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166.170.0.55
In Reply to: RE: I wasn't thinking of shielding Rick ....Power Supply !! posted by drlowmu on November 08, 2015 at 18:02:19
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The Mind has No Firewall~ U.S. Army War College.
Follow Ups:
I'm getting older. I've been building, designing DHT amps since 1982.
The VERY FIRST design advice my audio mentor, Mr. Robert W. Fulton told me in 1981 was this:
" A DHT is a "direct-access-to-the-music device " and as such, ALL the chokes have to be TWENTY Ohms or less, IF I can find them ".
I've experimented and listened to many different supplies, with his guide in mind, and Robert was RIGHT ON !!
After you hear ten Ohms or less, 55 uF or less, and PROPERLY wired, its truly impossible ( for me ) to go backwards, to your suggestion.
My NEXT choke build will likely be 4 Ohms in DCR, under two pounds in mass, with the equivalent of 9 AWG of choke lead wires, in and out. Likely in December 2015. Dowdylama and I decided ... we are going for it !!
I look forward in early 2016 to "A-B compare" 4 Ohms DCR versus 10 Ohms, in " my style of DHT SET DC amp build ".
See picture of under ten Ohms L1, L2, mid-2015 implementation, with wiring, above.
L1 is a lead-wire modified -otherwise stock Stancor C-2708, measures 500 mHY, located under the white, grey, and yellow wires at the top of the chassis, and it uses ONLY 1 1/2 inches of lead length from the 5U4GB Raytheon double getter rectifier tube. The green L2 is under 8 Ohms as I recall, 2.2 HY.
Jeff Medwin
I have a 25 ohm 5 henry right here... 500ma, weighs about 15 lbs.
That WAS a definite improvement. All the Ham guys extol what you say...
Low DCR chokes... they, like myself realize critical inductance.
4.3 is the minimum for choke loading, it is no coincidence there being so many chokes starting @ 5 Henrys.
The Mind has No Firewall~ U.S. Army War College.
I agree, Critical Inductance is cool if you are building an industrial DC power supply, but NOT ever for the highest possible performance audio amp. For audio power amps, SETs, I find Critical Inductance is NOT desirable at all. It forces you to use filters with too much energy storage, that are always EASILY out-performed by smaller Ls having NON-critical inductance.
No matter WHAT the DCR is, any 15 pound choke that you reference has too much mass and energy storage. I like Ls best - two pounds and under. Remember, I have been listening to different Ls in DHT amps since 1982, all types !!
Every Serious Stereo, state-of-the-art 2A3 monoblock is proof of this concept we are discussing, as it employs LSES ( low stored energy supply ) filters, as is any amp employing a Flywheel filter, which is typically 30 or 40 mHY as L1, 15 or 20 uF as C1, followed by L2/C2.
The LSES inductor approach is only a small part of what gets an amp to go.
The caps have to be small, low storage - under 50 uF, and they have to be multiple film cap bypassed in my SET experience. To get adequate filtering, the LSES approach to B+ filter building calls for a L1/C1/L2/C2 filter in ALL cases. The wiring has to be LARGE, because its all source-fed, and we wanna keep the peak currents, and transient nature of live music INTACT through the SET amp !!
The proof of the pudding, is in the eating. So I rest my case.
Jeff Medwin
I have 43 microfarads... total in the entire amp...dead quiet using modified Khorns.
The Mind has No Firewall~ U.S. Army War College.
Edits: 11/09/15
The whole point of a critical inductance input choke is keeping each diode on, in turn, for it's entire 1/2 cycle.
That keeps the current flow from the transformer to the filter cap low and steady. This gives a sinusoidal wave form ripple instead of a saw tooth wave form ripple.
With anything less than critical inductance each diode is only on for a short time. Therefore the current has to be high during it's short allotted time. These are current spikes.
They are very hard of the power transformer and the rectifier tube.
Lynn Olson says they create RF hash that can't be filtered out because it's airborne. It has to be shielded out.
BTW "Critical inductance" is the amount of inductance, for a given voltage and current, that causes the diodes to stay on, each in turn, for their entire 1/2 cycle.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Wow, what an interesting opinion, at least it is presented as experiential and not dogma, though some responses venture into the dogmatic world. But what would audio be without unsubstantiated, unproven dogma? I think many participants would leave the hobby.
Let's face it, the noisiest systems usually use horns and SETs. I would put forth that it is entirely possible that the dynamic systems are not dynamic because there is low level noise, but rather, there are great things about horns and SETs that include great dynamics and life, yet a common trait is also noise....that does not mean that noise makes things sound dynamic!.
Having many SETs, I happen to have 2 that are exceedingly quiet at the exit of the 100+ db horns. These happen to be some of my more dynamic amps.
Now, wouldn't it be ridiculous for me to say "Quiet SETs are the most dynamic"? Oops, there I go again, not spewing dogmatic conclusions based on a very small sample. I have to remember to be more dogmatic, more audiophile-like.
Other than the reference to Lynn Olson my entire post was pure fact, not opinion.
As to what a critical inductance choke input filter power supply does to the sound of a audio system....that might be seen as opinion. But I didn't say anything about sound.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
And its also a DEAD amp DYNAMICALLY !! I can guarantee you this, from years of experimenting, no, .... decades.A dead quiet amp .............is ALWAYS a dead amp!!!!!!!!!!
Your large chokes are KILLING the dynamic performance my friend. Likely your wiring is suspect also. If you build a amp optimally, you would easily run a SET Type 45 amp, and not have to revert to a P-P Type 45 amp on K-Horns !!
Your small caps ( 47 uF total ) are only PART. one third of the solution, there is (1) choke size and (2) wiring to optimize also, to get the highest possible performance. Believe me !!
Jeff Medwin
Edits: 11/09/15
Am sorry your perception leads you to believe your approach is the only correct one... that severely limits your progress and learning...Ihave never heard a more dynamic amplifier than the 801 I have built. Your perception is hobbled by your lack.of.vision, Jeff.
The Mind has No Firewall~ U.S. Army War College.
I will not criticize you, and I do not doubt your positive experience with 47 uF TOTAL in your 801 amp.
The best answer would be an A-B session on a decent high efficiency system, yours or mine. It would be informative and FUN for both of us.
We are likely located a thousand miles apart. Oh well.
Very nice corresponding with you.
Jeff Medwin
I love the 801.
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