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quick impedance question

Started by ilyaa, July 03, 2015, 04:13:40 PM

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ilyaa

i know with tube amps 2:1 impedance mismatch is OK -

too high stresses transformer a bit more
too low stresses tubes a bit more

what about with SS amps? if it can be turned on with no load at all, seems like going too high with the load impedance is not a problem? what about too low? stresses output transistors risks overcurrent?

just curious -

LateDev

You must never turn a solid state amp on with no load. If the impedance is too low or high it will more than likely blow the output stages.

Think of the load as an external component of the amplifier, without which the amp will not function correctly.

J M Fahey

#2
Quote from: LateDev on July 03, 2015, 05:48:02 PM
You must never turn a solid state amp on with no load.
Sorry but you are wrong.
SS amps can be turned on without load and in fact are recommended to do so while testing, until you are certain there is no DC present at the output.

QuoteIf the impedance is too low or high it will more than likely blow the output stages.
Too low? ... definitely.

Too high? (even infinite?) : no way.

We are trying to help people with problems here, not confuse them with technically incorrect statements.


Enzo

Solid state amps produce an output voltage signal.  The load itself determines the output current.  With no load on the amp, no current is drawn from the output.  A SS amp with a steady DC voltage on the output will draw heavy current when loaded, but you can safely leave the amp unloaded while determining where the DC is coming from.

It is standard procedure to leave a SS amp unloaded during service until it is stable and not producing DC.

phatt

Quote from: Enzo on July 03, 2015, 08:19:32 PM
Solid state amps produce an output voltage signal.  The load itself determines the output current.  With no load on the amp, no current is drawn from the output.  A SS amp with a steady DC voltage on the output will draw heavy current when loaded, but you can safely leave the amp unloaded while determining where the DC is coming from.

It is standard procedure to leave a SS amp unloaded during service until it is stable and not producing DC.

What Enzo said  :dbtu: :dbtu: :dbtu:

phatt

Quote from: J M Fahey on July 03, 2015, 07:08:01 PM


We are trying to help people with problems here, not confuse them with technically incorrect statements.

Don't worry Juan, even that chap Pittman did not know the basics when asked how a Valve worked Yet went on to make a fortune.
(Article found in Guitarist March 1992 page 88)

I found an interview with Mr Pittman where he stated that the *Positive* charged electrons are attracted to the high voltage potential on the Plate and controlled via the grid.  :duh xP :loco :lmao: :lmao: :lmao: :lmao:

I certainly would not trust him to design an amplifier from the ground up?

Err excuse me Aspen but unless I've read the wrong books Electrons are Negative on the cathode and are attached to the positive plate.

Sure he may have had a tiny brain fart in the moment but once in print your name is MUD.

Tiss even more disturbing that not one person in a guitar mag office (likely filled with guitar nut cases) picked up on the major flaw in his analysis of the basic workings of a Valve.

Heck I recall my own ignorance when I was young I assumed the speakers ran on DC because the terminals said Positive and Negative. I made a complete goose of myself in front of better minds and felt rather stupid at the time but at least I learned to not make hasty assumptions.

Lets hope that *LateDev* has the wisdom to learn from that because he obviously has experience which is good. :tu:

AT **LateDev** Chill out man it's not a talent contest here it's about helping out where you can and often less is more. If you take offense at what I've said then the scale goes even lower than MUD. 8|
Phil.

LateDev


No6h

I'm building a Noisy Cricket and am adding a headphone output (switched 6.35mm stereo jack), and am wondering how the impedance of my headphones 60Ω would affect the circuit? do I need to change anything or add a capacitor?

J M Fahey

You already have a (needed)  output coupling cap to drive the speaker, the headphone goes in parallel with the speaker (the jack switch usually cuts the speaker ground to mute it, look at what others do) but the headphone needs some resistance in series, try 100 or 200 ohms, to avoid blowing the phones and deafening you.

No6h

Also would adding a stereo 3.5mm aux in after the preamp before the 386 change anything? So I could play backing tracks...

J M Fahey

Yes`you can, but remember in this amp clipping comes from overdriving the power amp, so music will also be *very*  distorted.

Also: what sounds like light crunch for a guitar is unbearable distortion for music.

Now if you play clean, or with external pedals, may be achievable.