First Watt F4 - any users there?

Hello, it's quite some time since I noticed this interesting product from a lab of Mr.Pass that actually allows high efficient speakers to be driven directly from high output sources (or gain preamps).

Considering its DIY potential it would be interesting to hear if anyone had a chance to try it with some of the BD products, 114db of Orpheans sounds very inviting for F4.

Thanks Gordan

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Gordan,

I've got the boards created by Peter Daniel and collected some of the parts, but haven't built the monoblock F4s yet.

Hopefully in a year or two I'll be able to report.

I thought it would be interesting to try as the Orphean main amp, as well as trying it out as bass amps. Perhaps a voltage gain stage would be needed for bass amp duty, I don't know. It would be cool if the main amp supplied enough voltage gain by itself.

Based on my experience with various amps, I think that many normal sources are going to need an active preamp with the F4, even with the high efficiency Orpheans.

In the meantime, if anyone else has tried the F4, I'd be interested too in observations.

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Hi Gordan,

Considering its DIY potential it would be interesting to hear if anyone
had a chance to try it with some of the BD products, 114db of Orpheans
sounds very inviting for F4.

If the amp works like a "normal" voltage amplifier then this can be done but if it is a current amp then things might work out differently.

An impedance correction as used within the Orphean works well with "normal" amps, a current amp works out differently in that respect...

Perhaps I am mixing things though... :confused:

Bert

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BD-Design - Only the Best!

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Hi Bert

I really think, no I know, you are right about that this current amp does certainly not work well with things like the Orpheans neither being the main amp for the Swings.

It is an amp. created for unfiltered speakers and will likely work very well here.

So Gordan back to considerations about being a crazy CrazyA owner. Much better. :grin:

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I believe the amp should work fine with the Orpheans. Lots of people are using the amps with speakers other than full-range Lowther types. Pass designed the amp to be very flexible.

The main thing is that speakers need voltage gain as well as current, but in the case of this amp the voltage needs to be provided somewhere else, i.e. from an active preamp, or in some cases (probably rare, but haven't done the calculations) with a line level source.

From the F4 manual:

The F4 is Class A impedance converting amplifier, having no voltage gain or feedback. Its input impedance is 48,000 ohms, and its output impedance is about 0.2 ohms. It is suitable for driving a high sensitivity loudspeaker with the output voltage of a preamp or other line-level audio source. It is also useful with a less sensitive loudspeaker in a bi-amped configuration where it takes input from the output of a conventional amplifier.

As a stereo amplifier with single-ended inputs and outputs, it will deliver up to 25 watts into 8 ohms with a damping factor of 40. It will do 50 watts into 4 ohms, and as a mono-block amplifier with parallel inputs and outputs, it will do 100 watts into 2 ohms.

The bi-amped configuration is interesting:

There are a number of popular tube integrated amplifiers on the market, the so called “Flea Watt”amplifiers which don’t have much juice, but offer a warm “tubey” sound which is much prized. These amplifiers are good candidates for operation with an F4 in a setup where the loudspeakers have two separate sets of input terminals, one for the woofer and one for the midrange/tweeter.
In such a system the F4 is used to drive the bottom end, where it offers superior damping and higher current, and the flea watt amplifier drives the mid and top end, unburdened by the effort of driving the woofer but preserving the character of the tube amp.

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Okay, remains the question why I am confused because there is a typical amplifier out there that does not work as normal amplifiers do. Somewhere I was told that an impedance correction should be made different for such amplifiers....

Any idea which amplifier this is?

Bert

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BD-Design - Only the Best!

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Is this the same type of amp we are talking about?

http://forum.bd-design.nl/index.php?id=10304

Bert

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BD-Design - Only the Best!

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Bert,

I believe that Pass's current source amps were called the "F1" and "F2". The F3 and F4 are more amenable to other speaker types.

From 6moons:

The F1 was a transconductance or current-source amp primarily intended for crossover-less single-driver speakers. The F2 was another current-source amp but single-ended. The F3 uses a special JFET as output device but only makes 10wpc. The F4 looks at the über-gain scenario today where hi-output sources plus high-gain preamps mean that many amps, into many speakers, run well below unity gain most of the time. The F4 asks a good question. What'll happen if such redundant amplifier gain was essentially eliminated?

So as I understand it, the F4 is a voltage source amp, you just need to get the voltage somewhere else. :wink:

Basically it is a sophisticated buffer.

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Now the confusion is gone... :cool:

Bert

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BD-Design - Only the Best!

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Hi Cappy...

Everything OK overthere? :wink:

Indeed it is maybe difficult to understand what should be the gain using an F1 or 2 with fantastic performance being a current amp, and then fire it up through a high voltage output behind it? Where is the gain here in SQ?

However it is feed even by a 30 Voltage source it will still be a current amp.

Now because I am so old and rememberance is not what it was once, there was a similar amp on the market which brand name I simply forgot, made in Sweeden I think.

At that moment I had Lowther drivers going in gips casted back-loaded horns. On those horns that amp. simply sounded gorgeous to that days standards.

But having more conventional speakers in my listening room too, it didn't work out well with those.
Filter components reacts differently to current than to voltage, in particular components which are in series with the signal path. So it could be a problem to some speakers with rather many components in the filter as serial compared to parallel components reacts differently than expected been feed by a current amp.

But what the heck...we know as well that a Magnepan speaker caNot live from 10 watts amps regardless what, so the dear Nilson Pass were not thinking of that either constructing the F1-2. He just made a perfect amp for non-filtered speakers.

If the F3 and 4 is a voltage amp. OK. No obstructions to filtered speakers.

Should we wish to change the Firstwatt to a voltage amp, this can be done by introducing a trafo after the speaker terminals which will do opposite to a trafo in a tuby.

Never mind...Nilson Pass has a point when saying that the first watts counts when we use high efficient speakers.

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