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a few caps questions - urgent please!

post #1 of 12
11/25/09 at 7:06am
Thread Starter 
Hello. I've also posted on the diyaudio forum, but no reply so far. I'm about to place the order for the components of a Firstwatt F2 for my K1000's and I need a bit of guidance. I'll buy from Mouser. Please answer at least the first question, that is the most important by far (perhaps also the second one).

1. For the big electrolytics I can only get Nichicon VR (miniature, 2.81 €), VY (higher temp. raiting, 4.69 €) or KW (audio, 5.25 €). Which one? Is the KW worth the price difference?

2. For the 10uF C5 I can get a rather expensive EPCOS polypropylene at 6.31 €, an even more expensive WIMA polyprop at 10,38 € or some polyester ones: WIMA at 3,46 €, WIMA at 4,88 € (up to 100C) or a cheaper Nichicon at 1,67 €. Quite a large range of prices, what do you suggest?

3. For the 1uf C1 I can only get a polyester Vishay from Mouser, is it good enough?

4. For the 3300pF C9 polyprop. - WIMA or Vishay?


...And an extra non-capacitor related couple of questions: Vishay, Xicon or KOA Speer metal films resistors? Is there a particular resistor in the F2 schematic that would benefit from a higher quality (Takman metal, Takman carbon or Kiwame)?


Please give me your opinions! I'm really anxious to place the order. I'm a diy (and electronics) newbie and I've really worked a lot to do my homeworks.

Thanks a lot!



Edit: for those who understand better (and if numbers are relevant at all) here are the datasheets of the Nichicons:
- VR datasheet: http://products.nichicon.co.jp/en/pdf/XJA043/e-vr.pdf
- VY datasheet: http://products.nichicon.co.jp/en/pdf/XJA043/e-vy.pdf
- KW datasheet: http://products.nichicon.co.jp/en/pdf/XJA043/e-kw.pdf
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post #2 of 12
11/25/09 at 7:17am
1) What are the "big electrolytics" and what are they used for?
2) Shouldn't matter all that much.
3) Input coupling cap, go with something nice.
4) Can't find C9.

Resistors : I like to stick with Vishay/Dale RN line. If you want something fancy, consider PRP resistors.
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post #3 of 12
11/25/09 at 3:31pm
Thread Starter 
First, thank you.
1. The big electrolytics are those in the PSU as well as the C3 (output cap, bypassed with C2) and C4 & C6 (avoid turn on thump) on the main board. See the schematic linked in my first post. In the mean time, I got 2 votes for the KW on the diyaudio forum, so unless somebody disagrees it's kinda settled.
2. Ok
3. Oops, I was stupid!! There's plenty to choose from, I don't know why I couldn't find the polypropylene ones. I don't know how important are the tolerance figures. What would you pick:
- Vishay/Roederstein 5% at 1,90 €
- WIMA 5% at 13,88 € (oops!), or
- WIMA 10% at 3,14 €
 ?
4. You're right, there's no C9! Stupid again! I was guiding myself by an old BOM of another head-fi member and I think there was a mistake there, but I can't understand how come I didn't notice it!

So only question nr.3 remains.
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post #4 of 12
11/25/09 at 4:45pm
I don't remember the part # but I have measured more distortion from Nichicon Gold "audiophile" electros than one of their other standard types

Cyrill Bateman's "Capacitor Sound" series showed non-polar Al electros with full thickness Oxide grown on both foils to have lower distortion



f2 topology, power may be fine but its voltage, impedance is scaled/designed for 8 Ohms

for K1000's insane low sensitivity and 120 Ohm impedance you should want at least ~4x supply V and rework bias, heatsinking and Mosfet choice (why not laterals? to match your obsessing over passives)

impedance scaling the circuit makes the electrolytic value go down, helping in choice (though physical size would be similar since you need higher V rating)
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post #5 of 12
11/25/09 at 5:17pm
Thread Starter 
So you'd go for VY's?

K1000 + F1 is a well known synergistic match and I of know at least one head-fi member reporting good sound from K1000 + diy F2 clone. "Reworking" is much above my possibilities as I have no electronics background or diy experience.

This is the reason why, sorry, I don't understand your last phrase at all
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post #6 of 12
11/25/09 at 8:08pm
it does require some know-how but is fairly simple

for 120 Ohms the circuit should use ~4x the supply voltage and all of the bias settings should be adjusted to give 1/4 of the bias current

the power supply should be increased to ~ 100 V, some of the resistors should increase in value 4x, some of the Caps can be reduced in value by 4x - but their V rating must be increased 4x, others of the R and C can be changed 16x, a few stay the same value but the V rating may need to increase

the Mosfet V rating is OK but they are sized for much larger current and this makes them have large parasitic C which adds to distortion, much smaller Mosfets would be better - with lateral Mosfets having very low Crss compared to the Vertical Mosfets types specified - smaller lateral Mosfets are hard to find but the 2SK213, 2SJ76 pair would much better fit the impedance scaled amp

found this: http://www.bdent.com/search/part.jsp?partnum=2SJ79
has 2sk216 in stock too - the higher V rating parts are cheaper too
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post #7 of 12
11/27/09 at 9:05pm

warning leaving SELV zone - electrocution danger

a simplified, impedance scaled version of the f2 more appropriate for 120 Ohm load:



since the f2 is designed for 8 Ohm loads and the K1000 are 120 Ohms you should want to change power supply and bias to better match the higher impedance load

sqrt(120 Ohms / 8 Ohms) ~ 4 - so you need 4x Vsupply and ~ 1/4 the current

I'd like to recommend smaller Q at the lower current but power dissipation is the limit for such inefficient ccs Class A circuit
the irfp240/9240 TO-247 package would be the choice with hefty heatsinking - worst case is the ccs ~0.7 A * 100 V = 70 W from a single transistor

LtSpice asc file:
LL
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post #8 of 12
11/28/09 at 3:46pm
Thread Starter 
Oh my! You're making this so tempting! But I have already ordered all the parts needed for the regular F2 from Mouser. What do you think I'm going to loose by building the regular design as compared to your K1000 adapted one? Please tell me it shouldn't be such an important difference!?!

...and thanks for your participation to this thread!
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post #9 of 12
11/28/09 at 5:33pm

the spade lugs are there to wire K1000 to a power amp, >50W

sorry but with 24 V supply you'll be lucky to get 7 Vrms => ~400mW into 120 Ohms

most other headphones would be well driven by that much power but the K1000 has uniquely low sensitivity

K1000: 74 dB re 1mW + 10*log10(400) = 100 dB SPL


100 dB clipping level is not "audiophile" dynamic headroom - yes you can listen all day at 80-85 dB SPL ave and it won't clip with most audio source material out there - but tonal balance will be off if you're not listening at the same level as the real event - and some recordings have over 20 dB peak-to-ave on cymbal crashes or snare hits

to really approach "live event" music reproduction you can need up to 120 dB for transient peaks of orchestral or jazz music (see the musical instrument spl table in the headwize article):

HeadWize - Article: Preventing Hearing Damage When Listening With Headphones (A HeadWize Headphone Guide)

this review suggests 10 W into K1000 for dynamic headroom:
AKG K1000 Headphones Review By Alvin Gold


even with the impedance scaling and 100 V supply the modified f2 circuit won't put 10 Wrms into the K1000, more like 6 Wrms depending on how much shunt R you decide to use
but 112 dB SPL clipping level is a significant margin over 400mW, 100 dB

to get more power out of a f2-like circuit topology without heroic heatsinking effort (copper chill plate with running water?) you have to go to one of Pass' Zen variations with higher efficiency using modulated current source and bump the supply V up even more
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post #10 of 12
11/28/09 at 7:01pm
Quote:
Originally Posted by jcx View Post
I don't remember the part # but I have measured more distortion from Nichicon Gold "audiophile" electros than one of their other standard type
Damn! the essence stx is made with these Nichicon fine gold (guess these are the same) ...not too bad given the price of the card
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post #11 of 12
11/28/09 at 7:08pm
Quote:
Originally Posted by Gibertus Jeunus View Post
Damn! the essence stx is made with these Nichicon fine gold (guess these are the same) ...not too bad given the price of the card
Boutique capacitors are sort of like tubes - conventional wisdom regarding distortion, ESR, and ripple go out the window in the face of "what sounds good." The Nichicon Fine Gold is a very worthy capacitor in the signal path.
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post #12 of 12
11/29/09 at 10:05am
Thread Starter 
If it's only about the clipping point at 100dB, then I hope it's gonna be alright. My usual listening level is quite moderate, I don't know how many decibels but I'm sure I don't go over 90-95dB max for peaks, so around 75-80 dB on average. If my estimation is correct. To give you a term of reference, I'm listening on my 3030 Stax setup with the volume knob at 9:30 o'clock regularly and no higher than 10:30 for symphonic music with serious dynamics, and I don't feel the need to go any higher. I currently use the K1000 with a SLA battery driven 15 W / 8 ohms T-amp with 6 ohms (or 8?) resistors across outputs and I don't go past 12 o'clock, usually around 10-11 o'clock (the "0" or off position of the pot is at 6 o'clock).
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