[CButterworth]

I cannot stop tweaking, can I?

Right now I have a 1uF Dynamicap as the output cap (C208) on my Cornet2.  I assume that this means that the frequency cut-off on the output going into my 20K load Aikido is around 8Hz.  (my math is based on Cap Value = 159155/FqCutoff/impedence to be driven)

In my Aikido, I have a 0.68uF cap as the final capacitor (an Auricap).  This drives a 47K load and gives a Fq cut-off at 5Hz.

Now, I find that my Cornet2 is a little more bass intense than many CD's.  So, I was thinking of seeing if the Dynamicap would have a positive effect if placed in the Aikido, where it could add it's tonal qualities at the preamp stage benefitting both the Cornet2 and my CD player.  If things sound OK, I could always replace C208 with a 1uF Auricap, and then possibly invest in a 0.68uF Dynamicap.

If I put a 0.68 cap in the Cornet2 at C208, I get a frequency cut-off at around 11.7 Hz rather than 8 Hz with the stock value.

If I put the 1uF cap into the Aikido preamp, I get 3.4Hz fq cut-off rather than 5 Hz with the "stock" value.

Of course, there's is next to no music that has frequencies that low, and my speakers certainly can't reproduce it.

Hence, my question:

1. Will the different frequency cut-off value in the Cornet2 have an adverse effect?
2. Are my figures accurate?

By making the swap, I can hear the effect of a dynamicap in my Aikido without having to go out and buy one.  If it sounds good, I can leave it there, and maybe add a second different type of cap (as the PCB allows switching between output caps).

Furthermore, I hope to balance the bass between a good CD and a good piece of vinyl, or at least come close.

Any ideas, or am I just crazy?

Charlie

[hagtech]

Your analysis is correct.  The issue with cutoff frequencies is that you really want to go as close to dc as you can get.  Except for a phonostage.  In everything else, the idea is to preserve zero phase shift all the way down to 20Hz.  Same at upper end, 20kHz.  This typically means "full range" for electronics is 2Hz to 200kHz. 

However, there are problems with doing this with phono.  And we must compromise.  The issues are turntable rumble, LF acoustic feedback, footfalls, and tonearm resonances.  The arm/cart compliance mechanical resonances are usually around 10Hz or so.  I think a lot of experts like to design them to fall into the 8Hz to 12Hz range.  You can find out yours by using the HiFi Test Record.  We do not want the phonostage to amplify any of this mess.  We want to remove all rumble and arm resonance yet pass all audio.  What?  A brickwall high-pass filter at 20Hz?  Well, we already know what phase nasties can do to audio with steep filters.  So we must compromise.  The IEC modification to the RIAA curve puts a corner at 20Hz (-3dB).  This is good to get rid of rumble, but affects the sound of the bass.  The compromise depends on the quality of your table/arm/rack.  How much crap do they create?  The better the front end, the lower you can push the bandwidth of your phonostage.

And making matters worse, is that the Earth has a resonant frequency of 7.81Hz.  That's right at the typical 8Hz arm resonance some designers aim for.  Is that good?  I dunno yet.  Are they designed to cancel each other out, or do they stimulate each other?  I would guess the latter.  The 2nd harmonic of Earth is at 16Hz, so I would set my arm to somewhere between 8 and 16.  Or about 12Hz.  That is also where I would tune my rack and put the -3dB corner of my phonostage. 

But that's just me.  I like to think in terms of the big picture.  A system-wide approach.

jh

[hagtech]

What timing, I just found this on AA:

http://www.audioasylum.com/audio/vinyl/messages/68/684380.html

Check out the graph.  Oddly, it shows a null at 16Hz.  Maybe I'm wrong about the second harmonic?  Also related to the "schuman" resonance of the ionosphere.  Telsa was into this stuff.  And, ahem, the great pyramid at Giza, where the entrance tunnel not only points to the north star, but is also acoustically tuned to one of these resonances, like a flute (or coke bottle).  With the right wind, and a smooth face on the pyramid, it could shake the ground for miles.

jh

[CButterworth]

Jim,

very interesting, I love this stuff (being a nerd).  There was something on NPR where a guy recorded seismic activity and sped it up, it was very rythmic.

Can you detect Pele's rumbings on your phono-pre?

I suppose a test LP should be purchased, can you recommend one?

I'll try the 0.68 cap and see what a cut-off of 11Hz is like.

Charlie

[hagtech]

I like the HI FI NEWS one.  Also I think there is a good Ortofon record.  Me don't like that new Analog whateveritscalled one. 

jh

[tanchiro58]

Jim,

I just got a Hagerman Bugle phono preamp from an audiogoner. He custombuilt nicely but I have questions about the turntable and cartridge that can be used with a Bugle. How much gain does it have? What cartridge can I use to match with it like high or low MM and/or high or low MC? What TT do you suggest to buy with an average price from $500 to $1000. How about the vintage like Thorens, Empire, Dual, etc...? Thanks in advance.

Regards,
Tan

[CButterworth]

Well, I swapped the caps.  With the 1uF Dynamicaps in the Aikido into a 47K load, I get a 3.4 Hz cut-off.  In the Cornet2, I put in the 0.47uF Auricaps that were in the Aikido preamp.  The Cornet2 into a 20K load now has a cut-off of around 17Hz.  I mistakenly thought that I had put 0.68uF in the Aikido, not 0.47uF.

The Aikido preamp improves dramatically with CD's.  OK....I only tested two CDs.  I have the original CD release of Alan Parson's I-Robot.  We compared this a few weeks ago (with the un-cap-modded Aikido) alongside the Dynamicapped Cornet2 LP.  The LP sounded great, while the CD sounded weak.  After putting the Dynamicaps into the Aikido, this CD sounds very good, but not as good as the newest, Alan Parsons re-mastered CD version, which sounds amazing.

As for the Cornet2, vinyl always sounded great, although it felt a little "boomy" at times, and this was more noticeable with the Sylvania 5V4GA as opposed to the RCA 5V4GA, which has a more defined bass.  After replacing the 1uF Dynamicaps (C208) with the 0.47uF Auricap, the frequency cut-off is lifted from 8Hz to around 17Hz.  While my speakers cannot resolve 17Hz, it seems that these high-pass filters effect decadal harmonics such that they can sound out of phase.  Would I recognize this at all?  Anyway, there is a noticeable difference, and it is not a good one.  Bass sounds much weaker in comaprison with the Dynamicaps, and this could be more to do with capacitor flavouring than actual fq cut-offs, etc.

So, while I will leave the Dynamicaps in the Aikido, I will have to replace the final caps in the Cornet2.

But, what to replace them with?

Would a Dynamicap Cornet2 and Dynamicap Aikido be too much?

Maybe, I'll splurge on Sonicaps for the Cornet2.

Anyway, it has been very interesting.

Charlie

[hagtech]

I think you are hearing the differences between capacitor brands, and not values.  Put a 0.68uF Dynamicap into the CORNET2 and I bet all the good stuff you like will return.

jh

[CButterworth]

Jim,

I just arranged to buy Robertwstephens' 1uF Mundorf sio caps.  They'll be the same rating as your specs, and it seems that people really like them.  They were also the same price (used) as the Dynamicaps.

If their flavour isn't as good as the Dynamicaps, I'll add them to the second output cap position in the Aikido and add the cap selector that Broskie designed into the Aikido PCB, then but another set of 1uF Dyns for the Cornet2.

With the Dynamicaps in the Aikido, my CD's sound way better to me, much more like what I have been getting used to with vinyl.  However, some TV shows (mainly PBS) begin to sound a little boomy, probably due to beefed-up bass during announcements (and increasing commercials) between shows.  DVD's may also sound more boomy, as I expect (but am not sure) that they also have beefed-up bass for the HT crowd.  The cap selector switch would allow me to use a different flavour cap.

Of course, the Mundorfs may be just the thing for the Cornet2 and my LP's.  Then again, with 1uF caps, I could swap the Dynamicaps back into the Cornet2 and the Mundorfs into the Aikido.

I expect that next weekend will find me doing more experimenting with capacitor flavours.

Charlie