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Old 8th September 2008, 12:07 PM   #71
Calvin is offline Calvin  Germany
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Hi,

the only reason for a good cap to be changed could be that it has developed defects because of wrong design or faulty working conditions. Film caps e.g. that suffered from internal flashovers (overvoltage). If that is not the case, than there is no reason for change.
I“m not familiar with C4C5Itsywitsyteenybeeny... but i assume a schematic would help . If C4 and C5 are on the primary side (amplifier side) of the audio tranny than there is no need to use 5kV-rated types. 100V types would be ok. If they however are situated on the secondary side (Stator side, HV-signal side) their voltage rating must be high very high (I“d opt for at least 2x p-p signal voltage).

jauu
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Old 9th September 2008, 04:34 AM   #72
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If I wanted to change the signal path capacitors in my 2 +2's with audiophile grade caps, the highest working voltage I've seen are some Hovland's rated at 1200 V. For the .01 uF caps, should I just parallel 5 or six to get to the 5000 V range .
Same with the resistors. I would like to replace them with the best I can get, but don't see the audiophile types for sale in these High voltage ranges.
Paul
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Old 9th September 2008, 10:51 AM   #73
Calvin is offline Calvin  Germany
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Hi,

...to get to the 5000V range......you will have to connect them in series! Paralleling doesn“t increase voltage rating but the capacitance value. Series connecting increases voltage range but decreases the capacitance value. You have to keep in mind that the voltage range may be a specified as DC-value! The AC-value is typically just 1/3 of the DC-value. And if you look at the datasheets You“ll learn that the AC-value is specified for very low frequencies 50Hz/400HZ/1kHz because these caps were often intended for usage in power-management systems. With higher frequencies the voltage rating drops considerably. The WIMA MKP10, 0.01µF is rated at 2500Vdc and 900Vrms (AC). This later calculates to ~2.500Vpp. The value decreases with a constant rate above 2kHz and reaches 90Vrms (250Vpp) at 20kHz. Sounds slightly different, ey?

Luckily the high frequency content of music decreases too, but if you happen to test with higher power and a white noise signal -which You find on basically each and every test CD- you very probably blow the caps! With regard to this I wouldn“t trust the info on the izzywizzy site that just one cap with a 5000V rating (AC? DC?) will work reliably (I“ve got the impression that they don“t know exactly what they are dealing with anyway, since their parts choice looks rather like a try-and-error game than solid engineering)
You will rather need a string of series connected caps or a specialized HighVoltage cap with ~20kV rating. Series connected WIMA MKP10 or FKP1 will be very ok, as well as competitor“s caps in a comparable build and with comparable specs.
This only relates to C4 and C5 which must have high voltage ratings!
If the maximum signal voltage is far below 100V -as it is the fact for all the other caps- it is utterly nonsense and a lot of wasted money to use vastly voltage overrated caps!!
High voltage rating with capacitors just makes them big and expensive, not better. But in the end that“s what the HighEnder wants.....impressive, vastly oversized and preferably terribly costly looking stuff! Should it come out that its crappy stuff, don“t worry. Just tell everybody that it“s sounding better than You“ve ever heard before.
"Audio Grade" is only a marketing term but implies a superior quality of such a part over “standard“parts. It also seems to imply that this part is superior in any case, regardless of its position within a circuit. This simply does not hold true! Since the demands of Audio are fairly low compared to other technical areas the so called “Audio Grade“parts don“t need to be high quality in a technical sense. Just think of carbon resistors, oil-filled caps, electrolytics and especially some cables which are grossly inferior to standard parts.
The claimed superiority only relates to unmeasurable parameters like sonic behaviour. And that is a subjective and very debatable parameter.
So, apart from C4 and C5 all other caps in the circuit may happily be specified far below the kV-range.
For R2 and R3 (HV-Side) noninductive wound wire resistances are ok
Similar to the caps it may be necessary or even needed to series connect a couple of resistors. I wouldn“t use thickfilm resistors here and the probabely best Rs -made from metal foil- will be very expensive
On the lowvoltage side R1 and R4 can be of Metal foil build. The probabely best resistors here are the Isabellenhuette PBH and PBV and PSB. http://www.isabellenhuette.de

The HV-resistor R5 can be made from a chain of metal film resistors (0.5-0.6W, 1%-5%, size 0207). They are spec“d around 250V-300V, but in practise use them not above ~150V. For 5kV bias you need app 30pcs of 1MegOhm.
The original value of 500Megs is much higher than I“d use if a high ohmic coating is used on the diaphragm. 50Megs at maximum. You should be careful not to touch any HV-point, since the smaller resistance means higher currents and therefore more pain when getting shocked.
If someone reports sonic differences because of using a different resistor for R5 of same value, I“d say this would rather be a hint that the circuit itself is of minor design quality or psychology is playing games on him.
I“d rather make the HV stiffer by using larger Cap-values for C6 to C10 (>10nF) and use a negative polarity output instead of the positive. And adding a blinker cicuit (see Quad) will isolate the HV from the membrane.
The 10nF cap directly at the output of the cascade does no good. If you feel the need -a need that is actually nonexistent in praxis- that you have to smooth out the output than add a series resistor of 10M between output und 10nF-cap.
I don“t believe that a inductor could do anything positive here. The series resistance of R5 added to the high resistance value of the membrane coating works as ripple and noise filter already.
Besides the restrictions Mr. Beck mentioned (though I don“t see “noise signals“ of sufficiently high frequency anyway) we are talking here about microscopically small currents. Which leads to the Q: If there were any ripple and noise above 100/120Hz.....would it supply for enough current in the inductor to make any difference to a resistor of same DC-ohmic-value? Or in other words:" Does the inductor work as inductor, or merely like a low-ohmic wire wound resistor?" Replacing R5 alltogether by a inductor shouldn“t be done because of safety reasons (current limiter).

jauu
Calvin
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Old 13th September 2008, 10:18 PM   #74
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Default substitution of cap values 2+2 mod

Hi thanks again for your help.
I think I've found the parts I want to get.
The closest I've found for the 5000V ..01 uF is a 6000V (went over instead of under Voltage) .0047 uF. Polypropylene isnt available in this high of a voltage, but polyester is. Are either or both of these changes ok?
Also, the high frequency caps in the manual are 220uF,10uF, and .01uF.
I've seen in this forum to replace them with 50uF Blackgate, which I understand are discontinued. I have medallian and C updates. What values are people recommending.
Thanks again,

Paul
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Old 15th September 2008, 02:20 AM   #75
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Where are the measurements folks?!

I_Forgot did what folks should do, which is to use circuit theory to help guide the design process. The next step is to make the change guided by the math and then measure the change. Lets for a moment believe that the the choke and the cap before it made a difference, then that difference should be measurable. If you don't have the tools to measure it, then how to you know that you actually improved it? Ears are hardly reliable. And how do you optimize the change? Is 7H the right number? How about 5 or 10?

So until there are actual measurements, my advise is to stick with the stock acustat circuit.

Also 405man is right, the neon bulb circuit isn't my design, it's been around for decades.

Sheldon
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Old 15th September 2008, 03:20 AM   #76
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Measurements... right!

You can make a string of HV high resistance resistors (say, 10 50-meg-ohm units from your local surplus place) and maybe a 10 meg resistor on the bottom. Then you can read proportional AC and DC voltages or 'scope the signal off the bottom resistor (the one with one end attached to ground, that is).

Glad to see that some sound back-of-the-envelope electrical judgment made the silly choke idea go poof.

The izzy wizzy HV cap, on the other hand, raises the bias supply. Which makes ESLs louder and hence sound better (until you put the SPL back for a fair A-B comparison and then they might sound the same).

Don't forget the old rule for working around HV: always keep one hand in your pocket.
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Old 16th September 2008, 05:18 AM   #77
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Except Bent, the "silly choke" idea is anything but silly when you hear the effect.... It is not a subtle change at all, and no I am not hearing things. Your back of the envelope may disagree which is its privilege.

Regards,

Rob.
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Old 17th September 2008, 06:53 PM   #78
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I'm not going to discount your listening experience, but how do you design anything using your ears?

Electrically the choke is meaningless, so how do select the correct value, and how do you know that your "different" is "better"?

Sheldon
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Old 18th September 2008, 08:34 PM   #79
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Default some find it unbelievable....

but it can be done, has been done and is done. Kind of like paint by numbers without the numbers. Difficult yes that goes without saying but it is done. The best of all worlds is (I think) when both measurements and listening are used together as long as the ears have veto power. All the great masters built their instruments with their ears and their hands. That tradition holds to todays best as well.
Lets face it you can find good examples of both methods and this is not about right or wrong. Either method can suggest experimentation be done as long as the ears rule the day I dont think you can go wrong. You know what happens when the "bean counters" start to tell the engineers how to design a bridge.
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Old 18th September 2008, 10:06 PM   #80
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Quote:
Originally posted by stokessd
I'm not going to discount your listening experience, but how do you design anything using your ears?

Electrically the choke is meaningless, so how do select the correct value, and how do you know that your "different" is "better"?

Sheldon
Sheldon, I agree in terms of designing anything that measurements have to be used to get in the ballpark so to speak. However, In this case I agree that I cannot think of a mechanism explaining what I hear. I had it demonstrated to me (blind) in a friends system and it is very obvious.

That said, it is easy to decide whether different is better if you live with the change for a while, and IMO making a good design better requires the use of the ears.

Rob.
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