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First One - mosFET amplifier module

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Theodosis O.

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dadod

dadod

Member
Joined 2006
Lazy Cat said:
Today a guy from a local audio community called and asked about the damping factor of the First One amp module because it is not specified in post #1. I said that along the THD measurements I noted Zout to be under 10 mOhms, but in reality did not measured it very precisely or specifically on different frequencies.

So today some measurements were performed in order to determine Zout and consequently the damping factor (DF).

Sine signal of 100 Wrms on 20 Hz, 1 kHz and 20 kHz was thrown onto 4,08 Ohm load resistor, measured with FLUKE 289 True RMS Multimeter and here are the results.


1. 20 Hz, 100 Wrms/4,08 Ohm:

unloaded output: 20,205 Vrms (Iout=0)

loaded output: 20,199 Vrms (Iout=4,95 Arms)

voltage drop on Zout: 6 mVrms

Zout(20 Hz)=6 mV/4,95 A=0,00121 Ohm

DF(20 Hz)=Rload/Zout=4,08 Ohm/0,00121 Ohm=3371,9


2. 1 kHz, 100 Wrms/4,08 Ohm:

unloaded output: 20,201 Vrms (Iout=0)

loaded output: 20,199 Vrms (Iout=4,95 Arms)

voltage drop on Zout: 2 mVrms

Zout(1 kHz)=2 mV/4,95 A=0,0004 Ohm

DF(1 kHz)=Rload/Zout=4,08 Ohm/0,0004 Ohm=10200


3. 20 kHz, 100 Wrms/4,08 Ohm:

unloaded output: 20,207 Vrms (Iout=0)

loaded output: 20,199 Vrms (Iout=4,95 Arms)

voltage drop on Zout: 8 mVrms

Zout(20 kHz)=8 mV/4,95 A=0,00162 Ohm

DF(20 kHz)=Rload/Zout=4,08 Ohm/0,00162 Ohm=2518,5


Measurements specifics:

True AC voltmeter probes were connected directly to PCB output terminals, so no load's wires resistance voltage drop in the loop. Any mOhm of the wires and terminals resistance added in the equation will influence significantly to damping factor value. :yes:
Click to expand...

From Cordell book:
The damping factor can be inferred by measuring the amplifier frequency response
under no-load and with a known-load. This is a fairly crude approach.
A better approach is to inject a signal current into the output of the amplifier and
measure the resulting voltage.
 
Lazy Cat

Lazy Cat

Member
Joined 2007
dadod said:
Sorry, I presumed that everybody here knows about Bob Cordell's book.
"Designing Audio Power Amplifiers".
Click to expand...

I am sorry Dadod, but please leave this thread out from the marketing of other products. If you would like to promote some books please open new thread

You've said your statement, we understand clearly that there are many ways to measure DF, but author of this thread chosen the right and correct one.

This thread is about the First One power amplifier module and associated material recommended by me. :yes:
 
Lazy Cat

Lazy Cat

Member
Joined 2007
danny_66 said:
That's more than plenty of damping factor :)
Click to expand...

I agree, more than enough output voltage regulation from the First One module by itself. The question is how good someone's implementation of the amp in the chassis will be.

Fast-on terminal connectors implementation, internal cabling wire gauge, speaker terminals all these factors influence the final damping factor of installed amp in the case.

Regards, L.C. :cheers:
 
Speedskater

Speedskater

Member
Joined 2002
As audio consultant Dick Pierce wrote some time ago:

And what is "amplifier damping factor?" What difference is there between
that and the system damping factor, which, in and of itself, is a pretty
meaningless term invented SOLELY for specsmanship. As such, it is
officially defined as the ration of the nominal load impedance (say, 8
ohms) to the amplifier source resistance). It's a meaningless
specification, in that, again, ignores the fact that a factor of 100
change in the amplifier source resistance (say, from 0.001 ohms to 0.1
ohms), equivalent to a difference of damping factors of 8000 vs 80, is
not going to make one damned bit of difference how the system performs.

**********************
I would have thought that book's by Doug Self and Bob Cordell are on the self of anyone interested in amplifier design.
 
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Lazy Cat

Lazy Cat

Member
Joined 2007
Speedskater, I would not claim anything like that, since every little damn thing influences amp's final performance. DF is just one among many very important details and as we all know where the devil is hiding we should not ignore any of them.

Please take a look to post #1 and see how many specs gained from measurements are present there and they are not even near to be completed.

Regards L.C. :cheers:
 
Lazy Cat

Lazy Cat

Member
Joined 2007
At the moment classical arias on the menu and I am quite impressed. First One is so much better for classical music reproduction than any of my previous amps, pure pleasure. Also Soul Supreme are amazing speakers to listen to. They still have to gain some burn-in hours but things becomes very very good. :)
 
Nikos

Nikos

Member
Joined 2009
Lazy Cat said:
Of course up to 20 kHz, but not at 200 kHz since that would evaporate zobel resistors getting 10 times more power dissipation as they intend to. :cool:
Click to expand...
Also have you put resistor on gates Mosfets?
I made ​​this question because on the result of 200khz already on lateral vertical lines you have a few breaks. Do you think as following you have only one mosfet per rail .I have three mosfets lateral per rail TO3 72+-/V , and I find it difficult to take 200kηz so CLEAR under load but at 20V p-p no problem without breaks .
Nikos
 
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Lazy Cat

Lazy Cat

Member
Joined 2007
It is shown on Tek digital scope, breaking lines are there just because of LCD screen. Analog scope would show exactly the same form with smooth lines. 200 kHz test achieved by First One is hard to beat with any multi k$ amp out there, that's for sure.

Just real life measurements shown in this thred, no technical details about the amp, sorry.
 
Nikos

Nikos

Member
Joined 2009
Lazy Cat said:
It is shown on Tek digital scope, breaking lines are there just because of LCD screen. Analog scope would show exactly the same form with smooth lines. 200 kHz test achieved by First One is hard to beat with any multi k$ amp out there, that's for sure.

Just real life measurements shown in this thred, no technical details about the amp, sorry.
Click to expand...

On my scope those breaking lines mean something, and in the real life sounds harder the sound.Scope wave results with many small secrets.
That's why I made the question.
im stiil listening your amp VSSA VS GOLMUND Clone .
 
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