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Old 1st September 2007, 10:52 PM   #1
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Default value of output caps for Aikido - how low is too low?

The value of the output capacitor has an effect on the frequency that is allowed to pass. More importantly, the capacitor has to block DC doesn't it?

In my Aikido, I am using a 0.68uF Auricap which when put into a 47K load results in low frequency cut-off of 5Hz. I remember calculating this value (159155/5/47000). Now, to what extent, I can actually amplify and hear 5Hz I am unsure, although I expect that very, very little 5Hz sound is in any kind of music. I certainly expect that my speakers will be unable to resolve it.

I have 1uF Dynamicaps in my Phono-pre, which result in a cut-off of 8Hz. I love the sound of the phono-pre feeding my Aikido, and am wondering how much the flavour of the Dynamicaps is contributing to the sound. My CD's played through a Rega Apollo simply lack something in the vinyl (although it could be the analog magic that people envoke).

So, my thought is to swap the Auricaps and Dynamicaps and test. It is a three day weekend and I can buy better valued caps for my respective amps should I like what I hear. A lot of folk reckon that Sonicap platinums are the best, but pricey!

With 0.68uF in my Phono-pre, the frequency cut-off will be around 12Hz.

BUT

with 1uF in my Aikido, the frequency cut-off will be 3.4Hz.

How low is TOO LOW?

Afterall 0 Hz is DC, and I don't want to be sending that through to my ss poweramp, do I?

OK, so 3.4Hz is not 0Hz, but to my uneducated mind, it seems awfully close.

Charlie
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Old 2nd September 2007, 02:00 AM   #2
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bump (sorry)
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Old 2nd September 2007, 02:12 AM   #3
SY is offline SY  United States
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That's not too low at all. Remember that a first order rolloff will significantly affect phase up to about a decade higher- and that's 50 Hz. A lower rolloff would perform better unless you correct phase somehow upstream.

Why not raise the load impedance?
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Old 2nd September 2007, 02:39 AM   #4
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Stuart, the conventional wisdom calls for 5Hz, and that isn't so bad. Yes, there's noticeable (mathematically) phase shift up to 50Hz, but psychoacoustically meaningul (I suppose that means audible) phase shift is said to be below 20Hz, and this is not only a theoretical minimum to human hearing (which I'm not sure I agree with), but a good octave or so below the capability of 99% of all speakers, certainly mine.

There's a balance here, in that we want the bass rolloff to be out of the audible equation, but no matter what output cap we use, its sonic signature is going to go up as its value goes up. Charlie, as most DIY guys, is very fortunate in knowing what load his Aikido is going to be looking at, and so can calculate exactly. I put 2.2F on the outputs of the pre, because I put two parallel outputs on there, and what if it's a sand amp and a sub, a composite 10K load?

Charlie, caps are relatively cheap. Try some stuff, and report back. The polypropylene/tin foil Solen S* (depending on voltage rating) are ridiculously good, reasonably economical, and available. For me, 5Hz worst is a pretty good call.

Hi, Stu,

Poinz
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Old 2nd September 2007, 03:00 AM   #5
SY is offline SY  United States
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Quote:
what if it's a sand amp and a sub, a composite 10K load?
Then you're stuck unless the sand amp is amenable to increasing the input resistance. But that's why I asked the question- if the input resistor can be increased (tube amp, FET inputs, servo, whatever), then that's a really cheap, easy, and sonically optimal way to do things.

I really do think that these phase shifts can be audible if you have really good bass speakers. I haven't done proper blind testing so this is purely speculative, but with my setup, I believe that I hear something related to the articulation of notes and (with good live recordings) hall size when that rolloff is varied between 1 and 10 Hz (the gap I used for testing).
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Old 2nd September 2007, 03:33 AM   #6
mach1 is offline mach1  Australia
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Quote:
with good liver recordings
As reproduced with utmost fidelity on the Sy "Gall Bladder Machine" I assume ?
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Old 2nd September 2007, 04:12 AM   #7
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One of the few benefits of being a moderator is the ability to fix one's own typos.
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Old 2nd September 2007, 05:04 AM   #8
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Thanks, I don't quite fully understand about phase shifts, but will ponder over it and see if I can make sense of things.

So, 3.4 Hz would cause phase shift effects to around 34 Hz. I am sure that my speakers cannot reproduce this frequency that well, even with great liver and onion recordings

My main concern is simply not to go too low, if that is even possible.

Also, Jim Hagerman mentioned that between 8 and 12 Hz is good for a phono-pre due to turntable / cartridge oscillations, so my phono-pre should not be compromised by the simple swap of capacitor values (I can't say the same for cap type).

I'll report back tomorrow, after I have made the swap to 3.4 Hz on the Aikido and 11 Hz on the phono-pre.

Charlie
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Old 3rd September 2007, 12:07 AM   #9
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I swapped the caps between the Hagerman Cornet2 phono-pre and my 6SN7 Aikido preamp.

I had mistakenly read the output caps in the Aikido as 0.68uF Auricaps. They're 0.47uF caps.

So, the 1uF Dynamicaps that were in the Cornet2 were put into the Aikido. This dropped the low cut-off in the Aikido to 3.4Hz. There was quite an effect sonically. The bass became more robust and solid when playing CD's making my "poor quality" CD of Parson's I-Robot begin to sound closer to the analog. The newer "good remaster" of the CD was even better with bass that was focussed, thumping, but not boomy or overpowering. The highs also seemed more precise and sweet.

As for the Cornet2, the 0.47uF Auricap raises the low-fq cut-off to around 17Hz. Again there was a significant difference in sound. The LP version of I-Robot now sounds good, but less engaging. Bass is significantly less exciting. Where, I felt that the new CD release was on par with the vinyl, now the vinyl sounds inferior. I'll have to at the very least go back to a 1uF cap (maybe Dynamicap or Hovland).

This begs the question of capacitor flavour. My speakers begin to roll-off at 45Hz, and I doubt that my of my music really has any significant content below 20Hz, maybe even below 30Hz. So, I am noticing a difference in cap flavour? Maybe, although recent posts in this thread (by Sy) imply that phase effects on decadal harmonics of the low fq cut-off can also be noticeable. So, my original Aikido cut-off would have been at around 7.2Hz, such that out-of-phase effects would have been noticeable at around 72Hz. Would I know what to listen for? I doubt it.

Anyway, the Dynamicaps are staying where they are - in the Aikido, and new 1uF caps will be purchased for the Cornet2.

Any capacitor recommendations?

Charlie
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Old 3rd September 2007, 01:34 AM   #10
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Charlie, you ask a hundred experienced builders that question, you're going to get ninety nine different answers, but my current fave is the Solen S* series (* depending on voltage rating), which are also sold by Mundorf as ZN series. These are polypropylene/tin foil. Be advised, I have read other guys who don't like them, but I find them the most transparent I've tried, which includes Jensen copper, Mundorf Silver Supreme, Auricap, others.

I have a couple different values also of Rel RT, which are polystyrene/tin foil, but I haven't put them in anything yet. These are physically huge for their values, like the Jensens, and only come in values to .47uF, so their utility in my stuff is limited, but I've heard good things about them.

Aloha,

Poinz
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