F6 Amplifier

This is my chosen slant on amps, and this amp does it as well as any tube amp I have heard. I cannot wait to hear it through HE system, as this trait indeed shows itself most at low levels. Thank you gor the review.
I don't know if the problem is with my F6 build or my ears, but I could not get a sound that I really wanted to listen to for extended periods. One of my requirements is for speech intelligibility, which I found lacking in my F6.
 
I have the good fortune of a curve tracer and I believe this helped, but my opinion from the very beginning is just as Jon stated above. Of course i took it a step further and went balanced, but the nature of the amp remained. I listened to "Companion" by Patrica BArber, again on SACD last night and just cannot believe how enjoyable it is. Turn the lights off or close your eyes, whichever, and you are there. IMO, the soundstage is limited only by rooom size, and this is with 87dB speaklers. Pulled out 1/3 into a 15 x 32' room, sitting parallel with long walls, you might as well be sitting in a jazz club. It is not a "fast" amp, nor a "crisp" amp, but it still has wonderful air and space. I do not like it on real deep bass, as it seems to get a tad sloppy, but i hesitate on this, because I think with my balanced version, I have a slight amount of VLF oscillation, amounting to about a mV. It seems to be a result of the new modular board setup,as it was not present on the single board trial. I am still waiting on the six filar winding to try single trafo version. I cannot see how this would not be an improvement, but I could be wrong.
I do use a very small amount of degeneration on the FE, about 5r. I also use a resistor in the top degenration position, but have arranaged my fets to do away with it. MY suspicion about the low lever detail is lack of Rs. I noticed this in the Salas folded RIAA. He went to great lengths to mimimize any resistance in the source legs of input fets and i feel like it yielded the same results. Magnificent sense of space and placement.
Take all this with a grain of salt, as it is uneducated opinion, but it always feels good when your feelings are confirmed.
 
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?......

Straight out of the box, it was very dull and lifeless. Realized that the transformer needed breaking in. 40 hours later it was ready for some listening.

The first impression of it is the magnificent soundstage. ........

It is harmonically very rich, and to my ears just slightly too rich. ....
Thanks Jon!
Only a small comment.....:D
Maybe I did too much "hop and ex" building, so I got only the first point of Jons sound description to hear .......:(

transformers can be burnt in....?

That was John called "harmonic richness" was possibly too much with my Tiny Open Alnico Baffle, I prefered "cooler" amps.
The soundstage convinced me immediately!

We really have so different speakers systems....
Nevertheless F6 seems to split people more in two groups than F3 or F5 or J2...
 
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Buzz:
In your balanced F6, did you do anything other than bridge two F6s?
Your impression about the low frequencies being "sloppy" is likely due to the low damping factor of the F6 because of so little global feedback.
Bridged amps, with feedback resistors(100r) connected on either side of 40R(18-20R x2)with ground lifted, after biasing.
Funny thing that i never mentioned because no one has built the Funny^6. With the amp structured this way, it does not matter if midpoint of 40r is grounded or not, there is still some sort of balancing act going on between the two sides. I cannot bias one side and then the other. I have to bring both sides up together and adjusting one side can affect the opposing side.
 
Thanks Jon!
Only a small comment.....:D
Maybe I did too much "hop and ex" building, so I got only the first point of Jons sound description to hear .......:(

transformers can be burnt in....?

That was John called "harmonic richness" was possibly too much with my Tiny Open Alnico Baffle, I prefered "cooler" amps.
The soundstage convinced me immediately!

We really have so different speakers systems....
Nevertheless F6 seems to split people more in two groups tan F3 or F5 or J2...

That why they call it the Tubby:rofl:
 
Bridged amps, with feedback resistors(100r) connected on either side of 40R(18-20R x2)with ground lifted, after biasing.
Funny thing that i never mentioned because no one has built the Funny^6. With the amp structured this way, it does not matter if midpoint of 40r is grounded or not, there is still some sort of balancing act going on between the two sides. I cannot bias one side and then the other. I have to bring both sides up together and adjusting one side can affect the opposing side.
My understanding is that floating the node between the 20R resistors does nothing other than improve common-mode rejection and allow driving the bridged amplifier from an unbalanced source. In tests I did with my balanced F5, I found no significant difference in distortion characteristics with the node floating vs. grounded.
 
I am such a lucky boy. Nelson sent me an F6 to play with and enjoy.

Straight out of the box, it was very dull and lifeless. Realized that the transformer needed breaking in. 40 hours later it was ready for some listening.




A keeper? While at Threshold Corp, Mr. Pass burned in the amps; an operation like cycled logarthimcally at full power.
 
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I never thought of this... Language barrier....

I was just poking at you. Doesn't the Tiny OB use the Tone Tubby 15" woofer.

I am find it very interesting how differently we hear things. I have heard argument after argument about this, with technical guys sinking to the level of us subconsciously deceiving ourselves in our choices. I see it as being 100% possible that we literally hear things differently. Perhaps this can be taken further in that we are affected by the world we work and live in. Perhaps folks used to noisy environments like smooth, soft amps. Others who experience quiet or less audibly stressful places, like a cleaner, crisper amp. I just like that we had similar feelings. Makes me feel not so alone in the world:clown:
 
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My understanding is that floating the node between the 20R resistors does nothing other than improve common-mode rejection and allow driving the bridged amplifier from an unbalanced source. In tests I did with my balanced F5, I found no significant difference in distortion characteristics with the node floating vs. grounded.
Perhaps this is true. I quite happily yield to you in this area, as I cannot light a candle to your technical savy. I was surprised that I was able to maintain slighlty higher 2k, even with the balanced/bridged configuration. I have yet to find an amp that suits me that has higher 3rd over 2nd. OF course my ignorance continues in this regard, as I only view the output at 1K and have not looked at higher frequencies. I am trying to get setup to be able to look at these things in a proper way, but buying equipment for this is slow, as money is low.
 
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I don't know if the problem is with my F6 build or my ears, but I could not get a sound that I really wanted to listen to for extended periods. One of my requirements is for speech intelligibility, which I found lacking in my F6.

Lhquam,

May I ask you....

Did you really play with the k2/k3 ratio at the normal F6?

Did you hear F6 for instance k3 dominant like your F5?

Sorry when you wrote it already in a post.....:)
 
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......... I have yet to find an amp that suits me that has higher 3rd over 2nd. .........

The k3 dominant M2 that sounds darker and more round than the heavy k2 dominant J2......

Normally one pair of IRF96240/240 or FQAs sounds brighter than three pairs... Like in F4!

How does M2 do this? One reason I could imagine.......

The driving current of the input J-FETs.....when I choose lower value Idss, let's say 6mA, I have the impression that that the sound gets darker. With 10mA Idss for the j74/K170 combo the sound gets brighter.

In case of M2, k3 dominant I would take around 6mA at the 10R, means 8mA Idss J-FETs.

The following autoformer brings the voltage high 5x, isn't then the driving current going down 5 times....
Means that the output pairs capacity is driven with a very low current and we have in spite of the k3 a dark sound...

Latest genergs latest wild sound speculations.....:D:D
 
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I love it. Have you rebuilt F6 using matched fets from tracer? I amtrying to set mine up so that I have no degeneration on the output(using fet positioning for distortion manipulation) and a slight amount of Rs on input fets. SO much fun in one package.

Unfortunately I have at the moment heavy hip joint and/or back problems, so I begin to see more doctors than amps at the moment....today's hit was waiting in one's doctors room three hours and in the afternoon two hours...
But things turn better now...

So I do only small things and try to get familiar with the curve tracer and exchange the parts with the least weight means j-FETs....:D:D

Of course I will revisit F6 , my four Edcors 600:600 are still waiting and the fresh curvertraced SSs 100 too...