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    ST120 with IEC Inlet Question

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    Disles1

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

    ST120 with IEC Inlet Question

    Post by Disles1 on Sun Jan 29, 2012 6:04 pm

    I have been very happy with my ST120 using the stock power cable but I'm wondering about modifying it, by adding an IEC inlet, to accept different power cords.

    I know there isn't room within the chassis to add an IEC inlet, however, would this approach work? If I bolted a wood (or aluminum) block - with a cut-out for the IEC inlet - on the outside of the ST120 chassis, and then brought the line and neutral wires from the IEC posts into the ST120 using the existing power cord hole would that be OK; safety-wise, electrically? Same question, second part: If I attached the IEC safety ground wire to somewhere convenient on the ST120 chassis would that be OK (safety-wise) and/or would it create a ground loop (if it was different than the existing ground point for signal wires, etc.)?

    danf

    Posts : 58
    Join date : 2009-01-19

    Ground for IEC

    Post by danf on Sun Jan 29, 2012 6:52 pm

    Hi,

    If you use an IEC power connector, I would run the IEC ground to the star grounding lugs near the quad capacitor. This connection would have the least problem with ground loops. Generally, the possibility of ground loops will be lowest if your preamp doesn't also have a grounded chassis.

    I like a grounded chassis with a tube amp, but this is for safety, not sound. If you are hoping that changing the power cord will improve the sound, I think you are likely to be disappointed. For safety, it would be easier to enlarge the entrance hole for the new power cord, buy a suitable strain relief, and use a hard-wired three wire power cord.

    Best,
    Dan

    Bob Latino
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    Join date : 2008-11-26
    Location : Massachusetts

    Re: ST120 with IEC Inlet Question

    Post by Bob Latino on Sun Jan 29, 2012 7:41 pm

    I've had this discussion with other owners of VTA tube amps. Adding an IEC connector to the chassis would be a major undertaking and would be difficult. The reason is that the power transformer is "sunk in" on the back of the chassis and is about 1/2 inch from the inside back of the chassis. Every IEC connector that I looked at is sunk in (including the solder tabs) about 3/4 of an inch. The IEC connector will bang into the power transformer's bottom cover which is grounded. Even if you grind the solder tabs down, you will have 120 volts real close to the power transformer's bottom cover. You *could* move the IEC connector where the power switch is then move the power switch where the AC inlet hole is. Consider though that the design concept behind the ST-70/ST-120 amp kits was to make the kit LOOK LIKE an original Dynaco amp yet SOUND LIKE a modern tube amp. Altering the position of items defeats the original concept of making the amp look like an original Dynaco amp.

    The power cord on the VTA ST-70/ST-120 amps is a 13 amp rated cord of good quality. I have done as danf has suggested and put a 14 gauge 3 wire captured cord on the amp. I could hear no difference in the sound of the amp.

    You can add a 3 wire cord and ground the third wire to the chassis. This will work fine unless you have another component in your music system (as danf has mentioned) that ALSO has a 3 wire cord. Sometimes having another component with a 3 wire cord can create a ground loop and raise the almost non-existent hum level of your VTA amp. If that happens, either cut off the third ground wire inside the amp or use a 3 to 2 "cheater plug" on the end of your AC plug.

    As a side note > The VTA M-125 monoblocks are not a copy of any existing amp. They do have an IEC connector and come with a 14 gauge 15 amp rated power cord.

    Bob

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: ST120 with IEC Inlet Question

    Post by heyraz on Mon Jan 30, 2012 12:28 am

    I cut an IEC extension cord and have the socket end hanging out of my ST70 like a short tail.

    tubes4hifi
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    Re: ST120 with IEC Inlet Question

    Post by tubes4hifi on Tue Jan 31, 2012 3:09 pm

    where there is a will, there is a way. I did this for a customer about two years ago.
    I cut the hole, then mounted 3/8 or 1/2" long spacers on the outside of the chassis, and slide the end of the IEC connector into the chassis, with about 1/8" clearance. I have a photo somewhere, good luck trying to find that out of maybe 100K photos on my computer!
    Probably very similar to what heyraz did.

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: ST120 with IEC Inlet Question

    Post by baddog1946 on Tue Jan 31, 2012 9:52 pm

    Check out this site they have a lot of choices but this one seems to mount on the outside of the chassis with some clearance inside and has a screw terminal model available.
    Baddog


    http://www.schurterinc.com/en/Components/Connectors/Connectors-Inlets-Outlets/6048#abmessungen

    tubes4hifi
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    Re: ST120 with IEC Inlet Question

    Post by tubes4hifi on Tue Jan 31, 2012 11:33 pm

    nice find BadDog, but unfortunately I can't find any of the usual sources that actually stock it.
    Mouser, DigiKey, Newark, they all do not stock and have a quantity 50 minimum piece order.
    If anyone can find it stocked anywhere, let us all know, that's perfect for the Dyna ST70 amp!
    If anyone is handy machining either wood or aluminum, a spacer about 3/8-1/2" thick would work for the commonly available IEC input connectors.

    heyraz

    Posts : 58
    Join date : 2011-10-26

    IEC Socket "Tail"

    Post by heyraz on Thu Feb 09, 2012 9:43 am

    Here's a photo of how I installed an "IEC Socket Tail" in place of the power cord on my ST70. Having this socket enables quick swaps with my other amps (no need to thread a long power cord thru cabinet).
    The trick to keeping it from pulling out is to grip it from the inside. I used an appropriate grommet and twisted some baling wire (plumbing item) around the center of the grommet to grip the cord, then clipped off the excess wire flush with the grommet. I placed another grommet as a backup deeper within the amp behind a cable strap fastened to one of the power transformer mounting screws. The green safety ground wire is then attached to the chassis as close a possible to the entry point, NOT to the star ground by the main capacitor. In my case, I used a solder tag grounded to the chassis at the power switch.
    Another thing I added were a couple of 0.01uf ceramic caps from the input ground to chassis to catch any high frequency AC that may have been picked up by the input cables. The result is a clear and quiet amp. (Sorry it took so long for me to post the photos)


    Last edited by heyraz on Thu Feb 09, 2012 9:36 pm; edited 2 times in total

    heyraz

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    Join date : 2011-10-26

    Re: ST120 with IEC Inlet Question

    Post by heyraz on Thu Feb 09, 2012 11:02 am

    Apparently I don't know how to upload and attach photos. A little help, please! Rich

    Bob Latino
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    Re: ST120 with IEC Inlet Question

    Post by Bob Latino on Thu Feb 09, 2012 11:24 am

    Rich,

    Read the "Sticky" on how to post a photo on this forum ...

    Bob

    anbitet66

    Posts : 132
    Join date : 2009-12-23
    Location : Valley Stream, NY

    Re: ST120 with IEC Inlet Question

    Post by anbitet66 on Thu Feb 09, 2012 2:24 pm

    For those who can't wait: right click the box with the red x. Select properties. Go to address:(URL) Copy the entire address. Click to open a new tab (IE7 and up, firefox, etc...). Paste and click the go arrow.

    BTW heyraz: why is there a screw in the grommet?

    tubes4hifi
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    Re: ST120 with IEC Inlet Question

    Post by tubes4hifi on Thu Feb 09, 2012 3:45 pm

    I finally found a couple photos from 2 years ago last time I did this, but seems I didn't get a photo from the rear of the amp after it was done.
    I may do this mod to an amp I'm building next week. Seems I remember having to space the connector out about 1/4".
    Anyway, here are the photos:


    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: ST120 with IEC Inlet Question

    Post by heyraz on Thu Feb 09, 2012 4:39 pm

    Not a screw in the grommet. Some folks take a wire wrap and tighten it around the waist of the grommet till it grips the cord, I used a high tensile bale wire instead (plumbing supply. I looped it around the groove in the grommet then twisted it with Lineman's pliers till it gripped the cord tightly. Then I cut it flush with the grommet. It does resemble a screw though.

    tuberguy

    Posts : 1
    Join date : 2012-02-25

    Found an interesting product for adding an IEC connector to a Stereo 70

    Post by tuberguy on Sat Feb 25, 2012 11:31 am

    Just ordered some of these - it's a Switchcraft connector that looks a lot like the Schurter product discussed earlier here. I'll try to post an update about how it works out. It's not cheap when you consider shipping ($16 for two of them shipped to me), but seems like kind of a specialty thing, so I splurged.

    I wanted to post the link here (as this is where I found the discussion), but as a new member I can't post links here for 7 days, and I wanted to do this before I forgot it. It's a supplier called Fullcompass and it's the Switchcraft EAC323. Search around there or Google and you should be able to find it.



    tubes4hifi
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    Re: ST120 with IEC Inlet Question

    Post by tubes4hifi on Sat Feb 25, 2012 4:30 pm

    nice link and nice price, but I can't believe shipping was so expensive.
    Now the problem is cutting the hole. It was easy when I did it on an original ST70 from the 70s.
    18 guage steel, no problem with a nipping tool. But I tried it on one of our new 16g stainless steel chassis and broke the
    nipper on the 2nd bite, the nipper is only rated for 18g steel, 16g stainless is not only quite a bit thicker but is a much harder metal.
    I also found it extremely difficult to drill thru, while the 18g steel was easy.
    But I also found that a regular IEC input connector WILL fit, if you place it on the lower edge of the bottom, and cut the ground pin off.
    Clears the transformer by about 3/16".

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: ST120 with IEC Inlet Question

    Post by baddog1946 on Sun Feb 26, 2012 9:05 am

    FYI:
    I found the same "Switchcraft" IEC external connector at "Allied Electronics" at $3.79 + $5.00 for shipping.

    It mounts outside the chassis but I tried test mounting it from the inside on a piece of sheet metal the same thickness as a stainless chassis and found it still worked fine.
    Not to be satisfied with the possibility of the plug not being properly seated
    I then tried it with a cord I had ground off the outer flange the thickness of the sheet metal and it also worked fine. This made the protrusion of the chassis mounted plug more compact as it did not stick out as far. Looked pretty good that way.

    Check out the product at:https://www.alliedelec.com/search searchresults.aspx?dsNav=Ntk:Primary|switchcrafy|3|,Ny:False,Ro:220,N:106&SearchType=0

    Baddog

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