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PostPosted: October 14th, 2017, 7:15 pm 
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David McGown wrote:
I am not sure my reply ever posted but I would like to point out that just because you take output from the source or cathode does not mean the topology is the same. Remember, there are no complementary pairs of tubes, whereas the Pass F4 uses NPN/PNP Mosfets in a source follower. Rosenblit's design is a Circlotron, right?. Completely different animals. There is no patent on which way you take output on a device, just because the connections look the same at a high level doesn't mean the circuits are the same or even similar in operation. The difference is in the details, not the superficial similarities.

David


I was only referring to the output stage. Bruce’s design is based on Futterman/totem-pole which is similar to F4 output stage. I was wrong to imply Bruce invented the design, he got the patent for stabilizing the design and making it reliable.

BTW, you should try out an OTL amp. I built Bruce’s 15W SonOf Beast from the kit. I am never going back to transformer coupled amps again. I know there is a huge attraction for SETs, but why not a transformerless OTL.

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PostPosted: October 22nd, 2017, 6:12 pm 
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Joined: February 28th, 2013, 1:19 pm
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Well, I probably should post this over to the project discussion, but the First Watt F4 clone (based on DIYAudio boards and the Deluxe 4U chassis they sell) is up an running without a problem. Just put it in the system biamping my Basszillas with the F4 on the bass cabinets and 300B DRD amps on the mid/tweet panel (which are feeding the F4). My bass cabinets have come alive!

I will have to take some pictures, but it was pretty easy to put together. Once you get the parts in, it is basically a couple of evenings stuffing boards and a long afternoon of assembly. It would have gone quicker had I not tried to use Cardas wire for the output leads and finding I couldn't put the 12 Gauge wire in the damn hole on the board. Total parts cost is pretty reasonable, well under 1K including the chassis.

David


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PostPosted: October 22nd, 2017, 7:16 pm 
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David,

I would like to know if there is any alteration of the 300B sound. From your message it looks like you are using F4 only on the woofers which are probably crossed over below 100Hz, right? So there should not be any sacrifice of the 300B sound.

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PostPosted: October 22nd, 2017, 7:26 pm 
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My passive crossover on the bass cabinets is around 200Hz. This is too early to come to any firm conclusions (having less than 2 hours on the F4). But the 300B sound comes through clear, and the bottom end is phenomenal. Just played an SACD of Volodos playing Liszt, and the big piano sound really came through. Just now trying some large orchestral music.

A pretty exciting sound so far.

David


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PostPosted: October 22nd, 2017, 7:38 pm 
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drums go up to 114dB. More power, better bass.

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PostPosted: October 22nd, 2017, 7:45 pm 
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Shashi,

One of the things I am hearing is that the soundstage is bigger, which tells you a lot of our perception of space and ambiance must comes from the lower octaves.

Daivd


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PostPosted: October 22nd, 2017, 8:13 pm 
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Thats my experience too. Bass bring fullness the music as well as soundstage.

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