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The Yokes on me [message #9539] Fri, 10 February 2006 19:04 Go to next message
Manualblock is currently offline  Manualblock
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Illuminati (13th Degree)
I got the DIY TUBE driver board for my ST 70 so I think; let me replace a few parts and see if I can hear the change. Looking on Angelas site I see nice oil caps fopr 7$ each. On the resistor page I am scrolling down and I see these Tantalum resistors so I say what the heck and I order 8 of them for different values.
They came in the mail and for a bill I see 56$ for resistors and about 60$ for caps. I can't figure the bill because I am seeing 7$ for each part and so I call to tell them they made a mistake on the resistors.
Nope; I looked again and those sumbitches are 7$ a piece.
Am I crazy? 56$ for 8 resistors. There must be old guys with picks and shovels up in Alaska mining these resistors.
Oh well; so much for that nice valentines day necklace for my sweety; flowers are nice; right?


Re: The Yokes on me [message #9540 is a reply to message #9539] Fri, 10 February 2006 23:51 Go to previous messageGo to next message
Damir is currently offline  Damir
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Hey, this stuff has its price... I must admit that I recently bought 8 tantalum resistors, too. About $4 per piece, 0,5W - I need them for grid stop/grid leak positions (luckily, 1W=$8 and 2W=$13, locally).
And hey, you can always give a resistor or two with the flowers...

Re: The Yokes on me [message #9541 is a reply to message #9540] Sat, 11 February 2006 09:10 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
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I almost had a heart attack. That'll teach me to read carelessly. So why use them on the grid leak/grid stop side? Is there some sonic benefit to that? I need to find a use for these; they were so expensive I could not bring myself to solder them in.
So; you think they would make nice earring's?

Re: The Yokes on me [message #9542 is a reply to message #9541] Sat, 11 February 2006 10:15 Go to previous messageGo to next message
Damir is currently offline  Damir
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I hope there`s a sonical benefit, I didn`t try them so far - but my experiments with SE amp components convinced me that almost everything is audible
I just tried the grid chokes - there`s a nuance or two difference then 220k grid leak resistor. Little more that "3-D feeling", clarity and warmth. And yes, it`s better for output tube and for the driver, larger AC load. Amplification of the cascode goes "up" about 10%, and sound has more "finesse" :-). I can`t hear any loss of HF (Cw of the grid choke and rel. high Rout of the driver "filter"), but sound is maybe a little too "warm/soft" for my liking - more experiments are in order .
Not a "night and day" difference, I said just a nuances...is this worth that money? In my view, absolutely...

Re: The Yokes on me [message #9543 is a reply to message #9542] Sat, 11 February 2006 12:08 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
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Registered: May 2009
Illuminati (13th Degree)
Well Damir; leave it to you to get to the essence of the issue. Nuance is all we got; without that then we should all just go on E-Bay and buy old Sansui Recievers from the 70's. They get the job done with "Vanishingly Low Distortion", numbers. If the low distortion of .00001 is the indicator of good sound then my old Technics Reciever is the best sound money can buy. Very "Accurate". Thats the whole business of Audio in a nutshell; "Perfect Sound Forever."
Lets just toss all those old crappy tube amps from Harmon and Fisher and Marantz out the trash bin; they have at least 1% distortion; must sound like crap!

Re: The Yokes on me [message #9544 is a reply to message #9543] Sat, 11 February 2006 12:57 Go to previous messageGo to next message
Damir is currently offline  Damir
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Registered: May 2009
Illuminati (2nd Degree)
Hey, then what`s a few bucks in comparison with Absoluteness?
You earned and bought those resistors, for something you love.
It`s an interesting hobby - from engineering/math part to the building and listening, collecting parts...
E182CC has more amplification and more "bright" sound then 5687 (warmer) in this cascode driver. Stay tuned...

Re: The Yokes on me [message #9545 is a reply to message #9544] Sun, 12 February 2006 06:47 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
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Say Damir; you never said what you use for a pre-amp?

Re: The Yokes on me [message #9546 is a reply to message #9545] Sun, 12 February 2006 10:32 Go to previous messageGo to next message
Damir is currently offline  Damir
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"Say Damir; you never said what you use for a pre-amp?"

Nothing. Straight from CD player in the power amp, CD player has 2Vrms (0-VU) max. output, and I used volume function in it, adjustable in 2dB steps - in experiments phase.
Although CD through preamp/buffer can sound stronger, sharper, even cleaner and more detailed - IME, it`s a "sound effect", like additional EQ, or so. Nothing really wrong with preamps, but I don`t need them.

What size is the coupling cap? [message #9548 is a reply to message #9542] Mon, 13 February 2006 13:13 Go to previous messageGo to next message
Old Brown Eyes is currently offline  Old Brown Eyes
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I too have been playing with grid chokes. How many henry are your grid chokes and what size is the coupling cap? Due to the rising impedance of the grid choke I'd expect a gain rather than a loss of HF.

I have not tried nor confirmed but I have been told that the grid choke would not work well with a CCS or choke loaded driver. If one looks at "historical" amps you always see a "R" in there someplace...like LCR or RCL. My grid chokes will also be replacing 220K grid leak resistors. I am going to use RCL coupling and will try 0.47uF cap first...if I have a bass boost I might go up to a 1uF cap or perhaps play with a resistor in series with the grid choke (I'd like to avoid a resistor across the grid choke). I am now obsessing about where to place them (four of them) in my chassis as I hear they are prone to picking up noise.


Russ

Coupling cap/grid choke, etc. [message #9550 is a reply to message #9548] Tue, 14 February 2006 06:51 Go to previous messageGo to previous message
Damir is currently offline  Damir
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Registered: May 2009
Illuminati (2nd Degree)

My grid chokes are 1700H/8k amorphous "C"-core devices. The "Q" of the RCL circuit (choke model - inductor in series with resistor, and paralelled by winding capacitance) is Q=[(L/C)^0,5]/Rw. If we (simplified) observe L as a constant, and Rw=8k constant, too, then we can lower the Q (and avoid subsonic resonance) by enlarging the coupling cap, or by adding external resistance. Series external resistance Rout of the driver "dampens" the Q, and parallel R can also help a bit.
I simply used 4,7µF Mundorf Supreme coupling cap, "good compromise" between the cost/dimensions and value.

In the next couple of days I`ll post about this experiments on "Group Build" forum, but in short:
-E182CC cascode with ~20mA and Ra=15k has output impedance Rout=Ra`=Rin//Ra ~14kOhms. Amplification is A=gm*Ra`, and with gm~4ma/V and very large (infinity) loading impedance (grid choke, Zgch=2Pi*f*L) our amplification is A=4*14=56 times. We can say that we aproach this on high frequencies, say 10kHz, where Zgch=106,8MOhms theoretically and simplified. On larger frequencies, say 20kHz and up, Cw "comes into play" and with Rout of the driver forms low-pass filter. On the lowest frequency of interest, say 20Hz, our Zgch is "just" 213,6kOhms. In parallel with Ra`=14k, we have Ra``=14//213,6 = 13,139kOhms, and amplification is "only" 52,55 times. But, when we express this in dB, it`s a difference of only 0,55dB.
Is this negligible? In my listening tests these days I found that high Rout cascode in combination with grid choke isn`t really the best solution. Sound was bright, and bass was "anemic".
When I used the CCS parallel with Ra, and used Mu-out, then I got the "right" sound, from "bottom to top". Unfortunatelly, I don`t have measuring devices for objective evaluation of the circuit, just the subjective sound" results :-).
I didn`t notice bass boost / subsonic resonances, although Mu-out has low Rout (no ext. damping). As I said, good sound, bass "punch" returnes, and amplification is ~55.


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