume to 0