ST120 with IEC Inlet Question

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.)?

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

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

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.

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

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.

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)

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

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?

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:

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.

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.

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".

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