F5 power amplifier

[chrismercurio]

My personal experience with this has been via Jeff Rowland, Aesthetix, Sonic Frontiers gear...and of course Pass Labs. I can remember Cardas and Neutrik in a few cases....but I think Jim White at Aesthetix was using something else.

Chris

[Nelson Pass]

Originally posted by genome
I assume it is no harm if I remove R15/TH1 and R16/TH2, right?

As long as you don't mind more time spent warming up and adjusting.

[Tea-Bag]

Originally posted by GRollins
Neutrik makes some nifty three pole (positive rail, ground, negative rail) twist-lock connectors that are ideal for this. (Mouser has 'em.) I've been doing it for years. Why let the preamp guys have all the fun?

Grey

Is there a problem just running standard XLR's here, with some 18GA cable? Will too much current melt the connectors plastic?

My battery powered tube preamp is using them with Cat5 cable without any issue. ( I know of)

Mike

[Variac]

Speakon's have up to 8 contacts, and are made for higher amperage-30A continuous according to the spec sheet. . Also are non-shorting...

They are my plan- unless I have a row of speaker type terminals....
and spade connectors on the wires.

http://www.partsexpress.com/pe/showd...number=092-050
http://www.partsexpress.com/pe/showd...number=092-051
http://www.partsexpress.com/pe/showd...number=092-052
http://www.partsexpress.com/pe/showd...number=092-053
http://www.partsexpress.com/pe/showd...number=092-054
http://www.partsexpress.com/tech/092-051.html
etc

[tms0425]

Originally posted by mithomas



Is there a problem just running standard XLR's here, with some 18GA cable? Will too much current melt the connectors plastic?

My battery powered tube preamp is using them with Cat5 cable without any issue. ( I know of)

Mike

I think he's talking about the "PowerCon" version which is normally for 20a AC 3-wire line, sort of as a replacement for IEC connector, but locking. I try not to use 3-pin XLR's for power since they're too easily confused. Maybe the 4-pin version, but still great for much current.

[jacco vermeulen]

For that kind of connections i've been using Hirschmann Stas/Stak for decades, assembled a 3-piece Gerard Perrot (Mr Lavardin) amplifier design that was published in l'audiophile with them.
The Stas/Stak connector system is also highly water resistant, from 2 to 5 pole versions, example

A picture of the 2-pin types =>

[Babowana]

Originally posted by KSTR



"The feedback mechanism for this amplifier is R3 through R6, a dual pair of low impedance voltage dividers which feed the output to the Source pins of Q1 and Q2. Low impedance feedback has been (incorrectly) referred to as 'current feedback'"

I read a book:

Whenever the feedback voltage is proportional to output current, the circuit has current feedback. Current feed back stabilizes the output current. This means that a constant input voltage produces an almost constant output current, despite changes in open-loop gain and load resistance. For instance, suppose the open-loop voltage gain decreases. Then the output current tries to decrease. This results in less feedback voltage and more error voltage. In turn, this means more output voltage and current. The increased error voltage almost completely offsets the decrease in open-loop voltage gain, so that the output current remains almost constant. A similar argument applies to an increase in open-loop gain. Attempted increases in output current are almost eliminated by the negative feedback.

Noninverting Current Feedback:

Transconductance -- Decreases
Input impedance -- Increases
Output impedance -- Increases
Distortion -- Decreases
Output offset -- Decreases

Inverting Current Feedback:

Current gain -- Stabilizes
Input impedance -- Decreases
Output impedance -- Increases
Distortion -- Decreases
Output offset -- Decreases




For this, the load resitor (speaker) and feedback resistor are in series, as I understand...

Hope I did no mistyping...

[sandstorm33]

Originally posted by Babowana




I read a book:

Whenever the feedback voltage is proportional to output current, the circuit has current feedback. Current feed back stabilizes the output current. This means that a constant input voltage produces an almost constant output current, despite changes in open-loop gain and load resistance. For instance, suppose the open-loop voltage gain decreases. Then the output current tries to decrease. This results in less feedback voltage and more error voltage. In turn, this means more output voltage and current. The increased error voltage almost completely offsets the decrease in open-loop voltage gain, so that the output current remains almost constant. A similar argument applies to an increase in open-loop gain. Attempted increases in output current are almost eliminated by the negative feedback.

Noninverting Current Feedback:

Transconductance -- Decreases
Input impedance -- Increases
Output impedance -- Increases
Distortion -- Decreases
Output offset -- Decreases

Inverting Current Feedback:

Current gain -- Stabilizes
Input impedance -- Decreases
Output impedance -- Increases
Distortion -- Decreases
Output offset -- Decreases




For this, the load resitor (speaker) and feedback resistor are in series, as I understand...

Hope I did no mistyping...

I too did some research and found similiar info. The problem is it applied to a standard op-amp config which this amp is not. Oddly this feedback principle is not really covered in the article while it probably has a great deal to do with proformance. Anybody draw a diagram showing what goes on??

[Nelson Pass]

I think you have the wrong idea here. The F5 uses what I would
refer to as low impedance voltage feedback - as pointed out earlier
the circuit is a CFP "complementary feedback pair" variant.

Maybe it should be called a complementary-complementary-feedback-
pair-with-voltage-gain. CCFPWVG is a snappy acronym, no?

The point of my comment in the article is that this is routinely
referred to as "current feedback" in the op amp literature, but it has
been mis-named in this regard.

[Tea-Bag]

Originally posted by tms0425
I think he's talking about the "PowerCon" version which is normally for 20a AC 3-wire line, sort of as a replacement for IEC connector, but locking. I try not to use 3-pin XLR's for power since they're too easily confused. Maybe the 4-pin version, but still great for much current.

So in theory XLR's or "microphone" jacks can be okay (I use one per channel).
I have not tried it with 1stWatt amps yet, but plan on doing so as well. I have plenty of XLR's right now, no power or speakerconns.