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    ST 120 vs MKIII Sound

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    eric

    Posts : 6
    Join date : 2010-02-11

    ST 120 vs MKIII Sound

    Post by eric on Thu Feb 11, 2010 2:53 pm

    I really like the looks of the MKIII 60 watts but does the sound compare to the st 120?

    Bob Latino
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    Re: ST 120 vs MKIII Sound

    Post by Bob Latino on Thu Feb 11, 2010 5:06 pm

    eric wrote:I really like the looks of the MKIII 60 watts but does the sound compare to the st 120?

    Hi Eric,

    The purpose of the creation of the tube VTA ST-120 was to give the equivalent of two 60 WPC Dynaco Mark III's with VTA driver board on one chassis. By having two channels on one chassis the amp is more cost efficient than having two separate Mark III monoblocks.

    If you are comparing the tube Dynaco VTA ST-120 to two STOCK Dynaco Mark III's, IMHO the driver circuit, power supply and switchable triode/pentode mode of operation give the VTA boarded ST-120 some advantages.

    A. Driver circuit - The original Mark III used a pentode/triode driver circuit with one 6AN8 tube and one bias control for each PAIR of tubes. The VTA ST-120 uses an all triode driver circuit which is an adaptation of the VTA driver circuit as found on the VTA ST-70. The VTA boarded ST-120 has one bias control for each individual output tube. The VTA ST-120 also has an AC balance control to allow you to more precisely set the phase splitter/phase inverter section of the driver circuit.

    B. Power Supply - The power supply on each original Dynaco Mark III has 90 uF of B+ high voltage storage or a total of 180 uF on a PAIR of Dynaco Mark III monoblocks. The VTA ST-120 with capacitor upgrade options has 670 uF of B+ high voltage storage coupled with bypass capacitors to break up resonances in the power supply for better high frequency response.

    C. The stock Dynaco Mark III's may only operated in pentode mode unless you want to open the amp and rewire it into the triode mode. The VTA ST-120 maybe be operated in either triode or pentode at the flick of a switch. Which mode sounds best to you depends on your musical taste and your associated equipment. With the VTA ST-120 you have a choice.

    Any Mark III may be retrofitted with VTA upgrade driver boards and if you also beef up the power supply on each amp you would have a close equivalent of the VTA ST-120. To do so, however, is not as cost efficient as the VTA ST-120.

    As to your inquiry about "does the sound compare to the st 120?". The ST-120, IMHO, sounds better than two STOCK Mark III's and pretty much the same as two VTA boarded Mark III's with beefed up power supplys.

    Bob

    eric

    Posts : 6
    Join date : 2010-02-11

    Re: ST 120 vs MKIII Sound

    Post by eric on Thu Feb 11, 2010 7:59 pm

    Thank you Bob.
    I see the MK III kits advertised around $500.00 each. Do you have a close figure what it would cost to up grade them to be compareable to the ST-120? Would that include the switch to change what mode you wanted to listen to?

    Bob Latino
    Admin

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    Re: ST 120 vs MKIII Sound

    Post by Bob Latino on Thu Feb 11, 2010 8:16 pm

    eric wrote:Thank you Bob.
    I see the MK III kits advertised around $500.00 each. Do you have a close figure what it would cost to up grade them to be compareable to the ST-120? Would that include the switch to change what mode you wanted to listen to?

    Hi Eric,

    The ST-120 kit with the triode/pentode swiches and SCM power supply module included is $795 + shipping.

    The two Mark III kits are $500 each or $1000
    The two VTA driver boards with parts set are $125
    A triode/pentode kit for both Mark III's would be $30
    TWO SCM (supplementary cap module) modules @ $20 each = $40
    ------------------------------------------------------
    Total = $1195 + shipping for two Mark III kits set up with VTA driver boards and two SCM modules

    The ST-120 = $795 + shipping WITH SCM power supply upgrades

    Difference = Two Mark III's will cost $400 more if they are to be set up just like an ST-120

    Bob

    eric

    Posts : 6
    Join date : 2010-02-11

    Re: ST 120 vs MKIII Sound

    Post by eric on Thu Feb 11, 2010 8:53 pm

    [quote="Bob Latino]The two Mark III kits are $500 each or $1000
    The two VTA driver boards with parts set are $125
    A triode/pentode kit for both Mark III's would be $30
    TWO SCM (supplementary cap module) modules @ $20 each = $40
    ------------------------------------------------------
    Total = $1195 + shipping for two Mark III kits set up with VTA driver boards and two SCM modules

    The ST-120 = $795 + shipping WITH SCM power supply upgrades

    Difference = Two Mark III's will cost $400 more if they are to be set up just like an ST-120

    Bob[/size][/b][/quote]


    Ouch!!!!!!!!! Thank's Bob. I guess i have to decide if looks are worth $400 more. Would a pair of the MK III run any cooler than the st-120? I listen to my Lascala's pretty loud most of the time if it makes any differance.

    Bob Latino
    Admin

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    Re: ST 120 vs MKIII Sound

    Post by Bob Latino on Thu Feb 11, 2010 9:01 pm

    "Would a pair of the MK III run any cooler than the st-120? I listen to my Lascala's pretty loud most of the time if it makes any differance."

    Hi Eric,

    Yes - The two Mark III's, since they would be separated by some distance and have fewer tubes running on one chassis, would probably run a little cooler. That said, no one has ever reported to me any heat issues or overheating issues with the ST-120. Lascala's are very efficient and probably wouldn't tax either a pair of Mark III's or an ST-120 very much.

    Bob

    thevic24

    Posts : 29
    Join date : 2010-01-31

    Re: ST 120 vs MKIII Sound

    Post by thevic24 on Thu Feb 11, 2010 9:10 pm

    I dont have much experience with the MKIII's but my new ST-120 with a fresh painted and clear coated cage looks dead sexy.

    If I could only find my d*@ camera, I would show you.
    Outstanding amp!!


    -Vic

    eric

    Posts : 6
    Join date : 2010-02-11

    Re: ST 120 vs MKIII Sound

    Post by eric on Thu Feb 11, 2010 10:29 pm

    The ST-120 amps are beautiful but something about a pair of MK III amps just appeals to me a little bit more with the exception of the price.Lol

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: ST 120 vs MKIII Sound

    Post by Luddite on Fri Feb 12, 2010 12:35 pm

    eric wrote:The ST-120 amps are beautiful but something about a pair of MK III amps just appeals to me a little bit more with the exception of the price.Lol


    FYI: You don't necessarily have to purchase the complete MK-III kits. Dynakit Parts sells everything individually. You might check the cost to order the chassis, transformers, etc. from them and then order the VTA driver boards, etc. from Roy.

    Charlie

    eric

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    Join date : 2010-02-11

    Re: ST 120 vs MKIII Sound

    Post by eric on Fri Feb 12, 2010 9:11 pm

    bnc31 wrote:FYI: You don't necessarily have to purchase the complete MK-III kits. Dynakit Parts sells everything individually. You might check the cost to order the chassis, transformers, etc. from them and then order the VTA driver boards, etc. from Roy.Charlie

    I may do that. Do they have individual parts that are up grades compared to what comes in the kit?

    Jhoman

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    Age : 55
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    Re: ST 120 vs MKIII Sound

    Post by Jhoman on Sat Feb 13, 2010 3:12 pm

    I love my ST120, no heat issues driving my Cornwalls, love the triode mode for jazz and female vocals. Using Mullard 4024s on the pre, Ruby KT88s on the power side.

    Outstanding combo on my system!

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: ST 120 vs MKIII Sound

    Post by Luddite on Mon Feb 15, 2010 12:51 pm

    [/quote]I may do that. Do they have individual parts that are up grades compared to what comes in the kit?[/quote]

    The only upgrades they offer are a choice between carbon composition and metal film resistors on their driver boards (same circuit as the Dyna originals). However, if you buy the basics (ie. chassis, transformers, quad cap, etc.) from Dynakit Parts, then you can use the VTA driver boards and any other upgrades you might choose. You can check out everything Dynakit has to offer at www.dynakitparts.com

    Listens2tubes

    Posts : 15
    Join date : 2009-04-08
    Location : New Jersey

    Re: ST 120 vs MKIII Sound

    Post by Listens2tubes on Wed Feb 17, 2010 8:49 pm

    I am a monoblock guy. That said, I have been gathering a pair of MkIV's for a more aggressive mod build than my current pair. Finding not so pretty original amps with good tranformers can be a real cost saving method. Just my 2 cents.

    Neal

    Bob Latino
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    Re: ST 120 vs MKIII Sound

    Post by Bob Latino on Sat Mar 20, 2010 11:01 am

    bnc31 wrote:
    eric wrote:The ST-120 amps are beautiful but something about a pair of MK III amps just appeals to me a little bit more with the exception of the price.Lol


    FYI: You don't necessarily have to purchase the complete MK-III kits. Dynakit Parts sells everything individually. You might check the cost to order the chassis, transformers, etc. from them and then order the VTA driver boards, etc. from Roy.

    Charlie

    Re: What Charlie has mentioned above ..

    You can't really do what you are suggesting and make it cost efficient.

    Two Mark III transformer sets = $424
    Two Mark III chassis = $190
    Two quad caps = $106
    Two chokes = $25
    Two VTA driver boards and parts sets = $125
    Input and output jacks and mounting boards for two amps = about $40
    Eight tube sockets = $28
    Assorted small parts like TWO SETS of the following > fuse posts, fuses, switches, terminal strips, stainless steel hardware, power cords, grommets, grounding lugs etc. - maybe $50-$75
    -----------------------------------------------------------------------
    Total probably around $1000 for parts if parts are ordered separately ..

    Bob

    wgallupe

    Posts : 81
    Join date : 2014-05-18
    Age : 62
    Location : Central Mass.

    Re: ST 120 vs MKIII Sound

    Post by wgallupe on Fri Aug 05, 2016 6:00 am

    Bob Latino wrote:
    eric wrote:I really like the looks of the MKIII 60 watts but does the sound compare to the st 120?

    Hi Eric,

    The purpose of the creation of the tube VTA ST-120 was to give the equivalent of two 60 WPC Dynaco Mark III's with VTA driver board on one chassis. By having two channels on one chassis the amp is more cost efficient than having two separate Mark III monoblocks.

    If you are comparing the tube Dynaco VTA ST-120 to two STOCK Dynaco Mark III's, IMHO the driver circuit, power supply and switchable triode/pentode mode of operation give the VTA boarded ST-120 some advantages.

    A. Driver circuit - The original Mark III used a pentode/triode driver circuit with one 6AN8 tube and one bias control for each PAIR of tubes. The VTA ST-120 uses an all triode driver circuit which is an adaptation of the VTA driver circuit as found on the VTA ST-70. The VTA boarded ST-120 has one bias control for each individual output tube. The VTA ST-120 also has an AC balance control to allow you to more precisely set the phase splitter/phase inverter section of the driver circuit.

    B. Power Supply - The power supply on each original Dynaco Mark III has 90 uF of B+ high voltage storage or a total of 180 uF on a PAIR of Dynaco Mark III monoblocks. The VTA ST-120 with capacitor upgrade options has 670 uF of B+ high voltage storage coupled with bypass capacitors to break up resonances in the power supply for better high frequency response.

    C. The stock Dynaco Mark III's may only operated in pentode mode unless you want to open the amp and rewire it into the triode mode. The VTA ST-120 maybe be operated in either triode or pentode at the flick of a switch. Which mode sounds best to you depends on your musical taste and your associated equipment. With the VTA ST-120 you have a choice.

    Any Mark III may be retrofitted with VTA upgrade driver boards and if you also beef up the power supply on each amp you would have a close equivalent of the VTA ST-120. To do so, however, is not as cost efficient as the VTA ST-120.

    As to your inquiry about "does the sound compare to the st 120?". The ST-120, IMHO, sounds better than two STOCK Mark III's and pretty much the same as two VTA boarded Mark III's with beefed up power supplys.

    Bob

    Hi All,

    Resurrecting this old thread rather than starting a new one....

    I currently have a VTA ST120 which I love but I'm thinking about going to mono blocks to free up a shelf on my equipment rack. The mono blocks would be located behind each speaker which makes the compact size of the VTA MKIII desirable. However, I'm concerned that I would be going backwards as far as sound quality goes. Questions about the VTA MKIII:

    Can KT120 power tubes be used?

    What is an SCM module and how is it 'added' to the VTA MKIII?

    Aside from the output power difference, how does the MKIII compare to the M125? (Since the ST120's 60 watts drives my speakers very well I would most likely run the M125s with one pair of tubes each)

    Thanks
    Wayne

    Bob Latino
    Admin

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    Re: ST 120 vs MKIII Sound

    Post by Bob Latino on Fri Aug 05, 2016 7:04 am

    Hi Wayne,

    1. The power transformer on the VTA Mark III's has enough current handling ability to deal with driving 2 Tung-Sol KT120 output tubes.

    2. An SCM is a supplementary cap module which adds another 90 uF of capacitance to the amp's DC storage capacity. The use of the SCM will insure that the amp does not run out of DC storage when playing at high volume levels using 4 output tubes. The Mark III's chassis is small (9 X 9 inches) but there is room to add an SCM inside the chassis underneath the output transformer. You would have to drill one hole in the chassis underneath the output transformer to mount the SCM. IMHO > Since the Mark III's have just two output tubes, you do not need the SCM in a Mark III.

    3. The M-125 uses a VTA Mark III driver board (with a slightly different resistor set) so the sound of a VTA Mark III would be virtually the same as a VTA M-125 amp using two output tubes.

    Yes - the M-125's are more costly than the VTA Mark III. The larger chassis, larger power transformer, larger output transformer etc. add more $$$ to the cost of these amps - BUT - The M-125's do give twice the power of a Mark III in the 4 output tube mode and do allow more future speaker choices with their greater ability to drive less efficient speakers.

    Bob

    tubes4hifi
    Admin

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    Re: ST 120 vs MKIII Sound

    Post by tubes4hifi on Fri Aug 05, 2016 1:43 pm

    for anyone that may have forgotten, (or didn't follow the links on my main page)
    I've got the MK3 kits WITH the VTA mod, for $575 without tubes, or $700 with tubes (your choice of 12AU7 or 6SN7 driver tubes)
    also available fully assembled/tested/ready to play
    http://tubes4hifi.com/MK3.htm

    j beede

    Posts : 316
    Join date : 2011-02-07
    Location : California

    Re: ST 120 vs MKIII Sound

    Post by j beede on Fri Aug 05, 2016 11:50 pm

    My MkIIIs were rescued after being stored outdoors under a picnic table! I think they cleaned up okay...

    " />

    wgallupe

    Posts : 81
    Join date : 2014-05-18
    Age : 62
    Location : Central Mass.

    Re: ST 120 vs MKIII Sound

    Post by wgallupe on Sat Aug 06, 2016 9:21 am

    Wow! Those look like new. Great job!

    wgallupe

    Posts : 81
    Join date : 2014-05-18
    Age : 62
    Location : Central Mass.

    Re: ST 120 vs MKIII Sound

    Post by wgallupe on Thu Aug 11, 2016 8:49 am

    Thanks for the comments Bob and Roy. Really appreciate your direct involvement on this forum. Very comforting for a DIY novice like me...

    I've been searching and reading about the Mark III. One area of concern for me is using a tube rectifier. With only two power tubes and no additional capacitance (absence of an SCM) on the VTA Mark III is it realistic to assume that there is less stress on the rectifier? What about the VTA M-125 in two power tube mode? I have a couple GZ37s I'd like to use...

    Bob Latino
    Admin

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    Join date : 2008-11-26
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    Re: ST 120 vs MKIII Sound

    Post by Bob Latino on Thu Aug 11, 2016 9:03 am

    You can use a Mullard GZ37 or a Mullard GZ33 with a Dynaco Mark III - no problem .. With the VTA M-125's you can use a GZ37 or a GZ33 in either 2 output tube mode OR 4 output tube mode. I have a GZ33 rectifier in each of my own M-125's right now .. The have been in there since 2011. The output tubes in these two amps have been replaced once but the same two GZ33's are still in there. With 120 volts IN, the B+ voltage in these two amps are the same as they were 2011 ...

    Bob

    wgallupe

    Posts : 81
    Join date : 2014-05-18
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    Location : Central Mass.

    Re: ST 120 vs MKIII Sound

    Post by wgallupe on Mon Sep 12, 2016 2:53 pm

    Hi,

    Does anyone know the dimensions of the VTA Mark III PCB? I'm entertaining the idea of going with a custom chassis.

    Thanks,
    Wayne

    tubes4hifi
    Admin

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    Re: ST 120 vs MKIII Sound

    Post by tubes4hifi on Mon Sep 12, 2016 3:40 pm

    Wayne,
    to answer both of your questions, one, yes, you're correct, there is alot less stress on the GZ34 rectifier tube as it only has two power tubes and the two small driver tubes to power,
    so almost half the load of an ST70 or ST120 amp.
    2 - PCB dimensions of the VTA MK3 board are identical to the original PCB (4.2 x 3.4")

    wgallupe

    Posts : 81
    Join date : 2014-05-18
    Age : 62
    Location : Central Mass.

    Re: ST 120 vs MKIII Sound

    Post by wgallupe on Mon Sep 12, 2016 8:17 pm

    Roy, thanks for the info and have a great vacation...

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