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    New ST-120

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    jdm

    Posts : 45
    Join date : 2011-04-04

    New ST-120

    Post by jdm on Mon Apr 04, 2011 8:58 pm

    Just completed the ST-120 with all Gold Lion tubes. The amp sounds great, all the voltages match the manual, the bias is set at .55 and holding. I used Mundorf Mcaps for the coupling caps and upgraded half the resistors using the same values in the Takman and Shinkoh brands like others on the forum. My system is simple, a Mac Mini toslinked into a Rega DAC connected with RCA's to the ST-120 Amp.

    The Problem: I used a 3-wire modern power cord and connected the green neutral to the two lug star ground on the ST-120. When I went through the setup as described in the manual all checked fine. I played the amp for a couple hours and listened carefully. I noticed a very slight hum at high volume when the amp attenuator was 100% and the music was paused. Bob said the three wire may cause a hum so I disconnected the green neutral, reconnected the amp and a loud hum masked the music. So the two wire power cord as wired by the directions does not work and the three wire provides addional ground.

    I have re-traced all the connections and cannot find the ground problem assuming it is not a bad part or something I have overlooked. Can anyone recommend connections I should check?

    Moderator's note - Read post #4 below to see how the hum issue was resolved ..




    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: New ST-120

    Post by j beede on Mon Apr 04, 2011 10:04 pm

    You have probaly already made sure that no more than one component in your setup is using a three-wire plug. With the three-wire plug correctly wired, is the hum audible from your listening position? I've had people tell me that their amp was "dead quiet" but I can hear low level hum/hash/buzz/hiss when I position my ear near the speaker--especially small monitors.
    ,,,j

    jdm

    Posts : 45
    Join date : 2011-04-04

    Re: New ST-120

    Post by jdm on Mon Apr 04, 2011 10:34 pm

    That is correct, I can here the same low level hum/hiss when amp attenuator is 100% and the music is paused.

    I was just rereading the Optional Stepped Attenuator wiring instuction and noticed #3. Grounds should be conneted to the outer ground tab of the input jack and from the input jack to the PCB ground on the board. I will add the wire to the two wires to the input jack to see if that resolves the issue. I certainly looks like that is the cause of the ground issue.

    jdm

    Posts : 45
    Join date : 2011-04-04

    Re: New ST-120

    Post by jdm on Mon Apr 04, 2011 11:37 pm

    CASE CLOSED:
    I can now say this ST-120 is DEAD QUIET with my ear to the speaker! Ground loop closed. The amp is dead quiet with either the two wire OR three wire power cord as it should be.

    I misread the the Optional Attenuator instruction and did not ground the the input RCA's to the attenuator, RCA input and the PCB board. I assumed the attenuator provided ground to the chasis. A real rookie mistake.

    Yo-Yo-Ma and Mendelssohn's piano have never sounded better - now with a truely dead black background.

    JDM

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: New ST-120

    Post by Bob Latino on Tue Apr 05, 2011 10:03 am

    Hi David,

    Glad that you found the issue without too much trouble. You have to ground the driver board directly to the input jack grounding tabs as it mentions in the instructions.

    Nice photos and an excellent wiring job on your amp. Let us know how the amp works out with your other associated equipment?

    Bob

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: New ST-120

    Post by mantha3 on Tue Apr 05, 2011 10:59 am

    Nice Amp!

    I have a newer ST-120 that I built. Great feeling to be done with it and have it work perfect. Good to hear you got your last fix in and things are good.

    I pretty much went with the same build. I used Jantzen Silver caps. I'd love to hear the Mundorf... I hear great things and I'm sure the sound is great. It was a tough call for me to go away from the Russion PIO's that have great reviews.

    Question - Did you use the Mundorf Mcaps in .22 uf on all 8 spots or just the 4 coupling cap spots.. I guess I was just wondering if you used .10 uf on the 4 non coupling spots.

    I like the power cord... I may update mine as I dig the heavier duty look. I don't know why ;-)

    One thing you may want to do... And I'm not knocking your tubes... The center 12AT7 spot.. You may want to buy a Mullard for that spot and give that a try. If you search this forum you will see lots of "tube rolling" talk. All your tubes are solid... But this center spot is key and Mullards are nice. I had pretty much the same tube set as you and this one change was the one that really made an impact for the postitive. Again, not intending to knock anything... What you have is solid and I hope you are as happy as I owning an ST120.

    PS - on the Mullard bit... Just a warning that Tube Rolling can be addictive!

    Nice job wiring.. makes me want to re-do it. Shocked

    jdm

    Posts : 45
    Join date : 2011-04-04

    Re: New ST-120

    Post by jdm on Tue Apr 05, 2011 10:17 pm

    After fixing my minor wiring oversight it has taken a little time to recover from listening to this remarkable and stunning ST-120! With only 10 hours of operation it may be too early to comment. I am just lost for words to describe the holographic soundstage and smooth, articulate frequency response. Whatever digital-lossless music I push through my Rega DAC, it all flows through the ST-120 with pure musical grace that never exsisted in my 20 year old high-end AI solid state amp. The massive sound stage causes me to look across the room in different directions for insruments. I know some of the amp components take 150+ hours to mature, I just can not image it getting better! Hats off to all the guys who designed, modified and refined and marketed this Amp for decades. It is a true audio treasure I will enjoy!

    To answer the questions above, here is my cocktail of upgrades for this ST-120 Dynaco:
    Tubes:
    Matched Quad Gold Lion KT88 NEW
    Genalex Gold Lion 12AT7/ECC81/B739 NEW
    Sovtek 5AR4/GZ34 rectifier tube NEW

    Upgraded Capacitors, Resistors, Wire, Fuse/Holder:
    ANOTE- 2 Pair AN-SPKR, heavy Silver binding post
    ELNA- RFS 100uF 100V 16x25 RFS-100V
    MUNDORF- 4- 0.10 1200V SUPREME SILVER & OIL
    MUNDORF-4 - 0.33 1200V SUPREME Silver/Gold/Oil (Same size as .22)
    NEOTECH- 22AWG LIGHT BLUE UP-OCC Solid SILVER WIRE
    NEOTECH- 20-FEET 20 AWG RED UP-OCC COPPER/TEFLON
    SHINKOH- 7K5 1/2 WATT SHINKOH TANT RESISTO
    SHINKOH- 12K 1/2 WATT SHINKOH TANT RESISTO
    SHINKOH- 27K 1/2 WATT SHINKOH TANT RESISTO
    TAKMAN- 1K 0.5 Watt Metal Film 1%
    TAKMAN- 2K2 0.5 Watt Metal Film 1%
    TAKMAN- 10K 0.5 Watt Metal Film 1%
    TAKMAN- 1M 0.5 Watt Metal Film 1%
    TAKMAN- 51K 1/2 WATT CARBON FILM, 2%
    ACME- AGC FUSE HOLDER, CRYO SILVER
    FUSE- HiFi 5A SLOW BLO 1/4"x1 1/4" FUSE
    Lorad Power Cord 4’ 3x25 OFC/Silver ends terminated into Wattgate plug.





















    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: New ST-120

    Post by j beede on Tue Apr 05, 2011 11:27 pm

    Glad to hear that you have achieved "dead quiet" amplification. I finished my Mark III restoration about three weeks ago and had a similar experience. I found the depth of the soundstage to be startling. Compunding my surprise is the simplicity of this design, the component count is absurdly low. The only Dynaco tube amps I have heard before were ST-70s--several variations. I am running Sovtek 6550s in mine and it will play my Martin Logan CLS LOUD! As I have said before... I wonder if we have really learned anything about amplifier design in the last 50 years!


    jdm

    Posts : 45
    Join date : 2011-04-04

    Re: New ST-120

    Post by jdm on Tue Apr 05, 2011 11:56 pm

    Good question. It is hard for most of us to distiguish today between research driven engineering and and marketing. In audio, let your ears be the judge. I have used the Mundorf Caps three times now and the Germans have created something very special with that Silver/Gold Oil cap. It is a major upgrade. The silver/oil sounds just as good.

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: New ST-120

    Post by Bob Latino on Wed Apr 06, 2011 7:40 am

    Hi David,

    Using the stepped attenuator, as you do, takes the preamp out of the equation in regards to "the sound of the amp". I also run lossless FLAC files from my computer directly to my ST-120 through the stepped attenuator. I don't have a separate DAC but my computer is new and the DAC in the computer is pretty good. If you run a computer directly into an ST-70/ST-120, I guess you could also use the computer's volume control but the attenuator is simple to use and will also allow you to run a CD player, FM tuner and any other high level signal sources directly into the amp.

    I know that your amp is still new and not completely broken in, but when you get the chance let me know if you have any comments about any differences in the sound of the amp in ultralinear mode and triode mode.

    Bob

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: New ST-120

    Post by mantha3 on Wed Apr 06, 2011 9:59 am

    I def. dig it. The break in does make a difference. I actually let my amp run for a full two days at about 30% volume with an FM radio hooked up... I wasn't really listening too close for the 2 days but after I was done it did seem to make a difference.. For me I thought the low end bass end was better.

    You mentioned you went with the "MUNDORF-4 - 0.33 1200V SUPREME Silver/Gold/Oil (Same size as .22)
    " If you don't mind me asking.. Why did you go with the .33uf and not the .22uf? Just curious as my build is pretty similar to what you have.. I did the .22uf as that is what is more standard for the VTA board if I'm not mistaken... So I was just curious if the .33 was intended to add more sound in some area (like more bass... Or more midrange)


    jdm

    Posts : 45
    Join date : 2011-04-04

    Re: New ST-120

    Post by jdm on Wed Apr 06, 2011 9:30 pm

    I used .33 to increase the capacitance. By increasing the ratio of the electric charge on each conductor to the potential difference between them I think I am adding a little headroom to the signal path. I have a Audible Illusions 2D pre amp with 4 Mundorf 2.7Uf capacitors that are phyically 3 times larger than the .33's. I assume I cannot hear a differance in the .22 or the.33 95% of the time, they were the same physical size so I went with more capacitance. The change is small and I did not do the math or try and figure the optimal size given the voltages. Has anyone calculated the optimal cap sizes of C13-C16 with the current transformers? I assume they would be larger than .33uF.

    Disles1

    Posts : 17
    Join date : 2010-12-21
    Location : Calgary, Alberta

    Power Tube Rolling in ST-120?

    Post by Disles1 on Thu Apr 21, 2011 11:56 am

    The tube complement in my ST-120 is: 1960s Amperex 5AR4 Rectifier; two Siemens ECC801S (i.e., 12AT7); 1962 Mullard (Whyteleafe) CV4024 in center position; JJ Electronic KT88 (blue). As Mantha3 warns "...Tube Rolling can be addictive!" so I have a question about your impressions of various power tubes for the ST-120. A review on AudioGon regarding JJ KT88s - in a different amp, system and room set-up - indicates that JJ KT88s have good midrange but the soundstage is wide but not deep. I know that my current room set-up is not best for deep soundstage (I sit in near field and there is a large entertainment unit between the speakers) but I'm wondering if different power tubes, such as Shuguang Treasure KT88s or others, would be an improvement over the performance of JJ Blue Bottle KT88s.

    Partial Review from AudioGon member:
    "The JJ's first appeared dry and muted, however, after a few days they opened up, some. The JJ's exhibit a moderately strong midrange and somewhat less pronounced bass and upper frequency region. In the frequency areas where the cymbal and brass thrive, instead of a pronounced wailing of the cymbals, there was a slight burnish of the sound, somewhat subdued. The bass also felt the same way. My remarks are based mostly on a direct comparison to the Svetlana Winged C's and EH's. I can't help but to think the JJ's are made for perhaps other than home audio, like perhaps, guitar amps or something. Others talk about Class D exhibiting a certain dry sound, in my opinion; the JJ's exhibit the same. To be fair, I only have about 30 hours of use, vice 120 hours of break in. I am not sure about how much better these will get, but one thing is for sure, other tubes I have tested, sounded open and more holographic at the very beginning of use.

    The soundstage, well it is odd. It seems as if the width is great, however, the sound makes me believe I am sitting close in on an ensemble versus sitting back and listening more to the music being spread out. It is as if I am sitting up close but with a wide stage in front of me. The musicians seem to be one layer deep, not to holographic. There are some spatial ques but they are not exceptional."

    j beede

    Posts : 317
    Join date : 2011-02-07
    Location : California

    Re: New ST-120

    Post by j beede on Thu Apr 21, 2011 3:44 pm

    I have a VTL amp that I never tamper with for this exact reason... it is a benchmark that I can insert as needed to see if my other amplifiers are getting better/worse or are unchanged. I may need to get a different amp for benchmarking though... too frequently when I insert the VTL I forget what I am supposed to be listening for and end up just enjoy the music.
    ...j

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: New ST-120

    Post by mantha3 on Thu Apr 21, 2011 4:16 pm

    I really like my Shuguang Treasure KT88 tubes... I don't know if I'd buy them again. I had a quad of the re-issue Gold Lion KT88s and these sound awsome.

    I was just thinking the other day that I amy put the Gold Lions back in.. Just for the heck of it. Re-Bias

    Only note.. The Gold Lions sounded great from the start.. And got a bit better with some time on them. The Shuguang I thought were a step back from the lions at the start.. But really got better with time.

    I really like the 12AT7 updates.. these make a bigger difference. A modern 12AT7 front center compared to a Mullard is a big step back. I'm running a spendy Siemens front and center and then Mullard in the right and left phase splitter. I also got a Mullard GZ33 for the Rectifier... When blasting the ST120 this has a fuller sound. I think it handles the load better.


    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: New ST-120

    Post by mantha3 on Thu Apr 21, 2011 4:21 pm

    PS - That 1960s Amperex 5AR4 Rectifier is a nice tube... I would not go much beyond 60% volume on the ST120 with it.. I was blasting my ST120 (21 out of 21 with the stepped attenuator) and killed a really nice Sylvania big bottle GZ34. Too many Sat. night cocktails. I was outside of the house listening to see how loud it was... wondering how the sound was for the neighbors (To see if they'd call the cops) I had the blasting going for 20 min. Sounded like a rock concert... Then silent.. Dead fuse and dead nice NOS Sylvania GZ34 big bottle.. So I got 2 new ones... for 200 bucks!!!! Yikes!

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: New ST-120

    Post by Bob Latino on Thu Apr 21, 2011 4:40 pm

    Hi,

    If you were using the ST-120 with the stepped attenuator at the (last) 21st step of the stepped attenuator then you were passing a full 2 volts from your CD player into an amp that needs only 3/4 of a volt for full output. You were WAY overdriving the amp - and for 20 minutes! It's a wonder that the rectifier lasted for 20 minutes playing that loud and it's a wonder that you didn't smoke a resistor on the driver board or take out the power transformer.

    Moral of the story > Too many cocktails will alter your "musical judgment" and usually it's not for the better ...

    Bob

    Disles1

    Posts : 17
    Join date : 2010-12-21
    Location : Calgary, Alberta

    Re: New ST-120

    Post by Disles1 on Thu Apr 21, 2011 5:47 pm

    mantha3 wrote:PS - That 1960s Amperex 5AR4 Rectifier is a nice tube... I would not go much beyond 60% volume on the ST120 with it.. I was blasting my ST120 (21 out of 21 with the stepped attenuator) and killed a really nice Sylvania big bottle GZ34. Too many Sat. night cocktails. I was outside of the house listening to see how loud it was... wondering how the sound was for the neighbors (To see if they'd call the cops) I had the blasting going for 20 min. Sounded like a rock concert... Then silent.. Dead fuse and dead nice NOS Sylvania GZ34 big bottle.. So I got 2 new ones... for 200 bucks!!!! Yikes!

    Hi Mantha3, the real question is...did the neighbors LIKE the sound? Cool

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: New ST-120

    Post by mantha3 on Thu Apr 21, 2011 8:35 pm

    They are impressed! Man, that Amp with some 91 dB speakers can shake the foundation. One time deal... I had wondered what the thing would do on Spinal tap 11 out of 11... If ya know what I mean.

    It actually sounded amazingly clean... Just LOUD as HE!!

    Oh well. No need to do it again.. Much louder then I ever needed to go for sure. Science is fun. Being a dumb scheyat on a few cocktails can tax ya... I have scientific proof


    jdm

    Posts : 45
    Join date : 2011-04-04

    Re: New ST-120

    Post by jdm on Thu Apr 21, 2011 10:48 pm

    Compared to my other quality amps, the ST-120 with Gold Lion KT88's and the 12AT7 re-issues sound very musical,articulate, silky-smooth, and overall balanced resolution. The tubes sounded noticeably better as I put more hours on them. I have Mundorf Gold/Silver/Oil caps and I know from putting them in other audio equipment their unique signiture (silky-smooth and fast).

    I Have a full set of re-issue Tung-Sol that I have not tried yet. I think given the higher power they will make Steely Dan Gaucho rock. The guys at The Tube Store are a wealth of knowledge and get a lot of customer color on NOS and new tubles. I have purchased NOS Tungsram and others from them. They have a lot of positve feedback on the Gold Lions and don't think their NOS 12AT7's are any better base on customer comments.

    I would like to try some NOS 12AT7's that are not overly warm or dark, I have all the solid low-end I need. What is considered the best 12AT7? I have always liked the sound of Tungsgram.

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: New ST-120

    Post by Bob Latino on Fri Apr 22, 2011 6:35 am

    JDM,

    My favorite 12AT7 driver tubes for the ST-70/ST-120 are the Mullard CV4024's (12AT7 equivalent). Another one you can try is the RCA black plate 12AT7. Most who read this forum know that the CENTER 12AT7 on the VTA driver board (voltage amplifier) is the tube that has the most influence on the character of the amp. If you are on a budget you could try just replacing the center tube.

    Another factor that enters in is the long term durability of the tubes that you use. The Mullard CV4024's are very carefully crafted and should have a long life span in these amps. I have looked at the internal structure of these tubes with a magnifying glass and am amazed at quality construction of the tube.

    Bob

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