Dialing in the top end?

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Dialing in the top end?

Postby Normster » Sat Sep 12, 2009 11:54 am

I'm a complete hi-fi novice so I don't even know where to start. (???)
I'm trying to dial in some sweetness in the upper frequency range (8K-16K?) but not sure where to start. Tubes? Circuit? Tweeters? Crossover?

Amp is an ST70 "kit" build with VTA driver board (no upgrades), Triode OPTs, Dynakit PT. Mullard GZ34, Sylvania/JAN Phillips 12AT7 preamp tubes, JJ EL34 power tubes. Speakers are Pioneer CS-77A. Input is via an Echo Mia audio card. (The system is used in my home recording studio.)

So far I've tried the following:
    Replaced the surrounds on the original tweeters. No help really. I think the original tweeters are horrible.
    Replaced the tweeters with some Goldwood paper cone tweeters from Parts Express. Even at $5 each, these were a significant improvement over the original tweeters. They just don't seem to have any "air" or "space."
    Tried a few NOS preamp tubes (RCA, Sylvania, JAN Phillips) and like the combination of Sylvania voltage amp/JAN Phillips PI best so far.

In browsing the forum, I've seen more information than I can possibly digest in a year. Any suggestions on how to dial in upper frequencies that are crisp and airy without causing listening fatigue? Better power tubes? Tweeter recommendations? Crossover overhaul? Any suggestions are much appreciated.

Thanks,
Norm
Normster
 
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Airy highs

Postby msmpe » Mon Sep 14, 2009 4:51 pm

Hi Normster,

I'm hardly the speaker expert :P , but I'd start there, especially if the new GW tweeters made a diff. The caps in the xovers are an easy upgrade, try some from Daytons from PX if you're on a budget, or they, as does Madisound, have some boutique $) as well. I've used the Daytons and worked just fine for a rebuild.

Sounds like your ears may be tuned in and sensitive to those higher octaves, so spend a few bucks and get good tweeters. The only issue there is getting a good match with the woofers: driver impedance & SPL.
8>) Mike

If there's no sound in a vacuum, where'd the music come from?
msmpe
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Tweeters

Postby msmpe » Mon Sep 14, 2009 5:16 pm

Oh yea, make sure the new tweeters are flat below the crossover frequency by more than an octave, two is much better.

If you don't know the xover frequency, you'll have to study the xovers and detrmine from the number of elements (caps & chokes) in the tweeter and woofer circuits what the dB rolloff is, then from the cap ratings you can figure out where the xover frequency is (cig) , which is actually easy enough using one of the many "calculators" on the web (that ignores what "type" of circuit it is: Butterworth, Linkwirtz-Riley, etc, we'll assume it's a Butterworth, L-R is newer, others not used that much).
8>) Mike

If there's no sound in a vacuum, where'd the music come from?
msmpe
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Postby Normster » Mon Sep 14, 2009 10:02 pm

Thanks, Mike. I'm thinking speakers as well. I guess I'll have a bit of a learning curve. I was going to recap the crossovers, but there are no markings on the caps. Also no markings on the inductors. Still hunting for a crossover schematic.

I did find this info in a speaker review. Hopefully it's accurate:

Crossover frequency -
Lows.....Mid Ranges 450Hz
Mid Ranges.....Highs 3,600Hz
Highs....Super Highs 14,000Hz

Impedance: 8 ohms
Frequency Range: 35~20,000Hz
Sensitivity: 95dB/W (at/1m distance)


I assume I should be looking for a tweeter that has a steep climb to 3.6KHz and then falls off at 14KHz.
Normster
 
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Postby dannyr » Mon Sep 21, 2009 6:21 pm

Normster, in my opinion the VTA board sounds much better if you convert it to the low gain version that uses 12au7's etc. The high pitch should show up more along with a more balanced sound
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Postby msmpe » Wed Sep 23, 2009 1:17 am

Are the speakers 4-ways? If so, your super tweeter toots from 14K to 20K Hz, that's the top half (+) octave, while your tweeter squawks between 3.6K and 14K, about 2 octaves. The mid-range drivers go from 450 to 3.6K, which is about 3 octaves and the woofers provide the lower 4 octaves.

Did you replace the super tweeters or the tweeters? Look at both. A replacement tweeter should be flat from around 1500 Hz to over 14K. Also the hi-pass crossover caps are critical to good higher octave clarity.

Check out http://www.diyaudioandvideo.com/ and http://sound.westhost.com/lr-passive.htm#s3.0 for "theory" behind xovers. Check out http://diyaudioprojects.com/Speakers/speakers.htm for some projects. Madisound can provide some support, see http://www.madisound.com/services/retrofits.php to start, then their other links to upgrading vintage speakers.
8>) Mike

If there's no sound in a vacuum, where'd the music come from?
msmpe
KT88
 
Posts: 305
Joined: Wed Mar 26, 2008 12:31 pm
Location: central california coast

Postby Normster » Wed Oct 07, 2009 8:55 am

While poking around the web, I ran across the "Econowave" project at audiokarma. After converting the CS-77As to e-waves, the whole soundstage is bigger and more pleasing. No more ear fatigue but still lots of clarity. Long story short, I guess I just didn't care for the top end of the CS-77s.

I also want to try the lower sensitivity version of the VTA circuit. My sound card has both -10 and +4 dB settings and I think the -10dB attenuation loses something compared to the +4dB.

Overall, I still can't believe it took me this long to discover tube audio! :$
Normster
 
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