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Old 11th August 2012, 06:29 PM   #1
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Default FAST with Feastrex D9NF and Fertin 38EX

Hello DIYAUDIO-forummembers,

after the amplifier-projects (TB3/1000 and the 35TG), the turntable and tonearm project (18" tonearm based on the WTA) it was time for a new loudspeaker-project.
Till now i played with a selfbuilt Avalone-clone. That sounded quite allright but was not the best in "natural presentation". I invested serious money in the Thiel/Accuton-units and the crossover and the combination with the amplifiers was good.

Till an audio-collegue simply wanted to buy my Avalon-clones....that was the trigger to start the new project.

The idea was an Open Baffle (OB) with only 2 units. A fullranger for the most of the spectrum; and a woofer to take care of the serious low. It is almost mission impossible for a single unit to deliver serious low AND clear highs at the same time (resticted by space that ruled out extreme horn enclosures). So FAST: Fullrange And Subwoofer Technology.

For the (almost) fullranger i choose the Feastrex D9NF. A great performer. If i had to make a real single-unit-loudspeaker....this would be my choice. But if you lift the burden of high bas-energy from this unit it REALLY begins to shine !
For the woofer i took the Fertin 38EX. This is a fieldcoil-unit. In normal circumstances you can change the voltage in order to change the sensitivity AND the Qts. The sensitivity of the Fertin 38EX is between 90 and 99 dB. Going the lesser sinsitive region the Qts is going up; very favourable for OP-designs. So this gave me the option to actually optimise the unit to the enclosure !

In order to establish the correct crossover frequency i made a temporary setup of shores and 18 mm plywood. This worked quite well. Crossover point was set at 230 Hz (second order LR).

The crossover was built with a serious Mundorf VN390 coil and some old paper/oil Westcap-capacitors (outperforming Mundorf caps). For the correctioncapacitors i used polystyrene Component Research Capacitors. The really funny item here is the Silvercore autoformer.
As the sensitivity of the Feastrex and Fertins is not the same an attenuation of the Feastrex was needed. But resistors (even very good Caddocks / Mills / etc....) took away some of the magical "ease of perfomance" of the Feastrex. The Silvercore autoformer solved that problem.

The open baffle itself is made out of 30 mm plywood + 18 mm chipboard + 25 mm MDF in order to surpress resonances. Till now i used always massive MDF but an audio-collegue convinced me to go for the multilayer-design.....and he was right (thank you Helmuth !).
The baffle was milled on the inside of the OB in order to let both units breathe freely.

Now it is time for the last pints: a nice box over the crossovers (real dust collectors....) and of course some serious listening. The first impressions are very good: oodles of effortless bass (dry !) and the desired "natural" representation. Soundstage is already amazing 3D.

Pictures included
Enjoy the music !
Regards,
Reinout
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Last edited by ReinoutdV; 11th August 2012 at 07:46 PM.
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Old 11th August 2012, 09:44 PM   #2
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Hmmm...that's only what, about $10K for the drivers? Good golly Miss Molly, I guess with that kind of gear you couldn't afford a better view?

Your set-up looks like it costs more than my condo. Tell us more about it please, my keyboard has been drool free for a while. The TT alone is a piece of art.
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Old 12th August 2012, 05:30 AM   #3
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Default set details

Good morning Cal,

scanning through your speakers-systems....you are more than an average audio-enthousiast !!!!!!

Added some pictures of my set.
The turntable is made from a 50 cm platter (of a cutting lathe). Of course the added weight makes the turntable much more stable. Most manufacturors choose to make the turntable heavy by means of height. This works but is not efficient; for the flywheel-effect it makes much more sense to enlarge the platter. That is why i use the 50 cm platter (17 kg acryl). It takes several MINUTES to come to a stop after running at 33 1/3 rpm.
Problem of course is the need for an oversized tonearm. Theoretically a 12" arm would fit; but only with a very small armbase. There is simply not enough space. There are no commercial >> 12" arms available (however Clearaudio does currently have a 14"arm) so i took up the challenge making my own.
Based on the Well Tempered design and a lot of resonance tests i made my own 18" tonearm. It took time but the result was great. Surprisingly i made myself a tonearm with a light effective mass (i assumed it would become at least middleweight). The combination with a Van Den Hul Colibri cartridge is really optimal (and i do like to support national products).
The added picture shows a normal LP on the platter; it gives a good idea about the size.

For CD-reply i use a Bel Canto CD2 as transport. My own TDA1541A-DAC does the conversion. Different here is that i do not use a tube or opamp buffer as output; only high quality transformers. So from the NOS parallel TDA1541A through the transformer straigth in the preamplifier.

The amplifiers took the most time to build. These are monoblocks with dedicated external power supplies. Each required voltage does have a complete seperate supply line: transformer - rectifier - coil - capacitor - choke - capacitor. This makes the power supplies quite heavy (more than 100 kgs each). The audio-path is completely transformer-coupled: mumetal input transformer - 6SN7 (input tube) - permalloy interstage - 300B (driver tube) - armco interstage - TB 3/1000 (output tube) - armco output transformer. This amp started as an 833A-amplifier; but i conversed it to use the Philips TB 3/1000 triode. Depending on the set voltage i have between 70 and 100 watts single ended Class A.
The amplifier became so heavy (almost 400 kgs now....) that i had to construct my own rack as no commercial racks can hold this load.

I do use my Grado RS-1 headphone a lot. This is connected to my own tube headphone amplifier (6SN7 tubes) with external power supply. The transformers were specifically wound for the 32 ohm Grado; most headphones are in the 600 ohm region. It works great.

Bought pieces: a Nagra BB harddisk-recorder, a Mandozzi DART harddisk recorder and a Gryphon preamplifier.
I expect that the Gryphon will depart soon; i already made a good phonostage and there is certainly room improvement.

About the view....that is only part of the roof terrace....
Hopefully this reply does answer your questions.
Please do forgive my faulty English......
Regards, Reinout
(most of my projects are on this forum)
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Old 12th August 2012, 06:56 AM   #4
ScottG is offline ScottG  United States
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Bah, your English is excellent and so are your beautiful projects - ALL DROOL-WORTHY!

(..a veritable parade of porn for this forum. -cue the funky bass riff.)




The exquisite layout and wiring of your amps looks downright architectural.
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Last edited by ScottG; 12th August 2012 at 07:01 AM.
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Old 12th August 2012, 05:45 PM   #5
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Good evening Scott and Cal,

thanks for the comments !

I forgot to add the picture of the DAC (which started here in 2004 on this very forum !) with the step-up transformers. Currently totally nude/bare (awaiting a nice enclosure) and even ow there is totally NO hummmmmmmmm.

Just finished something very important: the OB-frontal-cover in order to prevent my 1 1/2 year old son to investigate the units with its little (but destructive) fingers.....AAAARRGGHHH.

Regards, Reinout
(also added some pictures of one of the other amplifiers. These monoblocks are based on the small but powerful Eimac 35TG. It pumps out around 10 Watts; and after when the OB's are correctly placed i really look forward to the combination with these amps)
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Old 12th August 2012, 06:35 PM   #6
fulken is offline fulken  United States
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Reinout、

Congratulations! Your system looks VERY nice!!

What is the small tube on the floor, 3C24? I like how it looks! How do you describe sound of this tube?

I have one more reason to visit Netherlands now!

Cheers!
Kenji
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Old 13th August 2012, 01:25 PM   #7
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Thank you for posting more of the details.
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Old 13th August 2012, 06:43 PM   #8
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Good evening Kenji,

the small tube on the ground is the "Eimac 35TG". It is a bit bigger than the 3C24; but certainly the same style. I made a picture of the 35TG next to a 300B.
It is a GREAT performer; but needs care and attention to the power supply (but isn't a amplifier nothing more then a very stable power supply ???). Although the size is small; it likes (needs !) to run red-hot ! I'm running them at more than 800 V but it can take more if really needed.

Please follow the link to an earlier thread on this forum Eimac 35TG amplifier glows !

The 35TG is very nice sounding (very detailed and powerful); problem is its availability. During the last years i gathered a lot of them in order to have my own personal supply. Prices are changing constantly and much !
That is not a problem when you choose the 3C24; very easy to source.
I've not made an amp with the 3C24; no idea how that sounds....

If the combination of the 35TG amplifier and the new OB is better then the combination with the (very large) TB3/1000 amplifier i have a problem......that means that the TB3/1000 amplifier is of no use to me anymore. Of course the TB3/1000 has one very big advantage: it kicks out amazing power (between 70 ~ 100 W) and the 35TG only 10 W; but theoretically the new OB will be sensitive enough.
But who is really interested in 400 kgs of amplifier.......it is REALLY large.
By the way i'm not completely finished with the 35TG amplifier. Just as in the TB3/1000 amplifier i make use of a Jensen input transformer. Very nice.....but it can be better. I will use the same transformers Silbatone puts in there grand preamplifier (see picture). That is the new project.....


Regards,
Reinout
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Old 16th August 2012, 06:02 PM   #9
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Default covers in place

Good evening all,

everything is running OK....but the crossovers act as dust-collectors.
At a shop which sells showcases (custom made) i bought 2 plexiglas covers. And now the crossovers are nicely covered.

Regards,
Reinout
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Old 16th August 2012, 06:50 PM   #10
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You do very nice work.
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