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    ST70 too bright...why?

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    tygr1

    Posts : 35
    Join date : 2014-12-08

    ST70 too bright...why?

    Post by tygr1 on Fri Dec 12, 2014 7:50 pm

    My new to me ST70, recapped and with VTA driver board sounds a little too bright to me. What ever has happened to that "tube warmth" I was expecting? Could it be the new EH tubes?

    I run it alone with just my Sony ES CD player with output level control and it's too bright. I run it with my Magi all tube preamp and Denon DVD player and it's still too bright for my tastes.

    Any insight? See pics on page 2 of this thread.


    Last edited by tygr1 on Wed Dec 17, 2014 7:59 am; edited 1 time in total

    sKiZo

    Posts : 1308
    Join date : 2013-04-01
    Location : Michigan USA

    Re: ST70 too bright...why?

    Post by sKiZo on Fri Dec 12, 2014 8:02 pm

    New tubes can take a while to break in. Give it time before getting too worked up. They should be about as good as they'll get after at most 100 hours.

    You want to experiment, try switching out the driver tubes. Lots of possibilities in the 12AU7 family. My ST120 was too bright for the room, and I went with a nice triplet of Westinghouse 5963's ... perfect! I also tried some 12BH7a's, and those were too dark.




    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Fri Dec 12, 2014 8:34 pm

    Thanks for that Skizo. I think I'll try a little tube rolling.

    Maintarget

    Posts : 209
    Join date : 2013-02-10

    Re: ST70 too bright...why?

    Post by Maintarget on Fri Dec 12, 2014 10:58 pm

    As sKiZo has mentioned I would resist any tube rolling until you have at least 100 hours if not more you might be surprised how much the sound actually changes in that time.
    I'd give a 12BH7 a try in the center position if you're still too bright after break.

    audiobill

    Posts : 270
    Join date : 2014-03-13
    Location : Philadelphia

    Re: ST70 too bright...why?

    Post by audiobill on Sat Dec 13, 2014 5:49 am

    Look at your speakers and speaker/room setup, too.

    Dampen first reflections.......

    corndog71

    Posts : 451
    Join date : 2013-03-19
    Location : It can get windy here

    Re: ST70 too bright...why?

    Post by corndog71 on Sat Dec 13, 2014 11:03 am

    I know one easy tweak that will also do the trick. Change the output caps to Clarity Cap ESA series.  They're a little darker in the upper treble region yet still offer a very clear and detailed midrange and low end.  Jolida uses them in their upgrades as do other high end companies. They're not crazy expensive either.

    That means giving up on those sexy Russian caps but the ESA's aren't too ugly.  

    http://www.partsconnexion.com/capacitor_film_claritycap_esa_630.html

    Oh yeah, what audobill said. Cover up those first reflection points. ATS Acoustics sells some really nice panels that work very well for this.

    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Sat Dec 13, 2014 12:21 pm

    They are 8 ohm single driver full range Audio Nirvana speakers with no crossovers.

    arledgsc

    Posts : 340
    Join date : 2012-11-30
    Location : SF Bay CA

    Re: ST70 too bright...why?

    Post by arledgsc on Sat Dec 13, 2014 12:59 pm

    Give the new components and your ears some time to adjust.  It took six months for my ST-120 to settle down after recapping.  I do though find the recapped, well broken in ST-120 has slightly more highs than my expensive 250W/ch. transistor amp that is +/- 0.1dB flat in the audio band.   But I can only listen for a short time to the sand amp before start missing the airy highs and switch back to valves.  But ultimately depends upon the tube types used.  Try some Mullard CV4003s either center or phase inverter position.  Those tubes will definitely roll off the highs.   Different tubes have been a tone control for tweaking the sound I like.  Has been expensive though rewarding experience.  However I would not have been as delighted today with the ST-120 without exhaustive tube rolling.  Give it time and don't be afraid to experiment.  Of course if your amp has a problem (like wrong value caps) then needs to be rectified.

    ramon68

    Posts : 87
    Join date : 2009-04-12
    Age : 76
    Location : naples fl

    Re: ST70 too bright...why?

    Post by ramon68 on Sat Dec 13, 2014 1:56 pm

    Does your full range driver have a rising high end? From what I've read, a lot (read most) of them do. There is a cheap tweak to fix that on Transcendent Sound's website under the heading diy speakers.

    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Sat Dec 13, 2014 2:53 pm

    It's not the speakers. The only thing that's changed in my setup is the amp.

    sKiZo

    Posts : 1308
    Join date : 2013-04-01
    Location : Michigan USA

    Re: ST70 too bright...why?

    Post by sKiZo on Sat Dec 13, 2014 4:49 pm

    I'd still try rolling to a darker driver tube first. That can completely change what you're hearing. I seem to remember you mentioning that this wasn't a problem with the old system setup?

    That don't work, then do some room tuning - never a wasted effort as even a room that you were happy with can usually sound SO much better with a little effort. Hardscaping first to kill hard reflections and the major issues, the a good parametric EQ works wonders to fine tune the room.

    My favorite test for high end problems is Norah Jones Come Away With Me. Her voice and piano would just pierce the ears until I tamed the hard reflections off the ceiling. Simple fix too ... tacked some memory foam carpets up there ...



    They weigh next to nothing and set me back less than $20 for both. Easy to do, and really killed the shrill. She's licking my ears now and I keep wanting more ...  ;-}

    PS ... I got a lot of real nice tubes off that auction site ... some well established sellers on eBay and you don't have to wait for the tubes to break in. I figure I average about $10 a pop.

    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Sat Dec 13, 2014 5:12 pm

    Thanks again Skizo! I'm taking your advice and have already ordered some tubes.

    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Tue Dec 16, 2014 7:54 pm

    OK, does anyone see anything out of the ordinary here.






    zx

    Posts : 194
    Join date : 2011-08-05

    Re: ST70 too bright...why?

    Post by zx on Wed Dec 17, 2014 1:17 pm

    Yes....Ck the b+.........I have my old hhshott 355 tuner-preamp running on one of my minny Varics
    I can give more topend just by tuning the B+down ....an bring the B+up an get better mids...
    All so with the B+ being to high the heaters may be to high....hhscott ran there input tube at 5.5v....some of the best sound I have had in 50 years of tubes....heaters  to high can also make the topend too hot....bring the B+ down brings the heaters down.....
    The Varic not only give me what ever sound I wont....it saves older partes that too me can still sound better than some new parts....have fun with tubes




    Thanks for the site Bob......

    PeterCapo

    Posts : 386
    Join date : 2008-12-05

    Re: ST70 too bright...why?

    Post by PeterCapo on Wed Dec 17, 2014 1:42 pm

    tygr1, just a heads-up, don't go poking around inside unless you are familiar with safe work practices around high voltages. When one of these amps (preamp, too) are powered on, there are lethal voltages present. Even when you power them off, the capacitors can store lethal charges.

    tygr1 had also mentioned, in another thread, that his bass might be rolled off. Could any of the VTA mod aficionados here please advise where the resistor is that establishes the input impedance of the amplifier now that the VTA PCB is in place? Where is the resistor and what value should it be, so tygr1 can verify it, please?

    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Wed Dec 17, 2014 1:53 pm

    Thanks Peter, I am very familiar with high voltage safety practices. Just new to tubes and not sure where to get the correct B+ voltage. Also, can it be checked with no speaker load on the amp?

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: ST70 too bright...why?

    Post by peterh on Wed Dec 17, 2014 2:00 pm

    tygr1 wrote:Thanks Peter, I am very familiar with high voltage safety practices. Just new to tubes and not sure where to get the correct B+ voltage. Also, can it be checked with no speaker load on the amp?
    Always have a load on tubeamps, speakers or a resistor.

    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Wed Dec 17, 2014 2:05 pm

    Thanks PeterH, I thought so.

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: ST70 too bright...why?

    Post by zx on Wed Dec 17, 2014 2:38 pm

    You can ck you B+ right at pin 8 of the 5AR4...Or the frist cap after the Choke...should be the multy cap ....also .Ck see what the B+ that feeds the driver board....looks like the red wire after the res.on the cap..............




    thanks for the site Bob.............

    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Thu Dec 18, 2014 7:56 am

    Well my meter is rated for 500v and it shows an overload when connected to pin 8 of the rectifier tube. I have already ordered another meter rated for 600v. What B+ voltage should I see? If I'm reading voltage in the right place for the driver board, I'm only seeing 15.2v. What should that voltage be?

    Thanks so much zx.

    PeterCapo

    Posts : 386
    Join date : 2008-12-05

    Re: ST70 too bright...why?

    Post by PeterCapo on Thu Dec 18, 2014 11:01 am

    tygr1 wrote:Well my meter is rated for 500v and it shows an overload when connected to pin 8 of the rectifier tube. I have already ordered another meter rated for 600v. What B+ voltage should I see? If I'm reading voltage in the right place for the driver board, I'm only seeing 15.2v. What should that voltage be?

    Thanks so much zx.

    This is where standard documentation for the VTA circuit would be most helpful.  A table of voltage values for different nodes in the circuit needs to be referenced to some value of AC line voltage, probably either 117VAC or 120VAC and exactly which one is another question for Roy.  The internal voltages will vary depending on the AC line.  

    It would probably be a good idea the measure your wall voltage during the times of day when you will typically use your system and then take note of how the wall voltage runs.  If it is too high, then it needs to be brought down, but, regardless of how it measures over time, you need to know what the reference AC line voltage needs to be for taking measurements inside the amp.  

    A variac would be most helpful in setting the reference AC line voltage for testing purposes so you can then take meaningful readings inside the amp and compare with a standard table of values.  Of course, how the power transformer primary is wound also affects how to gauge the other readings.  So, knowing the reference value for the PT secondaries may be the best way to set up the test with the use of a variac.

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: ST70 too bright...why?

    Post by zx on Thu Dec 18, 2014 2:51 pm

    Well the stock ST70 PIN 8 BZ34 435 B+ to grond.....so your way high....if you get over 500b+ I would turn it off...I say 450-70 at most an thats to high.....Free Dynaco tube schematics ...go here Bob has help us all with great info...
    PS next metter.....nothing less than 1KV dc.....save you a lot of time an give more head room....hehe....not spending you $$
    ...ever one need a good metter an iorn...if you working with tubes....have fun



    Thanks for the site Bob...............................

    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Thu Dec 18, 2014 3:27 pm

    Yeah, the owner's manual says 435v there too. I'm just not trusting my meter right now (maybe the batteries) so I'm going to wait for the new one and check B+ again.

    Thanks everyone.

    PeterCapo

    Posts : 386
    Join date : 2008-12-05

    Re: ST70 too bright...why?

    Post by PeterCapo on Thu Dec 18, 2014 3:32 pm

    Have a look at the fuse and make sure it is not greater than 3A slo-blo...

    tygr1

    Posts : 35
    Join date : 2014-12-08

    Re: ST70 too bright...why?

    Post by tygr1 on Thu Dec 18, 2014 3:42 pm

    Yes, it's a 3A 250v slo blo.

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