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Old 14th November 2012, 04:35 PM   #1321
qusp is offline qusp  Australia
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OK fair enough, well thats a pretty similar outlook to my own and is why i've been making so much noise.

yeah I wondered about that, I was just reading the 600R directly from the build manual, 1.2k makes more sense, why frame it as 600ohms? doesnt that just confuse matters since noone is ever going to be using the number to calculate a parallel cap value? its OK, I just didnt read carefully enough.

however going by my calcs a 22uf cap gives me a corner of 6.03Hz, with phase distortion up to 60Hz

F = 1/(2 * pi * C * R)
PI = 3.14
CAPS FORMULA 0
INPUT IMP FORMULA 1200
WORKING 0.03
WORKING 0.17
WORKING 6.03

soz looks as though you've mostly covered that above.

I may end up throwing an....electro (gasp, a bipolar) in there temporarily. they make a 20uf, but it adds 20ea to the price for 10uf.


you spoke of increasing the input Z for the headamps, what about doubling the input for the poweramp? making it 2.4K? then i'd be happy enough with 10uf. this is why I wasnt really thinking about my own caps for a while and why I was leaving this to Pinnochio, but seemed like a good opportunity to get the pricing down, i'm fine for the LPUHP

Last edited by qusp; 14th November 2012 at 05:00 PM.
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Old 14th November 2012, 04:38 PM   #1322
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Owen, Qusp,

I'll be using this on two different power amps. One with 5K and one with 10K input impedance. What would be the optimal value to satisfy both? Should I stick with the BoM value?

Thanks
Do
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Old 14th November 2012, 04:52 PM   #1323
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Hi Do,

With an input impedance of 5k worst case, you would want roughly a 16uF cap to fulfill the 10x rule. That basically means you're targeting an Fc of 2Hz which means you won't get any phase shift until about 20Hz.

I would say that with a loudspeaker, that rule is overkill since the amplifier's contribution is going to be swamped by variations in the loudspeaker, but if you want it to be technically perfect, then stick with that.

I strongly doubt you could hear a difference between a 10uF and a 16uF cap in your application though, so you'd be safe with either.

As a side note, there is no "ideal" value. The capacitor just has to be "big enough" to work correctly with your next stage's input impedance. If you went ahead and put a 100uF in there, you'd be safe for almost any reasonable impedance in the next stage.

Cheers,
Owen
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Old 14th November 2012, 05:03 PM   #1324
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Optimal depends on how particular you are about LF response. That said, 5k input impedance is "worse" than 10k, so that should probably be the target of your calculations.

So, using the formula for the cutoff (-3db) of a regular RC-filter:

Fc = 1/(2*pi*R*C)

R is 5000 in your case and C we haven't decided yet. Let's try out two values, 4.7uF and 10uF.

For 10uF Fc = 3.18Hz and for 4.7uF Fc = 6.77Hz. Bear in mind that in both cases, the roll off will start well before the cut-off, but only you can determine how low you *need* the amp to linear. For example, in the example Owen posted earlier, the -3db is somewhere between 6 and 7 Hz, but at 20Hz you do have a small attenuation too. If you can live with that, you should be fine with 4.7uF, if not, go for a higher value.

There are also phase properties to consider, but I leave that topic out for now.

Note: I don't mean you should make a decision based on the data I present here. I'm merely showing how to go about finding out what you need.
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Old 14th November 2012, 05:09 PM   #1325
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yeah i'm thinking we just stick with 10uF, i'll throw in a bipolar electro for a while, till I figure out what to do, maybe the auricap will end up being the bypass haha.
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Old 14th November 2012, 05:12 PM   #1326
qusp is offline qusp  Australia
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Quote:
Originally Posted by Emphrygian View Post
Optimal depends on how particular you are about LF response. That said, 5k input impedance is "worse" than 10k, so that should probably be the target of your calculations.

So, using the formula for the cutoff (-3db) of a regular RC-filter:

Fc = 1/(2*pi*R*C)

R is 5000 in your case and C we haven't decided yet. Let's try out two values, 4.7uF and 10uF.

For 10uF Fc = 3.18Hz and for 4.7uF Fc = 6.77Hz. Bear in mind that in both cases, the roll off will start well before the cut-off, but only you can determine how low you *need* the amp to linear. For example, in the example Owen posted earlier, the -3db is somewhere between 6 and 7 Hz, but at 20Hz you do have a small attenuation too. If you can live with that, you should be fine with 4.7uF, if not, go for a higher value.

There are also phase properties to consider, but I leave that topic out for now.

Note: I don't mean you should make a decision based on the data I present here. I'm merely showing how to go about finding out what you need.
no, I dont think we can completely disregard phase. I think maybe 10uf is the better choice for all concerned though, I already asked about their stock, it makes not much difference to the price, 20uf does.

i'm using a different dac and amp below 60Hz anyway

Last edited by qusp; 14th November 2012 at 05:17 PM.
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Old 14th November 2012, 05:16 PM   #1327
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Quote:
Originally Posted by qusp View Post
no, I dont think we can completely disregard phase
I agree, I just wanted to show some kind of starting point.
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Old 14th November 2012, 05:28 PM   #1328
qusp is offline qusp  Australia
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Quote:
Originally Posted by Emphrygian View Post
I agree, I just wanted to show some kind of starting point.
fair call. but i'm concerned that there is still only the usual suspects contributing here....

its only of pretty temporary concern to me, my speakers will be 3db down at 60Hz while they are just 2 way, till I get my subs going. the Subs will use a different dac and amp channel, not this IV and then when theyre ready i'll probably push that up to 120Hz.

plus i'm using digital crossover with convolution, so to be all precious about phase response is pretty funny really.

Last edited by qusp; 14th November 2012 at 05:32 PM.
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Old 14th November 2012, 05:51 PM   #1329
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For my uses, 10uf is adequate (headamp).
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Old 14th November 2012, 06:52 PM   #1330
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ok i've started putting together the emails (wish we could send more PMs at a time, its a pain having to send it multiple times multiple times... i'll send the keratherm and chassis stuff separately.

i'm buggered and I havent heard back about the 10uf stock yet plus it would be good if more can poke there head in here and see the conversation. its nearly 5AM and I havent gotten the work I needed to get done last night done yet, so ive gotta go, i'll finish it off when I get up. but at least there was some conversation here.
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