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    Sonic Characteristics of ST-120 vs M125s

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    arturo7

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    Sonic Characteristics of ST-120 vs M125s

    Post by arturo7 on Thu Nov 30, 2017 3:24 pm

    Hello all, first post here after a few weeks of lurking.

    I have an informant at the North Pole who tipped me off that Santa has me down for a tube amplifier kit this year. Fortunately, this particular elf works in the records department and has performed a Herculean feat to keep my name in the Nice column. He says that if I divert some of Santa's cookies directly to him he can sway the decision of which kit comes down the chimney.

    I'm looking at either the ST-120 or a pair of the M-125s.


    My question is this: What are the sonic differences between these amps, if any?


    I assume the 125's will keep the bass a little tighter, but my days of high-volume listening have long passed. My speakers, for now, are a pair of Thiel CS2s, rated at 40-250w at 6 ohms, 87bB. I mostly listen to jazz and classical, so based on what I've read here, I'll probably be listening in triode mode.

    Thanks
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    sKiZo

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by sKiZo on Thu Nov 30, 2017 5:13 pm

    It's all about the tubes, eh. Either amp is capable of providing most any sound you want based on driver selection. From there, capacitance (storage) is the biggie, and both amps have plenty of that to spare.

    Biggest difference will be headroom - spare power is good, and a lot would depend on how big a room you're working with and your musical preferences. My ST120 doesn't work that hard to give me more than enough to keep me smiling.
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    corndog71

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by corndog71 on Thu Nov 30, 2017 6:27 pm

    It is a tough choice except for the fact that the M125s are a more costly investment. However with the M125s you have the ability to run them with 2 output tubes per channel just like the ST120 or 4 tubes per channel for more power and headroom. Sound differences are based more on the tubes you decide to use in them not to mention the rest of your gear. If the cost isn't a limiting factor, go for the big guns! Compared to the competition they're still a bargain.
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    arturo7

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by arturo7 on Thu Nov 30, 2017 7:44 pm

    Can I assume that the two circuits are nearly identical save the stereo/mono configuration? Are the M125's basically the ST120 split in two with added output tubes for more power? Or is that over simplifying?

    My room is roughly 14 x 20.

    Question on the output tubes. With the M125 do I need 8 matched tubes?


    Last edited by arturo7 on Thu Nov 30, 2017 8:36 pm; edited 1 time in total (Reason for editing : typo)
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    Dave_in_Va

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by Dave_in_Va on Thu Nov 30, 2017 8:34 pm

    My room is approx. 12' x 17'. My speakers are Tylers (90db sens.). I use a VTA ST70 and 50% on the volume is about as loud as normal person can stand. I've never noticed any distortion at any volume level.
    I listen to psychedelic rock, acid folk and soundtracks from ancient Italian westerns.
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    cci1492

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by cci1492 on Thu Nov 30, 2017 10:41 pm

    Question on the output tubes. With the M125 do I need 8 matched tubes? wrote:

    You can use 2 matched quads or 2 matched pairs. As it has been already stated, you can run the M125s with just 2 tubes each, which is nice if you want to cut back on heat in the summer.
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    arturo7

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by arturo7 on Fri Dec 01, 2017 12:01 am

    cci1492 wrote:
    You can use 2 matched quads or 2 matched pairs. As it has been already stated, you can run the M125s with just 2 tubes each, which is nice if you want to cut back on heat in the summer.


    So all of the output tubes on the right M125 need to match, and all of the output tubes on the left M125 need to match, but output tubes of one amp don't need to match those of the other? If so, does setting the bias setting compensate for the mismatch?

    audiobill

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by audiobill on Fri Dec 01, 2017 7:57 am

    There are reviews on both of these done by our own boomzilla at Secrets of Home Theater and High Fidelity


    Last edited by audiobill on Fri Dec 01, 2017 8:19 am; edited 1 time in total
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    LeGrace

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by LeGrace on Fri Dec 01, 2017 8:16 am

    arturo7 wrote:So all of the output tubes on the right M125 need to match, and all of the output tubes on the left M125 need to match, but output tubes of one amp don't need to match those of the other? If so, does setting the bias setting compensate for the mismatch?

    Correct, even the tube type. I have KT120's in one M125 and KT88's in the other (long story), working fine. When I eventually convert the KT88 amp over to KT120 I plan to buy a matched quintet. Always nice to have a spare lying around, believe me.

    audiobill

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by audiobill on Fri Dec 01, 2017 8:20 am

    LeGrace wrote:
    arturo7 wrote:So all of the output tubes on the right M125 need to match, and all of the output tubes on the left M125 need to match, but output tubes of one amp don't need to match those of the other? If so, does setting the bias setting compensate for the mismatch?

    Correct, even the tube type. I have KT120's in one M125 and KT88's in the other (long story), working fine. When I eventually convert the KT88 amp over to KT120 I plan to buy a matched quintet. Always nice to have a spare lying around, believe me.

    This practice will not result in the best sonics (imaging, etc.)
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    cci1492

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by cci1492 on Fri Dec 01, 2017 8:46 am

    Arturo, what are you using now with those speakers and how does it sound to you? I was using a 250W/channel (Soundcraftsmen M5002A) before I swapped it out with the M125s. I have to say the M125s sound very similar to the old SS amp. My reason for moving to the M125s was 1) I always wanted to get into tubes and build a kit, 2) I repaired the SS amp twice (in 35 years) but I know my luck is running out, each time corrected what was wrong (lucky), but had to swap many other parts that looked a little toasted and 3) I didn't want to break the bank but I wanted a quality amp. I think you'll be happy with either choice. If you currently have a SS amp with about 100-120W (@8 ohms) output and you're happy, my guess is the ST120 would work (assuming you're keeping the speakers you're using now).
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    arturo7

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by arturo7 on Fri Dec 01, 2017 12:21 pm

    cci1492 wrote:Arturo, what are you using now with those speakers and how does it sound to you? I was using a 250W/channel (Soundcraftsmen M5002A) before I swapped it out with the M125s. I have to say the M125s sound very similar to the old SS amp. My reason for moving to the M125s was 1) I always wanted to get into tubes and build a kit, 2) I repaired the SS amp twice (in 35 years) but I know my luck is running out, each time corrected what was wrong (lucky), but had to swap many other parts that looked a little toasted and 3) I didn't want to break the bank but I wanted a quality amp. I think you'll be happy with either choice. If you currently have a SS amp with about 100-120W (@8 ohms) output and you're happy, my guess is the ST120 would work (assuming you're keeping the speakers you're using now).

    I had been using a Sumo Andromeda (200W/side). It sounded great but it just died. After 30 years of service, I can't complain.

    About 10 years ago a built a Bottlehead preamp and phono pre. It was always my plan to eventually build a tube power amp. Now is the time. I'm kinda leaning toward the 125s because my speakers are 87dB.

    .
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    cci1492

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by cci1492 on Fri Dec 01, 2017 1:01 pm

    The M125s are easier to build because you have more room to move around under there. I've had them for about a year and a half and have been very please with everything about them. Just my opinion, but to get similar performance to the Sumo, I think the M125s will do a fine job at that.
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    LeGrace

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by LeGrace on Fri Dec 01, 2017 1:14 pm

    audiobill wrote:This practice will not result in the best sonics (imaging, etc.)

    There are currently oh only about 400 reasons preventing me from addressing this in the short term, still working on the cc balance. Situation I find myself in because I neglected to order up a spare from the get go.
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    corndog71

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by corndog71 on Fri Dec 01, 2017 2:06 pm

    arturo7 wrote:
    cci1492 wrote:Arturo, what are you using now with those speakers and how does it sound to you? I was using a 250W/channel (Soundcraftsmen M5002A) before I swapped it out with the M125s. I have to say the M125s sound very similar to the old SS amp. My reason for moving to the M125s was 1) I always wanted to get into tubes and build a kit, 2) I repaired the SS amp twice (in 35 years) but I know my luck is running out, each time corrected what was wrong (lucky), but had to swap many other parts that looked a little toasted and 3) I didn't want to break the bank but I wanted a quality amp. I think you'll be happy with either choice. If you currently have a SS amp with about 100-120W (@8 ohms) output and you're happy, my guess is the ST120 would work (assuming you're keeping the speakers you're using now).

    I had been using a Sumo Andromeda (200W/side). It sounded great but it just died. After 30 years of service, I can't complain.

    About 10 years ago a built a Bottlehead preamp and phono pre. It was always my plan to eventually build a tube power amp. Now is the time. I'm kinda leaning toward the 125s because my speakers are 87dB.

    .

    To be fair even the 35 watt/ch ST70 would probably work well. At the same time I've been there. Started with an ST70. Traded it and built a pair of Mk IVs. Sold those and built several ST35s. Still have monoblock versions as my back up. Built the ST120 because I just wanted a little more power. Love it! Got a deal on a used pair of M125s. Still in the process of rebuilding them into a new layout.

    I still have my original Bottlehead Foreplay 2, Quickie, and Smash preamps. I also have the S.e.X. 2.0 headphone amp as well as Reduction phono preamp. My SP13 beats all of the Bottlehead preamps I own. I still use the Reduction in my main rig.

    This stuff can be addictive!
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    arturo7

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by arturo7 on Sat Dec 02, 2017 5:08 pm

    I assume that if one of the four matched tubes fails I need another set of 4 matched tubes, right?
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    LeGrace

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by LeGrace on Sat Dec 02, 2017 5:49 pm

    arturo7 wrote:I assume that if one of the four matched tubes fails I need another set of 4 matched tubes, right?

    Normally only the other tube in the same pairing as the one that failed. Can replace those two with a matched pair and soldier on. And why my next purchase will be 5 matched. That way will need to replace only the tube that fails. And given the MTBF of modern tubes is so variable its not unusual for one to pop noticeably sooner then its mates. At least that's my experience.
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    cci1492

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by cci1492 on Sun Dec 03, 2017 12:32 pm

    corndog I'm sure is right, it all depends on how you intend to use them is the bottom line. You did say "I mostly listen to jazz and classical, so based on what I've read here, I'll probably be listening in triode mode". The M-125s put out an amazing 65W in triode mode, which for me is just about enough to play anything with nice deep clean bass. I have to play something like Led Zep really LOUD to actually hear some compressing taking place. 65W is a very respectable amount of power when it comes to tube amp power. BTW, I have to get out to Irvine once per year and absolutely love Huntington Beach. Zubies is must visit for me, love the food and the general atmosphere of the place!

    Dogstar

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by Dogstar on Sun Dec 03, 2017 4:56 pm

    Dave_in_Va wrote:My room is approx. 12' x 17'. My speakers are Tylers (90db sens.). I use a VTA ST70 and 50% on the volume is about as loud as normal person can stand. I've never noticed any distortion at any volume level.
    I listen to psychedelic rock, acid folk and soundtracks from ancient Italian westerns.

    Would those ancient Italian westerns be those old Clint Eastwood movies?
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    Dave_in_Va

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by Dave_in_Va on Sun Dec 03, 2017 5:27 pm

    "Would those ancient Italian westerns be those old Clint Eastwood movies?"

    Not really. Mostly the obscure stuff. Check out a label called Dagored. They specialize in the great scores to obscure early '70's/late '60's Italian Westerns/thillers,etc. Also Cineploit and Cinedelic.
    I'm also now getting into the Euro library music from the same period. Just got a killer re-issue of a 1970 library music LP by Amadeo Tommasi called Zodiac. It sounds stunning through my VTA system.
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    bluemeanies

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by bluemeanies on Tue Dec 05, 2017 8:19 am

    I have the m125's with the KT 88's. Right now I am using just pairs in the m125's. I DID have quads in them but found after listening to them for about a month I really only needed 2KT88's b/c sonically there was no difference.
    I have the 803 diamonds and believe me they sound sweet in Triode mode with just 35watts per channel.
    May I suggest a GOOD driver tube to go along with your Output tubes...I recently invested in the Mullard CV4003's and noticed an immediate difference in the tweeter and mids but especially the mids.
    My room is not that big...25'long but only 10' wide with two ceiling heights. 7'+ and 6'4".
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    cci1492

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by cci1492 on Tue Dec 05, 2017 8:41 am

    Bluemeanies, good to know about the cv4003s. Couple of weeks ago I received 8 of those (6 for the pre-amp and 2 for the M-125s) cryo from Kevin at upscale. Just haven't gotten around to trying them, wasn't sure if to start with the M-125s or the pre-amp. But now it looks like I'm going with the M-125s first (i don't think the pre-amp is broken in yet anyway). I've been messing with the 6SN7s too with the adapter. I'm looking to tame the high frequencies a little, some recordings sound too bright to me.
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    cci1492

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by cci1492 on Wed Dec 06, 2017 7:40 pm

    I pulled 2 GE 12bh7's I got off of eBay which sound really nice BTW and replaced with the Upscale CV4003s. The CV4003's have an interesting sound, definitely took some edge off the top. I'm waiting till the darn tree is down before proceeding to the preamp. The tree is messing the acoustics in the room, I'm not saying anything cause I'll be accused of being a Grinch again around here!
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    deepee99

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    Re: Sonic Characteristics of ST-120 vs M125s

    Post by deepee99 on Fri Dec 15, 2017 1:58 pm

    Having had both M-125s and the ST-120, cci1492, is correct as regards kit-building. The M-125s are far less complex than the ST-120 as you've more elbow room in the -125s, albeit there are two of them. I run 90 dB Tylers as wel in a fairly large listening room and doubt if it ever gets out of Class A. If you're going to to run Maggies the M-125s are probably the better bet. Either way, remember this: tube watts are much fatter and more forgiving than s/s watts.
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    bluemeanies

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    Re-sonic characteristics between the ST120 and M125's

    Post by bluemeanies on Sat Dec 23, 2017 8:30 am

    cci1492 wrote:I pulled 2 GE 12bh7's I got off of eBay which sound really nice BTW and replaced with the Upscale CV4003s. The CV4003's have an interesting sound, definitely took some edge off the top. I'm waiting till the darn tree is down before proceeding to the preamp. The tree is messing the acoustics in the room, I'm not saying anything cause I'll be accused of being a Grinch again around here!


    Sorry cci I have been on the run.
    The CV4003's IMO sound sweet with the 803diamonds I hope that elf you bribed rewards you dearly.
    I have heard both the ST120 and the m125's and I believe there is no or at most little sonic differences. Tubes, however do make a difference both the output and driver tubes are the main ingredients.
    IMO

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