VTA ST-120 power cord question

Here's an easy one. Does the VTA ST120 amp come with a modern three cord grounded plug or an old fashioned two way non polarized cord like the original ST-70?

Elrick wrote:Here's an easy one. Does the VTA ST120 amp come with a modern three cord grounded plug or an old fashioned two way non polarized cord like the original ST-70?

the old fashioned twin, same as the St70

It comes with a 2-wire cord. With my unusual layout and crazy city power I ended up needing to add the ground wire to kill some really bad hum.

Thanks MWay, a friend who has one told so. But for some reason I doubted him. We were listening to my system last night. I have the Mark III kits w/ the octal driver board and a conrad johnson PV7 preamp. My amps have the three wire configuration but my listening room has the old original two wires, so mine are not grounded. I have a small amount of hum that can be heard if you get close to the speaker and he really has no hum with his SP12 and a VTA ST120. I have chosen the plug orientation on my preamp that gives the quietest results.

Corndog, that's a clean looking unit, but I would have included ventilation holes around the tubes on your chassis. I like the handle too.

Elrick wrote:Here's an easy one. Does the VTA ST120 amp come with a modern three cord grounded plug or an old fashioned two way non polarized cord like the original ST-70?

Mine (vta-70) has an IEC input well. Had a local workshop mill the hole.
I used a well with built-in fuses, that way i could reuse the space occupied by the fuse.

Standard VTA-70/120 has "the old fashioned way"

I understand that the VTA's all have polarized two way plugs, so you can only pug them in one way. Obligatory pic:

My house is old, I have only two prong plugs which are not grounded. All my stereo stuff is plugged into a power strip that goes into an old 20A variac that is also not grounded. It just has an old reversible two prong plug. So I'm probably not getting any grounds loop there. I think I'll try reversing the cord from my variac into the wall. That could make a difference humwise.

I've tied to separate the RCA source lines from the power lines as best I can with my set up. If they have to cross then do it at right angels.

My preamp is battery-powered which may be a factor too.   

As you can see, I've paid extreme attention to cable routing on my system ...



  

I originally intended to go three wire on my custom ST120 and even went so far as to cut a separate "floating" plate for the additional isolation ...



But got talked out of it. Bob's point about the two wire being inherently quieter, the fact that half a million Dynaco owners have survived without the additional ground, and a couple folk were kind enough to point out that the extra plate could also maybe act as an antenna for RF ... and I just went with the standard two wire. I do get just a bit of hum out of the speakers on idle if I really got it cranked up ... which for me, is normal also.  

I've always wondered why some people drill holes around the base of tube sockets. I heard it was for ventilation from one fella. But the tubes are on top of the chassis, so I can't seem to understand.   

Pulls air up to cool tubes. - heat rises.....

sKiZo wrote:As you can see, I've paid extreme attention to cable routing on my system ...



  

I originally intended to go three wire on my custom ST120 and even went so far as to cut a separate "floating" plate for the additional isolation ...



But got talked out of it. Bob's point about the two wire being inherently quieter, the fact that half a million Dynaco owners have survived without the additional ground, and a couple folk were kind enough to point out that the extra plate could also maybe act as an antenna for RF ... and I just went with the standard two wire. I do get just a bit of hum out of the speakers on idle if I really got it cranked up ... which for me, is normal also.  

with that spaghetti audionaise I'm surprised you're not getting cross talk!!!!   

sKiZo; Like that "rats nest" of wires

You shoulda seen it before I cleaned it up ...   

My problem is that as soon as I DO make the effort, I find some more gear I want to play with and it all goes south real fast. It DOES look a lot neater on paper ...



One thing for sure, I never get confused with being a "purist" ... Amazing thing is, it all works well together and I really can't think of one piece I would pull from the system as all the little fiddlybits create a gestalt of audio goodness ... oooooHHHHHHhhhhhhhmmmmmmm ...

Oh. And yes to the holes for cooling. Serves two purposes by pulling air up from below the chassis plate - cools the tubes by moving the superheated air up from the glass and transformers, AND provides air circulation inside the chassis. You'd be surprised how hot some of the other components can get under steam.

Of course, this all presupposes that there's inlets to provide the intake air in the first place. That's why a lot of cases will have perforated, slotted, or mesh bottoms.

Did you get your hum fixed?

I didn't drill vent holes in my modified ST120 because most of the pros don't.  Also I spaced my tubes out more than usual giving them lots of breathing room.

This is one of my inspirations.

Looks great - very professional!

corndog71 wrote:I didn't drill vent holes in my modified ST120 because most of the pros don't.  Also I spaced my tubes out more than usual giving them lots of breathing room.

This is one of my inspirations.

Elegant in it's simplicity.

Can we get a peek under the hood?

corndog71 -- Very, very nice!!!

I definitely second sKiZo .... how about a peek under the hood?

Stew

Wait! Hold on! That's not MY amp! I said it was one of my inspirations.

That's an RM-200 Mk II by Music Reference. I WISH this was my amp! THIS is what I mean by "made by pros".

It outputs 100 watts/channel with KT88 tubes! But it's also $$$$$ expensive!

Bob Latino wrote:To get 100 watts out of a PAIR of KT88's, those two KT88's have to be "rode hard". (High voltages and high current flow) I checked the Stereophile review of this amp. Link below ..

Stereophile measurements of the Music Reference RM-200 MK II

This amp has 2, 4, 8 and 16 ohm speaker taps. The 2 and 4 ohm taps would not produce 100 watts (according to Stereophile). If you look at the power output chart at the link above, the 2 ohm tap made only 40 watts and the 4 ohm tap would only make 70 watts before the power output line went straight up. (no more power available) At 8 ohms the amp did make 100 watts (barely).

It is probably a nice sounding amp but $4200 is still a lot of money for a power amp ..

Bob

I know Roger builds his amps a bit differently than everyone else. Here's a quote from the original RM-200 review:

"In describing his circuit to me, Modjeski advocated the use of low screen voltages and higher-than-usual plate voltages in the output stage. The RM-200 runs the screens and plates of its carefully matched set of four output tubes at 350V and 750V, respectively."

He is able to achieve somewhere around 10,000 hours of life from his tubes due to running them at half of max dissipation.

He gets similar results from his RM-10 which gets 35 watts from a pair of EL84s.

I swear I'm not trying to sound like an ad for his gear but I've done a lot of research on his amps and his tubes and I'm convinced the guy knows his stuff.

Roger Modjeski  may know his stuff on paper.... but ever amp i have had 4 .... 2 died in my home....for no good reason!..... an a pr of his OTLs flamed.....
An as far as the RM-200II i put this amp on my Apogee Stages....that my Dynaco all stock 50year old MK3s drive vary ezely an sound sweet like honey...RM-200 sounded like a 40 watt SS amp .....my Mk3s run on the 8ohm tap....on the RM-200 no matter what tap it sounded week....an it has all SS frount end .....I never could get the amp to sound good on any speakers..Sounds just like the ARC amps......ARC can make tubes sound like bad SS.....

But you never know ....if you dont go...justsaying..


Thanks to Bob showing that on paper......  may not be the hold story ...


Thanks fore the site Bob.....

I've never heard an ARC that I like, they use so much SS in the power supplies that it kills all the tubes in the main signal path!
That's why I won't build any tube preamp without a tube rectifier. Now I do use an SS regulator in there, but it acts as a shunt on the voltage,
and it drops the noise level 60db, and sounds better than a huge bank of capacitors, and doesn't seem to change any sonic flavors like some other designs.